Last edited: 7th Septmeber 2023
Much like the information found in the Split-System Buyers Guide, systems that fall under the category of ‘Multi-Split Systems’ follow all the same legalities and must be installed under the same regulations, meaning you must employ the services on an F-GAS registered engineer to carry out the installation. They also have the same requirement for servicing and will have the same manufacturer’s warranty terms.
Multi split systems consist of one outdoor unit being connected to and operating numerous indoor units. Sizing of a multi split system is also done in the same way as a single split system, ensuring that each internal unit used is matched to the size of the room. However, because there will be more than one internal unit connected to the outdoor unit, it is essential that the outdoor unit is sized correctly.
Most manufacturers allow for ‘diversity’ when sizing systems, which allows for outdoor units of a lower output rating to operate multiple indoor units with higher capacities.
As an example, if you wanted to have two 2.5kW indoor units connected to the outdoor unit, you would expect to have to use a unit of a minimum 5.0kW capacity. However, if you look at the LG Multi Split range, you’ll see the outdoor units are not available as a 5.0kW, you get the option of 4.7kW or 5.3kW, so which one do you choose?
The 5.3kW option will operate both 2.5kW indoor units without any diversity, so you will get 100% performance from both internal units, when they are operated at the same time. But, you could also use the 4.7kW unit, as due to the ability to work with diversity, this unit will still operate two 2.5kW internal units (at 113%) diversity and will save you money on the cost of the outdoor unit (the lower sizes are generally cheaper).
So you can choose either option, it simply depends on how you wish to use the system? If you are having internal units installed into 2 bedrooms, which will be occupied daily and used together every night, then you will likely wish to opt for the larger option, as there is no loss of performance (0% Diversity). However, if you were having 1 internal unit installed into a bedroom and the 1 unit installed into a living room, the majority of the time the two units wouldn’t be operated together. This means you could use the smaller option of outdoor unit (the option with 113% diversity) and still have a system functioning perfectly fine, as when you are in the living room with only that unit operating, you get 100% performance and when in the bedroom, with only that unit operating, you again get 100% performance from the unit.
You only get diversity if say, you are using the unit in the living room and then choose to switch on the unit in the bedroom (to pre-cool the room before going to bed) so both units are now operating. But when you decide to go to bed and switch off the unit in the living room, you again go back to getting the full capacity of the unit operating.
Without having access to manufacturer’s software or combination tables, it is hard to ensure you select the correct size unit you will require. That is why we have experienced staff on hand to assist with ensuring you make the best selection (as we do have access to all the required information).
If you choose to make a selection without getting assistance first, it is better to choose a larger outdoor unit that will be over capacity, as this will always ensure it has enough power to operate the system, not matter how you choose to use it.
When making your choice of external unit, always make sure you select a unit with enough ‘heads’ to handle the amount of internal units you wish to operate. Head refers to the internal ‘head’ units. If you desire to have 3 internal units connected to one external unit, you will need a minimum of a 3 head outdoor unit.
However, you may still need to select an outdoor unit labelled larger than ‘3 head’ if the internal units are larger and the system has a large capacity requirement.
All outdoor units will also have a maximum pipe length, which refers to the absolute maximum your engineer can run the connecting refrigerant pipes from the outdoor unit to the indoor unit(s). Along with this maximum distance, there is also a maximum elevation which must be factored in to designing the system (as this elevation will shorten the maximum pipe length). This information can be found in the technical data sheet for the specified unit.
One thing to be aware of with a multi-split system is that all internal units connected to the outdoor unit MUST be operated in the same mode. This type of system is not capable of having one unit operate in cooling mode, while the other connected units operate in heating mode.
Multi-split systems are usually provided with the same options as single split systems, so they come with the internal unit offerings of:
- High wall mounted
- Low wall (console)
- Ceiling Cassette
Which can be mixed and matched throughout the property, so you could have a high wall mounted unit in one room, a low wall in another and a ducted unit hidden in another room.
Some manufacturers actually offer a larger selection for their multi-split ranges too, which can extend the ranges available considerably (but it is better to see each manufacturer’s details individually for this information).
The majority of manufacturers have limited their offerings of outdoor units to a maximum of 5 heads. This means that even when you are looking to have a multi split system installed, if you are looking to have 6 or more rooms equipped with air conditioning, you will need to have more than 1 outdoor unit outside your property.