Seeing Jever's post reminded me of a scheme I might want to try on my next subdivision phase.  Since I did not want to hijack Jever's thread, I post the following for your thoughts and comments:

As a residential subdivision developer, designer and building consultant in Auburn, Alabama, I see that being able to advertise the lots as geothermal ready, should really enhance the value of each lot. If the houses are not too far apart, I wonder if all of the wells should be in one common area and then shared or should each lot have its own set of wells. If each lot should have its own set of wells, then can they be placed in front of the lot building setback lines so they will not be in the way of future homes? Not knowing the size and heating requirements of future homes, it might be difficult to size the wells to take care of an unknown future load. If so, then more wells can be drilled now or later.  Drilling later will probably cost more per foot.
 
Has anyone done this? What would be the best way to plan this assuming each lot is an acre or under? My guess is that larger lots would definitely require their own set of wells unless trenching is deep enough for the climate.
 
I can picture a subdivision with a central park (common ground) that contains enough wells for the subdivision. Or in areas with good trenching soil and suitable climate, installing a steel water line maybe parallel to the city's steel water line, but to make this water line a closed loop with two taps (input and output) for each home's geothermal. A master pump may be needed to move the water along in the main line so that temperature stagnation does not occur.

Would a large diameter shared closed loop work for several homes?  Would city water added to the the shared closed loop have to be replaced every so often or have chemicals added to it like a swimming pool?

Sharing wells or closed loop would probably have to be dictated by the covenants and each lot's deed.  Otherwise, without full community support, this scheme could not be justified.  And everyone would have to pay a small maintenance fee to maintain the pump and pay for the energy to run it.  This is probably no different than everyone paying to irrigate the common areas.

There are definitely savings to be had by putting loops in at the same time as the house. But given that you want loops widely spaced, I don't see much advantage to centralized wells or loops.

Centralized electricity + heat recovery from a nat gas generator might be interesting. There are big economy of scale savings in co-generation.

Non heat pump geothermal (hot water from deep underground) may also have large economies of scale.

There are some communities that are built around a community loop. Then each home is billed every month for the heat exchanged to or from the loop. There are even companies that will pay for and install the loop. Some will even return the ownership of the loop to the community after enough revenue has been collected to pay for the initial cost.

The quickest way to send me packing for the door is HOA(home owners association). Here it allways means decision by commitee, begging for payment, and planning ad nauseam that 50% of the time never sees execution. I am an advocate for individual loop fields. Here we are allowed to drill in set backs, flood zones, wetlands, under the building, in drive ways.

I think trying to plan a load before the method or size of the home to be built would be a night mare. Pulling permits ahead of time and saying it is drill ready would be an option.
Eric

How are you going to back into the engineering for the loads? There is a development hear that deeded each lot a parcel in the common area to drill a water well for each house due to a weird septic plan. Something like that may serve your needs.
Eric

Eric,

That is a good idea.  I did not know that anyone had been doing things like this.  Otherwise, I would have to oversize the wells or loop to take care of bigger homes than expected.  I guess sharing the geothermal earth exchanger would work better for spec built subdivisions where the developer controls the size of the house and the method of heating.

I am a big fan of common loopfields for the same building with multiple heatpumps. However, for single house developments, there no way I would consider it. We are just doing a 35 house development, and all the houses have their own individual loop. Keep in mind that pumping requirement go up with length of header pipe to the loopfield. Plus redundancy. If god forbids something happens to the loop (just had a customer ram in the poles for a deck, hitting the header coming in the house) one system goes down, not 35.

One of the golden rules in geo is to keep it simple. A lean but mean 2-3 ton system for each house was the way to go for us. The driller came to terms with us. After drilling the first hole, he knew the geology was very easy. Quick in and out for him. Plus he knows he gets the other 34 easy jobs....

Alton

When I was in Europe studying Geothermal I saw a layout for a town where the geoexchange pipes were under the streets.

 

Another system not allowed in Colorado uses the domestic water as the closed loop.

Perhaps a storm drain retention pond could offer pond loops to minimize expense for those who wish to go geo.

Another system not allowed in Colorado uses the domestic water as the closed loop.

I guess most potable (domestic) water systems would be concerned about re-introducing water back to the city main in a closed loop system.  I wonder how dangerous it would be to place water back into the main after it has been through the heat pump heat exchanger.  Is there much of a chance that coils will leak refrigerant into the water system, say in 15 years?

I understand that some subdivisions in Florida have a separate water system that uses reclaimed (recycled) water for irrigation purposes.  Using reclaimed water (non-drinking) system for irrigation and geothermal might make good sense provided the water lines were buried deep enough.  As long as the water lines are not on top of the ground, then the water temperature should be better than ambient and thus more efficient than using air as the exchange medium.

Would each home need a circulating pump or would the pressure on the reclaimed water system be enough to pass the water through the heat exchanger in each home?

I am wondering now if a subdivision with a lake as a water source will work well with an OPEN loop for all the homes.  Can a separate water system to be used for irrigation and geothermal be justified for one home per acre in an area without rock being close to the surface.  My guess is that the loop would have to either contain a pump and a back up generator or a water tower to be reliable during outages or repairs.  The system would probably be more efficient in summer during the irrigation season.  During heating (non-irrigating) season, I guess some type of bypass could be used to keep the water returning to the lake so the lines would not freeze.
 
Does anyone have any thoughts about this type of system and whether it will work for several homes in a subdivision as opposed to just one home using lake water with a private system?

Posted By joe.ami on 03 Jan 2012 09:13 AM
Perhaps a storm drain retention pond could offer pond loops to minimize expense for those who wish to go geo.

Joe,

You posted one minute before I did but I did not see your posting before I submitted mine.  What do you think now after my explanation of the system that I have in mind?  I would like to know whether my scheme has any merit before I spend any money.

Posted By Alton on 03 Jan 2012 09:14 AM
I guess most potable (domestic) water systems would be concerned about re-introducing water back to the city main in a closed loop system.  I wonder how dangerous it would be to place water back into the main after it has been through the heat pump heat exchanger.  Is there much of a chance that coils will leak refrigerant into the water system, say in 15 years?

I wouldn't want to assume the liability for doing this no matter what the chances are of a problem.

I actually just read about a subdivision like this in GeoOutlook the IGSHPA trade organization. There is also a subdivision here in portland that has a common area for wells/loops if a homeowner chooses to upgrade to geothermal that will be starting shortly, I am hoping to get into the project but have not had a chance to meet with the builder/developer yet.

Alton = if you haven't already checked this out you might be interested. Its very different from your proposal but has some similarities.http://www.dlsc.ca/borehole.htm

FBBP,

Thanks.  I will study the info in this link.

Posted By FBBP on 16 Jan 2012 10:30 PM
Alton = if you haven't already checked this out you might be interested. Its very different from your proposal but has some similarities.http://www.dlsc.ca/borehole.htm

Can't wait to see data from it.