Geothermal Question: split system requires two sep. wells?

17 years ago

Because of the layout of my older home, and that I do not currently have any ductwork, we're looking to get a split system with one heatpump serving the 1st floor, and another serving the 2nd/3rd. The bids we've gotten so far are for air-exchange heat pumps, but we're now seriously wanting to consider geothermal, so I'm doing as much research on it as I can.

FYI, it sounds like that around here (southern Delaware, about 10 miles from the ocean and surrounded by nearby wetlands) they primarily do vertical systems - I presume this because whenever I ask about it, I'm always told that it requires a well to be dug and well to me = vertical, so I'm presuming that it may be because of our high water table and taking advantage of the additional thermal properties of the water access. If anyone wants to help fill in the details or correct my incorrect presumptions I'd appreciate it!

In either case, vertical or horizontal, my question is basically the same: If I have a split duct system in my house, will I need to have two totally separate piping systems?!? If so, is there any way economize on that -- two horizontal systems in the same set of trenches, or two vertical systems in the same wells, anything like that?

I'm having trouble finding anything about this online, so if you have links that might help me learn more about this specific situation, I'd appreciate the links, as well as any guidance/advice on this!

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Comments (6)

bob_brown
17 years ago
In my area, N. Texas, each hole is drilled for a ton of btu exchange. 250 ft per ton. If you have a 3-ton system, you would drill 3 holes. Different areas require more or less depth. Each system should be seperate in case of failure. Piping could have controls to allow a system to use additional capacity. This increases the complexity in years to come. KISS.
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marknmt
17 years ago
Hi Tanama.

In any ground source heatpump system the cost of moving the circulant liquid has to be considered, and it has a very major bearing on the cost-effectiveness of the system. If the wells you're being told are needed are for an open-loop system then it means that you are going to pump groundwater up from the earth and through your system, and if they are part of a closed loop system then it means that your circulant is being pumped down into the earth and back up. Another closed loop system circulates through horizontal trenches just a few feet deep, but hundreds of yards long.

The open loop system may require lifting water any number of feet and may be expensive. My own open loop draws from about 57 feet and then discharges to a sump. I have to pay to lift the water that distance; closed loop are probably, as a general rule, less costly to operate that way.

It's not clear from your post whether the wells you mention are to provide water, like my open loop system, or to circulate liquid in a closed loop system. The difference could be important to you, especially if you have access to ample water that's too deep.

I'm hardly an expert, but I'm not selling anything and I'm willing to share my mistakes, so maybe there's something of value in what I say. I hope it helps.

