Energy Performance of Verandas in the Building Retrofit Process

Rossano Albatici, Francesco Passerini, Jens Pfafferott
2016 Energies  
Passive solar elements for both direct and indirect gains, are systems used to maintain a comfortable living environment while saving energy, especially in the building energy retrofit and adaptation process. Sunspaces, thermal mass and glazing area and orientation have been often used in the past to guarantee adequate indoor conditions when mechanical devices were not available. After a period of neglect, nowadays they are again considered as appropriate systems to help face environmental
more » ... environmental issues in the building sector, and both international and national legislation takes into consideration the possibility of including them in the building planning tools, also providing economic incentives. Their proper design needs dynamic simulation, often difficult to perform and time consuming. Moreover, results generally suffer from several uncertainties, so quasi steady-state procedures are often used in everyday practice with good results, but some corrections are still needed. In this paper, a comparative analysis of different solutions for the construction of verandas in an existing building is presented, following the procedure provided by the slightly modified and improved Standard EN ISO 13790:2008. Advantages and disadvantages of different configurations considering thermal insulation, windows typology and mechanical ventilation systems are discussed and a general intervention strategy is proposed. The aim is to highlight the possibility of using sunspaces in order to increase the efficiency of the existing building stock, considering ease of construction and economic viability. Energies 2016, 9, 365 2 of 12 Among the different passive systems, designers have often preferred sunspaces because they act not only as heat storage systems, but also because they define a space with high quality of living, often required by clients as winter gardens. In this field, one of the early works was from Wall [4], which investigates in depth several aspects linked to glazed spaces: examples from past architecture, proposals of simplified design tools, and evaluation and comparison of different design possibilities. Moreover, monitoring and analysis of a great variety of real cases in Sweden are presented, performing both stationary and dynamic calculations in order to investigate the influence of design on inner climate (comfort analysis) and energy requirements. Mihalakakou and Ferrante [5] performed a sensitivity analysis in order to investigate the impact of different parameters on the energy potential of sunspaces. Afterwards they focused on the simulation and monitoring of real cases [6] . Several studies have been made comparing monitoring of sunspaces in experimental setups and simulation results, in order to refine calculus tools. Blasco Lucas et al. [7] compared physical models of massive/Trombe walls and direct gain, sunspace and traditional buildings in order to establish the convenience of passive systems considering their thermal performance, finding that special care must be given to implementation of ventilation and incorporation of efficient protection. Similar results were found by Fernández-Gonzáles [8] for United States Midwest climate conditions, with special emphasis on human inner thermal comfort conditions. Several works analyse the performance of dynamic energy modeling on glazed spaces validating their assumptions on full-scale experimental data [9,10], often finding a good approximation of results of the model and of the measurements, even if proposing different approaches. Other researches focus on achieving an effective simulation of solar radiation distribution and reflection inside the sunspace [11-13] that remains one of the key central point of dynamic simulations. Two recent papers show that passive solar systems, and sunspaces in particular, are still nowadays strongly considered as appropriate systems for building heating, Ignjatović et al. [14] and Rempel et al. [15]. The former refers about the first building in Serbia that received the permission to apply a sunspace as an efficient strategy for energy saving. The latter concerns a deep investigation of the effect of thermal mass as heating storage in sunspaces, so to give users and designers (enthusiastic of sunspaces but usually wary of unproven systems) guidelines for contemporary passive solar design. The usefulness of a passive approach to building design in order to decrease energy need, the use of non-renewables and the emission of greenhouse gases in the atmosphere, are now also recognized by international legislature. Annex I of European Directive 2010/31/EU [16] states that passive solar systems must be taken into consideration in the building energy performance calculation procedure. The 32th preamble of the European Directive 2009/28/EC [17] states that "passive energy systems use building design to harness energy", meaning that concepts related to energy efficiency and to renewable energy exploitation are integrated in the architectural design. Besides, public authorities are now taking into consideration the possibility of including solar systems in urban planning tools, providing incentives for their use and considering them as technical volumes [18] . Nevertheless, dynamic simulation software generally gives several uncertainties on the proper evaluation of radiation through glasses and multi-reflection in closed spaces, depending also on the complexity of the building shape [19, 20] . Furthermore, software packages for dynamic simulation are not user friendly, they require several input data, often unknown even by the designers, and sometimes the interpretation of outputs requires specific knowledge, so quasi steady-state procedures are often used in everyday practice with good results. Annex E of EN ISO 13790:2008 [21] provides procedures for calculating the heat transfer and solar heat gains of special elements, such as unconditioned sunspaces. This methodology has been successfully included in several software packages approved by national certification bodies and so it is widely used by practitioners. Anyway, some aspects of the Standard can be improved: calculation of direct and indirect solar heat gains [22] , solar absorption factor in the sunspace [23], the correction factor F w of solar gains through glazed surfaces [24], the shading factor (influencing direct heat gains), indirect heat gains [25] and ventilation through the sunspace are considered the more relevant ones.
doi:10.3390/en9050365 fatcat:htexbhpd6vgnfbhlghml25rla4