Technology

a journalist saying that a COP above 1 means the heat pump “creates energy”

But what’s great is that this COP of 2, while bad, is not catastrophic. That’s still in territory where gas boilers are more cost efficient that a heat pump, but unless you are living in a place that is consistently under -10C for several months, then a heat pump has overall lower running costs than a gas boiler. And you are starting to hit pretty northern territories with this.

I actually have a hybrid furnace/heat pump system, and I live in southern Ontario, Canada. The furnace is the auxiliary heat source and it only kicks in when the outdoor temp is below -6C. I've only had this system through one winter so far, but I think I could count the number of days the furnace ran without running out of fingers. My electricity bill went up some of course, but my winter gas bill went down a lot.

Edit to add: I wasn't shopping for a hybrid system in particular, but I got this upgrade through the Canada Greener Homes Grant and there were limitations on which units qualified for rebates. For my install (forced-air with existing duct-work), the hybrid systems were the ones that qualified.

Even the study could have used some better clarification on geothermal HVACs, which is the direction we should all be heading towards:

Ground-source heat pumps typically provide a very high level of efficiency, even during cold weather. The reason is that soil temperature does not change significantly between seasons, resulting in a higher—and more constan—COP. In addition, ground-source heat pumps do not need to expend energy on defrosting.

This commentary focuses on the performance of air-source heat pumps in mild European winters with average January temperatures above −10°C. We refer to these heating conditions as “mild cold climates”, whereas those with average temperatures below −10°C in the coldest month are designated “extreme cold climates”.

No, why?! Gimme the COP on geothermal. Google tells me it's 3 to 5, but I would have liked a better source.

Regardless, while I understand that we should spread out our solutions, I don't understand why we're not talking more about geothermal HVAC systems. Household solar is all the rage, but my gas company is still charging me $25 a month just to have the gas on, never mind the winter costs.

If we're talking about $5K a hole to dig for geothermal, that seems like a hell of a lot more cost-effective solution than either gas-based HVACs, or these air-based heat pumps. If it's an area with only mild winters, you probably only need the one hole, which will last for 100 years at least. At most, we're talking about 3-4 holes for a large house in Canada, and that's going to pay for itself in 10-15 years.

brb putting in my window unit from the outside

Under the conditions you describe, a hybrid setup will work best.

In a hybrid setup, the heat pump is providing most heat when it isn't very cold, while the traditional heat source is providing heat on really cold days.

A few years ago, the temperature where the system would switch was 5 C. Nowadays it's more like -10 C. As heat pumps get better, hybrid loses territory, so you could also just wait a few years and then switch.

Hybrid gives best of both worlds at the cost of added complexity.

If you have A/C then the cheap way to do hybrid is to keep the traditional heating system but use the A/C in heating mode on mild days.

If you are comparing gas to heat pump efficiency, it is more like 85-90% vs 350-500% efficiency.

Because in the gas furnace efficiency they only calculate the efficiency of burning gas but miss to include the auxiliary electricity that is needed to run the system.

In a heat pump system everything (running fans etc.) is included in the efficiency calculation. The efficiency itself is depending on the source of the heat pump. In a really harsh climate a ground / geo thermal source might make sense. But usually the average temperature is higher than you might think.

And for the environmental effect: modern gas power plants run at 50-60% efficiency so with a heat pump you are always burning less gas even if the gas plant is less efficient then the gas furnace.

It would be interesting to know what extreme cold means.

Your mini-split isn't designed to function as a heat pump at low temperature.

In places like Sweden, they also use heatpumps that are designed for those conditions.

In other news, don't drive in a Swedish winter with summer tires.

My air heat pump has been ticking away happy for 15 years with no issues. It's worked fine warming up the house when it's -20°C in the winter and cooled nicely in the up to +30°C in the summer.

I do supplement it using electric heating and a fireplace though.

You used two temp scales in the same sentence

Yes, there are cold weather heat pumps that can thaw the coils to keep operating. There is a point where they just can't continue to operate.

When I design a heat pump system in cold climates, I always include a secondary hear source that kicks in if the heat pump gets overwhelmed. Might be a gas section in a furnace. Might be an electric heater in a fan coil. Might be electric baseboards or wall heaters.

Theres different technology but there are some that can function to -32° F and they often have a feature that allows them to detect when theyre frozen up and defrost and then automatically switch back to heating

They actually added a correction at the end for that