Two big advantages of closed-loop geothermal systems

Should you install a closed-loop or open-loop geothermal heating and cooling system? The advantages of closed-loop can save money.

When our heating contractor Tony Silverio told us we had a choice between a closed loop and an open loop geothermal system, our first inclination was simply to go with the least expensive.

That’s in part because we already knew we’d be spending significantly more upfront for a geothermal system than we would have for traditional heating in exchange for the long-term savings geothermal produces.

And one of our goals in renovating Sheep Dog Hollow is to test the assertion that building green and economically are no longer mutually exclusive. (I’m finding that they’re not, but only if you’re looking at a five- to 10-year time frame ... but more on that later.)

While we wanted to go for the less costly open-loop geothermal system, Tony was quite clear that he’d recommend the more expensive closed-loop system.

Now, when a contractor tells you have a choice of two types of systems – one is probably cheaper and produces more heat while the other costs more and produces less – you do have to wonder.

His explanation made sense, though. A closed-loop system is more reliable and requires less maintenance in the long term. With an open-loop system, he noted, you are also taking a chance that the wells dug on your property will produce as many gallons per minute of clean water necessary to make the system work.

It sounded convincing, but I still wanted to talk with someone else local who also had lots of experience in geothermal. So I called Ray Sima, a local well-driller who’d been putting in geothermal systems since the 1970s, including in nine homes of family members.

Here’s what Ray had to say:

In 1979, I dug the first well [for the geothermal system] for our house. I remember doing it in March before we did anything else, even the foundation. We knew we had to get a minimum of 10 gallons per minute for my system to work back then. My brother was building the house next to me [and wanted to put in geothermal, too.] I hit water and got my 10 gallons per minute. He dug a well and got two gallons a minute. So he couldn’t do geothermal. But I went ahead with it.

Thirty years ago, [open loop] was the only alternative we had, we used to call it "pump and dump" because we drilled one well to pump the water out and another to pump it back in. So I also had to drill another well.

In a few years, we realized the second well I'd dug didn’t always take in all the water we put into it. It turns out two wells weren’t geologically connected. Then we realized we had an iron problem and an acid problem with the water. So in a few years we found we were losing water pumps, condensers, and evaporators in the refrigerator units in the house. Let’s just say they weren’t trouble-free.

Over the next 10 years, Ray found that about half of the dozens of early open-loop systems he helped put in “had major problems.”

Then, about 15 years ago someone invented the closed-loop system. That essentially works by digging a series of holes underground where there’s a fairly constant 55 degree F. temperature and running pipes filled with water and antifreeze in them. The water and antifreeze is then circulated in and out of the house in a closed system.

“The water never comes into contact with the ground – it can’t get polluted from the ground or cause pollution to the ground," he says. " I like the system so much, we retrofitted my daughter’s house last year and even though I hit water, I told her we had to go closed loop. In the long run, it’s just cheaper. We never have any problems with them.”

But Ray is also clear, that if you’re fortunate and hit two good clean wells, an open-loop system could still cost less.

Still, it's not a sure thing. “It could go either way with the old pump-and-dump system [because] we’re guessing what our costs will be – maintenance can go through the roof,” he says. “With closed loop, we know what our costs are either way, and we’ve never had a problem with a closed-loop system that was installed properly.”

Experience is hard to argue with, so we opted for the closed-loop system for Sheepdog Hollow.

Next: Learning about spray foam insulation.

Editor's note: Alexandra Marks will be blogging twice a week about her green and budget-friendly restoration of a 1902 farmhouse in Connecticut. See a photo gallery of the early days of the project by clicking here. You can read all she's written about the project so far by clicking here and then looking for Sheep Dog Hollow under Topics on the right side of the page.

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