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This paper presents new approach for determining buildings technical system energy performance. This new methodology describes a mathematical model for accurately predicting indoor temperature and heat losses of the space heating and domestic hot water system components. The entire model is described by system of ordinary differential equations which can be solved using standard numerical techniques. The innovative aspect of the method is the integral approach in mathematical modeling of buildings energy needs and technical systems heat loss, taking into account heat accumulation in all considered parts (building envelope + technical system). Such approach allows a detailed insight of the system behavior for chosen working conditions. This model can serve for energy performance calculations in a wide variety of buildings types and their technical systems. The calculation example is given for family house, equipped with conventional space heating and domestic hot water heating system, with the time step of 1 min and for characteristic day of each month within a year. The results are compared against those obtain from EN ISO 13790 and standard series EN 15316. The comparison shows significant differences in determination of the annual delivered energy to the heating system (33%), as a consequence of difference in estimation of the energy need for heating (15%) and calculation of the technical systems recoverable heat losses utilization factor, which seems to be underestimated. The delivered energy to the space heating and domestic hot water heating system differs 25%, while the energy delivered to the generation system differs 4%. [ABSTRACT FROM AUTHOR]

This paper presents the methodology for conducting a cost-optimal energy performance calculation of a solar hot water system, used for space heating and domestic hot water needs. The calculation is based on dynamic hourly methods, according to the new Energy Performance of Buildings' (EPB) set of standards EN 15316:2017, and a revision of the standard EN 15316-5:2017 from the year 2021, dealing with storage-tank water temperature calculations. The paper provides proposals for modifications to these newly introduced standards, in order to overcome the observed ambiguities and shortcomings. The calculation of annual energy performance of a building was performed on an hourly basis over a year for the reference of an nZEB multi-apartment building, for a climate area of the city of Zagreb, taking into account water temperature change in the layers of the storage tank connected to solar collectors and hot water boilers. The cost-optimal solution was then determined by varying individual parameters of the building technical system. The influence of these parameters on the energy efficiency of the building was analyzed in detail. Furthermore, the results were compared against those obtained by the Croatian calculation algorithm based on the previous set of EPB standards, EN 15316:2008, currently used EU-wide for the energy performance certification of buildings. The results indicated that the calculation methods of the present algorithm underestimated the consumption of building primary energy by 12%. The energy delivered by solar collectors was underestimated by 18%. [ABSTRACT FROM AUTHOR]

This paper presents differences in calculations of annual heating and cooling energy need performed by numerical dynamic simulations software IDA ICE and those carried out by the modification of simple hourly method from EN ISO 13790 EN ISO 13790, widely used for determining building energy need. A simple model of a nearly-zero energy building was created and all heat gains and set-points that could lead to a mismatch in initial or boundary conditions were analysed. The impact of those on the annual heating and cooling energy need was examined by adding and/or removing every single one of them. Boundary conditions in numerical dynamic simulations were set up to match those in simple hourly method. Such an approach enables evaluation of differences in results and definition of their origin. The comparison of results has shown that in most cases, annual energy need for heating and cooling calculated using numerical dynamic simulations software differs from that calculated using EN ISO 13790. Among the others, more detailed heat accumulation model of heat gains in building's envelope in IDA ICE software was marked as the main reason. Fact that solar heat gains seem to be underestimated by EN ISO 13790 and differences in heat transfer towards ground contribute to the differences in results as well. [ABSTRACT FROM AUTHOR]