6 ms·

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

• Someone1234 4y ago
  Isn't the primary issue not the cost of installation, but rather the cost of the fuel? Natural gas in most of the US is far cheaper than electricity, and even if heat pumps are theoretically more efficient than natural gas (energy in:heat out), if the fuel is two or three times cheaper none of that matters.
  • onlyrealcuzzo 4y ago
    In most places in the US, in normal working conditions, Heat Pumps are 30%+ cheaper than a gas furnace to run. However, in some really cold places like Chicago, Minneapolis, etc - the days where current heat pumps are inefficient might be enough to make it cheaper to always run gas. OP is proposing to have both systems and only run the gas furnace on extreme days - which would lead to a ~30% reduction in running costs. I suspect the CapEx of having two heaters wouldn't make sense, though. It'd be better to just have a hear pump that can run efficiently at colder temps.
    • Scoundreller 4y ago
      I think it’s the opex of 2 grid connections that messes with the numbers. Depends on how your utility charges, but I feel like many/most sell you the gas roughly “at cost” and then some fixed monthly delivery/connection charge that covers their regulated rate of return on their network equity. Oil or propane supplemental heat might be cheaper than Natgas supplemental heat. My money is on wood pellet stoves for supp heat for those that don’t require full automation. Or maybe even dirty coal…
    • BobbyJo 4y ago
      Also, the capex of gas delivery. Not needing infra to deliver gas to each and every house would likely be a pretty big win.
      • bombcar 4y ago
        For new construction sure - for existing it’s already there and apparently needs little maintenance.
    • mrep 4y ago
      You generally have an air conditioner though as well as a furnace and you can get those that can also work as a heat pump. Mine supposedly works as both but they only set it up for cooling and my gas furnace does all the heating :(
    • deleted 4y ago
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  • Scoundreller 4y ago
    Maybe the gas is cheap, but the monthly and up-front connection costs mess with the economics. And that cost will only go up as people cut the gas cord. Depends on how your utility bills out it’s infrastructure: some charge minimal monthly connection fees, others a lot. I honestly wouldn’t want to own a residential-focussed gas distribution company unless someone revolutionizes stirling engines or micro cogen systems and people start cutting their electric cord.
    • lizknope 4y ago
      I live in a pretty standard suburban subdivision in the US. All the houses are 25 years old. I have about 60 coworkers in very similar situations. I think everyone of us has natural gas that was installed when the original company built all the homes in the subdivision over the course of a year. Stuff gets a lot cheaper when everything is put into the ground at the same time. My monthly gas connection fee is $10 so that in the summer my bill is around $19 which is $9 for the water heater and $10 for the connection fee.
  • kube-system 4y ago
    The thing with heat pumps is that they can be as much as 300% efficient (effectively) or more. This is because they can get "free" heat from the environment. So even if per unit of energy gas is way cheaper, heat pumps can still come out ahead.
    • Epa095 4y ago
      Modern heat pumps can be up to 500% efficient (using 1kWh of energy gives 5 kWh of heat) at optimal temperature.
      • kube-system 4y ago
        Yes, I went with "300 or more" because that's a more typical number for a run-of-the-mill unit.
        • a9h74j 4y ago
          And even the low-temperature-capable heat pumps reduce toward 100% at the low temperature end, IIRC.
          • mikeyouse 4y ago
            Yep, here's a spec sheet for a unit I'm looking at as a drop-in ducted replacement for my existing system -- it has all of the models listed, but I'm looking at the 4-ton unit (12k btu per ton, so 4-ton = 48k BTU, hence the MDU18048): https://mrcool.com/wp-content/dox_repo/mc-uni-perf-ss-en-01.pdf https://mrcool.com/wp-content/dox_repo/mc-uni-perf-ss-en-01.... It takes 7kw at 17ºF to provide 48k BTU. There are 0.293W/hr per BTU so 7,000W = 25k BTU "in" and 48k BTU "out" or a COP of 1.9. At -15ºF, it's using 5.9KW but can only produce 28,500. So a COP of ~1.4. Still better than electric resistive heating but not by much. At 40ºF, the COP is more like 3.3 which is in line with the very efficient numbers. Fortunately my 99% design temp is ~8ºF and my area only sees 20hrs below zero per year, so this will work just fine for me.
