automatic control systems. These add complexity and cost
to the installation.
The most common cold-weather system today is the
closed-loop antifreeze heat-exchanger system, or active
indirect system. When the collector is warm, a food-safe
propylene glycol antifreeze solution is pumped through the
collector and on through a heat exchanger, then back to the
collector. The heat exchanger heats city water for domestic use. The heat exchanger is
usually located at the bottom
of an insulated storage tank.
(Sometimes the storage tank
is also the home water heater,
with an electric or natural gas
heating mechanism for use
when the collector is cold.) a
breach in the heat exchanger
would leak antifreeze into
the drinking water, which is
why it’s necessary to use only food-safe propylene glycol in
these systems. many local plumbing code officials require
Maintenance >> All hot water heaters need to be
flushed annually, as do solar system storage tanks. The pumps
and valves in an active system are electromechanical devices
that will need periodic attention. Annual pressure testing can
identify potential problems before they become major leaks.
Long-term corrosion is an issue in any plumbing system, but
a well-maintained system can go 20 years or more before
replacement of major parts.
It’s the one thing that makes
Space heating >> DSWH can also be used for space
heating. The most efficient method is an in-floor radiant heating system that sends hot water through pipes embedded in
the floor. A gas backup water heater is typically used because
a house is coldest at night and in winter months. The solar
collector area needed is generally 10 to 30 percent of the
home’s floor area, depending on climate.
double-walled heat exchangers to permit systems in their
This article is adapted from the “Solar Energy Resource
Guide 2008,” published by the NorCal Solar Energy Associa-
tion ( norcalsolar.org), a chapter of the American Solar Energy
liz merry owns verve Solar Consulting ( vervesolar.com)
and writes SOLAR TODAY’s “ask ms. liz” blog. Diana young
( firstname.lastname@example.org) is an editor and designer who worked on
the Solar energy resources guide. Barry Butler, Ph.D., owns
Butler Sun Solutions ( butlersunsolutions.com) and heads the
aSeS Solar thermal division.
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