North Carolina Am I short cycling?

Discussion in 'Maintenance and Troubleshooting' started by Skyecat, Feb 16, 2021.

  1. Skyecat

    Skyecat New Member

    I have a water source heat pump that runs on a closed loop in a residential high rise. The system is 2 tons. The water is heated by a boiler in winter and cooled by a cooling tower in summer. Currently it is in the 30's outside and the supply temperature of the water is 70 degrees.

    I have an Ecobee 4 thermostat that is set to 70 degrees with a .5 threshold because I really don't like wide temperature swings. I do not have aux heat, so there is no heat strip coming on.

    So here is my problem, if it is a problem.

    The unit is satisfying the thermostat in 5 minutes to maintain 70. Then it stays off for 15 minutes before it comes on again. Is this short cycling? Im concerned that the compressor is not being allowed to run long enough.

    My only options seem to be to increase the threshold, which I am not really thrilled to do, or change the ECM blower speed (within reason) to reduce CFM and heat the house slower (maybe). One consequence of the short run times is the bedroom that is at the very end of the duct work is not heating enough, and a wider threshold I think would let this room cool off even more before the heat kicks in.

    Any thoughts on this?

  2. gsmith22

    gsmith22 Active Member Forum Leader

    i would think that the compressor would barely have to do any work given the high incoming water temp. so its likely that it does in fact run very briefly like you indicate. You probably need to zone the system (or possibly move thermostat). May want to check into airflow too as its possible the far bedroom sees little airflow even when the system is running. I don't know how the duct work is configured but better systems will have dampers that can be adjusted to reduce air flow to the closest rooms and move more air further downstream. The symptom of this issue is probably something like room closest to unit is really hot and one furthest away is really cool (during heating - reverse for cooling). Maybe have the unit fan on constantly (instead of auto with heat) to better distribute the air between rooms?
  3. SShaw

    SShaw Active Member Forum Leader

    You could try setting the system to run the fan continuously. This should help even the temperature throughout the space. Set the fan back to Auto in the summer though, as it will reduce the ability of the AC to dehumidify.
  4. Skyecat

    Skyecat New Member

    I can add a remote sensor to that room so the thermostat can generate an average temperature and run accordingly. My biggest concern is the compressor run times. If 5 minutes on time is not a concern then I can concentrate on air flow.

    Here is a graph of the last 24 hours. Each small block is 5 minutes of run time. Larger blocks are longer.

    Attached Files:

    Last edited: Feb 16, 2021
  5. Skyecat

    Skyecat New Member

    So I added sensors to the living room and the bedroom at the end of the duct run. The temperature in the condo is more comfortable now, but I did have to lower my temperature setting because the colder bedroom calls for heat more. Still the compressor only runs for 5 minutes. But I have a new question, starting a new thread on that.

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