Friction Lost

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Efficiency is the new conservation. In the '80s, it was "conserve fuel, conserve power." Today, as all global resources are subject to more and more pressure, the watchword is "efficiency." It's about more than just using less energy; it's about using energy more wisely . And energy isn't the only resource that causes concern. Water use, emissions and waste products can all be managed more carefully. For some it's a lifestyle choice, but increasingly, jurisdictions β€” municipal, state and federal β€” are making resource efficiency a matter of law.

Generally, the pressure is on manufacturers to make increasingly more-efficient equipment, and great improvements have been made in all kinds of products. The Energy Star program, launched in 1992 by the U.S. Environmental Protection Agency and the U.S. Department of Energy has encouraged manufacturers of common household appliances to reach energy-efficiency goals. According to the D.O.E., Energy Star was responsible for energy and cost savings of about $14 billion in 2006 alone.

Perhaps nudged a little by regulators, perhaps as a consequence of a maturing industry, the pool and hot tub sector has made progress too. Here are just a few examples: Pool heaters that are 85 to 95 percent efficient and emit less greenhouse gas are now available. Variablespeed pumps can decrease energy use by up to 90 percent. Solar blankets and insulating pool covers reduce heating needs and prevent evaporation of water and loss of chemicals. LED lighting is longerlived and uses far less energy than older types of lighting.

Whether it's customers demanding it or regulators requiring it, the need to be ever-more efficient is here to stay.

Making a Difference

It just makes sense to choose the most-efficient components when engineering a pool. That's pretty much pool building in a nutshell β€” bringing together the right parts to form a seamlessly operating system. Heaters, pumps and lighting are the obvious targets for reducing waste and operating costs, but what about the filter? Although the filter doesn't draw energy directly, it's a key component in the overall efficiency of the system.

There are several areas where filters impact efficiency: The power drawn by the pump that's required to run the filtration system. The amount of time in between cleanings. The amount of water, heat and chemicals lost to the cleaning process. The amount of run time required for turnover. The waste produced by the filter. We talked to experts on equipment, system design and technical training about how to get the most out of a filter, whether it's sand, DE or cartridge.

Do The Obvious First

"Probably the first thing is to install the filter per the manufacturer's instructions," says Steve Gutai, product manager for pumps, filters and valves at Jandy, and a sought-after speaker on hydraulics. "That means the pump flow and pipe size as it mates up to the filter. Beyond that, you get into some subtle differences with the different types [sand, DE or cartridge] of filters."

Sue Robach, a technical trainer with Pentair Water Pool and Spa, adds that, beyond the obvious, controlling flow rate is key. "The biggest thing that someone can usually do to improve efficiency is to slow the water flow down," she says. "The slower the water flows through the filter, the more efficient and the finer the filtration will become."

But the filter is part of an interdependent system. "It's important to select the pump first," Robach says, "to make sure we know how many gallons per minute the pump is putting out, and then size the filter accordingly." The benefits of slower water don't just accrue to the filter. "It improves the overall hydraulic efficiency, too," she says. "Now what we're doing is we're not overpumping the system, or pipe or filters, and we're selecting the proper horsepower pump."

But there is a point of diminishing returns for sand and D.E. filters. "We have to make sure we've got enough flow to be able to backwash the filter," Robach says. The same flow rate that facilitates backwashing also provides enough pressure to keep the media on the grid, which is a requirement for DE filters.

Subtle Differences

"In terms of energy efficiency with a [sand] filter, the biggest hog is loss of water due to backwashing a filter before its time," says Randy Mendioroz of Aquatic Design Group in California. Mendioroz mostly designs commercial projects and usually specifies high-rate sand filters. "You only want to backwash when it's absolutely necessary, that's why we incorporate automation into most of the systems we design. The system automatically backwashes based on pressure differential, so you can set the parameters, but it only backwashes when the filter is completely dirty."

It's certainly possible to monitor the filter pressure and manually backwash only when necessary. However, homeowners' and service technicians' schedules don't always allow for that. "There's a tendency when you're on a manual backwash system to do it once a week whether it needs it or not," says Mendioroz. "Maintenance people want to check it off their lists, so they don't even look at the difference between influent and effluent pressure on the filter. They just go ahead and backwash it."

Water isn't the only resource lost to backwashing. "Every time you backwash the filter β€” depending on the size of the system β€” on a commercial pool you're losing between 5,000 and 15,000 gallons of water to the sanitary sewer, and you're losing heat and you're losing chemicals in addition to the water resource," says Mendioroz. "So you want to maximize the amount of time between backwashes as much as possible."

With lost chemicals, the water balance may also be disrupted. "You may have to add some cyanuric acid or some stabilizer depending on the fil water you're adding to compensate for the loss," says Robach. "Is it a really major rebalance. No, but there will be chemical adjustments and there will be chemical consumption and there is time in that process."

