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  1. #1
    Join Date
    Nov 2007
    Posts
    47

    Split System Heat Pump Mismatch

    Is it a problem to have a mismatched indoor and outdoor components?

    Specifically, I have two systems with the following:

    System 1:
    Heat Pump-Goodman GSH130301AA (2-1/2 ton)
    Air Handler-Goodman ARUF364216AA (3 to 4 ton capacity)

    this cools/heats 1100 sq.ft. 2nd level with 151 sq.ft. of windows


    System 2:
    Heat Pump-Goodman GSH130421AA (3-1/2 ton)
    Coil-Goodman CAPF4860D6AA (4 to 5 ton capacity)
    Furnace- Goodman GMS91155DXAA

    this cools/heats two levels:
    main level of 2100 sq.ft. with 448 sq.ft. of winows and
    lower level of 1600 sq.ft. with 240 sq.ft. of windows

    I am having cooling problems because I think the system is undersized for our square footage and the number of windows, but I wanted to know if a below capacity range heat pump is generally acceptable or contraindicated.

    Thank you.
    TLY

  2. #2
    Join Date
    Sep 2006
    Posts
    1,253
    The only absolute way of knowing whether your equipment is properly sized is to have a load calculation done to determine the heat gain and loss. Contractors can do this for you but you may have a hard time finding one that would be willing to do it.

    The other alternative is to do it yourself. I have used and can recommend the software available on this site located under the tab labeled HVAC Calc near the top of the page. It is only $50 for a homeowner version. If you choose to go that route make sure you do it on a room by room basis (not whole house) which will then also detail the amount of air flow that is needed for each room (you may well find that your issue is an air flow issue and not equipment sizing). It took me about three hours to complete. Review carefully and don't be too surprised at how low the numbers come out. Many homes have over sized equipment and undersized ducts.

    Good luck.

  3. #3
    Join Date
    Nov 2007
    Location
    N.C.
    Posts
    170
    mchild is right. Sometimes companies don't do a load calculations. Some just go by what is already there as their reference which I feel that the customer is getting cheated. The company that I work for we check everything even ductwork

  4. #4
    Join Date
    Nov 2007
    Posts
    47
    Thank you for your responses.

    I am still curious if it is OK to match a 2.5 ton condenser with a 3-4 ton evaporator and match a 3.5 ton condenser with a 4-5 ton evaporator.

    Will a load analysis recommend such combinations? Seems to me the minimum size heat pumps ought to be a 3 ton for System 1 and a 4 ton for System 2. Thanks.

    TLY

  5. #5
    Join Date
    Oct 2003
    Location
    Florida's space coast
    Posts
    2,538
    Quote Originally Posted by TLY View Post
    Thank you for your responses.

    I am still curious if it is OK to match a 2.5 ton condenser with a 3-4 ton evaporator and match a 3.5 ton condenser with a 4-5 ton evaporator.

    Will a load analysis recommend such combinations? Seems to me the minimum size heat pumps ought to be a 3 ton for System 1 and a 4 ton for System 2. Thanks.

    TLY
    This is not a mismatch as long as the piston in the evaporator coil was changed to match the condenser.
    We've been doing so much,for so long,with so little, that now we can do almost anything, with nothing at all.

  6. #6
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    33,916
    go to www.goodmanmfg.com and look at the spec sheets. If they are an approved match, the specs will show it.

    When a mfr uses a piston coil, the way to get high SEER is use a big coil. So wouldn't surprise me that the big air handlers are fine. Besides changing the piston, the blower needs to be set for the size of the outdoor unit. Few bother.

  7. #7
    Join Date
    Nov 2007
    Posts
    47
    OK, thank you. I went to the Goodman website and found the air handler specifications for the System 1 indoor unit (ARUF364216AA) and did not see specified what heat pumps could be used with this model number. I did find the heat pump specifications for my heat pump (GSH130301AA) and did not find the air handler listed under the "performance ratings" section for the 2-1/2 ton unit. I did find the air handler listed under the performance ratings for the 3 and the 3-1/2 ton model heat pumps.

