Air conditioning guides

The thing worth understanding first

An air conditioner does not make cold. It moves heat from one place to another, using a refrigerant that changes state as it goes round a circuit. That is precisely what a heat pump does, and in fact almost every air conditioner sold now will run in reverse and heat the room.

Once that is clear, several things stop being surprising:

• It can produce more heat energy than the electrical energy it consumes, because it is moving heat rather than generating it. That is not a marketing claim, it is what a heat pump does.
• The outdoor unit gets hot in summer and cold in winter, because it is the end of the circuit that is dumping or collecting heat.
• It produces water. Cooling air below its dew point condenses moisture out of it, and that has to go somewhere – which is why condensate drainage is a real design item rather than an afterthought.
• Heating in winter is usually the better value function, and it is the one most people never use.

How air conditioning actually works sets this out properly, and air conditioning vs a heat pump explains why two things with the same physics are sold as different products.

Start here, depending on what you are deciding

Sizing, which is where most installations go wrong

The single commonest fault in domestic air conditioning is a unit sized from a website box – so many BTU for so many square metres. That calculation ignores almost everything that actually determines the load.

What a real sizing accounts for:

• Glazing area and orientation. A south or west-facing glass wall is an enormous solar gain and it dwarfs floor area as a factor.
• What the glass is – single, double, coated, shaded.
• Insulation levels and the construction, which in period property is a very different number from a new build.
• Occupancy, because people are a heat source.
• Equipment, which in an office or a comms room can be the dominant load.
• Air changes, including anything that leaks.
• Roof exposure, for a top floor or a room in the roof.

Sizing air conditioning goes through it properly.

Siting, noise and the neighbours

The outdoor unit is where most of the objections come from, and almost all of them are avoidable at design stage rather than afterwards.

• Condenser siting and planning – the planning position, boundary distances, and where a unit will and will not be a problem.
• Air conditioning noise – what is normal operation, what is a fault developing, and what constitutes a nuisance.
• Retrofitting into period buildings – routing, concealment, and what listed status changes.

The general rule: a unit sited thoughtfully, with a clear airflow path, on decent mounts, away from a bedroom window and away from a boundary, is something nobody complains about. One bolted to the nearest convenient wall is a long-running argument.

Refrigerant, compliance and servicing

Refrigerants are regulated, and the regime is tightening. The choice affects efficiency, the environmental figure attached to the system, and what happens at end of life.

• R32, R410A and R290 – what the three common choices mean practically.
• Air conditioning servicing – what a proper visit covers, beyond a filter clean.

For business premises the compliance obligations are real and they fall on the operator, not the contractor – see the F-Gas compliance guides and F-Gas compliance.

See also air conditioning installation and air conditioning servicing.