Nominal capacities should be based upon entering air temperature. The test conditions in the European standard are based on DT1 (DT1 = difference between the entering air temperature into the cooler and the temperature corresponding to the saturated refrigerant pressure at the outlet of the cooler).
Therefore it was decided that nominal capacities in leaflets, brochures, etc. should also be based on DT1.
This means a big change for the Industry as a significant number of manufacturers are still using Dtm to define nominal capacities (Dtm = difference between the mean of entering and leaving air temperature into the cooler and the temperature corresponding to the saturated refrigerant pressure at the outlet of the cooler).
Using the entering air temperature as reference temperature enables easier checking on the delivered capacity. With DT1 there is a direct relation between the tested capacity and the nominal capacity used in leaflets, brochures, etc.
All participants within the certification programme will use DT1 which will create an uniform presentation of capacity.
WARNING ! Do not compare capacity at DT1 = 8K with capacity at Dtm = 8K
An air cooler unit cooling air from 0°C to -3°C with an evaporating temperature of -8°C works at: DT1 = 8K, but Dtm = 6,5K.
The capacity for the same unit air cooler at Dtm = 8K will in figures be at least 25% higher. This is a matter of presentation because it is in fact the same air cooler.