Integrated Air Source Heat Pump System for Domestic Hot Water and Space Heating for Low Energy and Net Zero Energy Housing
Lead Proponent: Sumaran Inc.
Location: Ottawa, ON
ecoEII Contribution: $ 983,000
Project Total: $ 1,847,000
Advances in window and building envelope technologies are enabling houses to be built with very low space heating demand and reduced cooling demand. However, reducing energy consumption for year-round DHW heating remains a challenge. Cold climate air source heat pumps (CC-ASHPs) have emerged as an option for low-energy and/or NZE houses. Most efforts to generate DHW with ASHPs have focused on using desuperheaters and produced limited quantities of DHW. Recognizing this technology gap, SUMARAN proposed the project “Cold Climate Air Source Integrated Heat Pump with Zoned Distribution and Utility Control for Low Energy Demand Housing” for ecoEII funding. The Project was awarded $983K to develop prototype cold climate, air source integrated heat pump systems (AS-IHP systems) capable of providing year-round DHW, heating and cooling for low-energy and NZE houses. Assessing ways to improve the efficiency of ASHP systems, including the use of zoned air distribution systems and tempering of the outside air supply through a gravel bed thermal storage system, was also part of the project scope.
Different approaches to developing AS-IHP prototype systems were tried and tested. The first approach used Ecologix’s CC-ASHP which has a compressor integrated with a central air handler located indoors, and a complementary heat exchanger and fan unit located outdoors. In order to ensure optimal performance of the ASHP unit in low-energy and/or NZE housing, a more efficient compressor had to be sourced and incorporated into the system. The final system used the latest inverter compressor technology with advanced control strategies, and advanced refrigerant control. Initial tests determined that the rate of recovery for hot water production was close to that of a gas-fired tank. The second approach combined heat pump water heaters (HPWH) with Mitsubishi residential variable refrigerant flow (VRF) heat pumps. Two systems were developed: one with a Mitsubishi S-series outdoor 60,000 Btu/hour unit and two indoor air handlers equipped with hydronic coils (27,000 and 13,500 Btu/hour); and, the other with a Mitsubishi S-series outdoor 40,000 Btu/hour unit and a 20,000 Btu/hour indoor unit, as well as 5kW of backup in-duct electrical heat. One system was installed in an occupied net-zero-ready (NZEr) house and the other in a NZE demonstration house. Both were integrated with zoning systems using synchronized controls for VRF heat pumps, and equipped with extensive energy management monitoring equipment. The systems are performing well and monitoring is ongoing.
Research on zoned air distribution was carried out at the Canadian Centre for Housing Technology, with a Mitsubishi Zuba CC-ASHP and a standard system (gas furnace and standard air conditioner). Results suggest that zoning with set-backs has significant potential to improve comfort and reduce peak energy consumption with CC-ASHPs in both winter and summer. Zoning also improved comfort and reduced peak energy use with standard systems, especially in summer.
Research into gravel bed air tempering, using an Ecologix CC-ASHP, was carried out at the Urbandale Centre for Home Energy Research (CHEeR), a new research facility at Carleton University. Initial findings indicate that a gravel-bed sized to fit under a typical garage slab can provide air tempering to an ASHP at extreme cold temperatures, thereby improving winter performance. Research is ongoing.
Transient System Simulation Tool (TRNSYS) was used to simulate the performance of AS-IHP systems and zoned configurations. New TRNSYS components were developed to enable accurate simulation of residential buildings as well as variable-speed and variable refrigerant flow (VRF) heat pumps, and integrated into a multi-zone whole-house building model. Finally, a project component was added to identify optimal strategies for reducing or eliminating peak load in low-energy/NZE houses with ASHPs, PV and batteries. Results from initial testing indicate that with appropriate control algorithms, a PV grid/battery system has potential to meet ASHP load during peak periods, even in very cold weather.
Benefits to Canada
As Canada seeks to reduce greenhouse gas emissions and improve energy efficiency in the residential buildings sector, AS-IHP systems with zoning are poised to make a significant contribution. The research supported through this Project has contributed to the development of promising new systems and approaches.
SUMARAN will continue to monitor the installed AS-IHP systems, further research in gravel bed air tempering and PV grid/battery control systems, and further validate and refine the TRNSYS computer models and interface.
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