Heat transfer mechanisms in vertical green systems and energy balance equations

Abstract

Heat transfer mecHanisms in vertical green systems and energy balance equations f. convertino, g. vox & e. scHettini department of agricultural and environmental science -disaat -university of bari, bari, italy. abstract the use of vegetated vertical systems is a sustainable technology for improving the energy efficiency of buildings in cities in order to reduce the energy consumption for air conditioning in summer and to increase the thermal insulation in winter. increasing urban green infrastructure (ugi) in a city can contribute to improve urban climate in summer reducing buildings surface temperature and urban air especially in southern europe. the application of vertical green systems requires the knowledge of the energy performance of the applied greenery system. the choice of the green facades depends on the local climate, water availability, building shape.the presence of green facades affects the building microclimate all day, by reducing heat waves during the warm periods and heat losses from the building in the cold period.the heat and mass transfer between the external environment, the green facades and the building surface determine the building microclimate. solar radiation, long wave infrared radiation, convective heat transfer and evapotranspiration are the main mechanisms of heat transfer in a green façade.the paper describes the main parameters concerning heat flow in green facades that can be used in simulation models for predicting temperatures in buildings using the external weather conditions as model inputs. the input parameters are: external air temperature and relative humidity, solar radiation, wind velocity and direction, plants and building characteristics. the green facade was described by a schematic representation, four layers were defined: the green layer, the external surface of the building wall, the internal surface of the building wall, the air inside the building.the energy balance was defined for each layer and all the terms involved in the energy exchange between the layers were defined as a function of the plant, the weather conditions and the constructive characteristics of the wall.

Wintertime Thermal Performance of Green Façades in a Mediterranean Climate

“…The longwave infrared energy balance at the external surface of the bare wall and of the wall covered with Rhyncospermum jasminoides was evaluated. Calculations were performed for a representative winter day, according to Convertino et al [29].…”

Convective heat transfer in green façade system

“…1). The heat transfer mechanisms interesting each layer were defined (Convertino et al, 2019;Kimball, 1973;Kindelan, 1980). Both the sensible and the latent terms of the heat fluxes were identified.…”

“…In the present research the fitting of the different formulas with the measured data was carried out. The energy balance of the green layer was used to this end (Convertino et al, 2019) The term CV was evaluated by using the different aforementioned equations (Eqs. 6,7,9,10,12,13).…”

“…The energy behaviour of a vertical green system can be studied by schematizing the system through the different layers that compose it (Convertino, Vox, & Schettini, 2019).…”

Heat Transfer Modelling in Green Façades

“…The design of simulation tools needs the energy model of a GF. The GF modelling implies that all the heat and mass transfer mechanisms occurring at each layer must be defined [32]- [35]. Heat fluxes due to radiation, convection and evapotranspiration are the main ones.…”