Air conditioning - how it works

A (hopefully) simple explanation of the dynamics of air conditioning...

A fridge or freezer is an appliance, which removes heat from one area (where the food products are stored) and discharges this unwanted heat to another area (usually into the surrounding air at the back of the appliance).

The “refrigeration circuit” consists of

• a freezer section which has very cold refrigerant gas passing through it.
• a compressor (that’s the big black metal thing near the floor at the back) which drives the refrigerant through the pipes.
• and a condensor (a series of tubes at the back, which are quite warm to touch.  The condenser tubes are actually discharging unwanted heat into the surrounding air.

An air conditioning system is a larger version of the fridge freezer, which removes heat from one area (a room inside the building) and discharges it through its condenser to outside building.

In order to make it practical to install an air conditioning system in a building, the “refrigeration circuit” of an air conditioner is divided into two parts:-

                                                                                                                                                                                                                                                                                                                             The indoor units come in all shapes and sizes, some designed to fit on a wall, or ceiling, some hidden above a ceiling with air ducts connected, some half in half out of the ceiling. 

The indoor unit and the outdoor unit (which includes the compressor) are powered by electricity, an inter-connection cable joins the two.

Heat Pumps

A heat pump system, like an air conditioning system, has an indoor unit, interconnecting pipes and an outdoor unit, but it also has a reversing valve which pumps the refrigerant the other way around circuit.  This “reverse cycle” operation makes the outdoor unit cool the surrounding air, and the indoor unit discharge its heat into the room.  Whilst this may appear very elaborate, there are to very good reasons for having the heat pump option:

1. Most rooms, which require cooling, also require heating.

2. On average a heat pump system capable of providing 3KW of heating in the room, consumes only 1KW of electricity – very cost effective on running costs.  This means it is 1/3, or 35% of the running costs of an electric heater.

Operation & Controls

When the air conditioner is turned on, the thermostat, which is fitted to the indoor unit, will determine the temperature of the room.  If the room is too hot, the compressor will be started, and the “refrigerant circuit” will produce cooling within the room.  When the room temperature is at the desired level, the thermostat will be satisfied, and turn off the compressor.

If the system is also a heat pump, it will automatically control the heating process in a similar manner.

Most systems which are manufactured, provide heating as well as cooling, because the price difference of a cool only system is minimal.