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  1. #1

    Generator Back-up of Heat Pump

    I have 2 heat pumps in my house and would like to have one run on a generator in case of electric power failure. The main problem is that the heat strips take about 10kW which would call for a very large generator. Can I wire the one heat pump so that the heat strips are on one breaker panel that won't be powered by the generator and the heat pump on another panel that will be generator powered. I understand that the heat pump without the heat strips may not be able to keep up if it is very cold, but I am only looking that the pump keep the house from freezing if we are not home when the power fails.

  2. #2
    Join Date
    Oct 2006
    Location
    So. NH
    Posts
    765
    Electrically speaking that could be done but I'm not sure if that would really be best. You would still need a rather large generator, expensive automatic transfer switch and associated install expense. Then, if were cold enough the heat pump may not even work, so you may be better off looking at other emergency heat options or a big enough gen. to do the job.

  3. #3

    Generator Back-up of Heat Pump

    stvc - Thank you for the reply. We are in the process of remodeling our house and have installed a 200 A transfer switch already. The house has a 600A service (don't know why, but we bought it that way). We have several cb panels with 2 next to each other. I thought that I could have the heat pump on one (with generator back-up) and the furnace on the other (with no back up). In other words the transfer switch is already in place and I am now sizing the generator. I live in western Washington with relatively mild winters. I have tried to just shut off the furnace, but the whole system seems to shut down. It seems to me that the heat strips could be disabled in the case of a power failure. The power requirements for the heat pump are much lower than the heat strips.

  4. #4
    Join Date
    Apr 2002
    Posts
    11,808
    Too bad the generator is not liquid cooled.

    It's radiator would heat the house
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  5. #5
    Join Date
    Apr 2005
    Location
    NE PA
    Posts
    698
    While it is true that the running current for the heat pump may be lower than the heat strips, the starting inrush of the compressor can bring many generators to their knees. Most modern residential type generators are made without a penny to spare, and as a result they lack the copper and iron in the generator to handle much of a surge.

    I do not know the size of your heat pump, but an average size will draw 50-60 amps inrush at startup. This current will drag the generator RPMs down, the output voltage will drop and the unit will never start. If you are lucky you will blow a breaker of fuse before you damage the heat pump. Figure on a 7-8 KW minimum size to get the heat pump started. Lower current is all that is required once it is running, but you need to get it started first.

    paul

  6. #6
    Join Date
    Jun 2006
    Posts
    491
    in answer to your question. yes. it could be wired that way. i'm hoping you plan on having an electrician perform the work, he can give you the details after looking at what you have to work with. here is an article, for reference, that will give you an idea of what the electrician will be up against regarding electrical codes/saftey requirements. http://www.selfhelpandmore.com/homew...ator/index.htm
    now for my two cents. if you live in a mild area, i wouldn't worry about heating my house too terribly much (in the event of a power failure). if you're wiring in the generator to handle other loads, then of course you're intentions will hopefully justify your plans (financially). if my pipes weren't going to freeze (i'm saying this figuratively as i know there are better, more economical means of ensuring that that won't happen), i'd just go stay in a motel for the few days the power might be out. (i'm sure your c.p.a could find a way to write off that expense come tax time too ) regarding that link i provided - i thought the article would be a little more in depth ( i copied the address from my bookmarks and looked at the page after responding to your question. my bad. ) if you sift thru that web site, you might get a little more info that would provide you with insight beyond what that one page gives you.
    Last edited by mr horsepower; 12-09-2007 at 04:36 PM.

  7. #7
    Mr Horsepower - Thank you for the info. My house wiring was a real mix up so during the remodel we had professional electricians completely rewire the house including the automatic generator switch. My problem is I can't find someone that can set the heat pump up so the heat strips won't come on in a power failure yet have the heat pump work. The electrician says the HVAC person can do it. The HVAC person says he can't do it, the elcectrician is the one. I seem to be caught in a Catch 22 situation. Does anyone have something I can give to either the electrician or the HVAC person that would tell them what to do. The unit I am trying to modify is a 2 ton Trane from 2001. The electrician has the furnace on the non-backed up cb panel and the heat pump on the generator backed-up panel. When I flip the furnace cb the entire heat pump goes off including the thermostat.

  8. #8
    Join Date
    Jun 2007
    Location
    louisville ky
    Posts
    107
    get a kerosene heater.

  9. #9
    Join Date
    Jan 2005
    Location
    Denver, Colorado
    Posts
    306
    What you will need is to have the air handler (what you mistakenly called a furnace) and the heat pump on the same panel, and both will need to run on the transfer switch. Won't do any good to only have one on the gennie and not the other.

    Then you will need to get a relay, usually called an emergency power relay, which will disable just the heat strips in event of the generator running.

    Keep in mind what the other guys have said...please don't try to run something like a heat pump on a 5kw home depot gennie.
    Leadership...the ability to move forward even when you've burned your foot.

  10. #10
    Join Date
    Jun 2006
    Posts
    491
    Quote Originally Posted by Dr John E View Post
    Mr Horsepower - Thank you for the info. My house wiring was a real mix up so during the remodel we had professional electricians completely rewire the house including the automatic generator switch. My problem is I can't find someone that can set the heat pump up so the heat strips won't come on in a power failure yet have the heat pump work. The electrician says the HVAC person can do it. The HVAC person says he can't do it, the elcectrician is the one. I seem to be caught in a Catch 22 situation. Does anyone have something I can give to either the electrician or the HVAC person that would tell them what to do. The unit I am trying to modify is a 2 ton Trane from 2001. The electrician has the furnace on the non-backed up cb panel and the heat pump on the generator backed-up panel. When I flip the furnace cb the entire heat pump goes off including the thermostat.
    i'd have to know a little more regarding the specifics of your situation (mainly how the strips are controlled in the first place). i've never specifically done that before, but it really doesn't seem that making a load (the strips) not work if you have seperate panels should provide a hurdle that can't be cleared. maybe i'm being overly simplistic, but it seems contactor(s) in series with your load, controlled via a transformer which is powered off of the main panel (the dead panel during an outage, not the isolated panel the generator would be on) would create the open circut you need real quick. i came up with this in about a half a second and am in no way offering this as your solution. my point is this shouldn't be a deal breaker if you're set on making this work. whatever is decided, it has to be safe and capable of getting the head nod from your local inspectors. read: just because i'd do it at my house doesn't mean i can do it at yours.

  11. #11
    Join Date
    Jun 2006
    Posts
    491
    to further define what needs to happen and what needs to be where. your air handler (what you have called your furnace) will have to be on the panel the generator will power during an outage. your problem is powering up the system but not allowing a certain load within that system (the strips) to operate during a power outage. my solution is to further control that specific load without removing power from its source by 'splicing' in the extra controls needed. i have no idea, but i would guess that other solutions would revolve around a similar concept.

  12. #12
    Join Date
    Dec 2006
    Location
    Middle Tennessee
    Posts
    11,347

    *

    if you had a dual fuel system, you could use the furnace to heat the house

    then you could use a tiny generator, it would basically only need enough power to run the blower

    and a tad bit extra power needed for a relay or 2 and the gas valve, a 5 kw would be plenty



    .

  13. #13
    Join Date
    Sep 2001
    Location
    Vancouver Canada
    Posts
    996
    Use a Honeywell T8300 stat with outdoor probe and just lock the heat strips out at the lowest temperature available. Don't know what your climate is but if it is fairly moderate this should work for you.
    "Go big or Go Home"

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