| Direct expansion (DX) Air Conditioning (A/C) units are commonly seen in small to medium sized buildings. In the evaporator of a DX A/C unit, or a DX air cooling coil, usually simultaneous heat and mass transfer, in the form of cooling and dehumidifying of the warm and humid air flowing through the cooling coil, takes place, when the surface temperature of the DX cooling coil is lower than the dew point temperature of the air stream. DX A/C units having variable-speed compressor and air supply fan are increasingly used for pursuing a thermally comfortable indoor environment at a higher energy efficiency.;This thesis begins with addressing the calculation of an important dimensionless parameter, i.e., steady state Equipment Sensible Heat Ratio (SHR) of a DX air cooling coil, which is defined as the ratio of the output sensible cooling capacity to the total output cooling capacity from the DX cooling coil. A Calculation Method for the Equipment SHR of a DX cooling coil has been developed and reported.;Secondly, the thesis presents an experimental study on estimating on the dehumidification effect on the airside of the superheated region (SPR) in a DX cooling coil. A lumped parameter calculation procedure was developed specifically for processing the experimental data.;Thirdly, the thesis reports on the development of a modified Logarithmic Mean Enthalpy Difference (LMED) method for evaluating the total heat transfer rate in a wet air cooling coil operating under both unit and non-unit Lewis Factors (Le2/3) conditions. A modified LMED (m-LMED) method has been therefore developed for calculating the total heat transfer rate under both unit and non-unit Lewis Factors.;Finally, the analytical solutions for evaluating the heat and mass transfer in both a wet DX cooling coil and a wet chilled water cooling coil, respectively, have been developed and are reported. The analytical solutions were validated by comparing their predictions with those from numerically solving the fundamental governing equations of the heat and mass transfer taking place in wet air cooling coils. |
