HPAC Magazine

Water conservation in commercial apps


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The hot-water-conserving equipment and fixtures in a commercial kitchen are pivotal to an optimized hot water system.

Hot-water-conserving equipment and fixtures are the only parts of the hot water system in a commercial kitchen that regularly interface with the user. They are also the easiest to remove and replace, namely the dishwasher, the pre-rinse spray valve (PRSV) and the aerators on hand sink faucets. Efficient equipment or fixtures, as long as they offer equal performance to conventional models, will translate into long-term savings.
It should be noted that currently in Canada there are no energy efficiency regulations for commercial warewashing equipment – commercial dishwashers and pre-rinse spray valves. However, ENERGY STAR does prescribe voluntary energy efficiency specifications for commercial dishwashers. Look for the ENERGY STAR symbol to identify high efficiency equipment.

The PRSV is a handheld device designed for use with commercial dishwashing and warewashing equipment that sprays water on dishes, flatware and other foodservice items for the purpose of removing food residue (see Figure 1).
Low-flow, high-performance pre-rinse spray valves are the single most cost-effective piece of equipment for water and energy savings in commercial kitchens. Building on a successful California Public Utility Commission funded program in 2005, at least half of 100000 pre-rinse spray valves used in commercial kitchens in California have been retrofitted with efficient models (using 1.6 gpm (6 Lpm) or less). Realizing that efficient spray valves perform equally with inefficient or conventional counterparts, the federal government passed laws in 2005 limiting their flow rate. The federal regulations, combined with the success of efficient pre-rinse spray valves in kitchens have helped to support a market transformation.1 This momentum has propelled manufacturers even further, with the introduction of models that use less than one gallon per minute (3.79 Lpm).
A busy full-service restaurant can clock three hours of pre-rinse operation a day. Even at one hour of use per day, the best-in-class 0.64 gpm (2.42 l/min) spray valve can save 100 therms and $330 annually when compared to the federally regulated 1.6 gpm (6 Lpm) valve (see Figure 2). When compared to a high-flow value at 4.5 gpm (17 Lpm), the savings would be 400 therms and $1,350 annually.

Aerators are an inexpensive way to reduce the water flow rate while maintaining enough force for effective hand washing (a restroom lavatory sink or a kitchen hand-washing sink is used almost exclusively to wash or rinse hands). Large restaurants can have up to a dozen hand-washing sinks and it is still common to find high flow (typically 2.2 gpm (8.33 Lpm)) aerators installed. The maximum flow rate can be set much lower without negatively impacting user satisfaction (i.e. 0.5 gpm or less).
You can still purchase aerators that range from the federally mandated maximum 2.2 gpm (8.33 Lpm) aerator for a private lavatory down to the best-in-class 0.375 gpm (1.42 Lpm) high-performance model. But there is still a lack of awareness, or reluctance, in the restaurant industry to install low-flow aerators (0.5 gpm (1.89 Lpm)) on lavatory faucets.
A conventional hot water delivery distribution system (with a relatively large volume of water in the pipes that cools between draws) works poorly with 0.5 gpm (1.89 Lpm) aerators (see HPAC March 2015, p28). For this reason they are often exchanged for high flow aerators, or removed altogether after a new restaurant is in operation in order to reduce that wait time for hot water.
The peak flow rate of a hand sink faucet with the aerator removed could be as high as eight gpm. If this faucet was used one hour per day, the annual utility cost would exceed $2,800. The estimated utility costs of various aerators operated for one hour per day are displayed in Figure 3. An annual savings of 190 therms and $640 is estimated by replacing a 2.2 gpm (8.33 Lpm) aerator with a 0.375 gpm (1.42 Lpm) aerator.

The commercial dishwasher, also called a warewasher or dishmachine, uses cleaning chemicals, electricity, natural gas and water. Figure 4 illustrates the array of dishwashers available for use in restaurants, excluding the large flight-type machines used in very large foodservice operations. It is important to be familiar with the dishwasher specifications and to know the daily usage (racks per hour) in order to estimate operating costs and assess the value of choosing a more efficient model. The water use per rack is a fundamental measure of efficiency as it correlates with the energy used to heat water and the amount of cleaning chemicals required for each cycle.
Older and less efficient equipment on the market is being replaced with ENERGY STAR qualified models to save energy and water. Historically, manufacturers with efficiency-driven designs have focused on reducing the rinse water volume per rack. More recently, they have ramped up research and development and are introducing innovative technologies such as waste heat recovery, insulated panel and ventless models.

Amin Delagah is a project engineer at the PG&E Food Service Technology Center (FSTC). He holds a B.S. in mechanical engineering and M.S. in renewable energy engineering with a minor in environmental management. Highlights of his research include the completion of a Design Guide on Energy Efficient Heating, Delivery and Use. Material for this article is extracted from that document. Delagah is the upcoming Handbook Chair of the ASHRAE Technical Committee 6.6 Service Water Heating.

1. Dickinson, Mary Ann. California Urban Water Conservation Council Letter. ENERGY STAR. [Online] July 01, 2005. [Cited: March 04, 2010.] www.energystar.gov/index.cfm?c=archives.spray_valves

What should you consider when
selecting a pre-rinse spray valve?
• Opt for a high-velocity spray pattern.
• These models have substantially better cleaning performance. Look for a PRSV rated to clean at a rate of 26 seconds per plate or less.
• Look for models that can be disassembled for cleaning and maintenance. This is especially important in areas with hard water.
• Choose a model tested for efficiency.
• Check the packaging to ensure that the PRSV has been measured in accordance with ASTM F2324-03: Standard Test Method for Pre-Rinse Spray Valves.
• Check with your municipality or utility about rebates.
• PSRVs provide such substantial water savings that many Canadian municipalities and utilities offer programs providing free or discounted PRSVs to commercial or institutional users.
Operating tips
Follow these best practices for even more energy savings.
• Clean the spray head regularly.
• Remove scale build-up to keep PSRVs working at maximum efficiency.
• Replace badly clogged spray heads.
• Resist the temptation to “drill out” the scale from clogged spray heads; this will affect spray velocity and reduce cleaning efficiency.



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