underperforming geo system

We had a new geothermal system installed recently (completed May 2010). Entering our first heating season, I had been pretty happy with the operation. I drop the setpoint from 68 to 66 at night and when we leave for work. Until recently, the system had been very responsive and seemed to be performing well (achieving set point quickly and maintaining the set point.

Instead of repeating myself, I'm posting a property description of our setup from a previous post.

We have an old, converted stone schoolhouse with a newer, block construction wing. The School house has 2 foot thick stone walls and 11 foot ceilings and a crawlspace that had to be dug out for duct installation. About 6 years ago, the previous owner added a loft bedroom upstairs. The upstairs is roughly the same square footage as downstairs (20'x30'), but the volume is less than half (lower, peaked roof sloping down to kneewalls on both sides. The downstairs is served by 5 supplies and the upstairs is served by 2. There are 2 large returns downstairs and one medium sized return upstairs. The block wing is poorly insulated (for now) and has roughly the same square footage.​

Due to the wierd, unconnected layout, we have two 3T Waterfurnace envision units serving each of the two sections of the house. Over the last few days, outdoor temps have held between 25 and 35 degrees. And both units are running nearly constantly to maintain temperature. One of the two - the schoolhouse unit, is failing miserable. It's running in second stage constantly and only managing 65 degrees at a 68 setpoint (after 2+ hours at that setpoint). I have the auxiliary heat locked out down to 30 degree outside temp, but in my mind, it should never run at these kind of temperatures. In fact, I shouldn't be hitting 2nd stage, I think.

Both units share a loopfield with 900ft of vertical, hard rock bore with bentonite grout (reputable, highly recommended local loop installer with 20+ years of experience in the area). The inlet loop temp is 34 degrees and the outlet is 28 (measured today by an installer tech), which seems to be ridiculously low for a brand new system with 150' of hole per ton. The outlet air in the school house is around 79 degrees, which also seems way too low. At the time of testing, return air was 62 degrees. I guess these temperatures are directly related to the low loop temperatures. The wing is better, but still struggling a little and running all the time. It can reach and maintain temperature, however. The installer actually recommended a 2T unit over there, so it may be a little oversized. I went with 3T based on gut feeling and one other installer recommending 3T. The 3 quotes I got all agreed on 3T for the schoolhouse. Driller quotes (3) were all for 900 feet for 2 3T units.

So is my problem automatically with the loop field? Could this be explained by an undersized unit in the schoolhouse? If the unit is undersized and struggling to keep up and running constantly, would the loop temperature just keep falling?

I'm freaking out a little. Help me to understand!

thanks,
Kevin

 

Loop seems to be OK, appropiately size for this tonnage, also the temps do not concern me. Vertical loops tend to drop quicker, but also recover quicker. They simply do not have the surface area as a horizontal loop.
My biggest concern would be that the heatloss is off. Old buildings can be tricky and leak more than any "guestimate" will tell. Even a manual J depends on estimation of R-values and might not account for unknown leaks and air intrusions. Your installer should check the Heat Extraction and the other performance parameters.

 

I agree heat loss calc may be an issue. Loop temps seem OK especially given near continuous operation. Waterside Delta-T is OK

I wonder if the load calcs credited non-existent or planned insulation or perhaps assumed less infiltration than is the case

What jumps out at me is airside Delta-T. That should run around 25-30 in heating mode. 79*F Leaving air is, to me the smoking gun. 79-62 is just a 15 degree airside Delta-T, definitely a symptom.

Is that 62*F EAT a measurement at the unit? Is there a long lossy return duct that may be being chilled or inhaling some much colder unconditioned air?

 

Have you tried not using setback for the system. I also would tend to look at the load calc of the system. When that stone gets cold it stays cold. The temp split does not bother me as much as the equipment sizing. It is going to reduce in available BTU's as the temperature drops. You may need to raise your EH lockout for this system.

 

I missed the air delta. Was the unit running in 1st or 2nd stage when you had an air delta of 15 degrees? First stage should be at least at around 20 degrees, second at least at 25 degrees F. Since your loop appears to be within specs, you need to do the following in order to end the guesswork here.

1) Get the heat extraction for both units to see if they pull enough heat out of the ground.

2) If the air delta is at the unit, have the refrigerant charge checked. If the air delta is at the registers, check for leaks in the ductwork.

This should have been all part of the start up protocol. Do you have a copy of that? The technician checking out the units now should have answered those question.

 

It's cold in here...

Let me try to answer all your questions!

I think the tech may have measured the return air at a return duct which is about 4 feet directly below the thermostat. It is a pretty short run from there back to the unit - probably about 15 feet. All ductwork is brand spanking new. I can't vouch that it is completely air tight, but it should be pretty good. We recently (3 weeks ago) put 3 inches of sprayfoam under the entire floor and around the perimeter where an energy audit had found a lot of infiltration. We should be pretty darn tight, as old, drafty stone houses go. A very rough guess regarding square footage is about 1400 for the section of house served by this unit.

I have not tried running at a constant temp 24-7. That is what you mean by "no set back", right?

How do I get the "heat extraction" of both units? Is that something a tech is going to have to do? He looked at refrigerant charge (looks like 18psi?) - said this was normal.

I just went back to look at some of the design docs, and it seems like the system was designed with a whole house heat loss of 76,000 BTU/hr (72 degree design temp). I just got an email from the sales guy that says that it's "not impossible that you you need supplemental heat below 35 degrees." I almost want to laugh, but I'm kind of annoyed.

