3.9.1.2 Water Heaters

Applicability

All water heaters

Definition

A unique descriptor for each water heater in the system. Some systems will have multiple pieces of equipment, for instance a series of water heaters plumbed in parallel or a boiler with a separate storage tank.

Units

Text, unique

Input Restrictions

Where applicable, this should match the tags that are used on the plans such that a plan reviewer can make a connection

Baseline Building

The naming convention for the baseline building system shall be similar to the proposed design

Applicability

All water heaters

Definition

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

• Electric water heaters (storage and instantaneous)

– Small (≤ 12 kW)

– Large (> 12 kW)

– Heat pump

• Gas storage water heaters

– Small (≤ 75,000 Btu/h)

– Large (> 75,000 Btu/h)

• Gas instantaneous water heaters

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

– Large (≥ 200,000 Btu/h), <10 gal

– Large (≥ 200,000 Btu/h), >= 10 gal

• Oil storage water heaters

– Small (≤ 105,000 Btu/h)

– Large (> 105,000 Btu/h)

• Oil instantaneous water heaters

– Small (≤ 210,000 Btu/h)

– Large (> 210,000 Btu/h), <10 gal

– Large (> 210,000 Btu/h), >= 10 gal

• Gas hot water supply boiler
• Oil hot water supply boiler
• Heat exchanger from steam or district hot water

Units

List (see above)

Input Restrictions

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

If no service hot water system exists or has been specified, but the building will have service hot water loads, a service water system shall be modeled that matches the system type in the baseline building design.

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

Baseline Building

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

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

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

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

Applicability

All water heaters

Definition

The heating capacity of a water heater at the rated conditions specified in DOE 10 CFR Part 430 or ANSI Z21.10

Units

Thousands of British thermal units per hour (MBH)

Input Restrictions

As designed. If the loads are not met, then the system needs to be autosized.

Baseline Building

Autosize

Applicability

All water heaters

Definition

The storage volume of a gas-fired water heater. This is used in the standby loss calculations and baseline calculations of energy factor (EF).

Units

gallons

Input Restrictions

As designed. If the loads are not met, then the system needs to be autosized.

Baseline Building

Autosize

Applicability

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

Definition

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

Units

Unitless ratio (between 0 and 1)

Input Restrictions

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

Baseline Building

The EF for the baseline building system shall be determined from Table 7.8 of Standard 90.1-2019. Additional UEF efficiency requirements can be found in Table F-2 of Standard 90.1-2019.

Applicability

Oil and gas-fired water heaters not covered by NAECA

Definition

The full load efficiency of a water heater at rated conditions expressed as a dimensionless ratio of output over input

Units

Unitless ratio (between 0 and 1)

Input Restrictions

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

Baseline Building

From Table 7.8 of Standard 90.1-2019

Applicability

Water heaters not covered by NAECA

Definition

The tank standby loss for storage tanks, which includes the effect of recovery efficiency

Units

Btu/h for the entire tank

Input Restrictions

As specified in manufacturer data and documented on the construction documents

Baseline Building

As specified in Table 7.8 of Standard 90.1-2019

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:

$$UA=\frac{1/EF - 1/RE}{67.5\times \left( \frac{24}{41094}-\frac{1}{RE\cdot Pon} \right)}$$

Where:

EF    =   The energy factor of the rated water heater (unitless)

RE    =   The recovery efficiency of the rated water heater. If this data is not available, the default shall be 0.78 for gas water heaters and 0.93 for electric water heaters.

Pon  =   The input power to the water heater, in Btu/h

Baseline Building

The baseline loss coefficient for NAECA water heaters shall be:

10 Btu/h-°F for gas-fired water heaters

Applicability

Water heater

Definition

The rate of parasitic losses, such as a pilot light or controls, when the water heater is not heating. If modeled explicitly, pilot lights should contribute to off-cycle heating.

Units

Watts

Input Restrictions

As designed

Baseline Building

0

Applicability

Water heater

Definition

The type of fuel that serves energy using parasitic equipment, such as a pilot light or controls, when the water heater is not heating

Units

List: Electricity, Gas, Oil, Propane

Input Restrictions

As designed

Baseline Building

Not applicable

Applicability

Water heater

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 Building

0

Applicability

Water heater

Definition

The type of fuel that serves energy using parasitic equipment, such as a pilot light or controls, when the water heater is not heating

Units

List: Electricity, Gas, Oil, Propane

Input Restrictions

As designed

Baseline Building

Not applicable

Applicability

Water heater

Definition

The location of the water heater for determining losses and energy interaction with the surroundings

Units

List: Schedule, Zone, Outdoors

Input Restrictions

As designed. When “Schedule” is used, a time of day schedule needs to be specified with temperature schedule for each hour.

