Geothermal Heat Pump

[Golestan]

Hi,
I am doing a very basic study on costing (just a rough order of magnitude)for providing heating for a 6000 sq-ft. commercial building in North Texas area. We want to use ground source heat pumps and specifically the vertical well water as the thermal energy source. Can anyone provide info on:

1-Open loop vs closed loop systems
2-Aprrox. number or rule of thumb for wells per ton/heating
3-Approx costing
4-Any consultants/experts in the field I could contact

Thanks very much,

 

[atlas06]

I suggest you go to contractortalk.com.
Contractors have a better feel for costs.
This thread talks about geothermal, I had my two cents in tehre.

http://www.contractortalk.com/showthread.php?t=15954

 

[GMcD]

And make sure you design for a balanced energy load- if you use the closed loop geo-exchange system for "heating only" you will freeze the ground, and depending on soil conductivity, you may do it in the first year, or it may 4 years, but you'll lose system capacity pretty quick. You MUST have a relatively balanced energy load going into the ground system- reject heat into the ground from summer cooling and then suck heat out during the winter.

Direct ground water systems are problemetical- environmental concerns, legal access, water quality, etc. Stay with tried and true closed loop geo-exchange.

 

[atlas06]

GMcD
I looked into a study for an application a few years ago, the LCC showed a 15 year pay-back, but then again, I kinda used a lot of judgment in costs ($10,00 per foot of bore, 300 feet deep bores, one evey 400 SF, my rule of thumbs sort of, from various data collected here and there).
I do have a few questions:
What is the delta used for the geothermal loop when sizing the loop pump?
What is a good K factor that makes the gethermal viable?
Is there a gethermal map that you know of for the USA?

Golestan,
One thing you should not overlook is the tax breaks for gethermal in several states, and sometimes 0% financing in some areas.

Thank you

 

[Golestan]

The pump head is equal to the Delta P of the loop including all other equipment that flow passes through. An 8 ft. head in additional to all the frictional losses should be adequate. The system friction losses I think depends on the loop lenght mainly.

I am also looking for the Geothermal map of the US.

The conductivity of soil I am not sure of. However my thoughts were on making the well deep so the loop is well(completley) immersed in wet soil. Or most of. Is this the way it is done? Or the well is dry and loop is burried and sorrounded by soil?

Regards,

 

[GMcD]

Atlas06: Some answers- the delta T depends on the flow in the closed loop geo-exchange pipes. The flow must be high enough to be turbulent for good heat exchnage through the pipe walls to the soil - generally keep the pipe flow velocities above 3.5 fps. The delta T is then based on your soil conductivity and system capacities and the types of heat pumps you are running, but the general rule of thumb is a 5F min. to 10F max delta T.

A geothermal map of the USA isn't going to do much good- you need to know the specific soil conditions at the particular site, and those can vary widely even in the same city block. Wet soil is fine, good conductivity, bedrock is even better - you don't need to case the well in bedrock- cheaper that way.

In vertical borehole geo-exchange the tubes are generally encased in Bentonite inside the borehole so there is reasonably good contact from the tube to the borehole wall/soil interface.