3.9.1 Water Heating

Water heating systems shall always be modeled for both the proposed design and baseline building when the proposed building is expected to have a water heating load, even if no water heating is shown on the plans or specifications for the proposed design. In such instances, an electric resistance system shall be modeled for both the proposed design and baseline building, meeting the efficiency requirements of the baseline standard.

When the construction documents show a water heating system, the layout and configuration of the baseline building system shall be the same as the proposed design, e.g. the baseline building shall have the same number of water heaters and the same distribution system.

System Loads and Configuration

Water Heating System Name
Applicability	All water heating systems
Definition	A unique descriptor for each water heating system. A system consists of one or more water heaters, a distribution system, an estimate of hot water use, and a schedule for that use. Nonresidential buildings will typically have multiple systems, perhaps a separate electric water heater for each office break room, etc. Other building types such as hotels and hospitals may have a single system serving the entire building.
Units	Text, unique
Input Restrictions	Where applicable, this should match the tags that are used on the plans such that a plan reviewer can make a connection.
Baseline Rules	The naming convention for the baseline building system shall be similar to the proposed design.

Water Heating Peak Use
Applicability	All water heating systems, required
Definition	An indication of the peak hot water usage (e.g. service to sinks, showers, and kitchen appliances, etc.). When specified per occupant, this value is multiplied by design occupancy density values and modified by service water heating schedules to obtain hourly load values which are used in the simulation. Peak consumption is commonly specified as gallons per hour per occupant, dwelling unit, hotel room, patient room, or floor area. If consumption is specified in gallons per hour, then additional inputs would be needed such as supply temperature, cold water inlet temperature, etc. It is also common to specify peak use as a thermal load in Btu/h. In the latter case, there is an implied assumption for the cold water inlet temperature, supply temperature, distribution losses, and other factors. The thermal load does not include conversion efficiencies of water heating equipment.
Units	Btu/h or gallons/h
Input Restrictions	For the purpose of federal tax deductions, peak use shall be specified as a thermal load using the California 2005 ACM values from Appendix B, Table 5. For the purpose of green building ratings and Design to Earn ENERGY STAR, the inputs from Appendix B are default values, but other values may be used with justification.
Baseline Rules	Hot water consumption or load in the baseline building shall be the same as the proposed design, except in cases where a specific measure is specified for the proposed design that will reduce water consumption. Examples of such measures include: low-flow terminal devices or controls, alternative sanitizing technologies, or heat recovery laundry or showers drains.

Water Heating Schedule
Applicability	All water heating systems, required
Definition	A fractional schedule reflecting the time pattern of water heating use. This input modifies the water heating peak use, described above.
Units	Data structure: schedule, fractional
Input Restrictions	For the purpose of federal tax deductions, the schedules for the California 2005 ACM from Appendix B, Table 7 shall be used. For the purpose of green building ratings and Design to Earn ENERGY STAR, the inputs from Appendix B, Table 7 are default values, but other values may be used with justification.
Baseline Rules	Hot water schedules for the baseline building shall be the same as the proposed design, except in cases where a specific measure is specified for the proposed design that will reduce water consumption and the impact of the measure can be best approximated through an adjustment to the schedule. In general, such measures would be addressed through an adjustment to the water heating, peak use (see above).

Water Heating System Configuration
Applicability	All water heating systems, required
Definition	The configuration and layout of the water heating system, including the number of water heaters; the size, location, length and insulation of distribution pipes; recirculation systems and pumps; and any other details about the system that would affect the energy model.
Units	Data structure
Input Restrictions	None
Baseline Rules	The baseline building shall have the same configuration and layout as the proposed design.

Water Heaters

This section describes the building descriptors for water heaters. Typically, a building will have multiple water heating systems and each system can have multiple water heaters, so these building descriptors may need to be specified more than once.

Water Heater Name
Applicability	All water heaters
Definition	A unique descriptor for each water heater in the system. Some systems will have multiple pieces of equipment, for instance a series of water heaters plumbed in parallel or a boiler with a separate storage tank.
Units	Text, unique
Input Restrictions	Where applicable, this should match the tags that are used on the plans such that a plan reviewer can make a connection.
Baseline Rules	The naming convention for the baseline building system shall be similar to the proposed design.

Water Heater Type and Size
Applicability	All water heaters
Definition	This building descriptor includes information needed to determine the criteria from baseline standards. The choices are listed below. See Table 7.2.2 of ASHRAE Standard 90.1-2001 or Table 7.8 of ASHRAE Standard 90.1-2007 for more detail. Electric water heaters (storage and instantaneous) Small (≤ 12 kW) Large (> 12 kW) Heat pump Gas storage water heaters Small (≤ 75,000 Btu/h) Medium (> 75,000 and ≤ 155,000 Btu/h) Large (> 155,000 Btu/h) Gas instantaneous water heaters Small (> 50,000 and < 200,000 Btu/h) Large (≥ 200,000 Btu/h) Oil storage water heaters Small (≤ 105,000 Btu/h) Medium (> 105,000 and ≤ 155,000 Btu/h) Large (> 155,000 Btu/h) Oil instantaneous water heaters Small (≤ 210,000 Btu/h) Large (> 210,000 Btu/h) Gas hot water supply boiler Oil hot water supply boiler
Units	List (see above)
Input Restrictions	The water heater type shall agree with equipment specified in the construction documents.
Baseline Rules	Water heaters in the baseline system shall be the same as those in the proposed design, except when the proposed design has a heat pump water heater, in which case the baseline building system shall have an electric storage water heater.

Rated Capacity
Applicability	All water heaters
Definition	The heating capacity of a water heater at the rated conditions specified in Table 7.8 of ASHRAE Standard 90.1-2007 or Table 7.2.2 of ASHRAE Standard 90.1-2001
Units	Thousands of British Thermal Units per hour (MBH)
Input Restrictions	As designed. If the loads are not met, autosize.
Baseline Rules	Autosize

Energy Factor
Applicability	Equipment covered by NAECA, which includes small storage and instantaneous water heaters
Definition	The energy factor (EF) is the ratio of the energy delivered by the water heater divided by the energy used, in the same units. EF is calculated according to the DOE 10 CFR Part 430 test procedure, which specifies a 24-hour pattern of draws, a storage temperature, inlet water temperature, and other test conditions. These conditions result in the energy delivered for the test period. Energy inputs are measured for the same test period and the EF ratio is calculated.
Units	Unitless ratio
Input Restrictions	Building descriptors for the proposed design should be consistent with equipment specified on the construction documents or observed in the candidate building.
Baseline Rules	The EF for the baseline building system shall be determined from Table 7.2.2 of ASHRAE Standard 90.1-2001 or Table 7.8 of ASHRAE Standard 90.1-2007, depending on the purpose of the simulations.

Thermal Efficiency
Applicability	Oil and gas fired water heaters not covered by NAECA
Definition	The full load efficiency of a water heater at rated conditions expressed as a dimensionless ratio of output over input
Units	Unitless ratio
Input Restrictions	Building descriptors for the proposed design should be consistent with equipment specified on the construction documents or observed in the candidate building.
Baseline Rules	The thermal efficiency for the baseline building system shall be determined from Table 7.2.2 of ASHRAE Standard 90.1-2001 or Table 7.8 of ASHRAE Standard 90.1-2007, depending on the purpose of the simulations.

Tank Standby Loss
Applicability	Water heaters not covered by NAECA
Definition	The tank standby loss for storage tanks, which includes the effect of recovery efficiency.
Units	Btu/h for the entire tank
Input Restrictions	As specified in manufacturer data and documented on the construction documents
Baseline Rules	The tank standby loss for the baseline building system shall be determined from Table 7.2.2 of ASHRAE Standard 90.1-2001 or Table 7.8 of ASHRAE Standard 90.1-2007.

Fuel Water Heater Part Load Efficiency Curve

Applicability

Equipment not covered by NAECA for which a thermal efficiency, as opposed to an EF is specified

Definition

A set of factors that adjust the full-load thermal efficiency for part load conditions. Typically, the factor is set as a curve.

Units

Percent (%)

Input Restrictions

The following default curve shall be used unless detailed information is provided to justify alternative values. The default curve shall take the form of a quadratic equation as follows:

(6.9.1-1)

$$ Fuel_{partload} = Fuel_{design} \times F\!HeatP\!L\!C$$ $$F\!HeatP\!L\!C = \left ( a+ b \times \frac{Q_{partload}}{Q_{rated}} + c \times \left ( \frac{Q_{partload}}{Q_{rated}}\right )^2 \right )$$where

FHeatPLC	The fuel heating part load efficiency curve
Fuel_partload	The fuel consumption at part load conditions (Btu/h)
Fuel_design	The fuel consumption at design conditions (Btu/h)
Q_partload	The water heater capacity at part load conditions (Btu/h)
Q_rated	The water heater capacity at design conditions (Btu/h)
a	Constant, 0.021826
b	Constant, 0.977630
c	Constant, 0.000543

Baseline Rules

The baseline building equipment shall use the default curve

Recirculation Systems

This section describes the building descriptors for hot water recirculation systems. The baseline building has a recirculation system when the proposed design does. This is one aspect of the water heating system configuration (see above).

Recirculation System Name
Applicability	All recirculation systems
Definition	A unique descriptor for each water heating recirculation system
Units	Text, unique
Input Restrictions	Where applicable, this should match the tags or descriptions that are used on the plans such that a plan reviewer can make a connection.
Baseline Rules	The naming convention for the baseline building system shall be similar to the proposed design.

Pumping Power
Applicability	All recirculation systems
Definition	The electric demand of the pumps when the recirculation system is operating. This input is a function of the flow rate, the pumping head, the motor efficiency, and the pump efficiency. Some software may allow each of these factors to be separately entered.
Units	Watts (W)
Input Restrictions	Pumping power shall be consistent with the piping configuration, flow rate, and equipment specified on the construction documents.
Baseline Rules	Pumping power in the baseline building shall be the same as the proposed design unless specific measures are included in the proposed design to reduce the pumping power. Example measures could include reducing pumping head by oversizing distribution piping or specifying premium efficiency motors or pumps.

Schedule
Applicability	All recirculation systems
Definition	An on/off or fraction schedule that indicates when the recirculation system is expected to be operated
Units	Data structure: schedule, on/off or fraction
Input Restrictions	The schedule for operation of the recirculation system shall be consistent with the design intent of the system. Hotels, hospitals, and other 24x7 institutional buildings will typically have a system that runs continuously. The schedule should be consistent with the controls called for on the construction documents: no control (runs constantly), timer control, temperature control, timer/temperature control, or demand control.
Baseline Rules	Recirculation schedules for the baseline building shall be the same as the proposed design.

Piping
Applicability	All recirculation systems
Definition	The heat loss rate of piping for recirculating systems. This may be defined separately for pipe that is exposed to outdoor conditions, indoor or semi-heated conditions, or buried underground conditions. These losses may be modeled as additional loads on the water heater(s).
Units	Btu/h-°F specified separately for outdoor, indoor, or buried locations
Input Restrictions	All piping in the recirculation system should be included. Heat loss for each of the three conditions should be consistent with piping runs, sizes, and insulation as shown on the construction documents.
Baseline Rules	The length and size of piping in the baseline building shall be the same as the proposed design. Insulation in the baseline building shall be as prescribed in Table 6.8.3 for ASHRAE Standard 90.1-2007 and Table 6.2.4.1.3 of ASHRAE Standard 90.1-2001.

Water Healing Auxiliaries

External Storage Tanks
Applicability	All water heating systems that have an external storage tank
Definition	Some water heating systems have a storage tank that is separate from the water heater(s) that provides additional storage capacity. This building descriptor addresses the heat loss related to the external tank, which is an additional load that must be satisfied by the water heater(s). The heat loss shall account for the surface area and U-factor tank, as well as the average temperature conditions where the tank is located. Some software may allow these factors to be separately specified.
Units	Btu/h for the entire tank
Input Restrictions	As specified in manufacturer data and documented on the construction documents
Baseline Rules	Heat loss associated with the storage tank in the baseline building shall meet the requirements for an unfired storage tank in the baseline standards which is an insulation R-value of 12.5. The surface area and location of the storage tank shall be the same as the proposed design.

Heat Recovery
Applicability	Water heating systems that are coupled to heat recovery equipment
Definition	Building equipment such as air conditioners, chillers, gas fired generators, etc. produce thermal energy that may be recovered and used to heat water. The heat producing characteristics are generally defined for the equipment that is producing the heat, not the equipment that is receiving the heat (water heaters in this case). The building descriptors will vary depending on the equipment. The models for heat producing equipment need to produce output on an hourly basis so that the schedule of heat production and heating needs can be aligned and evaluated in the water heating model.
Units	Data structure: depends on the equipment producing the heat
Input Restrictions	There are no restrictions, other than agreement with the construction documents.
Baseline Rules	The baseline building has heat recovery when the baseline standard is ASHRAE Standard 90.1-2007 and the conditions of Section 6.5.6.2 of that standard are satisfied. The baseline building is modeled with heat recovery when all of the following conditions are true: The building operates 24 hours per day. The building has water cooled chillers with a heat rejection capacity greater than 6 million Btu/h. This equates to about 400 tons of electric chiller capacity. The water heating peak use is greater than 1,000,000 Btu/h. See the User's Manual for ASHRAE Standard 90.1-2007, page 6-82 for details on the requirements for the heat recovery system and exceptions to the requirement.

