Investigation Into Thermal Capacitance of the Building Envelope
Keywords: building envelope, enclosure, time constant, Fourier number, thermal capacitance, time delay, decrement factor
AbstractThe purpose of this research is to determine the actual effective thermal capacitance of the building envelope in respect of the place of thermal layer in the enclosure. The actual effective thermal capacitance of the building envelope is estimated by calculating the thermal capacitance of building enclosure layers in order to find out the active thermal capacitance of the enclosure. This research analyses unsteady heat transfer cases. The calculation principle of such transfers is based on the finite elements method. The specific value of the Fourier number, which gives calculations the optimal accuracy, is determined. This paper also discusses three types of envelope constructions. In all three cases, thermal resistance of the envelopes coincides; only the position of thermal insulation layer in the envelopes is different. In all three cases, time delay of the indoor air temperature in respect of the outdoor air temperature, as well as decrement factors of the oscillation amplitude are calculated. These factors of inertia were determined at the continuous outdoor air temperature oscillation. The research revealed that continuous outdoor air temperature oscillations through multi-layered building enclosures are suppressed by high thermal capacitance enclosure layers, independently from their position. High thermal capacitance enclosure layers oriented to the interior of the premises suppress the fluctuations more efficiently than those oriented to the exterior.
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