Building services · plain English and engineering detail
Six ways a building gets cooled, from the box outside a flat to a thousand-ton central plant, drawn as working schematics. Hover or tap anything to see what it is and what it does.
Start here
Nothing in a building creates cold. Every system on this page does the same single job: pick up heat where people don't want it, carry it somewhere else, and dump it outside. The differences are all about what carries the heat, and how far.
Your fridge does this to your kitchen. Put your hand behind it and you feel the heat it took out of the milk. A building works the same way, the heat comes out on the roof instead, which is why plant rooms and rooftops are hot places.
There are only two families. In the refrigerant family, a special fluid is piped straight to the room, boils inside a coil right there, and carries the heat back out to a box outside. That is your home air-conditioner, and the office version of it, VRF. In the chilled water family, that same boiling happens once, in a big machine in the basement, and water is pumped around the building instead. Water is heavy and slow, but it is safe in a ceiling and it scales to a whole tower.
The six drawings below run from the simplest to the largest. Hover or tap anything, every pump, valve, vessel and pipe explains itself. Switch Detail to Engineer if you want the design and operational notes instead of the plain-English version.
Teal is chilled water going to the building and coming back. Green is condenser water going to and from the roof. Amber is refrigerant. Grey is air. The key sits under each drawing.
The dashes and dots travel at the speed the water is actually moving. Drag the Building load slider and watch what speeds up, what slows down, and what stubbornly doesn't.
Run start-up walks through how a plant is actually brought online, and it is not the order most people guess. Nothing is allowed to start until the thing before it has proven it is really working.
Scroll the drawing sideways to follow the whole system →
Comparison
The honest answer is that the choice is mostly about how many rooms share one machine, and how far the heat has to travel. Everything else, cost, efficiency, maintenance, who you call when it breaks, follows from those two things.
A single split serves one room with one outdoor box. A multi-split, Singapore's familiar System 2, 3 or 4, lets several rooms share one box, which saves ledge space but means the rooms also share the compressor's capacity. VRF is the same idea again, much larger: one outdoor unit feeding dozens of indoor units across a floor or a building. A chilled water plant goes further still and stops piping refrigerant altogether, boiling it once in a basement machine and sending water out instead.
That last step is the real dividing line. Refrigerant is efficient and compact, but it can only travel so far. Daikin's VRV 5 allows about 165 m of actual pipe run and a 90 m level difference, roughly 20 to 25 storeys from one outdoor unit. Above that, you are putting plant on multiple levels, and at some point a water riser is simply the easier answer. No standard sets the crossover, and the consultancy rules of thumb you will find (10,000–15,000 m² is one published figure) are one firm's opinion, not an industry threshold. The pipe envelope is the constraint that actually bites.
A ceiling cassette is a shape, not a system. The square four-way grille you see in an office or shop ceiling tells you nothing about what is inside it. Daikin sells the identical form factor both ways: the FXFQ Round Flow cassette is a refrigerant (DX) unit for a VRV system, while the FWF and FWC cassettes are chilled-water fan coils rated at 7 °C in and 12 °C out. Same ceiling, same grille, completely different building services above it.
The distinction is not academic. One has two copper refrigerant lines and a condensate drain in the void; the other has insulated flow-and-return water pipes with valves, strainers and air vents. One leaks refrigerant, the other floods a ceiling. One is governed by refrigerant concentration limits in the room below; the other is not. If you are reading a tender and it says "cassette", you still do not know what system you are buying.
Every system type is rated by a different standard, at different conditions, with a different boundary around what counts. Room air-conditioners in Singapore are rated on weighted COP under ISO 5151, not SEER, and not the CSPF used by most of our neighbours. VRF is rated on IEER under AHRI 1230. Chillers are rated on kW/RT and IPLV under AHRI 550/590, and that figure is the compressor alone, not the pumps and towers around it. Putting "IEER 15.5", "SEER 20" and "0.55 kW/RT" side by side is meaningless.
