The Cooling Effect of Tree Canopy on Thermal Environment in View of Enthalpy

Abstract

The influence of vegetation canopy on environment is a blend of factors by blocking off evaporation and radiation which represents various degrees of effectiveness as an imperative cooling source in canopy, shade area and ground surface to improve the urban thermal environment. The research was conducted on the view of enthalpy to evaluate the cooling effect of vegetation commonly applied to temperature reduction strategy and to describe the changes of energy in the air more precisely. Trees on campus were the sample of the experiment, utilized to measure the temperature, humidity and enthalpy value of the canopy. The energy status within canopy was analyzed by Gird TIN Default from Map info Professional software. The disproportion of enthalpy value found between vegetation canopy and the control group was 6.43kJ/kg under the condition of outdoor temperature below 31°C and wind velocity less than 3m/s, equivalent to a temperature reduction of 4.86°C in the dry air of balanced state. Canopy center with 17.87kg, equivalent to 13900L, of lower enthalpy content can improve urban thermal environment by energy balancing if the volume of air was taken into account. The massive volume of cooling air between ground surface and the top of canopy has great potentials shown in vegetation as in improvement in thermal environment with the direction of wind field. It will benefit urban cities from creating massive volume of cooling source if the volume of cooling air can be employed as an assessment guide in the prospective planning and designing.