I live in a valley which is greener than most places in North America. Natural gas lines end about 80 kilometres to the south and the main source of power is hydro. As a secondary or emergency source of heat, most houses either have wood burning stoves or propane stoves or fireplaces. Propane has to be trucked over a few mountain passes so it is about 3 times as expensive as natural gas per unit of energy. Wood is the preferred fuel of the working man as it is cheap in the area, which harvests wood for pulp and paper, or lumber.
When I moved into the valley three years ago, the house came with a heat pump which was on its last legs. Two years ago, I replaced it with a new unit in the middle of the Covid epidemic. While I was limited in options, the technical specs on the unit seemed to be equivalent to units from other vendors and most importantly, I could get it in time for winter. Subsidies from the province, of course, did not apply since I was not replacing a fossil fuel heater. While my expectation were that the heat pump might work to -10C or -15C, much of the literature seemed to suggest -25C, which I expected was a bit exaggerated. The installer indicated that it was probably not advisable to run it in temperatures less than -10C.
During the fall it worked rather well and then with the arrival of weather below freezing it almost immediately failed. The installer would not service it, and a second HVAC company proved that they had no experience with the brand. I finally found a HVAC company which seemed to be willing to diagnose it but they could not come for another few weeks. In the interim, I went over the installation manuals and determined that he control wiring of the unit was wrong and I had to rewire it myself to at least look at the diagnostics from the heat pump without taking the service panel off. The tech which I eventually got diagnosed the problem as a faulty pressure sensor and replaced it. The fix however took most of the winter to get the diagnose the problem and fix it. The heat pump worked happily until the next freeze cycle when the error codes came back intermittently. This time he installed a new circuit board in the unit, which again worked for a while after which the problem came back. On a third visit, he finally diagnosed it a sticky reversing valve which seems to have fixed the problem. I am out about $10,000 Cdn in technician fees and excessive heating costs.
Who is to responsible? Apparently no one. The manufacturer will not even talk to home owners, only HVAC techs. Without the extended warrantee, only replacement parts are covered which take a long time arriving, and the warrantee does not even transfer when you sell the home. The diagnostics for the unit apparently could not correctly identify the problem assuming the sticky reversing valve was the problem all along. The HVAC tech that I ended up working with had no experience with the electronics embedded in the unit but did have generic HVAC experience, which at least gave us a start at a fix.
From the start of the experience there was a huge gap in the expectations of the green community and the actual experiences of others in the area. Most people with practical experience recommended only using heat pumps to -10C to -15C whereas the popular opinion of the green community was that they were good until -25C. Also the specifications from the manufacturers showed a significant drop in heat output with colder temperatures, some as much as 40%. What was likely not modelled by the manufacturer however was defrost cycles which impede the performance even more.
Around freezing, the outside condenser of a heat pump has to be cooler than the surrounding air, by about 5C, to transfer heat to the inside of your house . If the air is close to the dew point, this deposits moisture on the condenser in the form of ice. The defrost cycle reverses the heat pump and pumps heat out of your house to thaw the condenser which would otherwise collect ice until it was ineffective at transferring heat. In a lot of heat pumps, these cycles have options to time the defrost cycles at 30 minutes to 2 hours however in the right conditions, a heat pump can collect enough frost to impede its operation in as little as 10 minutes. Also, as the temperature decreases below zero the heat pump has to pump more heat to dissipate frost. Another problem is that the reversing valve which normally changes a handful of times per year is reversing up to 2 times per hour. When it fails, this results in an expensive bill to pull the refrigerant from the system, unbraise and replace the component, then refill the system with refrigerant.
Research has been done decades ago on the defrost problem but for a lot of heat pumps the same method of defrosting it have been used for a few decades. Why not? The manufacturers have a large market in the southern US and a hard to crack market in the north central US. Canada is an after thought. The US Democrats however have seen heat pumps as a way to replace natural gas heating and therefore seem to be promoting “cold weather” heat pumps although the designation may be more of an advertising gimmick than than a reality. No manufacturer seems to want to say how they have solved a fundamental problem with cold weather heat pumps but a google search will turn up pages of them plus government rebates.
Like a lot of green tech, being on the leading edge is living on the bleeding edge.