With D.E. filters, backwashing can include the added concern of reclaiming the used media, which is considered hazardous waste in some areas. On the other hand, longer times between backwashes of D.E. filters contributes to more-efficient operation. And the intervals between backwashes can be further extended through the selection of regenerative D.E. filters.

"You get extremely long backwash runs out of regenerative D.E. filters," says Mendioroz. "We did a project in South Africa called the Lost City, a large resort and water park with over 6 million gallons of water in it, and we used regenerative D.E. filters and we were getting eight-week backwash runs. On a commercial-scale project that is phenomenal. We figured we saved the client about $1 million a year just in water use."

A regenerative D.E. filter shakes up the D.E. periodically, rearranging it on the grid. The collected dirt is mixed in with the D.E. and becomes part of the filtering matrix. "You keep reusing the same D.E. over and over again," says Mendioroz. "It's a pressure filter and every time you shut the system down, there's a little bump that occurs either integrated into the filter or there's an air element that blows the D.E. off the grids. When you fire the thing back up, D.E. is lighter than any organics it traps so it is the first thing that goes back to the grid and then the dirt follows. So you can keep bumping it periodically to extend the backwash interval."

One residential model shakes itself up every night. "There are some elements that are designed to allow the D.E. to fall off," says Robach. "The material is a lot slicker than the standard grid material and doesn't hold the D.E. on so tightly, so it will actually fall off when the system isn't running."

One Web site says you can make your own regenerative D.E. filter by whacking a standard D.E. tank with a rubber mallet periodically. We don't necessarily advocate that method, but it illustrates the concept well.

Robach notes that using a separation tank with D.E. helps conserve water. "If you use a separation tank, when you put it into backwash mode, the water goes in through a bag, which catches the D.E. and debris, the clean water then goes back into the pool, and we don't lose water," she says. But if the D.E. filter is plumbed to backwash to waste, then the water is lost, just as with a sand filter.

Unfortunately, particulate matter isn't the only thing lurking in the pool. "You get oils mixed up with D.E. and you're going to have a hard time reusing that stuff," says Robach. "If you have teenagers that are using baby oil every single day in the summer and there's a slick on the top of the pool, I don't know that [a regenerative filter] is really going to elongate your filtration cycle."

Any time a system needs attention, human resources are also required.

""If we don't slow the water down, and we're blasting it into the filter β€” whether it's sand or D.E. or cartridge β€” it's going to make it a lot harder to clean," says Robach. "When you can't get all the debris out of a filter, the elements don't last as long. So we can talk about maintenance efficiency, too."

The Capable Cartridge

Gutai recognizes the pressure is on water resources (no pun intended) in the residential market, too. "The market is pushing in the direction of cartridge filters," he says. "Cartridge is the fastest-growing category of filter, and a lot of it has to do with the fact that you don't backwash, and you don't have to deal with the reclamation aspects of a D.E. filter.

"There are certain places in the United States where you cannot backwash β€” you have to typically go into a pea trap, go into a sewer or go into a reclamation tank," Gutai explains. "Certain jurisdictions do not allow you to backwash into waste."

Robach says cartridge filters do a good job of water conservation. "Especially with the larger cartridges, we're holding a lot more dirt before we have to clean it, and the water that we waste is just the water required to hose it down."

In the commercial realm, cartridge filters are rare, but Mendioroz chooses them from time to time under circumstances that may become more common in the future. "We recently specified a project where we chose cartridge filters," says Mendioroz. "That was because they didn't have access to a sewer. You don't backwash a cartridge filter, you just clean the cartridges. It makes a big mess, but I just have the owner buy two sets of cartridges and then we rotate them, take the dirty ones out, toss them in a big vat with water and a little chlorine and soak and agitate them. The other option is to hose them down and that's a mess and a bad use of water."

But in the residential market, Mendioroz agrees with Gutai's assessment. "Were seeing a lot more cartridge filters being utilized in the residential market. They're very simple for most homeowners to understand. Most people can figure it out, whereas with a D.E. filter, there's more to understand."

Which Is Best?

As is the case with most questions in engineering, the answer is, "It depends." Every pool is custom built in the sense that no two sites are identical. So the professional builder must consider the full range of factors when planning a system. But several concepts recur: Slowing down the water yields a host of benefits for all types of filters, including more-thorough filtration, reduced friction loss in the pipes and less power required to move the water through the system. If water conservation is a concern, it will be important to minimize the impact of backwashing. If the backwash water can be reclaimed, chemicals and energy used for heating are saved along with the water.

We hear a lot of bad news about the state of our natural resources. But the good news is that there are many small things β€” things that don't add expense to a project β€” that the pool industry can do that will add up. Progress is good.

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