GeoThermal Closed-Loop Vertical Wells

It depends on the flow rate and the pipe size(s). Given the 15°ΔT, I would guess that parallel is considerably better in this case. (Only a guess, though.)

It would be in parallel. Never ever heard of it being done in series - that is one well feeding the next to the next.

1) pressure drop considerations

2) heat exchange considerations - the longer the run the less the delta T

You do have to insure the 'right' amount of flow to each well - probably by temp in vs temp out.

I agree with russ123. Parallel makes sense to me. Once you've taken cold water out of the ground, sending it back into the ground is not going to make it significantly colder. (Unless you had a huge ΔT and the heat exchange rate was poor; but given what you said, that seems unlikely.)

One of my reasons for concern is that the path of least resistance is the 60 foot well. As in electricity, which is my area, there would or should be about double the flow of amperage/water through the path with the lower resistance. Thoughts about that?

You don't have 140 feet of head to overcome, just the resistance to flow depending on pipe size and fluid velocity.

Gravity pulls the water down the pipe and cancels the need for additional power to push it back up the pipe, except for friction losses.

Beat me to it. I though about that on my way back from the store. Evens everything out.

Cheers.

Now you're seeing it the way I saw it. It would have been the thing to do but it is a little late now that all the wells and piping are connected and buried 5 feet deep. This was all done 6 months ago and has bugged me since.

As long as the system performs as it should I'm not going to worry about it.

Thanks for all the comments and advise.

What you are looking for is balanced temperature - balanced flow is secondary.

Most domestic ground source heat pumps are installed in series as you first thought. It is usually when you are into more commercial applications such as schools, etc that you will see parallel systems. I have a link to the advantages and disadvantages of either series or parallel installation. The biggest difference is in making sure the parallel system is balanced properly. Your system as installed seems to work just fine and I wouldn't fret over not having a series system.

I have seen several hundred domestic systems and they were all in series, but that may be a local contractor preference. I know of at least two schools and they are in parallel. Another advantage with parallel (I am not sure if this is mentioned in the link) is the ability to add or subtract a section depending on the demand.

The only reason to go to series with wells is if there is not adequate heat transfer in a single well (pass).

In series the last well is going to be contributing very, very little!

Pressure drop in series would be greater - so build an energy saving system just to waste pressure drop which is energy?

You need to be able to monitor the temperature at the outlet of each well and need to be able to balance them (valves in the line). If the contractor didn't provide this then he is just taking a shot in the dark. Any obstruction in a pipe would cause the entire system to function at less than design parameters.

For loop design please see a pdf file (bing it) -

GROUND-COUPLING WITH WATER SOURCE HEAT PUMPS
Steve Kavanaugh
The University of Alabama

Tuscaloosa, Alabama

Russ

Russ, you mentioned a pdf file but no name or link. Please post again with the file or link.

1) GROUND-COUPLING WITH WATER SOURCE HEAT PUMPS

http://www.cres.gr/kape/pdf/geotherm/7.pdf

2) AN INFORMATION SURVIVAL KIT
FOR THE PROSPECTIVE

GEOTHERMAL HEAT PUMP OWNER

http://absolute-comfort.net/articles/GeothermalSurvivalGuide.pdf

3) Phil Rawlings University of Oklahoma

http://www.igshpa.okstate.edu/pdf_files/geo_outlook/GO_2009_Q3.pdf

All three have multiple documents on line concerning GSHP

I was wondering when someone was going to say the obvious, about balancing valves.

Both parallel and series systems are used for geo thermal. Geology of the area is the driving factor. Parallel systems should have one end of each loop into the building, shed, whatever. Balancing valves on all the loops can than set so that the best delta T is achieved. This also allows for future adjustment's as the the ground around the loops settle and the system begins to age.

To date

valved systems prove most inefficient as a worst loop dictates the balacing of all the others to the worst condition, so a reverse-return free-style even to 10% differentials in flows is acceptable .

Now the most efficient systems are over 24 tons per pump horsepower.

Cost and competition of a free-er market drives the looper's to just install a little more plastic per spec's of say a minimal temperature to use per a gpm per a condition... without circuit seters , either, as pumps can be ordered in units or for pairs of units,with speed and VFD selection to have a most variable flow for maximum efficiency, ie.) many of the very lowest cost schools operating at the GTHP of lowest costs per sq ft per school year of say hydro-Temp Corp of AR or Climate Master/ Carrier. Mechanical rooms have no pumps nor costly electrical "motor savers" switching devices.

Ashrae and others post maximums of flows in particular pipe diameters, but even under reynolds numbers in the contact-end-loops is fine when the PE is not perfectly smooth within the tubing and causes turbulence especially with 3/4" working very well at under 2gpm per circuit for instance. (knowing headers are built for purging, once, or once again in 5ft TDH at pump inlets, nearer-pressure-less designs, auto-purged "T" -off air separation, not requiring separate air splitter devices if those T's are large enough for flows under 3.1/3 feet per second, - simple T's receiving loop-field flows before the pump inlet do all a necessary purging to a small reservoir with a pin hole vent, 5 to 6 ft TDH above the pump inlet.)

if the contractor put a reducer on the pipe in the 60 foot well you are ok. otherwise all of your flow will try to go through the path of least resistance.... 60 foot well.

That "all the flow will try to go through the path of least resistance" is sort of a cliché, and a misconception. In wiring and piping networks alike, when there are parallel paths, the flows in each will be in inverse proportion to the resistance of each; not all in one path.

call the manufactuer and tell them you are joe shmo pe,phd and tell him you are thinking of specing out his company's system.let him tell you and send you all the info.i bet you could get him to come in for a lunch time seminar and get a free lunch for the boys.If i called and they wouldnt give me the info i requested when they were putting it in they would be removing it the same day. i would call it a safety issue.

There is a wealth of information about GSHP systems in the net.

The fellow and university I mentioned previously

Kevin Rafferty at Klamath Falls, OR Geo Heat Center

Phil Rawlings at the University of Oklahoma

Nothing gets a manufactures attention more, than dangling potential sales in front of them. I especially like the idea of a free lunch.

Agree.

I have a 5t geothermal heat pump at home with 6 parallel loops of 500' each.

I installed the manifolds in the mechanical room.

I could isolate any circuit if a leak would develop.

Regards,

On any heat exchanger, you always want the hottest water contacting the coldest water because the greater the differential temp, the greater the heat flow from hot to cold.In series, you are sending a lower differential temp to the next well,which will not absorb as much heat is if it were colder.So parallel seems to be the most efficient method if the delta temperatures are maximized by adjusting flow accordingly to compensate for well depth.

There is a patented methods of drilling the well on a certain angle, and inserting a "slinky" coil of pipe.The angle is such that the heat rising from the lower coils does not affect the coils above as it would if the coils were installed vertically.

Maybe a patented method but has anyone put it to use? You can patent most anything if you have the money - has nothing to do with an idea being usable.

Sounds totally impractical to me. Trying to get a slinky made of 1'' HDPE down a well is next to impossible.

Russ

It also wouldn't work very well, because heat would conduct easily to the relatively adjacent coils.

I have read about that system. Does it involve inserting a prefabricated spiral down a large diameter bore whole? This system has it's advantage's as it would reduce the number of holes required. The geology of where it is going in is still the deciding factor of what method to use if it can be done at all. In Ontario Canada, as soon as we encounter area called the Canadian Shield (mainly thin soil over Granite that protrudes everywhere. Drilling in not a cost effective option most of the time. Fortunately there are lots of ponds, lakes, streams, etc. for alternative ideas.