Indirect Evaporative
Cooling Systems
You don’t need grid power
to air condition a home.
cool dry air
to house
ILLUSTRATION BY KURT STRUVE
fan box
outside air in
By SETH MASIA
Seth Masia is managing
editor of SOLAR TODA Y.
Contact him at smasia@
solartoday.org.
It sounds like an oxymoron: Solar cooling? How can that work? One way is to use a photovoltaic (PV) system to
drive a low-power fan on an indirect evaporative cooling
(IEC) system, also called an advanced evaporative cooler
by some utility companies.
An IEC system looks like a rooftop air conditioner, but
it doesn’t have a compressor or refrigerant circuit. And,
unlike a swamp cooler, an IEC system doesn’t blow cool
but humid air into the house.
Instead, an IEC system evaporates water to cool one
side of a heat exchanger, which cools fan-driven dry air on
the other side of the exchanger. This cool, dry air is then
circulated through the house. A 6-ton unit — a ton means
removing enough heat to melt a ton of ice in 24 hours —
typically uses a 600-watt electric fan, small enough that it
can be driven by electricity from PV panels. A residential
unit;can;therefore;run;on;zero;grid;electricity.
In a typical design, a fan draws outside air through a
filter. The intake air is then split into two streams. One
stream is saturated with water and passes through the wet
side of the heat exchanger before being vented outside. The
other stream goes through the dry side of the heat exchanger and is vented into the house.
A;home-size;evaporative;cooler;uses;an;average;of;3;to;5
gallons ( 11 to 19 liters) of water per hour. According to the
National;Renewable;Energy;Laboratory,;the;average;electric
utility;company;in;the;Southwestern;United;States;uses;4.88
gallons of water to generate a kilowatt-hour of electricity —
which means a 3.5-ton refrigeration air conditioner sloshes
through;about;15;gallons;( 57;liters);of;water;per;hour;at;the
generating plant. In this part of the country, using an IEC
system instead of a refrigerant air conditioner will therefore
save;about;60;gallons;(227;liters);of;water;daily,;plus;an
average of about $290 in electric costs annually.
Because an IEC vents its evaporated water outside the
house, it can be effective even in muggy climates where a
traditional swamp cooler would not work.
This illustration features IEC technology pioneered by
Colorado-based Coolerado ( coolerado.com). The company’s systems are distributed nationally and sell for about 25
percent more than refrigerant air conditioners of equivalent
capacity. The smallest system is a 450-watt, 3-ton IEC unit for
houses under 1,500 square feet (about 139 square meters).
Competing;systems;are;sold;by;OASys;in;California
( oasysairconditioner.com) and Adobe Air in Arizona.
Many of these systems are eligible for energy-efficiency
rebates in some areas. Check with your local utility. ST
