Problem 1 (50 points)

Consider the VAV system shown in the diagram below and respond to the following.

a) Sketch a pressure (y axis) versus position (x axis) chart that shows a static pressure profile of the

air flow path. Begin the chart in the zones, and end the chart in the zones. On your chart, label all

components that appear in the diagram below.

b) If the fan is rated for 10,000 cfm and 4" TSP and draws 9.4 bhp of shaft power, what is its static

efficiency?

c) If the target duct static pressure (DSP) is 1.5" w.c. and the actual DSP is 2" w.c., show on a

pressure-vs-flow diagram how the system can adjust its inlet vanes to meet the target DSP.

d) Assume the inlet vanes are removed, and fan speed is then controlled with a VFD to maintain a

duct static pressure setpoint. Show the following scenarios on pressure-vs-flow diagrams. Clearly

identify the effect of VAV damper modulation and supply fan speed modulation with annotations,

and show where the operating point rides the system curve and where it rides the fan curve.

i. Zone temperatures are at cooling setpoint (baseline condition) and then an influx of

occupants warms the zones to above setpoint.

Zone temperatures are slightly above the cooling setpoint (baseline condition) and then

cooler outside conditions result in zone temperatures dipping below the zone cooling

setpoints.

ii.

OA

EA

RA

PREHEAT

FILTERS

COIL

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COIL

COOLING

RA

FAN WITH

INLET VANES

VARIABLE

VOLUME BOX

Figure 111-Variable Air Volume System

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