In summer a room is to be maintained at 20°C, percentage saturation 50% when the outside air is 26°C, percentage saturation 50%. The mass flow rate of dry air supplied to the room is 2.0 kg/s at 15°C Fresh air is mixed with re-circulated air in the ratio three parts re-circulated air to one part fresh air. The air after mixing is passed over a cooling coil with an apparatus dew point of 4°C and a coil contact factor, CCF=(h4-h5)/(h4-hA) of 0.86. On Leaving the cooling coil the air passes over a heating coil and is then delivered to the room by the fan; the fan and ducting cause a 2K rise in temperature of the air between the heating coil and room
a) what is the cooling coil load?
b) what is the heating coil load?
c) Since there is no need to control the humidity in the room it is decided to remove the heating coil and use the arrangement as shown in the figure below to supply the same mass flow rate of air at the same supply temperature as before. The design conditions for the room are assumed to be unchanged. The mixing ratio for the first mixing box is now one part fresh air (25% of the total air mass supplied to the room) to one part re-circulated air. Assuming the cooling coil has the same apparatus dew point and coil contact factor, and there is a 2K temperature rise from the fan and ducting as before, calculate the percentage saturation of the air supplied to the room.