On the determination of the overall heat transmission coefficient and soil heat flux for a fog cooled, naturally ventilated greenhouse: Analysis of radiation and convection heat transfer

A physical model for analyzing the radiative and convective heat transfer in a fog cooled, naturally ventilated greenhouse was developed for estimating the overall heat transmission coefficient based on the conduction, convection and thermal radiation heat transfer coefficients and for predicting the soil heat flux. The contribution of the water vapor of the inside air to the emission and absorption of thermal radiation was determined. Measurements of the outside and inside greenhouse environments to be used in the analysis were conducted around solar noon (12:19–13:00) on a hot sunny day to provide the maximum solar radiation transmission into the greenhouse. The net solar radiation flux measured at the greenhouse floor showed a reasonable agreement with the predicted value. The net fluxes were estimated around noon. The average net radiation (solar and thermal) at the soil surface was 220.0 W m−2, the average soil heat flux was 155.0 W m−2 and the average contribution of the water vapor of the inside air to the thermal radiation was 22.0 W m−2. The average overall heat transmission coefficient was 4.0 W m−2 C−1 and was in the range between 3.0 W m−2 C−1 and 6.0 W m−2 C−1 under the different hot summer conditions between the inside and outside of the naturally ventilated, fog cooled greenhouse.