get started with efficient water heating
PHotoS By dAvid SCHumACHer, tAken during tHe 2010 AnnuAl Convention of tHe floridA ASSoCiAtion of PlumBing, HeAting And Cooling ContrACtorS.
Above, minimizing the volume in piping between the source of hot water and the hot water outlets
reduces waste. Depending on diameter, pipes as small as 6 inches and as long as 25 feet can have
the same volume. Each of these pipe lengths holds 1 cup of water. Right, in addition to reducing
piping volume, we should also insulate pipes. For equal heat loss per foot, half-inch pipe gets half-inch wall thickness, three-quarter-inch pipe gets three-quarter-inch wall thickness and so on.
The cool-down phase begins when you turn off
the tap, with the temperature of the water in the
pipe cooling from the water heater all the way to
the hot water outlet. It takes on the order of 10
to 15 minutes for the water in uninsulated pipes
to cool from 120°F to 105°F when the pipes are
located in air at a temperature between 65°F and
Wringing out the wastes
and using water more
efficiently can reduce overall
hot water demand by 25 to
50 percent. It also reduces
70°F. The water cools more quickly when the
surrounding temperature is colder, such as in a
basement or a crawl space or when the pipes are
located in or under a concrete slab. Likewise, it
cools more slowly when the pipes are insulated
or in a hot attic.
The water heater must be set to a higher temperature than the mix-point temperature, and
the useful hot water temperature needs to be less
than the point at which you mix it. Why? You
need to have some headroom from the mixing
point down to the useful hot water temperature
point because of variations in desired temperature for any given application on any given day.
I would also observe that as solar practitioners,
we can do very little to effect behaviors directly.
What we can do is install systems that reduce the
structural wastes so that we can encourage water-and energy-efficient behaviors.
the size of a solar water-heating system required.
62 September/October 2010 SOLAR TODA Y solartoday.org
Copyright © 2010 by the American Solar Energy Society Inc. All rights reserved.