dT on Condensers

[refrigeracioncr]

Hi everybody.

Does anyone could helpme? I`m trying to understand what "DT" means in the selection of an air-cooled condenser?,

when I have to choose between different options, which value do I have to use?,

and specialy, which are the effects in the condenser`s efficience if I make a wrong selection?

Thanks.

[US Iceman]

Hi refrigeracioncr,

Welcome to the RE forums.

The DT relates to the temperature difference used for selecting the appropriate condenser capacity. The actual temperature difference is: Condensing temperature minus the temperature of the air entering the condenser. Thats the DT.

The compressor(s) will have a specific heat rejection for any given set of operating conditions. This amount of heat is rejected to the air-cooled condenser.

Therefore, if you take the heat rejection of the compressor(s) and divide it by the DT (described above), you have the basis for selecting the correct condenser.

It is also suggested you ensure the condenser heat rejection capacity is greater than the minimum value to provide some safety factor for operation. In other words, it helps to have the condenser slightly larger than necassary, but never smaller than the required heat rejection.

If the condenser is selected without enough heat rejection capacity, the condensing temperature will be higher. This increases the discharge pressure, lowers the overall system efficiency and cooling capacity, and increases the electrical use of the compressor.

I hope that helps.

[Peter_1]

Try to select with an as small as possible DT (10 K), will cost the customer more but will save much more money then the lower price for a bigger DT (15K as selected many times).

Difficult to explain this to your customer if you don't fully understand what's behind the numbers.

[wkd]

The condenser rejects the heat from the evaporator plus the added heat from compression.The question of Dt mainly influences the heat exchange surface area of the condenser.Generally the lower the better,however this will increase the cost of the condenser typical DT are 10-15 K although I have seen 20 K + on some air-cooled chillers mainly to reduce unit footprint but they do suffer from High Pressure problems at higher ambient temperatures.

Hope