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  1. #1
    Join Date
    Jul 2008
    Location
    DeLand, FL
    Posts
    37

    Heat Recovery Units

    For my new house, I asked my A/C guy (his own company, long time friend) to install a heat recovery unit for my domestic hot water like in my old house. He told me that it would require using an 'old tech' R22 system since the R410 units run too cool a temp at the compressor discharge. He installed an SEER 13 R22 system with the heat recovery unit and as in my last home, I get free hot water and switching the HRU's circulator pump off and on shows a 11.6 to 9.7 amp change in compressor draw. Obviously it's on the right track to save me considerable money...I run a summer power bill of $130 for a 2000 sq ft house here in cent FL. My question is, are HRU's becoming obsolete with the lower temps of an R410 system? If so, will the increased efficiency of the R410 HVAC compensate for the loss of free hot water? Still seems to me that since you are moving heat around anyway, you should 'put it in your hot water'. Thanks, Gary.:

  2. #2
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    66,807
    A 13 SEER R410A system has about the same compressor discharge temp as a 13 SEER R22.

    Your friend is mistaken.

    A higher SEER unit will have a lower compressor discharge temp.
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  3. #3
    Join Date
    Jul 2008
    Location
    DeLand, FL
    Posts
    37

    Discharge temp

    I wonder why the compressor discharge temp of higher SEER units would be lower? Wouldn't the temp difference be at the end of the condenser coil rather than the compressor? After all, you should still be removing the same amount of heat from the house and once the gas is compressed, I would think the temp would be about the same. Am I not understanding something about the refrigerant cycle?

  4. #4
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    66,807
    It is close.

    Higher SEER units use smaller BTU rated compressors then the rating of the condenser.
    So they aren't moving the same volume of gas, and the compression ratio is lower, so the compressor discharge temp is slightly lower.

    Remember, for every plus there is a minus, for every minus there is a plus.
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  5. #5
    Join Date
    May 2007
    Location
    Naples, Fl
    Posts
    889
    gary

    There are guys on here that are great with refrigeration theory and will give you the technical answer. I'll offer up field experience with a few high efficiency systems both R22 and R410a.

    The hot gas discharge temps on these high efficiency units will not get hot enough (normally) to close the NO furnace/fan klixon that is in series with the pump for heatpump applications. We have measured the temps with our clamp on thermometers. HRU aren't something we recommend but some customers insist on them. We aim to please.

  6. #6
    Join Date
    Jul 2008
    Location
    DeLand, FL
    Posts
    37

    Temp of compressor discharge

    Here in DeLand (cent FL), the compressor discharge temp is 195 degrees on an 88 degree temp day. The data from the HRU mfg states you need an minimum of 180 degree discharge temp so I'm ok there. Since the install my hot water heater has been turned off with no problems of hot water storage (I installed an 80 gal water heater). I also see compressor current draw drop from 11.6 to 9.7 amps when I switch on the HRU circulator pump. Apparently the HRU has about a 20% decrease effect on the head pressure...how this actually effects cooling capacity is something I'm not sure how to measure. I assume it probably does lower the system capacity but I don't know how to judge how it would balance out cost-wise. Hope I'm making my concerns clear....Thanks, Gary.

  7. #7
    Join Date
    Jul 2008
    Location
    DeLand, FL
    Posts
    37

    Thanks again!

    I'd like to thank the two of you for sharing your knowledge on this subject with me...I've had positive results with 3 HRU's but realize you guys have seen vast numbers of systems over the years and I really appreciate your valuable input...Gary

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