THE INFLUENCE OF THE DAILY FLUCTUATIONS OF OUTSIDE AIR TEMPERATURE ON THE INDOOR CLIMATE

Abstract

The investigation of indoor air temperature fluctuations within the occupied zone (habitable zone) induced by the periodic changes of outdoor air temperature was carried out with the use of numerical simulation of heat transfer processes in the heated room. The developed and programme-implemented two-dimensional physical and mathematical model takes into account unsteady nature of the complex conjugate heat transfer in building envelopes and indoor air spaces when using different types of heating devices. The design features of building structures and windows are considered. The model includes the equations of radiative heat transfer between indoor surfaces, window panes and outdoor environment. In the study, the harmonic changes of outside temperature are specified by the cosine law with the twenty-four-hour period. Two types of heaters are examined: radiator and underfloor heating. Heating output of the devices is specified time-invariable according to the thermal balance defined by the traditional method. Simulations are performed for the three combinations of heat-transfer properties of building structures. The quantitative characteristics of the induced indoor air temperature fluctuations within the occupied zone depending on the building envelope thermal inertia and the type of used heater were found out. The analysis of results yielded the following conclusions. Reducing inertia of glazing leads to more rapid penetration of outdoor temperature wave into the room. While the amplitude of the indoor air temperature fluctuations within the occupied zone remains constant by reason of the unchanged thermal inertia of the main building structures. The significant increase in the amplitude of harmonic changes of indoor air temperature within the occupied zone is observed when reducing inertia of walls and floors whereas the delay with respect to outside air temperature fluctuations remains almost invariable.