Effects of turfgrass evaporation on external temperatures of buildings

Abstract

Evaporative cooling of air by urban vegetation has been considered to be primarily a mesoscale process. Recent studies, however, indicate that localized evaporation may be equally as effective at lowering air temperatures and may substantially reduce summer cooling loads in buildings. An experimental study was conducted in a moderately humid environment to explore how changes in evaporation and the surface energy balance of turfgrass may affect external temperatures of buildings. Surface temperatures of a building shell and the energy balance of adjacent bermudagrass were measured as evaporation from the grass decreased during two drying cycles. In spite of large decreases in latent heat flux and increases in sensible heat flux from the turfgrass, no systematic changes in wall temperature were observed. If evaporative cooling occurred, it was obscured by other environmental factors. Wall temperatures did vary in response to changes in irradiance and wind speed. Changes in wind speed had a considerable effect on wall temperatures during periods of predominantly free convection. When forced convection was dominant, changes in wind speed had a relatively small effect on wall temperatures. Results support the view that evaporative cooling of air is mainly a mesoscale process, and that changes in evaporation within an individual landscapes are unlikely to have a major effect on building energy balance in many climatic regimes.