# 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.

Applicability Water Heating System Name All water heating systems 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. Text, unique Where applicable, this should match the tags that are used on the plans such that a plan reviewer can make a connection. The naming convention for the baseline building system shall be similar to the proposed design.
Applicability Water Heating Peak Use All water heating systems, required 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. Btu/h or gallons/h 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. 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.
Applicability Water Heating Schedule All water heating systems, required A fractional schedule reflecting the time pattern of water heating use. This input modifies the water heating peak use, described above. Data structure: schedule, fractional 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. 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).
Applicability Water Heating System Configuration All water heating systems, required 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. Data structure None 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.

Applicability Water Heater Name All water heaters 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. Text, unique Where applicable, this should match the tags that are used on the plans such that a plan reviewer can make a connection. The naming convention for the baseline building system shall be similar to the proposed design.
Applicability Water Heater Type and Size All water heaters 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 List (see above) The water heater type shall agree with equipment specified in the construction documents. 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.
Applicability Rated Capacity All water heaters 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 Thousands of British Thermal Units per hour (MBH) As designed. If the loads are not met, autosize. Autosize
Applicability Energy Factor Equipment covered by NAECA, which includes small storage and instantaneous water heaters 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. Unitless ratio Building descriptors for the proposed design should be consistent with equipment specified on the construction documents or observed in the candidate building. 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.
Applicability Thermal Efficiency Oil and gas fired water heaters not covered by NAECA The full load efficiency of a water heater at rated conditions expressed as a dimensionless ratio of output over input Unitless ratio Building descriptors for the proposed design should be consistent with equipment specified on the construction documents or observed in the candidate building. 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.
Applicability Tank Standby Loss Water heaters not covered by NAECA The tank standby loss for storage tanks, which includes the effect of recovery efficiency. Btu/h for the entire tank As specified in manufacturer data and documented on the construction documents 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 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).

Applicability Recirculation System Name All recirculation systems A unique descriptor for each water heating recirculation system Text, unique Where applicable, this should match the tags or descriptions that are used on the plans such that a plan reviewer can make a connection. The naming convention for the baseline building system shall be similar to the proposed design.
Applicability Pumping Power All recirculation systems 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. Watts (W) Pumping power shall be consistent with the piping configuration, flow rate, and equipment specified on the construction documents. 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.
Applicability Schedule All recirculation systems An on/off or fraction schedule that indicates when the recirculation system is expected to be operated Data structure: schedule, on/off or fraction 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. Recirculation schedules for the baseline building shall be the same as the proposed design.
Applicability Piping All recirculation systems 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). Btu/h-°F specified separately for outdoor, indoor, or buried locations 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. 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

Applicability External Storage Tanks All water heating systems that have an external storage tank 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. Btu/h for the entire tank As specified in manufacturer data and documented on the construction documents 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.
Applicability Heat Recovery Water heating systems that are coupled to heat recovery equipment 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. Data structure: depends on the equipment producing the heat There are no restrictions, other than agreement with the construction documents. 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.
Applicability Solar Thermal Water heating systems with a solar thermal system 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. Data structure: will vary with the software and system details There are no restrictions, other than agreement with the construction documents. The baseline building has no solar auxiliary system.
Applicability Combined Space Heating and Water Heating Projects that use a boiler to provide both space heat and water heating 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. Data structure The proposed design may have a combined space and water heating system. 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.

Applicability Water Heating System Name All water heating systems 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. Text, unique Where applicable, this should match the tags that are used on the plans such that a plan reviewer can make a connection. The naming convention for the baseline building system shall be similar to the proposed design.
Applicability Water Heating Peak Use All water heating systems, required 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. Btu/h or gallons/h 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. 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.
Applicability Water Heating Schedule All water heating systems, required A fractional schedule reflecting the time pattern of water heating use. This input modifies the water heating peak use, described above. Data structure: schedule, fractional 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. 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).
Applicability Water Heating System Configuration All water heating systems, required 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. Data structure None 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.

