Effect of convection on the Penman–Monteith model estimates of transpiration of hot pepper grown in solar greenhouse

• Heat transfer was conducted dominantly through mixed convection in the study period.
• The stomatal resistance was highly correlated with solar radiation.
• Stanghellini equation in the P–M model performed the best regardless of convection type.

Accurate estimate of transpiration in greenhouses is of great importance for developing water-saving management practices. In this study, we evaluated the performance of the Penman–Monteith (P–M) model using aerodynamic resistance values estimated from heat transfer coefficient (h) to predict transpiration of hot pepper grown in a solar greenhouse based on different convection types. The reference transpiration was measured by sap flow meters. Results showed that heat transfer was conducted through mixed convection in about 81% and 71% of the study period, respectively, for the 2010–2011 and 2011–2012 season, while the rest of the study period was pure free convection which occurred mainly at night and in the early morning when transpiration rates were low and no pure forced convection occurred in the study solar greenhouse. Under pure free convection, the P–M model with h calculated by the McAdams equation tends to underestimate the transpiration, and the model with h calculated by the Stanghellini equation performed similar to the one by the McAdams equation. Under mixed convection, the P–M model with h calculated by the Stanghellini equation can accurately estimate the transpiration of hot pepper. This study shows that the P–M model with h estimated by the Stanghellini equation can well predict the transpiration rates of hot peppers grown in solar greenhouses without distinguishing the convection types.