Optimizing Hot Water Temperature for Energy Savings

Start saving energy costs on one of the most energy-intensive appliances in commercial foodservice facilities: water heaters.

Most operators now know the benefits of energy-saving equipment. And many — especially those on the West Coast — already give water savings an extra thought these days. We're entering a time when some operators now manage water temperatures to save even more on utility costs.

Water heaters represent one of the most energy-intensive appliances in commercial foodservice facilities, according to a report by PG&E's Food Service Technology Center, which is run by Fisher-Nickel Inc. (Fishnick), a division of Frontier Energy. The lifeblood of any restaurant, commercial hot water heaters supply water for handwashing, cooking and dishwashing. California alone uses more than 340 million therms for commercial foodservice water heating, according to FSTC's study. A total of 85,500 foodservice facilities in that state with gas-fired hot water systems represent 16 percent of California's total commercial gas load.

Unfortunately, the design of hot water systems in commercial kitchens has not changed significantly in decades. More recent advances in hot water systems, however, concentrate on efficiency improvements at the heater, and water-reduction measures at end-use fixtures. The introduction of "smart" water heaters further control energy use.

"We're still far away from what could really be done in terms of hot water management," says Fisher-Nickel's Amin Delagah, water guru and engineer at PG&E's Food Service Technology Center. "But aside from investing in a super expensive, 'smart' water heater, there are some manual things operators can do to start saving energy costs now. We've been trying to demonstrate that you have more tools in your toolbox than you realize."

In fact, the PG&E Food Service Technology Center was recently awarded a grant to study the potential energy savings from optimized hot water systems in commercial foodservice facilities that use advanced gas-fired heaters, condensing water heaters, alternatives to continuous recirculation, improved distribution system design and controls, ultra-low-flow fixtures, and dishwashers with heat recovery.

While we await the results, Delagah agreed to share a few sure-fire tips for optimizing hot water temps with the readers of FE&S. He offers everything from very basic, inexpensive measures to more aggressive savings routes that include investing in state-of-the-art, "smart" water heater equipment for new facility projects.

Tip No.1: Temper the Water

Typically, the hot water thermostat sits somewhere hidden in the kitchen in a box, so it's not always on an operator's radar to check the reading, says Delagah. "Sometimes, one of the staff members might feel they don't have enough hot water and change the temperature without the manager even being aware it was raised to a higher temperature."

For one thing, hand sink hot water temperature set to 150 degrees F or higher can lead to scalding, especially among very young and elderly users. Hand sink hot water temperature — according to California regulations, for example — should only be set to about 100 degrees F to 108 degrees F max, according to Delagah.

In the kitchen, hot water used for cooking should generally hover around 122 degrees F to be hot enough to ward off harmful bacteria but not too hot to overuse energy and pose burn risks, Delagah says. Some larger volume institutions, like hospitals, might turn up the temperature to 140 degrees F. Most dish rooms operate at about 140 degrees F or more.

Sometimes, operators will turn up the dial even higher for kitchen use, upward of 165 degrees F. A condensing heater, assuming staff turned up the thermostat to 165 degrees F, can use up to 10642 therms and cost a whopping $11,706 extra per year.

Using something as simple as a valve can help manage hot water usage outside of thermostat settings, and improve accuracy overall.

"The best practice is to set the temperature, go to your sink, and check the actual temperature of the delivered water," Delagah says. Valves will do this, and then add cold water to regulate the temperature.

Tip No. 2: Reconfigure the Distribution System

Distribution systems consist of a network of piping, sometimes wrapped in insulation to reduce heat loss. In moderate to large systems such as full-service restaurants, a recirculation loop and pump help maintain hot water in the supply lines for faster delivery to appliances and faucets.

According to the PG&E Food Service Technology Center's Water Heating Design Guide, "delivering hot water more efficiently yields permanent energy savings and improved system performance. Once the fixtures and the sanitation equipment are specified, the placement of sinks and equipment in relation to the water heater is a key factor to the efficiency and performance of the distribution system."

Foodservice operators can choose from four main types of distribution systems: 1) simple distribution, supply piping with no return loop; 2) continuous recirculation, supply piping with return loop and pump; 3) demand circulation, demand pump with or without a return loop; 4) distributed generation (primary and point-of-use heating).

The majority of restaurants use either simple distribution or continuous recirculation systems. But, according to the design guide, demand circulation can dramatically improve hot water usage and manage temperatures to initiate better savings. Occupancy sensors in the vicinity of a hot water fixture initiate the operation of the pump. When the built-in temperature sensor measures an increase in water temperature, it assumes that hot water is about to arrive at the fixture and shuts off the pump.