Applicability Water Heater Name All water heaters 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. Text, unique Where applicable, this should match the tags that are used on the plans such that a plan reviewer can make a connection. The naming convention for the baseline building system shall be similar to the proposed design.
Applicability Water Heater Type and Size All water heaters 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 List (see above) The water heater type shall agree with equipment specified in the construction documents. 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.
Applicability Rated Capacity All water heaters The heating capacity of a water heater at the rated conditions specified in Table 7.8 of ASHRAE Standard 90.1-2007. Thousands of British Thermal Units per hour (MBH) As designed. If the loads are not met, autosize. Autosize
Applicability Energy Factor Equipment covered by NAECA, which includes small storage and instantaneous water heaters 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. Unitless ratio Building descriptors for the proposed design should be consistent with equipment specified on the construction documents or observed in the candidate building. 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.
Applicability Thermal Efficiency Oil and gas fired water heaters not covered by NAECA The full load efficiency of a water heater at rated conditions expressed as a dimensionless ratio of output over input Unitless ratio Building descriptors for the proposed design should be consistent with equipment specified on the construction documents or observed in the candidate building. 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.
Applicability Tank Standby Loss Water heaters not covered by NAECA The tank standby loss for storage tanks, which includes the effect of recovery efficiency. Btu/h for the entire tank As specified in manufacturer data and documented on the construction documents 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 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).

Applicability Recirculation System Name All recirculation systems A unique descriptor for each water heating recirculation system Text, unique Where applicable, this should match the tags or descriptions that are used on the plans such that a plan reviewer can make a connection. The naming convention for the baseline building system shall be similar to the proposed design.
Applicability Pumping Power All recirculation systems 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. Watts (W) Pumping power shall be consistent with the piping configuration, flow rate, and equipment specified on the construction documents. 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.
Applicability Schedule All recirculation systems An on/off or fraction schedule that indicates when the recirculation system is expected to be operated Data structure: schedule, on/off or fraction 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. Recirculation schedules for the baseline building shall be the same as the proposed design.
Applicability Piping All recirculation systems 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). Btu/h-°F specified separately for outdoor, indoor, or buried locations 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. 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

Applicability External Storage Tanks All water heating systems that have an external storage tank 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. Btu/h for the entire tank As specified in manufacturer data and documented on the construction documents 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.
Applicability Heat Recovery Water heating systems that are coupled to heat recovery equipment 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. Data structure: depends on the equipment producing the heat There are no restrictions, other than agreement with the construction documents. 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.
Applicability Solar Thermal Water heating systems with a solar thermal system 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. Data structure: will vary with the software and system details There are no restrictions, other than agreement with the construction documents. The baseline building has no solar auxiliary system.
Applicability Combined Space Heating and Water Heating Projects that use a boiler to provide both space heat and water heating 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. Data structure The proposed design may have a combined space and water heating system. 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.
90.1-2010

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.

Applicability Water Heating System Name All water heating systems 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. Text, unique Where applicable, this should match the tags that are used on the plans such that a plan reviewer can make a connection. The naming convention for the baseline building system shall be similar to the proposed design.
Applicability Water Heating Peak Use All water heating systems, required 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. Btu/h or gallons/h 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. 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.
Applicability Water Heating Schedule All water heating systems, required A fractional schedule reflecting the time pattern of water heating use. This input modifies the water heating peak use, described above. Data structure: schedule, fractional 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. 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).
Applicability Water Heating System Configuration All water heating systems, required 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. Data structure None 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.

