With four stories and 29 units, Portland’s Isaka Shamsud-Din building, an apartment complex owned by the affordable housing non-profit organization Sabin CDC, is using a central gas-fired water heating system to deliver hot water to individual apartments. Seeking increased efficiency and performance, the building operators are upgrading the three 100-gallon condensing, gas-fired water heaters, each with 199,000 btu/h of capacity, that serve the building’s hot water load using a recirculation loop, thermostatic mixing valve, and a circulation pump that operates all day, every day.

The proposed design will replace one of the condensing water heaters with a 115-gallon storage tank, connected in series upstream of the remaining existing water heaters. The storage tank temperature will be maintained by a new roof-mounted gas absorption heat pump (GAHP), sized to accommodate 100% of the site’s load. Hydronic piping filled with a freezeproof glycol mix will run from the first-floor mechanical room to the roof mounted GAHP. The two-remaining gas-fired water heaters will continue to provide backup, while also handling any peak loads that exceed the capacity of the GAHP.

Following installation, the system will be metered and monitored for up to one year to gain insight into the percentage of annual load met by the GAHP at the given setpoint temperature, the total hot water plant performance, and the energy savings of the GAHP configuration compared to the current system.

To watch highlights from this installation, check out this video from BetterBricks: