Rating System

LEED BD+C: New Construction

Rating System Version

v2 - LEED 2.2

Inquiry

The ASHRAE 90.1 rules appear contradictory about claiming energy credit for heat recovery used for domestic water heating. In the Simulation General Requirements, 11.2.3 Exception reads ".site-recovered energy shall not be considered purchased energy and shall not be included in the design energy cost?" Sections 11.3.7, 11.4.3 and 11.4.4 appear to require the proposed and budget service water heating to be modeled the same except for efficiency. Our project uses heat recovery from a WSHP return loop to pre-heat domestic hot water. Please confirm that we can take credit for pre-heating DHW make-up with heat recovered from the WSHP loop and that the proposed Exceptional Calculation method may be used to model these savings. We suggest that the site-recovered energy provision, part of the general requirements, takes precedence over the apparent limitation for DHW. Furthermore, the heat-recovery equipment is separate from and is not directly affecting the service water heating equipment, which is what the limitation appears to apply to. Proposed Exceptional Calculation Methodology The heat recovery to DHW cannot be modeled directly in DOE-2. We propose to use a spreadsheet calculation. Hourly report data for the WSHP loop return temperature and for hourly DHW demand will be generated from the proposed design model. A heat exchanger will be used in the design with the warm WSHP loop water and DHW make-up at either inlet. A simple calculation using the inlet temperatures, and design approach of the heat exchanger will be used to determine the DHW make-up outlet temperature. The savings will be calculated as the energy required to heat the DHW make-up from the city supply temperature to the heat exchanger DHW make-up outlet temperature. This would be subtracted from the design energy cost as site-recovered energy.