Can a naturally ventilated office outperform a mixed mode office? Pilot study on occupants' comfort

Abstract

Abstract:It is established that a mixed mode indoor environment provides the best for occupant comfort by augmenting the passive system with a mechanical system when and where required. However, the recent desperation for near zero energy environments, of which natural ventilation provides, warrants the need to explore the possibility of achieving this without sacrificing occupants' comfort. The purpose of this study was to investigate if a naturally ventilated building can outperform a mixed mode building in providing comfort for occupants. The Building in Use (BUS) questionnaire was used to carry out this survey on occupants' comfort in two office buildings in Auckland, New Zealand. The findings showed that occupants of the naturally ventilated office building were slightly more satisfied and comfortable than their counterparts in the mixed-mode office building for almost all the variables of comfort investigated. Thus, the results indicate that naturally ventilated office spaces can provide more comfort than mixed-mode office spaces, if well-designed. This finding suggests that the use of natural ventilation in office environments by designers and building owners should be encouraged. A limitation of this study is that it was carried out in the winter season. The winter season could have affected the results obtained. Also, the study was carried out on only two office buildings. As such, the results cannot be generalised to all office buildings in New Zealand. More surveys on ventilated systems are required for results to be generalisable.Keywords: Natural Ventilation, Mixed Mode Ventilation, Post Occupancy Evaluation, Occupant Comfort. IntroductionMixed-mode buildings have been reported to provide better environmental comfort and occupant satisfaction than naturally ventilated buildings (Brager & Baker, 2009;Alessi et al., 2014, Rasheed et al., 2017. The basic benefit of mixed-mode ventilation over natural ventilation is the maintenance a satisfactory indoor environment by alternating between and combining natural and mechanical systems (air-conditioners) to avoid the cost, energy penalty and consequential environmental effects of full year-round air conditioning (Brager, 2006). The implication is that air conditioners are used only when the indoor comfort conditions are outside the acceptable range for occupants. According to Ward et al., (2012), whereas naturally ventilated buildings (in most cases) offer near zero-energy at the expense of occupant comfort, mixed mode buildings achieve both by combining actual and predicted conditions in a dynamic building model to allow preemptive actions -not just responding to conditions, but actively controlling towards an optimal outcome. However, buildings are nowadays expected to be more environmentally sustainable -using lesser energy throughout its lifespan and sustaining itself in the event of unfavourable climatic conditions. As pointed out by Kwok and Rajkovich (2010), it is important that we begin to futureproof our buildings with adaptive opportunities for pa...

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