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April 2003

By Mike Sherer
TECH REPORT: Low-Flow The Way To Go

Low-flow pre-rinse spray nozzles save more than water, and they perform, too.  

Water, water everywhere, nor any drop to drink,” Sam Coleridge once wrote. Strange phrasing, maybe, but we get his point. The fact is there aren’t too many areas of the country that haven’t been hit at some time or another by a water shortage. When that happens, you either voluntarily cut back consumption, or the local water constabularies find ways to encourage you. If that doesn’t work, they put a thumb in your eye and invite you to visit with the judge.

So where do you look to save water? A clue: Serving your customers water only upon request may not be the place to look first.
If you said the dish room is your biggest user, you’re probably right.

Fortunately, saving water doesn’t require a change in your dish machine. Low-flow pre-rinse spray valves, it turns out, are a slam dunk when it comes to water conservation. And the savings can amount to way more than you might think.

To find out just how much water these devices can save, and to make sure they rinse properly, the friendly folks at the Food Service Technology Center, San Ramon, Calif., did what they do best—they devised a standard test method. Then they put four popular spray nozzles to the test.

Rigging For No Rigging
The set-up looks pretty simple, but as with all the FSTC tests, the lab-coat brigade there does everything possible to eliminate or minimize variables, as well as reflect real-life conditions, or something close to them.

So for this test, the FSTC team starts by attaching spray valves to a 36” flex tube, the same sort of pre-rinse unit standard in most dish rooms. Since most municipal water is supplied at about 60 pounds per square inch (psi), that’s what FSTC procedures call for during all test runs. The tubing has to accommodate a minimum flow rate of 7 gallons per minute (gpm) at a water pressure of 60 psi without the nozzle attached. The pre-mix valve is set to maintain a water temperature of 120°F ± 4°F.

Lest any variables slip by, testers attach, in order, a mixing valve, a pressure regulator, a temperature sensor, and a pressure gauge between the municipal water source and the flex tubing. The test procedure calls for no more than six feet of pipe between the mixer and the flex tube, all of which must be insulated with half an inch of foam. Also, the pressure gauge must be located at the base of the flex tube.

FSTC testers set up a simple procedure to find the flow rate of a spray valve. They record the weight of a five-gallon carboy container (and keep a second handy). Then they hold the spray valve over the container and squeeze the handle to maximum flow, recording elapsed time with a stopwatch.

Spraying stops after one minute, at which point testers weigh the container. Subtracting the weight of the empty container leaves the weight of the water (one gallon weighs 8.337 lbs.). Three test runs provide an average flow rate.

The four-pack recently tested consisted of two standard and two low-flow spray valves. Not surprisingly, test data did confirm the standard spray valves use more water than the low-flow valves. What was more surprising, however, was that the two standard valves flow notably different amounts of water, and the low-flows do, too.

Also of interest, and important to any comparisons you yourself will do: Manufacturers’ specs and the actual flow rates differ. Some, though maybe not all, of the difference can be attributed to the fact that FSTC tests at 60 psi, while makers’ claims are based on 80 psi.

But How Much In Dollars?
So how different is different? The first standard spray valve, which we’ll call Valve A, flowed wide open at an actual average rate of 2.6 gpm. The other standard valve, Valve B, registered a heavy 6.09 gpm—more than twice as much. The first low-flow valve, Valve C, used an average of 1.2 gpm in its test runs. Valve D, also a low-flow, came in at 1.8 gpm, 50% more than the other low-flow, but still better than the standards.

So yes, there’s a substantial difference among standard-flow valves, and among low-flows as well. But there’s an enormous difference between standard and low-flow rates.

What are the savings? The test results show that the difference in flow rate from the lowest to the highest in this group is about 4.9 gpm. To put that in perspective, FSTC polled restaurants to find out how much they use their pre-rinse spray valves. Very small restaurants use them about two hours each day, small operations about four hours a day, and medium operations about six hours, their sampling indicated.

So if a small restaurant, using a sprayer four hours a day, switched from using the biggest water user in this group, Valve B, to the sippingest low-flow, Valve C, for example, it could save about 1,175 gals./day. Even switching from the standard valve with the lower flow rate, Valve A, to the low-flow model with the higher rate, Valve D, would end up saving the same operation about 192 gals./day.

So at bare minimum, FSTC folks figure, the average small restaurant will save about 200 gals./day switching from a standard spray valve to a low-flow. The average medium size restaurant will save at least 300 gals/day.

What that means in terms of cost savings may surprise you. If you operate 363 days a year and save 300 gallons of water per day, you’ll end up saving 108,900 gallons of water. Most water utilities sell water in units, each of which is 100 cubic feet, or one ccf, of water. There are 748 gallons of water in one ccf. So, you’ll save about 145.58 units of water.

The cost of a unit of water varies depending on your location. But at an average cost of about $2.00 per unit, you’d save $291.16 a year just on the incoming water charge using the example above. Spray valves cost around $50, which means an ROI of about two months in this case. And that’s not even counting energy charges for heating water, nor sewer charges for getting rid of it.

Now That’s A Spray
There’s gotta be a catch, right? When you think low-flow nozzle, you’re thinking of those shower heads you have to run around under to get wet, right? Lab testers wondered about that, so the second half of their test for spray valves is whether or not they actually rinse dishes properly.

