Analysis of buildings’ energy consumption by means of exergy method

Among the objectives of the Directive 2002/91/EC and of the Council “Energy performance of buildings”, (Energy Performance of Building Directive – EPBD) the energy certification of buildings represents a fundamental role. However, the complexity of EU standards and assessment procedures do not allow an easy evaluation of heating losses during realization works nor of existing buildings. The exergy audit, however, comparing the designed indoor temperature with thermal insulation of the building, heating units and boiler, allows considering the exergy consumption of the system. Moreover, the same procedure could be applied also in summer season, even though the evaluation of thermal impact of shadowing and ventilations could be quite complicated. The method here described starts from the LowEX tool, previously developed in the IEA ECBCS Annex 37 framework. Following the energy conservation principle, the total consumed exergy is obtained summing the exergy exchanged in the subsystems (building envelope; distribution plant; heat generation). Finally, the efficiency of the system could be calculated, comparing the costs of energy consumption and exergy exchanges. By using the exergy approach, new (non economic) indexes could be utilized, as TOE (Tonne of Oil Equivalent), CO2 emission, or not-renewable energy uses. Therefore, the boiler would be fundamental, as well as the total amount of energy utilized, and the ratio between TOE and CO2 produced per exergy consumed in the system. The ratio between TOE produced by the boiler and the exergy used by the system represents the exergy parameter. This new exergy parameter has finally been applied in a real case history. It would represent a further application of exergy method to the design of new solutions.