Baseline Building

Same as proposed

Applicability

Water heating equipment for which a thermal efficiency as opposed to an EF is specified

Definition

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

Units

Percent (%)

Input Restrictions

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

Where:

FHeatPLC    =     The fuel heating part load efficiency curve

Fuel_partload    =     The fuel consumption at part load conditions (Btu/h)

Fuel _design      =     The fuel consumption at design conditions (Btu/h)

Q_partload         =     The water heater capacity at part load conditions (Btu/h)

Q_rated             =     The water heater capacity at design conditions (Btu/h)

a                   =     Constant, 0.021826

b                   =     Constant, 0.977630

c                   =     Constant, 0.000543

Baseline Building

The baseline shall use the default curve

Applicability

All water heaters

Definition

A unique descriptor for each water heater in the system. Some systems will have multiple pieces of equipment, for instance a series of water heaters plumbed in parallel or a boiler with a separate storage tank.

Units

Text, unique

Input Restrictions

Where applicable, this should match the tags that are used on the plans such that a plan reviewer can make a connection.

Baseline Building

The naming convention for the baseline building system shall be similar to the proposed design.

Applicability

All water heaters

Definition

The choices are presented below from 90.1 2022 Table 7.4.1-1.

Units

List (see above)

Input Restrictions

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

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

G3.2 New Construction/Major Alterations

If no service hot water system exists or has been specified, but the building will have service hot water loads, a service water system shall be modeled that matches the system type in the baseline building design.

G3.3 Minor Alterations

If no service hot water system exists or has been specified, no service water heating system shall be modeled.

Baseline Building

G3.2 New Construction/Major Alterations

Where a complete water heating system exists or a new service water heating system has been specified in the proposed design, the water heaters in the baseline system will be based on the building area type classification. See Table 121 below.

For new service hot water systems, the system will be sized according to the provisions of Standard 90.1-2022, Section 7.4.1, and the equipment shall match the minimum efficiency requirements in Standard 90.1-2022, Section 7.4.2. Where the energy source is electricity, the heating method shall be electrical resistance. When the energy source is ‘Gas Storage’, the water heater shall be modeled using natural gas as their fuel. Where natural gas is not available at the proposed building site, as determined by the rating authority, gas storage water heaters shall be modeled using propane as their fuel.

If no service hot water system exists or has been specified, but the building will have service hot water loads, a service water system shall be modeled for each building area type in the proposed design, in accordance to Table 121. and matching minimum efficiency requirements of Standard 90.1-2022, Section 7.4.2.

Where the baseline service water heating system is required to be an electric resistance storage water heater the efficiency can be based on a water heater with an input capacity less than or equal to 12 kW and 50 gallons of storage. Where storage greater than 50 gallons is required, multiple electric resistance storage water heaters shall be assumed to be included in the single system.

Table 121. Baseline Building Water Heater Type (Standard 90.1-2022 Table G3.1.1-2)

G3.3 Minor Alterations

Where a complete water heating system exists or a new service water heating system has been specified, the water heaters in the baseline model will be modeled as the same type as the proposed.

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. Please note, this should not be mistaken for the first hour rating.

Units

Thousands of British thermal units per hour (MBH)

Input Restrictions

As designed.

Baseline Building

Size based on requirements of Standard 90.1-2022 Section 7.4.1. Baseline water heater system(s) are required to be sized according to the provisions of Section 7.4.1 which points to generally accepted engineering standards and handbooks acceptable to the adopting authority (e.g., ASHRAE Handbook—HVAC Application). As a result, the baseline rated capacity should be determined using generally accepted engineering standards and principles applicable to the loads being served and the baseline system type. 

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 uniform energy factor (UEF).

Units

gallons

Input Restrictions

As designed.

Baseline Building

Size based on requirements of Standard 90.1-2022 Section 7.4.1. Baseline water heater system(s) are required to be sized according to the provisions of Section 7.4.1 which points to generally accepted engineering standards and handbooks acceptable to the adopting authority (e.g., ASHRAE Handbook—HVAC Application). As a result, the baseline storage volume should be determined using generally accepted engineering standards and principles applicable to the loads being served and the baseline system type. 

Applicability

Storage and instantaneous water heaters subject to 10 CFR 430 Appendix E.

Definition

UEF is the ratio of the energy delivered by the water heater divided by the energy used, in consistent units. UEF 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 UEF ratio is calculated.

Units

Unitless ratio (between 0 and 1)

Input Restrictions

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

Baseline Building

G3.2 New Construction/Major Alterations

The UEF for the baseline building system shall be determined from Table 7.4-1 of Standard 90.1-2022 including references to the additional UEF efficiency requirements found in Table F-2 of Standard 90.1-2022. Where the baseline service water heating system is required to be an electric resistance storage water heater the efficiency can be based on a water heater with an input capacity less than or equal to 12 kW and 50 gallons of storage. Where storage greater than 50 gallons is required, multiple electric resistance storage water heaters shall be assumed to be included in the single system.