    Additionally, the ARI website does not list the 2-1/2 ton heat pump as a match for the air handler, but it does give a match for the 3 ton (ARI ref #: 1038066) and the 3-1/2 ton (ARI Ref#: 1038070) heat pumps.

    So, basically I still remain confused since I cannot find a match within the Goodman specifications and the ARI certification. How improtant is it to have an ARI Certified match and to stay within specifications of the manufacturer?

    TLY

    (Sidenote: In my previous posts I did incorrectly state that the System 1 air handler has a 3 to 4 ton capacity...it actually has a 3 to 3-1/2 ton capacity.)

    (Sidenote: I could easily find information for my System 1, but I am having difficulty finding specification information for my System 2 gas furnace)

  8. #8
    Join Date
    Apr 2004
    Posts
    7,680
    If it aint in the spec sheets, don't do it. Consider yourself warned. You may also want to look at the warranty. You may find it null and void if you mismatch (and it should be).

  9. #9
    Join Date
    Nov 2007
    Posts
    47
    Quote Originally Posted by BaldLoonie View Post
    If they are an approved match, the specs will show it.

    How critical is the approved match? I've gotten conflicting answers from "this is not a mismatch" to "don't do it." As a new homeowner who knows little about HVAC systems, I am seeking objective information and I want to give proper weight to that information. For example, I don't know if lack of an ARI Certification is common practice and occurs most of the time, or if it is a basis for one to request (or demand) correction.

    I am trying to treat the indoor capacity/outdoor size as a separate entity independent of proper sizing.

    I do feel that our heat pumps are undersized based primarily upon comfort (kitchen reaches 80 deg, main floor 76, and upstairs 77 with an outdoor temp of 94 and the thermostats set on 72). I think I need to have an independent professional perform a load calculation as a basis to make corrective decisions. The HVAC company who did our install maintains the right sized system was installed based upon their load calculations. But, load calculation results are only as good as the input data used. When I play around with a load calculation software (RHVAC by Elite Software) and I see what the sensible heat gain can be from just our windows alone (giving consideration to type, size, orientation, etc.), it makes me think our system is undersized.

    But, back to topic...even if we are properly sized, is my combination of indoor and outdoor components a problem for me? Thanks.

    TLY

  10. #10
    Join Date
    Apr 2007
    Posts
    6,285






    735259
    735151 735082 735090 735087 735222 735108 735228 735841 735189 735824 735823 735844 735812 736494 736495 736496 735832 735834 735106 735219 735817 735808 735254 735079 735819 735829 735201 735170 735835 735804 735041 735215 735836

    Ari ref. numbers for your GSH13030


    "Goodman is not responsible for:
    1. Damage or repairs required as a consequence of
    faulty installation or application.
    2. Damage as a result of floods, fires, winds,
    lightning, accidents, corrosive atmosphere or other
    conditions beyond the control of Goodman.
    3. Use of components or accessories not compatible
    with this unit.
    4. Products installed outside the United States or
    Canada.
    5. Normal maintenance as described in the
    installation and operating manual, such as cleaning
    of the coils, filter cleaning and/or replacement and
    lubrication.
    6. Parts not supplied or designated by Goodman.
    7. Damage or repairs required as a result of any
    improper use, maintenance, operation or servicing.
    8. Failure to start due to interruption and/or inadequate
    electrical service.
    9. Any damage caused by frozen or broken water pipes
    in the event of equipment failure.
    10. Changes in the appearance of the product that do
    not affect its performance."
    Attached Images Attached Images
    Last edited by BigJon3475; 11-19-2007 at 10:04 AM.

