CONTROLLED BUILDING ENVELOPES FOR ENERGY STORAGE A. Borodinecs, A. Kreslins Institute of Heat, Gas and Water Technology, Construction faculty, Riga Technical University P. o .box 526, LV-1010, Riga, Latvia Tel.: +371-26079655,Fax.: +371-7615191 E-mail: anatolijs.borodinecs@rtu.lv U. Bratuskins Faculty of Architecture and Urban Planning, Riga Technical University Āzenes iela 16/20 - 410 E-mail: af@bf.rtu.lv Keywords: energy performance, low energy buildings, energy storage ABSTRACT The paper is devoted to the analysis of possibility for construction of low energy buildings with envelopes controlled for minimization of energy consumption by air conditioning systems. It describes the possibilities to reduce energy consumption of large public buildings mainly in summer time when there are the highest electricity demands for cooling. The paper gives a complex mathematical model for controlled envelope’s thermal resistance depending on outdoor parameters. It proposes constructive suggestion to create buildings whose walls, roofs and glassed surfaces have changeable thermal characteristics and methodology of control for separate elements. Building energy performance simulation models during the whole year allow choosing optimal characteristics of building envelope on the basis of annual heat consumption. The paper analyses the impact of building envelope thermodynamic characteristics on the parameters of supply air in air conditioning systems. It describes the change modes of thermal resistance, resistance to water vapour transfer and resistance to solar radiation considering the different states of inside and outside air conditions. 1. BACKGROUND Traditionally low energy buildings are supposed to have maximally big thermal resistance of building envelope. In reality big thermal resistance is justified only in coldest winter days in countries with cold climate or in hot summer days with intensive solar radiation. In other periods buildings with full air conditioning would have to have different properties of building envelope that could allow heat flow in one or another direction. There are also periods when minimal resistance to vapour transfer is required. Sometimes the building envelope is needed only to prevent from rain, insects or to give the intimacy and it is not needed from the point of energy efficiency, as it does not have to form the shield against the heat or vapour flow (Todorovic 2004). Building energy performance simulation models allow choosing optimal characteristics of building envelope on the basis of annual heat consumption. The model described in this paper would help to optimise building energy performance even more on the condition that we can change the properties of building envelope.