Ohio Should I replace my possibly-improperly-installed geothermal heat pump?

Discussion in 'General Discussions' started by madnah, Nov 14, 2019.

  1. madnah

    madnah New Member

    Hi all-

    Been reading this site for a while, great resource, finally have a question of my own.

    We built our home in 2010. It's 2 stories plus full finished basement, approximately 5000 sqft. 2x4 exterior walls with spray foam insulation, Anderson 400 series windows, R42 in the attic. Having been used to the high gas prices of the early 2000s, we took advantage of the tax credit to have a ClimateMaster Tranquility 27 (5T, closed loop) installed. I did not have the time, foresight, or know-how to supervise the install.

    It's been mostly trouble-free up until the last couple of years. The blower was replaced last summer (parts under warranty), and around the same time, we had an incident or two where the reversing valve would not switch to cooling. Thankfully the latter issue disappeared, because it would have been a very costly repair. This past summer, the unit went on high pressure lockout. I power cycled a couple of times to no avail. I called another company this time. He and the first technician both told me the same thing: the fly-by-night company that installed our unit was notorious for installing undersized loop fields. His diagnosis apparently corroborated this. Here are the notes from the call:

    Unit was locked out on a high pressure fault upon arrival. Reset power. System kicked on. Tested loop. PSI drop off 4 psi. Entering water is at 20 PSI. Leaving water is at 16 PSI. 12° temp split on loop. Entering water temp is 84° Leaving water temp is 96° Unit is moving 15 GPM. Both loop pumps are working correctly. Recommend adding water to the loop to bump up loop pressure. 80 uF compressor capacitor tested @ 78.9 uF. Pumped loop up. 56 PSI IN. 52 PSI OUT. 4 PSI drop. 84° IN. 96° OUT. 12° spilt. Unit is operating @ 15 GPM x 12° split x 485 brine = 87,300 BTUs This is way too high. Unit is rated @ 64,000 BTU. It appears there is an issue with the side of the loop in the ground. Unit is cooling with a temp drop of 23°.​

    He said it was possible to add more loop, with the associated cost and destruction of the yard.

    Adding on, we've had a cold snap these last few days. I've been watching my desktop electric meter, and it's been running on backup nearly the whole time. Our electric bill can reach $450 after a very cold month (appx. $300 of which is heat).

    I am all for efficiency, but wonder if it's performing even close to how it should. Plus, parts availability around here is terrible, and most companies aren't very familiar with them. Knowing what you all know, should I kick this thing to the curb? Is it costing me too much money to operate, and/or is it a ticking time bomb? It would not cause a financial hardship to have it replaced.

    Greatly appreciate any input.
  2. SShaw

    SShaw Member

    I'm not an HVAC expert, but the BTU figures don't necessarily indicate a problem to me. The 87,300 figure is the heat of rejection (HR), not the total cooling capacity (TC) of the unit. The TC would be the 64,000 BTU rating to which the tech referred. To arrive at the TC, you need to subtract the energy used by the system from the heat of rejection. According to the Tranquility 27 manual, the 5T unit uses 4.28 kW at full load. That's 4.28 x 3.413 = 14,600 BTU. So, if the tech's measurements are correct, your system is operating at 87,300 - 14,600 = 72,700 BTU. Also according to the manual, the system is rated at 63,000 BTU at 85 degree entering water temp. The difference is thus only 9,700 BTU. A 1.3 degree error in the tech's temperature measurement would account for that. The 15 GPM is correct for your unit. An entering water temperature of 85 degrees would also be typical for a properly designed loop field at the end of a cooling season. It sounds like you need to get someone who knows what they are doing to evaluate your system for you, but the specs you shared don't seem out of whack.
  3. wing

    wing Member

    It’s all about the (closed) loop

    Do you have the installation parameters of your closed loop system ? How many feet of pipe ? What size of pipe ? How many loops in parallel ? How deep was the loop buried ? Soil type and wetness at burial depth ? Where is your location ? Inside or outside header ? Anti freeze parameters ? What model pump circulates your closed loop.

    A diagram would extremely useful.
  4. madnah

    madnah New Member

    Unfortunately, I don't have any of this information. The company that installed it is long gone, and it wouldn't surprise me if they never did any of the research or calculations to begin with. I'm left trying to infer based on what I can measure and observe.
  5. madnah

    madnah New Member

    Late on the reply to this, but thanks so much for the detail. The tech quickly explained the math to me but I didn't want to waste his time trying to understand it. This gives me a lot more information and is somewhat of a reassurance.

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