Influence of sunspaces on the heating demand in rooms – comparison of ISO 13790 calculation methods

The calculation method presented in ISO 13790 was developed during the research project PASSYS. It aimed to work out the way of estimating energy demand while taking into account different passive solar systems. The standard includes two calculation methods for sunspaces – a full and simplified method. They differ in terms of basic assumptions and the treatment of solar gains in the sunspace and conditioned rooms. There are some doubts about the interpretation of equations presented in the standard, especially when it comes to modelling the solar radiation distribution within the solar space. The paper presents a discussion on the basic hypotheses applied in full and simplified methods, together with the author’s suggestions regarding modifications to the ISO 13790 calculation methods. The modified methods allowed to satisfactorily predict the functioning of the exemplary sunspaces with a smaller area of glazed partitions and higher radiation absorptivity of the casing, that is spaces similar in terms of solar radiation utilisation to traditional living spaces. The phenomena typical for sunspaces with a high degree of glazing, such as the retransmission of reflected radiation, were not sufficiently taken into account in the calculation methods of the standard.