North Carolina Waterfurnace Woes

Discussion in 'Maintenance and Troubleshooting' started by Mark Dixon, Jan 30, 2019.

  1. Mark Dixon

    Mark Dixon New Member

    I am having ongoing problems with my split system (info on system below). My winter time settings for heat are 64F overnight and 68F during the day using a programmable thermostat. When it's above about 40F, there's never a problem.

    When the temperature drops overnight to less than 40F, we have been waking up to aux heat, air handler running on high, and the compressor not running. No faults are shown on the door or inside on the Comfort Alert Monitor. The compressor starts right back up on its own after a while (never know how long it has been off), and even started up while I had the door open to check codes the first time this all started.

    After 3 days of this, I changed the thermostat setting to be "less aggressive" in its recovery so the aux heat would not come on so quickly. Today we woke up to the house at 66F, air handler running on high, and the compressor not running. Again, no faults are shown on the door or inside on the Comfort Alert Monitor. Thermostat was calling for heat to be running ("Heat On" displayed).

    The temperature in the garage, where the heat pump is located, never got below 35F (keep a small heater out there for some items that need to stay above freezing).

    Tonight the low is going to be around 30F. I've changed the night time set back to 66F to see how it does, still on the "less aggressive" recovery setting.

    Heat pump covers the 1st floor only, 1100 sqft. Filter is new, standard type, 20x20.
    Heat pump: Waterfurnace Envision Series NDZ026A11AC split unit (located in garage)
    Desuperheat feature set to ON for hot water
    Freeze detection set for 15F (DIP SW 2-2)
    Air Handler: Trane 4TEE3F31B1000BA (located in a closet inside the house)
    Closed Ground Loop (4 'wells'), shared with a single stage Waterfurnace 2 ton split system for upstairs
    Thermostat: Trane TCONT800
  2. Tamar

    Tamar Member Forum Leader

    Try just leaving it at 66 and leaving it until you get up, then bump it up 1 degree at a time if needed (I'm just a homeowner, so take this for what it's worth--but geo systems perform better without setbacks).
  3. Mark Dixon

    Mark Dixon New Member

    After having the setback changed to 66F instead of 64F, and with temperatures over the last 2 nights around freezing, and the thermostat set at its less aggressive rovery, there were no problems at all.

    Tamar, thanks for the advice. I'm definitely starting to see what you're talking about.

    Since the new setup is working, I'm not going to fuss with it. But I'm still hoping someone out there can tell me what might be the problem.
  4. ChrisJ

    ChrisJ Active Member Forum Leader

    I continue to hear of problems with air handlers and aux heat. Almost always the mention of outdoor temp is mentioned.

    Seems like a control problem, Looking into how the tstat handles aux is where I would start.

    Outdoor temp doesn't matter here, if there was an outdoor unit, maybe.

    Just reread that. Duel fuel set ups shut off the compressor because the air is too hot coming from a fossil burner. Might be a setting in the tstat that relates to thhat kind of aux heat.
  5. Tamar

    Tamar Member Forum Leader

    Again, I'm no expert, but it might be that your thermostat is set to switch over to auxiliary heat and turn the geo off if there has been a certain amount of time when the system has not been able to meet the call for heat. Do you think that would explain the behavior you're seeing? I once had an engineer recommend that my system be set up to turn off geo and only use aux heat if the EWT was below 35 degrees.

    Today in MN my geo is happily plugging along with an EWT of 29. If that engineer's advice had been followed, I would've been in auxiliary heat only for most of the past month.
    Last edited: Feb 1, 2019
  6. nc73

    nc73 Member Forum Leader

    That was no engineer. Turn off geo below 35, that's funny.
  7. Tamar

    Tamar Member Forum Leader

    It was an engineer hired by my first installer to try to convince me that the way to fix the botched job was via controls and relying more on back-up boiler.
  8. Mark Dixon

    Mark Dixon New Member

    Tamar and ChrisJ, thanks for the replies. I can't find any specific setting in the TCONT800 thermostat for aux heat. The only thing was the recovery setting for how aggressive it is, which I set to the less aggressive one. I've stayed with the 2 degree setback at night and the problem hasn't repeated. I'm going to drop to a 4 degree setback again to see if it does repeat, and see if there is a code flashing in the compressor unit that I may have missed before. I'll post again when it happens.
  9. geoxne

    geoxne Active Member Forum Leader

    I am not familiar with your TCONT800 thermostat or its available settings to control aux heat. Some thermostats just do not handle aux heat the way it should for your installation.
    It is possible your HP is experiencing performance issues due to ambient temperatures below 45F.

  10. Mark Dixon

    Mark Dixon New Member

    Does the "ambient" temperature listed refer to the temperature at the heat pump? If so, I may be building a closet around my system and ducting a small amount of heat to it.
  11. geoxne

    geoxne Active Member Forum Leader

    I would make sure that low ambient air temperature is the problem before you start building a closet. You could temporarily heat the garage to normal temperatures to see if it makes a difference first.

    It is possible your thermostat is calling for aux heat before it is needed. Or even shutting the HP off during an aux heat call (Dual Fuel setup?). Again I am not familiar with your thermostat. Some thermostats just don't handle aux heat efficiently depending on your system capabilities and available thermostat settings.

    It is possible your HP system is undersized and requires aux heat to maintain temperture.

    The heat of extraction should be calculated and compared to published performance capacity tables for your unit (within 10%) to confirm there is no problem with the refrigerant circuit. This could be done with the garage cold and again when heated to see if there is a difference.
  12. Mark Dixon

    Mark Dixon New Member

    We haven't had any more sub 35F days, and none in the forecast. Even then, I don't have the means to heat the garage that much. If temperatures do drop again, I can fashion a tent around the heat pump with tarps and use a small space heater.
    I dug into the thermostat settings a little more (It's actually a TCONT802a which is for multi-stage heat pumps). It is set up for a 3 heat/2 cool heat pump with aux heat.
    I think you're correct and that it is calling for aux heat too soon during the 'recovery period' because it was set too aggressively. The installation manual appears to say the heat pump stays on with aux heat. But again, I found the heat pump off with no fault code. I'm hoping it happens again so I can verify there is no fault code and I just missed it before.
    My 1st floor is 1100 sqft . The ratings table for my system shows 19500 btu/hr at full capacity with entering water temperature (EWT) of 32F. The EWT was about 50F on the days I had issues. We've got a very high water table in my area (Coastal NC). I don't know what the actual output of the system is in heating mode with EWT of 50F, but it should be well above the rated value. The installer did a calculation based on area, rooms, flow rates, sun exposure, and said the NDX026 would be more than adequate for the first floor.
    The specification manual has the calculations for heat extraction. I'll run those over the next couple evenings and see what I can come up with.

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