A Novel Integrated Exergetic Approach for the Optimization of Building Conditioning Systems

The space conditioning sector is at the same time one of the highest energy consumers and one of the least efficient from the point of view of primary-to-end-use matching. Both in general and on the average, the gross inadequacy of building structures and insulation combines with an equally gross ill-management of space conditioning plants. In spite of the emergence in the last decade of innovative technical solutions based on renewable energy converters, installing them without considering the whole air conditioning system will hardly remedy the current situation. The present study proposes a systemic approach to the joint design-and-analysis of space conditioning (building + heating/cooling element + primary energy supply system) that leads to the correct identification of the thermodynamically most convenient configurations. The method consists in a complete and rational integration of thermal building dissipation modelling, thermal consumption simulation and exergy efficiency calculation. In the selection of the "optimal" solution for an air conditioning system different factors should be considered: first the thermal characteristics of the building to be conditioned, then the type of heating element and finally the type of the primary energy conversion system. The first step is the correct modelling of both the geometry and thermal characteristics of the building. For the sake of simplicity, the application discussed here is based on an extremely simplified geometry (a cubic room), on which thermo-fluidodynamic simulations of the effects of heaters elements have been performed via a commercial CFD code (Fluent®). The temperature maps within the room obtained via these CFD simulations are then used to compute, for each type of heating element, the actual thermal power required to meet the environmental comfort standards. The second step is the simulation of the "external" plant needed to provide the prescribed thermal power, and it was carried out by means of a general purpose process simulator (CAMEL-Pro™): this global simulation enables the designer to compare the performance of all feasible different combinations of internal and external systems and to identify the most exergetically convenient pairings (for a better end-use/primary source matching).