Hi everyone.

I found this site a few days ago while searching for info on geothermal systems.  I was hoping to get some input as I am having trouble deciding which route to go. 

I got 2 quotes for installing a new geothermal system.  Both contractors agree that our house needs a 4 ton unit.  I am in Southern Illinois and my soil is mostly clay with some gravel in it. 

One guy wants to go with the horizontal loops.  My concern with his bid is that he is putting 6 lines in a 5' deep trench that will be 2' wide.  He will put 3 lines on the bottom, 2 lines 1' up and the last one a foot above that.  It seems to me that with so many lines so close together it won't be as efficient as it could be.  The trench will be 590' long.

The other guy wants to go vertical.  He will drill 4-125' deep holes.  That sounds like it might be better than the horizontal lines, but it's also over 3k more.

Initially I wanted both contractors to give me a bid for a pond loop since the house is about 30' from a 1 acre 16' deep pond.  The ponds only water source is runoff so it can loose 5' to 6' of water in a drought.  Both contractors advised against using the pond because of concerns about beavers or muskrats biting through the lines.  Is that a legitimate concern?  I know that there are beavers and muskrats in the area, but I've never seen them on my property(probably because of our dogs).  And with the house being so close to the pond, I would notice them if the did get in the pond and could get rid of them if needed.  From everything I've read, the pond loop would be the cheapest way to go and should be very efficient too. 

At this point I am confused as to which way to go,  I want the job done right but I don't want to spend more money than is necessary.  Any help would be appreciated. 

Thanks,
Doug

I agree that a pond loop should be your most cost effective option. I doubt that animals chewing the lines would be a problem.

Hello?
It is Minnissotta calling.

They had a huuuuge beaver problem that became evident about 10/15 years ago. You see beavers are industrious and a lot smarter than you think. Because the hdpe does not deteriorate they began harvesting it to construct their lodges!!! Your mileage may vary as well as your beaver. I would not do a pond loop out of hdpe unless you are willing to roll the beaver dice. A slim jim out of stainless steel would be the option I looked at, however pricing for the modules is unknown to me.
Eric

Can you do open loop from the pond or is the water quality too low? Pump the water in and send it right back.

All kinds of filtration problems with that.

Bergy

4 wells 125' deep seems to be insufficient for 4 tons of heating/cooling capacity unless you have exceptional ground to work with. The norm is closer to one (1) ~180' deep well per ton. But this can vary depending on many local factors.

In my area we use at least a 200' deep well for each ton.  Some of my projects have been in granite almost all of the way.

Thanks for the replies.

I got a call from a third contractor today and I asked him about using the pond loop. He said it would be the same cost as the horizontal loop. I called the original contractor that gave me a price on a horizontal loop and he said that the cost for the pond loop would be the same also. So with the potential problems with the pond loop, I guess I should go with horizontal. I am waiting for a price from the third contractor for the horizontal loop. I asked him what the trench depth, length and how many pipes would be in it. He said it would be 5' to 6' deep with 2 pipes. He will call me back when he calculates the length. Of course, that is different from the other guy who will put 6 pipes in a 5' deep trench. Apparently there are no standards that everyone adheres to regarding the loops.

I did ask one of the guys about an open loop system using a well or the pond and like Bergy said, the filtration would be expensive and require quite a bit of maintenance.

I've been reading the "What to ask before you buy geothermal - Shoppers Checklist" and will be asking the contractors a few more questions, and getting some references.

One thing I didn't mention is that the system will be put in a new double wide trailer that will be delivered in about a week and a half. I need to decide what I'm going to do before then because I have to let them know whether or not to install the ac, or get credit for it. It's my own fault for waiting too long to start getting quotes and not educating myself properly. I appreciate the help.

Doug

Posted By arkie6 on 09 Sep 2010 07:00 PM
4 wells 125' deep seems to be insufficient for 4 tons of heating/cooling capacity unless you have exceptional ground to work with. The norm is closer to one (1) ~180' deep well per ton. But this can vary depending on many local factors.

Posted By Alton on 09 Sep 2010 07:14 PM
In my area we use at least a 200' deep well for each ton.  Some of my projects have been in granite almost all of the way.

I was wondering about that too, because I thought that I read that each well should be between 150' and 300' per ton somewhere.  This is the kind of thing that has been giving me doubts.  Just like  guy that wants to do the horizontal loops, he wants to put 6 pipes in a 2' wide 5' deep trench.  I read somewhere that what he is proposing does meet the minimum requirements, but it seems to me that they will be too close together and will affect each other. 

Doug

The thing jumping out at me here is HUD standard duct work will not likely support a 4 ton anything let alone geo.
Horizontal if you have room makes more sense than vertical.
Pond loops do cost nearly as much as horizontal and have more potential for problems.
We need a reality check on ducts before we desgn the system.
joe

Posted By chrisbiker on 09 Sep 2010 04:41 PM
Can you do open loop from the pond or is the water quality too low? Pump the water in and send it right back.

How is that gonna work? At the 1.5 gallon per minute, the delta T will be about 10 degrees, the pond will be colder in the winter, at the deepest part if you are lucky 39 degrees F, you are sending it back at 29 degrees F...... If you have a well, you pump it up with usually around 50 degrees or more in the continental US, dumping it at least 40 degrees.... Much below, your discharge line, and before that, water in your source coil, will freeze. For that reason, we dump HDPE pipe with antifreeze in those ponds.

