Paper 13: Volume 5 No.1 June 2006 Edition
Thermal Mass Design in Buildings – Heavy or Light?
Yuguo
Li1 and Pengcheng Xu1,2
1Department
of Mechanical Engineering, The University of Hong Kong,
Pokfulam Road, Hong Kong SAR
2Institute of Applied Mathematics, Academy of Mathematics and
Systems Sciences,
Chinese Academy of Sciences, Beijing, China
Abstract
Thermal mass, including
the building envelope, the interior partition, the furnishing, or even the
air inside a building, is defined as the mass that can store thermal
energy (heat or cooling energy). For storing heat in buildings, there are
two important thermal properties of the materials that need to be
considered, i.e. the heat capacity by volume and the heat-absorption rate.
The first property determines the ability of the element to store
thermal energy, and the second property determines the ability of the
element to conduct the thermal energy. The combined convective and
radiative heat transfer coefficient and the surface area of the thermal
mass determine the rate of heat transfer between the thermal mass element
and the air. One of the good examples in using thermal mass is night
cooling, which can avoid or minimize the need for mechanical cooling in
buildings. We present a simple design formula for use by architects and
engineers which involves only three design related parameters, i.e. the
time constant of the system, the dimensionless convective heat transfer
number and the Fourier time constant. The present method allows the fast
determination of the amount of thermal mass as well as key design
parameters when the phase shift of indoor air temperature and the
attenuation of the indoor air temperature fluctuation are specified.
Key words: Night
ventilation, natural ventilation, thermal mass, design method, passive
cooling, heat storage, thermal time constant.
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