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. Zone temperatures are at cooling setpoint (baseline condition) and then an influx of occupants warms the zones to above setpoint. i. ii. 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. OA RA RA VARIABLE VOLUME BOX PREHEAT COIL FAN WITH H INLET VANES B > FILTERS COIL COOLING Figure 111-Variable Air Volume System ASHRAE ASHRAE PSYCHROMETRIC CHART NO. 1 NORMAL TEMPERATURE BAROMETRIC PRESSURE: 29.921 INCHES OF MERCURY COPYRIGHT 1992 ASHRAE 0.6 0.5 -0.4 1500 0.3 SEA LEVEL SENSIBLE HEAT TOTAL HEAT = 2 o o 0 10 ENTHALPY HUMIDITY RATIO 15 35 40 1000 Ah = AW 20 25 -1.0 2.0 4.0 8.0 -8.0 4.0 -2.0 500 ENTHALPY BTU PER POUND OF DRY AIR 45 50 10 55 g 70 SATURATION TEMPERATURE - F Prepared by: CENTER FOR APPLIED THERMODYNAMIC STUDIES, University of Idaho 60 65 15 45 75 80% 70% 65 60% 50% 55 50 85 85 WET BULB TEMPERATURE- F 80 40% 10% RELATIVE HUMIDITY 20 5 6 DRY BULB PERATURE- 60 25 CU. FT. PER LB. 15.0 HUMIDITY RATIO-POUNDS MOISTURE PER POUND DRY AIR 028 60 .026 024 55 022 020 50 018 016 014 45 012 2010 40 008 006 35 .004 .002 30 ENTHALPY-BTU PER POUND OF DRY AIR