Shophouse airwell install: heat rejection set the position

The airwell in a conservation shophouse is often the only outdoor space a system can use. Here, three outdoor units were planned into a shaft narrower than a corridor. Warm air leaving one unit becomes the air the next one has to breathe.

By Team Snowflake | Reviewed 25 Jul 2026

Case summary

Gree Wall-mounted2 years oldShophouseSingapore River, Singapore

Concern: Whether the airwell could take three outdoor units at all, and finding out it could not only after the pipework was already run.
Found: The airwell cannot clear the heat thrown off by three stacked outdoor units. Two moved to the rear service ledge, leaving the shaft one unit with full clearance
Key check: Measured the airwell width and traced the hot air path of each proposed unit against the one mounted above it
Result: All three systems hold their design cooling through the afternoon peak, including the head served from the airwell. Nothing was fixed to a protected elevation, so the conservation approval stood. The shaft stays open enough to service the remaining unit without dismantling anything around it.

What we were told

The shophouse was under refurbishment with conservation limits on the front and rear elevations. Three indoor units were to be served across both storeys. The only outdoor space anyone had considered was the internal shaft running up the middle of the building, and the first plan put every unit into it.

What we checked

A shaft that narrow behaves like a chimney, so each proposed position was checked against the one directly above it. We measured the width, the open height and the path the hot air takes on its way out of the top. An outdoor unit throws heat into the space around it, and that space has to keep clearing.

The shaft measured narrower than the clearance a single outdoor unit needs on its coil side.
Warm air from a lower unit would rise straight into the coil of whichever unit sat above it.
A rear service ledge at second-storey level sat outside the protected elevation and stood unused.
Pipe runs to that rear ledge measured longer than the shaft route by a useful but manageable margin.

What we found

An outdoor unit works only while it can dump heat into air cooler than its own coil. A narrow airwell holding three units recirculates that heat instead of clearing it. The upper units would have been drawing in air already warmed twice over, pushing operating pressure up and cooling capacity down on exactly the afternoons the system is needed most. Bracket strength was never the limiting factor here. Available air was.

What fixed it

We kept one outdoor unit in the airwell at the lowest position, with full clearance on the coil side and an unobstructed path up the shaft. The other two moved to the rear service ledge, which sits outside the protected elevation and takes brackets without touching any conserved fabric. Pipe runs to the rear are longer, so the charge was topped up against the route we actually measured, not a table value.

Outcome

All three systems hold their design cooling through the afternoon peak, including the head served from the airwell. Nothing was fixed to a protected elevation, so the conservation approval stood. The shaft stays open enough to service the remaining unit without dismantling anything around it.

What this case teaches us

An airwell is outdoor space only while the air inside it keeps moving

Stacked outdoor units feed warm air to one another, and the top one loses most on hot afternoons.
Clearance on the coil side is a working requirement, not a fitting tolerance to be shaved down.
Count how much air a shaft can clear before counting how many brackets will fit inside it.

Questions this case answers

How many outdoor units can fit in a shophouse airwell?

Fewer than the brackets would hold. This Singapore River shaft measured narrower than the clearance one outdoor unit needs on its coil side, so it took a single unit at the lowest position with a clear path up. Count the air a shaft can clear before counting the brackets that fit inside it.

Is it bad to stack condensers one above the other?

In a narrow shaft, yes. Warm air leaving the lower unit rises straight into the coil of whichever unit sits above it, so the upper one draws air already heated once or twice over. Operating pressure climbs and cooling drops on exactly the hot afternoons the system is needed. Bracket strength was never the limit here.

Where can outdoor units go in a conservation shophouse?

Anywhere outside the protected fabric that still clears heat. The rear service ledge at second-storey level sat outside the protected elevation on this building and had been overlooked entirely, so two units went there on brackets touching nothing conserved. One stayed in the airwell. The conservation approval held because nothing was fixed to a protected elevation.

Will I still be able to service an outdoor unit sitting in an airwell?

Only if the space around it was planned for. Keeping one unit at the lowest position left enough room in the shaft to reach it later without dismantling anything around it. Pack a shaft to its bracket capacity and every future service call starts with taking something apart. Clearance on the coil side is a working requirement, not a fitting tolerance.

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