Chilled water aircon: when the cold is made elsewhere
Nothing on the ledge belongs to your unit, and there is no gas in the room to lose. The cooling arrives as cold water made in a plant somewhere else in the building, which means a warm room might be reporting somebody else's fault.
By Team Snowflake | Updated 5 Aug 2026
Where the cold is made, and how it reaches the room
A chilled-water system separates the machine that makes cold from the box that delivers it. Chillers stand in a plant room, usually in a basement or on a roof. They cool water down to whatever supply temperature the building runs at. That water is the product. Everything after it is distribution.
Pumps push the cold water into risers, which are heavily insulated pipes climbing through the core of the building. Branches leave the riser at each floor and cross the ceiling void towards individual units. Each unit holds a coil. A blower pulls room air through a filter and across that coil, and what leaves the grille is cold.
Water leaves the coil warmer than it arrived, because the heat from the room has moved into it. It runs back down a second pipe, gets cooled again, and goes straight back up. Heat gathered from hundreds of rooms is rejected in one place, normally through cooling towers standing on the roof.
None of the equipment in the occupied space contains refrigerant. Whatever a chiller uses stays sealed inside the chiller, in a plant room, under the care of whoever maintains it. In a flat running a split system, refrigerant travels through the wall and into the bedroom. Here it never leaves the plant room at all.
The flat or the tenancy owns no outdoor equipment either. There is nothing on the ledge to inspect, no condenser fan to hear labouring on a hot afternoon, no service deck position to argue over. The machinery that would have been yours is shared, and it stands somewhere you have no access to.
The temperature difference across the coil is the whole job
How much cooling a unit delivers rests on two numbers. One is how cold the water arriving is. The other is how much of it passes through the coil. Both are decided outside the room, by equipment the occupant will never see.
So a chilled-water complaint often has nothing wrong inside the box. The blower runs, the filter is clean, the coil is clean, and the space still will not hold temperature. On a split system that combination points straight at refrigerant. Here it points upstream, towards the water and whoever is responsible for it.
Where these systems turn up in Singapore
Commercial buildings are the default case. Office towers, hotels, hospitals and large retail podiums run on chilled water almost without exception, because one large plant is cheaper to run and simpler to maintain than several hundred separate condensers scattered across the facade.
Newer integrated developments stretch the same plant across mixed uses. A single development can hold offices, a mall, a hotel and residential blocks, all drawing cooling from one source. A resident living there is sitting on a commercial building service, whatever the flat itself feels like.
District cooling takes it one step further. The plant occupies its own building and sends chilled water out to several buildings across a precinct, so the cold is bought in rather than produced on site. Marina Bay runs on a network of that kind. The Tengah centralised cooling system is the public housing version of the same idea.
Mixed buildings are perfectly ordinary. A tower on chilled water will still carry split systems on server rooms and security offices, because those spaces need cooling while the plant is shut down. Smaller buildings with no plant room of their own usually run a VRF system instead. Being inside a chilled-water building is no guarantee that one particular unit is on the plant.
Your unit, your floor, or the building: telling them apart
The first useful question here is not what failed. It is how far the failure reaches. A fault confined to one unit, a fault covering a floor, and a fault covering an entire building are three separate problems with three separate owners. All three feel identical to somebody sitting in a warm room.
Scope is something an occupant can establish without any tools. Walk the floor. Check whether the units either side are still cooling. Ask the tenancy next door, or the neighbour sharing the same riser. If everybody is warm, nothing inside your own space is going to account for it.
Timing carries the same information. A unit fading over weeks is behaving like a fouled coil or a tired part. A whole floor going warm together is behaving like a supply. Warmth that arrives at a fixed hour, or on one particular day, makes the building's schedule a better suspect than any component.
Getting this wrong costs money in a specific way. A technician sent out while the plant is offline finds a clean filter, a healthy blower, and a coil that never turns cold. The only report available is that the water is not doing its job. That was already known upstairs, and the occupier has now paid to hear it.
| What you can observe | Where the fault probably sits | Who to raise it with first |
|---|---|---|
| What you can observeOne unit warm while the rest of the space is fine | Where the fault probably sitsThat unit, its valve, or its filter | Who to raise it with firstWhoever maintains the units inside your space |
| What you can observeEvery unit on the floor going warm together | Where the fault probably sitsThe branch feeding that floor | Who to raise it with firstThe managing agent, or building management |
| What you can observeWarmth across several floors at once | Where the fault probably sitsThe plant, a pump, or the supply itself | Who to raise it with firstBuilding management, before any contractor is called |
| What you can observeCold until a fixed hour, then fading away | Where the fault probably sitsThe building's operating schedule | Who to raise it with firstBuilding management, as a scheduling question |
| What you can observeWeak airflow but the air is properly cold | Where the fault probably sitsThe filter, blower or grille inside your unit | Who to raise it with firstWhoever services the terminal units in the space |
How to ask so the answer is useful
Building management can settle a scope question quickly, because the plant is monitored and the answers already sit on a screen. What turns a vague complaint into a dated record is asking for the right five things.
