Capturing Waste Heat for FREE Hot Water

April 1, 2003
by Marc Sandofsky Harrys Farmers Market in Atlanta is well-known for providing a unique shopping experience by offering a diverse selection of exotic

by Marc Sandofsky

Harry’s Farmers Market in Atlanta is well-known for providing a unique shopping experience by offering a diverse selection of exotic staple goods from around the world. Since opening its first store in 1988, Harry’s has grown to include three mega-stores and six Harry’s In A Hurry convenience stores.

A growing end of Harry’s business is its prepared foods and on-site soup and salad bar. Those services require a great deal of hot water, which historically has been provided by large gas-fired water heaters.

Don Laird, director of construction and maintenance for Harry’s, is always seeking to introduce more energy-efficient equipment and reduce operating expenses. To that end, last year Laird had a 40-hp desuperheater/
water heater (D/WH) installed into a new Peachtree City store.

The D/WH is manufactured by Doucette Industries of York, PA. By capturing just a small percentage of the available heat rejection, a D/WH can satisfy the entire hot water requirements of a typical food store.

John Lebo, president of Doucette Industries, explains that the D/WH uses free-floating vented double-wall construction to avoid contamination. By allowing the inner tubing to expand and contract as needed, damage from thermal shock due to temperature differences is avoided.

The D/WH can be easily rodded out and flushed. This is important because the heat transfer performance of a system deteriorates as it becomes clogged with minerals from the water. At the Peachtree City installation, Laird had his crew place the D/WH on a refrigeration rack, then added two 120-gallon insulated tanks for water storage. This allowed him to satisfy the store’s entire hot water needs.

“With the D/WH system, there was no need to put in separate water heaters,” says Laird, noting that he paid roughly the same for the D/WH as he would have for two 120-gallon, 325,000 Btu, gas-fired water heaters.

“We’re also saving about $275 a month from what it would have cost to heat the water with natural gas.”

Laird had the work crew run a hot water loop from the storage tanks to provide hot water to the sinks and added a mixing valve to lower the water temperature to 120F to prevent scalding. They also ran a line directly from the water tanks to the dishwashers. That eliminated the need for a booster heater, which Laird characterizes as being expensive and difficult to maintain.

Utilizing the D/WH, the Peachtree City store obtains heated water for the dishwashers at 140 to 155F and saves nearly $7,000 per year in energy costs.

Laird also had a flow switch installed and tied into a rack controller to provide an early indication should water stop moving through the D/WH.

“It limits downtime,” he explains. “Normally you aren’t aware there’s a problem until there’s no hot water. With the flow switch, I know about the problem as soon as it arises and have up to eight hours to correct it.”

Laird, who doesn’t use a heat reclaim valve because he says it can shock a system and cause a premature failure, explains that he has come to rely on the dependable performance of the D/WH. “No damage can occur because refrigerant flows continuously through the system.”

“One of the things I like best about the D/WH is the way it lowers the head pressure,” he adds. “I also think it makes a lot more sense to recover the heat and use it for hot water than discharge it to the atmosphere.”

Lebo notes that by rejecting the heat into the potable water, condenser capacity is effectively increased by up to 15% , which comes in handy on warmer days. He explains that the added capacity is derived by adding coil surface to the high side of the system.

“The desuperheater ends up handling all the sensible cooling, which is the most difficult part. The original condenser is then left to do the latent cooling, which means lower head pressures on design days. That provides additional energy savings and added capacity.”