G3.3 Minor Alterations

The UEF for the baseline building system shall be determined from Table 7.4-1 of Standard 90.1-2022. Additional UEF efficiency requirements can be found in Table F-2 of Standard 90.1-2022.

Recovery Efficiency

Applicability

Storage and instantaneous water heaters subject to 10 CFR 430 Appendix E.

Definition

Recovery efficiency is computed as the energy required to maintain the tank storage water temperature plus the energy content associated with the water removed from the tank divided by the total energy used by the water heater during the first recovery period during following the 10 CFR 430 Appendix E test procedure including auxiliary energy such as pilot lights, pumps, fans, etc.

Units

Unitless ratio (between 0 and 1)

Input Restrictions

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

Baseline Building

G3.2 New Construction/Major Alterations

A default value of 0.78 for gas water heaters and 0.99 for electric water heaters can be used9F[1].

G3.3 Minor Alterations

Recovery efficiency should be modeled consistently with the values used in the tank off-cycle standby loss calculation as described in the Tank Off-Cycle Loss Coefficient descriptor below.

Applicability

Oil and gas-fired water heaters not covered by 10 CFR 430 Appendix E.

Definition

The full load efficiency of a water heater at rated conditions expressed as a dimensionless ratio of output over input

Units

Unitless ratio (between 0 and 1)

Input Restrictions

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

Baseline Building

As specified in Table 7.4-1 of Standard 90.1-2022.

Applicability

Gas storage water heaters >105,000 Btuh, gas instantaneous water heaters ≥200,000 Btuh with ≥10 gallons of storage, electric storage water heaters > 12 kW or other service water heating equipment with standby loss requirements in 90.1 Table 7.4-1

Definition

The tank standby loss for storage tanks, which includes the effect of recovery efficiency

Units

Btu/h for the entire tank

Input Restrictions

As specified in manufacturer data and documented on the construction documents

Baseline Building

As specified in Table 7.4-1 of Standard 90.1-2022.

Tank Off-Cycle Loss Coefficient

Applicability

Water heaters rated in UEF according to 10 CFR 430 Appendix E.

Definition

The tank standby loss coefficient (UA) for the water heater. The loss coefficient is a derived parameter, a function of the uniform energy factor (or energy factor) and recovery efficiency.

Units

Btu/h-°F

Input Restrictions

For water heaters rated in UEF according to 10 CFR 430 Appendix E, the loss coefficient is calculated using the following equation:

$$UA=\frac{1/UEF - 1/RE}{57.5\times \left( \frac{24}{A}-\frac{1}{RE\cdot Pon} \right)}$$

Where:

UEF =   The uniform 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 0.99 for electric water heaters.

Pon  =   The input power to the water heater, in Btu/h

A =       The daily hot water energy load for the water heater (Btu/day) during the DOE rating. Determine A from the table below based upon draw pattern/first hour rating.

Baseline Building

G3.2 New Construction/Major Alterations

The baseline loss coefficient for water heaters rated according to 10 CFR 430 Appendix E. can be calculated as follows:

$$UA=\frac{\frac{A}{UEF} - A}{24\times 57.5}$$

• For gas water heaters, calculated using the equation above in the Input Restriction section of this descriptor using a 0.78 recovery efficiency, the same draw pattern as the proposed and a Pon based on equipment sizing or a default of 50,000 Btuh1.
• For electric water heaters, calculated using the equation below using the same draw pattern as the proposed.

An estimate, using engineering judgment based on the use case of the water heater, of the draw pattern can be used if it is not applicable to the proposed water heater type.

G3.3 Minor Alterations

The baseline loss coefficient for water heaters rated according to 10 CFR 430 Appendix E. shall be determined using the equation above in the Input Restriction section of this descriptor.

Water Heater Ambient Temperature Indicator

Applicability

Water heater

Definition

The location of the water heater for determining losses and energy interaction with the surroundings

Units

List: Schedule, Zone, Outdoors

Input Restrictions

As designed. When “Schedule” is used, a time of day schedule needs to be specified with temperature schedule for each hour.

Baseline Building

Same as proposed

Applicability

Water heating equipment for which a thermal efficiency as opposed to an UEF is specified

Definition

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

Units

Percent (%)

Input Restrictions

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

Where:

FHeatPLC    =     The fuel heating part load efficiency curve

Fuel_partload    =     The fuel consumption at part load conditions (Btu/h)

Fuel _design      =     The fuel consumption at design conditions (Btu/h)

Q_partload         =     The water heater capacity at part load conditions (Btu/h)

Q_rated             =     The water heater capacity at design conditions (Btu/h)

a                   =     Constant, 0.021826

b                   =     Constant, 0.977630

c                   =     Constant, 0.000543

Baseline Building

G3.2 New Construction/Major Alterations

The baseline shall use the default curve.

G3.3 Minor Alterations

Same as proposed.