COMPARING AIR COOLER RATINGS – PART 2:
Why DTM Ratings Cost You Money
As explained in a previous article, manufacturers of refrigeration evaporators publish ratings based on either average ”room” temperature difference ( DTM), or air on temperature difference (DT1). Compared to DT1 ratings, the DTM rating method results in evaporator selections which are undersized for the cooling load and will cause the system to operate with lower than expected suction temperatures. This article calculates the energy efficiency penalty resulting from selecting evaporators using DTM ratings, and puts the benefit of reduced power consumption when using DT1 ratings in terms of incremental return on investment (IROI). Depending on the room temperature and type of compression system (single or 2-stage) the IROI when using DT1 ratings can be as high as 156%, a simple payback of as short as 8 months!