North Carolina Horizontal Loops Temps Too High

Discussion in 'Maintenance and Troubleshooting' started by Neil Heuer, Sep 18, 2022.

  1. Neil Heuer

    Neil Heuer New Member

    Hey guys! I've posted here a little bit about my home. I've lived in it for about a year now and have some observations and concerns. Currently, I have a 3-ton and 2-ton WaterFurnace series 5 units in my home that the previous owner installed. Both units share the original horizontal closed loops that I know very little about (length and depth). I live in a pretty dense clay soil environment. The original guy who specified the loops and oversaw it said he did remember they went a "full bucket depth" meaning its 5 feet deep despite not needing that depth by code (again I don't know much about this if it's valid but the house is about 15 years old and peoples memory is foggy.

    My bill/consumption is higher here in South Charlotte NC than my home in SWFL (tropics) with 5 AC air cooled units. The house there was block vs this house which is ICF. Last Fall I installed open cell foam on the underside of the roof to seal the attic space and make it conditioned. The AC unit in the attic is no longer soaking wet all summer long and my bill was down year over year for the months of May and June, but July and August haven't been good.

    My loop temps are 99 entering and 109 leaving. I suspect I have a loop capacity issue - either too short or too shallow - not sure. Im running my AC units various times depending on outdoor temps but on the hottest days I'm running them for 21 hours and on average days 14 hours or so? The unit upstairs I believe is multi-stages. We set the thermostats to 72 upstairs and 71 main level. We don't believe the house is cool enough and humidity can be in the mid to high 50's on humid days and if I am lucky sits in the high 40's.

    I spoke briefly to the installing contractor and he was suggesting drilling vertical wells to replace the horizontal loops and add capacity. I don't think that's inexpensive and would require boring to get to the units in the garage. I considered replacing the upstairs unit with an air-cooled unit and then I might have less strain on my loops. I've been told, perhaps here, that to make sure there are no bubbles in the loop and the AC company assures me there are not - I'm not 100% sure.

    Anyway thanks for reading this much and any insight is greatly appreciated.
  2. SShaw

    SShaw Active Member Forum Leader

    It's not clear what problem you are trying to solve, and whether there's a problem at all.

    Standard design practice is to size the loop so the EWT maxes out at 90F at the end of the summer. The 5 Series documentation gives performance figures for EWT up to 120F, so it can operate fine with 99F incoming water, just slightly less efficiently. So, the 99F entering water temp isn't much of a problem. Certainly not something that would warrant replacing the unit.

    If you added the attic to the conditioned space and it wasn't considered when sizing the system, you would have increased the load compared to the design conditions, which would raise the EWT. It's also likely the design was based on the typical indoor temperature of 74-75. Setting the thermostat at 71-72 would also increase the load and raise the EWT.

    Running 14 hours on average and 21 hours on the hottest days doesn't indicate a problem either. I have a 7 Series, but I have a report that indicates a 5 Series should run 1773 hours per year in cooling. Assuming four months of cooling, that's an average of 14.8 hours per day.
  3. Neil Heuer

    Neil Heuer New Member

    well, the problem is my geothermal AC which is supposed to be super-efficient is consuming more power than 5 air-cooled units in the tropics.

    I have 100 degree incoming and 110 degree outgoing water now.

    Nothing was added after the fact. It is my understanding, that the capacity (tonnage) was increased slightly and a mini split was added to the TOP attic floor to reduce the load on the upstair unit.

    I guess the hours add up - I just don't see how 5 tons of cooling in this house vs 12 tons of air to air cooling can consume less power and be considered more efficient?
  4. SShaw

    SShaw Active Member Forum Leader

    Obviously, a properly functioning geothermal AC will use less energy than a conventional air source AC of the same size, under the same load. However, you need to consider that a geothermal AC isn't drastically more efficient than a modern air source AC. It's maybe 20-25% more efficient, so the savings won't be huge. Running with a 100F vs 90F entering water temp won't hurt anything, but for a 3T 5 Series in stage 2, it will cut your efficiency down from 15.6 to 13.3 EER, which will erase most of the difference in efficiency vs air source.

    If you think you have a problem, you should measure your geo unit's performance. It's simple to measure the power consumption of your geo unit and compare it to the specs in the docs on the Waterfurnace website. The procedure is in the installation manual, which is also on the website. Your unit is either operating within spec or it's not. If it's out of spec, have a tech figure out the problem. If it's in spec, look elsewhere in your home for excessive electricity usage.

    Also, the humidity readings you reported are normal. The standard recommendation for indoor comfort is 75F and 50% RH. This gives a dew point of 55F. The dew point represents the actual moisture content of the air (RH does not) and dew point is what you feel. For every degree you turn down the thermostat you will raise the indoor humidity by about 2%. If you are running at 71F, that same 55F dewpoint air will register 57% humidity, so your dew point should be around 55F.

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