Saving refrigeration power

The actual operation is quite simple. A solid state control device slows down the condenser coil, evaporator and cold air flow circulating fan speed when the chilling compressor is in the off mode. This reduces the heat generated from the drive motors of these fans, thus reducing heat input into the cold room and delaying the restart of the chilling compressor. Reduction of heat generated by the fans reduces the compressor duty cycle, saving energy as well as compressor mechanical wear and tear.

Incorporation of these evaporator fan controllers which have been recently developed and are commercially available overseas can reduce overall power consumption of the cold unit by about (twenty five) 25 percent. Given the high cost of power today, the annual savings in power costs could be quite substantial! The block circuit diagram of a fan controller for a typical cold room set up is given below:

A commercial or industrial type walk-in cold compartment or cold room has a refrigeration compressor associated with fans in the condenser, evaporator and for cold air circulation in the cold room. About (forty) 40 percent of the heat is generated by these fan motors inside the cold compartment. The fan controller reduces this heat load by about (seventy five) 75 percent, and hence the thermostat based gap between compressor running cycles increases resulting in overall power savings by about (twenty five) 25 percent.

A typical cold room evaporator coil fan set-up generates around 12,000 BTU/ hour at normal cold state even when the chilling compressor is off! With the fan controller reducing the evaporator coil fan speed, the heat generation could be around 2,300 BTU/hour, while maintaining the cold compartment temperature. Continuously operated over the month (30 days) the process can save electric power corresponding to cooling 4,284,000 BTU to cold room temperature.

Apart from this direct power savings, the slower fan speed in the cold room reduces the air movement. This slows down dehydration of perishable foodstuff and thereby extends their shelf life. This is an additional saving in the storage of food, through enhancing shelf life, and reducing wastage by spoiling, which has not been considered in the power cost saving exercise.

In the hot and humid climate of Bangladesh, as we develop our food retail system through large supermarkets, the usage of large walk-in cold room concept of preserving fresh foodstuff is bound to increase. It will be a very useful and cost effective solution if these evaporator fan controllers with a very attractive pay back option can be incorporated in the refrigeration set- up.