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Old 01-18-2010, 09:56 AM   #1
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New Geothermal Heat Pump/Thermostat Problems

For the past month I have been trying to figure out why my Climatemaster TTS 5 ton split system has not operated up to expectations, or specs.

We were happy with the performance when we turned it on back in mid October and up until the cold snap before Christmas. Something happened and the system ran more and the consumption more than doubled. In wanting to track efficiency, I check my electric meter every morning and record the reading and outside temp.

Last Friday I had a tech come to the house and we spent two hours checking refrigerant pressures, loop temp. & pressures and air temps. Although not happy, we called it a day when we got a delta T of 23 F ( 67 & 90) at the vent and a delta T of 3.5 deg through the water coil. The tech did notice that the loop ( 5 200' wells) dropped 4 deg. while we were running the compressor in 2nd stage.

My unit concerns are the output air temp, which varies from 82-90, is less than the 30-36 deg. rise in specs and long run times. This brings up my concern about the Honeywell TH8320U thermostat that appears to malfunctioning.

I should add here that my former heating system was a propane fired Polaris water heater with coil in duct downstream of air handler. I left it in place for aux. heat.

Saturday morning the house was up to the set temp. of 68 deg. at 6:00AM and the unit cycled off. A short time later it came on and continued to run for over an hour even though the thermostat indicated it was satisfied. I turned the system off for a few minutes and then back on. It cycled at 3 CPH as programmed until early evening when it started to cycle on about once per hour. I left it alone and would check during the night, when nature called. At 4:00 this morning I heard the compressor come on (it is under our bedroom floor) and go into second state and the blower speed increaded. I know this because is hums in 1st stage and the noise diminishes in stage 2. Checking the thermostat I found it in recovery mode. It ran well past 6:00 ( over 2 hours) and only brought the temp up to 66 from the 65 deg night-time set point.

I found that I had to "trick" the thermostat by programming electric aux. heat so that I could set a a lockout for the aux. heat thus providing a range where both heat pump and aux. heat would operate. This worked great Saturday morning, but not today. The system runs excessivly with outlet temps around 85 deg.

My question concerns the thermostat. Why would it cycle at 3 CPH, then change to a random cycle ( about once per hour) and why will it run the system continuously after the room temp reaches set point? I will add that it appears the 2nd stage heat takes too much heat from the coil and output temps drop.

I'm thinking I have a faulty thermostat and a performance problem by not getting the temp rise as per the specs.


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Old 01-18-2010, 06:03 PM   #2
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Sounds like your thermostat is working fine.
It has a rounding function. So it displays a rounded temp. But it responds to the actual temp by tenths of a degree.

So it is very common for that model to run a system for a while after it reads set temp(on some systems, a very long while).

I believe you'll find your problem is your Geo system is not installed right.
Namely your wells are probably not deep enough, or not enough wells at 200 foot each. or, may not be grouted properly.

Air temp rise should be measured at the air handler, not at registers. A good tech knows that.

You may have too much water flow through the coil, if your only getting a 3.5 difference between entering and leaving water temp. Do you know how many gallons per minute are going through the coil?

What was the entering water temp to the coil?


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Old 01-18-2010, 07:40 PM   #3
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We measured the air temp in the air handler and got readings within a degree or two as the registers that are located only a few feet away.

The EWT was 51.5 and LWT was 48. Not knowing any better, or thinking it through, I installed two pressure gauges in the fittings at the unit. They both register 25 PSI with the system off and read 38 PSI in and 33 PSI out when checked on Friday. My installation chart says that should be about 14 GPM. The temp chart says I should see 4-8 deg. temp drop across the coil at 15 GPM.

The tech expressed concern that the well company installed the manifolds in the trench and there is no positive way to determine if each loop has been totally purged. He suggested that the manifolds should have been installed above ground with valves on each loop. Before drilling I checked several sources and found the geology on the Eastern Shore to require 200' wells per ton.

We had to close the ball valves on the loop side of the pumps to get a temp change through the coil. I had done this earlier without having proper equipment to check the temp accurately. I think I got the flow off enough to cause the coil temp to drop enough to trigger a lock-out. This happened once that I know of.

I did not mention my concern that the operating pressures did not match the charts. We added 5 oz of refrigerant to get the high side pressure up to 320 PSI and the low side was operating at 75 PSI. The pressure chart in the manual calls for suction pressure to be 100-110. I'm wondering if this could be due to heat transfer in the coil or a mechanical problem with an expansion valve.
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geothermal , thermostat help

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