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  1. #14
    Join Date
    Jun 2006
    Location
    SW MO.
    Posts
    5,212
    I'm gonna put my in here. These are my thoughts and not the industry norm. So take it with a grain of salt.

    The indoor coil technically is a hx. The definition of exchange is to give and receive. The air over the
    indoor coil in cooling is giving. The refrigerant in the coil is receiving the heat. The refrigerant in turn is giving back a cold coil and exchanging the warm air for cold air.

    In hp mode the cool air over the warm coil is giving to the the refrigerant inside, and the refrigerant is receiving the cool air, the refrigerant in turn is exchanging the cool air for warm air.

    The term heat exchanger in a 80% furnace is not a true heat exchanger. Because the hx is not receiving anything from the cool air over it. It is only giving heat to the air and warming it. The flue gasses are not absorbing the cool air cause its not condensing or changing the state of the heat or flue gasses in the HX.

    Now on a hi eff. furnace the secondary coil which is actually first in the air stream is a true hx cause the warm coil is giving heat. The flue gasses are receiving the cool air and are condensing. So there is an exchange of heat before the warm air passes over the primary heat exchanger.
    Again these are not terms normally used in our industry interchangeably. Just trying to help you understand how things work.
    Let the flaming begin.

  2. #15
    Join Date
    Aug 2012
    Posts
    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?

  3. #16
    Join Date
    May 2011
    Location
    Western, KY
    Posts
    3,226
    Quote Originally Posted by mikem201 View Post
    Do you think based on this being my second semester in HVAC that my knowledge and description is pretty good?
    For now just know that you don't know enough.

    Spend the next five years operating with an unquenchable thirst for knowledge and experience, take every job you are asked to do, within reason, like your next paycheck depends on it being accomplished the best way possible, if you're asked to change filters you be the best filter changer ever(remember what the components are from your books and remember where they are located on various units while you're at it), once you start installing/servicing units know that you have a huge amount of info and experience to get under your belt, stay humble and appreciative that you have a job, know that there is something to learn from everyone, even if it's what not to do. If you do this ^ and become a member of this site and are willing to take the lickings for doing things wrong and getting schooled by the more experienced members here without acting like a baby, and you have some natural abilities related towards this occupation you will turn out better than at least 80% of the folks who get into this business.

  4. #17
    Join Date
    Jul 2009
    Location
    South Carolina
    Posts
    3,261
    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. #18
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    4,378
    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. #19
    Join Date
    Sep 2002
    Location
    Virginia
    Posts
    3,234
    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.

  7. #20
    Join Date
    Aug 2012
    Posts
    2,682
    Quote Originally Posted by Trehak01 View Post
    Correct me if I am wrong but, I believe you would also need a bi flow metering device for both indoor and out coils.
    you are correct. So just have the dude install that for the cost of a new coil and air handler.
    My name is TooCoolforschool and I am a chronic over charger.

  8. #21
    Join Date
    Dec 2012
    Location
    Westerville, Ohio, United States
    Posts
    24
    Back to your original question - never add a condenser (ac or hp) to an unmatched coil (evap or fan coil). This system is supposed to serve someone well for 15-20 years, why would you want something that isn't factory tested for performance and if not matched probably not warrantied?

    Don't get cheap on this customer, or you will be back to repair it for life

  9. #22
    Join Date
    Jul 2005
    Posts
    5,576
    Quote Originally Posted by chaard View Post
    I'm gonna put my in here. These are my thoughts and not the industry norm. So take it with a grain of salt.

    The indoor coil technically is a hx. The definition of exchange is to give and receive. The air over the
    indoor coil in cooling is giving. The refrigerant in the coil is receiving the heat. The refrigerant in turn is giving back a cold coil and exchanging the warm air for cold air.

    In hp mode the cool air over the warm coil is giving to the the refrigerant inside, and the refrigerant is receiving the cool air, the refrigerant in turn is exchanging the cool air for warm air.

    The term heat exchanger in a 80% furnace is not a true heat exchanger. Because the hx is not receiving anything from the cool air over it. It is only giving heat to the air and warming it. The flue gasses are not absorbing the cool air cause its not condensing or changing the state of the heat or flue gasses in the HX.

    Now on a hi eff. furnace the secondary coil which is actually first in the air stream is a true hx cause the warm coil is giving heat. The flue gasses are receiving the cool air and are condensing. So there is an exchange of heat before the warm air passes over the primary heat exchanger.
    Again these are not terms normally used in our industry interchangeably. Just trying to help you understand how things work.
    Let the flaming begin.
    Yes, you're correct....those thoughts aren't the industry norm. I'd say that your definition of heat exchanger is different than pretty much every textbook definition.

  10. #23
    Join Date
    Jun 2006
    Location
    SW MO.
    Posts
    5,212
    Quote Originally Posted by hvacrmedic View Post
    Yes, you're correct..
    That's all that matters.

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