Heat Pump Water Heaters and pre-heated water

Discussion in 'General Discussions' started by Altnrgy, Jun 10, 2012.

  1. Altnrgy

    Altnrgy Member


    I already have a ground source for heating and cooling and I love it. My larger than recommended preheat tank rarely gets much above 100f which I'm relatively confident is not out of line since I have an efficient house and we use a lot of hot water.

    That tells me that a Heat Pump water heater will make at least a little bit of sense for me. My water heater sits in my basement which would benefit from whatever cooling and de-humidification the HP water heater would do.

    I'm wondering how well these HP water heaters deal with warmer and especially hot water? My current electric water heater has a "smart"board and will occasionally go on the fritz when the preheat water get it's hottest. I've called the manufacturer about this and the only answer they'll give me is they don't support applications with preheated water.

    Have others installed HP water heaters that are fed preheated water with success?

    Thanks, Travis
  2. Bergy

    Bergy Member Industry Professional Forum Leader

    The GE HP Water Heater's control board will go into a lock out if the supply water temp is higher than the set point. A mixing valve may be needed to allow a higher set point in the tank and mixing output back to 125*.

  3. Altnrgy

    Altnrgy Member

    Thanks for that quick reply Bergy.

    Do you happen to know if that's a hard fault? Specifically, does it require a manual reset to return to normal operation?

    A friend with a solar water heater got tortured with something similar. Every time the tank went above a certain temp it tripped out the stat on the water heater which wasn't a problem until the next cloudy spell or period of high usage at night.

    Best, Travis
  4. Bergy

    Bergy Member Industry Professional Forum Leader

    I'm not sure about the hard lock out. We just installed our first unit last week.

  5. I own a smaller 2 ton heat Carrier/Climate Master heat pump that preheats a 55 gallon Whirlpool unpowered electric heater buffer tank. (Tank #1)

    I have been told that circulating water to the G.E. can confuse algorythyms that the heater uses to calculate operation from multiple sensor inputs.

    Those algorythyms try and tell the heater how long to run, speed of fans, and so forth. A quick example would be sending 4 gallons of cold water into the bottom of the heater tank while running an additional whole house circulator for three minutes.

    But my experience has been that my 80 - 90F degree incoming preheated water from my Climatemaster desuperheater allows larger overall capacity and quicker recovery, with no apparant issues or problems.

    I have never not had a temp increase at least 10 degrees F of incoming water even with the heat pummp satisfied and not running. (spring/fall) It made a big difference on my power bill during 2012 because hot water is @ 33% of the total electric bill. So I bring heat into the house from geo thermal (during winter) I preheat a buffer tank to 80 or 90 degrees or more much of the year.

    And the G.E. makes economical hot water at 2-3 amps, (under this circumstance) beating their advertized numbers for yearly KW consumption. (You could also achieve this with solar) The only real issue is the quality and durability of these electric heat pump water heaters. I started out with a single tank system but hit the jackpot after I ran the buffer in series with the final G.E. heat pump water heater (#2). There was also a bit of piping to do.
  6. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    The first air to water heat pump DHW unit I have touched lives in Maryland with mtrentw. It is a GE. There are others who make these units. We used an existing tank as a buffer tank to advantage the larger of the two water to air units we installed after digging up the yard. It worked well and life was good. Trent tells me that he now, seven months in service, has an issue with the GE unit. They, GE are standing behind their warranty, (I could use a road tip to DC area to fence of the fiscal cliff, slap a few Ohio folks, and their oponaints, and visit my daughter.), so I will not be in MD sooner than later.

    On to the concept.

    I run into products that are too smart to interface with lots of other "smart systems" a lot as some one gave me a box cutter and taught me to read and I have been roaming out side the box for a good while.
    It occurs to me as I go to schools all the time that there are work arounds to stuff that is too smart for each other. Ask the manufacturer's help desk to send you to someone who knows how to dumb down the electronics if needed.

    The laws of thermal dynamics have not changed, heat goes to cold. There are no new magic refrigerants, we are just learning how to keep the ones we have from killing the planet with their release.

    A air to water heat pump water heater should be able to be made to handle the output of a heat pump desuperheater, either by changing the piping or changing the programming. If that can not happen the world is loosing some good thinking by folks on the leading edge.

    For your free box cutter please call 1.800.out of the box. If you can read who to call thank a teacher.

    >>>> jumps off soapbox, puts on tin foil hat, and runs to duck and cover.

  7. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    I forgot to mention that a heat pump works best when the lift in temperature is low, so DHW heat pumps need to be able to respond to that situation. If you want/need 135*F DHW and send 110*F water from the buffering tank to the finishing tank, it should be able to work.


    jumps back under desk, covering and holding hat.
  8. I had thought for years about installing an add on aftermarket desuperheater unit to a 1/2 to 1 ton upsized air to air heat pump unit and taking a standard solid state winter head pressure controller accessory (used for air to air winter air conditioning) and figuring out how to get it to control a permanent split capacitor motor during the heat pump heating cycle.

    (I would have had to carefully think out actual control). The idea was first desuperheat and then let liquid line temperature control the speed of the indoor blower motor. the motor would have modulated up and down to match liquid line temperature. Based on original function and design, a drop in liquid line temp either would reduce speed of the outdoor fan motor or stop the motor until more heat was released by the condensor. A temperature shut off switch on the circulator pump for the desuperheater, would then send more heat to the heating coil, or something like that.


    Different "outside of the box"

    I just recently got introduced to the new Mitsubishi Slim Jims and their cousins. The specs say they run MUCH MORE efficiently at MUCH LOWER ambient temperatures than traditional american brands. They run very energy efficient variable speed fan motors, variable speed compressors. They also are reliable. They need to add desuperheaters to these units.
    Not dissing geo, I simply saying that air to air is a majority of what is being sold.


    We also need to cycle our geo systems less for greater efficiency and less wear and tear. Heat the hot water first or at the same time or even switch back and forth.
    Last edited: Dec 13, 2012

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