| Advanced
Two-Stage Design Hits the Market
Until recently, most residential two-stage evaporative
coolers were of the down-discharge variety and were generally installed
on the roof. Although a rooftop cooler offers certain advantages, including
a more central location, installing and maintaining these coolers can be
problematic. Some developers also consider the bulky rooftop cooler cabinets
unsightly, and have been reluctant to use them.
To help minimize the problems associated with
two-stage coolers, the Davis Energy Group (DEG), with funding from the
California Energy Commission's Energy Technologies Advancement Program
(ETAP), embarked on a program in 1992 to develop an advanced two-stage
cooler. In March 1995, DEG completed the project and unveiled its production
prototype two-stage cooler.
DEG's advanced two-stage cooler unit improves
on prior designs by relying on a compact vertical configuration for ground-,
wall-, or attic-mounted residential applications (see figure below). Other
unique design features include
· A single blower upstream of the
cooling media to reduce cost, size, and noise.
· Through-the-wall delivery, eliminating
duct losses.
· A variable-speed blower motor
to increase energy efficiency and to provide quiet, low-speed operation.
· A shared pump and reservoir for
both stages.
· An automatic reservoir that purges
and drains completely during off cycles to prevent biological growth and
odors.
· Reduced maintenance through the use
of high-quality components and an improved design.
In developing its advanced two-stage cooler, DEG
first performed detailed simulations. The simulations indicated that the
advanced unit could provide cooling sufficient for a typical 1,700 ft2
new house or a 1,400 ft2 existing house at 70°F peak wet-bulb temperatures.
Following the simulations, six units were field-tested
in Northern and Southern California, beginning in the late summer of 1994.
The field-test houses ranged in size from 1,000 to 1,600 ft2 and had existing
ducted central air conditioning that could be used in lieu of the two-stage
cooler. Monitoring results showed the advanced units had average operating
efficiencies of 50 Energy Efficiency Ratio (EER), or approximately six
times higher than that of conventional cooling systems.
In June 1995, DEG continued performance monitoring
on two units that had been installed in homes located near Sacramento.
The primary objective of this monitoring was to obtain performance data
under hot summer conditions. Other objectives included evaluating indoor
air circulation and assessing homeowner satisfaction. Neither home used
its existing air conditioner during the study, except when a motor failure
put one of the coolers out of commission. This allowed for the collection
of conventional cooling data that would otherwise not have been available.
Monitoring results for the two-stage cooler that
operated throughout the study showed EERs of 34-38. Average daily energy
use of the conventional air conditioner was over five times higher than
that of the advanced cooler. Peak condensing unit demand for the air conditioner
exceeded 3kW, while peak demand for the advanced cooler was less than 0.7
kW.
A survey conducted among the original six residences
revealed generally favorable impressions of the advanced two-stage cooler.
Among the more valued features were energy savings, environmental benefits,
and improved cooling comfort. Drawbacks cited included unknown maintenance
requirements and uncertain equipment life.
Davis Energy Group has licensed the design of
the advanced unit to I.D.A.C. Technologies. Production is currendy under
way on the first 30 units and installation is expected to begin early this
summer. The estimated cost to contractors is $2,250, with the possibility
of utility rebates in California. For more information contact I.DA.C.
Marketing: HSC, 1051 Folger St., Berkeley, California 94710. Phone: (510)
548-1377; Fax: ( 510 ) 548-7962.
Leo Rainer is a senior engineer
with Davis Energy Group in Davis, California.
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| Figure 1. Diagram of the components of Davis Energy
Group's advanced two-stage evaporative cooler. Note that a single blower
and water reservoir serve both indi-rect and direct stages. |
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