Gas Engine-Driven Heat Pump (GHP) Cold Climate Field Demonstration

Ms. Patricia Rowley | Gas Technology Institute



Gas engine-driven heat pumps (GHPs) are an emerging space conditioning technology that offers a cost-effective and environmentally friendly option to reduce lifecycle costs, primary energy, and peak electric demand as compared to conventional equipment or electric air-source heat pumps. GHPs can significantly reduce energy costs and improve energy security for Department of Defense (DoD) facilities. Ongoing GHP developments, such as black start capability, have potential to improve reliability for critical operations and reduce the dependency of DoD facilities on the commercial electric infrastructure. The objective of this project is to evaluate the annual performance of a GHP system in a side-by-side comparison with an electric cold climate heat pump (CCHP) relative to the baseline performance of the existing packaged heating and cooling rooftop unit at Naval Station Great Lakes (NSGL), Illinois. The project will determine the energy and economic benefits of each technology for cold climate DoD applications.

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Technology Description

The GHP design is similar to an electric heat pump, but utilizes an advanced natural gas engine in place of an electric motor. Both gas and electric heat pumps selected for this demonstration utilize variable refrigerant volume (VRV) configurations to provide multi-zone heating and cooling. The NextAire™ Multi-Zone GHPs combine high efficiency scroll compressors and an Aisin/Toyota engine with a demonstrated long life (30,000 hours). GHPs combine high efficiency heating (1.2-1.4 coefficient of performance [COP]) and cooling (0.95-1.2 COP), offering reduced operating and lifecycle costs as compared to conventional HVAC equipment. During cooling, GHPs consume natural gas in place of electricity, significantly reducing peak electric demand in comparison to electric chillers or electric heat pumps. During heating, GHPs are almost 50% more efficient than standard gas furnaces or boilers (80% efficient) commonly used at DoD facilities. Heat recovered from the engine cooling jacket and exhaust can supplement the GHP output during heating mode, similar to a combined heat and power system, to increase the overall system efficiency. Heat recovery allows GHPs to deliver a higher supply temperature at low ambient conditions. In contrast, electric heat pumps require inefficient resistance heating to supplement the heat pump output at low outdoor temperatures.

Although GHPs have a significant share of the Japanese and European space conditioning markets, they have only recently been introduced in the United States. The IntelliChoice Energy’s NextAire™ GHP was introduced in 2009. GHPs were developed and marketed as gas cooling options with known benefits such as reduced electric use and peak electric demand, as well as significant savings in water use as compared to electric chillers. As a result, current GHP installations are concentrated in warmer climates. However, based on preliminary analyses, the high heating efficiency of the GHP has potential to increase savings in primary energy and lifecycle costs for colder climates, in addition to the benefits of gas cooling. The NextAire™ GHP for cold climates is commercially available and requires no development work prior to the demonstration. The demonstration will be one of the first cold climate installations of the Model E and is needed to properly assess the installed annual performance and economics of a new cold climate application of this emerging technology.

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Based on preliminary modeling of GHP performance for a small office building, one 15-ton GHP would reduce electric use by 24 MWh per year and reduce electric demand by 62 kW compared to an electric heat pump. Savings in electricity are offset by an increase in natural gas use of 1,654 therms per year. Each 15-ton GHP would decrease greenhouse gas emissions by 29,393lb CO2e per year. Net energy cost savings are estimated at $4,465 per year based on current utility rates for NSGL. (Anticipated Project Completion - 2019)

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Points of Contact

Principal Investigator

Ms. Patricia Rowley

Gas Technology Institute

Program Manager

Energy and Water