Air Conditioning

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What is an Air Conditioner?

An air-conditioner is designed to cool down a room/area. True air-conditioners actually reduce the air temperature. When it gets hot and stuffy there are many types of products available to cool you. They range from cool blowing fans to fixed air-conditioner units.

Coolers with limited effect include;

  • Fan Heaters with cool air facility
  • Oscillating Fans

Units that actually reduce the air temperature include;

  • Single Unit Mobile Air Conditioners
  • Split Mobile Air Conditioners
  • Fixed Installation Systems

Mobile air-conditioners range in size (their cooling capacity), the smaller capacity models are single units and the larger models are split systems.

Where can I use a mobile air conditioner?

  • Mobiles are an instant solution to true air-conditioning, having the advantages of fixed systems but portable and ready to use immediately.
  • Perfect for commercial or domestic use.
  • No major installation costs, upheaval or waiting time involved, they connect into a normal 13amp socket.
  • When different rooms need to be cooled at different times the units can be moved from room to room.
  • More than one unit can be used to cool a larger room if needed.

Remember, to air-condition a room, windows and doors should be kept closed, otherwise cooled air will be lost.

Where does the heat go?

Air-conditioning units work by taking heat from a room and expelling to the outside.

In the simplest forms of mobiles, the hot (and damp) air is extracted from the roof and expelled through a tube. The tube, similar to a tumble dryer hose (around 1m long), has to be vented to the outside ideally through a small venting hole made in the wall or window. For a quick fix (temporary solution) you can, with the use of the flattened oval adaptor supplied, put the hose out or a partially opened door or window.

In the more powerful split system mobile type, the heat along with excess humidity is discharged by the external (condenser) unit. Because the condenser unit is placed outside, it can be larger – making potential cooling capacity on split systems far greater.

How does a mobile Work?

Essentially warm air is drawn into the machine from the room, heat is removed by cooled refrigerant and cool air is passed out by a fan.

There are 3 main components to an air-conditioner.

  • the compressor
  • the evaporator (or heat exchanger or cold coil)
  • the condenser (or hot coil)
  • The compressor is the ‘engine’ of the air-conditioner, it pushes the refrigerant around the air-conditioner.
  • Air is drawn in by a fan over the evaporator which contains refrigerant under low pressure and very cold.
  • The air is instantly cooled and moves out through the front air vents.
  • Heat is gathered by the evaporator, held in the refridgerant, and taken to the condenser.
  • Air passes over the condenser where it takes the heat from the refrigerant.
  • This heated air is expelled through a hose or from the condenser box and split units.

Are there different types of mobile?

There are 2 main types of mobile – Single Units and Split Systems

Single Units

Single units are instantly recognized by the hot air exhaust hose. Single units posses all three main components in one, and are vented to the outside by means of the hose (similar to a cookerhood extractor or tumble dryer hose.

There are 2 types of single units;

  • Air Cooled
  • Air water cooled

Air plus water cooled units give a larger cooling power but do need regular filling and descaling in hard water areas.

Split Systems

For larger rooms or rooms that have bigger heat loads Split Systems are normally required. They are easily recognizable by the separate box that needs to be placed outside the room.

The condenser box can be placed either on a window sill or hooked over the edge of a window frame, or on the ground if on the ground floor. The condenser is connected to the main (inside) unit by means of refrigerant lines – these are sometimes also known as umbilical lines. These can usually be detached from the outside unit, so they can also be passed through a whole in the wall, about the size of a half brick.

What should I consider when deciding unit size?

It is important to remember that to cool a room properly there are many other factors to take into account, such as;

  • Equipment e.g. computers being used.
  • Number of windows in the room, especially south facing.
  • Number of people that will be in the room (each person generates on average an additional 150W of heat)

All of these contribute to additional heat gain in the room and the air-conditioner would need to be more powerful to cope with these factors as well as room size.
It is easy to forget that the hotter the outside the more heat the air conditioner has to deal with to make the area feel cool. So a unit coping with a cloudy day, say 24C, may struggle in 29C with a bright sunshine.

Approximately 1000W (3400 BTU’s) are needed to compensate for 1kW of generated heat.

What happens if I buy an air-conditioner smaller than is needed?

An air conditioner is actually refrigerating the air passing through the unit. It is taking heat from the room, so what ever the heat load, the environment in the room will be improved.

When the heat load is greater that the units’ cooling capacity. It will be acting as a ‘’comfort cooler’’ or ‘’spot cooler’’. Taking heat out of the room but not actually reducing the temperatures.

To cool the room properly a second unit should be a condsideration.

How much does a mobile air-conditioner cost to run?

Most of the single unit air conditioners input power is below is below 1000W (1kW) per hour. Therefore, the cost to run on full power would be around 5p / 6p (average domestic tariff of 1 unit of electricity = 6p).

Split system air conditioners having inputs of around 1.3W/hr would cost around 8p per hour to run on full power.

Can I extend the hose?

We would not recommend that you extend the hose provided in the single unit air conditioners, but if you have no other option it is important to vent into a much larger diameter vent pipe. If the air-conditioners’ fan cannot expel heat fast enough i.e. there is a back pressure or constriction to the airflow the unit will not work and could even be damaged.

Whenever possible avoid extending the hose length, so site the mobile next to an outside wall or window.

If you have difficulty in venting the hose to the outside you may find that you can vent into a room where temperature doesn’t matter, for example office to a warehouse.

On Split Systems, the refrigerant lines cannot be extended.

How low can I make the temperature?

There are limits to how cold the room temperature can be made. When operating in a suitably sized room most air conditioners will cool to around 21°C. Mobile air conditioners are designed for ‘people’s comfort’. The ideal summer temperature for most people is around 21-24°C

What happens if the unit stops working?

  • Check that the protection switch has not cut in, and that the plug fuse is rated at 13amp.
  • Check there is no condensation or blockage, to either the exhaust hose or refrigerant lines.
  • Drain any condensate that may have built up in particularly humid conditions.