I was fortunate to have the opportunity to work on the Arts West Redevelopment at the University of Melbourne, which was designed by ARM & Architectus.
Author: Lauren Clay, Building Physics Engineer at ARUP
The project incorporated new teaching and learning spaces and the enclosure of an existing courtyard to form an atrium in amongst old and new buildings. In addition to guiding the project to a 5 star Green Star rating, we analysed the atrium design to holistically understand likely conditions in the space.
The atrium was proposed to be naturally ventilated with a significant amount of roof glazing and both transient and non-transient spaces, such as elevated walkways, stairs and seated areas. This makes for an interesting and dynamic space, with sunlight shifting around the space over the course of the day and penetrating to varying degrees, as well as retaining strong links to the outdoors. However, the design also had the potential to cause thermal discomfort, condensation and hot surfaces in some locations under certain conditions.
We undertook both daylighting and dynamic thermal modelling to understand the performance of the atrium glazing and the degree of mechanical ventilation provided by smoke exhaust fans to supplement the natural ventilation under peak thermal conditions. For the atrium glazing, we were particularly interested in the visible light transmittance (VLT; the amount of light in the visible portion of the spectrum that passes through the glazing) and solar height gain coefficient (SHGC; the amount of solar radiation that is transmitted).
For example, from a thermal comfort perspective, it is usually beneficial to reduce the solar gains (reduce the glass SHGC). However, from a glass performance perspective, a lower SHGC generally results in a lower VLT, which can be detrimental for the daylighting performance.
Therefore, we needed to achieve a balance and we made a number of design and operational recommendations to achieve this, including a recommended SHGC and VLT in the range of readily available glass performance, localised shading for areas with seating on the elevated walkways, installation of sensors to monitor temperatures at various heights within the atrium and minimum mechanical exhaust rates for peak summer conditions, with the potential to run overnight for consecutive hot days to flush the space.
We primarily focused on passive strategies (e.g. glass performance), but also provided advice around operational, active strategies (e.g. provision of local shading and use of the smoke exhaust fans). This enabled the atrium to remain unconditioned, as per the design intent, all whilst making use of existing design features (e.g. making use of the smoke exhaust fans that need to be incorporated for regulative purposes) to optimise likely conditions in the space year-round.
In parallel to the daylight and thermal analysis, we also considered the condensation risk of the glazed roof design. In Melbourne, condensation is likely to form on the interior glass surface when the internal glass temperature is lower than the dew-point temperature of the adjacent air. Factors affecting the glass temperature include the outside temperature and the thermal characteristics of the glazing system. Given that the atrium is naturally ventilated, the number of people in the space and their activities will influence the humidity levels.
We looked at the glazing and structural beams individually. This was because condensation forming on the beams could be mitigated during construction (e.g. by adding insulation, drip trays or cladding), whereas the glass performance needed to be addressed in the design stage. We looked at the worst case scenario for the glazing, which was a winter’s morning, firstly when there are no occupants and then also mid-morning, when it is still fairly cold but humidity levels are raised due to occupants.
We identified that double glazing would minimise the risk of condensation forming on the glass for a number of scenarios, whereas single glazing could result in condensation. For the single glazing case, we identified that the risk of condensation forming was very sensitive to the occupancy levels and outside temperatures, both of which are hard to predict at any given point. This really highlighted the need for double glazing to be incorporated to provide comfort that condensation would be unlikely to occur.
Finally, we also investigated the health and safety risk associated with metal handrails in atrium getting hot when in direct sun. Two mechanism of impact were considered, including direct burn and discomfort leading to a trip/fall. These were compared to the existing risk associated with metal handrails and seating elsewhere on campus that are exposed to direct sun.
As part of the risk analysis, we considered the probability of occurrence of various peak environmental conditions, the corresponding likely handrail temperatures and the potential consequences. We ultimately concluded there was a low-medium risk of health and safety impacts and identified a series of potential control measures to further minimise the risk, including material selection, localised shading and operational controls.
Article courtesy of ARUP