Designing Thermal Mass in Naturally
Ventilated Buildings
Yuguo
Li1 and Jimmy
Chi Wai Yam2
1Department
of Mechanical Engineering, The University of Hong Kong, Hong Kong SAR, China
2Ove
Arup & Partners Hong Kong Ltd, Kowloon Tong, Kowloon, Hong Kong SAR, China
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Abstract
According to its location, thermal mass can be
approximately classified into two types: external and internal. Internal thermal
mass, such as furniture and purpose-built internal concrete partitions, does not
expose to ambient temperature directly, while external thermal mass, such as
walls and roofs, expose directly to ambient temperature variation. A virtual sphere method for modelling thermal mass is introduced
and its application in building thermal mass design is discussed. When the
ventilation rate is constant, three key design
related parameters are identified, and both the phase shift and
fluctuation of the indoor temperature are determined by the time constant of the
system, the dimensionless convective heat transfer number and the Fourier time
constant. A simple design method for architects and engineers is described. The
present method allows the rapid determination of the amount of thermal mass, as
well key design parameters when the phase shift of indoor air temperature and
the attenuation of the indoor air temperature fluctuation are specified. This
paper also presents an explicit formula for predicting phase shift when the air
flow is driven by buoyancy force alone.
Key words: thermal
mass, modelling, phase shift, natural cooling.
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