PHOENIX - It is no surprise that swimming pools are popular in Phoenix. When temperatures regularly zoom past 100ºF in the summer, there’s nothing better to do than find relief in a backyard pool. While cooling off and relaxing are the main advantages to owning a pool, there is now potentially another benefit to having that hole in the ground: Energy savings achieved through a renewable energy source.

That sounds too good to be true, given that most Phoenicians pay a substantial premium on their electric bills in order to run their pool pumps during the hot summer months. But genuine energy savings can be had if that pool is also used as a source for a geothermal heat pump. Most do not think of the desert Southwest as being very conducive to this type of technology, but several companies in town are trying to change that way of thinking.

Bill Sund designed numerous geothermal systems in Minnesota and decided he could bring this experience to Arizona as well.


William Sund, owner, Tuxedo Air, Gilbert, Ariz., has long been an admirer of geothermal technology, as well he should be. He designed hundreds of these types of systems while working in Minnesota, and he kept extensive notes on the details of each project.

When he came to the Phoenix area in 2004, he started thinking about how geothermal technology could be applied here as well.

“I noticed that a lot of people had swimming pools, and I thought, why not use a swimming pool as a heat sink to heat and cool their homes?”

When a next-door neighbor had a swimming pool installed, Sund took notes on every stage of the process. Then he went back and consulted his notes and asked himself, “What’s the difference between installing a system on a pond in Minnesota or a swimming pool in Arizona? Nothing.” After carefully engineering the details of the system, he started talking to friends and family about this new way to heat and cool a home.

One acquaintance happened to be having trouble with his older heat pumps, and he was intrigued by Sund’s vision of using the existing swimming pool to heat and cool his home. The 3,800-square-foot home previously had 7 tons of air conditioning, but after performing the calculations, Sund decided that a 5-ton Bryant Geo unit combined with two air handlers would work nicely. The system was also designed to utilize a desuperheater, which provides domestic hot water as it is able.

Sund used one off-the-shelf sprinkler valve to modify the pool equipment, then ran the piping up and across the attic of the house to connect the pool to the Geo unit, which was installed in the garage. No excavation was needed, because there are no pipes in the ground. In fact, Sund is averse to ever putting piping in the ground, noting that, “Once the loops are in the ground, people have no idea if they’re working or not. I just don’t like that.”

The system Sund installed is an open loop system, so when the unit gets the signal to run, it starts the pool equipment, and the pipe fills with pool water. As soon as the flow is correct, the unit starts to operate, either heating or cooling the home. When the indoor space conditions are met, the unit turns off, and all the water drains out of the system and into the pool so that the water in the pipes does not soak up heat from the attic.

Sund has no concerns about using treated pool water with the heat pump, noting that neither chlorine nor salt will affect the equipment at all. As for the quality of the water in the pool after being used in the system, Sund noted, “The pool would be better suited for use as drinking water than the water that comes out of the faucet. We monitor the water conditions very closely.”

Pools in Phoenix do get warm in the summertime, leading some to say that the heat transfer might not be as effective during the warm months. Sund disagrees, noting, “The warmest I’ve ever seen a pool get is 87°F at the drain. As soon as the heat starts to build up in the pool, it’s going to permeate into the ground, because the ground underneath the pool is about 74°F.”

That being said, Sund will only install the Geo system on pools that are 7 feet or deeper, as opposed to the more common play pools, which are only about 5 feet deep. He also designs the system so that cooler water is taken from the bottom of the pool into the system and then discharged at the top of the pool.

Now that Sund has finished his first geothermal system installation in Arizona, he’s ready to move on to the next. The homeowner is pleased as well, given that his utility bill is modeled to be 60 percent less than what it was last year. The federal tax credits will also allow him to recoup some of his $15,000 investment in the geothermal system. Sund couldn’t be happier at how it all turned out. “This system has no downsides. There’s nothing negative about it.”

The heat from the geothermal system Sund installed dissipates heat through the water feature in the pool, similar to how a cooling tower functions.


Shasta Industries, one of the largest pool builders in the state of Arizona, has also been thinking about how to incorporate a swimming pool into a geothermal system. The company recently teamed up with WaterFurnace to develop a new geothermal heating and cooling system known as BLU eQ™.

BLU eQ is essentially a hybrid geothermal system that consists of a closed loop, an open loop, and a heat exchanger. Steve Ast, vice president of sales, Shasta Pools and Spas, explained, “We use a closed loop system for the home itself, and we put a heat exchanger in the line with a small pump to pump pool water through the exchanger. The system does not introduce pool water into the heat pump itself. The heat that the ground can’t absorb is removed at the exchange process and then put into a spa or water feature, which acts as a cooling tower. The water in the spa or water feature then spills over into the pool and the heat is dissipated overnight.”

Ast stated that the spa is basically a cooling reservoir and must be elevated slightly above the pool. “We let that warmer water sit there in the upper reservoir, so that most of the heat is dissipated there, before moving into the pool itself.” The system can be installed as a retrofit or in new construction, and the only limitation is that the pool has to contain enough water so that the system can run efficiently.

Shasta Industries is partnering with several local air conditioning contractors to install the heat pumps, which are a very new technology for this area. As Ast noted, some contractors have been interested, and others haven’t. “Shasta still takes care of the formulas and the scope of the pool construction experience, so we sit down with the contractors to make sure we act as a team. That’s not always typical in the trades.”

Ast estimates that the company has installed between 10 and 20 BLU eQ systems so far, including one on his own home, and he expects that number to increase as the economy improves. The federal tax credits and generous rebates from one of the local utilities could also help, given that those incentives may result in a BLU eQ system costing only slightly more than a traditional air-source heat pump.

“The custom building market has been really interested in pursuing BLU eQ, and we have a lot of cutting-edge people in the home building business. I see this as a product that slowly makes traction,” said Ast. “One day we’re going to wake up and find 70 percent of a subdivision has BLU eQ in their homes.”

Publication date:06/22/2009