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Are air heat pumps effective on very cold or very hot days

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GeneSh
GeneSh Member Posts: 2

Hi all

I'm in upstate New York. Right now it's 95 degrees and will be that hot for the rest of the week. It actually got to 99. In the winter, it often is pretty well below freezing for many days, often around 15 degrees, some times zero or below.

Can air heat pump systems handle that and keep our house comfortable, around 68-72? I have a split level, two bedrooms above the garage. Main floor is kitchen, dining room, master bedroom, bathroom. Basement is half finished.

By the way, I searched this forum up to last December. I thought I would see that question already, but I didn't. Sorry if I'm repeating. Also, if I need to put in more info, please let me know.

Thanks

Comments

  • pecmsg
    pecmsg Member Posts: 4,966
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    there are heat pumps that are capable to -15*F and lower. Are they economical, practical, comfortable I don’t think so. I still prefer hot water or steam over heat pumps when that NE Wind is blowing!

    GeneSh
  • JUGHNE
    JUGHNE Member Posts: 11,109
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    How do you heat now?

    Heat pump in the cooling mode is just like any other AC.

    At some lower temps the heat pump will need supplemental heat.

    GeneSh
  • Hot_water_fan
    Hot_water_fan Member Posts: 1,917
    edited June 18
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    Yes, they can. They work down to -15F or so. And for cooling, work the same as an air conditioner (they’re mechanically almost identical). They, like ACs, lose efficiency as it gets hotter.

    For heating, they can easily outperform fossil fueled boilers on cost, but costs everywhere are different and change constantly, so your situation will of course be different than others.

    GeneShethicalpaul
  • Steamhead
    Steamhead Member Posts: 17,008
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    From time to time, someone comes out with a heat pump that they say can handle such low temps. Then it doesn't quite do the job and requires supplemental heat, or breaks down frequently (remember the Acadia?).

    In a building with forced-air ducts, the supplemental heat is generally electric resistance, which is the most expensive heat source on a per-BTU basis. A standard furnace or boiler can also be used.

    If your house currently has hot-water heat, definitely keep that whatever else you might do.

    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting
    GeneSh
  • Jamie Hall
    Jamie Hall Member Posts: 23,655
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    My own experience — northwest Connecticut — is that they work as well as a good air conditioner in the summer, and they work nicely for winter heat — down to perhaps 20 or so. Below that, dear old Cedric's steam heat is cheaper and simpler..

    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    GeneSh
  • fentonc
    fentonc Member Posts: 241
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    BTUs are BTUs, so an appropriately designed system will probably work fine. A badly designed or installed heat pump system will work badly, as will a badly designed or installed steam or hydronic system. The economics of any system are dependent on local electricity/oil/gas prices.

    What’s your design temperature for your location and what is your home’s heat loss? https://www.greenbuildingadvisor.com/article/replacing-a-furnace-or-boiler

    hot_rodGGrossGeneSh
  • PC7060
    PC7060 Member Posts: 1,240
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    Can you clarify if you were trying to keep your house at 68 to 72F with an outside temperature approaching 100°?

    If that is the case, it can be a challenge for your HVAC system depending on the size of the unit and tightness of envelope

    On hot days it’s not essential to hit a specific number to achieve comfort. Lowering the inside temperature by 15-20 degrees and lowering relative humidity to 45-55% range will often yield a comfortable environment without over taxing your HVAC.

    hot_rodGeneSh
  • SuperTech
    SuperTech Member Posts: 2,205
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    I'm in the Hudson Valley. What I have found is that when relying solely on a heat pump all year long without a boiler or furnace, the heat pump needs to be sized to cover the entire heating load on the coldest days of the year. But then it ends up being so oversized for cooling that dehumidification suffers, even with fully variable speed equipment.

    And the variable speed inverter equipment is a royal pain to repair and service. If a heat pump is installed I prefer to see it installed for a dual fuel system, that works with a boiler or furnace.

    PC7060WMno57GeneSh
  • DCContrarian
    DCContrarian Member Posts: 305
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    You can look up the heating and cooling design temperatures for your county here: https://www.energystar.gov/ia/partners/bldrs_lenders_raters/downloads/County%20Level%20Design%20Temperature%20Reference%20Guide%20-%202015-06-24.pdf

    There is a non-profit called NEEP.org — the Northeast Energy Efficiency Partnership — that performs testing of the cold weather performance of heat pumps. At their website, https://ashp.neep.org/, they have a database of the cold-weather performance of over 100,000 tested configurations.

    "Upstate New York" is a huge geographic area. If you're in Erie County, the heating design temperature is 7F. At 5F, a Mitsubishi M-Series produces 94% of its production at 47F. So it should have no problem keeping up if it's properly sized. If you're in Essex County where the design temperature is -11F you might have a little more trouble.

    At 5F, the COP is 1.93.

