Through this project United Technologies Research Center (UTRC) demonstrated a nominal 10TR (tons of refrigeration) high-efficiency cost-competitive Cold Climate air-source Heat Pump (CCHP) system at a Department of Defense installation in a relevant climate zone. The CCHP demonstration achieved >40% annual combined space heating and cooling energy savings, in the American Society of Heating, Refrigerating and Air-Conditioning Engineers climate zone 6A, while meeting the current pricing of state-of-the-art (SOA) mid-tier heat pumps. The demonstrations were conducted at the Maine Army National Guard headquarters at Camp Keyes in Augusta, ME and at UTRC’s psychrometric chamber in E. Hartford, CT. This project aimed to (1) bring the prototype CCHP components and system to TRL8, (2) demonstrate > 20% decrease in annual energy consumption over state-of-the-art systems in all cold climates (Zones 4A through 7), and (3) demonstrate site autonomous operation of the prototype CCHP, operability and functionality.
The goal of the CCHP field trail was to significantly improve on SOA industry standard heat pumps that can degrade by up to 60% in capacity and 50% in system efficiency (COP) at extreme heating conditions. Two key enabling technologies, high-efficiency high-lift compression and system-level design optimization for cold climates enabled this performance. The CCHP is scalable beyond 40TR (140kW) nominal capacity, cost effective, and has no change to footprint and installation complexity from existing roof top units.
During Phase I of this project a SOA Carrier heat pump unit was used at the Maine field trial site, and a full year of data was obtained. During Phase II this unit was replaced by the new UTRC CCHP and another year of data was obtained. The new CCHP significantly outperformed the baseline unit, achieving >40% energy savings over the year while providing supply air temperature >100F thus avoiding “cold blow.” The annual energy savings due to lower electric use ($3500) exceeded the incremental customer cost ($1200) and therefore meets the sales target of less than two year payback.
A targeted goal of doing this field trial is to advance the controls to TRL8. Several modifications were successfully made to control set points to avoid nuisance trips and improve overall performance. There were several issues relating to the field trial implementation and data: a) the Building Management and Control System provided outdoor air temperature was found to be inaccurate, especially in cooling seasons, b) the temperature-averaged load between the two seasons was not consistent even though the zone was the same and the 2018 and 2019 temperatures were very similar, c) changing zone set points can have significant effect on load and the use of electric heat thus affecting unit efficiency, and d) cooling COP was lower than expected; this was due to cool return air temperatures and running at colder outdoor temperatures when the economizer option should have been utilized.