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That massive spike of 50c/kWh at the left looks tiny compared to today even though that's already insanely expensive
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this post was submitted on 05 Jan 2024
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Mildly Infuriating
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This is such an outdated information. Modern heatpumps work just fine even in temperatures of -20C and below. Ofcourse the efficiency gets worse the colder it is but even at worst it's still 100% efficient. On a typical year there's only a handful of really cold days. It doesn't make sense not to get a heatpump just because it's inefficient for few days. It's not like it stops heating or something. It just effectively turns into electric radiator which is what my house was heated with before I got the heatpump anyways.
This is true only if you have a heat pump with electric/resistive backup heat. But for some reason, it's pretty easy to buy one in the US that doesn't. (Which is where I assume that poster is, because most anti-heat-pump sentiment seems to come from here.)
Not quite, in my experience on really cold days my heat pump struggles to keep up. This is expecially true when the outside unit is frosting up. The unit has to reverse and pump heat out of the house.
That's one of the reasons i run my wood pellet stove on those days. The secondary source of heat takes the load off the heat pump.
Sure, but as I said it's just a handfull of days in a year. If the heatpump alone struggles to keep my house warm I can just switch on one or two electric radiators.
In an area that gets very cold, a geothermal heat pump (which uses the ground rather than the air for heat exchange) would work better than an air-source heat pump. More expensive to install though, and you need a good amount of land
It's basically what modern homes should have built below them. Then it doesn't need extra space. Wonder if it's already enough to put some pipes a meter below the basement?
Most heat pumps will use the aux coils to defrost. It's also ok for the heat pump to literally run 24/7 if it needs to. A lot of people freak out when the heat pump runs all day and blows "cool" 80F at from the vents, but it's still working as intended. Though I totally get how that can make a place feel "drafty" without some backup running
It’s true they’re at worst 100% efficient, but they’re also typically sized lower than resistive electric heaters in terms of input power. In the US, a residential heat pump likely draws about 4kW, whereas resistive heat strips or baseboard heating could be multiples of that. As an air source heat pump’s output drops on very cold days, a unit rated for e.g. 48000BTU/hr at 47°f might produce only half of that at 5°f/-15c. A “good” unit here would produce perhaps 75%. The way we do HVAC sizing, unless you radically oversized the system for most weather (including air conditioning) you’ll need a backup source of heat on the coldest days.
Code (law specifying how much heating / cooling capacity is required in normal worst-case weather conditions) where I live would require me to use about 2x the normal sizing to achieve pure heat pump heating at the required design temperature (around 5f/-15c). That means at the peak of summer (about 100f/38c) the unit would be operating at less than half of its full cooling capacity.
Apologies for weird units; I live in MAGAland.
I live in a very cold part of the world where the temps can easily exceed your -20C for night times for several weeks at a time. And even as the daily high for a week stretch or two over a winter. And while I could have purchased a heat pump that would work to that low of a temperature, it would have cost over twice the price. Going from $5000US installed to over $10,000US for just the heat pump. And that included the rebate incentives.
My heat pump is set to set to cut out and switch to LP heat at -10C because it becomes cheaper to run an LP furnace at that point - cost of electricity = 6.5 cents per kilowatt hour vs $1.75US gallon LP. The loss of efficiency matters to my pocket book. And I chose my particular heat pump with my advice of my Daughter who has a PhD in ME and works as a research engineer for a non-profit studying HVAC systems and the efficiencies of the technology used in them. And she won't install a heat pump in her house because for where she lives, they literally do not make financial sense. There is zero savings to be had with switching from natural gas heat to electric.
So installing a heat pump is not a universal no brainer. You still need to to the math to see if it pays.
Yeah obviously it's a whole different game when you live in a place like that. That's just quite rare usecase. The vast majority of people who keep repeating the "heatpumps don't work in cold climates" lives in a climate much warmer than I do. Even mine struggles on the really cold days we get few times a year but that's fine because it gets the job done flawlessly for the remaining 350 days.
My issue with these arguments is the blanket statements that get made. Both arguments on this particular subject can both be true at the same time. And until you do the math for your specific situation, you can't tell if it pays until you know the answer
Now, I believe it works out for you just as it does for me. But I had to the math to figure it out to know for sure. Most people who argue over this subject have never done the math.
If your intention is to heat or cool air using as little electricity as possible, a basic heat pump split air conditioning unit is going to be more than adequate for 90% of people. If you live in a place like Yakutsk, then yeah, you probably need to look into something else, but for the vast majority of people it's going to be just fine. A general recommendation doesn't mean it's the best choice for literally every single person.
But it very often catches many who simply take it as an irrefutable truth.
As I gave as an example, my one Daughter who is recognized by her peers as an expert in this field, and is all about improved efficiency and renewable energy, did the math and found that it doesn't work for her. And it's not because she lives in a terrible climate - it's warmer and varies less than where I live by a noticeable amount. It's because when you compare total costs, over the life span of a heat pump, she would end up paying extra to have one verses a simple natural gas furnace. It would be even sillier for my neighbor who is a logger. He uses 100% wood heat. Because he can literally harvest, process, and store enough firewood for several years in one afternoon. Anything else is far more expensive. But the math says it works for me.
You can't make general statements about 90% of all people until everyone does the math. This is just one of the field studies my Daughter is doing. Trying to collect enough real time data on real homes and families and doing the math to help pinpoint locations where it makes sense and where it does not make sense at this time. It does not always workout like you and I might think it would.
In very cold climates, having a hybrid system like the one you're describing is that universal no brainer in my opinion. Especially since most cold regions also typically have really long transitional periods where your heat pump is most efficient and pays itself off fastest. Combining that with turning it off during harsh winter weeks gives you the best of both worlds.
It's not even a no brainer even then. You absolutely need to actually do the math for your particular situation to make that determination. For me it works out. For my neighbor down the road who is a logger, it does not. He can harvest, process, and store 2 years worth of firewood in a mere handful of hours. Any other heat source makes little sense for him.
You really, really, really need to do the math!
I am also an engineer and used to have LP backup heat and the only way the LP is cheaper per BTU is if you rapidly deprecate the heat pump asset.
A gallon of propane has 91,000 BTU, and a kWh of electricity has 3400 BTU. 91k/3.4k ~ 26kWh x 0.065 ~ $1.73 for electricity equivalent at 1.0 coefficient of performance. But your COP is likely around 2-3, so the heat pump will be at least 2x cheaper than the LP. It would take like 6000 hours of operation to break even on the bigger heat pump, and that's ignoring the cost and maintenance of the propane furnace
They work, but efficiency is near 1:1 when it's that cold so there's no cost advantage over a space heater.
It's non-sensical to base the cost effectiveness of a heat pump on the handful of really cold days when it's no more efficient than electric resistive heating. You have to take into account the entire heating season. Electric resistive heating is allways 100% efficient. Air sourced heat pump is 100% efficient in the worst possible conditions. In normal conditions it's from 300% to 500% efficient. While your 650 watt space heater puts out heat at the constant rate of 650 watts, a heat pump outputs 3000 watts worth of heat while using that same 650 watts of energy.