Oxford study proves heat pumps triumph over fossil fuels in the cold::Published Monday in the scientific journal Joule, the research found that heat pumps are two to three times more efficient than their oil and gas counterparts, specifically in temperatures ranging from 10 C to -20 C.
The Oxford study is really good. But I can’t say the same about this article.
A COP of ~2 is not great for a heat pump, calling this a triumph is really weird. But from a journalist saying that a COP above 1 means the heat pump “creates energy”, I am not sure I should have expected more.
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.
What’s important is also to be able to store heat during the day so that the heat pump runs at its most efficient time. But that can unfortunately coincide with the higher consumption time, so the timing needs to be adjusted properly to avoid using it during consumption peaks.
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.
I’m a 4th year AC/R mechanic born and raise in Southern Ontario, currently in BC.
You mebtioned your hydro was up but gas was down. Out of curiosity, can you tell me how your total cost of heating changed before/after your first winter with your heatpump? Did you end up saving money?
Was there any specifig brand/seer rating restriction with the GHGrant? I just applied and will be going this route, but I don’t want to be paying $15000 for a specific brand or something if I can get similiar equipment that might not be on a list.
Was there any specifig brand/seer rating restriction with the GHGrant?
It’s more complicated than that. The major components of the system all have to be qualified for the rebate, down to the component model numbers. There’s a lookup tool to see which model numbers qualify. For a hybrid setup like mine, there are three parts:
- Outside model number: this is the actual heat pump component that gets installed outside
- Inside model number: this is the condenser coil that gets installed on top of the furnace
- Furnace model number: this is the model number of the furnace itself
A ductless system would only have two part numbers involved, the outside heat pump unit and the inside wall unit (though a ductless install can have multiple inside units in multiple rooms). No furnace for a ductless system of course. Edit to add: and all of the major components you get have to be certified with each other by the GH program. They don’t want you mixing and matching.
Every HVAC company I talked to was pretty knowledgeable about the GH program, so if you tell them you’re an applicant then they should put together a quote that qualifies. Multiple HVAC reps advised me to make sure that all rebate-covered part numbers were listed clearly on the invoice. Apparently if that info is missing it can derail the rebate until the invoice is updated with full info.
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.
Geothermal has advantages, but air source is getting so good that it’s really becoming a niche.
Spending $5K on insulation or heat recovery ventilation will be more effective than spending it on a hole.
I saw an awesome home refurbishment in Montreal, they just went all-in on insulation. The heating was just done with a 500W resistive heating coil, just for the coldest days. They didn’t even have a heat pump, except for the heat pump boiler. The heat recovery ventilation did the rest.
What if you already have good insulation? It’s already well-known that old houses have shit insulation, so of course it’s worth investing money into that if you already need it. But, even heating a new house can be expensive.
What is HRV? I thought it meant a ground loop heat exchanger. I’ve heard about it in the passivhaus model but don’t understand it.
That’s still in territory where gas boilers are more cost efficient that a heat pump… a heat pump has overall lower running costs than a gas boiler
You just contradicted yourself… what did you mean here?
Electricity is 3x the cost of gas, so unless the heat pump has the COP of 3 or above it is more expensive to run. Once you factor in the high cost of installation people aren’t installing these things to save money.
It’s not a contradiction if you put my whole sentence. When it is really cold, a heat pump will be more expensive than a gas boiler. But over a full winter (hence “overall”), the period where it is more efficient make up for it, especially since that when it is bad, it is not that bad.
But you are right to mention the high cost of heat pumps. I would not advise anyone to get a heat pump with a goal of saving money, the return on investment is slow and rather small.
I don’t agree with generalizing that ROI is slow and small. There are too many variables here specific to each market, location, and home. Someone with an old propane or oil boiler that is already planning to buy a new AC will absolutely see massive ROI going with a heat pump. In the US, federal standards will make furnaces more expensive (condensing only soon) and heat pump costs can be heavily subsidized. I bought a new HP that was cheaper than my neighbors new AC/furnace after incentives, and my running costs will be lower.
Heat pumps are A/C in reverse. It makes total sense instead of using fire to heat air.
You’d need to collect the condensate, but that would actually work quite well.
You think you are being a smartass but that’s exactly what heat pumps do. The only functionality difference between an AC unit and a heat pump is a reversing valve.
But without a reversing valve you could put your AC unit in backwards and heat your house in the winter.
The whole premise of an AC unit is to take the heat from inside the house and put it outside, leaving you with cooler air inside.