For this test, FSTC techs devised a procedure of coating 9-inch white ceramic plates with tomato sauce and letting the sauce dry. For uniformity, the FSTC found that the most consistent tomato sauce was produced by using a store or generic brand of tomato paste (national brands often have too many bits of tomato skin and so on, creating the potential for inconsistency in a head-to-head rinse-off) and mixing it with water.

Testers pour one tablespoon on a dry plate at room temperature (75°F ± 5°F), tipping and turning the plate until the sauce coats the entire inside diameter of the plate. (Using a utensil might leave an uneven layer of sauce and some sauce will adhere to the utensil.)

Coated plates are put in a dish rack and left at room temperature to dry for 24 hours. Once dry, testers place a dish upright in a dish rack, hold the spray nozzle so the tip is about 11 inches from the top of the plate and 14 inches from the bottom of the plate. Testers spray the plate, timing how long it takes to rinse off all the tomato sauce. Everyone knows it’s much easier to clean dishes with hot water than cold, which is why the test procedures call for incoming water that is 120°F.

Test results are the average rinsing time per plate based on sixty test runs. Here’s where things get interesting. Standard spray valves have a round spray pattern much like a showerhead. To get the same kind of rinsing ability from a low-flow valve, manufacturers have designed them with a fan-shaped spray pattern.

Valve A, the more moderate water user of the two standard valves, rinsed plates most quickly, with an average time of 19.1 seconds. Standard Valve B, at a guzzling 6.09 gpm, took 24.9 seconds on average to rinse the tomato-pasted plates. Valve C, a low-flow using just 1.2 gpm, cleaned plates in 21.0 seconds on average. Valve D, also a low-flow, required an average of 26.5 seconds to rinse each plate.

So the redesigned heads for the low-flow units work. Their rinse times are within two seconds of the standard units. In other words, saving a ton of water doesn’t sacrifice much on the performance side.

How often can you find such easy ways to save? Not often. Mr. Coleridge would be impressed.


SIDE BAR: Figuring The Real Cost Of Water

Ever take a close look at your water bill? If you have, you know you’re not just paying for the water coming into your operation. Most water utilities not only charge you for the units of water that flow through your water meter, but also a usage fee, a sewer fee for the wastewater that flows down your drains, and often a sewer maintenance fee.

The dish room uses a lot of hot water, so factor in the energy cost to heat water, too. Add it all up and suddenly saving water, especially hot water, looks very attractive.

In our main report, we used the example of a restaurant saving 300 gals./day, or about $291 in water costs. If you figure $3.00 per unit of water for sewer costs, you save an additional $436.74.

Now factor in energy costs. Most of your operations use gas-fired water heaters. To heat the 108,900 gallons you’d save in a year by switching to a low-flow spray valve would require about 349 therms. If gas costs you $0.60 per therm, that’s a savings of $209.40 on top of water and sewer costs. Total savings: $937.30. Payback on a $50 spray valve: less than three weeks.

The friendly folks at the FSTC have a neat water calculator that lets you plug in your own variables—water, sewer and energy (gas or electric) costs and low-flow water savings—to find out how much you’ll actually save. Check it out at their Web site, www.fishnick.com, or call 800/398-3782.—MS


SIDE BAR: California's Low-Flow Giveaway

Not long ago, a funny thing happened in California. The California Urban Water Conservation Council in Los Angeles went looking for ways commercial operations could save energy, not water. At the same time, the Food Service Technology Center in San Ramon, which usually focuses on energy efficiency, was looking for a way to help foodservice operations save water.

The result is that now a dozen CUWCC employees are canvassing foodservice operations across the state, installing low-flow spray valves for free. The “Rinse & Save” program, which kicked off last October, had installed more than 5,000 valves by the end of February with a goal of 16,900 by the end of the year. The FSTC originally estimated a conservative 1.0 gpm savings for each valve replaced. They’ve tested 80 of the valves replaced in the field, and the average is actually 1.6 gpm. Each low-flow spray valve is expected to save the state, and the operation using it, an acre-foot of water over its five-year life.

About 18 months ago, in an unrelated effort, the FSTC staff was investigating ways foodservice operations could save energy by using less hot water. Pre-rinse spray nozzles looked promising on that count, too. FSTC tested two in the lab and noted that they had different flow rates. Realizing how much water, and energy, could be saved by using more efficient spray valves, FSTC learned that a few manufacturers actually make “low-flow” valves. Armed with the data, the FSTC made a series of presentations to various agencies in the state, including the CUWCC.

Meanwhile, the California Public Utilities Commission, the agency that regulates utilities in the state, made $100 million available for programs that promote energy efficiency to small business. The CUWCC decided to go after some of the funds.

“We were looking to focus on the commercial market,” says Maureen Erbeznik, program manager. “We were thinking about a rebate on dish machines, but we met with FSTC, and they showed us that low-flow spray valves could save more.”

The CUWCC received a $2 million grant from CPUC augmented by an additional $1 million from energy utilities in the state. Even if it doesn’t receive another round of funding from the CPUC next year, the CUWCC hopes to continue the program with money from the gas utilities. There are about 150,000 spray valves being used in the state, Erbeznik estimates, and replacing each one with a low-flow valve saves an average of two therms per day, something gas companies and foodservice operations can live with.—MS


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