Hybrid design strategies for recommended indoor air quality: The case of Hillside Clinic, Beaufort West

Abstract

The high occupancy that typically occurs in South African clinics, and the accompanying risk of airborne infection, make ventilation and thermal comfort particularly important considerations in the design. Passive (natural) ventilation offers a low-cost, energy efficient alternative to mechanical ventilation to dilute air, decreasing the concentration of contaminated particles (Nice et al., 2015). However, the performance of natural ventilation is variable and its success is reliant on constant monitoring. Passive design takes advantage of local environmental and climatic conditions to provide lighting, thermal comfort and ventilation, with the principal aim of minimizing the energy consumption and subsequent carbon footprint of a building (New Zealand Ministry of Education, 2017).The following case study considers the efficacy of a hybrid (passive and mechanical) design strategy to achieve suitable indoor conditions for a healthcare facility. The Hillside Clinic, Beaufort West, was completed in 2017 by the Western Cape Government (WCG) Department of Transport and Public Works, for the WCG Department of Health (the end user). The design brief set out to achieve a suitable indoor environment for a healthcare facility, while challenging designers to consider green building principles, a zero-emission design, and affordability of construction and operation within the specific context. The appointed consultants responded with a number of passive design strategies, including, amongst others, the installation of rock-bed thermal stores and attention to the building envelope materials. These passive techniques were supplemented with mechanical ventilation systems to form a hybrid design. The authors conducted an independent study of the performance of the facility, a year after completion. Beaufort West is situated in a relatively extreme climate, currently classified as cold arid desert, with high diurnal and seasonal temperature differences. Assuming a 2 °C global warming, it is predicted that this area will become a hot arid climate. Furthermore, the area of South Africa resembling the current Beaufort West climatic conditions could increase by up to 16% (Engelbrecht and Engelbrecht, 2016). The Hillside Clinic thus provides a useful study precedent for the application of hybrid design principles applied in healthcare buildings in these arid climates in South Africa. While stating a preference for natural ventilation, the client’s brief recognised that conditioned, mechanically driven air is necessary to achieve the required ventilation rate in certain areas where 100% ducted fresh air supply is recommended.