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This current paper intends to present the modeling of heat exchange between the surrounding environment and heated concrete on the basis of the "virtual tube" method and Lumped IntroductionThis Radiant Panels used in heating or cooling systems presuppose the control of the temperature on their surface, temperature which is determined by the parameters of the used thermal agent. Panel heating and cooling system offer conditions of acceptable inner thermal comfort by the control of the temperature on their surface [1].The low-temperature radiation system also called "heated concrete" represents a simple solution for the use of building elements as heating radiators, the heat transfer from the heating radiators to rooms being done mostly by radiation. The thermal agent pipes, transporting heated water, are inserted into the mass of the concrete at the level of floors, namely the floors of the rooms, the temperature of the thermal agent being under 30°C [2]. The solution of heat accumulation in the mass of the building element, of the concrete, and its transfer towards rooms, represents a solution for increasing the thermal comfort within buildings and a technique for an efficient use of heat sources which make use of renewable energies [3] , [4]. Similarly, we can use the system called "heated concrete" in order to absorb the heat from rooms. In this situation, the thermal agent that circulates in the pipes inserted into the mass of the concrete is below 20°C being influenced by the temperature of the dew drop inside rooms in order to avoid the formation of condensation on the surface.The issue of heat transfer between the air and the heated concrete can be appreciated with acceptable, results by using the equation [1]:

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A building energy model is a simulation tool which calculates the thermal loads and energy use in buildings. Building energy models provide valuable insight into energy use in buildings based on architecture, materials and thermal loads. In addition, building energy models also must account for the effects of the building’s occupants in terms of energy use. In this paper we discuss building energy models and their accuracy in predicting energy use. In particular, we focus on two types of validation methods which have been used to investigate the accuracy of building energy models and on how they account for their effects on occupants. The analyzed building is P + M located in the climatic zone 4, Sânpetru / Braşov. We have carried out a detailed and exemplary energy needs analysis using two methods of analysis.