VRF and VRV Aircon: Between a Multi-Split and a Chiller

VRF is an arrangement where one outdoor unit serves many indoor units. The refrigerant reaching each indoor unit is varied continuously. Every indoor unit carries its own electronic expansion valve. That valve opens and closes against what its room is asking for moment by moment.

The outdoor unit varies along with them. A variable-speed compressor changes its own output to match what the indoor units are drawing between them, so the system settles at whatever share of capacity the building currently wants.

The difference fits in one line: capacity is allocated, not divided. A multi-split also hangs several indoor heads off one outdoor unit, but it does not redistribute output between those heads while they are running. This class does, and that is what holds it up across a floor plate.

Scale follows from the same property. Systems in this class take many more indoor units on one outdoor unit than any residential product, across floors and along pipe runs far longer than a flat contains.

Rooms in one building sit at very different loads at the same moment. A meeting room fills up and its load jumps, a west-facing office bakes through the afternoon, and a store room asks for almost nothing all day. In a flat those differences are small; across a floor plate they are not.

A system that divides its output crudely suffers under that spread. Something has to give when one zone demands far more than its neighbours, and what gives is usually the zone furthest from where the output is taken. Varying the flow sends refrigerant towards the units calling for it.

So a heavily loaded zone and an idle one can share a circuit without either dictating the other's outcome. That is what the class is bought for, and it lets one outdoor unit serve a whole floor rather than one household.

Part load is where the running cost shows up. Cooling demand in a building spends most of its life below the peak it was sized for. A compressor able to hold a partial output runs steadily at that output; one that only knows on and off has to cycle instead, and cycling costs efficiency.

Three arrangements cover most of what is cooled in Singapore, and this class is the middle one. A split or multi-split serves one household from one outdoor unit. A VRF system serves a floor, a shophouse or a small building. A central chilled-water plant serves a tower, or several on a district supply.

What separates it from the plant above is the medium, not the size of the building. This class is refrigerant-based: refrigerant is made cold at the outdoor unit and piped, still as refrigerant, all the way to the coil in the occupied room. A chilled-water plant makes cold water centrally and sends it up risers to coils in the space.

Distribution is the other dividing line. A chiller gathers the machinery into one plant room, with risers, pumps and a regime built around that room. This class spreads out instead: outdoor units sit on roofs, ledges and service decks close to the zones they serve.

Spreading out is what makes it attractive to a building too small to justify a plant room. It also suits a landlord who wants each tenancy controlled and metered on its own. A shophouse converted into offices, a two-storey clinic, a mid-sized retail unit and a large landed house are all ordinary homes for it.

One pair of pipes leaves the outdoor unit and has to become many. The fitting that performs the split is where this class differs physically from anything in a flat.

Branch fittings are the common answer. These are Y-shaped joints and headers brazed into the pipe run, dividing one line into two, then again further along. They carry no power and no controls; their job is to split the flow so refrigerant and oil keep moving properly down each leg. Refnet is Daikin's word for its own fittings.

A branch box is the other approach. It is a housed unit sitting between the outdoor unit and a group of indoor units, holding the valves that meter each branch, with power and control wiring run to it. The metering has been lifted out of the indoor units and gathered into one place.

Where this hardware sits decides how a fault gets handled. Joints and boxes live above false ceilings, inside risers and along service corridors, often sealed behind finished plasterboard once the fit-out completes. Tracing a leak across a distributed run is slow work even before the ceiling question.

Ask for the as-built drawing before anybody needs it. It records where the joints, boxes and isolation points are, and which indoor units sit on which branch. A contractor searching a system without one is charging for the search.

• •The as-built drawing, showing pipe routes, branch fittings and isolation points.
• •The indoor unit schedule, listing each unit by room or zone with its address on the system.
• •Access notes: which ceiling panels open, and where the sealed sections run.
• •The commissioning report, including the refrigerant charge the system was filled to.
• •The controller documentation, and whatever login the system was handed over with.

Servicing moves from ad hoc to contracted. A household calls somebody when the aircon stops; a building on this class runs a maintenance contract, with scheduled visits, a named contractor and condition recorded against each unit. A system with many indoor units and a long distributed run degrades quietly.

Faults are read through a controller rather than off a blinking light. Centralised controllers list units by address and report fault codes against them, so the first news of a problem is a code and a unit number on a screen in an office or a lobby.

A refrigerant leak is a far bigger event than on a split. The charge is larger, the run is longer, and the loss reaches every indoor unit on that circuit rather than one room. Recovering, repairing, pressure-testing, evacuating and recharging a distributed system is a different order of job.

Watch for the quote that treats a system this size like a split. Putting the charge back without finding where it went sends the same volume out through the same hole. On a distributed run the leak search is the job; the top-up is what happens once it succeeds.