Techno-economical Analysis based on a Parametric Computational Evaluation for decision process on envelope technologies and configurations

Abstract

Energy saving is crucial for existing buildings which is present a huge potential of improvement by a strong energy retrofitting. Often, the existing envelope components are not adequately insulated and deep refurbishment is required to comply current regulations to improve energy efficiency and address Nearly Zero Energy Building (NZEB) goals. The strategies to enhance buildings energy performance involve heating and cooling demands strongly dependent by envelope quality (i.e. insulation, thermal mass, internal gain storage capacity and solar heat gains exploitation). Commonly, the suggested main retrofit interventions on envelope are glazed surfaces replacement, Solar Heat Gain Coefficient (SHGC) reduction and thermal transmittance (U value) improvement by additional insulation layers or even components replacement. However, it is worthy to note that the resulting thickness of the external envelope and the payback time of the interventions are important supports for decision-making. The environmental issue related to CO2 emissions during the operational phase of the building is encompassed into the standard energy certification of the asset and the conversion factors to define fuels’ impacts are available and updated. However, the calculation excludes the environmental impact due to energy used for materials’ production and few official information sources provide accredited values, e.g. the Environmental Product Declaration (EPC). Going towards a Zero Energy Building, which reduces its environmental impact during the running phase, embodied energy claims an increasing weight. Thus, materials and components with low embodied energy should be favoured and endorsed. For this reason, the most influential rating systems worldwide available for building sustainability assessment (e.g. LEED, BREEAM, etc.) updated their checklists including criteria related to reduced energy for extraction, production and materials transportation on the field.The technological optioneering of envelope solutions to achieve both energy efficiency and economic affordability is inevitably based on and supported by multicriteria assessment frameworks. These frameworks should include energy, environmental and economic parameters to define the technological suitability in different climate conditions identifying accurate optimization points, e.g. thickness of the insulation layer or heat storage capacity, considering energy saving and management costs in the life cycle. When actual optimization processes are required, computational parametric tools support to ease the options’ performance comparison and to compute different combinations. Nowadays some tools are available into the main authoring software on the energy simulation market. Although different tools could be adopted, the need of transparency and custom workflows is crucial. In the present research, a specific multi-criteria methodological approach enables to outline a synoptic diagram for each considered climate to compare the envelope technological solutions by aggregating LCA (Life Cycle Analysis) and LCC (Life Cycle Cost) factors. For LCA, Embodied Energy (EE) of the envelope materials and Primary Energy (EP) used during the running phase have been considered. For LCC Investment Cost (C) of the materials to enhance a baseline performance and related operational costs of the building based on Net Present Value (NPV) and Discounted Payback Period (DPP) have been adopted.The present study focuses as first on the construction coherency of different technologies used to define the external envelope of a test room, able to manage the energy flows resulting from different external conditions. Subsequently the definition of the technological basket, a parametric analysis based on reducing thermal losses and increase solar gains has been performed defining the most suitable technologies and façade configuration in three representative climate conditions at national level by calculating heating and cooling demand and related primary energy.