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Home Energy Magazine Online July/August 1994
Low-Flow Showerheads, Family Strife, and Cold Feet
This article, which initially appeared in 1985, is another installment in
Home Energy's Tenth Anniversary series. Its conclusion--that energy
savings from showerhead retrofits can sometimes be less than predicted--was
just slightly ahead of its time.
It is a documented fact that low-flow showerheads generally save less
energy than a simple change in flow calculation would indicate. Home
Energy is as guilty as others of blithely assuming that a reduced flow
translates directly into energy savings. The problem is our faith in laboratory
measurements that are performed without confirming field studies. One must
remember that people use showers, not buckets and stopwatches. We outline below
two reasonable situations where energy savings will be less than predicted by
simple calculations. Auditors must recognize these situations and make
adjustments in their energy savings estimates.
First of all, Americans no longer use their showers only to get clean. We can
see small clues to this behavior in the gadgets being developed for the
bathroom. For example, there are shower radios, shower clocks, shower mirrors,
and, of course, easily accessible telephones. "Wet" shavers have appeared as
yet another excuse to dawdle in the shower. A few people simply enjoy showers;
indeed, this editor gets his best ideas in the shower. Given these distractions
and entertainments, many people remain in the shower until they run out of hot
water. In other cases, several showers in a row deplete the hot water tank.
Then there is the notorious teenager who causes family strife by using all the
hot water before a parent gets his or her turn.
Shower time can be extended by increasing the hot water capacity or reducing
shower flow. Hot water capacity can be increased somewhat by raising the water
heater temperature setting. The desired shower temperature will require less
hot water mixed with cold, thus extending shower time. However, this option
always increases energy consumption, so an auditor will not typically recommend
this measure.
A low-flow showerhead is another strategy to increase showering time. The
auditor may unwittingly recommend installation of low-flow showerheads in
houses where in fact it will merely extend shower time or permit more family
members to shower before that ominous temperature drop occurs. Clearly,
installing a low-flow showerhead simply to increase immersion time does not
save energy; instead the household obtains a new benefit. Researchers describe
this effect as "converting energy savings into increased amenity." In the worst
case, all of the savings are converted to increased amenity. There will be NO
energy savings, if, after installing a low-flow showerhead, the user (or users)
continue to drain the hot water tank. On the other hand, some users will extend
their "immersion time" only a few minutes. In this case, only a part of the
saved energy is converted into increased amenity.
Probably only a small fraction of shower use falls into the above categories,
but so little research has been conducted in this area that we can only
speculate. A Southern California Gas Company survey of 500 homes, for example,
indicated the average shower length was 7.5 minutes. Unfortunately, they
neglected to ask: "Do you shower until you run out of hot water?" Some
households, especially apartments, have small water heaters where even an
eight-minute shower can drain the tank. (The arithmetic is simple: three
gallons per minute of hot water should drain a 30-gallon tank in ten minutes,
but cold water mixing and stratification reduce the effective capacity to under
25 gallons, or eight minutes of showering time.)
The "cold feet syndrome" is the second reason why simple flow calculations tend
to overestimate energy savings from low-flow showerheads. A common complaint
from very low-flow showers is that the water is cold by the time it reaches the
feet. The user compensates by raising the temperature of the shower water.
Actually, the problem begins earlier. Aeration is often used in the low-flow
showerheads to give them extra body, but it results in rapidly declining
temperature between the time the water leaves the showerhead and hits the naked
body. (Aeration is in fact the principle behind power plant cooling towers and
evaporative coolers.) Without knowing it, many users raise the temperature of
the water 1deg.F to 10deg.F to maintain the same "impact temperature." Our
friends at Consumer Reports carefully measured the flow and comfort
levels of thirty-three energy saving showerheads but failed to note this
effect. Other reports have alluded to the "cold feet syndrome," but have not
recognized it as a small scandal.
The simple calculation of energy savings based on the difference in the flows
of the old and new showerheads fails when the shower temperature also changes.
Adjusting for increased temperature could reduce savings by as much as 20%. It
is not difficult to include an adjustment for this phenomenon, but do you know
anybody who does?
Low-flow showerheads save energy and should be installed. But sometimes there
are unexpected complications. Family strife and cold feet are just two
examples.
-- Alan Meier
Related Articles
"Big Flush, The: Saving Water in the Big Apple" (Anderson)
"Everything I Know about Energy-Efficient Showerheads I Learned in the Field" (Warwick and Hickman)
"Graywater: An Option For Household Water Reuse" (Bennett)
"Pulling Utilities Together: Water-Energy Partnerships" (Jones, Dyer, and Obst)
"Remodeling Bathrooms: Let the Energy Savings Flow" (Johnston)
"The Rise of Water Service Companies" (Berlin)
"Savings and Showers: It's All in the Head" (Proctor, Gavelis, and Miller)
"Xeriscape: Winning the Turf War Over Water" (Iwata)
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