Exergy analysis of a residential building in Southern Italy: lessons for low-exergy buildings and systems.

The energy performance of energy systems in buildings is commonly studied by applying the First Law of Thermodynamics, which allows to quantify the energy losses and to measure the energy conversion efficiency of the single components. However, different forms of energy have different potential to produce useful work, mainly depending on the temperature at which they are available. For this reason, the Second Law of Thermodynamics should be also considered. The main scope of this paper is to apply the exergy analysis to a residential building located in Southern Italy, including its energy systems. The calculation is based on a quasi-steady-state approach, where dynamic simulations are used to describe the energy performance of the building, and steady-state equations are used to assess the exergy flows. The selected residential building contains eight dwellings, heated by a conventional gas boiler and cooled by individual split-units; however, the calculations refer to only one apartment. The outcomes of this simulation effort show that the exergy efficiency for space heating and cooling in the current state is very low, being of 6.2 % and 3.8% respectively. This is mainly due to the use of combustion processes for producing heat, and to the use of electricity (i.e. pure exergy) to feed the cooling systems. However, the implementation of typical refurbishment strategies such as improving the insulation of the envelope and adopting more performing mechanical systems, not only reduces the energy needs for heating and cooling by around 20 %, but also raises the exergy efficiency for heating and cooling up to 13.1 % and 6.2 %, respectively.