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As planet warms, HVAC seeks a cooler future

June 2023

As covered in The Urban Developer by Ralph Nicholson.

The Sackett and Wilhelms Lithography and Printing Company had a problem.

Humidity at its Brooklyn, New York plant was causing havoc with the colour register of its high-quality, multi-colour printing. The different coloured inks kept misaligning as the damp paper stock expanded, contracted and wrinkled.

Enter Willis Carrier, a 25-year-old research engineer working with the Buffalo Forge Company. He designed and patented an “apparatus for treating air”, which used cooling coils to either humidify air by heating water or dehumidify by cooling it.

It was 1902 and Carrier had solved Sackett and Wilhelms’ printing problem … and invented Heating, Ventilation and Air Conditioning, or HVAC. The first residential air conditioner was installed 12 years later.  At 2m high, almost the same depth and more than 6m wide, it needed a room of its own. Nearly 110 years later and in a warming and energy-expensive world, heating and cooling is still vexing designers, engineers and developers.

But in a new report commissioned by build-to-rent platform Local, the Macquarie-back group believes it may have found some answers. And a few surprises.

Local chief executive Matt Berg asked the multi-national professional services firm Arup Group to use real-world modelling to work out the most optimal HVAC system for two of its build-to-rent projects.

In a 67-page report, Arup compared centralised HVAC with equipment on a roof controlling units in apartments below, to the other option—a decentralised system where each apartment has a small, independent air conditioning unit on a balcony.

Arup compared both technologies in Local’s 483-apartment, campus-style development in Kensington, as well as its proposed 421-apartment, 40-storey tower project in South Melbourne. The two buildings are very different. But in both scenarios, individual split-units were judged to be the best in each of four categories, according to Arup.

Split units used less floor space and less floor-to-floor height, they were more energy-efficient, had lower lifetime carbon and leaked less refrigerant than central units. And, over 30 years the total cost of ownership was lower.

Local’s senior development manager Peter Smith says the results surprised everyone.

“When we’re working through the viability of the project’s cost, it’s a big factor. And the mechanical services of a project are a big component of that overall cost,” he says.

“There was a general belief in the industry that a centralised HVAC system is a better outcome for every given metric. And certainly, the belief out there is that it’s a better quality outcome, it’s a better sustainability outcome, and it’s not cost prohibitive. What we found was that every aspect of that can be challenged and when challenged, it has gone the other way.”

Arup’s research showed a central system, or Packaged Air Conditioning (PAC), needs 100mm more space between the ceiling of an apartment and the floor above it. 

Smith estimates in a tower scenario, over 31 floors, that 100mm would allow for another full floor of apartments. “It depends on how big the floorplan is, but if it’s 10 additional apartments for no increase in height, no increase in structure or facade, then it’s a huge uplift to the project,” he says. 

“When you’re looking at a more campus style development like we have a Kensington, you don’t have the number of floors to be able to gain a floor back. But over just 10 floors you’ve got a metre less structure, you’ve got a metre less facade, which is inherently less material that you’re putting into the project.”

PAC units need more roof space—about 240sqm for a campus building and 160sqm for tower scenarios—for cooling towers, air-source heat pumps and other ancillaries, the report found.

Arup found split units had no water consumption and saved tenants between $140 and $190 a year on energy bills.

PAC units used roughly three times the embodied carbon of split systems. “This is explained by the fact that PAC units plus centralised air-source heat pumps have a larger total refrigerant charge than split systems, provided that split system indoor and condenser units are kept close together,” the authors of the report wrote.

Critically for Local, the report says the total cost of ownership over 30 years of a PAC unit is between $700 and $800 a square metre, compared to $250 to $300 a square metre for a split system.

Berg estimates using a split HVAC system in their Kensington build-to-rent project will save up to $10 million on the development. “That is a cost that ultimately the tenant would have to bear,” he says.  “It’s obviously a really easy decision for us regarding which is the right choice here.”

Energy costs and green credentials being what they are and where they are, the debate over HVAC is unlikely to end with Arup’s report, although it does have significant implications for the build-to-rent and residential sector, says Berg.

“We haven’t put this in front of any government body yet or any council but it’s certainly something that we’ll be talking to them about if it ever comes up, because there is that bias in the industry—whether it’s driven by architects or in-house town planners—that somehow central is the only option.”

It’s a far cry from Willis Carrier’s “apparatus for treating air” the machine he invented which blew air over cold coils to control room temperature. Carrier left Buffalo Forge Company in 1915 and founded the Carrier Engineering Corporation in New York.

Today Carrier is traded on the New York Stock Exchange, has 52,000 employees in 160 countries on six continents. As of last year, it was valued at about $30.9 billion.

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