Abstract
A dynamic heat transfer model was developed for simulation of freeze protection of trees by tree wraps and microsprinkler irrigation. Heat exchange at the surface of the tree wrap was a function of heat input from irrigation and heat losses to evaporation, radiation, and convection. A finite difference form of a transient heat conduction equation was used to calculate rates of trunk temperature change as a result of heat exchange at the wrap surface. Predicted trunk temperatures were generally within 1 s.e. of observed means when simulating the effects of tree wraps without irrigation, with high correlation (r = 0.99) between observed and predicted minimum temperatures. When simulating the effects of microsprinkler irrigation combined with tree wraps, however, predicted trunk temperatures were generally 1-3°C lower than observed means (r = 0.81). Under-prediction of trunk temperature was attributed to underestimation of sensible heat transfer from the irrigation water and/or inaccuracies in parameters associated with irrigation. The behaviour of the real and model systems was qualitatively similar in a majority of validation trials. Thus, the simulation model could be used to analyse factors affecting freeze protection.