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Another heat pump question

Discussion in 'Home Power and Microgeneration' started by Caleb Hess, Feb 11, 2005.

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  1. Caleb Hess

    Caleb Hess Guest

    Does anyone here know the inside details of heat pump defrost controllers?
    Are they smart enough to tell when the coils actually have ice forming, or
    do they just do it preventively whether there's frost accumulating or not?
    Is the energy cost of the defrost cycle included in the SEER/COP ratings?
  2. Gymmie Bob

    Gymmie Bob Guest

    I believe they can measue it with pressure.
  3. daestrom

    daestrom Guest

    It varies. Some older units are just timers. But a low suction pressure
    can be an indication of excess frost.

    SEER ratings are for air conditioning mode, HPSF (Heating Season Performance
    Factor) are what you want for heating.

    But yes, they include the total cycle including any defrost. The *very
    gory* details of calculating both are in 10CFR430, Subpart B, Appendix M.

    For air-souce heat pumps, there is a 47F 'high temperature test', (with 43F
    wet-bulb temperature), a second 'high temperature test' with 62F outside
    air, a 'frost accumulation test' with drybulb of 35F and wetbulb of 30F, and
    a 'low temperature test' with drybulb of 17F and wetbulb of 15F.

  4. daestrom

    daestrom Guest

    I disagree. The HSPF rating calculations are specifically detailed in the
    federal law. They include performance under frost conditions. And they
    specify the testing details. So they work much like the mpg ratings on new
    car stickers. Your exact performance might not meet the stated rating, but
    all manufacturers are testing to the same conditions so the *relative*
    rating between units/manufacturer's are a useful comparison.

  5. daestrom

    daestrom Guest

    Scrolling down to the 87th page in the pdf (reads 212 at the bottom of the
    page though), 'Frost Accumulation test conditions'. This is the
    section describing the testing required for air source heat pumps in order
    to calculate their HSPF.

    "....The Frost Accumulation Test requires that the unit undergo a defrost
    prior to the actual test. The test then begins at defrost termination and
    ends at the next defrost termination.. Defrost termination occurs when the
    controls normally installed within the unit are actuated to cause it to
    change defrost operation to normal heating operation. ..."

    So the test explicitly *includes* the defrost cycle. Section 5.2 then goes
    into detail of how the heating for a defrost cycle is converted to a heating
    capacity. The calculation of Q(T) for 17 < T < 45 uses the heating capacity
    from the 'Frost Accumulation Test'. So obviously, it depends on which
    climate region you're calculating the HSPF for, but it does seem to have the
    defrost part of the cycle in there.

    There is some good information in this appendix as well. For example, later
    in section 6.2, there is a chart of HLH (Heating Load Hours). It's kind of
    interesting to note that although the Pacific Northwest is in zone VI and
    has 2750 HLH, and the upper midwest as well as NY and parts of New England
    have only 2250 HLH. *BUT* the temperature profile for the Northwest is
    almost all above 30 F, while region IV and V have a significant portion of
    temperatures much colder. So a heat pump that works well in Oregon with
    2750 HLH would probably perform very poorly in parts of NY and PA.

  6. Pete C

    Pete C Guest


    Some electronic ones look at the rate of change of the evaporator

    I reckon it's possible to run a air-air heat pump by circulating water
    indirectly from ground source (eg pond) over the evaporator.

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