In this communication, thermal model of a greenhouse has been developed by incorporating the effect of water wall in the north side. Various temperatures, namely plant, water wall and room temperatures as a function of climatic and design parameters have been obtained by solving coupled single-order differential equation using Runge-Kutta method. Numerical methods have been carried out for a typical day of winter for Delhi condition. It has been observed that there is significant effect in the plant, room air and water temperatures due to change in fraction of solar radiation incident on north wall (F,,) and heat capacity of water wall. Experimental validation of the proposed model for a greenhouse with brick north wall has also been carried out. It has been observed that there is a fair agreement between experimental and theoretical values. Copyright (C) 2002 John Wiley Sons, Ltd.