Solar Assisted DX System

The goal of this project is to assess the energy and demand savings resulting from a solar assisted direct expansion (DX) system.  

A field test was conducted in a 1,600 sq. ft. single-story residential home located within SDG&E territory. In this test, an emerging technology that consists of a solar thermal collector, a bypass valve, and a controller was added onto a new 2-ton variable-speed split heat pump. Since the technology was installed onto the new heat pump, baseline operation was simulated by bypassing the solar thermal collector. The technology performance was recorded in between November 2019 to April 2020, alternating the technology on and off weekly. The heat pump operated in both cooling and heating modes during the testing period.

The field test observed no apparent savings either in cooling or heating mode. However, the study was limited in scope and the following next steps were recommended:

• Although this field test did not result in savings, the manufacturer of tested technology lists numerous case studies exhibiting notable savings with larger systems in commercial applications, including refrigeration systems. Since the field test was done on a small residential unit, an additional study is recommended to evaluate the demand and energy savings potentials of the technology in commercial applications such as larger packaged unit and/or refrigeration system.
• The effectiveness of the technology with the heat pump in heating mode was inconclusive due to lack of low ambient temperature conditions at the test site. A testing in a climate with more heating hours is recommended to further investigate the saving potential in heating mode.
• Only one manufacturer model was examined in this test while there exist a few variations of the same technology. Thus, it is recommended that an additional study be performed to evaluate the demand and energy savings potential of the other technology vendors in commercial applications.