Applicability Water Heater Name All water heaters 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. Text, unique Where applicable, this should match the tags that are used on the plans such that a plan reviewer can make a connection. The naming convention for the baseline building system shall be similar to the proposed design.
Applicability Water Heater Type and Size All water heaters 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 List (see above) The water heater type shall agree with equipment specified in the construction documents. 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.
Applicability Rated Capacity All water heaters The heating capacity of a water heater at the rated conditions specified in Table 7.8 of ASHRAE Standard 90.1-2007. Thousands of British Thermal Units per hour (MBH) As designed. If the loads are not met, autosize. Autosize
Applicability Energy Factor Equipment covered by NAECA, which includes small storage and instantaneous water heaters 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. Unitless ratio Building descriptors for the proposed design should be consistent with equipment specified on the construction documents or observed in the candidate building. 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.
Applicability Thermal Efficiency Oil and gas fired water heaters not covered by NAECA The full load efficiency of a water heater at rated conditions expressed as a dimensionless ratio of output over input Unitless ratio Building descriptors for the proposed design should be consistent with equipment specified on the construction documents or observed in the candidate building. 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.
Applicability Tank Standby Loss Water heaters not covered by NAECA The tank standby loss for storage tanks, which includes the effect of recovery efficiency. Btu/h for the entire tank As specified in manufacturer data and documented on the construction documents 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 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).

Applicability Recirculation System Name All recirculation systems A unique descriptor for each water heating recirculation system Text, unique Where applicable, this should match the tags or descriptions that are used on the plans such that a plan reviewer can make a connection. The naming convention for the baseline building system shall be similar to the proposed design.
Applicability Pumping Power All recirculation systems 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. Watts (W) Pumping power shall be consistent with the piping configuration, flow rate, and equipment specified on the construction documents. 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.
Applicability Schedule All recirculation systems An on/off or fraction schedule that indicates when the recirculation system is expected to be operated Data structure: schedule, on/off or fraction 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. Recirculation schedules for the baseline building shall be the same as the proposed design.
Applicability Piping All recirculation systems 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). Btu/h-°F specified separately for outdoor, indoor, or buried locations 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. 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

Applicability External Storage Tanks All water heating systems that have an external storage tank 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. Btu/h for the entire tank As specified in manufacturer data and documented on the construction documents 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.
Applicability Heat Recovery Water heating systems that are coupled to heat recovery equipment 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. Data structure: depends on the equipment producing the heat There are no restrictions, other than agreement with the construction documents. 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.
Applicability Solar Thermal Water heating systems with a solar thermal system 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. Data structure: will vary with the software and system details There are no restrictions, other than agreement with the construction documents. The baseline building has no solar auxiliary system.
Applicability Combined Space Heating and Water Heating Projects that use a boiler to provide both space heat and water heating 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. Data structure The proposed design may have a combined space and water heating system. 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.
90.1-2016 BM

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.

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.

Building EQ

Applicability Water Heating System Name All water heating systems 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. Text, unique Where applicable, this should match the tags that are used on the plans such that a plan reviewer can make a connection.
Applicability Water Heating Peak Use All water heating systems, required 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. Btu/h or gallons/h 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.
Applicability Water Heating Schedule All water heating systems, required A fractional schedule reflecting the time pattern of water heating use. This input modifies the water heating peak use, described above. Data structure: schedule, fractional 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.
Applicability Water Heating System Configuration All water heating systems, required 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. Data structure 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.

Applicability Water Heater Name All water heaters 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. Text, unique Where applicable, this should match the tags that are used on the plans such that a plan reviewer can make a connection.
Applicability Water Heater Type and Size All water heaters 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 List (see above) The water heater type shall agree with equipment specified in the construction documents.
Applicability Rated Capacity All water heaters 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 Thousands of British Thermal Units per hour (MBH) As designed. If the loads are not met, autosize.
Applicability Energy Factor Equipment covered by NAECA, which includes small storage and instantaneous water heaters 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. Unitless ratio Building descriptors for the proposed design should be consistent with equipment specified on the construction documents or observed in the candidate building.
Applicability Thermal Efficiency Oil and gas fired water heaters not covered by NAECA The full load efficiency of a water heater at rated conditions expressed as a dimensionless ratio of output over input Unitless ratio Building descriptors for the proposed design should be consistent with equipment specified on the construction documents or observed in the candidate building.
Applicability Tank Standby Loss Water heaters not covered by NAECA The tank standby loss for storage tanks, which includes the effect of recovery efficiency. Btu/h for the entire tank 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 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

