Cooling Efficiency: Are fouled condensers costing you ££££?

It is well documented that fouled condensers can have a drastic effect on cooling efficiency - but why?

The purpose of a condenser is to transfer heat from refrigerant to the surrounding air. This is achieved by passing air across the condenser, and as the refrigerant is cooled it condenses to a liquid and passes to the evaporator.

 

Condenser

 

Heat Exchange

For heat exchange, there needs to be a temperature differential between air and refrigerant. At low ambient temperatures, heat can be transferred relatively easily and minimum airflow is required (in the example on the left 2 of 14 fans may operate).

As ambient temperatures increase, it is necessary to operate more fans to maintain heat rejection.

 

Condenser

 

Fouled Condensers

If the condensers are fouled heat transfer is not effective, meaning more fans will be required to maintain the same level of heat rejection.

When all fans are operating, refrigerant temperature will increase until the temperature differential with the surrounding air is sufficient to transfer heat from the fouled condenser. At these increased temperatures, many fouled systems fail to deliver the required cooling capacity.

 

Explanation

We should be referring to pressure / superheat, but to explain the concept we will simplify and explain in terms of temperature…

Work carried out by a refrigeration compressor is commonly referred to as the “lift”. This is the difference between the temperature of refrigerant entering and leaving the compressor. 

Fouled condensers will increase the temperature of refrigerant leaving the compressor.  A well-used rule of thumb states “for every 1 deg C that this temperature is increased, efficiency is reduced by 2-4%”.

To quantify this, it is not unusual for a condenser that hasn’t been cleaned for 12 months to reduce heat rejection by 5 deg C, increasing energy consumption by 10-20%.

In extreme cases we have seen instances where this is closer to 15 deg C!

 

For more information on condenser cleaning click here!