Dear Team,
We would appreciate your guidance regarding the appropriate baseline modelling methodology for residential service water heating systems under ASHRAE 90.1 Appendix G for a LEED project.
The proposed design utilizes residential Heat Pump Water Heaters (HPWHs) with a COP of approximately 3.5.
Our understanding of ASHRAE 90.1 Appendix G, specifically Table G3.1.11, is that where the complete service hot-water system exists, the baseline building design shall reflect the actual system type using the actual component capacities and efficiencies.
Based on this requirement, it appears that the baseline service water heating system would be modelled using the same system type as the proposed design. If this interpretation is correct, we would like clarification on how energy savings associated with the use of HPWHs can be claimed within the Appendix G methodology.
Specifically:
- Should the baseline service water heating system be modelled using the same HPWH technology, capacities, and efficiencies as the proposed design in accordance with Table G3.1.11? If so, would this mean that no energy savings can be claimed solely due to the selection of HPWH technology, and that savings can only be attributed to efficiency improvements beyond the baseline requirements?
- Alternatively, is there any accepted LEED or Appendix G methodology that permits comparison against a different baseline service water heating technology, thereby recognizing the efficiency benefits of HPWHs?
- Are there any LEED interpretations, precedents, or review guidance that specifically address the treatment of residential HPWHs in the baseline and proposed models?
Thank you for the assistance.