Solar Thermal
Applicability	Water heating systems with a solar thermal system
Definition	A solar thermal water heating system consists of one or more collectors. Water is passed through these collectors and is heated under the right conditions. There are two general types of solar water heaters: integrated collector storage (ICS) systems and active systems. Active systems include pumps to circulate the water, storage tanks, piping, and controls. ICS systems generally have no pumps and piping is minimal. Solar systems may be tested and rated as a complete system or the collectors may be separately tested and rated. SRCC OG-300 is the test procedure for whole systems and SRCC OG-100 is the test procedure for collectors. The building descriptors used to define the solar thermal system may vary with each software application and with the details of system design. Heat produced by solar thermal systems will generally not align perfectly with the need for heating, so the model needs to account for the temporal mismatch in some manner.
Units	Data structure: will vary with the software and system details
Input Restrictions	There are no restrictions, other than agreement with the construction documents.
Baseline Rules	The baseline building has no solar auxiliary system.

Combined Space Heating and Water Heating
Applicability	Projects that use a boiler to provide both space heat and water heating
Definition	A system that provides both space heating and water heating from the same equipment, generally the space heating boiler. Such systems are restricted by the baseline standards, but may be modeled in the candidate building. The restrictions are due to the misalignment of the space heating load and the water heating load. The first is highly intermittent and weather dependent, while the latter is more constant and not generally related to the weather.
Units	Data structure
Input Restrictions	The proposed design may have a combined space and water heating system.
Baseline Rules	The baseline building shall be modeled with separate space heating and water heating systems, meeting the prescriptive requirements for each. The water heating system shall use the same fuel as the combined boiler.

90.1-2007

Water heating systems shall always be modeled for both the proposed design and baseline building when the proposed building is expected to have a water heating load, even if no water heating is shown on the plans or specifications for the proposed design. In such instances, an electric resistance system shall be modeled for both the proposed design and baseline building, meeting the efficiency requirements of the baseline standard.

When the construction documents show a water heating system, the layout and configuration of the baseline building system shall be the same as the proposed design, e.g. the baseline building shall have the same number of water heaters and the same distribution system.

System Loads and Configuration

Water Heating System Name
Applicability	All water heating systems
Definition	A unique descriptor for each water heating system. A system consists of one or more water heaters, a distribution system, an estimate of hot water use, and a schedule for that use. Nonresidential buildings will typically have multiple systems, perhaps a separate electric water heater for each office break room, etc. Other building types such as hotels and hospitals may have a single system serving the entire building.
Units	Text, unique
Input Restrictions	Where applicable, this should match the tags that are used on the plans such that a plan reviewer can make a connection.
Baseline Rules	The naming convention for the baseline building system shall be similar to the proposed design.

Water Heating Peak Use
Applicability	All water heating systems, required
Definition	An indication of the peak hot water usage (e.g. service to sinks, showers, and kitchen appliances, etc.). When specified per occupant, this value is multiplied by design occupancy density values and modified by service water heating schedules to obtain hourly load values which are used in the simulation. Peak consumption is commonly specified as gallons per hour per occupant, dwelling unit, hotel room, patient room, or floor area. If consumption is specified in gallons per hour, then additional inputs would be needed such as supply temperature, cold water inlet temperature, etc. It is also common to specify peak use as a thermal load in Btu/h. In the latter case, there is an implied assumption for the cold water inlet temperature, supply temperature, distribution losses, and other factors. The thermal load does not include conversion efficiencies of water heating equipment.
Units	Btu/h or gallons/h
Input Restrictions	For the purpose of green building ratings and Design to Earn ENERGY STAR, the inputs from Appendix B are default values, but other values may be used with justification.
Baseline Rules	Hot water consumption or load in the baseline building shall be the same as the proposed design, except in cases where a specific measure is specified for the proposed design that will reduce water consumption. Examples of such measures include: low-flow terminal devices or controls, alternative sanitizing technologies, or heat recovery laundry or showers drains.

Water Heating Schedule
Applicability	All water heating systems, required
Definition	A fractional schedule reflecting the time pattern of water heating use. This input modifies the water heating peak use, described above.
Units	Data structure: schedule, fractional
Input Restrictions	For the purpose of green building ratings and Design to Earn ENERGY STAR, the inputs from Appendix B, Table 7 are default values, but other values may be used with justification.
Baseline Rules	Hot water schedules for the baseline building shall be the same as the proposed design, except in cases where a specific measure is specified for the proposed design that will reduce water consumption and the impact of the measure can be best approximated through an adjustment to the schedule. In general, such measures would be addressed through an adjustment to the water heating, peak use (see above).

Water Heating System Configuration
Applicability	All water heating systems, required
Definition	The configuration and layout of the water heating system, including the number of water heaters; the size, location, length and insulation of distribution pipes; recirculation systems and pumps; and any other details about the system that would affect the energy model.
Units	Data structure
Input Restrictions	None
Baseline Rules	The baseline building shall have the same configuration and layout as the proposed design.

Water Heaters

This section describes the building descriptors for water heaters. Typically, a building will have multiple water heating systems and each system can have multiple water heaters, so these building descriptors may need to be specified more than once.

Water Heater Name
Applicability	All water heaters
Definition	A unique descriptor for each water heater in the system. Some systems will have multiple pieces of equipment, for instance a series of water heaters plumbed in parallel or a boiler with a separate storage tank.
Units	Text, unique
Input Restrictions	Where applicable, this should match the tags that are used on the plans such that a plan reviewer can make a connection.
Baseline Rules	The naming convention for the baseline building system shall be similar to the proposed design.

Water Heater Type and Size
Applicability	All water heaters
Definition	This building descriptor includes information needed to determine the criteria from baseline standards. The choices are listed below. See Table 7.8 of ASHRAE Standard 90.1-2007 for more detail. Electric water heaters (storage and instantaneous) Small (≤ 12 kW) Large (> 12 kW) Heat pump Gas storage water heaters Small (≤ 75,000 Btu/h) Medium (> 75,000 and ≤ 155,000 Btu/h) Large (> 155,000 Btu/h) Gas instantaneous water heaters Small (> 50,000 and < 200,000 Btu/h) Large (≥ 200,000 Btu/h) Oil storage water heaters Small (≤ 105,000 Btu/h) Medium (> 105,000 and ≤ 155,000 Btu/h) Large (> 155,000 Btu/h) Oil instantaneous water heaters Small (≤ 210,000 Btu/h) Large (> 210,000 Btu/h) Gas hot water supply boiler Oil hot water supply boiler
Units	List (see above)
Input Restrictions	The water heater type shall agree with equipment specified in the construction documents.
Baseline Rules	Water heaters in the baseline system shall be the same as those in the proposed design, except when the proposed design has a heat pump water heater, in which case the baseline building system shall have an electric storage water heater.

Rated Capacity
Applicability	All water heaters
Definition	The heating capacity of a water heater at the rated conditions specified in Table 7.8 of ASHRAE Standard 90.1-2007.
Units	Thousands of British Thermal Units per hour (MBH)
Input Restrictions	As designed. If the loads are not met, autosize.
Baseline Rules	Autosize

Energy Factor
Applicability	Equipment covered by NAECA, which includes small storage and instantaneous water heaters
Definition	The energy factor (EF) is the ratio of the energy delivered by the water heater divided by the energy used, in the same units. EF is calculated according to the DOE 10 CFR Part 430 test procedure, which specifies a 24-hour pattern of draws, a storage temperature, inlet water temperature, and other test conditions. These conditions result in the energy delivered for the test period. Energy inputs are measured for the same test period and the EF ratio is calculated.
Units	Unitless ratio
Input Restrictions	Building descriptors for the proposed design should be consistent with equipment specified on the construction documents or observed in the candidate building.
Baseline Rules	The EF for the baseline building system shall be determined from Table 7.8 of ASHRAE Standard 90.1-2007, depending on the purpose of the simulations.

Thermal Efficiency
Applicability	Oil and gas fired water heaters not covered by NAECA
Definition	The full load efficiency of a water heater at rated conditions expressed as a dimensionless ratio of output over input
Units	Unitless ratio
Input Restrictions	Building descriptors for the proposed design should be consistent with equipment specified on the construction documents or observed in the candidate building.
Baseline Rules	The thermal efficiency for the baseline building system shall be determined from Table 7.8 of ASHRAE Standard 90.1-2007, depending on the purpose of the simulations.

Tank Standby Loss
Applicability	Water heaters not covered by NAECA
Definition	The tank standby loss for storage tanks, which includes the effect of recovery efficiency.
Units	Btu/h for the entire tank
Input Restrictions	As specified in manufacturer data and documented on the construction documents
Baseline Rules	The tank standby loss for the baseline building system shall be determined from Table 7.8 of ASHRAE Standard 90.1-2007.

Fuel Water Heater Part Load Efficiency Curve

Applicability

Equipment not covered by NAECA for which a thermal efficiency, as opposed to an EF is specified

Definition

A set of factors that adjust the full-load thermal efficiency for part load conditions. Typically, the factor is set as a curve.

Units

Percent (%)

Input Restrictions

The following default curve shall be used unless detailed information is provided to justify alternative values. The default curve shall take the form of a quadratic equation as follows:

(6.9.1-1)

$$ Fuel_{partload} = Fuel_{design} \times F\!HeatP\!L\!C$$ $$F\!HeatP\!L\!C = \left ( a+ b \times \frac{Q_{partload}}{Q_{rated}} + c \times \left ( \frac{Q_{partload}}{Q_{rated}}\right )^2 \right )$$where

FHeatPLC	The fuel heating part load efficiency curve
Fuel_partload	The fuel consumption at part load conditions (Btu/h)
Fuel_design	The fuel consumption at design conditions (Btu/h)
Q_partload	The water heater capacity at part load conditions (Btu/h)
Q_rated	The water heater capacity at design conditions (Btu/h)
a	Constant, 0.021826
b	Constant, 0.977630
c	Constant, 0.000543

Baseline Rules

The baseline building equipment shall use the default curve

Recirculation Systems

This section describes the building descriptors for hot water recirculation systems. The baseline building has a recirculation system when the proposed design does. This is one aspect of the water heating system configuration (see above).

Recirculation System Name
Applicability	All recirculation systems
Definition	A unique descriptor for each water heating recirculation system
Units	Text, unique
Input Restrictions	Where applicable, this should match the tags or descriptions that are used on the plans such that a plan reviewer can make a connection.
Baseline Rules	The naming convention for the baseline building system shall be similar to the proposed design.

Pumping Power
Applicability	All recirculation systems
Definition	The electric demand of the pumps when the recirculation system is operating. This input is a function of the flow rate, the pumping head, the motor efficiency, and the pump efficiency. Some software may allow each of these factors to be separately entered.
Units	Watts (W)
Input Restrictions	Pumping power shall be consistent with the piping configuration, flow rate, and equipment specified on the construction documents.
Baseline Rules	Pumping power in the baseline building shall be the same as the proposed design unless specific measures are included in the proposed design to reduce the pumping power. Example measures could include reducing pumping head by oversizing distribution piping or specifying premium efficiency motors or pumps.

Schedule
Applicability	All recirculation systems
Definition	An on/off or fraction schedule that indicates when the recirculation system is expected to be operated
Units	Data structure: schedule, on/off or fraction
Input Restrictions	The schedule for operation of the recirculation system shall be consistent with the design intent of the system. Hotels, hospitals, and other 24x7 institutional buildings will typically have a system that runs continuously. The schedule should be consistent with the controls called for on the construction documents: no control (runs constantly), timer control, temperature control, timer/temperature control, or demand control.
Baseline Rules	Recirculation schedules for the baseline building shall be the same as the proposed design.

Piping
Applicability	All recirculation systems
Definition	The heat loss rate of piping for recirculating systems. This may be defined separately for pipe that is exposed to outdoor conditions, indoor or semi-heated conditions, or buried underground conditions. These losses may be modeled as additional loads on the water heater(s).
Units	Btu/h-°F specified separately for outdoor, indoor, or buried locations
Input Restrictions	All piping in the recirculation system should be included. Heat loss for each of the three conditions should be consistent with piping runs, sizes, and insulation as shown on the construction documents.
Baseline Rules	The length and size of piping in the baseline building shall be the same as the proposed design. Insulation in the baseline building shall be as prescribed in Table 6.8.3 for ASHRAE Standard 90.1-2007.

