Comparison of the ranking capabilities of the long-term discomfort indices

The scientific literature and some standards offer a number of methods for the long-term evaluation of the general thermal comfort conditions in buildings and indices for predicting the likelihood of summer overheating in the indoor environment. Such metrics might be useful tools for operational assessment of thermal comfort in existing buildings, for driving the optimization process of a new building, or for optimizing the operation of building systems. Focusing exclusively on the summer period, 16 long-term discomfort indices have been applied for assessing 54 different variants of a large office building. Such 54 building variants were obtained by combining different performance levels of four key-parameters of the building envelope: (i) insulation and airtightness (ii) solar factor of glazing units (iii) exposed thermal mass and (iv) night natural ventilation strategies. The calculated values of the 16 indices were compared in order to identify their similarities and differences. The indices returned different results in ranking the 54 variants and hence, when used to drive an optimization process of a building design, they would identify different building variants as the optimal ones. Suggestions for improvement of the indices and their use are drawn from this analysis.