Using Passive Design For Offices In A Subtropical Climate:a Case Study In Shenzhen

Building energy consumption has become a subject of a lot of attention in a contextof upcoming global energy shortage.Rapidly developing countries such as China and Brazil will build important numbersof new office buildings over the twenty years to come. Research shows that on averagenew buildings tend to consume more energy than the ones they replace, mainly due tohigher standards for environmental control through mechanical devices and higher levelsof artificial lighting.Mixed-mode buildings using natural ventilation for part of the year and air condi-tioning during the warmest summer months appear as a promising solution to create com-fortable working environments while reducing energy consumption. However, althoughthermal comfort standards for naturally-ventilated buildings confirm the feasibility of thisstrategy,therearefewactualapplicationcases. Thereisthereforeaneedforproofthroughexample.To achieve this goal, an office building located in Shenzhen (on the south coast ofChina, near Hong Kong), which–among other passive design strategies–uses naturalventilation through user-controlled windows except during the warmest summer months,was analyzed over the course of a year.The investigation results show that indoor temperatures in the working areas are forthe most part in accordance with the results of Ashrae55standard on thermal comfortin naturally-ventilated buildings, the biggest issue being temperatures too cold in winter.For indoor temperatures above21oC, the acceptability reported by occupants was over80%. During summer the air conditioning system succeeds in maintaining temperaturearound26.5oC during summer. Overall temperatures rise above28oC during only4.3%of working hours in the year.The electricity use intensity of the office-related part of the building is about60.2kWh.m2, a value smaller than the lower standard deviation born of energy use datafrom a57-building sample of Shenzhen offices. Comparison of the breakdown energyuse with values found in literature showed that the low energy consumption could be at-tributed both to low levels of AC electricity consumption and energy use for lighting anoutlets. Simulation analysis indicated that the main contributors to the dehumidification loadreduction compared with an equivalent closed office building were the limitation of airconditioning time during the day and during the year. As far as temperature control wasconcerned, savings were more homogeneously distributed between these two aspects, theuse of a rooftop shading device in the real building, a higher AC set point, and low levelsof lighting due to good use of natural light. These elements are made possible by thefact that common areas are outdoor spaces, enhancing natural ventilation and daylightingefficiency in worspaces.The results of this study strongly support the feasibility and efficiency of using natu-ral ventilation in a mixed-mode building context to create energy efficient and satisfyingoffice buildings in warm and humid subtropical climates, while providding new possibil-ities for architects to connect occupants with the outside environment.