Question

It is required to maintain the air in a building at 20oC and 40% saturation when the
outside conditions are 28oC, 50% saturation with a barometric pressure of 1.01325
bar. The total heat gains to the room (sensible plus latent) are 15 kW, and the latent
heat gains are 3 kW. There is no reciculation and the fresh air passes over a cooling
coil to dehumidify it, and then a heater, before entering the room. The cooling coil by
pass factor is 0.2; the volume flow of fresh air is 5 m3/s, calculate:
a. The temperature of the air leaving the cooling coil;
b. The refrigeration load for the coil;
c. The heat supplied in the heater
d. If the air-con system is to be adapted for use in winter with the same room
conditions of 20oC and 40% saturation. The mass flow rate of dry air from
the heater is to be kept the same as in summer. The outside conditions are
-5oC, 100% saturation, and the sensible heat loss from the conditioned
space is 34.5 kW with the same latent heat gain of 3 kW. A saving in
energy is obtained by recirculating a portion of the room air using a mixing
box and dispensing with the washer. Calculate
i. The ratio of room air to fresh air that must be used for the system to
operate satisfactory;
ii. The heat supplied in the heater under these conditions.

Answer 1