Water Healing Auxiliaries

External Storage Tanks
Applicability	All water heating systems that have an external storage tank
Definition	Some water heating systems have a storage tank that is separate from the water heater(s) that provides additional storage capacity. This building descriptor addresses the heat loss related to the external tank, which is an additional load that must be satisfied by the water heater(s). The heat loss shall account for the surface area and U-factor tank, as well as the average temperature conditions where the tank is located. Some software may allow these factors to be separately specified.
Units	Btu/h for the entire tank
Input Restrictions	As specified in manufacturer data and documented on the construction documents
Baseline Rules	Heat loss associated with the storage tank in the baseline building shall meet the requirements for an unfired storage tank in the baseline standards which is an insulation R-value of 12.5. The surface area and location of the storage tank shall be the same as the proposed design.

Heat Recovery
Applicability	Water heating systems that are coupled to heat recovery equipment
Definition	Building equipment such as air conditioners, chillers, gas fired generators, etc. produce thermal energy that may be recovered and used to heat water. The heat producing characteristics are generally defined for the equipment that is producing the heat, not the equipment that is receiving the heat (water heaters in this case). The building descriptors will vary depending on the equipment. The models for heat producing equipment need to produce output on an hourly basis so that the schedule of heat production and heating needs can be aligned and evaluated in the water heating model.
Units	Data structure: depends on the equipment producing the heat
Input Restrictions	There are no restrictions, other than agreement with the construction documents.
Baseline Rules	The baseline building has heat recovery when the baseline standard is ASHRAE Standard 90.1-2007 and the conditions of Section 6.5.6.2 of that standard are satisfied. The baseline building is modeled with heat recovery when all of the following conditions are true: The building operates 24 hours per day. The building has water cooled chillers with a heat rejection capacity greater than 6 million Btu/h. This equates to about 400 tons of electric chiller capacity. The water heating peak use is greater than 1,000,000 Btu/h. See the User's Manual for ASHRAE Standard 90.1-2007, page 6-82 for details on the requirements for the heat recovery system and exceptions to the requirement.

Solar Thermal
Applicability	Water heating systems with a solar thermal system
Definition	A solar thermal water heating system consists of one or more collectors. Water is passed through these collectors and is heated under the right conditions. There are two general types of solar water heaters: integrated collector storage (ICS) systems and active systems. Active systems include pumps to circulate the water, storage tanks, piping, and controls. ICS systems generally have no pumps and piping is minimal. Solar systems may be tested and rated as a complete system or the collectors may be separately tested and rated. SRCC OG-300 is the test procedure for whole systems and SRCC OG-100 is the test procedure for collectors. The building descriptors used to define the solar thermal system may vary with each software application and with the details of system design. Heat produced by solar thermal systems will generally not align perfectly with the need for heating, so the model needs to account for the temporal mismatch in some manner.
Units	Data structure: will vary with the software and system details
Input Restrictions	There are no restrictions, other than agreement with the construction documents.
Baseline Rules	The baseline building has no solar auxiliary system.

Combined Space Heating and Water Heating
Applicability	Projects that use a boiler to provide both space heat and water heating
Definition	A system that provides both space heating and water heating from the same equipment, generally the space heating boiler. Such systems are restricted by the baseline standards, but may be modeled in the candidate building. The restrictions are due to the misalignment of the space heating load and the water heating load. The first is highly intermittent and weather dependent, while the latter is more constant and not generally related to the weather.
Units	Data structure
Input Restrictions	The proposed design may have a combined space and water heating system.
Baseline Rules	The baseline building shall be modeled with separate space heating and water heating systems, meeting the prescriptive requirements for each. The water heating system shall use the same fuel as the combined boiler.

Water heating systems shall always be modeled for both the proposed design and baseline building when the proposed building is expected to have a water heating load, even if no water heating is shown on the plans or specifications for the proposed design. In such instances, an electric resistance system shall be modeled for both the proposed design and baseline building, meeting the efficiency requirements of the baseline standard.

When the construction documents show a water heating system, the layout and configuration of the baseline building system shall be the same as the proposed design, e.g. the baseline building shall have the same number of water heaters and the same distribution system.

System Loads and Configuration

Water Heating System Name
Applicability	All water heating systems
Definition	A unique descriptor for each water heating system. A system consists of one or more water heaters, a distribution system, an estimate of hot water use, and a schedule for that use. Nonresidential buildings will typically have multiple systems, perhaps a separate electric water heater for each office break room, etc. Other building types such as hotels and hospitals may have a single system serving the entire building.
Units	Text, unique
Input Restrictions	Where applicable, this should match the tags that are used on the plans such that a plan reviewer can make a connection.
Baseline Rules	The naming convention for the baseline building system shall be similar to the proposed design.

Water Heating Peak Use
Applicability	All water heating systems, required
Definition	An indication of the peak hot water usage (e.g. service to sinks, showers, and kitchen appliances, etc.). When specified per occupant, this value is multiplied by design occupancy density values and modified by service water heating schedules to obtain hourly load values which are used in the simulation. Peak consumption is commonly specified as gallons per hour per occupant, dwelling unit, hotel room, patient room, or floor area. If consumption is specified in gallons per hour, then additional inputs would be needed such as supply temperature, cold water inlet temperature, etc. It is also common to specify peak use as a thermal load in Btu/h. In the latter case, there is an implied assumption for the cold water inlet temperature, supply temperature, distribution losses, and other factors. The thermal load does not include conversion efficiencies of water heating equipment.
Units	Btu/h or gallons/h
Input Restrictions	For the purpose of green building ratings and Design to Earn ENERGY STAR, the inputs from Appendix B are default values, but other values may be used with justification.
Baseline Rules	Hot water consumption or load in the baseline building shall be the same as the proposed design, except in cases where a specific measure is specified for the proposed design that will reduce water consumption. Examples of such measures include: low-flow terminal devices or controls, alternative sanitizing technologies, or heat recovery laundry or showers drains.

Water Heating Schedule
Applicability	All water heating systems, required
Definition	A fractional schedule reflecting the time pattern of water heating use. This input modifies the water heating peak use, described above.
Units	Data structure: schedule, fractional
Input Restrictions	For the purpose of green building ratings and Design to Earn ENERGY STAR, the inputs from Appendix B, Table 7 are default values, but other values may be used with justification.
Baseline Rules	Hot water schedules for the baseline building shall be the same as the proposed design, except in cases where a specific measure is specified for the proposed design that will reduce water consumption and the impact of the measure can be best approximated through an adjustment to the schedule. In general, such measures would be addressed through an adjustment to the water heating, peak use (see above).

Water Heating System Configuration
Applicability	All water heating systems, required
Definition	The configuration and layout of the water heating system, including the number of water heaters; the size, location, length and insulation of distribution pipes; recirculation systems and pumps; and any other details about the system that would affect the energy model.
Units	Data structure
Input Restrictions	None
Baseline Rules	The baseline building shall have the same configuration and layout as the proposed design.

Water Heaters

This section describes the building descriptors for water heaters. Typically, a building will have multiple water heating systems and each system can have multiple water heaters, so these building descriptors may need to be specified more than once.

Water Heater Name
Applicability	All water heaters
Definition	A unique descriptor for each water heater in the system. Some systems will have multiple pieces of equipment, for instance a series of water heaters plumbed in parallel or a boiler with a separate storage tank.
Units	Text, unique
Input Restrictions	Where applicable, this should match the tags that are used on the plans such that a plan reviewer can make a connection.
Baseline Rules	The naming convention for the baseline building system shall be similar to the proposed design.

Water Heater Type and Size
Applicability	All water heaters
Definition	This building descriptor includes information needed to determine the criteria from baseline standards. The choices are listed below. See Table 7.8 of ASHRAE Standard 90.1-2007 for more detail. Electric water heaters (storage and instantaneous) Small (≤ 12 kW) Large (> 12 kW) Heat pump Gas storage water heaters Small (≤ 75,000 Btu/h) Medium (> 75,000 and ≤ 155,000 Btu/h) Large (> 155,000 Btu/h) Gas instantaneous water heaters Small (> 50,000 and < 200,000 Btu/h) Large (≥ 200,000 Btu/h) Oil storage water heaters Small (≤ 105,000 Btu/h) Medium (> 105,000 and ≤ 155,000 Btu/h) Large (> 155,000 Btu/h) Oil instantaneous water heaters Small (≤ 210,000 Btu/h) Large (> 210,000 Btu/h) Gas hot water supply boiler Oil hot water supply boiler
Units	List (see above)
Input Restrictions	The water heater type shall agree with equipment specified in the construction documents.
Baseline Rules	Water heaters in the baseline system shall be the same as those in the proposed design, except when the proposed design has a heat pump water heater, in which case the baseline building system shall have an electric storage water heater.

Rated Capacity
Applicability	All water heaters
Definition	The heating capacity of a water heater at the rated conditions specified in Table 7.8 of ASHRAE Standard 90.1-2007.
Units	Thousands of British Thermal Units per hour (MBH)
Input Restrictions	As designed. If the loads are not met, autosize.
Baseline Rules	Autosize

Energy Factor
Applicability	Equipment covered by NAECA, which includes small storage and instantaneous water heaters
Definition	The energy factor (EF) is the ratio of the energy delivered by the water heater divided by the energy used, in the same units. EF is calculated according to the DOE 10 CFR Part 430 test procedure, which specifies a 24-hour pattern of draws, a storage temperature, inlet water temperature, and other test conditions. These conditions result in the energy delivered for the test period. Energy inputs are measured for the same test period and the EF ratio is calculated.
Units	Unitless ratio
Input Restrictions	Building descriptors for the proposed design should be consistent with equipment specified on the construction documents or observed in the candidate building.
Baseline Rules	The EF for the baseline building system shall be determined from Table 7.8 of ASHRAE Standard 90.1-2007, depending on the purpose of the simulations.

Thermal Efficiency
Applicability	Oil and gas fired water heaters not covered by NAECA
Definition	The full load efficiency of a water heater at rated conditions expressed as a dimensionless ratio of output over input
Units	Unitless ratio
Input Restrictions	Building descriptors for the proposed design should be consistent with equipment specified on the construction documents or observed in the candidate building.
Baseline Rules	The thermal efficiency for the baseline building system shall be determined from Table 7.8 of ASHRAE Standard 90.1-2007, depending on the purpose of the simulations.

Tank Standby Loss
Applicability	Water heaters not covered by NAECA
Definition	The tank standby loss for storage tanks, which includes the effect of recovery efficiency.
Units	Btu/h for the entire tank
Input Restrictions	As specified in manufacturer data and documented on the construction documents
Baseline Rules	The tank standby loss for the baseline building system shall be determined from Table 7.8 of ASHRAE Standard 90.1-2007.

Fuel Water Heater Part Load Efficiency Curve

Applicability

Equipment not covered by NAECA for which a thermal efficiency, as opposed to an EF is specified

Definition

A set of factors that adjust the full-load thermal efficiency for part load conditions. Typically, the factor is set as a curve.

Units

Percent (%)

Input Restrictions

The following default curve shall be used unless detailed information is provided to justify alternative values. The default curve shall take the form of a quadratic equation as follows:

(6.9.1-1)

$$ Fuel_{partload} = Fuel_{design} \times F\!HeatP\!L\!C$$ $$F\!HeatP\!L\!C = \left ( a+ b \times \frac{Q_{partload}}{Q_{rated}} + c \times \left ( \frac{Q_{partload}}{Q_{rated}}\right )^2 \right )$$where

FHeatPLC	The fuel heating part load efficiency curve
Fuel_partload	The fuel consumption at part load conditions (Btu/h)
Fuel_design	The fuel consumption at design conditions (Btu/h)
Q_partload	The water heater capacity at part load conditions (Btu/h)
Q_rated	The water heater capacity at design conditions (Btu/h)
a	Constant, 0.021826
b	Constant, 0.977630
c	Constant, 0.000543

Baseline Rules

The baseline building equipment shall use the default curve

Recirculation Systems

This section describes the building descriptors for hot water recirculation systems. The baseline building has a recirculation system when the proposed design does. This is one aspect of the water heating system configuration (see above).

Recirculation System Name
Applicability	All recirculation systems
Definition	A unique descriptor for each water heating recirculation system
Units	Text, unique
Input Restrictions	Where applicable, this should match the tags or descriptions that are used on the plans such that a plan reviewer can make a connection.
Baseline Rules	The naming convention for the baseline building system shall be similar to the proposed design.

Pumping Power
Applicability	All recirculation systems
Definition	The electric demand of the pumps when the recirculation system is operating. This input is a function of the flow rate, the pumping head, the motor efficiency, and the pump efficiency. Some software may allow each of these factors to be separately entered.
Units	Watts (W)
Input Restrictions	Pumping power shall be consistent with the piping configuration, flow rate, and equipment specified on the construction documents.
Baseline Rules	Pumping power in the baseline building shall be the same as the proposed design unless specific measures are included in the proposed design to reduce the pumping power. Example measures could include reducing pumping head by oversizing distribution piping or specifying premium efficiency motors or pumps.

