Four buildings, shown in Figure as A, B, C, and D, are to be cooled using a central chilled-water facility, shown
as Supply. The figure is close enough to a scale drawing to be used for preliminary layout purposes. Ethylene
glycol, a commonly employed heat transfer liquid medium, is to be used. Average properties of the ethylene
glycol in the temperature range of interest are density = 68.6 lbm/ft3
, specific heat = 0.619 Btu/lbm-R, and
viscosity = 0.0133 lbm/ft-s. Cooling requirements are as follows:
The head loss through the air-handling unit in each building is a function of the flow rate (cfs) through the unit.
An approximate expression is 15.5Q
, where Q is the flow rate in cubic feet per second (cfs) through an AHU
and the head loss is in ft-lbf/lbm. The head loss in ft-lbf/lbm across the chiller is taken to be 1.25Q
, where Q is
the total flow rate in cfs. The temperature exits the chiller 25°F cooler than it enters. The lines are well insulated,
so that heat loss is minimized. In addition, the following specifications must be met:
1. Provide valves to isolate each building.
2. Provide valves to isolate supply and return lines.
3. Provide 35 ft of pipe in each mechanical room.
4. Minimize tunnel length by placing lines in the same tunnel.
5. Use a “Z” network (like Fig. P1-7).
6. Pipe velocities more than 10 ft/s should be avoided.
7. Limit the number of sizes (ANSI schedule 40) to 4 (buildings A and B, building C, building D, and the
supply/return loop to the chiller and main pump).
8. Provide valves to isolate each pump. (Note that items 1 and 2 may do the job.)
Accomplish a preliminary system design. At least the following should be specified for the system:
1. Layout of the network
a. Actual physical layout
b. Loops arrangement for Hardy-Cross input
2. Lengths and sizes of all pipes required
3. Number and type of valves and fittings
4. Increases in head and power delivered to the fluid for all required pumps
5. List of materials (diameters, lengths, valves) required
Building Cooling Load
A 400 120
B 500 150
C 900 270
D 550 165