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.
greg Aldred of Star Maxx
Solar demonstrates a new
installation in St. george,
Maintenance: all hot water heaters and solar
system storage tanks need to be flushed annually. the pumps and valves in an active system
are electro-mechanical 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 35 years or more before replacement of major parts.
A thermosiphon takes advantage of the fact that water
rises as it’s heated. Solar-heated water in a flat-plate collector rises through tubes and flows into the top of an insulated storage tank. Colder water at the bottom of this tank
is drawn into the lower entry of the solar collector. Water
thus flows in a continuous loop, continually reheating during daylight hours. When a hot water tap is opened in the
house, hot water flows from the top of the storage tank,
and is replaced with cold city water flowing into the bottom of the storage tank.
Although the system is simple, thermosiphons put an
800-lb storage tank high on the roof, which should be rein-
forced to support it. Other solar water-heating systems put
the storage tank at ground level or in the basement, where
it’s not a structural challenge.
active Solar water-heating Systems
Active systems use an electric pump to circulate water
through the collector. In warm climates, a direct (or open-loop) system is practical: City water goes into an insulated
storage tank. A pump draws water out of the storage tank to
pass through the solar collector and go back into the tank.
Hot water for household use is drawn from the top of the
storage tank, sometimes passing through a booster heater.
An automatic control system starts the pump whenever
the collector is warmer than the storage tank.
Butler Sun Solutions
installed this system in a
home in Ramona, Calif.
In freezing climates, the rooftop part of the system
must be protected either by draining down when the temperature dips, or by running an antifreeze solution. These
cold-weather systems require temperature sensors, electric
pumps and automatic control systems, adding 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 hot-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 double-walled heat exchangers to permit systems
in their jurisdictions. GS