    Here's the NEEP page for the M-series.

    https://ashp.neep.org/#!/product/34583/7/25000/95/7500/0///0

    GeneSh
  • GeneSh
    GeneSh Member Posts: 2
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    Thanks all. No one is super enthusiastic about heat pumps, and no one is super criticizing heat pumps. Pluses and minuses. Sounds about right.

    Hot_water_fan
  • ChrisJ
    ChrisJ Member Posts: 15,922
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    What exactly is meant by "Over taxing" ?

    To me, a system running non-stop is actually better for it than cycling.

    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
    Hot_water_fanpecmsgSuperTech
  • DCContrarian
    DCContrarian Member Posts: 305
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    The NEEP.org website has a feature where you put in your zip code, your calculated heating load and select a model and it predicts performance. It's pretty slick.

  • hot_rod
    hot_rod Member Posts: 22,483
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    Air to air heat pumps blow luke warm air in cold outdoor conditions from my experience, not the most comfortable heat, especially for older folks.i

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    JUGHNE
  • PC7060
    PC7060 Member Posts: 1,240
    edited June 19
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    Well you asked so here goes….. 😉

    Over taxing - running a system to the point of failure or inefficiency.
    Failure is obvious and maybe unavoidable.
    inefficiency may be subject but an example would be cooling your house beyond what is needed for reasonable comfort. For example 75 versus 65 degrees.

    PS: Agree with concerns about short cycling but that issue would probably have more to do with the system sizing or the situation @supertech described above than thermostat setting. Provided you aren’t jacking temp up and down.


  • pecmsg
    pecmsg Member Posts: 4,966
    edited June 19
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    compressors don’t die from running, there murdered by excessive superheat, excessive head pressure and excessive or too low superheat and excessive start stop cycles!

    ChrisJSuperTech
  • ChrisJ
    ChrisJ Member Posts: 15,922
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    It's actually amazing how many hours a compressor can last when treated correctly.

    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • HVACNUT
    HVACNUT Member Posts: 5,890
    edited June 19
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    @GeneSh , what are you using for heat now?

    Going to a heat pump will be fine IMO, as long as it's not your only heat source. If you plan on eliminating the "fossil fuel" boiler or furnace, then you'll need electric resistance heat for when the heat pump doesn't heat… or pump. And for when the outdoor unit goes into defrost. Parts aren't always on the truck. Especially those defrost boards.

    With my own situation, I have and oil fired boiler with fin tube baseboard and one radiant zone. If (when) either the X13 blower motor or compressor goes, I'm going to install a 2 stage heat pump. Not communicating. Not an inverter system. 2 stage. Simple. More common parts availability. The 3rd stage will be the boiler and for defrost.

    Whatever you do, vet the contractor, and make sure they do the math to size the system and the ductwork correctly.

    SuperTechPC7060
  • PC7060
    PC7060 Member Posts: 1,240
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    I give up. I officially modify my post…

    “Without overtaxing your HVAC electric utility bill”

  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,840
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    @ChrisJ

    "It's actually amazing how many hours a compressor can last when treated correctly." Isn't that the truth.

    It's amazing the beating they can take.

    People who say they "go bad" for no reason are wrong. You can always have a lemon but if they get reasonable maintenance. they will run for a long time.

    In the Northeast if you study heat loss and heat gain calculations. You will find that in most but certainly not all cases the cooling load is half the heating load. Where I am we design for 0 deg. which is fine for MA & CT but NH, VT & Maine would need more heat.

    With that being said what @SuperTech posted is exactly correct. If you have a building that needs 3 tons of cooling and you install a heat pump your capacity will be 36,000 btu on cooling and about (36000 x 1.3) or 46,000 btu on heat due to the heat of rejection.

    If the cooling load is 1/2 the heating load which is common, you have to do as @SuperTech mentioned oversize the heat which will make the cooling suffer.

  • DanInNaperville
    DanInNaperville Member Posts: 43
    edited July 7
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    It varies by model and manufacturer. Most newer designs will produce some heat even at very low ambient temperatures, but you'll get less heat just when you need it most. You need to check the specs for the specific heat pump you're considering. In this example, MBh of heat produced drop from 60 to 15 as ambient temp drops from 65 to -5. It's why they always want you to install heat strips in the air handler that can supplement the heat pump during the few days or weeks (depending on climate) that the heat pump can't keep up.

    ethicalpaul
  • Harvey Ramer
    Harvey Ramer Member Posts: 2,261
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    R32 invertor systems change this conversation. They have significant performance improvements over R410A at extreme temps.

    Doesn't change the fact that hydronic heating is much more comfortable in nearly all cases.

  • Steamhead
    Steamhead Member Posts: 17,008
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    @GeneSh , short answer is fine for cooling, not good for heat.

    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting
  • DCContrarian
    DCContrarian Member Posts: 305
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    At NEEP.org there is a thing called the "Advanced Sizing Tool."

    Pick a heat pump, put in your zip code and your heating and cooling loads. It gives you a report like this:

    There's no need to guess.