    • anikom15 4y ago
  • Epa095 4y ago
    Unless gas is subsidised I don't really understand how gas can be cheaper. A modern heat pump can give 3-5 kWh of heat using 1 kWh of electricity. And a modern gas generator is roughly 50% effecient at creating electricity (according to the Internet). So by using electric and a heat pump you should be able to get 1.5-2.5 times more heat from the same gas by making electricity of it first compared to burning it directly.
    • njarboe 4y ago
      At least in the US, electricity rates and natural gas prices are highly regulated for retail customers. Thus the wholesale price of gas does not generally correlate to the retail price of electricity. In places like California electricity prices are very high due to renewable generation requirements. You would definitely want to have your own solar installation before converting over to all electricity in that state.
      • DoneWithAllThat 4y ago
        We’re being forced to. After 2030 no more gas water heaters or furnaces can be sold. The cost of heating your house and water here is going to probably triple or more, and will fail every time there’s a blackout.
        • njarboe 4y ago
          You used to be able to buy water heaters that would last forever. My house had one from the 1950's with a copper tank. Still going strong. Just don't be convinced b y the repair man to get a new one when you have to replace the thermocouple every 8 years or so. The furnace is from the late 1980's, still fine. I'm not sure if such well made devices are still available for purchase however.
    • SoftTalker 4y ago
      Modern residential gas furnace is 90% or more efficient.
      • 4y ago
  • a_square_peg 4y ago
    Interesting thing here is that natural gas is about 1/3 the cost of electricity per energy unit, so when the COP is above 3, it's cheaper to heat home using heat pump. The reason why natural gas is about 1/3 of the cost of electriciy is because most natural gas power plants run at thermal efficiency of about 30%.
    • pfdietz 4y ago
      Combined cycle natural gas plants have an efficiency of about 60% (lower heating value). Even simple cycle NG plants are about 40% efficient (again LHV).
• doikor 4y ago
  Yup. And at least here in Finland the pumps come with the resistive heater included so it automatically switches over to it once it gets too cold. Which where most people live here averages to less then 1 day per year so not a big deal. Way bigger issue here is some fall storm destroying the power lines and being without electricity for multiple days when it already is cold enough they one needs heating.
  • kube-system 4y ago
    That's an issue even with gas furnaces here in the US, as they won't run without electricity.
    • jacamera 4y ago
      Yes but it only requires a couple hundred watts to power the blower motor and electronics of a gas furnace. They're easy to power off of a small portable generator or even a cheap inverter hooked up to your car. The same cannot be said of a heat pump or resistive heater.
      • kube-system 4y ago
        They are, and I have a contingency plan for this myself, but few people have the tools and knowledge required to accomplish this.
        • bombcar 4y ago
          Anyone with $200-500 can go buy a kerosene heater and some sealed kerosene which will keep one ventilated room warm for awhile in an absolute emergency.
          • lazide 4y ago
            With the common skill set people have now, half the people trying it would kill themselves. :s
    • 4y ago
• loloquwowndueo 4y ago
  Millions of Canadians would disagree with that assessment.
  • a_square_peg 4y ago
    I'm Canadian myself. Heat Pump is actually very popular in the eastern maritime provinces and is gaining in popularity elsewhere also.
• scojomodena 4y ago
  Sort of, but really we need both. Yes cheaper for most people. But as someone who lives in Minnesota, we definitely get below those temps. By code we require full backup resistive heaters for a heat pump at such a rating which increases the full cost and installation cost. Plus, it is much less efficient than a heat pump (though efficiency lowers as the temp gets colder due to defrost cycles).
