Help figuring out portable generator sizing

Discussion in 'General Discussions' started by d_rek, Jan 11, 2020.

  1. d_rek

    d_rek Member

    Can some please help me figure out what the minimum sized portable generator Is I would need for my geothermal unit? All of the calculators online seem to be equally worthless.

    Here is a picture of the specs from my unit. It is a Bosch 2 ton water source heat pump.

  2. mrpac

    mrpac Member

    Hi D Rek,

    First of all, there is no "portable" generator that will start your Geo.

    Based on the LRA (Locked Rotor Amps) consumed by your unit 83amps, the math is basically calculate for Power -

    Power = E (voltage) x I (current)
    Power = 240 v x 83 amps
    Power = 19,920 watts (20kw)

    This is starting current based - this means the genset needs to be able to start the compressor from a locked state - inrush current only lasts momentarily - the GEO would operate on far less once started.

    You need to be looking for a decent propane NG powered genset - not a portable unit.

    I have a geo with similar current ratings, I have a 100amp circuit feeding the monster, 40amp Circuit for the GEO and 50amp for the Heaters

    Let us know if you require further clarification.
    Last edited: Jan 11, 2020
  3. JeffInCO

    JeffInCO New Member

    You might look into whether there is a "soft start" option for your Bosch, which would significantly reduce the needed starting current (i.e., the LRA). My 6500W peak/5500W continuous portable generator starts my 4-ton WaterFurnace unit, which has the "Intellistart" soft-start module.

  4. JeffInCO

    JeffInCO New Member

    Also, you'll want to make sure that you have a way of making sure that the aux heat does not engage, which would require 9.6 kW continuous (in addition to the power needed by the compressor). 9.6kW puts you outside of the capability of any portable generator that I've ever seen.

  5. d_rek

    d_rek Member

    This is perfect. Thanks for the response.

    I don’t want a standby because that would mean I need to store propane on the property. Currently we are 100% electric household with no utilities at the road so, again, if I were to do a propane genny I’d have to store it on the property which is an additional expense I’m not really looking to pay for at the moment.

    We may just look into electric space heaters instead.
  6. d_rek

    d_rek Member

    It does appear Bosch has a “smart start” unit that can be installed on this series of heat pumps that reduces LRA by 40-65% but I’m not sure if it’s installed on my unit or not. I’ll have to remove the panels and look for a device similar to what I have found online. If that were the case I think a smaller portable genny would probably work.
  7. d_rek

    d_rek Member

    Thanks for the replies. I picked up a 10k running/8k starting generac today to combat the “ice storm” were currently getting in Michigan. It’s more than enough for my main, which I can power, and has everything but our geo and hot water tanks on.

    Currently I have no way to feed my geo panel so Until I have a transfer put in I won’t be using it during power outages anyway. I guess I’ll cross that bridge when I get there. In the meantime the house holds heat well enough and I think a couple space heaters would hold us for a day or two until power is restored.
  8. mrpac

    mrpac Member

    I didnt want to go down the whole house generator route either, and decided upon another solution.

    A Pellet Stove. (Burns wood pellets)

    The unit that I purchased is central in the house, heats up to 2200 sq feet, and runs on 1 amp of voltage. This means I can hopefully survive if the power goes out, or if the geo craps out while technicians are requested. A little bit more money invested, but in my opinion supplement s the GEO in a time of need.

    It's always good to have options.

  9. d_rek

    d_rek Member

    Definitely not a bad idea. I considered a wood burning stove for supplemental heat when we built but decided I didn't want the hassle of locating, cutting, and hauling cord wood. Pellet stove would be a little more managable as far as managing fuel source goes. However we are also rarely without power for more than a 1 or 2 days. 3 days seems to be the max. when it goes out (knock on wood).
  10. Eric Kurtz

    Eric Kurtz Member

    Locked Rotor Amps is not the same as starting Amps. That's why there is start and/or run capacitors on every compressor. I start my 3 T geothermal unit with a similar size generator (30 amp breaker) In theory, there may be an extremely small fraction of a second where current draw spikes above 30A but it is no problem whatsoever. The number to look at is RLA which is only 15A. And when running is probably only pulling 10 to 12A.

    But it is absolutely correct that you do not want aux to come on. That will overload your generator.

    As long as the generator breaker is rated for at least as much as the breaker powering the HP (not aux strips) you will be fine.

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