Request for feedback.

Discussion in 'General Discussions' started by HVAC Technician, May 28, 2010.

  1. I am addressing 3 things here. May 28, 2010

    One, low temperature compressor lockouts on water source heat pumps on the coldest days of winter,

    Two the use of auxiliary heat to help my water source heat pump after night set back;

    Three, the use of a GE Hybrid hot water heater which would be fed from a earlier buffer tank preheated by my Carrier heat pump hot water generator.

    I would like to ADD the new GE Hybrid hot water heater to my home. I currently have a single 50 gallon low boy Whirlpool as my only water storage. I plan on running the Whirlpool in series to the GE Hybrid heat pump water heater in my house.

    I was thinking of using a simple hydronic copper coil with 120 volt blower (have to figure out where I would get it from) and mounting it floor level in a hallway 90 degrees perpendicular to my main hallway directly facing my largest air return.

    The 120 degree water would be circulated from the GE hot water tank and turn on with a simultaneous y1 call to my TACO water valve. Thus I would blow 100 air for 12 minutes (coming ultimately from the hot water tank) into that return buffering start up after a night set back.

    What do you other professionals think?
  2. geome

    geome Member Forum Leader

    Aux heat and setbacks

    I'm a homeowner. To help recover without the use of aux heat you can:

    Use a thermostat with an auxiliary heat lockout. Get one that has a lockout range that will work for you. Disengage the lockout if you go away overnight (to be safe).

    Turn off the auxiliary heat breakers. Only do this if there is nothing else on the breakers (like the blower, for instance). Again, turn on the breakers if you go away overnight (to be safe).

    Don't use setbacks of more than 2 degrees. Even still, depending on your balance point and outdoor conditions (wind, clouds, etc.) your system may still need aux heat to recover when conditions are such that your system can't handle on its own.

    Don't set back (had to say it.) :)

    Thermostats with staging based on droop and time may help a bit, but may still engage aux if the system can't catch up in the specified time (like 2 hours for instance).
  3. Looby

    Looby Member Forum Leader

    I have my doubts as to how effective that would be -- but locating a 120V
    hydronic coil/blower should be easy enough:

    google: "kickspace heater"

    These are compact little units designed to be installed beneath kitchen
    cabinets -- with heated air discharged at floor level. Before switching to
    geo we had one and it worked great (it's impossible to find space for a
    normal HW baseboard radiator in a typical kitchen floorplan).

    ...good luck,

  4. In general I agree, heat pumps don't seem to like big set backs; but please note that when I talk about aux heat I am NOT talking about electrical resistance heaters. I am describing using a small hot water hydronic coil using already stored 120 degree HOT WATER produced by the GE Heat pump hot water heater to speed up recovery and buffer return air so that the coil receives ~ 68 - 74 degree return air for the first 10 - 12 minutes of start up. Assuming that you start circulating this hot water through a coil blowing into or at the return, you have 100 air coming out 45 - 60 seconds BEFORE the compressor comes on. That is the idea I am testing.
  5. Bergy

    Bergy Member Industry Professional Forum Leader

    Seems a bit Rube Goldbergish to me. I really don't see any advantage to 60 seconds of warm air helping the home recover from a set back.

  6. Looby

    Looby Member Forum Leader

    That ain't gonna happen with such a huge CFM mismatch between the
    heat pump's 220V blower and a small 120V fan coil. The small volume
    of preheated air from the fan coil will be massively diluted by colder
    return air from the rest of the house. The net effect will be a very small
    rise in the return air temperature at the heat pump's air coil.

    Rethink the problem in terms of BTUs -- rather than degrees F. How
    many BTU/hr can a small fan coil provide? How many BTU/hr does a
    10 kW heat strip supply? How many BTU/hr to jump-start your house
    from a deep setback?
  7. epf55

    epf55 New Member

    Attn: Looby (Geo installer in Chester County)

    Looby, I need your recommendation of Chester County WF installer that you used. Tried to PM you, but it won't allow PM's to you. Thanks so much.

  8. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    Thank you. Small radiators and kick space heaters are seriously derated with low temperature water.
    It's all about how many btu's ya need and where they are coming from. A radiator with 100 degree water in it may only offer 100 btus/foot.
  9. Thanks

    Good Comments.
  10. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    Robbing Peter to pay Paul

    In order for a HPWH to warm its tank of water it withdraws heat from the surrounding house. Using its stored hot water to reheat the house ultimately returns the heat extracted from the house back to the house. There will be some additional heat added back to the house air, about equal to the kwh consumed by the HPWH, the water pump and other system auxiliaries. That extra heat will be generated at a COP of 1.0, and there are FAR easier ways to do that.

    Other issues - just as HPWH-assisted setback recovery begins, the HPWH will activate, cooling the surrounding air just as it is trying to be reheated. Moreover, if anyone wants a shower after getting up in the morning, the contents of the HPWH will likely disappoint them. Finally, the amount of heat available is fairly small in terms of effect on a house. Cooling 50 gallons of water from 120 to 80 yields a bit shy of 17kbtu, not much in the grand scheme of things.

    If you had several hundred gallons of hot water available from a solar thermal storage system, this idea would have merit.
  11. geome

    geome Member Forum Leader

    Rube Goldberg

    Thanks Bergy. Just looked up this gentleman. And I was afraid I wasn't going to learn anything today. :)
  12. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    Bergy has just dated himself!
  13. Bergy

    Bergy Member Industry Professional Forum Leader

    Pot...Kettle...Black...Ringin' any bells?? :D

  14. geome

    geome Member Forum Leader

    I'm sure -

    - it was great grandfathers that learned you youngsters 'bout him. :)

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