EFFECT OF AERODYNAMIC RESISTANCE ON ENERGY-BALANCE AND PENMAN-MONTEITH ESTIMATES OF EVAPOTRANSPIRATION IN GREENHOUSE CONDITIONS

The transfer of sensible heat flux between a greenhouse crop and the surrounding air was calculated from measurements of canopy surface temperature. air temperature, and aerodynamic resistance to momentum transfer. The aerodynamic resistance was determined by non-dimensional groups, Three relationships for estimating the aerodynamic resistance were compared. The aerodynamic resistance in a cooler-than-air situation was found larger than that in a warmer-than-air situation owing to downward mixing of warmer, tighter air. The calculated sensible heat fluxes were compared with energy balance estimates. The resistance form equation for sensible heat flux and the Penman-Monteith equation are sensitive to the errors in aerodynamic resistance, but these errors have much less effect on latent heat flux estimates from the energy balance equation. Estimates of evapotranspiration from both the energy balance and the Penman-Monteith equations are close to measured evapotranspiration. In this study, the energy balance equation outperformed the Penman-Monteith equation.