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Why DTM Ratings Cost You Money


COLVILLE, Wash. – Bruce Nelson, President of Colmac Coil Manufacturing, Inc. recently completed a technical article on the subject of comparing refrigeration air cooler ratings. The article examines how different rating methods affect system energy efficiency and operating costs.

Refrigeration air cooler manufacturers publish ratings based on either average "room" temperature difference (DTM), or on initial (air-on) temperature difference (DT1).

According to Nelson, the DTM rating method results in customers making evaporator selections which are undersized for the cooling load and will cause the system to operate with lower than expected suction temperatures. The result is greater compressor power consumption compared to DT1 rated coolers.

Air coolers selected using DT1 ratings, on the other hand, have higher first cost but operate at the expected design suction temperature. This DT1 energy efficiency benefit can be calculated and expressed in terms of simple payback, or as an Incremental Return on Investment (IROI). The IROI resulting from using DT1 air cooler selections ranges from 32 to 156 percent per year, depending on the room temperature and type of compression system.

"By selecting air coolers based on DT1 ratings, customers avoid the DTM power consumption penalty and enjoy significant energy savings due to higher operating suction temperatures," said Nelson.

For more information contact: Jeremy Olberding, Vice President of Sales, 509-684-2595,

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