Thermal Energy Efficiency Analysis for Residential Buildings Lorentz JÄNTSCHI*, Mugur BALAN*, Margareata Emilia PODAR*, Sorana Daniela BOLBOACA † * Technical University of Cluj-Napoca, 15 Constantin Daicoviciu, Cluj-Napoca, 400020, Romania, e-mail: lori@academicdirect.org , Mugur.Balan@termo.utcluj.ro , emilia@chimie.utcluj.ro † “Iuliu Haţieganu” University of Medicine and Pharmacy, 13 Emil Isac, Cluj-Napoca, 400023, Romania, e-mail: sbolboaca@umfcluj.ro Abstract—The paper presents an interactive software application, for the calculus of the heat flux demand in residential houses, based on international trends, standards and specifications in the fields of thermal energy in buildings. These types of calculations are considerable useful in the context of the large and constant interest on the subjects of energy conservation, reduction of polluting emissions and use on large scale of renewable energies. In order to reach the objective of the research, the heat flux demand was parameterized to identify each influence on the thermal energy consumption and costs. The development of the mathematical model had the aim to allow the minimization of the heat losses into the environment and to choose the correct thermal power for the residential houses heating devices. By the use of PHP language, the mathematical model has been transposed into a client-server application. The interactive software system has been validated through a case study and the obtained results were consistent and relevant. Based on the results it was possible to extract key conclusions about the parameters that contribute to the heat losses. Keywords—Energy efficiency, heating demand, residential building. I. INTRODUCTION The concern of energy conservation, the reduction of green house gases and sustainability was continuously growing in last years [1]. The concept of green building has been introduced, and refers the practice of increasing the efficiency with which buildings and their sites use and harvest energy, water, and materials, and reducing building impacts on human health and on environment, through better design, construction, operation, maintenance, and removal [2]. In the green building concept, an important issue is the energy efficiency. An energy efficient house is a building that provides a high level of thermal comfort without over reliance on artificial heating and/or cooling. The economical strategy of sustainable development imposes the promotion of global energy efficiency and the rational use of thermal energy in buildings, the major energy consumer, globally speaking. In Romania, there were inherited from the communism a huge amount of home buildings that are heating by a central system (a thermal power station that is use to heat more than one buildings of flats with four to ten floors - for example in a building with ten floors there are sixty- four apartments with two or three rooms). The heat is distributed towards and around the building through ducts (hot air) or pipes (hot water). Since 2000, many flats owners renovated their apartments, getting insulated walls, changing windows and installing individual heating system that use natural gases as fuel. Note that, according to the Association for the Study of Peak Oil & Gas the natural gases will be depleting in sixty-six years [3]. In Romania, the standard of residential building construction was redefined in 2006 by the government, the new regulations being imposed through Minister Decree No. 729 [4]. Starting from the national [4] and international trends [5-8] in development of environmental performance of new and existing home buildings, an interactive system for assisting the calculation of home energy efficiency has been created and validated, and its performances are presented. II. MATERIAL AND METHOD A. Mathematical Model According to [9], the total heat flux losses through a building (Ф) is given by the formula: Ф = Ф 1 + Ф 2 + Ф 3 (1) where Ф 1 = the heat flux losses through transmission, Ф 2 = the heat flux losses through ventilation, and Ф 3 = the heat flux needed for preparing the domestic hot water. The heat flux lost through transmission is distributed between the walls, the floor, the ceiling and the windows. According to these, the formula of the Ф 1 is: Ф 1 = Ф 1.1 + Ф 1.2 + Ф 1.3 + Ф 1.4 + Ф 1.5 (2) where Ф k.j = heat flux losses through: walls (Ф 1.1 ), ceiling (Ф 1.2 ), windows (Ф 1.3 ), main floor (Ф 1.4 ), and basement (Ф 1.5 ). The heat flux losses through ventilation depend directly by the global insulation of the building in conformity with formula: Ф 2 = İ·Ф 1 (3) where İ = a coefficient correlated with the global insulation of the building. This coefficient is assumed equal with 0.7 for buildings without insulation, 0.8 for buildings with minimal insulation, 0.9 for buildings with good insulation, and 1 for buildings with very good insulation (buildings with low energy consumption, passive buildings regarding the energy consumption). EUROCON 2007 The International Conference on “Computer as a Tool” Warsaw, September 9-12 1-4244-0813-X/07/$20.00 2007 IEEE. 2009