  11. #11
    Join Date
    Nov 2007
    Posts
    47
    Quote Originally Posted by BigJon3475 View Post


    "Goodman is not responsible for:
    1. Damage or repairs required as a consequence of
    faulty installation or application."
    I know most people don't like to say so directly, but I must conclude that you think this is a faulty application and it should be corrected to specifications/standards.

    I did call Goodman and talked to a representative to see what they think of my combination of equipment. The representative said she would email tech support and get back with me. She called back an hour later and said that technical support could not recommend this combination and recommends combinations that are within specifications. I asked her about warranty, and she did not think this voided any warranty...but who knows.

    So where do I go from here? To my builder? To the HVAC company? Get an independent load analysis done at my expense? And what do I request (demand)? I want to handle this appropriately, so any suggestions would be greatly appreciated.

    TLY

  12. #12
    Join Date
    Apr 2007
    Posts
    6,285
    You need to figure out a load calc. Are you confident in the one you have already done through RHVAC?

    Once you figure that out then look into which size you actually need instead of mixing a heat pump system. You can never get the charge correct on a mixed heat pump system. There are ways rig it up and half fix it but it's still not really the correct way. Since the heat pump reverses it's cycle both coils act as a evaporator and a condenser depending on which mode your in. For this combo to work correctly it must be compatible with each other.


    Can it be done? .....Yes...... Does it work correctly?..... Most studies and Mfg. data say no........... Does it heat and cool?...... Yes but for how long?

  13. #13
    Join Date
    Nov 2007
    Posts
    47
    Quote Originally Posted by BigJon3475 View Post
    You need to figure out a load calc. Are you confident in the one you have already done through RHVAC?

    Once you figure that out then look into which size you actually need instead of mixing a heat pump system. You can never get the charge correct on a mixed heat pump system. There are ways rig it up and half fix it but it's still not really the correct way. Since the heat pump reverses it's cycle both coils act as a evaporator and a condenser depending on which mode your in. For this combo to work correctly it must be compatible with each other.


    Can it be done? .....Yes...... Does it work correctly?..... Most studies and Mfg. data say no........... Does it heat and cool?...... Yes but for how long?

    No, I only have the demo version which doesn't allow for more than three rooms. What I was able to do, though, is calculate the sensible heat gain for my goegraphic location, window type, window size, and window orientation. I simply added the sensible gain that I was able to calculate per window. I don't really have the knowledge or expertise to do a complete analysis myself, but windows are easy and here are my results for the windows alone:

    • 2nd level, 151 sq.ft. of windows with 6,934 Sensible Btuh
    • Main Level, 448 sq.ft. of windows with 19,631 Sensible Btuh
    • Lower Level, 240 sq.ft. of windows with 11,368 Sensible Btuh

    So, after adding the main and lower Btuh and dividing by 12,000 and dividing by .75 to account for the Sensible Capacity of the heat pump, I get 3.44 Tons required just for the windows alone. So I am not surprised we are having cooling problems with a 3.5 Ton heat pump. I would't be surprised if we have air flow problems as well that contribute to our cooling problems.

    Thank you for that information about evaporator-condenser reversing function, that's good to know. I would anticipate we would not notice any heating problems because the supplemental heating would just kick on. I would anticipate, though, energy efficiency and equipment longevity would be adversely effected.

    The installing HVAC company said it was not a problem to have a larger indoor coil, and that it is commonly done. They also faxed me a summary copy of the load analysis which contained:

    • 2nd Level: requires 1.43 Tons (Based On 75% Sensible Capacity)
    • Main Level: requires 2.89 Tons (Based On 75% Sensible Capacity)
    • Lower Level: requires 0.42 Tons (Based On 75% Sensible Capacity)

    So, as you can see, the reports support what was installed. I question the input data and have requested to review the data (since I can do windows) just to check and see what heat gain considerations they have given to everything, both latent and sensible. They did their load analysis with the RHVAC software, which is why I have looked at this software myself. The HVAC company has been unresponsive for over a month to my request and my attemts to talk to the owner.

    TLY

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