CAE - 464

Mid-term Recovery Plan

System and Ductwork Design

100 Points

Problem 2

Given:

• Design the complete ventilation system for an industrial facility that is maintained

under a negative pressure

• The system schematic is shown in Figure 2.1

• Outside air at 95 F DB/78 F WB is to be filtered and cooled to 75 F DB and 71.3 F

WB. The supply fan will add an additional two degrees to the supply air

temperature.

• This air will be supplied to the general area of the facility to off-set the general

area cooling load. The general area has an internal sensible load of 554,000 Btu/hr.

The sensible heat ratio is 1.0.

• The general area will be under a negative pressure of -0.125 in. w.c. , and as a

result, 3000 SCFM of outside air will be infiltrated

• Equipment and Filter casings are sized based on a face velocity of 500 fpm

• The ductwork single line diagram is shown in Figure 2.2

• The supply system fitting and components are as described in Table 2.1

• The exhaust system fitting and components are as shown in Table 2.2a & b

Problem 2a

Find:

A. Calculate the supply air quantity in SCFM necessary to cool internal load, offset the

infiltration air load and maintain the general area leaving air temperature at 104 F

DB.

B. Determine the effective mixed air conditions (supply air and outside air)

C. Determine the resultant general area relative humidity.

D. Air is then passed from the general area into the cubicles through backdraft

dampers. The air is then heated to 122 F with a SHR of 0.60.

E. Determine the resultant cubicle leaving air conditions, DB and WB temperatures

F. Plot this process on the attached psychrometric chart (A high temperature chart is

too high). [You may use a computreized psych chart plotting program]

G. Calculate to cooling coil capacity is Btu/hr and tons

H. Complete the psychrometric properties table.

Problem 2b

Find:

A. Based on your determination of the supply air quantity, size all of the ductwork in

the system based on a nominal velocity of 3200 fpm and even final duct sizes

B. Select all the three supply grilles (equal flow rate)based on a terminal velocity of 150

fpm and a throw of nominally 80 ft. with a NC of 45 or less and a blade setting of 0

degrees

C. Select the return grilles (one per cubicle) based on an NC of 50 or less

D. All fitting data and grille data is included in the supplementary information file.

E. Using the table structure provided, calculate the suction and discharge pressure

drops for both the supply and return fans assuming a density of 0.075 lbm

/ft3

F. Determine the fan entering air density conditions assuming an elevation of 1000 ft.

above seal level (28.85 in. Hg) and the psychrometric conditions calculated

previously.

G. Establish the performance requirements for each fan, actual air flow quantity and

pressure required at a density of 0.075 lbm

/ft3

H. Plot the pressure grade line through out the facility on Figure 2.1 at the reference

nodes provided

Duct Fittings

Duct Fittings

Duct Fittings

Duct Fittings

Duct Fittings

Supply Grille

Return Grille

Friction Chart for Round Ducts