Image Credit: Peter Yost
Image Credit: Peter Yost This photo shows a water pressure gauge screwed into a hose bib. The gauge has a red needle that "saves" the highest reading.
More Water Efficiency
What is a Pressure Reducing Valve (PRV)?
PRVs have spring-loaded diaphragms that resist the incoming pressure of the water supply to a home. They are typically installed just after the water meter on the system side (see photo). PRVs usually come set at 45 pounds per square inch (PSI) but have a set-screw adjustment so that the PRV’s range of operation is from approximately 30 to 80 psi. PRVs cost around $80; installation costs may double the total cost, depending on installation circumstances (new or existing home, location of incoming line, ease of shutting off water service to the home, etc.).
Why are PRVs included in the WaterSense new homes specification?
The 2009 WaterSense Single-Family New Home Specification requirement is for static water pressure no greater than 60 psi. For homes with wells, a pressure tank must be installed as part of the domestic water system. For homes on municipal water distribution systems, you need either a PRV or a determination the home complies with the static pressure maximum (see the Inspection and Verification Guidance for WaterSense¯ Labeled New Homes).
PRVs save water by reducing flow rates. The greater the water pressure, the greater the rate of flow for many plumbing fixtures. Reducing the system pressure by as little as 10 to 20 psi can save thousands of gallons a year in a typical home. Reflecting this benefit, it is not uncommon for PRV installations to be supported by water utilities. The City of Austin’s water utility gives a $100 rebate for PRV installations in homes with greater than 80 psi water pressure.
But PRVs in homes with high water pressure are green and smart for other reasons. Many residential plumbing fixtures are engineered for pressures no greater than 75–80 psi; some manufacturers void their warranties if pressures are above this range. Fixtures such as storage-type water heaters, dishwashers, refrigerator icemakers, and pressure-assisted toilets can be particularly prone to reduced service life or leaks at pressures above 75–80 psi.
Is high water pressure really that common?
Municipal water systems vary tremendously in water-delivery pressure, depending on distance from water plant, elevation, and other factors. Pressures in excess of 100 psi are not unusual. In my own home, we measured water pressures ranging up to 110 psi routinely over a week-long period.
It’s easy to test your water pressure—you can screw a pressure gauge right on to a hose bib (see photo). If pressures exceed 200 psi, two PRVs can be installed in series to manage the load. But leave the installation of the PRV to a plumbing professional, hopefully a green one.
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7 Comments
Can you harness that energy instead of suppressing it?
Peter,
I've long been troubled by failed plumbing fixtures because of our high-pressure city water. I really should add a pressure reducer, but instead of just holding it back, do you think it would be practical to have a mini turbine that could harness some of that force? There are folks designing flooring and even clothing that could harness sources of wasted energy that we take for granted. I know it would be in small, intermittent bursts, but if you already had an inverter for solar, couldn't you send the water pressure energy into the power grid?
Showerheads
I’m not a scientist nor have I done a scientific study about showerhead efficiency, but I have notice most of these new low-flow, low-pressure fixtures make me take longer showers, perhaps to the point that negates the potential water savings. In the spirit of taking shorter and comfortable showers, I look for showerheads that I can take out the flow reducer and I even travel with them to replace them in hotels while I’m there. For the record, I’ve talked to several people about it and quite often they feel the same.
Response to Rob Wotzak
Rob,
I reported on a device the does what you describe in the October 2005 issue of Energy Design Update. Here's the story:
"A company called Rentricity has developed small turbines designed to generate electricity from the flow of water through water supply pipes. The company hopes to market the turbines to owners of high-rise buildings. The turbines, called “Flow-to-Wire devices,” harvest surplus energy from over-pressurized water mains. Rated at 20 kW to 100 kW, the turbines function like pressure-reduction valves, with the added benefit of electricity production. For more information, contact Rentricity at (212) 334-5434 or http://www.rentricity.com."
Leave it to Martin
Cheesh Rob. Glad I waited before I expressed an opinion along the lines of "what? are you nuts?" Martin, sure sounds as though Rentricity is along the lines of municipal- or building complex-level efforts to tap this "water pressure energy" rather than in individual homes. Got to love the acronym <a
Armando and showerheads
Not to worry, Armando--we will be covering showerhead performance in a water efficiency blog very soon.
"Green", as in $MONEY$
I'm sorry boys, but here is a rant from the real side of life. The 2007 median income for the US was $50,233.00. 73% of the Nation make <$75K (that's 73% of the homes). I live in CA and at $100+K/yr. (and I own my cars, don't have credit cards, i.e., live within my means), there is NO WAY I could afford to the "green" retrofits, the "analysis" say I must do - NO WAY - short of increasing MY debt, to make someone else rich (that upper 6-13%). I priced out the real cost of kW PV solar installation, if I installed it; <$15,000. So. Cal solar businesses quote me $53K and then come back a couple days later and say, "OH we're sorry, we got the numbers wrong, can we come back out and give you a new quote? How about $33K?" and then a week later, because I don't sign a contract, "OK, how about $25K?" - do the math! And these guys are a reputable Co? If I do it myself, the Gov. won't give me a rebate. If I build a solar collector that supplies 50% of my heating and hot water needs, for less than $1k - no rebate. I build a solar power turbine and it's illegal to operate. On this site there are notifications of energy retrofits contracts for $400K this and $600+K for that, who's paying for it? Not the 73%, they can't! If you've got the green, you get the "green". What about the majority? Who out there is offering the 73% a truly affordable product? 400 % markup is obscene.
Wrong blog?
Frederick - Your comments on a blog about pressure-reducing valves (PRV) about PV and green retrofits seems out of place--I think you cross-posted--try again.
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