by jbrins1 on 12/28/22, 1:19 PM with 330 comments
by brilee on 12/28/22, 2:59 PM
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.
by sokoloff on 12/28/22, 2:58 PM
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".
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).
by a_square_peg on 12/28/22, 3:21 PM
by PreInternet01 on 12/28/22, 3:02 PM
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...
by lizknope on 12/28/22, 4:03 PM
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.
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.
by svdr on 12/28/22, 3:29 PM
by londons_explore on 12/28/22, 5:19 PM
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.
The homeowner wants the average 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.
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.
by Scoundreller on 12/28/22, 3:27 PM
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.
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.
Relatively straightforward install: just need a wall to punch through and a standard power outlet. Minimal clearance requirements. Fun to watch the fire tornado.
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.
by sneezesForAttn on 12/28/22, 3:55 PM
by ape4 on 12/28/22, 2:59 PM
by NorwegianDude on 12/29/22, 4:09 AM
Is this just the US being far behind when it comes to heat pumps or something?
by DIVx0 on 12/28/22, 5:18 PM
I plan to install a huge solar array with a battery house. I'd like to run everything off electric, including the heat.
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.
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.
*edit cloudy
by Ottolay on 12/28/22, 4:04 PM
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.
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.
by the-alchemist on 12/28/22, 10:00 PM
by moffkalast on 12/28/22, 3:15 PM
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.
by moloch-hai on 12/29/22, 10:35 AM
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.
So in practice, well above such temperature, your controller has turned it off, and is burning propane instead.
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.
by pitaj on 12/28/22, 3:00 PM
My concern is two-fold:
- my house is not well air sealed
- my house is not well insulated
So I worry that I'll need an extremely oversized heat pump in order to have enough capacacity for the coldest days.
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.
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.
by rohan_ on 12/29/22, 12:24 AM
1. Heat pumps are only for extremely cold weather
2. The heat from heatpumps is too hot, they only install them at elder care facilities where they need extra heat
3. It's far more complicated than a furnace / AC setup, and will require a lot more maintenance.
Not sure what this all means for the industry if common HVAC guys don't even know about heat pumps yet.
by throw0101c on 12/28/22, 5:13 PM
by ethagknight on 12/28/22, 2:58 PM
by agentwiggles on 12/28/22, 3:46 PM
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!
by yosito on 12/28/22, 3:21 PM
by therusskiy on 12/28/22, 4:10 PM
Are heat pumps the same thing as split air conditioners that can heat air?
by lxmorj on 12/29/22, 12:40 AM
by sandworm101 on 12/28/22, 4:14 PM
by EVa5I7bHFq9mnYK on 12/28/22, 6:09 PM
by hooverd on 12/28/22, 4:49 PM
by nashashmi on 12/28/22, 4:59 PM