3. Variable air volume (VAV) HVAC system can vary circulation flow rate for different operating

conditions. Consider a VAV HAVC system operates at the same part load as in Problem 2 with

ambient conditions of 86 F dry-bulb and 70 F wet-bulb. The total load is 350,000 Btu/hr with

the same sensible heat ratio of 0.8 and the same zone temperature of 77 F. The ventilation flow

rate is the same at 1600 cfm. The bypass factor for the coil is 0.175 and the chilled water

temperature is 50 F, which is the same as design conditions. Reheat is zero.

Use the same method in problem 1 to calculate the zone relative humidity, coil load, and reheat

heat transfer rate. List the results in Table 2.

CAV at design

condition

CAV in part load

VAV in part load

Table 2 Properties of thermodynamics states of two iterations

Circulation

flow rate

lbm/hr cfm

Zone

relative

humidity

Total load

Btu/hr

500000

350000

350000

tons

Coil load

Btu/hr tons

Reheat

Btu/hr

0

0