the weather and time of day, the PV array must
be coupled with either a battery bank or alter-
native electricity source, such as a generator.
Efficiency & Economics: PV is ideal for
offsetting air-conditioning loads because its
peak power production is a nearly perfect match
for maximum air-conditioning power draw on
summer afternoons. a PV system installed to
help power an air conditioner may pay for itself
quickly in a hot, sunny climate with high electricity rates. The match against heating load is
weaker but worth pursuing in the context of
new construction or a major remodel incorporating significant passive-solar elements.
More Information: for a breakdown of
state and local incentives applicable to hVaC
efficiencies, see dsireusa.org. find a local PV,
hVaC or solar water-heating installer in the
Get Started buyers’ Guide, beginning on page
34. DC airco ( dcairco.com) and Securus
( securusair.com) manufacture 48-volt DC,
18,000-btu air conditioners that can be coupled with solar energy off grid.
coolers are approximately 75 percent more
efficient than central air-conditioning systems,
according to the DOe. IeC manufacturers
claim efficiency that’s up to 90 percent better
than conventional air conditioners. The only
power draw is a fan to push air through the heat
exchanger and on into the house, and the fan
may be run off a PV array, eliminating the cost
of electric power. however, an IeC scaled to
cool a house may evaporate 3 to 5 gallons ( 12
to 20 liters) of water per hour, which may be a
significant expense in desert country.
mike koshmrl (mkoshmrl@solartoday. org) is the
editorial intern at SOLAR TODA Y.
Indirect Evaporative Cooling
Wherever it’s warm and there is consistent
low humidity, such as in the arid mountain
West, evaporative coolers, also known as swamp
coolers and wet air coolers, can be an energy-
efficient, money-saving means to cooling a
building space. In recent years, several compa-
nies have introduced a more sophisticated ver-
sion of the evaporative cooler, the split-stream
or indirect evaporative cooler (IeC).
How It Works: a swamp cooler passes
warm air over a wet surface, and the evapo-
rating water cools the air while increasing its
humidity. This may be ideal in a desert environ-
ment but not so ideal where the air is already
humid. The IeC, instead of spraying cooling
water into the airstream directed indoors,
uses cooled humid air on one side of a heat
exchanger to cool dry air on the other side. The
temperature drop can be up to 20°f ( 10°C),
depending on conditions. That cool, dry air is
blown into the living space while the humid air
exhausts to the environment.
a video tutorial illustrating how a solar-powered evaporative cooler works can be
viewed on Coolerado’s website at coolerado.
Efficiency & Economics: Per ton of cooling capacity, the DOe estimates that the installation costs of evaporative coolers are about
half that of central air conditioning. because
they don’t have compressors, evaporative