### 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).

Applicability Recirculation System Name All recirculation systems A unique descriptor for each water heating recirculation system Text, unique Where applicable, this should match the tags or descriptions that are used on the plans such that a plan reviewer can make a connection.
Applicability Pumping Power All recirculation systems 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. Watts (W) Pumping power shall be consistent with the piping configuration, flow rate, and equipment specified on the construction documents.
Applicability Schedule All recirculation systems An on/off or fraction schedule that indicates when the recirculation system is expected to be operated Data structure: schedule, on/off or fraction 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.
Applicability Piping All recirculation systems 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). Btu/h-°F specified separately for outdoor, indoor, or buried locations 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

Applicability External Storage Tanks All water heating systems that have an external storage tank 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. Btu/h for the entire tank As specified in manufacturer data and documented on the construction documents
Applicability Heat Recovery Water heating systems that are coupled to heat recovery equipment 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. Data structure: depends on the equipment producing the heat There are no restrictions, other than agreement with the construction documents.
Applicability Solar Thermal Water heating systems with a solar thermal system 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. Data structure: will vary with the software and system details There are no restrictions, other than agreement with the construction documents.
Applicability Combined Space Heating and Water Heating Projects that use a boiler to provide both space heat and water heating 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. Data structure The proposed design may have a combined space and water heating system.
Energy Star

Applicability Water Heating System Name All water heating systems 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. Text, unique Where applicable, this should match the tags that are used on the plans such that a plan reviewer can make a connection.
Applicability Water Heating Peak Use All water heating systems, required 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. Btu/h or gallons/h 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.
Applicability Water Heating Schedule All water heating systems, required A fractional schedule reflecting the time pattern of water heating use. This input modifies the water heating peak use, described above. Data structure: schedule, fractional 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.
Applicability Water Heating System Configuration All water heating systems, required 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. Data structure 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.

Applicability Water Heater Name All water heaters 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. Text, unique Where applicable, this should match the tags that are used on the plans such that a plan reviewer can make a connection.
Applicability Water Heater Type and Size All water heaters 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 List (see above) The water heater type shall agree with equipment specified in the construction documents.
Applicability Rated Capacity All water heaters 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 Thousands of British Thermal Units per hour (MBH) As designed. If the loads are not met, autosize.
Applicability Energy Factor Equipment covered by NAECA, which includes small storage and instantaneous water heaters 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. Unitless ratio Building descriptors for the proposed design should be consistent with equipment specified on the construction documents or observed in the candidate building.
Applicability Thermal Efficiency Oil and gas fired water heaters not covered by NAECA The full load efficiency of a water heater at rated conditions expressed as a dimensionless ratio of output over input Unitless ratio Building descriptors for the proposed design should be consistent with equipment specified on the construction documents or observed in the candidate building.
Applicability Tank Standby Loss Water heaters not covered by NAECA The tank standby loss for storage tanks, which includes the effect of recovery efficiency. Btu/h for the entire tank 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 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

### 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).

Applicability Recirculation System Name All recirculation systems A unique descriptor for each water heating recirculation system Text, unique Where applicable, this should match the tags or descriptions that are used on the plans such that a plan reviewer can make a connection.
Applicability Pumping Power All recirculation systems 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. Watts (W) Pumping power shall be consistent with the piping configuration, flow rate, and equipment specified on the construction documents.
Applicability Schedule All recirculation systems An on/off or fraction schedule that indicates when the recirculation system is expected to be operated Data structure: schedule, on/off or fraction 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.
Applicability Piping All recirculation systems 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). Btu/h-°F specified separately for outdoor, indoor, or buried locations 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

Applicability External Storage Tanks All water heating systems that have an external storage tank 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. Btu/h for the entire tank As specified in manufacturer data and documented on the construction documents
Applicability Heat Recovery Water heating systems that are coupled to heat recovery equipment 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. Data structure: depends on the equipment producing the heat There are no restrictions, other than agreement with the construction documents.
Applicability Solar Thermal Water heating systems with a solar thermal system 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. Data structure: will vary with the software and system details There are no restrictions, other than agreement with the construction documents.
Applicability Combined Space Heating and Water Heating Projects that use a boiler to provide both space heat and water heating 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. Data structure The proposed design may have a combined space and water heating system.