Distributed generation is a 100-percent distributed system utilizing point-of-use water heaters or a hybrid hot water system that combines a central water heater (storage type or tankless) with point-of-use electric heaters.

"It's possible to skip a recirculation system and turn up the hot water temperatures, or install a booster, only in the dish room, where you might want it set at upwards of 150 degrees F for performance reasons," says Delagah. "That way, extra hot water isn't circulating around the whole restaurant, but only in the dish room where it's
most needed."

In this case, using a booster that can handle higher temperatures and allow for a 70-degree F rise, versus just a 40 degree F increase, works best. "That way you can then turn down your overall hot water temperature circulating throughout the space," says Delagah.

Pipe insulation is by far the most effective solution, if not the most overlooked, to improve the effectiveness of the distribution system to deliver hot water on demand, according to the FSTC design guide. Typically, fiberglass or foam insulation can prevent heat loss. This saves energy, extends the cool-down time, reduces operating cost, and improves the effectiveness of the distribution system to deliver hot water.

Tip No. 3: Stagger Usage Times

It's easy to want to crank up the temperature when the water heater doesn't seem to be performing well.

"But cranking up the water to a certain temperature doesn't mean you're going to get more hot water right away," says Delagah. "It's a false impression that you're going to get more hot water in the kitchen." Not to mention, operating hot water in this way can easily destroy a hot water heater sooner rather than later.

Operators are better off staggering cooking processes in the kitchen to ensure they have a constantly well-performing flow of hot water. "In other words, don't fill a three-compartment sink at the same time you're slammed in the dish room," says Delagah. "Fill the sink earlier, well before the lunch or dinner rush."

Tip No. 4: Invest in Smarter Water Heaters

High-efficiency, condensing storage heaters installed in new facilities or as replacement units in existing restaurants can reflect a payback of one year or less, according to the FSTC design guide. In new installations, condensing heaters may be less expensive to install than standard efficiency heaters, presenting an immediate payback. Tankless water heaters, which use an external storage for hot water, have become more popular.

Next on the horizon are smart water heaters that go beyond rudimentary set point controls with more advanced controls and touchscreen displays, allowing for precise control of the heater.

At least one smart water heater provides on-site and offsite monitoring, reporting daily, monthly and yearly water and energy use profiles. It can also alert operators via email or text if hot water has been overdrawn. Managers can set and lock temperatures, even reduce temperatures overnight during non-peak times. The operator can collect the data in a log and analyze it over time to enhance operational efficiencies.

"You can sit at your desk or be on your phone and check all the diagnostics," Delagah says. "Even your plumber could be alerted if something is not working right."

Condensing heaters with smart controls allow managers to lock the thermostat and keep it at the proper temperature of 145 degrees F. This can save $2,230 per year, at least a 19 percent drop in cost, according to Delagah.

Combine this with some of the other mentioned distribution improvements and there's potential for even greater savings.

Tip No. 5: Consider Heat Recovery Systems

If operators take the step to implement smarter or more efficient hot water heaters, Delagah encourages them to also consider integrating preheating technologies, such as refrigerant heat recovery, dishwasher heat recovery or solar.

Some newer model dishwashers can plumb to the cold water supply line and use waste heat recovery to preheat the supply water, thereby bypassing the hot water distribution system entirely.

A refrigerant heat recovery system (RHRS) works by harvesting the super heat that would otherwise be rejected by the condenser in a refrigeration cycle. A RHRS can be added to walk-in coolers and freezers, ice machines, and air conditioning systems.

As a renewable resource, solar water heating holds tremendous potential to preheat incoming water, according to the FSTC design guide.

A condensing heater with smart controls, paired with a dishwasher with exhaust air heat recovery requiring only cold water at 125 degrees F, results in more dramatic savings of 35 percent, or about $4,784 per year.

The combination of smart water heaters and heat recovery helps in the case where managers might not be motivated to deal with manually tempering valves, or larger operations that experience a lot of staff turnover, Delagah says.

The PG&E Food Service Technology Center will update its water heating design guide in the next year following the results of the California Energy Commission project, which wraps up in 2018.

"The major focus of the study has been on hot water delivery performance and overall system efficiency that projects measured energy use of the water heater and measured energy use at each point of use," Delagah says. "By studying systems in these ways we can measure true efficiencies and suggest even more ways operators can manage their hot water temperatures to save costs in the long run."