• mindslight 4y ago
  AFAICT one of the main difficulties with heat pumps is that they want to use low temperature heat emitters, similar to condensing boilers. This is a general thermodynamic rule, but hits sources aiming for high efficiency extra hard, since they've been designed around exploiting it. So you can't just take a decades old system with oil/gas using finned radiators, just replace the boiler, and have it supply enough heat on the coldest day ("design day"). Rather you'd at least need to add some additional emitters, greatly increasing the scope of the project for a professional installer. What I haven't been able to find an answer to is that everybody says hydronic heat pumps need low delta T of 5-10 degree F (implying high flow rate for given heat transfer). But I would think the real constraint would be just on their leaving water temperature, and a heat pump (load side) that took in 100F and put out 120F (at say 5GPM) would be happier and more efficient than one that took in 110F and put out 120F (at 10GPM). But I've yet to find anything that confirms this.
  • amluto 4y ago
    > What I haven't been able to find an answer to is that everybody says heat pumps need low delta T of 5-10 degree F (implying high flow rate for given heat transfer) I don’t see why this would matter at all. Maybe the heat exchanger would need to be sized differently for a different flow rate, but in general a lower entering water temperature on the hot side seems preferable.
  • sokoloff 4y ago
    Your intuition is correct on the last point. Where the "everybody says" side is coming from is the average water temperature in the emitters (and therefore heat flux from emitters to the building) will be higher if the flow (supply) is 120°F and return is 110°F than if the flow is 120°F and return is 100°F. That's why designers are often specifying lower delta-Ts for low-temperature emitters: to allow the flow temperatures to remain as low as possible [for efficiency] at a given average water temperature [for effective heating].
    • mindslight 4y ago
      It's definitely in line with general thermodynamics. One would expect lower entering water temperature to be more efficient (especially with the condenser being counterflow). I'm just not sure if there's something specific about the design of real world heat pumps that makes it so that higher delta T across the pump is problematic. I thought I would have come across some hydronic professional explaining this a bit more in depth while focusing on each variable, but so far I have not. Maybe it never comes up in practice because heat pump systems inevitably need some kind of buffer tank. If you're designing a system from scratch then you design for lower delta-T in the emitters to keep the max water temperature down. And if you're using existing emitters then you just live with the inefficiency due to higher max water temp, but still keep the flow from the heat pump to buffer tank high regardless (to keep the max water temp from being even higher).
• sigmar 4y ago
  I'm not an expert on the topic, but I imagine that a heat pump that can handle -20F is also much more energy efficient when the temp is 0F (in comparison to a heat pump that was rated only for -5F, operating at 0F).
• deleted 4y ago
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• 2OEH8eoCRo0 4y ago
  I think a cheap heat pump and a cheap wood stove for emergencies would be ideal. Depending on resistive heat can be dangerous if power goes out.
• Auracle 4y ago
  Eh, for the first time I got an alert message on my cell phone asking people to reduce their electricity usage during a blizzard here in rural Minnesota. If everyone is suddenly using electric heat when it’s -20 in an area there might be load issues.
  • mirrorlake 4y ago
    The number of electric devices added to the grid is likely a predictable percent increase every day/month/year, and likewise, the acceleration of that change is probably somewhat predictable, too. This is not to say we shouldn't be concerned, but denying yourself the most energy efficient technologies available (EVs, heat pumps, etc) because you're afraid of power outages 5-10 years from now seems like overkill.
• bowow 4y ago
  If everyone uses resistive heat during that 1% of the time that it's -20F or below, the electric grid goes down and then no one gets heat. Consider what just happened in the southeast with TVA and rolling blackouts. That was precisely because it was too cold for heat pumps and so everyone's resistive heat engaged at the same time. I don't think your EV range comparison is a particularly good one. You can control your stops on a road trip, you can't control when it's colder than -20F outside.
  • ledauphin 4y ago
    If they can manage the grid granularly enough and isolate critical environments like hospitals, nursing homes, etc., I really don't see a good reason for us to overbuild to handle the third standard deviation of electricity demand. It makes a lot more sense to set the expectation that on the coldest days of the year, your house may spend a few hours disconnected from the grid in order to shed load. Not only does the avoid overbuilding, but it also contributes to less overall fragility in society, because black swan events that happen once every 50 or 100 years are the sorts of things we can't build for anyway, so it's better if people are prepared to endure the unexpected from time to time anyway.