Where's the primary electric consumption in a geothermal system?

Discussion in 'General Discussions' started by BlueHawk, Jan 25, 2020.

  1. SShaw

    SShaw Member

    I made measurements using the virtual AID tool at three compressor speeds, each with two fan speeds. In each case the total power and COP is slightly better using the higher fan speed. The small upstairs zone was off, so the ductwork was a little more restrictive than it would be if both zones were calling for heat.

  2. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Your math does not add to calculate the COP. The pumping power does not add to the heat capacity which ends up in the house. It stays in the loop.

    In addition, you need to consider the the "hunting expansion valve". The valve is controlled by the board, but is reactive, not proactive. The temp sensors have an inertia to keep up with the fluctuating valve. so the LWT is fluctuating, by 1F, which is 20%. If you take a whole hour, with 360 measurements, that evens out. But a single instantaneous measure, you can be significantly off.
    Last edited: Mar 3, 2020
  3. SShaw

    SShaw Member

    Thanks. I double-checked my math and I had incorrectly included the pumping power in the heating capacity. The loop water cools the pump and the pump is cold to the touch, so clearly the pump is not radiating heat into the house.

    The corrected table is below. It doesn't change much because the pumping power is low relative to the total.


    For each measurement, I allowed the system to run at the same state for ~10 minutes to let the values stabilize. If it's necessary to average 360 measurements, then what's a practical way to measure and optimize the system? Seems like averaging 360 measurements would be impractical to do with an AID tool.
  4. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    take it down to stage 3 and repeat the measurements. Systems run less than 35% in stage 6 or above. Your fan power should go way down, same with your pumping power.
  5. SShaw

    SShaw Member

    I'll take some more measurements this weekend.
  6. SShaw

    SShaw Member

    I took additional measurements today at compressor speeds 2 and 6. With Intellizone2 and only one zone active, in heating mode my system runs at C2 most of the time and will upstage to C6 and C8. The two fan speeds tested correspond to fan speeds used by Intellizone2 when the fans settings for Low/High are either 2/7 or 3/9.


    The blower wattage reported by Symphony and the AID tool seems inaccurate at the lower fan speeds. The system reports 47W or 48W for speeds 1-4. I ordered a clamp power meter that measures amps and watts. I will try that when it arrives to see if I can get a better measure of fan power.
  7. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    We usually see the opposite. We see a savings with lower settings for the blower and the pump. While the compressor power increases, the savings of the lower blower and pumping settings outpace the increased compressor energy usage. Plus it also significantly increases comfort.
  8. SShaw

    SShaw Member

    I don't know why my system would be different. C2/F5 is substantially higher power than C2/F4, but C2/F4 seems to be the sweet spot.

    I'll see what I get with the power meter.
  9. SShaw

    SShaw Member

    I took some measurements of the fan wattage with a power meter. The meter has a wireless interface, so I was able to take measurements with the meter inside the closed fan compartment. I measured with only Zone1 open and with both Zone1 and Zone2 open. As expected, the power was slightly more with only Zone1 open, due to the increased static pressure in the supply ducts.

    Except for fan speed 4, the fan wattage measured with the meter is lower than reported by Symphony. The meter readings seem more believable to me, since Symphony never reports fan wattage below 47W. Either my Symphony current transducer is bad, has insufficient resolution to measure below 47W, or Waterfurnace is adding something to the fan reading to account for circuit board power, etc.

    If I use the new fan wattage values with the old compressor and pump wattage reported by the virtual AID Tool, the result still shows a slightly better COP with the higher fan speed.

  10. gsmith22

    gsmith22 Member Forum Leader

    fantastic data. thank you for all that work
    SShaw likes this.

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