- Whether the chilled-water supply to the floor is running normally at this moment.
- Whether the supply temperature or the flow has been reduced for any reason.
- Whether any part of the plant is out of service or held on reduced capacity.
- Whether other units on the same riser have reported the same complaint.
- Written confirmation that the supply is normal, where that turns out to be the answer.
What an occupant owns, and what the building owns
The occupier's territory ends where the water arrives. Everything touching room air is normally the occupier's to look after. Everything carrying, cooling or moving the water belongs to the building.
That leaves an occupant with a short list, and it is worth knowing by heart. The fan coil unit itself, the filter in front of the coil, the coil face, the blower, the drain pan and drain line, the control valve with its actuator, and the controller on the wall. All of it is reachable from inside the space, and all of it fails in ways that are recognisable from inside the space.
The building holds everything else. Chillers, pumps, cooling towers, risers, branch isolation, water treatment, and the balancing that decides how much flow each branch receives. None of that is reachable from a tenancy, and none of it is work an aircon contractor should be pricing during a visit to a warm room.
Plant-side work belongs to the building's appointed contractor. That contractor holds the access, the permits, and the duty of care for the system as a whole. An aircon contractor called in by an occupier works on the terminal unit and nothing past it. Those are two jobs with two scopes. Mixing them up is how an occupier pays to survey somebody else's equipment.
Where the line falls exactly is written down somewhere. A tenancy agreement, a handover pack or a maintenance schedule will state which side owns the valve, the actuator and the branch isolation. Those three sit at the boundary between the water and the box, which is why they are the usual grey area. Read the clause while nothing is broken.
- The unit casing, the coil face and the blower behind it.
- The filter, which fouls at the same rate as any indoor unit's.
- The condensate route, from the pan under the coil to wherever it discharges.
- The control valve and its actuator, where demarcation puts them on the occupier's side.
- The room controller, along with the settings and schedules held in it.
Servicing still means something here
Taking the compressor out of the picture removes half the fault list and none of the cleaning. Air still passes through a filter. A coil still collects whatever the filter misses. Condensate still forms and still has to drain away. A blower still loads up with dust and quietly loses output as it does.
So the cleaning scope on one of these units looks much like the cleaning scope on any indoor unit. What changes is the diagnosis in front of it. A fouled coil and a warm supply produce a similar complaint, and cleaning cures only the first. Establishing which of the two is present, before quoting, is the real value of the visit.
Buildings often maintain the plant well and the terminal units badly. Plant maintenance is contracted, monitored and audited by people who understand it. The unit above a tenant's desk is somebody's afterthought. A chilled-water office running a healthy plant and filthy coils at the same time is a common finding, not a strange one.
Why the cooling bill does not look like an electricity bill
Cooling on this kind of system usually sits outside the occupier's electricity account. The energy is burned at the plant, so the electricity making the cold belongs to the building. What reaches the occupier is a charge for cooling, and it can be arranged in more than one way.
Metering is the cleanest version. A meter on the branch records how much cooling the space actually drew, and the occupier is billed against that reading. The number moves with usage, so switching units off changes it. Commercial tenancies are commonly set up this way.
Service charge is the other common version. Cooling gets folded into a building charge levied by floor area, and individual consumption never enters the calculation. Switching a unit off under that arrangement saves the building money and saves the occupier nothing. It also leaves the occupier with no lever on the figure at all.
The unit's own power sits separately again. Blower, controls and valve actuator all run on the space's electricity, and that draw is small. An occupant reading a low electricity bill and concluding the aircon is cheap has looked at one line out of two. The cooling is on the other one.
