Quantification of safety factors for simplified heating and cooling demand calculation methods for Vienna
The method used in Austria for calculating building heating and cooling demand is a monthly quasi-steady-state calculation. This method is presented in the European draft ISO/FDIS 13790. The simplified monthly calculation method is based on utilization factors. For these factors there is no specific mathematical derivation. The factor is based on an empirical formula. For increasing the practicability of the simplified calculation methods, the precision of the method is important, as well as the prediction accuracy by modifying the building parameters. Both requirements for a simplified calculation method are verified in this investigation. A simplified investigation of the calculation method precision for the cooling demand for offices leads to a 40 percent margin of error when using the simplified method for Vienna climate. The prediction accuracy of the monthly balanced method for changing the building parameters was verified for a six zone office model. At the end, the precision of the simplified method was quantified for an office model for the heating and cooling demand. Safety factors for the simplified method resulted from the investigation of the office model. The imprecision of the simplified method is greater than the validation of the monthly calculation method, as is exposed in the draft ISO/FDIS 13790. For the cooling demand for Vienna, the safety factor is 1.25 for the one zone method and 1.15 for the multi-zone method. For the heating demand no safety factor is necessary if the simplified method is not used for low air change rates and uncoupled models.