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  1. #1
    Join Date
    Nov 2010
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    Montreal, Quebec.
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    71

    Sizing HP to heat load

    Have you ever sized a heat pump to the heat load of a house and if so under what circumstances. I'm thinking this may make sense in certain areas of North America.

  2. #2
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,374
    What do our Canadian friends do?
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  3. #3
    Join Date
    Nov 2010
    Location
    Montreal, Quebec.
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    71
    Quote Originally Posted by dan sw fl View Post
    What do our Canadian friends do?
    Keep in mind I'm a homeowner not a pro but all my research points to HP= 125% of cooling load (heat gain)

  4. #4
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,752
    Go multi-stage or inverter driven, particularly if you live in a humid climate... Oversized ac is a complaint complaint around here.
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  5. #5
    Join Date
    Dec 2008
    Location
    Ontario Canada
    Posts
    549
    we always size them to heat load, I like to push 2 stage units for that very reason that tedkidd stated.

    I have never heard of the HP=%125 cooling load rule of thumb before, must be a Quebec thing.

    do heat load calc, size accordingly

  6. #6
    Join Date
    Nov 2010
    Location
    Montreal, Quebec.
    Posts
    71
    Quote Originally Posted by LKJoel View Post
    we always size them to heat load, I like to push 2 stage units for that very reason that tedkidd stated.

    I have never heard of the HP=%125 cooling load rule of thumb before, must be a Quebec thing.

    do heat load calc, size accordingly
    I don't understand how you do this in Ontario, your avg house heat load must be 80KBtu. Surely you don't install heat pumps for 80kBtu??

  7. #7
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,455
    Let's see, if we did that in a typical family home here, this is what we'd have to do.

    Typical coldest winter morning: 0 to -5
    Heat loss would be around 60K so we would normally put in 20kw or 80K backup furnace.

    Typical heat gain at 95 would be around 31K so we'd put in a 3 ton.

    BUT, to size the heat pump to the heat loss we'd need a 10 ton unit. That's not counting having a bunch of inverter minis or if Carrier's new machine is 100% at -5 and can give us that 60K from a 5 ton.

    So with conventional technology a Rheem RPWL-120 puts out around 66K at 17 degree rating point so at 0 or slightly less, around 60K.

    So until we can get conventional split heat pumps that put out 100% at 0°, in a cold climate sizing a heat pump to the heating load isn't feasible!

  8. #8
    Join Date
    Dec 2008
    Location
    Ontario Canada
    Posts
    549
    Quote Originally Posted by Norm01 View Post
    I don't understand how you do this in Ontario, your avg house heat load must be 80KBtu. Surely you don't install heat pumps for 80kBtu??
    your right, its rarely sized to satisfy the entire heat load, let the electric back-up get it the rest of they way.

  9. #9
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    4,434
    Are heat pumps even effective once the temperature starts dipping below freezing?

  10. #10
    Join Date
    Dec 2008
    Location
    Ontario Canada
    Posts
    549
    Quote Originally Posted by 54regcab View Post
    Are heat pumps even effective once the temperature starts dipping below freezing?
    the COP definitely starts to decrease as the temperature drops,

    but take for example a 3 T 14 Seer HP, the one I am looking at has a COP of 3.4 at 47 Deg F, that does drop to 2.4 at 17 Deg F, but keep in mind that electric heat only has a COP of 1 (at every temperature), so although efficiency drops off significantly below freezing, its still more efficient than electric heat.

    COP of 3.4 means that ON AVERAGE for every 1 KW of electrical energy put into the HP, we will get 3.4 KW of heat put into the house. someone can correct me if I'm wrong, but i believe COP factors into account expected time spend in defrost.

    hope this answers your question

  11. #11
    Join Date
    Jan 2002
    Location
    East Grand Forks, MN
    Posts
    1,375
    Quote Originally Posted by Norm01 View Post
    Have you ever sized a heat pump to the heat load of a house and if so under what circumstances. I'm thinking this may make sense in certain areas of North America.
    I think you meant Heat-loss!
    And if so, never, unless they want it that way and will never use the cooling portion; unless the unit is at or under 125% max in first stage or single stage.

  12. #12
    Join Date
    Feb 2009
    Location
    Portland OR
    Posts
    2,022
    I usually size to the setpoint just above freezing(around 35 degrees for comfort and to stop the heat pump from going into a defrost cycle) I live in the portland oregon area where our heating design temp is 24 and our cooling design temp is 98 so our systems heat load and cooling load are fairly similar. If it is an electric backup and not gas then I will size the heat pump a little larger to run it closer to the design temperature.

    I think this really just depends on where you are located.

  13. #13
    Join Date
    Nov 2010
    Location
    Montreal, Quebec.
    Posts
    71
    Quote Originally Posted by arc8 View Post
    I think you meant Heat-loss!
    And if so, never, unless they want it that way and will never use the cooling portion; unless the unit is at or under 125% max in first stage or single stage.
    Yes I did mean heat-loss, winter load.

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