General terms

Split system - where the system has two main units (evaporator and condenser). One situated internally the other externally. Interconnecting pipe-work, drain and cable are run between the two components.

Can be cooling only or heating & cooling (heat-pump).

The internal unit (fan coil) contains a fan, PCB & evaporator.

The external unit contains a fan, condenser, PCB & compressor (reversing valve if heat-pump).

Heat-pump - where the system has a reversing valve in the external unit. This allows reverse flow of refrigerant around the system to maintain either heating or cooling in the required space. (refrigerant passes through the compressor in the same direction at all times).

Compressor - a vapour pump that forms a pressure differential. Draws low pressure gas and squeezes it into a high pressure state to be condensed back in to a liquid ( via the condenser).

Compressor types


Semi-hermetic - where the electrical & mechinical components are together.

Open-type - Where mechinical & electrical components are seperate.

Reciprocating - using mechinical pistons to pump the refrigerant.

Scroll - using two scrolls, one fixed and one orbits to create pumping action.

Rotary - where a rotating mechinism is used to provide the pumping action.

Screw - consists of rotors having one male one female gears. They engage a screw and two gate rotors to give the pumping action.

Centrifugal - where the compressor has a impeller that rotates at approx 10,000 rpm. It generates such force that the gaseous refrigerant changes into speed energy that is converted into pressure energy for compression.

Condenser - this is the part of the system that receives hot high pressure gas from the compressor. As the gas is cooled in the condenser it changes state from high pressure vapour back to a liquid state.

Evaporator - the part of the system that absorbes heat energy in to the refrigerant.

Expansion valve - a device that maintains the pressure difference between high & low sides of the system.

Humidity - ammount of moisture/dampness present in the air.

Relitave Humidity - the ratio of water present in air to greatest amount posible at the same temperature.

Subcooling - the cooling of liquid refrigerant below its condensing temperature.

Superheat - the temperature of vapour above boiling temperature of its liquid at that pressure.

Temperature conversions

C = (F - 32) divided by 1.8
F = (1.8 x C) + 32






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