A room is air conditioned by a fan-coil unit (FCU) as shown in Figure Q2. A primary air-handling unit (PAU) is used to pre-treat the outdoor air (150 L/s) to 16 C and 90% saturation. Temperature rise due to PAU fan and duct heat gains is 1 C. The FCU fan runs at a constant speed to supply 700 L/s air to the room. The indoor air temperature is maintained at 24 C by adjusting the chilled water flow rate to the FCU using a modulating control valve. At the design condition, the design space sensible and latent loads are 7.5 kW and 1.8 kW, respectively. The fan heat gain in FCU can be neglected. 2-a) Determine the supply air temperature, the indoor air relative humidity (RH) and the sensible and latent cooling capacity of the fan coil at the design condition. Assume that the air leaving the FCU at the design load condition is 90% saturated. 2-b) At part load condition, the space sensible load falls to 4 kW, and the latent load remains to be 1.8 kW. The primary air state and flow rate as well as the supply air flow rate of FCU remain unchanged. Assume the air leaving the FCU at the part load condition is 80% saturated. Determine the space RH, the sensible and latent cooling capacity of the fan coil at the given part load condition. 2-c) Based on the results obtained in a) and b) as well as the control of the two-way chilled water valve, analyse the major problem with this system operating at part load condition, recommend a better design method of fan-coil unit when operating at part load condition and briefly introduce it's working principle. Outdoor air Primary air handling unit Cooling coil Primary air Room Figure Q2 A Fan-coil Return air grille Supply air