I'm looking at the GeoLink document for the 5T system (consisting of 3T and 2T units) that was initially proposed and it shows not needing aux heat until you get below 15 degrees for a total of 109 kWh ($9) per year! I thought with 6 tons, I should be doing even better. As it is, I am running full time in second stage and not able to make temp without aux heat when it is 30 degrees outside!

Thanks for the help, people!

 

Yes, try to run the house at a constant temperature 24-7.
Try to measure the temperature at the return air intake of the heatpump, and the return air output, usually we stick a needle thermometer through the flex connection of the ductwork.

Heatextraction: You need to get an idea of the flow of the water, usually by using a pressure gauge with a hollow needle and stick it into the p/t port. Let us know how much that pressure delta you have between ground water in and out.

72KBUT/H usually is a 5 ton load in your climate, six tons should not even go into 2nd stage. That heatloss is for both buildings, correct?


Web Energy Logger:
This is a link to a 3259 sqf house, built 1952, with a 91800 btu/h heatloss at 0 degrees. It has a 6 ton heatpump. The only thing which is off is the outside temperature, it is currently 19 degrees F outside, 16 degrees less than it shows (I need to place the sensor elsewhere). In the last 21 hours, it ran 13 hours in 1st stage (60%). It might help you to get an idea. Just for you as a reference.
No! Supplement heat should not come on in SE Pennsylvania anywhere below at least 20 degrees, actually less than that.

 

another thought

"72KBUT/H usually is a 5 ton load in your climate, six tons should not even go into 2nd stage. That heatloss is for both buildings, correct?"

Yes, 72,000 BTU/hr for both sides of the house (schoolhouse and addition) It's about 2600sf total. The house is leaky, but much tighter than when the system was installed.

that the sales guy and his colleagues had was that there might be air in the loop. Is this a possibility? How would I know if this is the case?

Thanks for posting that data logger link. Confirms that my system is performing really poorly compared with that one! I have pondered this kind of monitoring setup, but it seems like it would be pretty unwieldy with 2 systems on opposite sides of my house.

I'm interested in monitoring how much time I spend in Stage 1 vs. Stage 2, and how much time I use aux heat. Do any of the Waterfurnace thermostats do that? My system was supposed to come with Waterfurnace stats, but switched to Honeywell VisionPro IAQ during the install. While the programming is nice and easy, it doesn't seem to give me a lot of information about how the system is performing. It doesn't even say which Stage I'm operating in.

 

Most thermostats are this way.

 

Your loop appears to be fine, our vertical loops under load are at 34F EWT and around 28-29F LWT right now. You are putting our 6 degrees delta, which is right on target. If you have air in the loop, and you have a non-pressurized flow center, you can check it by taking the lid off. When the pumps turn on and the water level drops, it should not drop more than 2 inches. If it drops significantly more you have air in the loop. As I mentioned, giving the performance numbers, this is unlikely.

The WEL monitoring is pretty neat since it uses a 1 wire bus, you can run the wire from one house end to the other clip all the sensors on it, and then plug it into the WEL box. Connect that one to the internet, and you have all you need.

 

Air in Loop?

The design document I have (GeoLink) shows minimum average loop temperature at 31 degrees. That means something like 34 in and 28 out, right? It bothers me that my loop is hitting those temperatures when it is 30-35 degrees outside. I think a couple of you have said that the temperatures I'm seeing are normal, but it doesn't "feel" normal.

Nobody's really biting on the air-in-the-loop theory. I must have a pressurizeed loop, because I can't make sense of docjenser's statement below about taking the lid off the flow center. It's a packaged unit. The loop pumps on the two WF units are a little noisy, like they are pumping a mixture of water and a few bubbles, but I thought it would be normal to have a small amount of air in the loop. Is this normal?

Thanks for the help!

 

I know it doesn't feel normal

Our system had EWT below freezing most of the winter last year. That definately did not "feel" normal. But the house stayed warm. Our EWT is currently at 38, which "feels" low too, but with last years experience, I am not as concerned about it, even though it still feels that it is to low, to soon.

 

In a word...NO! There should not be any air in the loop.

Bergy

 

If you hear the fluid running there is air.

Air will stop FLOW. I do not like most geo piping because it does not address air. Pumping up the pressure in a loop system does not get rid of the "air", it just puts it in suspension in the fluid.

I do not like the "cheap" alcohol antifreeze's because they can make "air" in a system. They work, but they can make "air".

Geothermal heat transfer is all about FLOW. You have it or you do not.

I am never the lowest bidder.

 

Loop programs only deal with EWT. You add EWT and LWT together and average them.

When does the geo link program say you will hit those temps?

 

air in the loop?

Below 17 degrees!

I don't know what I'm hearing with the loop pump. Maybe I'm imagining air where there isn't any? Should the loop pump be virtually silent?

 

kclaus

My pair of loop pumps are silent. In order to "know" they are running I must put my hand on them and feel the tiny amount of vibration.

Absolutely silent.

Z

 

Well>>

I would have only used one pump.

 

Mark

LOL, would enjoy hearing from you by email sometime.

Its all water thru a pump now.

Merry Christmas

Z

 

Happy Holidays

To my dear freinds in Albaney.

I am mending, you will get your wish....

M