Evaluation of Greenwalls Efficiency for Building Energy Saving
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The research moves from thermo-hygrometric data collected during a campaign to monitor energy exchanges at “Building F92” ENEA ‘La Casaccia’, with particular reference to the sections of the building facing south-east, south-west, screened by a green wall. In spring 2018, ENEA installed many sensors to detect parameters such as air temperature, internal and external surface temperature of walls, solar irradiation, wind speed, on the one hand, to validate the reliability of the parameters that can be extrapolated from the critical analysis of data, on the other to derive indications for a possible schematization of the contribution offered by the green-wall to the improvement of the conditions of indoor comfort. The research focused on the interpretation of the values measured by the sensors for the validation of simplified calculation models available in bibliography. The analysis allowed the extrapolation of data useful for the calculation of the Kv-parameter, the so-called “green factor”, an index describing the contribution to indoor cooling offered by the green-wall. The evaluation of the Kv-parameter demonstrates the substantial contribution of the green-wall to the reduction of the energy flux entering the opaque wall.
KeywordsGreen-wall Building energy saving Green factor
Thermal transmittance of the opaque element, W/m2 K
Green constant, –
Absorption coefficient of the opaque wall, –
Solar radiation incident on the outer surface, W/m2
Coefficient of convective exchange, W/m2 K
Surface temperature of the opaque wall not subjected to effects of the green wall, K
Surface temperature of the opaque wall subjected to effects of the green wall, K
Temperature of the external environment, K
Convection coefficient, W/m2 K
Irradiation coefficient, W/m2 K
Wind speed near the surfaces, m/s
Emissivity of the surface, –
Irradiation coefficient of a black body:
Stefan-Boltzmann constant of 5.67 × 10−8 W/m2 K4
Average thermodynamic temperature of the surface and of the neighboring surfaces, which will be assumed equal to the temperature of the leaf layer.
We thank the National Agency for New Technologies, Energy and Sustainable Economic Development (ENEA) for the granting of experimental data collected at the F92 building, ENEA Casaccia Research Center. The research and development activities of general interest for the national electricity system are financed by the Ministry of Economic Development (MiSE), with the Three-Year Research Plan in the so-called National Electric System 2015–2017, within the 2015–2017 Program Agreement stipulated to ENEA, the Annual Implementation Plan (PAR) 2018, as part of Project D.1 “Technologies for building buildings of the future”, Research Theme: Intelligent Buildings.
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