When the performance compliance method is used, the water heating energy budget is based on the performance of a heat pump water heater in most climate zones. In addition to a heat pump water heater, a compact hot water distribution system is required in climate zone 1 and 16 and a drain water heat recovery device also is required in climate zone 16. The water heating energy budget in climate zones 3, 4, 13, or 14, is based on the performance of a gas instantaneous water heater. Both gas and electric water heaters used in the standard design meet the minimum requirements in California’s Title 20 Appliance Efficiency Regulations Section 1605.1(f) for federally regulated appliances

The computer performance approach allows for the modeling of water heating system performance by taking into account building characteristics, climate, system type, efficiency, and fuel type. The standard design water heating budget is defined by the corresponding prescriptive requirements. The performance method allows for modeling alternative water heater and distribution system combinations. Some of these options will offer compliance credits, and others will result in penalties.

In the case of single dwelling units, any type or number of water heaters supported by the software can be installed. The calculated energy use of the proposed design is compared to the standard design energy budget based on either a single gas instantaneous water heater with a standard distribution system for gas water heaters, or a HPWH with compact distribution system and drain water heat recovery for electric water heaters. Adding multiple water heaters to a single-family design will generally result in an energy penalty in the water heating budget that must be offset elsewhere in the total energy budget.

A standard distribution system serving a single dwelling unit does not incorporate a pump for hot water recirculation and does not take credit for any additional DHW design features. All mandatory pipe insulation requirements must be met, such as insulating all hot water pipes. Alternative distribution systems are compared to the standard design case by using distribution system multipliers (DSMs), which effectively rate alternative options.

Table 5-9 lists all the recognized distribution systems that can be used in the performance approach with the assigned distribution multiplier. The standard distribution system has a multiplier of 1.0. Distribution systems with a multiplier less than 1 represent an energy credit, while distribution systems with a multiplier greater than 1 are counted as an energy penalty. For example, pipe Insulation with HERS Inspection Required (PIC-H) has a multiplier of 0.8. That means that it is modeled at 20 percent less distribution loss than the standard distribution system. For more information or installation requirements on any of the systems, refer to Section 5.6.

1. The multiplier for the Compact Design – Expanded credit varies depending on the home’s floorplan and water heater location. See Section 5.6.2.4 for more information.

For information on how water heater efficiency is considered in terms of modeling energy performance using the compliance software tool, please refer to the Residential Alternative Calculation Method (ACM) Reference Manual.

Water heating is becoming more important to overall building compliance as building envelope performance and mechanical efficiency improve. When the performance approach is used, a high-efficiency water heater and an efficient distribution system can significantly affect the overall performance margin of a building, especially in the milder climates like Climate Zones 4 through 9, where water heating typically represents a larger fraction of the overall energy budget.

Asking for a cut sheet on the installed equipment to verify efficiency is a simple shortcut to checking compliance. When used in a combined hydronic system, it is important to check the capacity of the system to verify that both space and water heating loads can be met.