Honeywell On System
Honeywell On System
Honeywell On System
AN INTRODUCTION TO REFRIGERATION
APPLICATION NOTE
If you were to place a hot cup of coffee on a table and leave it for a while, the heat in the coffee would be transferred to
the materials in contact with the coffee, i.e. the cup, the table and the surrounding air. As the heat is transferred, the
coffee in time cools. Using the same principle, refrigeration works by removing heat from a product and transferring that
heat to the outside air.
The Evaporator
The purpose of the evaporator is to remove unwanted heat from the product, via the liquid refrigerant. The liquid
refrigerant contained within the evaporator is boiling at a low-pressure. The level of this pressure is determined by two
factors:
- The rate at which the heat is absorbed from the product to the liquid refrigerant in the evaporator
- The rate at which the low-pressure vapour is removed from the evaporator by the compressor
To enable the transfer of heat, the temperature of the liquid refrigerant must be lower than the temperature of the product
being cooled. Once transferred, the liquid refrigerant is drawn from the evaporator by the compressor via the suction line.
When leaving the evaporator coil the liquid refrigerant is in vapour form.
The Compressor
The purpose of the compressor is to draw the low-temperature, low-pressure vapour from the evaporator via the suction
line. Once drawn, the vapour is compressed. When vapour is compressed it rises in temperature. Therefore, the
compressor transforms the vapour from a low-temperature vapour to a high-temperature vapour, in turn increasing the
pressure. The vapour is then released from the compressor in to the discharge line.
The Condenser
The purpose of the condenser is to extract heat from the refrigerant to the outside air. The condenser is usually installed
on the reinforced roof of the building, which enables the transfer of heat. Fans mounted above the condenser unit are
used to draw air through the condenser coils.
The temperature of the high-pressure vapour determines the temperature at which the condensation begins. As heat has
to flow from the condenser to the air, the condensation temperature must be higher than that of the air; usually between -
12°C and -1°C. The high-pressure vapour within the condenser is then cooled to the point where it becomes a liquid
refrigerant once more, whilst retaining some heat. The liquid refrigerant then flows from the condenser in to the liquid line.
This low-pressure, low-temperature vapour is then drawn from the evaporator by the compressor. When vapour is
compressed it rises in temperature. Therefore, the compressor transforms the vapour from a low-temperature vapour to a
high-temperature vapour, in turn increasing the pressure. This high-temperature, high-pressure vapour is pumped from
the compressor to the condenser; where it is cooled by the surrounding air, or in some cases by fan assistance. The
vapour within the condenser is cooled only to the point where it becomes a liquid once more. The heat, which has been
absorbed, is then conducted to the outside air.
At this stage the liquid refrigerant is passed through the expansion valve. The expansion valve reduces the pressure of
the liquid refrigerant and therefore reduces the temperature. The cycle is complete when the refrigerant flows into the
evaporator, from the expansion valve, as a low-pressure, low-temperature liquid.
Diagram 1
EN5B-0024UK07 R0505