Extensive research work on modeling the simultaneous heat and mass transfer taking place in a direct expansion (DX) cooling coil which is a key element in a DX air conditioning (A/C) system has been carried out. A steady-state model (coil model) has been developed for evaluating the equipment sensible heat ratio (SHR) and the total cooling capacity (TCC) of the DX cooling coil in an experimental variable speed DX A/C system under different operating conditions based on known evaporating temperature and the air flow rate passing through the cooling coil. On the other hand, a previous mathematical model (system model) for the complete experimental DX A/C system has also been developed. The evaporating temperature of the DX A/C system may be predicated using this system model, and can then be used as an input to the coil model. Therefore, by combining the coil model and the system model, a new steady-state model for the DX A/C system, which links the compressor and fan speeds on the input side with the Equipment SHR and TCC on the output side, will be developed. The new model will be experimentally validated, and the validated model will be used as a base to develop a model-based controller for a variable speed DX A/C system to achieve the simultaneous control of indoor air temperature and humidity.

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