Texts: Problem 3-32 An air-conditioned space has a sensible heat load of 200,000 Btu/h, a latent load of 50,000 Btu/h, and is maintained at 78°F DB and 60% RH. On a mass basis, 25% outdoor air is mixed with return air. Outdoor air is at 95°F DB and 76°F WB. Conditioned air leaves the apparatus and enters the room at 60°F DB. The fan must produce a pressure increase of 3.5 in. water to overcome the system pressure loss. Fan efficiency is estimated as 55%.
1. Draw and label the schematic flow diagram for the complete system. (Hint: See Figure 3-1.)
2. Complete the table below.
Dry Bulb t, Point Ho
?, %
Enthalpy h, Btu/lb
W, lb/lb
mass lb/h
CFM
SCFM
OA
r
m
f
S
3. Plot and draw all processes on a psychrometric chart.
4. Specify the fan size, SCFM, and fan motor rating, hp.
5. Determine the size refrigeration unit needed, in Btu/h and tons.
6. What percent of the required refrigeration is for (1) sensible cooling and (2) for dehumidification?
7. What percent of the required refrigeration is due to the outdoor air load?