C21 - Decarbonization Potential of 9 Water Heating Technologies for California

Decarbonizing California’s residential buildings is essential in order to achieve California’s zero-emissions goals. A primary avenue for decarbonization is the deployment of low-emissions water heating equipment in both new and existing residential buildings. Which then begs the question – what are the water heating technologies with the greatest potential for reducing greenhouse gas (GHG) emissions in California?

This project takes an in-depth look at the GHG emissions reduction potential of nine water heating technologies:
• conventional natural gas water heaters in both storage tank and tankless configuration;
• conventional electric resistance tank water heaters in both grid-only and PV-assisted configurations;
• heat pump water heaters (HPWH) in both grid-only and PV-assisted configurations;
• solar thermal water heaters (SWH) with three different forms of auxiliary backup.

A comprehensive annual performance analysis was performed for three representative California cities – Sacramento, San Jose, and Los Angeles – using the simulation program TRNSYS with equal residential water heating loads for each DHW technology. The following water heating technologies are listed in order of the greatest GHG emissions reduction potential based on the EPA-listed power generation mix for California. (Detailed results are included in the poster.)

1) Solar thermal water heaters with natural gas backup – tankless;
2) Solar thermal water heaters with natural gas backup – storage tank;
3) PV-assisted heat pump water heaters;
4) Solar thermal water heaters with electric resistance backup;
5) Heat pump water heaters (in homes where the HPWH is installed in an unconditioned space like a garage) – grid-connected;
6) Hybrid PV-assisted electric resistance water heaters;
7) Natural gas water heaters – tankless;
8) Natural gas water heaters – storage tank;
9) Electric resistance water heaters – grid-connected.