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  1. #1
    Join Date
    Mar 2009
    Posts
    4

    dual fuel systems

    I came across a Carrier Dual Fuel system recently. The coil and heat pump have been changed out in the last few years. The existing furnace is bryant 80%. This is the typical Dallas area horizontal application in the attic. The coil was installed on the return air side of furnace. I believe this was done to prevent heating the evaporator coil during defrost cycle. Is this a standard procedure? I have looked at installation instructions and all show discharge side. What are advantages and disadvantages to this layout??? Thanks Jay

  2. #2
    Join Date
    Oct 2008
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    Coming to a town near you soon
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    774
    Its recommended that the coil not be installed on the return side of the furnace so that the heat exchanger doesn't condensate in A/C mode. the coils going to get heated in emergency heat anyway, and it will help the defrost cycle to heat the coil.

  3. #3
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,594
    Coil belongs on the discharge side of furnace.
    So as not to cause condensate in the HX and rot/rust it out.
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  4. #4
    Join Date
    Sep 2008
    Location
    Western N.C
    Posts
    15
    Quote Originally Posted by beenthere View Post
    Coil belongs on the discharge side of furnace.
    So as not to cause condensate in the HX and rot/rust it out.
    Also if coil is not multi-pos. doesnt this cause problems with system eff. when i worked for a guy who installed heat pumps this way we had to change them back. Another words arnt u sapposed to have blower blow through vortex of coil not draw from apex of coil. And would this apply if its a slant coil instead of a A coil?

  5. #5
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,594
    Most slant coils are pull through.

    Acoils, the main difference between pull through and push, is a condensate baffle.
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  6. #6
    Join Date
    Sep 2008
    Location
    Western N.C
    Posts
    15
    Quote Originally Posted by beenthere View Post
    Most slant coils are pull through.

    Acoils, the main difference between pull through and push, is a condensate baffle.
    Ok this makes sense to me this is y Goodman air handlers can b converted to down flow by just fliping the coil and pan there acoils r no dif. then others[that is at a glance].

  7. #7
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,594
    York has one air handler.
    That in a right hand flow, the air travels into the opening of he A.
    But, in a left hand flow, the air flows into the point of the A.
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  8. #8
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    I haven't noticed any issues heating hte coils during defrost. We had some icy weather last night and after having some imbalance on the outdoor unit fan blades, I went to em heat. When I switched it back this morning, it defrosted for almost 3 minutes. Not suprisingly, the furnace on low stage still didn't generate enough heat to match the cooling capacity of the heat pump. The heat pump didn't seem to mind the 105 degree air temp on the indoor coil.

    The only advantage I could see with the coils downstream of the HE is that with very low electric rates, you could use the furnace as supplemental heat as long as the incomming air was under 80F (the upper limit of hte furnace operating range)

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