A simplified method for the evaluation of building energy requirements for space conditioning

Among simplified multiple-measure methods for the evaluation of building energy requirements, methods based on the use of temperature frequency (bin) analysis allow a better tracking of the relation between building loads and energy consumption if compared with methods based on traditional time analysis. The reason is that plant efficiency strongly depends on the load factor, which is related to the outside temperature. A simplified method is presented which consists of a particular version of the ASHRAE "bin method", modified in order to fit Italian standards and rules about design and operation of buildings and HVAC systems. The proposed method only requires the knowledge of temperature frequency distribution of the considered place and the preliminary evaluation of design winter and summer loads in order to predict heating/cooling energy requirements. The accuracy of the method has been assessed by means of a parametric analysis performed using a detailed simulation method based on weighting factors (DOE2 version 1.E). In order to assess the reliability of the method for a wide field of application, different Italian climates and building typologies have been analyzed. A comparison has also been made between the use of complete test reference years (TRY) based on hourly data and the use of average monthly days for the specification of meteorological conditions. This analysis points out that errors related to the use of average monthly days in detailed simulation models are of the same order of magnitude and sometimes even larger than errors related to the use of a simplified "non-dynamic" model, like the bin method.