## B1. Purpose and Scope

This appendix documents the methods and assumptions used for calculating the hourly energy use for residential water heating systems for both the proposed design and the standard design. The hourly fuel and electricity energy use for water heating will be combined with hourly space heating and cooling energy use to come up with the hourly total fuel and electricity energy use to be factored by the hourly TDV energy multiplier. The calculation procedure applies to low-rise single family, low-rise multifamily, and high-rise residential.

Calculations are described below for gas and electric water heaters. The internal water heater modeling is performed within the CSE simulation engine. The compliance modeling rules documented here are implemented in the CBECC-Res ruleset and determine the input values passed to CSE.

When buildings have multiple water heaters, the hourly total water heating energy use is the hourly water heating energy use summed over all water heating systems, all water heaters, and all dwelling units being modeled.

The following diagrams illustrate the domestic hot water (DHW) system types that shall be recognized by the compliance software.

1 | One distribution system with one or multiple water heaters serving a single dwelling unit. The system might include recirculation loops within the dwelling unit. |
2 | Two water heaters with independent distribution systems serving a single dwelling unit. One or more of the distribution systems may include a recirculation loop within the dwelling unit. |
3 | One distribution system without recirculation loop and with one or multiple water heaters serving multiple dwelling units. |
4 | One distribution system with one or multiple recirculation loops and with one or multiple water heaters serving multiple dwelling units. |