Vapour barriers and air-conditioned spaces in the tropics
The Insight
As temperature and humidity soars in the tropics, our reliance on comfort cooling within the built environment increases. Air-conditioning reduces the temperature down to comfort conditions, however in the tropics this is generally at or below the ambient dew point temperature. This means that when the ambient outdoor air is introduced into the air-conditioned space, the moisture in the air condenses into water droplets on any surfaces that are at or below the dew point.
Moisture build up can result in mould and mildew growth in spaces and areas of the building that can go unnoticed. Mould and mildew have a significant impact on the occupants’ health and should be avoided at all cost.
Moisture damage to building elements can also have a significant impact on buildings. Moisture in cavities or spaces that do not have the opportunity to dry through evaporation can cause damage to the structural elements of the building and, in some cases, can be an electrical hazard. These problems can result in buildings requiring full replacement or refurbishments within a couple of years of construction.
It is important to control the ingress of ambient air into the air-conditioned space and, where possible, control the internal temperature. This can prove quite difficult in the built environment, particularly in older buildings that were never intended to be air-conditioned.
The Impact
There are three main aspects that must be considered in the design and construction of air-conditioned spaces to avoid the impacts of moisture from condensation:
Control and treatment of outdoor air conditions.
Control of the air-conditioned space temperature and subsequent surface temperature of building elements.
Thermal bridging or cold tracking between the external ambient conditions and the internal air-conditioned space.
Vapour barriers play an important role in preventing hot ambient air from reaching cold surfaces. While architects are responsible for detailing vapour barriers, HVAC designers need to take an active role in reviewing and assisting with the detailing of vapour barriers to ensure a sealed envelope is formed and maintained around the air-conditioned space. HVAC designers need to take an active role in reviewing the architectural details for windows, door framing and other steel structural elements which cause thermal bridging and cold tracking.
From an occupant’s standpoint, the internal temperature can be actively varied to suit the seasonal conditions. Occupant health can be adversely impacted by sudden temperature changes when going from external ambient conditions of high temperature and humidity to internal conditions that are cold and dry. Increasing the internal set point conditions during hotter seasons will ensure the surface temperature of building elements are maintained above the dew point temperature while also creating a safer environment for the building occupants.