Schedule
Applicability	All recirculation systems
Definition	An on/off or fraction schedule that indicates when the recirculation system is expected to be operated
Units	Data structure: schedule, on/off or fraction
Input Restrictions	The schedule for operation of the recirculation system shall be consistent with the design intent of the system. Hotels, hospitals, and other 24x7 institutional buildings will typically have a system that runs continuously. The schedule should be consistent with the controls called for on the construction documents: no control (runs constantly), timer control, temperature control, timer/temperature control, or demand control.
Baseline Rules	Recirculation schedules for the baseline building shall be the same as the proposed design.

Piping
Applicability	All recirculation systems
Definition	The heat loss rate of piping for recirculating systems. This may be defined separately for pipe that is exposed to outdoor conditions, indoor or semi-heated conditions, or buried underground conditions. These losses may be modeled as additional loads on the water heater(s).
Units	Btu/h-°F specified separately for outdoor, indoor, or buried locations
Input Restrictions	All piping in the recirculation system should be included. Heat loss for each of the three conditions should be consistent with piping runs, sizes, and insulation as shown on the construction documents.
Baseline Rules	The length and size of piping in the baseline building shall be the same as the proposed design. Insulation in the baseline building shall be as prescribed in Table 6.8.3 for ASHRAE Standard 90.1-2007.

Water Healing Auxiliaries

External Storage Tanks
Applicability	All water heating systems that have an external storage tank
Definition	Some water heating systems have a storage tank that is separate from the water heater(s) that provides additional storage capacity. This building descriptor addresses the heat loss related to the external tank, which is an additional load that must be satisfied by the water heater(s). The heat loss shall account for the surface area and U-factor tank, as well as the average temperature conditions where the tank is located. Some software may allow these factors to be separately specified.
Units	Btu/h for the entire tank
Input Restrictions	As specified in manufacturer data and documented on the construction documents
Baseline Rules	Heat loss associated with the storage tank in the baseline building shall meet the requirements for an unfired storage tank in the baseline standards which is an insulation R-value of 12.5. The surface area and location of the storage tank shall be the same as the proposed design.

Heat Recovery
Applicability	Water heating systems that are coupled to heat recovery equipment
Definition	Building equipment such as air conditioners, chillers, gas fired generators, etc. produce thermal energy that may be recovered and used to heat water. The heat producing characteristics are generally defined for the equipment that is producing the heat, not the equipment that is receiving the heat (water heaters in this case). The building descriptors will vary depending on the equipment. The models for heat producing equipment need to produce output on an hourly basis so that the schedule of heat production and heating needs can be aligned and evaluated in the water heating model.
Units	Data structure: depends on the equipment producing the heat
Input Restrictions	There are no restrictions, other than agreement with the construction documents.
Baseline Rules	The baseline building has heat recovery when the baseline standard is ASHRAE Standard 90.1-2007 and the conditions of Section 6.5.6.2 of that standard are satisfied. The baseline building is modeled with heat recovery when all of the following conditions are true: The building operates 24 hours per day. The building has water cooled chillers with a heat rejection capacity greater than 6 million Btu/h. This equates to about 400 tons of electric chiller capacity. The water heating peak use is greater than 1,000,000 Btu/h. See the User's Manual for ASHRAE Standard 90.1-2007, page 6-82 for details on the requirements for the heat recovery system and exceptions to the requirement.

Solar Thermal
Applicability	Water heating systems with a solar thermal system
Definition	A solar thermal water heating system consists of one or more collectors. Water is passed through these collectors and is heated under the right conditions. There are two general types of solar water heaters: integrated collector storage (ICS) systems and active systems. Active systems include pumps to circulate the water, storage tanks, piping, and controls. ICS systems generally have no pumps and piping is minimal. Solar systems may be tested and rated as a complete system or the collectors may be separately tested and rated. SRCC OG-300 is the test procedure for whole systems and SRCC OG-100 is the test procedure for collectors. The building descriptors used to define the solar thermal system may vary with each software application and with the details of system design. Heat produced by solar thermal systems will generally not align perfectly with the need for heating, so the model needs to account for the temporal mismatch in some manner.
Units	Data structure: will vary with the software and system details
Input Restrictions	There are no restrictions, other than agreement with the construction documents.
Baseline Rules	The baseline building has no solar auxiliary system.

Combined Space Heating and Water Heating
Applicability	Projects that use a boiler to provide both space heat and water heating
Definition	A system that provides both space heating and water heating from the same equipment, generally the space heating boiler. Such systems are restricted by the baseline standards, but may be modeled in the candidate building. The restrictions are due to the misalignment of the space heating load and the water heating load. The first is highly intermittent and weather dependent, while the latter is more constant and not generally related to the weather.
Units	Data structure
Input Restrictions	The proposed design may have a combined space and water heating system.
Baseline Rules	The baseline building shall be modeled with separate space heating and water heating systems, meeting the prescriptive requirements for each. The water heating system shall use the same fuel as the combined boiler.

Water heating systems shall always be modeled for both the proposed design and baseline building when the proposed building is expected to have a water heating load, even if no water heating is shown on the plans or specifications for the proposed design. In such instances, an electric resistance system shall be modeled for both the proposed design and baseline building, meeting the efficiency requirements of the baseline standard.

When the construction documents show a water heating system, the layout and configuration of the baseline building system shall be the same as the proposed design, e.g. the baseline building shall have the same number of water heaters and the same distribution system.

System Loads and Configuration

Water Heating System Name
Applicability	All water heating systems
Definition	A unique descriptor for each water heating system. A system consists of one or more water heaters, a distribution system, an estimate of hot water use, and a schedule for that use. Nonresidential buildings will typically have multiple systems, perhaps a separate electric water heater for each office break room, etc. Other building types such as hotels and hospitals may have a single system serving the entire building.
Units	Text, unique
Input Restrictions	Where applicable, this should match the tags that are used on the plans such that a plan reviewer can make a connection.
Baseline Rules	The naming convention for the baseline building system shall be similar to the proposed design.

Water Heating Peak Use
Applicability	All water heating systems, required
Definition	An indication of the peak hot water usage (e.g. service to sinks, showers, and kitchen appliances). When specified per occupant, this value is multiplied by design occupancy density values and modified by service water heating schedules to obtain hourly load values which are used in the simulation. Peak consumption is commonly specified as gallons per hour per occupant, dwelling unit, hotel room, patient room, or floor area. If consumption is specified in gallons per hour, then additional inputs would be needed such as supply temperature, cold water inlet temperature, etc. It is also common to specify peak use as a thermal load in Btu/h. In the latter case, there is an implied assumption for the cold water inlet temperature, supply temperature, distribution losses, and other factors. The thermal load does not include conversion efficiencies of water heating equipment.
Units	Btu/h or gallons/h
Input Restrictions	As designed. If data is unavailable, the defaults in Appendix B may be used.
Baseline Rules	Hot water consumption or load in the baseline building shall be the same as the proposed design, except in cases where: A specific measure is specified for the proposed design that will reduce water consumption. Examples of such measures include low-flow terminal devices or controls. SHW energy consumption can be demonstrated to be reduced by increasing makeup water temperature or reducing SHW temperature (e.g., alternative sanitizing technologies for dishwashing and heat recovery to entering makeup water). SHW energy consumption can be demonstrated to be reduced by reducing the hot fraction of mixed water. Examples include heat recovery laundry or showers drains. NOTE: Calculations need to be provided to support the difference in service hot water loads between the proposed and baseline model.

Water Heating Schedule
Applicability	All water heating systems
Definition	A fractional schedule reflecting the time pattern of water heating use. This input modifies the water heating peak use, described above.
Units	Data structure: schedule, fractional
Input Restrictions	As designed. If information is unkown, use the defaults from Appendix B and C.
Baseline Rules	Hot water schedules for the baseline building shall be the same as the proposed design, except in cases where a specific measure is specified for the proposed design that will reduce water consumption and the impact of the measure can be best approximated through an adjustment to the schedule. In general, such measures would be addressed through an adjustment to the water heating, peak use (see above).

Water Heating System Configuration
Applicability	All water heating systems
Definition	The configuration and layout of the water heating system, including the number of water heaters; the size, location, length and insulation of distribution pipes; recirculation systems and pumps; and any other details about the system that would affect the energy model.
Units	Data structure
Input Restrictions	None
Baseline Rules	The baseline building shall have the same configuration and layout as the proposed design, except that a separate system shall be provided for each building area classification.

Water Main Temperature Schedule
Applicability	All water heating systems
Definition	A monthly temperature schedule indicating the water mains temperature. This temperature and the setpoint temperature are used to convert the load into a water flow rate.
Units	Data structure: schedule, °F
Input Restrictions	Entering water temperature can be defaulted to the values in Table 3.9.1-1 or provided by the user.
Baseline Rules	Same as proposed

Table 3.9.1-1: Monthly Average Water Main Temperatures (°F)

	Climate Zone
Month	1A	1B	2A	2B	3A	3B	3C	4A	4B	4C	5A	5B	5C	6A	6B	7	8
January	76.5	70.2	64.6	65.8	56.5	59.4	59.7	50.8	52.3	52.9	45.5	48.0	50.6	43.1	43.1	37.6	32.0
February	77.1	72.2	65.0	67.3	56.4	59.5	59.5	50.0	51.7	52.3	44.1	47.0	49.9	41.6	41.6	35.6	32.0
March	79.0	77.6	67.9	72.2	59.5	62.4	60.1	52.2	53.8	53.4	45.8	48.7	50.7	42.7	42.5	36.1	32.0
April	81.7	85.1	72.7	79.5	65.0	67.4	61.5	57.0	58.3	56.1	50.1	53.1	52.7	46.4	45.6	39.0	32.0
May	84.6	92.6	77.9	87.2	71.6	73.3	63.2	63.1	64.0	59.5	56.0	58.8	55.5	51.6	50.2	43.5	32.9
June	86.8	98.1	82.3	93.1	77.4	78.4	64.8	68.9	69.3	62.9	61.9	64.3	58.3	57.0	54.9	48.5	36.9
July	87.7	100.2	84.6	95.8	80.8	81.3	65.9	72.7	72.8	65.2	66.2	68.2	60.4	61.1	58.6	52.6	40.7
August	87.1	98.1	84.2	94.3	80.9	81.3	66.1	73.6	73.5	65.9	67.6	69.4	61.1	62.8	60.2	54.7	43.1
September	85.1	92.6	81.2	89.2	77.8	78.3	65.4	71.3	71.3	64.7	65.9	67.6	60.3	61.6	59.2	54.2	43.4
October	82.4	85.1	76.4	81.8	72.2	73.2	64.0	66.4	66.7	62.0	61.5	63.2	58.2	57.9	56.0	51.3	41.5
November	79.5	77.6	71.1	74.2	65.6	67.3	62.3	60.3	61.0	58.5	55.6	57.5	55.4	52.6	51.4	46.7	38.0
December	77.4	72.2	66.8	68.3	59.9	62.3	60.7	54.6	55.8	55.2	49.7	51.9	52.6	47.2	46.7	41.7	33.8

Water Heaters

This section describes the building descriptors for water heaters. Typically, a building will have multiple water heating systems and each system can have multiple water heaters, so these building descriptors may need to be specified more than once.

Water Heater Name
Applicability	All water heaters
Definition	A unique descriptor for each water heater in the system. Some systems will have multiple pieces of equipment, for instance a series of water heaters plumbed in parallel or a boiler with a separate storage tank.
Units	Text, unique
Input Restrictions	Where applicable (This should match the tags that are used on the plans such that a plan reviewer can make a connection.)
Baseline Rules	The naming convention for the baseline building system shall be similar to the proposed design.

Water Heater Type and Size

Applicability

All water heaters

Definition

This building descriptor includes information needed to determine the criteria from baseline standards. The choices are listed below.

Electric water heaters (storage and instantaneous)
- Small (≤ 12 kW)
- Large (> 12 kW)
- Heat pump
Gas storage water heaters
- Small (≤ 75,000 Btu/h)
- Large (> 75,000 Btu/h)
Gas instantaneous water heaters
- Small (> 50,000 and < 200,000 Btu/h)
- Large (≥ 200,000 Btu/h) and < 10 gal
- Large (≥ 200,000 Btu/h) and ≥ 10 gal
Oil storage water heaters
- Small (≤ 105,000 Btu/h)
- Large (> 105,000 Btu/h)
Oil instantaneous water heaters
- Small (≤ 210,000 Btu/h)
- Large (> 210,000 Btu/h) and < 10 gal
- Large (> 210,000 Btu/h) and ≥ 10 gal
Gas hot water supply boiler
Oil hot water supply boiler
Heat exchanger from steam or district hot water

Units

List (see above)

Input Restrictions

The water heater type shall agree with equipment specified in the construction documents.

If no service hot water system exists or has been specified, but the building will have service hot water loads, a service water system using electric resistance heat shall be assumed.

For buildings that will have no service hot water load, no service water heating system shall be modeled.

Baseline Rules

Water heaters in the baseline system shall be based on the building classification. See Table 3.9.1-2 below.

