Design and optimization of a CO2 heat pump system for a low-rise multi-unit residential building

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Buildings account for 28% of secondary energy use in Canada and represent a large source of greenhouse gases. Approximately 80% of residential use is attributed to space heating and cooling and hot water demands. Additionally, the Canadian residential market has seen an increase in intensification in recent real estate developments (as a strategy to reduce carbon footprint while taking advantage of existing infrastructure) with a significant increase in the number of multi-unit residential buildings (MURBs) being constructed. Currently, the building loads are being met in each unit using three independent systems, whereas improvements in efficiency and reduced capital costs would be possible with one integrated system meeting the building loads of all units. Ecologix has proposed developing a novel heat pump utilizing transcritical CO2 as the refrigerant. Elevating the CO2 to the transcritical region is required to achieve the ability to heat DHW at the required 60oC. This project examines the potential of, and the development of a control system for using a CO2 heat pump to meet the space heating, space cooling and domestic hot water loads of a MURB. This project will first experimentally evaluate the CO2 heat pump under steady-state conditions to develop a baseline performance map including its heat transfer characteristics. Using this data, a model in TRNSYS will be built and calibrated to the experimental data and integrated into existing models of a typical MURB in Canada. Using this model, a parametric study will be conducted to determine the optimal configuration and control strategy for the integrated energy system.