Quasi-steady state calculation method for energy contribution of sunspaces: a proposal for the European standard improvement

Problems concerning global warming have been faced in the building sector by diminishing energy consumption in buildings by means of three main modes of action: the use of highly efficient systems powered preferably by renewable energy sources, the improvement of the energy characteristics of the envelope and the design of passive devices both for heating and for cooling. The latter are also encouraged by the recent Directive 2009/28/EC. In particular, sunspaces have been and are still nowadays widely used because they meet two different requirements: the heating of adjacent rooms and/ or of supply air with the creation of comfortable spaces to live in especially in the cold season. Although an extensive literature is present on the subject, calculation methods for appropriate dimensioning of sunspaces still suffer from a lot of uncertainties concerning both the real management of the users, the correct characteristics of the materials and the environmental boundary conditions (solar radiation and wind velocity above all) that strongly influence the performance of passive devices. Dynamic simulation tools are not largely used in this field especially because they are not yet user friendly. Moreover, problems are experienced when facing multiple reflections, precise estimation of convective coefficients, two and three-dimensional heat transmission. So, quasi-steady state calculation methods are generally preferred especially in the pre-design phase. Method 5000 and the Standard EN ISO 13790:2008 are the most common ones. Concerning the latter, research has been carried out in order to identify problems and propose solutions so to improve the results maintaining the simplified and easy approach. Calculations based on the technical standard and on the new proposal have been compared among them and with dynamic simulations concerning some particular features of sunspaces. The difference in results are pointed out and a critical analysis is presented.