Table 3.9.1-2: Baseline Building Water Heater Type (Table G3.1.1-2)

Gas Storage

Electric Resistance Storage

Automotive facility

Dining: Bar lounge/leisure

Dining: Cafeteria/fast food

Dining: Family

Dormitory

Exercise center

Fire station

Gymnasium

Health-care clinic

Hospital

Hotel

Manufacturing facility

Motel

Multifamily

Penitentiary

Performing arts theater

School/university

Sports arena

Workshop

All Others

Convention center

Courthouse

Library

Motion picture theater

Museum

Office

Parking garage

Police station

Post office

Religious building

Retail

Town hall

Transportation

Warehouse

Rated Capacity
Applicability	All water heaters
Definition	The heating capacity of a water heater at the rated conditions specified in DOE 10 CFR Part 430 or ANSI Z21.10.
Units	kBtu/h
Input Restrictions	As designed.
Baseline Rules	Autosize

Storage Volume
Applicability	All water heaters
Definition	The storage volume of a gas-fired water heater. This is used in the standby loss calculations and baseline calculations of energy factor (EF).
Units	gallons
Input Restrictions	As designed.
Baseline Rules	Autosize

Energy Factor

Applicability

Equipment covered by National Appliance Energy Conservation Act (NAECA), which includes small storage and instantaneous water heaters

Definition

The energy factor (EF) is the ratio of the energy delivered by the water heater divided by the energy used, in the same units. EF is calculated according to the DOE 10 CFR Part 430 test procedure, which specifies a 24-hour pattern of draws, a storage temperature, inlet water temperature, and other test conditions. These conditions result in the energy delivered for the test period. Energy inputs are measured for the same test period and the EF ratio is calculated.

Units

Unitless ratio

Input Restrictions

Building descriptors for the proposed design should be consistent with equipment specified on the construction documents or observed in the candidate building.

Baseline Rules

The EF for the baseline building system shall be determined from Table 7.8 of ASHRAE Standard 90.1-2007, depending on the purpose of the simulations.

Table 3.9.1-3: Baseline Water Heater Efficiency

	Size Category (Input)	Performance Required
Electric Storage	≤ 12 kW	EF= 0.97 - 0.00035 V
	> 12 kW	%h = 0.3 + 27/Vm
Gas Storage	≤ 75,000 Btu/h	EF = 0.67 -0.0005V
	> 75,000 Btu/h	Et = 80%, SL = Q/799 + 16.6 √V
SL = Standby loss in percent per hour; V = Rated tank volume (gallons; Vm = Measured volume in the tank; Q = nameplate input rate (Btu/h); Et = thermal efficiency; %h = tank loss per hour expressed as a percentage

Thermal Efficiency
Applicability	Oil and gas fired water heaters not covered by NAECA energy factor requirements
Definition	The full load efficiency of a water heater at rated conditions expressed as a dimensionless ratio of output over input
Units	Unitless ratio between 0 and 1.0
Input Restrictions	Building descriptors for the proposed design should be consistent with equipment specified on the construction documents or observed in the candidate building.
Baseline Rules	Thermal efficiency is only used when the baseline system is a gas storage water heater > 75,000 Btu/h. In this case, the thermal efficiency (Et) is 80%.

Tank Standby Loss
Applicability	Water heaters not covered by NAECA energy factor requirements
Definition	The tank standby loss for storage tanks, which includes the effect of recovery efficiency.
Units	Btu/h for the entire tank or percent standby loss (%h)
Input Restrictions	As specified in manufacturer data and documented on the construction documents
Baseline Rules	See Table 9.1.3-3.

Tank Off-Cycle Loss Coefficient
Applicability	Water heaters
Definition	The tank standby loss coefficient (UA) for the water heater. For small water heaters covered by NAECA, the loss coefficient is a derived parameter, a function of the energy factor and recovery efficiency.
Units	Btu/h-°F
Input Restrictions	For NAECA covered water heaters, the loss coefficient is calculated by the following: (Equation 3.9.1-1) $$UA = \frac{1/EF = 1/RE}{67.4 \cdot (\frac{24}{41094}-\frac{1}{RE \cdot P_{on}})}$$ Where: EF = The energy factor of the rated water heater (unitless) RE = The recovery efficiency of the rated water heater. If this data is not available, the default shall be 0.78 for gas water heaters and 0.93 for electric water heaters. Pon = The input power to the water heater, in Btu/h
Baseline Rules	The baseline loss coefficient for NAECA water heaters shall be 10 Btu/h-°F for gas-fired water heaters

Off-Cycle Parasitic Losses
Applicability	Water heaters
Definition	The rate of parasitic losses, such as a pilot light or controls, when the water heater is not heating. If modeled explicitly, pilot lights should contribute to off-cycle heating.
Units	Watts
Input Restrictions	As designed
Baseline Rules	0

Off-Cycle Fuel Type
Applicability	Water heaters
Definition	The type of fuel that serves energy using parasitic equipment, such as a pilot light or controls, when the water heater is not heating
Units	List: electricity, gas, oil, propane
Input Restrictions	As designed
Baseline Rules	Not applicable

On-Cycle Parasitic Losses
Applicability	Water heaters
Definition	The rate of parasitic losses, such as a pilot light or draft fan controls, when the water heater is heating. This may be different than off cycle losses if the flue energy is considered.
Units	Watts
Input Restrictions	As designed
Baseline Rules	0

On-Cycle Fuel Type
Applicability	Water heaters
Definition	The type of fuel that serves energy using parasitic equipment, such as a pilot light or controls, when the water heater is not heating
Units	List: electricity, gas, oil, propane
Input Restrictions	As designed
Baseline Rules	Not applicable

Water Heater Ambient Temperature Indicator
Applicability	Water heaters
Definition	The location of the water heater for determining losses and energy interaction with the surroundings
Units	List: Schedule, Zone, Outdoors
Input Restrictions	As designed. When “Schedule” is used, a time of day schedule needs to be specified with temperature schedule for each hour.
Baseline Rules	Same as proposed

Fuel Water Heater Part Load Efficiency Curve

Applicability

Equipment not covered by NAECA for which a thermal efficiency, as opposed to an EF is specified

Definition

A set of factors that adjust the full-load thermal efficiency for part load conditions. Typically, the factor is set as a curve.

Units

Percent (%)

Input Restrictions

The following default curve shall be used unless detailed information is provided to justify alternative values. The default curve shall take the form of a quadratic equation as follows:

(Equation 3.9.1-2)

$$Fuel_{PartLoad} = Fuel_{Design} \times FHeatPLC$$

$$FHeatPLC = a + b \cdot \frac{Q_{PartLoad}}{Q_{Rated}} + c \cdot \left ( \frac{Q_{PartLoad}}{Q_{Rated}} \right ) ^{2}$$

where

FHeatPLC	The fuel heating part load efficiency curve
Fuelpartload	The fuel consumption at part load conditions (Btu/h)
Fueldesign	The fuel consumption at design conditions (Btu/h)
Qpartload	The water heater capacity at part load conditions (Btu/h)
Qrated	The water heater capacity at design conditions (Btu/h)
a	Constant, 0.021826
b	Constant, 0.977630
c	Constant, 0.000543

Baseline Rules

The baseline building equipment shall use the default curve

Recirculation Systems

This section describes the building descriptors for hot water recirculation systems. The baseline building has a recirculation system when the proposed design does. This is one aspect of the water heating system configuration (see above).

Recirculation System Name
Applicability	All recirculation systems
Definition	A unique descriptor for each water heating recirculation system
Units	Text, unique
Input Restrictions	Where applicable, this should match the tags or descriptions that are used on the plans such that a plan reviewer can make a connection.
Baseline Rules	The naming convention for the baseline building system shall be similar to the proposed design.

Pumping Power
Applicability	All recirculation systems
Definition	The electric demand of the pumps when the recirculation system is operating. This input is a function of the flow rate, the pumping head, the motor efficiency, and the pump efficiency. Some software may allow each of these factors to be separately entered.
Units	Watts (W)
Input Restrictions	Pumping power shall be consistent with the piping configuration, flow rate, and equipment specified on the construction documents.
Baseline Rules	Pumping power in the baseline building shall be the same as the proposed design unless specific measures are included in the proposed design to reduce the pumping power. Example measures could include reducing pumping head by oversizing distribution piping or specifying premium efficiency motors or pumps.

Schedule
Applicability	All recirculation systems
Definition	An on/off or fraction schedule that indicates when the recirculation system is expected to be operated
Units	Data structure: schedule, on/off or fraction
Input Restrictions	The schedule for operation of the recirculation system shall be consistent with the design intent of the system. Hotels, hospitals, and other 24x7 institutional buildings will typically have a system that runs continuously. The schedule should be consistent with the controls called for on the construction documents: no control (runs constantly), timer control, temperature control, timer/temperature control, or demand control.
Baseline Rules	Recirculation schedules for the baseline building shall be the same as the proposed design.

Piping
Applicability	All recirculation systems
Definition	The heat loss rate of piping for recirculating systems. This may be defined separately for pipe that is exposed to outdoor conditions, indoor or semi-heated conditions, or buried underground conditions. These losses may be modeled as additional loads on the water heater(s).
Units	Btu/h-°F specified separately for outdoor, indoor, or buried locations
Input Restrictions	In accordance with Standard 90.1-2016, Section G3.1.3.6, piping heat losses are not modeled for the proposed building
Baseline Rules	Same as proposed design.

Water Healing Auxiliaries

External Storage Tank Insulation
Applicability	All water heating systems that have an external storage tank
Definition	Some water heating systems have a storage tank that is separate from the water heater(s) that provides additional storage capacity. This building descriptor addresses the heat loss related to the external tank, which is an additional load that must be satisfied by the water heater(s). The heat loss shall account for the surface area and U-factor tank, as well as the average temperature conditions where the tank is located. Some software may allow these factors to be separately specified.
Units	R-value (h-ft2-°F/Btu)
Input Restrictions	As specified in manufacturer data and documented on the construction documents
Baseline Rules	The baseline building does not have an external storage tank.

External Storage Tank Area
Applicability	All water heating systems that have an external storage tank
Definition	Some water heating systems have a storage tank that is separate from the water heater(s) that provides additional storage capacity. This documents the entire exterior surface area of the tank.
Units	ft²
Input Restrictions	As specified in manufacturer specifications
Baseline Rules	The baseline building does not have an external storage tank.

Heat Recovery
Applicability	Water heating systems that are coupled to heat recovery equipment
Definition	Building equipment such as air conditioners, chillers, gas fired generators, etc. produce thermal energy that may be recovered and used to heat water. The heat producing characteristics are generally defined for the equipment that is producing the heat, not the equipment that is receiving the heat (water heaters in this case). The building descriptors will vary depending on the equipment. The models for heat producing equipment need to produce output on an hourly basis so that the schedule of heat production and heating needs can be aligned and evaluated in the water heating model.
Units	Data structure: depends on the equipment producing the heat
Input Restrictions	There are no restrictions, other than agreement with the construction documents.
Baseline Rules	The baseline building has heat recovery when the when all of the following conditions are true: The building operates 24 hours per day. The building has water cooled chillers with a heat rejection capacity greater than 6 million Btu/h. This equates to about 400 tons of electric chiller capacity. The water heating peak use is greater than 1,000,000 Btu/h.

Solar Thermal
Applicability	Water heating systems with a solar thermal system
Definition	A solar thermal water heating system consists of one or more collectors. Water is passed through these collectors and is heated under the right conditions. There are two general types of solar water heaters: integrated collector storage (ICS) systems and active systems. Active systems include pumps to circulate the water, storage tanks, piping, and controls. ICS systems generally have no pumps and piping is minimal. Solar systems may be tested and rated as a complete system or the collectors may be separately tested and rated. SRCC OG-300 is the test procedure for whole systems and SRCC OG-100 is the test procedure for collectors. The building descriptors used to define the solar thermal system may vary with each software application and with the details of system design. Heat produced by solar thermal systems will generally not align perfectly with the need for heating, so the model needs to provide storage to account for the temporal mismatch.
Units	Data structure: will vary with the software and system details
Input Restrictions	There are no restrictions, other than agreement with the construction documents.
Baseline Rules	The baseline building has no solar auxiliary system.

Combined Space Heating and Water Heating
Applicability	Projects that use a boiler to provide both space heat and water heating
Definition	A system that provides both space heating and water heating from the same equipment, generally the space heating boiler. Such systems are restricted by the baseline standards, but may be modeled in the candidate building. The restrictions are due to the misalignment of the space heating load and the water heating load. The first is highly intermittent and weather dependent, while the latter is more constant and not generally related to the weather.
Units	Data structure
Input Restrictions	The proposed design may have a combined space and water heating system.
Baseline Rules	The baseline building shall be modeled with separate space heating and water heating systems, meeting the prescriptive requirements for each. The water heating system shall use the same fuel as the combined boiler.

90.1-2019

Water heating systems shall always be modeled for both the proposed design and baseline building when the proposed building is expected to have a water heating load, even if no water heating is shown on the plans or specifications for the proposed design. In such instances, an electric resistance system shall be modeled for both the proposed design and baseline building, meeting the efficiency requirements of the baseline standard.

