Air Source Cold Climate Heat Pump
William Hutzel | Purdue University
Objectives of the Demonstration
A university/industry team from Purdue University, Trane, Emerson Climate Technologies, Danfoss, and Automated Logic Corporation of Indiana demonstrated a new air-source heat pump technology that was optimized for colder climates. The technology has significant potential to reduce the primary energy used for heating small commercial or residential buildings and to expand the range of air-source heat pumps to Department of Defense (DoD) facilities in the northern half of the United States. Cold Climate Heat Pumps (CCHPs) are less expensive to operate than an electric furnace and are cost competitive with fossil fuel sources of heat, even though the cost for natural gas is very low at this point in time. CCHP technology also has the potential to reduce greenhouse gas emissions because they are powered by electricity that could come from renewable energy.
Six performance objectives were established to evaluate the technology when compared to a natural gas furnace: (1) reductions of primary energy by 25%; (2) reductions of heating costs by 10%; (3) reductions of carbon dioxide (CO2) emissions by 15%; (4) compliance with American Society of Heating, Refrigeration, and Air Conditioning Engineers (ASHRAE) Standard 55 for comfort; (5) ease of installation; and (6) maintenance.
The field demonstration was conducted at the Camp Atterbury Joint Maneuver Training Center in Edinburgh, Indiana. Two barracks were selected for the test because they are typical of the small to medium size buildings encountered on military bases. Each building was approximately 6,000 square feet and constructed of cinderblocks. Even though the barracks were roughly 50 years old, they had recently been updated with insulation, a sheet metal roof, and a modern central heating, cooling, and air conditioning (HVAC) system. Both buildings had two zones for heating and cooling, which allowed for a direct comparison of the CCHP technology to a modern gas furnace. The buildings were modified so that one zone used the CCHP and the other zone used its original modern central HVAC system. Both zones were instrumented so that energy consumption and comfort could be evaluated using a web-based control platform.
The CCHP reduced the primary energy for heating by 19% as compared to the gas furnace. Although the energy savings was substantial, this did not meet the success criteria of 25% that was established at the start of the project. Cost savings and reductions in emissions can be computed directly from the energy savings. The operating cost of the CCHP was approximately the same as the gas furnace, which also did not meet the success criteria of 15% cost savings that was established at the start of the project. The field demonstration did meet the target for reductions in CO2 emissions by achieving a 19% reduction as compared to the success criteria of 15%. The project achieved the performance objectives for comfort, ease of installation, and maintenance.
This was the first full-scale field demonstration of the CCHP technology. Implementation issues encountered were mostly resolved during the course of the project, but included managing the flow of return oil to the compressors, flooding of the compressors with liquid refrigerant, and maintaining an appropriate level of subcooling at the condenser outlet. The refinement of control algorithms used to manage the operation of multiple compressors, a variable speed drive for the high stage compressor, and expansion valves for modulating refrigerant flow were essential for correcting problems and improving operation.
The CCHP technology is being further developed and commercialized in partnership with Unico, Inc. of St. Louis, Missouri. The units used in this demonstration will be partially decommissioned to allow for future use of the demonstration site. There is significant potential for improvements in performance and ultimately delivering a new HVAC technology that will help DoD meet its energy reduction goals.