Modification method of heat transfer model for fan-coil units in air conditioning systems

Based on the performance test data of fan-coil unit samples provided by the equipment manufacturers, the heat transfer model of the fan-coil unit is established, including the heat transfer coefficient model, total heat exchange efficiency model and general heat exchange efficiency model. The heat transfer model is verified, the modified correlation of the model is put forward, and the modified and unmodified models are compared. The results show that the error of the total heat exchange efficiency model is mainly due to the pure countercurrent assumption in the fan-coil units heat transfer process, and the models correction coefficient is mainly related to the air volume. Before the correction of the model, the model error of total heat exchange efficiency is 8.9% to 21.8%, the error of calculated value of total heat model is 12.0% to 22.0%, the error of sensible heat is 8.3% to 12.6%, the error of outlet water temperature is 5.0% to 8.5%, and the error of outlet air temperature is 6.6% to 10.8%. After the modification of the model, the model accuracy and prediction accuracy have been greatly improved, the model error of total heat exchange efficiency is less than 3.3%, the error of total heat model calculation is less than 7.1%, the sensible heat error is less than 2.9%, the outlet water temperature error is less than 3.3%, and the outlet air temperature error is less than 2.5%. The fan-coil heat transfer model simplifies the demand parameters and significantly improves the model accuracy, and can be used for fan-coil performance evaluation and system optimization control.