So in the winter a heat pump simply reverses the flow of the freon and moves the heat from outside to inside. Yes. You are “cooling the whole neighborhood” when you run a heat pump.
I wish it was standard to be able to do both. My heat pump is unreal efficient and cheap and great but I’d love a cool breeze every now and then.
WELL FUCKING OBVI-
Oh right, I forgot some people are really pulling for this fossil fuel think to pull through.
Maybe someone can help me answer this question as I’ll be replacing my old furnace in the near future and am curious about the heat pump systems.
Studies like this are only looking at efficiency and not total energy usage or heating capacity so how do you compare apples to apples? A high efficiency forced-air furnace using natural gas is something like 95% efficient, and a heat pump can be something like 150%-200% (because you’re moving the heat instead of creating it), but the total output capacity matters as well as the efficiency of generating and transmitting the electricity. Also, I don’t think the power needed to run the fans gets factored in from what I can tell and I expect a heat pump system to need fans running far more often and for longer. Since heat is constantly being lost to outside then whichever can work faster might have an advantage keeping ahead of that entropy too…
I’m living in a climate considered “extreme cold” in this study btw. Best I’ve been able to figure out, a gas furnace is still much cheaper to install/operate (it’s pretty cheap here) but is also still be better for the environment as my electricity tends to be generated primarily from natural gas and coal (at an efficiency lower than a natural gas furnace does).
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.
That’s a good point about the furnace fan!
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”.
I’m using what the study calls extreme cold, which would account for about 3 months of the heating season where I live, and that’s where I got the lower efficiency numbers from too as they state the COP is around 2.75 (roughly 3 months of the year here) in the “mild cold” and only around 2 at best in the colder months.
We have a bit of an unusual climate here with fewer people so most of the info I find tends to focus on where more people live and the climate is different so it’s tough to figure out. There’s a good three months where no heating is required at all (and increasingly, ac units are in demand). A couple of years ago we had close to an 85°C temperature swing from the end of February to mid June!
Natural gas is plentiful and cheap so it’s used for central heat and hot water here, sometimes clothing dryers too but that’s less common. I still end up paying a gas bill in the summer months essentially just for admin fees and such, so the temptation is to go fully electric (would have to change the HWH) with a heat pump system and resistive backup heat. The problem is from what I can tell, the additional cost isn’t quite worth it yet (the system might not even save any money and is more expensive to install/maintain), and the emissions difference is tough to calculate when a third of the power comes from coal and over half from natural gas…
You’re right to be concerned about emissions, if you live in a place where a significant portion electricity comes from coal its almost certainly cleaner to just burn the natural gas. Which area of the world is this if you don’t mind saying?
For sure look into any subsidies available to you and see if they make a dual fuel system feasible. In your situation if you buy a high efficiency furnace, it may never make economic sense to run the heat pump, but things could always change and it’s a simple enough task to find your break even (economic balance) point when fuel prices change. My current break even point is well beyond the temperature you would consider running heat, but I still run my heat pump in the shoulder seasons to exercise it.
They’re only two to three times more efficient if they aren’t frozen solid. Don’t know how it works in Canada, but my mini-split heat pump can’t handle a week of 10F let alone -20 C - sure it will put out some heat, but it absolutely needs to be supplemented with my wood stove. And I live in the South. Maybe there’s some new high tech heat pumps that cost a fortune and don’t freeze over in the insane temps of the great white north? EDIT: hey, folks, how about actually responding instead of downvoting me? If I don’t have a clue, please enlighten me. Fuckers.
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.
Excellent. Now I know that there are different classes of heat pump. Mine is not for prolonged crazy-low temps, others are. Thank you.
Indeed, but yours is probably cheaper and more effective at cooling when it’s hot and humid out.
For people up north, they will buy a “cold climate air source heat pump”. In temperate regions, an “air source heat pump” will suffice, while down south you will buy an “A/C with a heating mode” (also called reversible A/C).
And it’s not just about whether the coils can defrost. The whole machinery and refrigerant are different to optimize under those conditions. A cold climate heat pump has a setup that is more similar to a freezer than it is to an A/C.
Sorry about the downvotes. People need to re-learn internet etiquette.
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.
Thank you for responding and sharing your counter-experience. Greatly appreciated. What keeps your unit from icing over? Are they designed differently in northern climates?