When the construction documents show a water heating system, the layout and configuration of the baseline building system shall be the same as the proposed design, e.g., the baseline building shall have the same number of water heaters and the same distribution system.

3.9.1.1 System Loads and Configuration

Water Heating System Name
Applicability	All water heating systems
Definition	A unique descriptor for each water heating system. A system consists of one or more water heaters, a distribution system, an estimate of hot water use, and a schedule for that use. Nonresidential buildings will typically have multiple systems, perhaps a separate electric water heater for each office break room, etc. Other building types such as hotels and hospitals may have a single system serving the entire building.
Units	Text, unique
Input Restrictions	Where applicable, this should match the tags that are used on the plans such that a plan reviewer can make a connection
Baseline Building	The naming convention for the baseline building system shall be similar to the proposed design

Water Heating Peak Use
Applicability	All water heating systems, required
Definition	An indication of the peak hot water usage (e.g., service to sinks, showers, and kitchen appliances). When specified per occupant, this value is multiplied by design occupancy density values and modified by service water heating schedules to obtain hourly load values that are used in the simulation. Peak consumption is commonly specified as gallons per hour per occupant, dwelling unit, hotel room, patient room, or floor area. If consumption is specified in gallons per hour, then additional inputs would be needed such as supply temperature, cold water inlet temperature, etc. It is also common to specify peak use as a thermal load in Btu/h. In the latter case, there is an implied assumption for the cold water inlet temperature, supply temperature, distribution losses, and other factors. The thermal load does not include conversion efficiencies of water heating equipment.
Units	Btu/h or gallons/h
Input Restrictions	As designed. If these values are not available, the hot water use specified in COMNET Appendix B (COMNET 2017) may be used.
Baseline Building	Hot water consumption or load in the baseline building shall be the same as the proposed design, except in cases where: · A specific measure is specified for the proposed design that will reduce water consumption. Examples of such measures include low-flow terminal devices or controls. The baseline flow rates shall be determined based on prescriptive requirements in Standard 90.1-2019. When no such prescriptive requirement exists, it shall be equal to requirements of other efficiency or equipment codes or standards applicable to the design of the building systems and equipment. · SHW energy consumption can be demonstrated to be reduced by increasing makeup water temperature or reducing SHW temperature (e.g., alternative sanitizing technologies for dishwashing and heat recovery to entering makeup water). · SHW energy consumption can be demonstrated to be reduced by reducing the hot fraction of mixed water. Examples include heat recovery laundry or showers drains. NOTE: Calculations need to be provided to support the difference in service hot water loads between the proposed and baseline model.

Water Heating Schedule
Applicability	All water heating systems
Definition	A fractional schedule reflecting the time pattern of water heating use. This input modifies the water heating peak use, described above.
Units	Data structure: schedule, fractional
Input Restrictions	As designed. If these values are not available, the hot water use specified in COMNET Appendix B (COMNET 2017) may be used.
Baseline Building	Hot water schedules for the baseline building shall be the same as the proposed design, except in cases where a specific measure is specified for the proposed design that will reduce water consumption and the impact of the measure can be best approximated through an adjustment to the schedule. In general, such measures would be addressed through an adjustment to the water heating, peak use (see above).

Water Heating System Configuration
Applicability	All water heating systems
Definition	The configuration and layout of the water heating system, including the number of water heaters; the size, location, recirculation systems and pumps; and any other details about the system that would affect the energy model. Piping heat losses shall not be modeled per Standard 90.1-2019.
Units	Data structure
Input Restrictions	None
Baseline Building	The number of water heaters in the baseline building are dependent on the building area types. Section 3.8.1.2 discusses the requirements for the baseline building model.

Water Mains Temperature Schedule
Applicability	All water heating systems
Definition	A monthly temperature schedule indicating the water mains temperature. This temperature and the setpoint temperature are used to convert the load into a water flow rate.
Units	Data structure: schedule, °F
Input Restrictions	Entering water temperature can be defaulted to the values in Table 95 or provided by the user
Baseline Building	Same as proposed Table 95. Defaults for Water Mains Temperature Based on Climate Zone

3.9.1.2 Water Heaters

This section describes the building descriptors for water heaters. Typically, a building will have multiple water heating systems and each system can have multiple water heaters, so these building descriptors may need to be specified more than once.

Water Heating Name
Applicability	All water heaters
Definition	A unique descriptor for each water heater in the system. Some systems will have multiple pieces of equipment, for instance a series of water heaters plumbed in parallel or a boiler with a separate storage tank.
Units	Text, unique
Input Restrictions	Where applicable, this should match the tags that are used on the plans such that a plan reviewer can make a connection
Baseline Building	The naming convention for the baseline building system shall be similar to the proposed design

Water Heater Type and Size

Applicability

All water heaters

Definition

This building descriptor includes information needed to determine the criteria from baseline standards. The choices are listed below.

· Electric water heaters (storage and instantaneous)

Small (≤ 12 kW)

Large (> 12 kW)

Heat pump

· Gas storage water heaters

Small (≤ 75,000 Btu/h)

Large (> 75,000 Btu/h)

· Gas instantaneous water heaters

Small (> 50,000 and < 200,000 Btu/h)

Large (≥ 200,000 Btu/h), <10 gal

Large (≥ 200,000 Btu/h), >= 10 gal

· Oil storage water heaters

Small (≤ 105,000 Btu/h)

Large (> 105,000 Btu/h)

· Oil instantaneous water heaters

Small (≤ 210,000 Btu/h)

Large (> 210,000 Btu/h), <10 gal

Large (> 210,000 Btu/h), >= 10 gal

· Gas hot water supply boiler

· Oil hot water supply boiler

· Heat exchanger from steam or district hot water

Units

List (see above)

Input Restrictions

The water heater type shall agree with equipment specified in the construction documents. If no service hot water system exists or has been specified, but the building will have service hot water loads, a service water system shall be modeled that matches the system type in the baseline building design. For buildings that will have no service hot water load, no service water heating system shall be modeled.

Baseline Building

Where a complete water heating system exists or a new service water heating system has been specified in the proposed design, the water heaters in the baseline system will be based on the building area type classification. See Table 96 below.

For new service hot water systems, the system will be sized according to the provisions of Standard 90.1-2019, Section 7.4.1, and the equipment shall match the minimum efficiency requirements in Standard 90.1-2019, Section 7.4.2. Where the energy source is electricity, the heating method shall be electrical resistance. When the energy source is ‘Gas Storage’, the water heater shall be modeled using natural gas as their fuel. Where natural gas is not available or the proposed building site, as determined by the rating authority, gas storage water heaters shall be modeled using propane as their fuel.

If no service hot water system exists or has been specified, but the building will have service hot water loads, a service water system shall be modeled for each building area type in the proposed design, in accordance to Table 96. and matching minimum efficiency requirements of Standard 90.1-2019, Section 7.4.2.

Table 96. Baseline Building Water Heater Type (Standard 90.1-2019 Table G3.1.1-2)

Gas Storage	Electric Resistance Storage
Automotive facility	Convenience Store
Dining: Bar lounge/leisure	Convention center
Dining: Cafeteria/fast food	Courthouse
Dining: Family	Health-care clinic
Dormitory	Library
Exercise center	Motion picture theater
Fire station	Museum
Grocery Store	Office
Gymnasium	Parking garage
Hospital and Outpatient Surgery Center	Police station
Hotel	Post office
Manufacturing facility	Religious building
Motel	Retail
Multifamily	Town hall
Penitentiary	Transportation
Performing arts theater	Warehouse
School/university	Workshop
Sports arena
All Others

Rated Capacity
Applicability	All water heaters
Definition	The heating capacity of a water heater at the rated conditions specified in DOE 10 CFR Part 430 or ANSI Z21.10
Units	Thousands of British thermal units per hour (MBH)
Input Restrictions	As designed. If the loads are not met, then the system needs to be autosized.
Baseline Building	Autosize

Storage Volume
Applicability	All water heaters
Definition	The storage volume of a gas-fired water heater. This is used in the standby loss calculations and baseline calculations of energy factor (EF).
Units	gallons
Input Restrictions	As designed. If the loads are not met, then the system needs to be autosized.
Baseline Building	Autosize

Energy Factor
Applicability	Equipment covered by the National Appliance Energy Conservation Act (NAECA), which includes small storage and instantaneous water heaters
Definition	The EF is the ratio of the energy delivered by the water heater divided by the energy used, in the same units. EF is calculated according to the DOE 10 CFR Part 430 test procedure, which specifies a 24-hour pattern of draws, a storage temperature, inlet water temperature, and other test conditions. These conditions result in the energy delivered for the test period. Energy inputs are measured for the same test period and the EF ratio is calculated.
Units	Unitless ratio (between 0 and 1)
Input Restrictions	Building descriptors for the proposed design should be consistent with equipment specified on the construction documents or observed in the candidate building
Baseline Building	The EF for the baseline building system shall be determined from Table 7.8 of Standard 90.1-2019. Additional UEF efficiency requirements can be found in Table F-2 of Standard 90.1-2019.

Thermal Efficiency
Applicability	Oil and gas-fired water heaters not covered by NAECA
Definition	The full load efficiency of a water heater at rated conditions expressed as a dimensionless ratio of output over input
Units	Unitless ratio (between 0 and 1)
Input Restrictions	Building descriptors for the proposed design should be consistent with equipment specified on the construction documents or observed in the candidate building
Baseline Building	From Table 7.8 of Standard 90.1-2019, also documented in .

Tank Standby Loss
Applicability	Water heaters not covered by NAECA
Definition	The tank standby loss for storage tanks, which includes the effect of recovery efficiency
Units	Btu/h for the entire tank
Input Restrictions	As specified in manufacturer data and documented on the construction documents
Baseline Building	As specified in Table 7.8 of Standard 90.1-2019, also documented in

Tank Off-Cycle Loss Coefficient
Applicability	Water heaters
Definition	The tank standby loss coefficient (UA) for the water heater. For small water heaters covered by NAECA, the loss coefficient is a derived parameter, a function of the energy factor and recovery efficiency.
Units	Btu/h-°F
Input Restrictions	For NAECA covered water heaters, the loss coefficient is calculated by the following: Where: EF = The energy factor of the rated water heater (unitless) RE = The recovery efficiency of the rated water heater. If this data is not available, the default shall be 0.78 for gas water heaters and 0.93 for electric water heaters. Pon = The input power to the water heater, in Btu/h
Baseline Building	The baseline loss coefficient for NAECA water heaters shall be: 10 Btu/h-°F for gas-fired water heaters

Off Cycle Parasitic Losses
Applicability	Water heater
Definition	The rate of parasitic losses, such as a pilot light or controls, when the water heater is not heating. If modeled explicitly, pilot lights should contribute to off-cycle heating.
Units	Watts
Input Restrictions	As designed
Baseline Building	0

Off Cycle Fuel Type
Applicability	Water heater
Definition	The type of fuel that serves energy using parasitic equipment, such as a pilot light or controls, when the water heater is not heating
Units	List: Electricity, Gas, Oil, Propane
Input Restrictions	As designed
Baseline Building	Not applicable

Water Heater Ambient Temperature Indicator
Applicability	Water heater
Definition	The location of the water heater for determining losses and energy interaction with the surroundings
Units	List: Schedule, Zone, Outdoors
Input Restrictions	As designed. When “Schedule” is used, a time of day schedule needs to be specified with temperature schedule for each hour.
Baseline Building	Same as proposed

Fuel Water Heater Part Load Efficiency Curve
Applicability	Water heating equipment for which a thermal efficiency as opposed to an EF is specified
Definition	A set of factors that adjust the full-load thermal efficiency for part load conditions. The factor is set as a curve.
Units	Percent (%)
Input Restrictions	The following default curve shall be used unless detailed information is provided to justify alternative values. The default curve shall take the form of a quadratic equation as follows: Where: FHeatPLC = The fuel heating part load efficiency curve Fuelpartload = The fuel consumption at part load conditions (Btu/h) Fuel design = The fuel consumption at design conditions (Btu/h) Qpartload = The water heater capacity at part load conditions (Btu/h) Qrated = The water heater capacity at design conditions (Btu/h) a = Constant, 0.021826 b = Constant, 0.977630 c = Constant, 0.000543
Baseline Building	The baseline shall use the default curve

3.9.1.3 Recirculation Systems

This section describes the building descriptors for hot water recirculation systems. The baseline building has a recirculation system when the proposed design does. This is one aspect of the water heating system configuration (see above).

Recirculation System Name
Applicability	All recirculation systems
Definition	A unique descriptor for each water heating recirculation system
Units	Text, unique
Input Restrictions	Where applicable, this should match the tags or descriptions that are used on plans such that a plan reviewer can make a connection
Baseline Building	The naming convention of the baseline building shall be similar to the proposed design

Pumping Power
Applicability	All recirculation systems
Definition	The electric demand of the pumps when the recirculation system is operating. This input is a function of the flow rate, the pumping head, the motor efficiency, and the pump efficiency. Some software may allow each of these factors to be separately entered.
Units	Watts (W)
Input Restrictions	Pumping power shall be consistent with the piping configuration, flow rate, and equipment specified on the construction documents
Baseline Building	Pumping power in the baseline building shall be the same as the proposed design unless specific measures are included in the proposed design to reduce the pumping power. Example measures could include reducing pumping head by oversizing distribution piping or specifying premium efficiency motors or pumps.

