Thermal improvement by means of leaf cover on external walls — A simulation model

Abstract

A dynamic computer model, simulating the thermal effects of deciduous and evergreen vegetation cover on exterior walls, has been formulated using the DEROB system of programs. The simulations were validated against field measurements, producing correlation coefficients of 0.93 during summer and 0.97 during winter at a probability level of p = 0.0001. Field measurements taken on English ivy (Hedera helix) as well as Boston ivy (Parthenocissus tricuspidata), Virginia creeper (Parthenocissus quinquefolia) and grape (Vitis vinifera) produced identical temperatures in the shade at a cover depth of 200 mm. The validated model has been applied to standard lightweight building types in hot inland climates, showing that in summer the leaf cover produces a constant 5 K cooling effect in room temperature of buildings facing the equator. The indoor temperature range was reduced from 17°C – 33°C to 18°C – 28°C in an ambient temperature range of 21°C – 31°C dry bulb. In winter, the indoor temperature range was reduced from 10°C – 30°C without leaf cover to 12°C – 27°C with leaf cover, for an outdoor range of 7°C – 18°C. Comparable indoor air temperature improvements were attained for west-facing buildings. Further simulations on high- and low-mass buildings of the same design were executed for equator-facing and west-facing orientations in hot-humid and mediterranean climates for summer and winter design days. The thermal improvement of the indoor environment was found to be most pronounced in low-mass buildings in hot-arid climates where the best results were obtained with equator-facing walls of high radiation absorptance in winter, but covered by vegetation during summer, while all other outside walls were covered with evergreens. This design (which can be retrofitted on existing and poorly orientated buildings) can obviate the need for artificial heating or cooling in the given climates.