Tap bodies of water for economical, efficient geothermal energy
A typical geothermal installation uses water and a heat transfer liquid similar to an anti-freeze to transfer heat from the ground to and from the home in a process that provides for efficient and cost-effective air handling methods for countless homeowners. In this traditional geothermal design, high-density lines are buried horizontally or vertically just a few feet deep to hundreds of feet beneath the surface.
But pond or lake loops offer an alternative to the familiar installation process that is less messy and less time-consuming, one that provides the same benefits but goes in much more quickly and easily.
Pond loop applications, considered the most economical of the geothermal designs, make up a considerably smaller amount of the total geothermal applications in use because of the restrictions that come with them.
“When I build, even though there’s a little distance, without hesitation I’ll drop a heat exchanger in water,” said Sean Hogan, a technical trainer for ClimateMaster who has installed hundreds of pond loops. “It’ll be a better performer, and it’s going to cost less to apply.”
Perhaps the biggest hurdle in most geothermal projects is a price tag that can easily exceed $10,000, depending of course on the size and scope of the system. It’s not only pricey, but installation in some cases can take weeks and ravage the surrounding landscape in the process.
Pond loop systems can run about half the cost of standard geothermal systems, according to ICF Home, a Canadian geothermal installer. The applications can only be used when a structure is close – generally within a few hundred feet – to a body of water, namely a pond or lake. So the extent of installation entails laying a pipe loop into the water, digging a trench from the water to the home – something that can sometimes be done by hand because the pipes only need to be a few feet underground, Hogan said – and connecting it to a heat pump.
Applications can be installed in virtually any body of water. Hogan has even placed them in the ocean, so long as the exchanger can be anchored to a dock or other stable object to prevent it from being knocked around by the constant motion.
Many heat exchangers come with 50- year warranties. But, Hogan says, they could last much longer because they are shielded from ultraviolet light.
Pond loops are popular in new-home subdivisions where the homes can be sited near the water source. For instance, the 15 Nest area homes at the Serenbe sustainable development in Chattahoochee Hills, Georgia, will use a pond loop geothermal system in a six-acre lake.
How it works
There are a number of different types of loop applications, the most common being coiled piping.
Heat exchangers are lowered into the water. They are weighted down enough to sink them deep enough – eight feet or deeper – to capitalize on consistent temperatures, regardless of how hot or how cold the surface gets.
The water circulating around the exchanger transfers its temperature to non-toxic antifreeze inside, just as it does with ground pipe setups, and up to a geothermal pump. While ice might form on the surface of the body of water, the temperature at the bottom remains constant and unfrozen, providing a plentiful supply of heat.
“I’ve always told my clients that if you have a body of water large enough and deep enough, that’s like living next to a volcano and you need heat,” Hogan said.
After dropping pipes into water, thermal dynamics take hold. As water moves around the exterior of pipe, the temperature inside is replenished quickly by warmer water – oftentimes quicker than systems relied on the ground heating.
Despite the benefits and attraction, water loop systems aren’t always an optimal solution or possible for many geothermal users.
In most instances, lines need to be positioned at least eight feet below the surface. But in places such as the Northeast, the body of water must allow for lines to be sunk even lower because of the need for them to be below the frost line. Without that available depth, the water won’t conduct enough natural heat to warm a home when needed.
So bodies of water where levels can change drastically threaten to expose pipes and disrupt functionality.
“We want that depth because if you get a hot period or cold period, we’re not affected by those temperatures because of the depth we’re sitting in,” Hogan said.
Besides that, homeowners want the pipes deep enough to where swimmers won’t become entangled in them.
A home more than a few hundred feet from the water won’t reap as much benefit. Beyond that distance, the heat cycling through the exchanger won’t carry fast enough to the home.
Nevertheless, the inability to install a water loop doesn’t prevent a homeowner from reaping the benefits of geothermal, Hogan said. It just means the consumer must opt for alternative form of natural earth heating and cooling, relying instead on either horiztonal or vertical ground pipes.
“But in most cases, if a body of water is close enough and deep enough, that’s your best (geothermal) choice by far,” Hogan said.
Download more information about geothermal pond loops.
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Companies: Climate Master