Green Tip: Hot Water Heaters

With an equipment-wide update to Energy Star qualifications coming down the pipe early next year, the Food Service Technology Center has been actively working on developing specifications for commercial water heaters, a new venture for the industry and for the FSTC.

The new specifications for efficiency apply to gas storage, electric heat pump and tankless water heaters. And this past August, the Energy Star team released the first draft of the water heater specifications for review.

"We received some feedback right away, and most likely it's going to be expedited to a final draft soon," says Amin Delagah, FSTC project engineer. "Potentially by the New Year we'll have a labeling program set up for commercial storage and tankless water heaters that are high efficiency and condensing."

While standard water heaters rank at about 80 percent efficiency, high-efficiency units can meet a level of 94 percent or more. "We could have stopped at the standard 90 percent, but decided to aim higher," Delagah says. "This rate is consistent with the federal energy management program and CEE Tier 2 guidelines."

The EPA pointed out the ample opportunity for energy savings with high-efficiency water heaters in its first draft for Energy Star regulations. But the time is right for such a standard as there has been an increase in the purchase and use of commercial storage water heaters in all foodservice segments. "The EPA estimates that the incremental cost associated with efficient commercial water heaters is on average $750 and is paid back within two years through energy savings in applications...such as restaurants," the Energy Star draft stated.

Commercial Water Storage Heaters

The four main water heaters coming under close scrutiny as of late are standard efficiency storage and standard efficiency tankless heaters, and high-efficiency storage and high-efficiency tankless water heaters.

Electric water heaters are naturally more efficient than gas, but the extra step of heating a coil causes some of the initial energy to be wasted in the warming and transmitting process, Delagah says. Newer electric models with heat pumps are three times as efficient as standard electrical heaters because they transfer heat directly to the unit. "The problem is that the test standards and metrics are not developed yet, so this is something that might happen in the future or perhaps even in the next version of the Energy Star program."

Gas water heaters, while they are the preferred type of unit and cost three to four times less than electric, at least in California, only reach 80 percent efficiency compared to standard electric models, Delagah says.

High-efficiency gas water heaters, however, have served as the focal point of the FSTC's main work with the EPA, with efficiency levels of about 90 percent to 94 percent. What makes the storage units efficient are their condensing abilities and down-fired burner approach. Standard models, in comparison, heat from the bottom up, which causes some of the warmth to go to waste before it reaches the water. "With conventional water heaters you lose about 20 percent of that energy through your exhaust when operating the water heater," Delagah says. "With condensing water heaters you only lose 5 percent of that energy."

The top-down vertical heating and heat exchanger units with high-efficiency storage units "allow 350-degree exhaust gasses to connect with the coldest water at the bottom of the tank," he says. "When that exhaust gas cools, it condenses and changes to a liquid. By going from a gaseous to a liquid state, some of that heat is passed onto the water. Through this more intricate heat exchanger, you are able to take more heat through the flue gas stream before it exits." Still, these condensing units are not perfect — some acidic water goes down the drain and must be neutralized.

But the benefits are gas savings and a faster recovery rate. "The fact that you can heat up water faster potentially downsizes the unit you would need in your facility," Delagah says, however, operators don't always realize this.

Tankless Water Heaters

Tankless heaters are slowly making their mark on commercial foodservice. Long a staple in the residential sector, where most units have an Energy Star rating, tankless heaters' slowness to catch on in commercial foodservice mainly has to do with their smaller size and slight water-heating delay. But with more point-of-use placement and strategic design, they offer tremendous energy-saving potential versus one large storage heater for the entire kitchen, according to Delagah. They also save space in tight quarters because they can be affixed to a wall where there is little floor space, or even set outside.

To meet the new Energy Star qualifications for commercial tanklesss water heaters, the unit has to be 94 percent efficient for models generating 199,000 or more Btus. Also referred to as gas instantaneous, tankless heaters can sense when cold water begins flowing through a fixture and flip on the burner in just 1 to 2 seconds. It takes 15 seconds for the water inside to reach the desired temperature. Problem is, many operators don't want to wait that long. In the home, where hot water is only used a few times a day, this doesn't pose as large an issue. Once the hot water kicks in, it's on –— you can take a hot shower for an unlimited amount of time. For smaller coffee or sandwich shops requiring less hot water, this delay also poses little issue. But in a large restaurant setting, most operators want their water hot –— and they want it now. High-volume operators also tend to remain reluctant to purchase 2, 3 or 4 tankless heaters at about 200,000 Btus a piece, just to meet the needs of 1 storage heater capability at 400,000 or more Btus.

Design Implications for Efficiency

There's a way to work around this issue of tankless versus storage and water delays while still being able to use super high-efficiency tankless heaters, Delagah says.

The most efficient setup for a water heater and/or booster would be to minimize the distance between the unit and the dishwasher, or other point-of-use, he says. Operators may complain about a 15 second lag time for tankless, but in many cases, it already takes 15 seconds or longer for hot water to reach a hand sink or even pot sink at the opposite end of the kitchen.

Through clustering, "you reduce the piping in between the two positions and possibly eliminate the need for a recirculation system and you can reduce the thermostat temperature a bit," Delagah says. This simple design change can save significant — and otherwise wasted — energy use over time. "Instead of supplying 145-degree F water to the dish machine to get to 140 degrees F, you can supply 141-degree F water to get to 140," he says.

While it may be a challenge to elevate a storage water heater with 100-gallon water capability above a mop sink near the dish room, it's far less challenging to elevate a smaller tankless unit in the same place.