There is one clean way through it, and Singapore has already built it. BCA Green Mark 2021 assesses VRF and chilled water on the same yardstick, total system kW/RT, including outdoor units or chillers, pumps and air distribution, with VRF converted as 3.517 ÷ IEER. A new building has to reach 0.8 kW/RT whichever technology it uses. The regulator refuses to give either one a handicap, which is the most useful answer anyone is going to give you.
In a temperate climate, cooling means lowering the temperature. Here, most of the work is removing moisture, and the two are not the same job. Direct-expansion fan coils, whether split or VRF, typically run a sensible heat ratio of 0.70–0.85, meaning limited capacity to dehumidify. They also condition only the air already in the room; they bring in no outdoor air at all. Introducing raw outdoor air at an indoor unit is usually limited to about 10% of supply volume before it overwhelms the coil.
So a VRF building in Singapore still needs a separate unit to bring in fresh air and dry it first. That unit is not optional, it is not cheap, and leaving it out is why some buildings feel clammy at 23 °C. A chilled water system gives the designer a second lever, the water temperature and the depth of the coil, to set how dry the air leaves. That is the strongest technical argument for water in this climate, and it is rarely the one used in the sales meeting.
Refrigerant safety is usually assumed to be a chiller problem. It is the opposite. A chiller keeps its entire refrigerant charge inside a plant room. A VRF or split system puts refrigerant inside occupied rooms, which is why it falls under the ASHRAE 15 charge-versus-room-volume check, and the smallest room on the circuit governs the whole system. It is one of the most commonly overlooked items in VRF design.
| System | Heat carried by | Typical scale | Pros | Cons |
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| Single splitWALL / CASSETTE / DUCTED | Refrigerant, direct to the room (DX) | 2.5–7 kW · one room |
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| Multi-splitSYSTEM 2 / 3 / 4 | Refrigerant, direct to the room (DX) | 6–12 kW · one flat or small office |
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| VRF / VRVVARIABLE REFRIGERANT FLOW | Refrigerant, piped through the building (DX) | 22–56 kW per module · up to 64 indoor units |
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| Air-cooled chilled waterCONFIG 01 | Water to the coils; heat to outdoor air | 100 kW–2 MW · medium buildings |
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| Water-cooled chilled waterCONFIG 02–04 | Water to the coils; heat to a cooling tower | 350 kW–20 MW+ · large buildings |
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| District coolinge.g. MARINA BAY | Chilled water from a shared central plant | Precinct scale · many buildings |
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"VRF saves 30–55% energy." Most published savings compare operating regimes, not equipment. The most-cited field study found VRF buildings running part-time and part-space at 26 °C against VAV buildings running full-time at 24 °C, the biggest single driver of the saving was that the VRF buildings were run warmer and switched off. Bonneville Power Administration, reviewing the literature, settled on 5–20% for regional planning and warned that real performance "may not be as good as" manufacturer claims.
"VRV and VRF are different technologies." They are the same technology. Daikin says so itself: VRV is its 1982 trademark, so everyone else calls it VRF. What varies is refrigerant mass flow rate, not the amount of refrigerant in the system.
"Heat recovery VRF is always more efficient." US DOE's own minimum standards require a lower IEER of heat-recovery models than of standard ones in every capacity band, the branch selector costs efficiency in cooling-only operation. Heat recovery pays only where heating and cooling genuinely happen at the same time, which in Singapore is rare enough to need a specific justification.
Glossary
About this page: drafted with an AI assistant at my direction, engineering content checked by me against the sources below, and restyled to this site. The load model is indicative and says so above. Views are my own, not my employer's.
Verification
Every sequence, figure and rule of thumb on this page was checked against primary sources before publishing, and several earlier drafts were wrong. The start-up order originally showed the cooling tower fan starting with the condenser water pump, and the coil valves modulating as the final step. Both are incorrect: tower fans stage up later on rising condenser water temperature, and the coil valves' requests are what enable the plant in the first place. An earlier draft also put the air-cooled energy penalty at 30–40%; it is closer to double.
The plant model is indicative and deliberately simple. It illustrates how each arrangement behaves as load falls, it is not a selection tool, and it is not calibrated to any real installation.