Putting lines about a foot apart does not concern me too much, they will steel some heat from each other, but you save excavation length. Slinkies are a good example for that. Putting them between 3 and 5 feet depth does concern me, the temperature at that depth might not be stable enough to support an entering water temperature above 30 degrees in southern Illinois. The other concern I have is a trench length of 590 ft, that would mean a loop length of at least 1180ft, way too long for 3/4 inch pipe. The rule of thumb is is to keep individual loop length below 800 ft, other wise you need a bigger circulation pump for the increased head loss, costing you efficiency. That changes with bigger pipe, like 1". So total length is about 3600 ft, that would be fine for 4 tons with nice thermal conductivity (you sitting beside a pond might suggest that), but at 5-6 ft depth, lesser likely at 3-5 ft. For vertical, I agree, 125' would be on the short side, but maybe you have better conductivity then anybody else in the country. Lots of ground water helps. It is possible that a pond loop is not cheaper than a horizontal loop, since you still need an excavator for the header trench. By the time you dig the header, construct the loop, fixate it, put weights on it.......and so on, you have dug your horizontal field and know all the variables. A lot of literature suggest ponds are the cheapest, but in reality, this is not necessarily true.

> How is that gonna work? At the 1.5 gallon per minute, the delta T will be about 10 degrees,

While I wouldn't recommend open loop to a pond in a very cold climate, to answer the question, you would use more than 1.5 gpm when the pond is that cold.

WITH would a pond loop be the 'same' as a horizontal loop????? You've got to be kidding here!!....With a pond loop, you would only need about a 40' trench vs 590'.....Someone try to explain this senario. Trenching 590' is gonna take a looong time. They 'still' have to install the piping and then all of the time to refill the trench, watering down every foot or so to let the soil compact. 590'...yea....that's gonna take aloot of time again.  It would take maybe a couple of hours to dig the 40' trench. Then all they have to do is fill the slinkies up with water and tie weights to make them sink in the pond. NO WAY IN HELL would this take as long as a 590' trench!!!!!  Am I missing something here?????.....Hell.....the homeowners could do this part with a neighbor helping them!...This is one of the areas where IMO, gets to be a rip off with geo!!!!! Don't get me wrong.....I'm ALL for geo....when the installers come back down to earth with their pricing!! This is what soooo frustrating with geo!!!.......We need ALOT more competition to get geo pricing within reason! I hope to have it in the future.

Rob... calm down a little

Hate to break it to you Rob, but a pond loop only costs a little less than horizontals. That's because the digging is the cheapest part of a horizontal loop system.
Equipment is there either way and 2 hours vs a day of operator wage is only a couple hundred bucks tops.
Miles of pipe are not cheap however in that quantity.
j

Posted By jonr on 14 Sep 2010 09:40 PM
> How is that gonna work? At the 1.5 gallon per minute, the delta T will be about 10 degrees,

While I wouldn't recommend open loop to a pond in a very cold climate, to answer the question, you would use more than 1.5 gpm when the pond is that cold.

Let me clarify: 1.5 gpm/ton of capacity is the usual flow for open systems! The open loop systems usually take 10 degrees out of the water before they discharge, closed systems are usually around 5 degrees, since flow is twice as high.

Posted By geodean on 14 Sep 2010 10:35 PM
Rob... calm down a little

I second this...!

Ok Rob...now to respond to you. What I said was: "It is POSSIBLE that a pond loop is not cheaper than a horizontal loop, since you still need an excavator for the header trench. By the time you dig the header, construct the loop, fixate it, put weights on it.......and so on, you have dug your horizontal field and know all the variables. A lot of literature suggest ponds are the cheapest, but in reality, this is not NECESSARILY true." A lot about this has to do with mobilization costs, logistics and local variation. To put an excavator on a trailer drive them out to the customer usually takes 1.5 hours (most of our customers are in rural areas without access to natural gas), so that is 3 hours, two hours by your standard to dig a 40ft header trench, but sometimes the pond is 200ft away, plus 50 ft further in the pond to hit the deepest spot) versus the horizontal loopfield closer to the house). Our loop crew has the logistics down to install up to 6 tons of horizontal capacity within a day. So the excavator I need to pay for the day no matter what, maybe a couple hundred bucs less for lesser fuel, and about half the amount of pipe. A pond loop I have to go out and measure depth at different spots first to ensure I have the right location, need to put weights on them, and have usually much more header pipe, which is more expensive. Then I might need a different circulation pump for the longer header trench, more pump power....so it depends. So at the end of the day, it takes us a day to install horizontal loopfield with 2-6 ton capacity (assuming everything goes right), and also a day to install a pond loop. Maybe I need $500-$800 lesser material, maybe I need more for more circulation power, but usually costs are similar for us, so we charge the customer the same (low) cost. So Rob, before you use your "no way in hell" language again, you need to be reminded what this forum is all about, namely the exchange of ideas, know-how, and what methodology might work better. In that process you might want to consider the possibility that something that does or does not work for you might work for someone else, and by being able to freely exchange this kind of information helps us to learn. Wouldn't that be something....?

Well said Doc