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This dissertation, Effect of Internal Thermal Mass on Building Thermal Performance by Chi-wai, Yam, 任志偉, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled Effect of Internal Thermal Mass on Building Thermal Performance Submitted by Yam Chi Wai for the degree of Master of Philosophy at The University of Hong Kong in August 2003 The heat storage effect of external thermal mass such as walls or roofs on improvement in thermal performance of mechanically ventilated buildings has been extensively studied. However, the effect of internal thermal mass such as purpose- built concrete partitions and furniture has not been systematically investigated, in particular for naturally ventilated buildings where internal thermal mass design has recently been considered as an effective design option. This dissertation considers an ideal naturally ventilated building model that allows a theoretical study of the effect of internal thermal mass associated with the non-linear coupling between the airflow rate and the indoor air temperature. A number of key thermal mass numbers are identified. When the ventilation rate is constant, both the phase shift and fluctuation of the indoor temperature are determined by the time constant of the system and the dimensionless convective heat transfer number. When the ventilation rate is a function of indoor and outdoor air temperature difference, the thermal mass number and the convective heat transfer air change parameter are suggested. The new thermal mass number measures the capacity of heat storage, rather than the amount of thermal mass. The effects of these thermal mass parameters on the system responses are studied. Both mathematical analyses and numerical results show that the non-linearity of the system does not change either the periodic behaviour of the system or the behaviour of phase shift of the indoor air temperature when a periodic outdoor air temperature profile is considered. The maximum indoor air temperature phase shift induced by the direct outdoor air supply without control is shown to be 6 hours. The impact of wind force on the thermal mass performance is also considered. The effect of thermal mass on multiple solutions when there is an opposing wind is also studied. A new method for modeling the effects of thermal mass with arbitrary geometry using the concept of virtual sphere is introduced. The behaviour of phase shift and temperature attenuation of the indoor air modeled by the virtual sphere method is examined. The possibility of applying this virtual sphere method for thermal mass design in real building is investigated, and it appears to have great potential for practical applications. Some limited computational fluid dynamics simulation is also carried out to study the heat storage effect of thermal mass. Preliminary results show that the performance of thermal mass, whatever its amount, may be ineffective without detailed consideration of the thermal interaction between the thermal mass and indoor airflow. Keywords: Thermal mass, natural ventilation, periodic heat flow, thermal coupling, buildings, passive design, phase shift, attenuation in temperature fluctuation, virtual sphere, CFD. DOI: 10.5353/th_b2777063 Subjects: Buildings - Thermal propertiesVentilation

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