BUILDING THERMAL PERFORMANCE ANALYSIS BY USING MATLAB / SIMULINK

This paper is focused on a mathematical model applied to both building thermal analysis and control systems design. A lumped approach is used to model the room air temperature and a multi-layer model for the building envelope. The capacitance model allows to study the transient analysis of room air temperature when it is submitted to sinusoidal variation of external air temperature, representing a case study for a cold day in the south Brazil. To evaluate the building performance with thermal parameters, we use MATLAB/SIMULINK. In the results section, we show the influences of thermal parameters on the building air temperature, heating system performance, energy consumption and the advantages of using MATLAB/SIMULINK in building thermal and energy analysis. INTRODUCTION The mathematical description of building systems is complex due to several non-linearities and uncertainties such as convection coefficients, material properties, external weather, radiation effects, HVAC systems modeling and building schedules in terms of people, light and equipment. In the literature, some researchers used MATLAB/Simulink to simulate thermodynamic models and analyze their characteristics in terms of efficiency and temperature control. Hudson and Underwood (1999) presented a mathematical model for building simulation that can be represented by an RC electric circuit. The model is considered adequate for high mass buildings since they are predominantly capacitive. Athienitis et al. (1990) and Dion et al. (1991) presented some approaches for the study of building thermal simulation and HVAC systems so that they could analyze advanced control strategies. Mendes et Al. (2000a) elaborated a simplified model for control strategy analysis of heating systems for low mass constructions, which makes a worse condition to be met by the heating system than that found in a real situation. Mendes et al. (2000b) improved their model by considering a capacitive multi-layer building envelope so that high mass constructions could be analyzed as well. The solar radiation was indirectly included by using the concept of equivalent temperature (air-sun). It was considered a dynamic lumped model so that it could be included the transmission loads and internal gains (lighting, equipment and people). The convection coefficients were considered constant and they adopted external temperature values varying as a sine function to simulate a cold day in south Brazil with a thermal amplitude of 14oC. In this paper, the capacitive multi-layer model presented by Mendes et al. (2000b) is improved by adding the inter-surface long-wave radiation in the thermal model which means that we have included the radiation phenomena on all internal surfaces and on the heater surface as well. The model is implemented in the MATLAB/Simulink environment and comparisons are made in terms of building envelope capacitances, heater performance, heater convection and radiation losses and energy consumption sensitive analysis. It is shown an efficient way to analyze building thermal performance and heating system control strategies by using MATLAB/Simulink in order to reach thermal comfort conditions and reduce energy consumption. MATHEMATICAL MODEL This work presents a dynamic model for thermal building performance analysis, which includes an electric heater. The room is considered hermetically closed with a uniform distribution of internal energy. We considered thermal losses just by heat transfer through the building envelope. Applying the energy conservation equation for each element, the following mathematical formulation is obtained. For the room enclosed by m surfaces, we find, Seventh International IBPSA Conference Rio de Janeiro, Brazil August 13-15, 2001