Can anyone help me? I believe my vertical ground loops were installed with the wrong size pipes. I am looking for an expert to confirm this and give me an idea how much efficiency I’m loosing by this mistake.

 
I have 3 wells hooked up in parallel with reverse return, however they only used one size pipe for loops and headers/manifolds (2 ¼” pipe). The installer said they usually use 1” pipes for the well, but bigger is better and easier to use all one size. I questioned him and he kind of blew me off. The system has never worked right and the installers can’t seem to figure out why.

 
Does anyone know how I can show on paper how much % loss I get because of the inadequate manifolds. I assume since they are all the same size that I am getting a pressure drop on each well. Any help would be appreciated. Thank you!!

 

Tim

 

Hi, I am assuming that "2 1/4" is OD and what you really have is 2" pipe. This is quite strange.
Where do you live?
How deep are the wells?
How big is your heat pump?
How many square feet is your house?
What brand heat pump do you have?
When you say "it has never worked right" what is it doing or not doing?
How many gpm's are circulating through the loop when the heat pump is working?
How long has it been installed?
What is the loop temp coming out of the ground?
What is the loop temp coming out of the heat pump?
I find it really hard to believe that anybody could put a 2" loop in the ground!!
2" pipe would cause some problems:
The wall thickness is probably double what 1" pipe is which would inhibit heat transfer.
Also with 2" pipe the velocity through each verticle loop is going to be too slow to give turbulent flow.


You said "how much % loss I get because of the inadequate manifolds" the problem here is not the manifolds, but the loop size.


With three loops your system should have had 1 1/4 manifolds and home runs, with 3/4 or 1" loops max.

Sorry that some one gave you such an odd ball system.

I know I have asked a lot of questions. If you can answer all of these, maybe we can make some sense out this mess.

geodean, Thank you so much for answering!!
I just grabbed a piece of the pipe and realized I made a mistake it is 1 1/4"ID pipe (1 5/8" OD), but still, they used the same size for both manifolds and loops. Off the top of my head I know they are 250' deep wells (3 of them 15 foot apart), and the unit is a Water Furnace, 3000 sq ft. house. I began to suspect the field when one service guy was surprised at how fast the loop temperature decreased in the Winter, went the unit was turned on. I'll place some thermometers and get decent data, and I'll get the rest of the answers and post it in an organized fashion, so not to waste your time. thank you very much for taking the time to help!!
Tim

tl3659,

I do not have an answer for you. But I can tell you that an IGSHPA certified loop installer (Well Driller) in my area of South East PA proposed 3 loops for me ( 250 ft deep) with 1 1/4" PE pipes or 2 loops 375 ft deep with 1" pipes. Why the difference in pipe diameter for different depth loops I do not know at this time but hope to find out. I am looking at a 5 ton system so the situation is very similar to yours. Climatemaster GeoDesign suggested using 1" pipes for total of 680 ft. The loop depth was suggested at 150 ft as per Climatemaster's recommendations.

Geodean,
Look forward to your response to tl3659's questions. Also, would you know the reason for a installer recommending different diameter pipes depending on the number and depth of loops used.

I agree with your reasoning that thicker walled pipes will reduce heat transfer coefficient and hence reduce heat transfer. On the other hand higher diameter pipes reduce pressure drops and increase effective heat transfer area. I also believe that at 10 Gallons/min through either pipe ( 1" or 1 1/4" ) flow would be in the turbulent regime. I will check on that later today.

Good thread.

Regards,

VK

Oops! Made a mistake. The above note from me should read as follows:

"But I can tell you that an IGSHPA certified loop installer (Well Driller) in my area of South East PA proposed 3 loops for me ( 250 ft deep) with 1 " PE pipes or 2 loops 375 ft deep with 1 1/4" pipes."

Sorry. I should have read the note carefully before posting.

VK

In both proposals above there is 1500' of pipe in the ground.  The reason the 2 hole version is 1 1/4'  is to manage  the pressure drop.

