Roof cooling helps cut
Cutler-Hammer’s cooling costs
It’s easy to figure out how to
keep cooling costs low: Don’t let heat in in the first place.
That was the theory behind the
garden-type sprinkling system installed on the roof of a small, hot, paint building at
Cutler-Hammer’s Greenwood, SC facility. However,
when the system was on, the sprinkling heads flooded the roof with too much water. Also, the system sometimes issued too little water
because of its manual controls.
Despite these problems, Cutler-Hammer
maintenance supervisor Mike Mattison felt the systems he built was on the right track.
The Greenwood facility had 600 tons of
existing air conditioning equipment, enough to cool the building adequately, but he wanted
a roof-misting system that would reduce the cooling load on the air conditioning units,
and reduce energy usage and demand enough to make it cost effective.
An energy analysis was performed by
Sprinkool System International, Inc., Killen, AL. It
indicated that the roof-misting system conservatively would provide 175 tons of cooling
for the 250,000 sq.ft. facility, and save an estimated $13,200 in power costs from
April through August, 1994.
The analysis also showed the system
would supply an insulation value of about R-100 during operation. That meant the additional insulation to be added
for cooling purposes during the planned reproofing project could be eliminated – a
saving of more than $66,000.
The system consists of sprayheads mounted in a hydraulic network of ultraviolet-resistant polyvinyl chloride (UVR-PVC) piping mounted on the roof. The piping, specially mode for Sprinkool, has more than 10 times the titanium dioxide used in commercially available UVR-PVC piping for additional UV protection, the company says.
The network was divided into 60 fields,
each controlled by a low-voltage solenoid valve. Special
adjustable plastic supports allow the piping to “float” freely, to accommodate
expansion and contraction caused by temperature fluctuations. The supports are affixed to the roofing surface
with mastic rather than mechanical supports. The
plastic supports don’t absorb water and are not subject to splitting and breaking
during freezes, the company says.
Sensors monitor the roofing
membrane’s temperature. That data is fed
to a rate of evaporation (ROE) PLC controller, which determines when a spray should be
emitted and how much, thus preventing waste and runoff.
The 24-vac electrical control wiring
system is housed in conduit to protect the wiring from UV radiation and foot traffic. The 24-vac pressure differential-type solenoid
valves contain the only moving components in the entire system.
The sprayheads, which contain small
water-emitting orifices, are designed specifically for roof mist cooling. Each sprayhead has a stainless steel filter to
prevent foreign material from clogging the orifice.
The system was activated in April;
costs were carefully tabulated. The 1994
production profile, including equipment, people, lights, and other sources that could
alter the internal heat load, was the same as in 1993.
Thus, Sprinkool officials could make a viable comparison.
While estimated savings for the first
five months were expected to be $13,200, actual savings were $27,600, or 699,000 kWh.
“We saved $27,000 in just five months,” Mattison said. “The savings were twice what we expected and that pleases us. But if the system had been in operation earlier, we would not have needed to activate our Number 1 chiller in March, and the savings would have been greater.” ES
MONTH |
KWH(1,000) |
DECREASE |
$(1,000) |
DECREASE |
||
1993 |
1994 |
1993 |
1994 |
|||
APRIL |
660.4 |
515.7 |
22% |
34.4 |
28.5 |
18% |
MAY |
678.2 |
591.3 |
13% |
35.2 |
31.3 |
12% |
JUNE |
819.2 |
687.4 |
17% |
40.6 |
35.4 |
13% |
JULY |
818.1 |
591.3 |
28% |
40.8 |
31.4 |
24% |
AUGUST |
868.3 |
789.5 |
10% |
43.1 |
39.9 |
8% |
TOTALS |
3844.2 |
3175.2 |
|
194.1 |
166.5 |
|
This chart shows the energy savings from
the Sprinkool system installed at a Cutler-Hammer facility.
