## 2.9 Domestic Hot Water (DHW)

Water heating energy use is based on the number of dwelling units, number of bedrooms, fuel type, distribution system, water heater type, and conditioned floor area. Detailed calculation information is included in Appendix B.

Beginning June 12, 2017, EF ratings are replaced with the new federal standard for water heating energy efficiency, Uniform Energy Factor (UEF). The classification of small and large water heater change to consumer and commercial heaters, respectively, and a new class of residential-duty commercial water heater.

For the remainder of the 2016 Building Energy Efficiency Standards cycle, any UEF input is converted to EF by the software using methods described in Appendix B.

Proposed Design

The water heating system is defined by the heater type (gas, electric resistance or heat pump), tank type, dwelling unit, distribution type, central system distribution, efficiency (either EF, UEF or recovery efficiency with the standby loss), tank volume, exterior insulation R-value (only for indirect), rated input, and tank location (for electric resistance only).

Heat pump water heaters are defined by their energy factor, volume, and tank location or, for Northwest Energy Efficiency Alliance (NEEA) rated heat pumps, by selecting the specific brand, model and tank location.

Water eater and Tank types include:

• Consumer small storage: ≤ 75,000 Btu/h gas/propane, ≤ 12 kW electric, or ≤ 24 amps heat pump. Rated with UEF or EF.

• Consumer/small instantaneous: ≤ 200,000 Btu/h gas or propane, or ≤ 12 kW electric. Instantaneous water heater is a water heater with an input rating of ≥ 4,000 Btu/h/gallon of stored water. Rated with a UEF or EF.

• Residential-Duty Commercial storage: > 75,000 Btu/h, and ≤ 105,000 Btu/h gas/propane, ≤ 12 kW electric, ≤ 24 amps heat pump, and rated storage volume < 120 gallons. Rated with a UEF.

• Residential-Duty Commercial (large) instantaneous: ≤ 200,000 Btu/h gas/propane, ≤ 58.6 kW electric, and rated storage volume ≤ 2 gallons. Rated with a UEF.Mini-tank (.

• Commercial/large storage: > 75,000 Btu/h gas/propane, >105,000 Btu/h oil, or > 12 kW electric. Rated with thermal efficiency and standby loss.

• Commercial/large instantaneous: >200,000 Btu/h gas/propane, > 12 kW electric. Instantaneous water heater is a water heater with an input rating of ≥ 4,000 Btu/h per gallon of stored water. Rated with thermal efficiency.

• Mini-tank (only modeled in conjunction with an instantaneous gas water heater): a small electric storage buffering tank that may be installed downstream of an instantaneous gas water heater to mitigate delivered water temperatures (e.g. cold water sandwich effect). If the standby loss of this aftermarket tank is not listed in the Energy Commission appliance database, a standby loss of 10035 W must be assumed.

• Indirect: a tank with no heating element or combustion device used in combination with a boiler or other device serving as the heating element.

• Boiler: a water boiler that supplies hot water, rated with thermal efficiency or AFUE.

Heater element type includes:

• Electric resistance.

• Gas, or

• Heat pump.

For water heating systems serving a single dwelling unit, a dwelling unit distribution type must be specified. Dwelling unit distribution system types for systems serving individual dwelling units include:

• Standard (all distribution pipes insulated)

• Point of Use

• Central Parallel Piping

• Recirculation, Non-Demand Control

• Recirculation, Demand Control Push Button

• Recirculation, Demand Control Occupancy/Motion

• HERS Required Pipe Insulation, All Lines

• HERS Required Central Parallel Piping

• HERS Required Recirculation, Demand Control Push Button

• HERS Required Recirculation, Demand Control Occupancy/Motion

• HERS Required Compact Distribution System

When a multi-family building has central water heating, both a dwelling unit and a central system distribution type must be specified. Dwelling unit distribution types for this case include:

• Standard ( all distribution pipes insulated)

• HERS required pipe insulation, all lines

Multi-family central hot water heating central system distribution types include:

• No loops or recirculation system pump

• Recirculation with no control (continuous pumping)

• Recirculation demand control (standard design for new construction)

• Recirculation with temperature modulation control

• Recirculation with temperature modulation and monitoring

Some distribution systems have an option to increase the amount of credit received if the option for HERS verification is selected. See Appendix B for the amount of credit and Reference Appendices, Residential Appendix Table RA2-1 for a summary of inspection requirements.

Standard Design

The standard design is based on Section 150.1(c)8.

### 2.9.1 Individual dwelling units

For systems serving individual dwelling units the standard design is a single gas or propane consumer instantaneous water heater for each dwelling unit. The standard design is natural gas except if the proposed water heater is propane; then the standard is modeled as propane. The consumer instantaneous water heater is modeled with an input of 200,000 Btu/h, a tank volume of zero gallons, high draw pattern, and a UEF meeting federal standards. The current federal standard for a high draw pattern, instantaneous water heater is (0.81 UEF, or the equivaltent of 0.82 energy factor for the standard system.

### 2.9.2 Multiple dwelling units:

When the proposed design is a central water heating system the standard design consist of the water heating devices, a recircultaion system and solar systems as follows:

Water heating device. The standard design consists of the same number of water heating devices as the proposed design using the efficiencies required in the Appliance Efficiency Standards. The standard design is natural gas except if the proposed water heater is propane, then the standard is modeled as propane. Each water heating device in the proposed system is examined separately. If the proposed water heating device is gas or propane, the standard design is set to the same type and characteristics as the proposed design. If the proposed water heating device is not natural gas or propane, then the standard design is converted to a gas or propane water heater of a similar type and characteristics as the proposed design. The appropriate efficiencies and standby losses for each standard water heating device are then assigned to match the minimum requirements of the definitions and Tables F-2 and F-3 of the 2015 Appliance Efficiency Standards.

Recirculating system. The standard design includes a recirculation system with controls that regulate pump operation based on measurement of hot water demand and hot water return temperature, and capable of turning off the system as described in Appendix B4 Hourly Recirculation Distribution Loss for Central Water Heating Systems. When a building has more than eight dwelling units, the standard design has one recirculation loop when a building with eight or fewer dwelling units includes a recirculation system, the standard design has on recirculation loop.

Solar. The standard design has a solar water heating system meeting the installation criteria specified in Reference Residential Appendix RA4 and with a minimum solar savings fraction of 0.20 in climate zones 1 through 9, or 0.35 in climate zones 10 through 16.

Verification and Reporting

All modeled features and the number of devices modeled for the water heating system are reported on the CF1R. Electric resistance and heat pump water heaters indicate the location of the water heater. NEEA-rated heat pumps are identified by the heater type, which must be verified by the building inspector.

Where distribution systems specify HERS verification, those features are listed in the HERS required verification listings on the CF1R.

### 2.9.3 Solar Thermal Water Heating Credit

When a water heating system has a solar thermal system to provide part of the water heating, the Solar Fraction (SF) is determined using the CEC Solar Water Heating Calculator, OG-100 calculation method or the certified OG-300 rating. (Note: The OG-300 rating can only be used for system serving individual dwelling units and not central systems.) The calculation method requires that the user specify the climate zone and conditioned floor area, 'in 'addition to published data for the solar thermal water heating system.