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  1. #1
    Join Date
    Jul 2008
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    86

    Heat recovery systems on residential split-systems

    Heat recovery systems on air conditioners used to be quite popular here in Florida but you don't see many of them being installed these days. I've heard some A/C contractors make claims that they don't make sense anymore with the new more efficient equipment but I don't know if that is just uninformed talk.

    I've personally put a kWh meter on a hot water heater that had such a system and I can verify that, over the several weeks time that I was testing it, the element came on very little. Of course, it only works when the A/C is running. Speaking of which, wouldn't it do just the opposite (cool your hot water) when used on a heat pump that is in heating mode, barring any control to prevent it from circulating in that mode?

    It also seems like they would increase the efficiency of the A/C when they were running.

    Bottom line, what are the issues with heat recovery systems on residential straight cool or heat pump systems? For any non-experts here, this is an example of what I am talking about.

    Thanks for your input.

  2. #2
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    Feb 2009
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    Tallahassee, FL
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    I think this has a lot to do with the clever marketing of tankless heaters.

    Even with the new heat pump water heaters...they still use more electricity than a reclaim unit.

    People seem to think these are the holy grail of efficiency.

    With a heat reclaim unit in Florida and with your a/c set around 75 you have practically Free hot water.

    As far as in Heat mode...they still heat the water, however this takes away a small amount of heat that would be going in the home.

    Bottom line is they work fantastic.

    As far as the effiiciency question..any increases would be small...and would differ from home to home and system.

  3. #3
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    Jul 2008
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    86
    How prevalent are heat recovery units outside of Florida, at least in other hot states using a lot of A/C? I suspect that the market penetration level is very low. It really seems like they are a great product that just haven't been discovered. Assuming that there is very little market penetration, what are the reasons that you A/C contractors don't promote this as an add on?

    Considering the large percentage that a water heater is of a total energy bill, it appears to be a low-hanging fruit level of opportunity. Any more thoughts on the subject?

  4. #4
    Join Date
    Jun 2001
    Location
    DFW
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    684
    With higher efficiency A/C systems came lower temperature outputs from the compressor which lowers the efficiency of heat recovery sytems. They could be used for a preheat tank that feeds a water heater, but most people are not willing to pay that much or give up that much space for the extra tank.

  5. #5
    Join Date
    Apr 2010
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    115
    I had no idea such a system existed.
    Smart idea.

  6. #6
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    Feb 2009
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    Tallahassee, FL
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    Quote Originally Posted by paul42 View Post
    With higher efficiency A/C systems came lower temperature outputs from the compressor which lowers the efficiency of heat recovery sytems. They could be used for a preheat tank that feeds a water heater, but most people are not willing to pay that much or give up that much space for the extra tank.
    Thats not true..... discharge temps are actually higher with R410a

  7. #7
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    Feb 2009
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    Tallahassee, FL
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    Basically it is the costly installation that deters most people.

    And they are not something a "average" or "below average" tech understands enough to install properly. Also im not sure what they do to the factory warranty. It requires opening up the brand new unit and teeing off the compressor.

    And the fact everyone has been hypnotized to think "tankless"

    A while back I really tried to sell a few. Didnt..dont talk about them much anymore.

    I stay busy enough just fixing the ones that break.
    Last edited by SBKold; 09-10-2010 at 10:07 PM. Reason: oop\s

  8. #8
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    67,754
    There are several of those type of units in my area. Don't think any of the ones I've seen were Lennox brand. But they all work on the same principles.

    The people that have them. And the units still work. Love them.

    Just not a common add on, due to expense/cost.
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  9. #9
    Join Date
    Dec 2007
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    4,670
    unless you are using this as a reference, Lennox lists these as out of production with an initial date of 1983.
    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

  10. #10
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    Nov 2004
    Location
    SW FL
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    6,243

    What's the delta T?

    Quote Originally Posted by DavidJ View Post
    Heat recovery systems on air conditioners used to be quite popular here in Florida but you don't see many of them being installed these days. I've heard some A/C contractors make claims that they don't make sense anymore with the new more efficient equipment but I don't know if that is just uninformed talk.

    I've personally put a kWh meter on a hot water heater that had such a system and I can verify that, over the several weeks time that I was testing it, the element came on very little. Of course, it only works when the A/C is running.

    It also seems like they would increase the efficiency of the A/C when they were running.

    What are the issues with heat recovery systems on residential straight cool system?
    How do you recovery any heat from the A/C lines
    when the water in the HW Tank is > 110'F?
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  11. #11
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    Feb 2009
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    Tallahassee, FL
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    Why would you ask that?

    Surely you know that discharge temps are much higher than 110°

  12. #12
    Join Date
    Jul 2008
    Posts
    86
    Quote Originally Posted by dan sw fl View Post
    How do you recovery any heat from the A/C lines
    when the water in the HW Tank is > 110'F?
    I honestly have not measured actual water temperatures. I can tell you that my mother commented recently about how much hotter the water coming to the tap is in the summer. The only difference is that is when her straight cool A/C is running and it is bringing the temperature higher than the set point of the thermostat (not sure what it is set at).

    I know of others who turn off the breaker in the summer because they are getting enough heat from their A/C heat recovery unit.

    I mentioned in my first post where I have measured kWh consumption over several weeks (I don't remember how long the time period was) from a water heater in the summer equipped with a heat recovery system and the numbers indicated that the element was not doing much of the heating.

    There is no question that they work when installed properly. I think that this is a greatly under utilized product considering how well I've seen them work.

  13. #13
    Join Date
    Jul 2008
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    86
    Quote Originally Posted by amasuperbike View Post
    Thats not true..... discharge temps are actually higher with R410a
    Can you give us ballpark temps with the R410a and contrast that with the older R22 refrigerant?

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