All air-conditioning systems work on the same principle: an outdoor unit exchanges heat with the outside air and one or more indoor units condition the rooms. There are two separate choices: the type of system (how the outdoor unit connects to the indoor units) and the type of indoor unit (how the air reaches the room).
Three types of system
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The simplest solution: one outdoor unit for one indoor unit, connected by a pair of copper pipes. Very good value for one room.
A single outdoor unit serves 2 to 5 indoor units. Each indoor unit has its own pair of copper pipes running directly to the outdoor unit, and its own controller.
A single outdoor unit for many indoor units, with a main pair of pipes that branches out to each unit, like a water supply network. It takes more work (soldering and brazing), but makes sense from about 8 indoor units.
A split connects one outdoor unit to one indoor unit with a pair of copper pipes. In a multi-split, a single outdoor unit serves 2 to 5 indoor units, and each has its own pair of pipes running directly to the outdoor unit. In a VRF, a single outdoor unit serves many indoor units through a main pair of pipes that branches out to each unit, like a water supply network in a house.
When a VRF makes sense
A VRF takes more installation work (soldering and brazing at the pipe branches), but needs only one outdoor unit for many indoor units: from 5, 6, 7 or 8 in a house to 80 or 100 in hotels, depending on the capacity required. As a rule of thumb, from about 8 indoor units it is worth considering a VRF.
It can also make sense in a house with fewer units: when it has many rooms and you want a single outdoor unit, for appearance, rather than several spread around the facade.
Types of indoor unit
Whether it is a split, multi-split or VRF, the indoor units can be of several types, and they can be mixed within the same system.
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The most common, usually the cheapest and easiest to install. It goes high on a wall.
It sits in the false ceiling and only the panel shows, with 4 outlets, usually one for each direction. It is installed at a central point and spreads the air across the whole space.
It works like any other unit, but stands on the floor, against the wall, and blows the air upwards.
It is hidden in the false ceiling and the air comes out through grilles connected by ducts, which can go wherever you like. It is the most discreet, but needs more work.
| Type | Where it goes | Advantage | Keep in mind |
|---|---|---|---|
| Wall-mounted | High on a wall | The most common, usually the cheapest and easiest to install | Visible in the room |
| Cassette | Recessed in the false ceiling; only the panel with 4 outlets shows | Spreads air in every direction from a central point | Needs a false ceiling |
| Floor-standing | On the floor, against the wall | Works like the others and blows the air upwards | Takes up floor space |
| Ducted | Hidden in the false ceiling, with ducts and grilles | Clean look and freedom to place the grilles where you like | Needs much more work and a false ceiling |
Cooling, heating, dehumidifying and ventilation
Any type of unit can cool. Reversible models (heat pump), which are almost all modern ones, also heat. All have a dehumidifying mode and a ventilation mode.
How to choose
- How many rooms you want to air-condition, and whether they are used at different times.
- Whether there is space on the facade or roof for several outdoor units, or whether you prefer a single one (VRF).
- Whether you accept visible units (wall-mounted, floor-standing) or prefer hidden equipment (cassette, ducted).
- Whether the equipment will also provide heating: almost all modern models are reversible (heat pump).
- Whether the space is new, under construction, or existing: in existing buildings a split or multi-split is simpler.
Residential and commercial
| Residential | Commercial | |
|---|---|---|
| Most common choice | Split or multi-split, with wall-mounted units | Multi-split or VRF depending on size, with cassettes or ducted units |
| When to consider VRF | Houses with many rooms and a single outdoor unit | From about 8 indoor units |
| Priority | Comfort, quiet and appearance | Reliability, operating hours and zone control |
| Watch out for | Condensate and noise from the outdoor unit | Continuity of service and planned maintenance |
Installation and maintenance
Air conditioning contains refrigerant gas, which only certified technicians may handle. The filters should be cleaned regularly, and periodic preventive maintenance prevents breakdowns and maintains efficiency. The right capacity for each room depends on its area, its exposure to the sun, the people and the equipment in it.
Can I connect several indoor units to a single outdoor unit?
Yes: in a multi-split, 2 to 5 units depending on the model; in a VRF, many more. There are limits on the number of units and the total capacity per outdoor unit, set by the manufacturer.
What is the difference between a multi-split and a VRF?
In a multi-split each indoor unit has its own pair of copper pipes running directly to the outdoor unit. In a VRF a main pair of pipes branches out to each unit, like a water supply network: it takes more work to install, but serves many more units with a single outdoor unit.
When does a VRF make sense?
As a rule of thumb, from about 8 indoor units. In a house it can make sense with fewer, if it has many rooms and you want a single outdoor unit.
Is ducted a type of system?
No: it is a type of indoor unit. Split, multi-split and VRF can all have ducted units, cassettes, wall-mounted units or floor-standing units.
Do they all provide heating?
Reversible models (heat pump), which are the majority, cool and heat. All also have dehumidifying and ventilation modes.
Which is the quietest?
It depends more on the installation and the model than on the type. With a ducted unit, the noise is further from the rooms.