Establish which arrangement applies before drawing any conclusion about running cost, because it decides what savings are even available. On a metered supply, setpoints, schedules and empty rooms left running all translate into money. On an area-based charge they translate into nothing, and an efficiency measure sold on that basis cannot pay back.
| How cooling is charged | What the occupier can influence | What the figure will not respond to |
|---|---|---|
| How cooling is chargedMetered on the branch serving the space | What the occupier can influenceSetpoints, hours of use, empty rooms left running | What the figure will not respond toThe rate itself, which the operator sets |
| How cooling is chargedFolded into a service charge by floor area | What the occupier can influenceVery little, since consumption is never measured | What the figure will not respond toAnything done inside the space |
| How cooling is chargedA standing availability charge plus metered usage | What the occupier can influenceThe usage half of the bill | What the figure will not respond toThe standing half, payable regardless of use |
| How cooling is chargedIncluded in the rent under a tenancy | What the occupier can influenceNothing directly, though comfort complaints still land | What the figure will not respond toThe building's schedule and supply temperature |
Operating hours belong to the building
A plant running to a schedule stops cooling when the schedule says so. In an office building that normally means the supply winds down after working hours and at weekends. Space needing cooling outside those windows has to be requested and paid for as an extension.
Residential buildings on shared cooling run continuously, because the demand never stops. Mixed developments run both patterns together, and that is where confusion starts. A retail tenant inside a residential development can find the supply following the mall's hours rather than the tower's.
None of this can be negotiated from inside the space. A wall controller can only ask for cooling that is available to ask for. While the supply is off the controller still lights up, the blower still runs, and the air leaving the grille is room temperature. That one behaviour generates more false fault reports than any component in the system.
Faults with no equivalent on a split system
One of these units cannot lose gas, seize a compressor or fail an outdoor fan. What replaces those faults sits on the water side, and most occupants have never read a word about any of it, because almost everything written for homeowners describes a split.
A control valve that has stopped modulating is the headline fault. The valve sits on the pipe feeding the coil, opening and closing according to what the controller asks of it. Once it stops responding it stops in a position, and that position decides which symptom the room gets.
Stuck shut reads as a dead unit that is still running. Airflow is normal, the filter is clean, the blower sounds right, and the air is not cold. Nothing about the box suggests a fault, because the box is fine. Water simply is not reaching the coil.
Stuck open is the one that gets missed, because the space is cold rather than warm. Cooling carries on regardless of what the controller asks for, so the room overshoots and turns clammy. Occupants raise the setpoint, watch nothing happen, then switch the unit off. The complaint arrives as humidity or a sweating grille rather than as a fault.
Blockage upstream of the coil comes next. A strainer sits in the pipe to catch debris, and it does its job by filling up. A partly blocked strainer starves the coil of flow, so the unit behaves like one with a valve barely cracked open. Air trapped in a coil produces something similar, holding a pocket that water cannot push out of the way.
The supply itself is the third family. Water arriving warmer than the design figure, flow reduced because a pump is out, or a branch throttled during balancing after a fit-out. Each of them surfaces in the room as a unit that will not hold temperature, and not one of them is inside the room.
Treat a quote for refrigerant or a compressor on one of these units as a scoping failure. Neither component is present in the space. A contractor pricing them has not traced the pipe leaving the box, which takes a moment and settles the question outright. Asking somebody to name the failed equipment and say where it physically stands is fair before agreeing to anything.
| What the room reports | What it points at on the water side | Whose side of the line it falls on |
|---|---|---|
| What the room reportsNormal airflow, air never gets cold, one unit only | What it points at on the water sideA control valve stuck shut, or a blocked strainer | Whose side of the line it falls onThe occupier's, under most demarcations |
| What the room reportsThe room overcools and turns clammy | What it points at on the water sideA control valve stuck open, ignoring the controller | Whose side of the line it falls onThe occupier's, under most demarcations |
| What the room reportsCooling fades every afternoon across the floor | What it points at on the water sideSupply temperature or flow slipping under peak load | Whose side of the line it falls onThe building's |
| What the room reportsCooling stops at the same time each day | What it points at on the water sideThe plant schedule, rather than a fault at all | Whose side of the line it falls onThe building's |
| What the room reportsOne zone poor ever since the space was refitted | What it points at on the water sideBranch balancing that no longer suits the layout | Whose side of the line it falls onThe building's, with the fit-out contractor |
What a competent visit measures
Air going in and air coming out is the first reading, because it says whether the unit is doing any work at all. A healthy coil drops the air passing through it by a wide margin. A coil with no cold water in it barely drops the air, whatever the blower happens to be doing.
Pipe temperature on either side of the coil is the second. Cold in and warm out means water is moving and heat is going with it. Cold in and cold out means water is present but almost none is passing through. Warm in means the trouble arrived from upstream and was never the unit's to solve.
Valve position is the third, and it separates a stuck valve from a starved one. A valve commanded fully open with almost no temperature change across the coil is not doing as it was told. Those three readings together settle most complaints on this kind of system before anything gets opened.
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