Designing HVAC for the tropics
The Insight
The La Niña phase of the El Niño Southern Oscillation allows more moisture to be lifted into the air, leading to increased rainfall. As November begins, we welcome her.
The changes expected to come with La Niña are similar to the challenges often faced when designing HVAC for northern Australia. The tropics are consistently subjected to extreme temperatures and humidity amidst the added variables of vermin, moisture ingress, and dust and pollen ingress. Achieving a healthy indoor environmental quality with effective air conditioning and ventilation isn't always as clean-cut as the NCC and the Australian Standards' framework suggests. With the arrival of La Niña, the theory behind 'tropic-proofing' is about to be put to the test.
The Impact
Standard design principles and compliance items that are used in southern Australia are not suitable for the tropics. To achieve the desired temperature and humidity, special care needs to be given to control infiltration and engineer make-up air paths.
Mould and mildew can thrive in relative humidity as low as 60%. Without implementing active humidity controls or achieving a continuous vapour barrier, it's extremely difficult to keep the humidity under 60% in the tropics.
Whilst the architect or builder often determine the real estate allocated for mechanical services, HVAC designers need to play an active role in determining if the space can also sufficiently contain a continuous vapour barrier around the conditioned space.
When selecting packaged and proprietary air conditioning equipment, it's essential to ensure it can operate continuously in high ambient temperatures and low load conditions. It's not uncommon for manufacturers to boast low load efficiencies based on statistics gathered in low ambient temperatures and humidity.
While design principles, code requirements and the Australian Standards are developing to include requirements specifically for the tropics, there is still a long way to go. Designers must play an active role in the whole building process to ensure HVAC systems are suitable for the tropics.