Topcial Article: Heat Pumps and Thermal Storage: Canadian Perspectives

The increased use of heat pumps might be a challenge for the electricity grid, especially when the heat pumps operate during peak hours, when also other appliances are mostly used. This article explores how this can be solved with a more flexible link between the building and the electricity grid, through a system combining heat pump and storage, in a Canadian context.

The Canadian context means focusing on high performance in a cold climate, minimizing storage size, and 2-hour peak events during morning or evening. The storage material is most likely a phase-changing material, with a phase-changing temperature around 40-45°C. Differing preconditions might give differing results.

On an individual level, the increased electricity demand from one heat pump is not problematic. But since the demand is connected to ambient temperature, the increase in demand typically happens simultaneously across areas or regions. Combined, this might lead to a huge demand peak. Also, in Canada, air-source heat pumps are popular. As their performance degrades with lowering temperatures, there is an even higher load on the grid during the coldest hours when supplemental electric heating has to be used.

This grid capacity challenge could be overcome, though. A flexible link could be created between the thermal and electric grids in the building, by integrating the heat pump with thermal storage. During electricity peak hours, the system uses storage for thermal energy. During off-peak, electricity is used for the heat pump to deliver heat, and for charging the storage.

The setup consists of three elements: outdoors unit, indoors unit and storage unit. During off-peak hours, refrigerant is passing through the storage material, charging it. During peak hours, a fan is steering indoors air over the storage surface, and the air is heated. In this way, heat pump operation is transferred from peak hours to off-peak. If there are multiple peaks during a day, simulations show that at least 70% of the heat pump capacity has to be dedicated to charging between peaks.

A simulation is made for a single-family home in Montreal. This compares three scenarios: electric baseboards, a variable-capacity heat pump without storage, and a variable-capacity heat pump with storage. Both scenarios with heat pumps greatly reduces electricity demand for 99% of operating hours. The system with storage also reduces the maximum demand (peak) by approximately one-third. Thermal comfort is not significantly affected.

Justin Tamasauskas, Arash Bastani, Canada


This text has been shortened by the HPC team 

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