Good luck,

Mark
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Re: bob brown Hi Bob, IÂm glad to see youÂre paying attention. "We saw 2 supplys and 2 returns. Is this typical installation, or did the contractor go cheap?" Your answer is in the 1st sentence of this entire thread. "I have two split systems each 3 tons. Running off 6 vertical loops of 175 feet each." They in fact did what you suggested in another thread, 2 separate systems. "RE: Geothermal Question: split system requires two sep. wells? Posted by bob_brown (My Page) on Mon, Mar 19, 07 at 20:11 In my area, N. Texas, each hole is drilled for a ton of btu exchange. 250 ft per ton. If you have a 3-ton system, you would drill 3 holes. Different areas require more or less depth. Each system should be seperate in case of failure." If you carefully examine the photos provided in the above link, you will see 2 separate systems with 2 separate loop pumps. Parallel is the preferred way to go, in my opinion. One of the 1st things that has to be done is get a qualified installer in there with the proper flush cart to flush and verify flow rate Â with the cart! This should ÂresetÂ the ground loops should there still be trapped air or debris. If there is still a problem, additional measures will have to be taken as deemed appropriate by the professional on site. As you correctly pointed out, reconfiguring to series would be inefficient and non-advisable at this point Â even if additional boreholes were drilled! The solution lies in solving the problem(s) at hand. Tom may even have the additional advantage of having 2 separate systems on site where comparisons can be made. Bottom lineÂ Parallel is the way to go; BIG FLUSH CART REQUIRED! Flow velocity of 2ft/sec required at flush cart. Professional has to determine just how many GPM are required to achieve this flow rate. I suggest starting here if all else checks out. SR
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"Pressureless" simply means that when the pumps are not running, the fluid in the groundloop pipe is at zero pressure. My HVAC guy began doing it this way about a year ago. There is a small storage tank which the pumps are mounted to. I guess you could call it a closed loop that is not under pressure. 600 feet per ton is standard as well as 6-7 feet deep for the trench. My HVAC guy usually oversizes the groundloop because the extra cost is minimal. The manpower and equipment is already there. The plastic pipe (very thick and very hard to bend) is cheap and a backhoe around here runs $85 an hour with the operator. I wasn't talking much more money and there are no codes (or "safety measures") used where I'm at. Took about eight hours to install the 2 return and supply lines, hot melt the 5 loop headers, dirtwork, and dropping in the pipe. While the excavator was digging the trench, the 2 hvac guys were uncoiling the pipe and using zip ties to hold the pipe in a nice swirled pattern that was then just flipped into the approximately 4 foot wide trench. My system will be fired up shortly. 2 people I know have the same system and are very happy. Geothermal systems have the highest customer satisfaction. Only bad comments I ever hear are the larger upfront costs. BTW, I would price the cost to pipe it at 4 tons. If you ever add on or want to heat more space...you will be very limited.
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tanama
Original Author
17 years ago
Bob, thanks for explaining that - I'm still taking baby steps at learning about (and actually understanding!) about this technology.

Mark, my understanding is that it would be a closed-loop system - we have "city" water so any well would be just for the geothermal piping.

Is there a "geothermal 101" primer anywhere that's not put out by a company trying to sell you a system? I have HVAC folks who are familiar with geothermal who I can ask questions, but I could easily keep them occupied for hours with my questions, and I'd rather learn enough about the basics on my own so that I turn to them with questions that have at least some knowledge behind them. So thanks for any knowledge that you (and anyone else!) can share!

Leslie
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bob_brown
17 years ago
A primer? Try waterfurnace.com. Geo is similar to an air cooled heatpump but with a constant temperature source. This makes the heatpump more efficient when the ambient is either very hot or very cold. The design should be left up to someone who has done it with success several times. he heatpupm can be incorporated into a radiant floor with an air handler for remaining btu delivery.

In some areas a water cooled coil is more efficient for cooling. Solar water heat can be used to provide some or all of the Btu's needed. And also hot water. Both systems are not needed.

Using someone like waterfurnace to design a system, will ease fears of an installation that does not work.
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marknmt
17 years ago
Hi again Leslie. Sorry to be late in responding, but Spring caught up with me ...

As I've said, I'm no expert. Bob is giving you good advice, though.

I have a Climatemaster unit and it performs very well. But their website is pretty superficial. Our installer has done a lot of these and the system went in quite nicely. It wasn't cheap, and if it doesn't last a long time I'm going to be unhappy, but for now I think we may have done OK, nothwithstanding our disappointment with the cost of pumping water for the system.

Good luck,

Mark
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fsq4cw
17 years ago
Re: tanama

"Âwill I need to have two totally separate piping systems?!?" Not necessarily.

"is there any way economize on that?" Perhaps.

"Is there a "geothermal 101" primer anywhere that's not put out by a company trying to sell you a system?" http://www.geoexchange.org/

There are no simple answers. Every solution will have its plus and minuses. You will have to educate yourself, as you are doing here Â and consult with the best professionals! Your best information will come from an IGSHPA Certified GeoExchange Designer found at the link below. Next best will be an IGSHPA accredited geothermal installer.

The link above is an excellent starting place as well, watch the mini clips; donÂt forget Google.

Keep drilling (for info)!

SR

Here is a link that might be useful: International Ground Source Heat Pump Association (IGSHPA)
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Geothermal Question: split system requires two sep. wells?

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