I wrote up a brief discussion here on the boiling points of refrigerants <a href="https://www.moderndescartes.com/essays/refrigerants/" rel="nofollow">https://www.moderndescartes.com/essays/refrigerants/</a><p>The long and short of it is that if the heat pump works below -20F, then the boiling point of the refrigerant must be below -20F. This, in turn, implies a higher pressurization (as per the Clausius-Clapeyron eq) required in order to achieve a T_hot of 80F (or whatever output temperature you want. The higher pressurizations require more expensive components and compressors.
> “additional efforts are needed to address common technical and market barriers to wider adoption by consumers – which include performance at temperatures of 5F and below, installation challenges, and electricity grid impacts during peak demand periods.”<p>There are definite market barriers at play. In my house in New England, I tried to replace my aged boiler with an air-to-water heat pump (after carefully verifying, via experiments during a cold week in February, that my heat distribution would indeed work fine at a supply of 130°F). Only one company was even willing to come out and provide a quote and their quote was around 2.5x the costs of "put another boiler in", such that the payback period would be "literally never".<p>If, after doing the research to find out about them and specifically seeking one out, I couldn't manage to make an air-to-water heat pump make sense, I doubt that very many of them are being sold. I suspect it's one of those items that, if more were sold, more firms would sell/install them, bringing the costs into the realm of economically reasonable (and lowering the risk of having a difficult-to-support heating plant in the decades to come).
We need heat pump that work below -20F like we need an electric car that can go 1000 miles in a single charge - which is we really don't for the 99% of the use case. What's needed is a heat pump that's cheaper to install than gas furnace or oil boiler for the 80% of the population. On few days of the year when it's -20F or below, it's ok to use resistive heater as a back up.
Having heat pumps that can operate during arctic freezes is of course, and pardon my pun, pretty cool, but I wonder which percentage of the consumer market actually requires this? Especially keeping in mind that your pump not actively heating its internal storage for a few hours every day is not a huge issue: it only becomes problematic when the external heat exchange is unavailable for 6-8 hours or so.<p>Another comment in the article, regarding electricity grid impacts during peak demand periods, is more interesting to me. Currently, there is no mechanism whatsoever for heat pumps to automatically shift their grid draw (or re-delivery) to certain time slots, and/or to coordinate those slots with other units nearby. Both of these would greatly help to balance the grid, but won't be available until standardization gets off the ground and expensive retrofits are done. That's a shame, really...
I'd like to see an efficiency curve of this heat pump at -20F, 0F, +20F, +40F<p>I have a heat pump that can be used for both cooling an heat along with a natural gas burner. The installer has set the system to use the heat pump at 40F and above and switch to natural gas at below 40F below based on the efficiency of the heat pump dropping at low temperature.<p>My heat pump is a SEER 18 unit primarily for cooling in the US south so I'm sure a heat pump designed specifically for northern cold climates will be more efficient than mine at low temps but I'd like to see how much.
A nice explanation of the working of heat pumps from Technology Connections: <a href="https://www.youtube.com/watch?v=7J52mDjZzto">https://www.youtube.com/watch?v=7J52mDjZzto</a>
The needs of the homeowner and the needs of the grid are at odds with one another here.<p>The electricity grid wants the highest possible efficiency on the coldest days, so that they can serve as many users as possible without building more infrastructure.<p>The homeowner wants the <i>average</i> efficiency to be as high as possible over the whole season, to reduce heating/cooling costs. They don't care if one or two really cold days have bad efficiency, as long as the system has sufficient output to keep the house comfortable.<p>Someone needs to use laws or incentives to align those two - because if every home owner used one of todays heat pump systems, then the electricity grid would fail on the coldest days of the year.
I think the ultimate combo will be heat pumps + wood pellet stove as supplemental heat.<p>Then you can cutoff the gas grid connection and its associated standby/account/blah blah charges. It’s a big sunk cost in a lot of places that messes with the economics of switching to heat pump as primary heat.<p>Pellet stoves are semi-automated. Around 90% efficient. If you already have central heat pumps, you can install one and let your HVAC circulate the heat around. Can stockpile as much fuel as you want. Cheaper than oil or propane and not much more expensive than firewood once accounting for improved burn efficiency. Just need to empty the ash gray once a week or so, and dump a nice smelling bag in for every ~24h of operation.<p>Relatively straightforward install: just need a wall to punch through and a standard power outlet. Minimal clearance requirements. Fun to watch the fire tornado.<p>Big downside is they need some electricity (mainly for for the powered vent). Hit or miss when it comes to insurance companies that think explosive gas systems or high current electric devices are safer.
We just installed a Solstice Inverter Extreme[0] before the the storm hit. The low in our area was -24F. The heat pump is advertised to work at -22F, but was still heating the house at the low. Efficiency and capacity are reduced with as the temperature drops. We have backup resistive heat in the buffer tank of our hydronic setup. It is early but we are happy with the performance during this first cold snap.<p>[0] <a href="https://www.spacepak.com/solstice-inverter-extreme" rel="nofollow">https://www.spacepak.com/solstice-inverter-extreme</a>
How is this news? The last air-air heat pump I looked at was guaranteed working down to -35°C/-31°F.(Mitsubishi Electric UWANO 8700)<p>Is this just the US being far behind when it comes to heat pumps or something?