Here’s a good video showing how the heat pump will reverse and basically dethaw the coils when it freezes over: https://youtu.be/7J52mDjZzto?t=1317
They’re spreading all over the Alps too. Easily a 50° temperature difference between summer and winter, and they tick over nicely for years with no problems
I think in Europe it’s a fairly common method now so reliability has been sorted out.
Generally the US is a decade or so behind everyone else though so it might take a while
You asked, you got it.
Educated adults know not to do that, and now you’re educated. Good luck out there
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
Mine has a defrost cycle but it doesn’t work very well. But then again, it’s use case is primarily AC - it only gets frigid temps in my area every couple years. EDIT: yes, downvote me for stating my own personal experience, asshats.
Many parts of Canada will regularly see colder than -40F, so I can sympathize easily with a view that solely relying on them might not be safe in that environment.
Tbf, most Canadians don’t live in those areas. Places like Toronto/Montreal/Vancouver rarely get that cold.
It’s fine. We use geothermal heat pumps with the lines buried below the frost line. (6-8 feet below the surface.) I know quite a few houses and even a few factories (30,000 square feet+) that use them in temps that drop well below -30c to -40c without any issues.
The initial setup cost is a fair bit more because of having to bury the lines, but after that they’re fine.
Yes, most installations do require a backup heat source in the event outside temperature is too low for optimal heat pump usage. On my ecobee thermostat, you can set what this temperature threshold is (i.e. 20F) and then if the outside temperature falls below this value, the heat pump is stopped and the natural gas in my case kicks in. Granted, this doesn’t happen often where I live, but for those few weeks in the winter, it is not something I even have to think about. And the rest of the time, I am saving money using the heat pump and not natural gas.
I doubt there can ever be high tech heat pumps which can operate at -25 C or less, because there’s so little heat energy outside and the heat pump would probably spend a majority of the time running in reverse to dethaw the unit to prevent it freezing over.
I doubt there can ever be high tech heat pumps which can operate at -25 C or less, because there’s so little heat energy outside and the heat pump would probably spend a majority of the time running in reverse to dethaw the unit to prevent it freezing over.
It could probably be done, but then it wouldn’t operate at higher temperatures. Realistically you’d probably need two heat pumps, a low temperature pump and a high temperature pump and switch between them as the temperature rises or falls. It’s double the cost and double the points of failure, and for a situation that rarely happens probably not worth it.
I’d have to imagine at some point, more heat is leaving the house than entering, and given enough time, inside and outside will eventually reach a cold equilibrium.
Oh I have no idea, I just got to this thread and see you’re at -6.
It’s weird because I thought it was an informative post. Made me want to look more into it and if it was just a subsection of heat pumps that was affected.
I think because I left open the possibility that there’s any utility at all to fossil fuel usage, they’re treating me like a whacko that’s hoarding incandescent light bulbs because I believe LED light bulbs are distributed computing nodes for mind control space lasers or something. I’m not - I was reacting to the article based on my experience with a mini-split heat pump that can’t handle a week of 15F weather without freezing into an iceberg, even with a defrost cycle.
Man they pitchfork mob came out in full force for this one. I also live in the south and during the freeze of 2021 it was a struggle for it to deal with those low temps.
That’s precisely the freeze that led me to experience the inability of my Senville mini-split heat pump to keep up. So glad I had a wood stove. Even then, my shower drain trap froze solid. I was living in an “insulated” yurt at the time - good floor insulation, and somewhat okay wall/ceiling insualtion.
My attic insulation needs work. I swear I’m gonna get that sorted this year now that the heat has (hopefully) calmed down.
Mind me asking what yours cost?
Just got a Toshiba unit installed in Norway and it was $3500.
Built in de froster.
Price might be what makes yours strugle in colder temps.
Mine has Toshiba guts. I don’t know what I paid for it - now it appears to be selling for $1100. Mine defrosts but its defrost cycle just turns on AC for a bit instead of heat. Edit: Mitsubishi guts.
Hell that’s cheap.
Cheapest quote I ever had was £15k, not including all the improvements to insulation required before the house is compatible…
Your mini split probably doesn’t have a defrost function. This would all be specified in the users manual.
Oh it does, it’s just that it the defrost cycle in 15F gets off just enough ice for it to barely work, and this was when it was brand-new and verified to be working properly. I now understand that it is just not designed for ultra-cold weather, and that some are better suited for such demands.
That does kind of imply it could need a recharge. These cheaper units don’t actually have active monitoring for ice buildup - they just do it on a schedule based on temperature (and sometimes humidity). If you are getting ice buildup, it’s either outside the rated performance envelope, or it is not functioning as intended.
