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Original Date: 10/07/2002
Revision Date: 01/18/2007
Best Practice : Roof Mist Cooling
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 Company’s (GTC’s) 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 system’s 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.
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