A five ton system would need 15 gpm flow.  If you have three 1" loops, then you have 5gpm per loop.   With a 250' bore hole the pressure drop for each loop would be about 8 ft of head.   If you switch to two 1" loops 375 deep, then you have 7.5 gpm per loop and the pressure drop per loop jumps to 22 ft of head.  If you increase the two 375' deep loops to 1 1/4 pipe then the pressure drop reduces to 7 ft of head, 1/3 third of the pressure drop for 1" loops.

My concerns about thicker wall pipe and non turbulent flow were in reference to 2" pipe being used for the verticle pipe.  Since we now know that the loops are 1 1/4, wall thickness and turbulent flow are no longer factors.

With 20% methanol and loop temp of 25°,  1" pipe needs 3.1 gpm and 1 1/4" pipe needs 3.9 gpm to achieve turbulent flow.

Geodean,

Thanks for your input. Your note clarifys a lot. Nevertheless, I intend to calculate the over all heat transfer coefficients for different geothermal pipes and see what makes sense, once I have some free time - I am a nerdy chemical engineer.

My gut feeling is that the pipe diameter may not be the cause for TL's problems. It could be due to poor contact of the geoloops with the ground - poor grouting maybe or something else. Could there be a leak in the loop?

Geodean,
Could you also please tell us what Geo systems you install or think highly of. I had requested information on a HydroDelta heat pump in a recent post, but alas I did not get any input. I am most probably going to go with the contractor that has quoted a ClimateMaster system.

Best regards,

VK

I am fairly certain that pipe diameter of the loops is not an issue for the OP of this thread. The header pipes might be a problem. Once we get the answers to the questions that I posted we can start to pin point the problem. A leak in the loop would only be an issue if the loop pumps sucked air and quit pumping through the loop.

I would go with what ever heat pump your installer is using. He has to service and warrant the unit. Climate Master makes a good heat pump.

Getting back to the original question are the headers and loop pipe sizes the source of any mal-performance of the system?

When designing the header system the primary concern is the pressure drop for each header segment. In the parallel flow arrangement, the first supply header pipe carries the total volume for all loops. As each loop is supplied, the flow rate to the next supply segment is reduced by one loops worth of flow. A well designed header system should have roughly 4' of head loss per 100' of pipe length.  In larger systems, this is very important to reduce pumping power costs. However, for a small 3 borehole system, using 1 1/4" inch pipe for the main header is not a huge problem. The impact is a small increase in pumping power.

More important to the system operation is the actual flow rate being achieved through each loop. As long as the flow is within the turbulent flow regime, there should be good heat transfer between the circulating fluid and the pipe wall. Also important to the heat transfer is the proper grouting outside the pipe. If the loops were not grouted properly there could be air spaces between the pipe and the soil. The air spaces dramatically impede the system performance.

Although not normally addressed in residential systems, the thermal conductivity of the soil has a significant impact on the system performance. Soil conductivity can triple the amount of loop length required to meet a given system load. It is possible that this installation is in low conductivity soil. Due to the high cost for a thermal conductivity test (~$4000-$5000), it is often wise to simply investment in more holes. However, if there is a concern with the performance of an existing system, it is possible to determine the ground thermal conductivity by measuring the flow rate, supply temperature, and return temperature over an extended period of time. Thermal modeling software can then be tuned to match the system performance and thus determine what ground thermal conductivity would yield the same performance.

It is important to perform basic troubleshooting on the system prior to examining the detailed performance but it is possible to model virtually any system design to determine the impact of improper design or installation.

I hope this adds to the discussion,

Jim Bererton, P. Eng.
Manna Solutions Ltd.
[email protected]

The initial drop in loop temperature when the system is turned on in winter is caused by the circulating fluid cooling down quickly. After the initial transient, the ground temperature will drive the loop temperature. It is for this reason that the first 10-15 hours of thermal response test data is discarded when determine ground thermal conductivity. So the fact that the fluid temperature dropped quickly when the system was turned on does not point to a problem with the ground field. Further investigation of the system flow rates and temperatures will determine where the problem lies. Performance curves are available from the manufacturer. Using the flow rate and inlet and outlet temperatures on the ground side of the heat pump, the design delivered heating/cooling temperature can be read from the table. This will determine if the heat pump itself is the problem or if the problem is in the ground field.

FYI,

Jim Bererton, P. Eng.
Manna Solutions Ltd.
[email protected]