I recently bought some land in Minnesota on a lake. I really want to do a 'no compromise' off-grid setup. Water and septic wont be a problem but I am worried about the heat.<p>I plan to install a huge solar array with a battery house. I'd like to run everything off electric, including the heat.<p>I am in early days of thinking about this and I have time to plan. Anyone have insights on electric heat in ultra cold environments? I assume I can simply scale up a solar array and battery capacity to meet needs (dead of winter, with spans of cloudy days). The only fossil fuels I want on property are for equipment and if I must have it, a backup NG generator.<p>I don't know anyone who runs heat pumps in MN, I'm sure there are some but most folks are burning NG or wood pellets. Electric heat seems relegated to secondary needs, like base boards or heated floors.<p>*edit cloudy
The issue with heat pumps is that most of the ones currently being installed in South East of the US don't work well below +20F let alone 0F or -20F. Most of them are being installed with an electrical resistive backup heat, which is incredibly inefficient.<p>The problem is when a cold spell like Christmas 2022, with temperatures down towards 0F. All the heat pump users switch to resistive backup heat and it overloads the electric grid and we get rolling blackouts.<p>In my opinion, heat pumps are amazingly efficient at moderate cold temps, but they really need propane or wood heat backup for the really cold temperatures instead of resistive heaters.
If you want an (entertaining) deep dive into heat pumps, I can recommend Technology Connection's <a href="https://www.youtube.com/watch?v=43XKfuptnik">https://www.youtube.com/watch?v=43XKfuptnik</a> and its followup, <a href="https://www.youtube.com/watch?v=MFEHFsO-XSI">https://www.youtube.com/watch?v=MFEHFsO-XSI</a>
Do we really need heat pumps that work that far into the negative? You can always turn on an internal resistive heater to compensate after all.<p>Not quite something you can do on the other end though, when trying to cool with exceptionally high ambient temperature. It's such bullshit that the physics of this universe does not allow for resistive cooling.
What no one tells you about heat pumps that work down to 10 degrees F, zero degrees, minus 10 degrees, is that you probably cannot get <i>anywhere near</i> enough BTUs out of your heat pump, at such an outside temperature, to keep your house above freezing. But it will draw a great deal of power getting what BTUs it can.<p>As outside temperature goes down, the amount of heat input, in BTUs per hour (or kilowatts, really) needed to maintain a comfortable temperature rises linearly with the difference. When the difference is greatest, the heat pump can deliver least.<p>So in practice, well above such temperature, your controller has turned it off, and is burning propane instead.<p>Of course, the better-insulated your house is, the fewer BTU/hr it takes to keep it warm. Spending a lot on a beefy heat pump without making sure your insulation is in good shape would be a mistake.
It was down to -8F (not including wind chill) a couple days ago here. I have a small, old house but I'm considering replacing the old system I have now with a heat pump.<p>My concern is two-fold:<p>- my house is not well air sealed<p>- my house is not well insulated<p>So I worry that I'll need an extremely oversized heat pump in order to have enough capacacity for the coldest days.<p>I suppose having a backup heating source would prevent needing such a large unit. Plus it would provide some amount of redundancy of the heat pump were to fail in the winter.<p>The question then is, should I use electric backup heat, or stick with my existing gas connection? Electric is simpler and there's no exhaust fumes or CO risk to worry about, but gas is still cheaper here I think.
The furnace at my mother's house in Houston went out and I tried to get her HVAC guy to replace it with a heat pump. (The AC is 30 years old and also needs to be replaced) He clearly had no idea what a heat pump is and came up with the following excuses to not install a heatpump:<p>1. Heat pumps are only for extremely cold weather<p>2. The heat from heatpumps is too hot, they only install them at elder care facilities where they need extra heat<p>3. It's far more complicated than a furnace / AC setup, and will require a lot more maintenance.<p>Not sure what this all means for the industry if common HVAC guys don't even know about heat pumps yet.
Anyone know how these pumps manage to squeeze enough heat out of ambient air to make it worth the while? -20 is down there! I understand how heat pumps work, but what's the differentiator?
My Senville mini split claims to work at temps down to -22F. During this recent winter storm, temps got down to about -10 where I am, and it managed to keep my garage around 50F. Nowhere near comfortable, but pretty damn impressive to be able to keep my relatively poorly insulated garage 60 degrees above the weather.<p>I was quite happy that this storm occurred while I was in Christmas PTO, since my garage is my office. I could have made it workable with a supplemental space heater but it was nice not to have to!
Meanwhile, most people in the US don't even know what a "heat pump" is, and think that "air conditioners" are inherently wasteful and bad for the environment.
Why not just use a natural gas or electric heating element to heat up the air coming into the heat exchanger when it's below the operating window? In most of the US below zero is a <10 day per year issue. Sure it's terribly inefficient on those days, but I'd bet it's cheaper than maintaining an entire secondary heating system.
My AC runs just fine at -15C (+5F), the problem is when temperature swings between zero and sub-zero, it causes formation of the ice in the outer unit which can break the fan.
How expensive would it be to run source water to an entire neighborhood for heating and cooling? Have one heating/cooling plant and per building heat pumps.