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  1. #1
    Join Date
    Aug 2012
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    Residential Heat Pump

    Hello,

    If you wanted to add a heat pump can you add one to your existing a/c unit or do you have to buy a whole new all in one unit? Also, on my furnace evaporator coil there are the two obvious vapor and liquid lines entering the evaporator but I noticed an extra connection for another line. Would that be for a heat pump?

  2. #2
    Join Date
    Dec 2007
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    4,710
    need new outdoor unit and possibly new indoor coil.

    connection is NOT for add on of heat pump.
    The Food Stamp Program, administered by the U.S. Department of Agriculture, is proud to be distributing the greatest amount of free meals and stamps EVER.
    Meanwhile, the National Park Service, administered by the U.S. Department of the Interior, asks us to "Please Do Not Feed the Animals". Their stated reason for this policy "... the animals become dependent on handouts and will not learn to take care of themselves."
    from an excerpt by Paul Jacob in Sun City, AZ

  3. #3
    Join Date
    Aug 2012
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    Quote Originally Posted by pacnw View Post
    need new outdoor unit and possibly new indoor coil.

    connection is NOT for add on of heat pump.
    why would I new evap coil. I know in heat pumps the evap coil and condensor are reversed but don't they just reverse the refrigerant flow to absord heat from outside and extract inside?

  4. #4
    Join Date
    Jul 2009
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    South Carolina
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    3,226
    The way I explain heat pumps is to think of how a window AC unit blows out cold air inside & hot air outside. If you could just turn it around in the winter & let the hot air blow inside & the cold air blow outside that is what a heat pump does. It just takes some extra controls & valves to do it.
    Gary
    -----------
    http://www.oceanhvac.com
    An engineer designs what he would never work on.
    A technician works on what he would never design.

  5. #5
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
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    4,299
    Quote Originally Posted by garyed View Post
    The way I explain heat pumps is to think of how a window AC unit blows out cold air inside & hot air outside. If you could just turn it around in the winter & let the hot air blow inside & the cold air blow outside that is what a heat pump does. It just takes some extra controls & valves to do it.
    I use this explanation also, easy for new guys and customers alike to understand.

  6. #6
    Join Date
    Jun 2006
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    SW MO.
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    Indoor coil may not be large enough to handle the extra capacity in heat mode.

  7. #7
    Join Date
    Aug 2012
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    Quote Originally Posted by chaard View Post
    Indoor coil may not be large enough to handle the extra capacity in heat mode.
    So for the reversing valve instead of hot vapor running from compressor to condensor in AC mode. In heat pump mode it would start at compressor then to evaporator coil, on the outside unit absorbing heat from the ground or air then there is a metering device before arriving at the indoor condensor where the heat is then extracted over the coils where the cool return air is absorbing that heat when blowing over the coils, correct? There is no heat exchanger in heat pump mode, correct?

  8. #8
    Join Date
    Sep 2002
    Location
    Virginia
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    3,181
    Quote Originally Posted by mikem201 View Post
    So when the reversing valve switches to heat , hot vapor goes from compressor towards indoor coil, the heat is then extracted from the indoor coils as the hot vapor runs through the coils, and Air passes over them. The gas then turns into liquid as it exits coil because the heat has been taken out. This now warm liquid travels towards the outside unit , passes though a metering device , causing it to turn into vapor again ,absorbing more heat from the outdoor air as it passes through coils, then vapor is sucked into the compressor , then discharged as a really hot gas back through the maze again.
    I fixed it for you ....

    Quote Originally Posted by mikem201 View Post
    There is no heat exchanger in heat pump mode, correct?
    Those are used in refrigeration , not in your average central home air conditioners . Refrigeration is generally termed as anything used to keep food / beverage cold. You might find heat exchangers in many of those units.

    A heat exchanger will have the liquid line and vapor line running tight beside each other ( this is Very lamens terms ) and one sucks the heat from the other

  9. #9
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    Aug 2012
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    Quote Originally Posted by Snapperhead View Post
    I fixed it for you ....

    Those are used in refrigeration , not in your average central home air conditioners . Refrigeration is generally termed as anything used to keep food / beverage cold. You might find heat exchangers in many of those units.

    A heat exchanger will have the liquid line and vapor line running tight beside each other ( this is Very lamens terms ) and one sucks the heat from the other
    In a gas furnace the evaporator coils are not the actual heat exchanger, correct? I have an upflow furnace and the evaporator coil is above the heat exchanger is what I am seeing I believe.

  10. #10
    Join Date
    Sep 2002
    Location
    Virginia
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    Quote Originally Posted by mikem201 View Post
    In a gas furnace the evaporator coils are not the actual heat exchanger, correct? I have an upflow furnace and the evaporator coil is above the heat exchanger is what I am seeing I believe.
    OH ! So THATS the heat exchanger you were referring about , in a FURNACE ... You had me confused because you were talking about Heatpumps and the refrigerant cycle and something about an exchanger. There are heat exchangers in refrigeration units and I thought thats what you were speaking about.

    So yes , you are right , if you have a gas furnace as "back-up heat" in addition to a heatpump in your scenereo above, then yes , a FURNACE has a HX ( heat exchanger )

    Sorry for the confusion , but our friend Chaard above explains it as well.

    But just so you know , having the correct terms helps alot.

    For example , (technically ) Heatpumps have indoor and outdoor units , you dont call them evaporators and condensers , because once you run it in Heat, the indoor unit is suddenly the condenser. Make sense ?

    In straight AC , yes the outdoor is a condenser , indoor is a evap , always

    In refrigeration , like a walkin cooler , outdoor is condenser , indoor evap

    In refrigeration you have heat exchangers , but you will have to get your teacher to show you one.

    In furnaces you have heat exchangers
    Last edited by Snapperhead; 01-08-2013 at 08:43 AM.

  11. #11
    Join Date
    Aug 2012
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    25
    Quote Originally Posted by Snapperhead View Post
    I fixed it for you ....

    Those are used in refrigeration , not in your average central home air conditioners . Refrigeration is generally termed as anything used to keep food / beverage cold. You might find heat exchangers in many of those units.

    A heat exchanger will have the liquid line and vapor line running tight beside each other ( this is Very lamens terms ) and one sucks the heat from the other
    Do you think based on this being my second semester in HVAC that my knowledge and description is pretty good?

  12. #12
    Join Date
    Feb 2004
    Location
    Pacific NW
    Posts
    567
    What pacnw said.

    HP function requires reversing valve (or setup to NOT have any AC capability), different controls, etc. Indoor coil for HP is typically 20% or more larger than AC only, unless you have an old 8 SEER POJ.

    You will likely save money in the long run with a new high HSFP rated unit if you want heat from your vapor cycle equipment.

  13. #13
    Join Date
    Oct 2011
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    between here and over there
    Posts
    453
    Correct me if I am wrong but, I believe you would also need a bi flow metering device for both indoor and out coils.

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