Question

4. Air-Conditioning Unit [20 Marks] 1 m3/s of moist air at 32 °C with a relative humidity of 70% is to be treated by a simple air condition system to produce air at 18 °C with a relative humidity of 50% The system will have two stages. In the first stage, the air will pass over cooling coils to dehumidify it, and in the second stage it will be heated electrically to the specified outlet conditions You may ignore the power supplied to any fan and assume a pressure of 1.01325 bar throughout the system. COOLING SECTION HEATING SECTION T,-32 °C 70 % Q 1 m3/s ø,-100 % Figure 2 a) Plot states 1, 3, and 4 on the Psychrometric Chart, and submit this with your [3 Marks] b) Determine the dew-point temperature corresponding to the specified system [1 Mark] c) Determine the rate of heat transfer in kW to the cooling coils, assuming that the water draining from the cooling section is at the same temperature as [8 Marks] d) Determine the rate of heat transfer in kW, in the heating section. [2 Marks] e) Thermodynamically, what would be the most efficient way to carry out the required cooling and the heating in the above air-conditioning unit? Explain and justify your reasoning briefly. You may wish to include a hardware [3 Marks] f) Explain the terms wet bulb temperature, dry bulb temperature, and dew [3 Marks] solution. outlet conditions the air leaving the section diagram for your explanation. point temperature

Answer 1