
Best Practice : Roof Mist Cooling
The
Best Manufacturing Practices Center of Excellence is in College Park, Md. It defines a
best practice as a "process, technique or innovative use of resources that has a
proven record of success in providing significant improvement in cost, schedule, quality,
performance, safety, environment or other measurable factors which impact the health of a
company."
The BMP program is a joint
effort of the Navy, the U.S. Department of Commerce and the University of Maryland. Its
mission is to validate, document, publish and share best practices used throughout
industry, government and academia. To do that, BMP teams conduct on-site surveys of
organizations that wish to participate.
General Tool Company installed a roof misting evaporative cooling system to provide
additional cooling for the machine shop. Compared to the cost of conventional air
conditioning systems, the installation costs for the system are less than 20%, and the
annual operating and maintenance costs are less than 10%.
The air conditioning for General Tool Companys (GTCs) machine shop became inadequate
to provide the cooling necessary for the added heat load from new equipment. Additional
airflow to facilitate the clean shop air was also needed. The conventional air
conditioning equipment would require an air handler and a 100-ton condenser for the 60,000
square foot machine shop, which would have cost $130,000 and required $28,000 per year in
operating and maintenance costs.
An investigation into alternative solutions showed a system utilizing roof mist sprinkling
to provide evaporative cooling of the roof and ceiling zone of the plant to reduce heat
build-up and the radiant heat load of the roof. The roof misting system includes a micro
controller and sensors to monitor roof surface temperatures by zones. This enables the
controller to minimally mist water on the roof surface independently as the roof
temperature rises. The materials and installation cost for the 60,000 square foot facility
was less than $25,000 to provide the equivalent of 100 tons of cooling on a 90-degree day.
GTC installed a roof misting evaporative cooling system to provide additional cooling for
the machine shop. During the systems six seasons of operation, the annual operating and
maintenance costs have averaged less than $2,500. The system also provides the additional
benefit of extending the life of the roof surface by keeping it at a lower temperature.
The heat load has been reduced sufficiently for the original air conditioning system to
cool the shop floor adequately on the hottest days. The system has provided excellent
results and has only required minimal maintenance.
Date:Oct-18-2006 http://www.bmpcoe.org/bestpractices/internal/gtc/gtc_9.htm