Schedule
Applicability	All recirculation systems
Definition	An on/off or fraction schedule that indicates when the recirculation system is expected to be operated
Units	Data structure: schedule, on/off or fraction
Input Restrictions	The schedule for operation of the recirculation system shall be consistent with the design intent of the system. Hotels, hospitals, and other 24x7 institutional buildings will typically have a system that runs continuously. The schedule should be consistent with the controls called for on the construction documents: no control (runs constantly), timer control, temperature control, timer/temperature control, or demand control.
Baseline Building	Recirculation schedules for the baseline building shall be the same as the proposed design

Piping
Applicability	All recirculation systems
Definition	The heat loss rate of piping for recirculating systems. This may be defined separately for pipe that is exposed to outdoor conditions, indoor or semi-heated conditions, or buried underground conditions.
Units	Btu/h-°F specified separately for outdoor, indoor, or buried locations
Input Restrictions	In accordance with Standard 90.1-2019, Section G3.1.3.6, piping heat losses are not modeled for the proposed building
Baseline Building	Piping losses shall not be modeled for the baseline building.

3.9.1.4 Water Heating Auxiliaries

External Storage Tank Insulation
Applicability	All water heating systems that have an external storage tank
Definition	Some water heating systems have a storage tank that is separate from the water heater(s) that provides additional storage capacity. This building descriptor addresses the heat loss related to the external tank, which is an additional load that must be satisfied by the water heater(s).
Units	R-value (h-ft2-°F/Btu)
Input Restrictions	As specified in manufacturer data and documented on the construction documents
Baseline Building	Heat loss associated with the storage tank in the baseline building shall meet the requirements for an unfired storage tank in the baseline standards (Standard 90.1-2019, Table 7.8), which is an insulation R-value of 12.5. The surface area and location of the storage tank shall be the same as the proposed design.

External Storage Tank Area
Applicability	All water heating systems that have an external storage tank
Definition	Some water heating systems have a storage tank that is separate from the water heater(s) that provides additional storage capacity. This documents the entire exterior surface area of the tank.
Units	ft2
Input Restrictions	As specified in manufacturer specifications
Baseline Building	Same as proposed

External Storage Tank Location
Applicability	All water heating systems that have an external storage tank
Definition	Location of the storage tank, used to determine the heat loss rate and energy exchange with the surroundings
Units	List: Schedule, Zone, Outdoors
Input Restrictions	As designed
Baseline Building	Same as proposed

Solar Thermal
Applicability	Water heating systems with a solar thermal system
Definition	A solar thermal water heating system consists of one or more collectors. Water is passed through these collectors and is heated under the right conditions. There are two general types of solar water heaters: integrated collector storage (ICS) systems and active systems. Active systems include pumps to circulate the water, storage tanks, piping, and controls. ICS systems generally have no pumps and piping is minimal. Solar systems may be tested and rated as a complete system or the collectors may be separately tested and rated. SRCC OG-300 is the test procedure for whole systems and SRCC OG-100 is the test procedure for collectors. The building descriptors used to define the solar thermal system may vary with each software application and with the details of system design. The solar fraction shall be estimated by the f-chart procedure for solar water heating systems.
Units	Data structure: will vary with the software and system details
Input Restrictions	As designed. The proposed design may have a combined space and water heating system.
Baseline Building	Not applicable

Combined Space Heating and Water Heating
Applicability	Projects that use a boiler to provide both space heat and water heating
Definition	A system that provides both space heating and water heating from the same equipment, generally the space heating boiler. Such systems are restricted by the baseline standards, but may be modeled in the candidate building. The restrictions are due to the misalignment of the space heating load and the water heating load. The first is highly intermittent and weather dependent, while the latter is more constant and not generally related to the weather.
Units	Data structure
Input Restrictions	As designed. The proposed design may have a combined space and water heating system.
Baseline Building	The baseline building shall be modeled with separate space heating and water heating systems, according to the baseline system type and corresponding reqirmenets in Section 3.1.1 and baseline water heating system type and requirments identified in Section 3.8.1 .

System Loads and Configuration

Water Heating System Name
Applicability	All water heating systems
Definition	A unique descriptor for each water heating system. A system consists of one or more water heaters, a distribution system, an estimate of hot water use, and a schedule for that use. Nonresidential buildings will typically have multiple systems, perhaps a separate electric water heater for each office break room, etc. Other building types such as hotels and hospitals may have a single system serving the entire building.
Units	Text, unique
Input Restrictions	Where applicable, this should match the tags that are used on the plans such that a plan reviewer can make a connection.

Water Heating Peak Use
Applicability	All water heating systems, required
Definition	An indication of the peak hot water usage (e.g. service to sinks, showers, and kitchen appliances, etc.). When specified per occupant, this value is multiplied by design occupancy density values and modified by service water heating schedules to obtain hourly load values which are used in the simulation. Peak consumption is commonly specified as gallons per hour per occupant, dwelling unit, hotel room, patient room, or floor area. If consumption is specified in gallons per hour, then additional inputs would be needed such as supply temperature, cold water inlet temperature, etc. It is also common to specify peak use as a thermal load in Btu/h. In the latter case, there is an implied assumption for the cold water inlet temperature, supply temperature, distribution losses, and other factors. The thermal load does not include conversion efficiencies of water heating equipment.
Units	Btu/h or gallons/h
Input Restrictions	For the purpose of green building ratings and Design to Earn ENERGY STAR, the inputs from Appendix B are default values, but other values may be used with justification.

Water Heating Schedule
Applicability	All water heating systems, required
Definition	A fractional schedule reflecting the time pattern of water heating use. This input modifies the water heating peak use, described above.
Units	Data structure: schedule, fractional
Input Restrictions	For the purpose of green building ratings and Design to Earn ENERGY STAR, the inputs from Appendix B, Table 7 are default values, but other values may be used with justification.

Water Heating System Configuration
Applicability	All water heating systems, required
Definition	The configuration and layout of the water heating system, including the number of water heaters; the size, location, length and insulation of distribution pipes; recirculation systems and pumps; and any other details about the system that would affect the energy model.
Units	Data structure
Input Restrictions	None

Water Heaters

This section describes the building descriptors for water heaters. Typically, a building will have multiple water heating systems and each system can have multiple water heaters, so these building descriptors may need to be specified more than once.

Water Heater Name
Applicability	All water heaters
Definition	A unique descriptor for each water heater in the system. Some systems will have multiple pieces of equipment, for instance a series of water heaters plumbed in parallel or a boiler with a separate storage tank.
Units	Text, unique
Input Restrictions	Where applicable, this should match the tags that are used on the plans such that a plan reviewer can make a connection.

Water Heater Type and Size
Applicability	All water heaters
Definition	This building descriptor includes information needed to determine the criteria from baseline standards. The choices are listed below. See Table 7.2.2 of ASHRAE Standard 90.1-2001 or Table 7.8 of ASHRAE Standard 90.1-2007 for more detail. Electric water heaters (storage and instantaneous) Small (≤ 12 kW) Large (> 12 kW) Heat pump Gas storage water heaters Small (≤ 75,000 Btu/h) Medium (> 75,000 and ≤ 155,000 Btu/h) Large (> 155,000 Btu/h) Gas instantaneous water heaters Small (> 50,000 and < 200,000 Btu/h) Large (≥ 200,000 Btu/h) Oil storage water heaters Small (≤ 105,000 Btu/h) Medium (> 105,000 and ≤ 155,000 Btu/h) Large (> 155,000 Btu/h) Oil instantaneous water heaters Small (≤ 210,000 Btu/h) Large (> 210,000 Btu/h) Gas hot water supply boiler Oil hot water supply boiler
Units	List (see above)
Input Restrictions	The water heater type shall agree with equipment specified in the construction documents.

Rated Capacity
Applicability	All water heaters
Definition	The heating capacity of a water heater at the rated conditions specified in Table 7.8 of ASHRAE Standard 90.1-2007 or Table 7.2.2 of ASHRAE Standard 90.1-2001
Units	Thousands of British Thermal Units per hour (MBH)
Input Restrictions	As designed. If the loads are not met, autosize.

Energy Factor
Applicability	Equipment covered by NAECA, which includes small storage and instantaneous water heaters
Definition	The energy factor (EF) is the ratio of the energy delivered by the water heater divided by the energy used, in the same units. EF is calculated according to the DOE 10 CFR Part 430 test procedure, which specifies a 24-hour pattern of draws, a storage temperature, inlet water temperature, and other test conditions. These conditions result in the energy delivered for the test period. Energy inputs are measured for the same test period and the EF ratio is calculated.
Units	Unitless ratio
Input Restrictions	Building descriptors for the proposed design should be consistent with equipment specified on the construction documents or observed in the candidate building.

Thermal Efficiency
Applicability	Oil and gas fired water heaters not covered by NAECA
Definition	The full load efficiency of a water heater at rated conditions expressed as a dimensionless ratio of output over input
Units	Unitless ratio
Input Restrictions	Building descriptors for the proposed design should be consistent with equipment specified on the construction documents or observed in the candidate building.

Tank Standby Loss
Applicability	Water heaters not covered by NAECA
Definition	The tank standby loss for storage tanks, which includes the effect of recovery efficiency.
Units	Btu/h for the entire tank
Input Restrictions	As specified in manufacturer data and documented on the construction documents

Fuel Water Heater Part Load Efficiency Curve

Applicability

Equipment not covered by NAECA for which a thermal efficiency, as opposed to an EF is specified

Definition

A set of factors that adjust the full-load thermal efficiency for part load conditions. Typically, the factor is set as a curve.

Units

Percent (%)

Input Restrictions

The following default curve shall be used unless detailed information is provided to justify alternative values. The default curve shall take the form of a quadratic equation as follows:

(6.9.1-1)

$$ Fuel_{partload} = Fuel_{design} \times F\!HeatP\!L\!C$$ $$F\!HeatP\!L\!C = \left ( a+ b \times \frac{Q_{partload}}{Q_{rated}} + c \times \left ( \frac{Q_{partload}}{Q_{rated}}\right )^2 \right )$$where

FHeatPLC	The fuel heating part load efficiency curve
Fuel_partload	The fuel consumption at part load conditions (Btu/h)
Fuel_design	The fuel consumption at design conditions (Btu/h)
Q_partload	The water heater capacity at part load conditions (Btu/h)
Q_rated	The water heater capacity at design conditions (Btu/h)
a	Constant, 0.021826
b	Constant, 0.977630
c	Constant, 0.000543

Recirculation Systems

This section describes the building descriptors for hot water recirculation systems. The baseline building has a recirculation system when the proposed design does. This is one aspect of the water heating system configuration (see above).

Recirculation System Name
Applicability	All recirculation systems
Definition	A unique descriptor for each water heating recirculation system
Units	Text, unique
Input Restrictions	Where applicable, this should match the tags or descriptions that are used on the plans such that a plan reviewer can make a connection.

Pumping Power
Applicability	All recirculation systems
Definition	The electric demand of the pumps when the recirculation system is operating. This input is a function of the flow rate, the pumping head, the motor efficiency, and the pump efficiency. Some software may allow each of these factors to be separately entered.
Units	Watts (W)
Input Restrictions	Pumping power shall be consistent with the piping configuration, flow rate, and equipment specified on the construction documents.

Schedule
Applicability	All recirculation systems
Definition	An on/off or fraction schedule that indicates when the recirculation system is expected to be operated
Units	Data structure: schedule, on/off or fraction
Input Restrictions	The schedule for operation of the recirculation system shall be consistent with the design intent of the system. Hotels, hospitals, and other 24x7 institutional buildings will typically have a system that runs continuously. The schedule should be consistent with the controls called for on the construction documents: no control (runs constantly), timer control, temperature control, timer/temperature control, or demand control.

Piping
Applicability	All recirculation systems
Definition	The heat loss rate of piping for recirculating systems. This may be defined separately for pipe that is exposed to outdoor conditions, indoor or semi-heated conditions, or buried underground conditions. These losses may be modeled as additional loads on the water heater(s).
Units	Btu/h-°F specified separately for outdoor, indoor, or buried locations
Input Restrictions	All piping in the recirculation system should be included. Heat loss for each of the three conditions should be consistent with piping runs, sizes, and insulation as shown on the construction documents.

