A researcher’s quest to make heat pumps frost-free

A Saskatchewan researcher is looking for ways to help heat pumps stay frost-free in the cold.

Amirreza Mahmoudi, a doctoral candidate at the University of Saskatchewan, said that while heat pump technology is improving, frost is proving to be a formidable enemy because it sticks to the coils and reduces performance during freezing winters.

Heat pumps, which act as heaters in the winter and air conditioners in the summer, are becoming an increasingly popular trade-in for homes that run on natural gas or oil. Fossil fuel heating systems can reach up to 98 percent efficiency, while heat pumps can be between 200 and 540 percent efficient because they transfer heat rather than generate it.

Because they use much less electricity and do not run on fossil fuels, heat pumps are an important way to reduce emissions, especially as Canada moves toward its 2050 net-zero emissions goal.

Mahmoudi’s research focuses on finding a solution to modernize heat pumps that are already manufactured and make them frost-resistant. The most promising so far is a membrane attached to the outside of a heat pump to prevent frost.

Heat pumps typically look like air conditioners and are located outside a home. The refrigerant fluid runs through exterior coils, transferring heat from the outside air to the interior of the house. In humid climates, like Atlantic Canada, condensation can stick to those coils and freeze.

Heat pumps have a defrost cycle to solve the problem of frost buildup. When it is very cold and frost accumulates, heat pumps turn off and go into defrost mode. When that happens, a backup heat source, such as oil, gas, or electricity, is turned on. While some heat pumps can operate without backup sources, cold climates typically require them; Otherwise, cold air enters homes during the defrost cycle without heat to replace it.

Reducing frost on heat pumps would reduce the need for backup heat sources and at the same time reduce emissions and, as a result, home heating bills, explains Mahmoudi. He says the key to a frost-free system could be covering the coils with membrane energy exchangers, which have small pores to allow air but not moisture to pass through. Inside the exchanger is a liquid desiccant, much like the silica gel packets you might find in a box of new electronics, to absorb moisture.

These membranes have been shown to prevent frost formation in other machines such as air conditioners, but have not yet been used with heat pumps, Mahmoudi said.

The research focuses on finding a solution to modernize the heat pumps that are already manufactured and make them frost-resistant. The most promising so far? Membrane attached to the outside of a heat pump to prevent frost.

“We just have to figure out how to combine these two things, membrane energy exchangers and heat pumps, so that they work as a single device that can be marketed,” he explained.

“It’s important because when you think about commercial products, you have to think about all the capabilities of the manufacturer and their profitability.”

At the University of Saskatchewan, Mahmoudi works with Siddhartha Gollamudi on a research group to address current barriers hindering the widespread adoption of heat pumps in Canada. Mahmoudi said the group’s frost research is at a preliminary stage and will help it discover how potential membranes could hinder heat pump performance and ways to avoid it.

While frost is the most pressing issue for humid coastal communities, in places like the prairies, the challenge has more to do with heat pump performance in extremely cold temperatures. In Saskatchewan, temperatures can reach as low as -40 C, but it’s very dry, so Gollamudi is researching how to make heat pumps efficient in especially cold temperatures.

Natural gas is much cheaper than electricity in Saskatchewan, so efficiency is key, Gollamudi explained. A recent paper from the University of Oxford found that heat pumps are two to three times more efficient (or use two to three times less energy) than their oil and gas counterparts, specifically at temperatures ranging between 10 C and -20 c.

But for widespread adoption of heat pumps to be successful and feasible across Canada, issues of frost and efficiency in temperatures below -20 C will need to be addressed.

“Each province has its own challenge in terms of performance, in terms of economy, in terms of emissions. Heat pumps are part of a solution, and not the only one, because it is necessary to have a cleaner network for these systems to work,” explained Gollamudi.

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