Chapter 6 - Energy Balance of a Building with Regard to Solar Radiation Exposure

Abstract

The energy balance of air in a building is considered with focus on solar radiation influence. This energy balance is formulated with different levels of complexity. Steady state heat flow in one-dimensional models as well as unsteady quasi three-dimensional heat transfer through a building opaque and transparent elements are considered. Application of the thermal resistance method for modeling heat transfer through walls, roofs, and glazing is presented. Numerical simulation of building dynamics in changing external conditions has been performed. Heat transfer across boundary surfaces of a building envelope from the exterior and interior is described, and boundary conditions are formulated. In case of windows, also the energy transfer through a gas gap between glass panes is considered in detail and all phenomena are described mathematically. Simulation studies of a building dynamics and thermal behavior of its main elements have been performed. Results of simulation for different hypothetical standard and innovative structures of walls and flat roofs, including phase change material (PCM) application, are presented. Some recommendations leading to the maximization of energy efficiency of opaque elements of a building envelope, with focus on high-latitude countries, are presented. Energy transfer through windows is considered in detail to show high impact of solar radiation on the energy balance of a building. Fundamentals of energy transfer through glazing are presented. Some examples of unsteady energy flow through windows, including all their components (central part and edges of glazing, and a frame) are discussed. Daily distributions of energy flow through windows of different location (orientation and inclination) for all months of a year are presented in graphical form to enable easy comparison between different cases. Numerical simulations of dynamics of a building and its surroundings have been used to create a number of patterns of heating/cooling demand and other components of energy balance of a building. Calculations have been performed for some selected examples of room locations and structure of envelope elements. Obtained results have been analyzed, and selected cases are shown graphically. During the daytime, the heating and especially cooling load is mainly influenced by solar radiation, whereas at night dependency on ambient air temperature can be seen. However, the relation to ambient temperature is very weak, as buildings are well insulated and have high thermal capacity. Results of simulation studies show how important it is to determine the heat load and heat fluxes exchanged between the interior and outside of a building, taking into account the variability of these energy fluxes in time, in order to ensure thermal comfort inside rooms. As it is shown by the calculation results and confirmed by practice, the cooling demand during summer is very prominent, especially for certain room locations. Cooling demand shows great importance of windows in a design of an energy-efficient building, especially during summer, which usually has been neglected at higher latitude countries. As proved by calculations, overheating mainly concerns rooms in attics.