Washington DC Power spike at end of cycle

Discussion in 'Maintenance and Troubleshooting' started by KTfixit, Jun 30, 2020.

  1. KTfixit

    KTfixit New Member

    My Waterfurnace geothermal heatpump has been working fine for many years (500 foot vertical loop). I recently installed and had it connected to an emergency generator (Cummins natural gas unit that has load shedding capability). When the generator runs with the Geo system running, the generator load display shows less than half generator capacity. When the Geo system stops (thermostat satisfied), a power surge/spike shows on the display that appears to exceed the generator load capacity leading to it shed the Geo power supply. A time delay occurs before the can start up again.

    The generator installers thought the power surge was related to head pressure when the Geo system stopped. Does this sound like the cause and is there a suggestion to resolve the surge/spike?
     
  2. gsmith22

    gsmith22 Member

    I'm mostly interested in the outcome and not real sure of the problem because I have considered getting a generator but was weary of the size I would need to run two geo units. Probably need some more specs on the geo - what model WF heatpump do you have? single, double, or variable speed compressor? Does it have the soft start "intellistart" module? Generator size? Was an anmeter placed on the heat pump circuit to measure if there is an actual current spike to distinguish from some phantom thing that the generator thinks it sees? I wonder if there is a voltage spike when it turns off (since power/watts = volts*amps). Maybe a grounding issue? I'm shooting in the dark here but just some things that i would probably check out and/or you are going to be asked by others.
     
  3. KTfixit

    KTfixit New Member

    The WF heatpump is Envision Model NDV038A101CTL (dual capacity scroll compressor). Low capacity is 2/3rds of full capacity. Unit always starts in low. It has a variable speed ECM blower motor. Generator is Cummins RS20AC model C20N6HC rated 75 amp, 20kw with intelligent load management. An anmeter was not used, I'll try that.
     
  4. gsmith22

    gsmith22 Member

    if you don't find anything unusual happening with voltage or current on the power feed to the heat pumps, I'm thinking its something to do with the load shedding aspect of the generator. I'm not familiar with the inner workings of how that is accomplished but I did some google searching on generator load shedding for heat pumps and found a number of forum posts describing what you experienced traced back to the interaction between the load shedding monitoring the compressor power draw. Might want to start there and just generically search for generators powering heat pumps rather than a geothermal heat pump. I doubt it matters to the generator how the heat is exchanged so an air source heat pump or air conditioner is probably just as susceptible to your issue. I was hoping someone was going to pop on here and tell you how to solve this (thinking ahead for me too if I were to go this route) but unfortunately no one has responded yet.
     

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