Water Healing Auxiliaries

External Storage Tanks
Applicability	All water heating systems that have an external storage tank
Definition	Some water heating systems have a storage tank that is separate from the water heater(s) that provides additional storage capacity. This building descriptor addresses the heat loss related to the external tank, which is an additional load that must be satisfied by the water heater(s). The heat loss shall account for the surface area and U-factor tank, as well as the average temperature conditions where the tank is located. Some software may allow these factors to be separately specified.
Units	Btu/h for the entire tank
Input Restrictions	As specified in manufacturer data and documented on the construction documents

Heat Recovery
Applicability	Water heating systems that are coupled to heat recovery equipment
Definition	Building equipment such as air conditioners, chillers, gas fired generators, etc. produce thermal energy that may be recovered and used to heat water. The heat producing characteristics are generally defined for the equipment that is producing the heat, not the equipment that is receiving the heat (water heaters in this case). The building descriptors will vary depending on the equipment. The models for heat producing equipment need to produce output on an hourly basis so that the schedule of heat production and heating needs can be aligned and evaluated in the water heating model.
Units	Data structure: depends on the equipment producing the heat
Input Restrictions	There are no restrictions, other than agreement with the construction documents.

Solar Thermal
Applicability	Water heating systems with a solar thermal system
Definition	A solar thermal water heating system consists of one or more collectors. Water is passed through these collectors and is heated under the right conditions. There are two general types of solar water heaters: integrated collector storage (ICS) systems and active systems. Active systems include pumps to circulate the water, storage tanks, piping, and controls. ICS systems generally have no pumps and piping is minimal. Solar systems may be tested and rated as a complete system or the collectors may be separately tested and rated. SRCC OG-300 is the test procedure for whole systems and SRCC OG-100 is the test procedure for collectors. The building descriptors used to define the solar thermal system may vary with each software application and with the details of system design. Heat produced by solar thermal systems will generally not align perfectly with the need for heating, so the model needs to account for the temporal mismatch in some manner.
Units	Data structure: will vary with the software and system details
Input Restrictions	There are no restrictions, other than agreement with the construction documents.

Combined Space Heating and Water Heating
Applicability	Projects that use a boiler to provide both space heat and water heating
Definition	A system that provides both space heating and water heating from the same equipment, generally the space heating boiler. Such systems are restricted by the baseline standards, but may be modeled in the candidate building. The restrictions are due to the misalignment of the space heating load and the water heating load. The first is highly intermittent and weather dependent, while the latter is more constant and not generally related to the weather.
Units	Data structure
Input Restrictions	The proposed design may have a combined space and water heating system.

System Loads and Configuration

Water Heating System Name
Applicability	All water heating systems
Definition	A unique descriptor for each water heating system. A system consists of one or more water heaters, a distribution system, an estimate of hot water use, and a schedule for that use. Nonresidential buildings will typically have multiple systems, perhaps a separate electric water heater for each office break room, etc. Other building types such as hotels and hospitals may have a single system serving the entire building.
Units	Text, unique
Input Restrictions	Where applicable, this should match the tags that are used on the plans such that a plan reviewer can make a connection.

Water Heating Peak Use
Applicability	All water heating systems, required
Definition	An indication of the peak hot water usage (e.g. service to sinks, showers, and kitchen appliances, etc.). When specified per occupant, this value is multiplied by design occupancy density values and modified by service water heating schedules to obtain hourly load values which are used in the simulation. Peak consumption is commonly specified as gallons per hour per occupant, dwelling unit, hotel room, patient room, or floor area. If consumption is specified in gallons per hour, then additional inputs would be needed such as supply temperature, cold water inlet temperature, etc. It is also common to specify peak use as a thermal load in Btu/h. In the latter case, there is an implied assumption for the cold water inlet temperature, supply temperature, distribution losses, and other factors. The thermal load does not include conversion efficiencies of water heating equipment.
Units	Btu/h or gallons/h
Input Restrictions	For the purpose of green building ratings and Design to Earn ENERGY STAR, the inputs from Appendix B are default values, but other values may be used with justification.

Water Heating Schedule
Applicability	All water heating systems, required
Definition	A fractional schedule reflecting the time pattern of water heating use. This input modifies the water heating peak use, described above.
Units	Data structure: schedule, fractional
Input Restrictions	For the purpose of green building ratings and Design to Earn ENERGY STAR, the inputs from Appendix B, Table 7 are default values, but other values may be used with justification.

Water Heating System Configuration
Applicability	All water heating systems, required
Definition	The configuration and layout of the water heating system, including the number of water heaters; the size, location, length and insulation of distribution pipes; recirculation systems and pumps; and any other details about the system that would affect the energy model.
Units	Data structure
Input Restrictions	None

Water Heaters

This section describes the building descriptors for water heaters. Typically, a building will have multiple water heating systems and each system can have multiple water heaters, so these building descriptors may need to be specified more than once.

Water Heater Name
Applicability	All water heaters
Definition	A unique descriptor for each water heater in the system. Some systems will have multiple pieces of equipment, for instance a series of water heaters plumbed in parallel or a boiler with a separate storage tank.
Units	Text, unique
Input Restrictions	Where applicable, this should match the tags that are used on the plans such that a plan reviewer can make a connection.

Water Heater Type and Size
Applicability	All water heaters
Definition	This building descriptor includes information needed to determine the criteria from baseline standards. The choices are listed below. See Table 7.2.2 of ASHRAE Standard 90.1-2001 or Table 7.8 of ASHRAE Standard 90.1-2007 for more detail. Electric water heaters (storage and instantaneous) Small (≤ 12 kW) Large (> 12 kW) Heat pump Gas storage water heaters Small (≤ 75,000 Btu/h) Medium (> 75,000 and ≤ 155,000 Btu/h) Large (> 155,000 Btu/h) Gas instantaneous water heaters Small (> 50,000 and < 200,000 Btu/h) Large (≥ 200,000 Btu/h) Oil storage water heaters Small (≤ 105,000 Btu/h) Medium (> 105,000 and ≤ 155,000 Btu/h) Large (> 155,000 Btu/h) Oil instantaneous water heaters Small (≤ 210,000 Btu/h) Large (> 210,000 Btu/h) Gas hot water supply boiler Oil hot water supply boiler
Units	List (see above)
Input Restrictions	The water heater type shall agree with equipment specified in the construction documents.

Rated Capacity
Applicability	All water heaters
Definition	The heating capacity of a water heater at the rated conditions specified in Table 7.8 of ASHRAE Standard 90.1-2007 or Table 7.2.2 of ASHRAE Standard 90.1-2001
Units	Thousands of British Thermal Units per hour (MBH)
Input Restrictions	As designed. If the loads are not met, autosize.

Energy Factor
Applicability	Equipment covered by NAECA, which includes small storage and instantaneous water heaters
Definition	The energy factor (EF) is the ratio of the energy delivered by the water heater divided by the energy used, in the same units. EF is calculated according to the DOE 10 CFR Part 430 test procedure, which specifies a 24-hour pattern of draws, a storage temperature, inlet water temperature, and other test conditions. These conditions result in the energy delivered for the test period. Energy inputs are measured for the same test period and the EF ratio is calculated.
Units	Unitless ratio
Input Restrictions	Building descriptors for the proposed design should be consistent with equipment specified on the construction documents or observed in the candidate building.

Thermal Efficiency
Applicability	Oil and gas fired water heaters not covered by NAECA
Definition	The full load efficiency of a water heater at rated conditions expressed as a dimensionless ratio of output over input
Units	Unitless ratio
Input Restrictions	Building descriptors for the proposed design should be consistent with equipment specified on the construction documents or observed in the candidate building.

Tank Standby Loss
Applicability	Water heaters not covered by NAECA
Definition	The tank standby loss for storage tanks, which includes the effect of recovery efficiency.
Units	Btu/h for the entire tank
Input Restrictions	As specified in manufacturer data and documented on the construction documents

Fuel Water Heater Part Load Efficiency Curve

Applicability

Equipment not covered by NAECA for which a thermal efficiency, as opposed to an EF is specified

Definition

A set of factors that adjust the full-load thermal efficiency for part load conditions. Typically, the factor is set as a curve.

Units

Percent (%)

Input Restrictions

The following default curve shall be used unless detailed information is provided to justify alternative values. The default curve shall take the form of a quadratic equation as follows:

(6.9.1-1)

$$ Fuel_{partload} = Fuel_{design} \times F\!HeatP\!L\!C$$ $$F\!HeatP\!L\!C = \left ( a+ b \times \frac{Q_{partload}}{Q_{rated}} + c \times \left ( \frac{Q_{partload}}{Q_{rated}}\right )^2 \right )$$where

FHeatPLC	The fuel heating part load efficiency curve
Fuel_partload	The fuel consumption at part load conditions (Btu/h)
Fuel_design	The fuel consumption at design conditions (Btu/h)
Q_partload	The water heater capacity at part load conditions (Btu/h)
Q_rated	The water heater capacity at design conditions (Btu/h)
a	Constant, 0.021826
b	Constant, 0.977630
c	Constant, 0.000543

Recirculation Systems

This section describes the building descriptors for hot water recirculation systems. The baseline building has a recirculation system when the proposed design does. This is one aspect of the water heating system configuration (see above).

Recirculation System Name
Applicability	All recirculation systems
Definition	A unique descriptor for each water heating recirculation system
Units	Text, unique
Input Restrictions	Where applicable, this should match the tags or descriptions that are used on the plans such that a plan reviewer can make a connection.

Pumping Power
Applicability	All recirculation systems
Definition	The electric demand of the pumps when the recirculation system is operating. This input is a function of the flow rate, the pumping head, the motor efficiency, and the pump efficiency. Some software may allow each of these factors to be separately entered.
Units	Watts (W)
Input Restrictions	Pumping power shall be consistent with the piping configuration, flow rate, and equipment specified on the construction documents.

Schedule
Applicability	All recirculation systems
Definition	An on/off or fraction schedule that indicates when the recirculation system is expected to be operated
Units	Data structure: schedule, on/off or fraction
Input Restrictions	The schedule for operation of the recirculation system shall be consistent with the design intent of the system. Hotels, hospitals, and other 24x7 institutional buildings will typically have a system that runs continuously. The schedule should be consistent with the controls called for on the construction documents: no control (runs constantly), timer control, temperature control, timer/temperature control, or demand control.

Piping
Applicability	All recirculation systems
Definition	The heat loss rate of piping for recirculating systems. This may be defined separately for pipe that is exposed to outdoor conditions, indoor or semi-heated conditions, or buried underground conditions. These losses may be modeled as additional loads on the water heater(s).
Units	Btu/h-°F specified separately for outdoor, indoor, or buried locations
Input Restrictions	All piping in the recirculation system should be included. Heat loss for each of the three conditions should be consistent with piping runs, sizes, and insulation as shown on the construction documents.

Water Healing Auxiliaries

External Storage Tanks
Applicability	All water heating systems that have an external storage tank
Definition	Some water heating systems have a storage tank that is separate from the water heater(s) that provides additional storage capacity. This building descriptor addresses the heat loss related to the external tank, which is an additional load that must be satisfied by the water heater(s). The heat loss shall account for the surface area and U-factor tank, as well as the average temperature conditions where the tank is located. Some software may allow these factors to be separately specified.
Units	Btu/h for the entire tank
Input Restrictions	As specified in manufacturer data and documented on the construction documents

Heat Recovery
Applicability	Water heating systems that are coupled to heat recovery equipment
Definition	Building equipment such as air conditioners, chillers, gas fired generators, etc. produce thermal energy that may be recovered and used to heat water. The heat producing characteristics are generally defined for the equipment that is producing the heat, not the equipment that is receiving the heat (water heaters in this case). The building descriptors will vary depending on the equipment. The models for heat producing equipment need to produce output on an hourly basis so that the schedule of heat production and heating needs can be aligned and evaluated in the water heating model.
Units	Data structure: depends on the equipment producing the heat
Input Restrictions	There are no restrictions, other than agreement with the construction documents.

Solar Thermal
Applicability	Water heating systems with a solar thermal system
Definition	A solar thermal water heating system consists of one or more collectors. Water is passed through these collectors and is heated under the right conditions. There are two general types of solar water heaters: integrated collector storage (ICS) systems and active systems. Active systems include pumps to circulate the water, storage tanks, piping, and controls. ICS systems generally have no pumps and piping is minimal. Solar systems may be tested and rated as a complete system or the collectors may be separately tested and rated. SRCC OG-300 is the test procedure for whole systems and SRCC OG-100 is the test procedure for collectors. The building descriptors used to define the solar thermal system may vary with each software application and with the details of system design. Heat produced by solar thermal systems will generally not align perfectly with the need for heating, so the model needs to account for the temporal mismatch in some manner.
Units	Data structure: will vary with the software and system details
Input Restrictions	There are no restrictions, other than agreement with the construction documents.

Combined Space Heating and Water Heating
Applicability	Projects that use a boiler to provide both space heat and water heating
Definition	A system that provides both space heating and water heating from the same equipment, generally the space heating boiler. Such systems are restricted by the baseline standards, but may be modeled in the candidate building. The restrictions are due to the misalignment of the space heating load and the water heating load. The first is highly intermittent and weather dependent, while the latter is more constant and not generally related to the weather.
Units	Data structure
Input Restrictions	The proposed design may have a combined space and water heating system.