Problem 3 (20 points) Consider a building that is located in a humid climate. It has rooftop units that use direct expansion (DX) refrigerant coils. Respond to the following with a full engineering explanation, including equations and a diagram sketch if needed. a. Relative to if the building were in a dry climate, how can lowering AHU airflow help maintain reasonable indoor relative humidity levels? Justify your answer. b. If latent loads are high and sensible loads are low, how can reheating the supply air provide a viable means of humidity control? Justify your answer. ASHRAE 8 ASHRAE PSYCHROMETRIC CHART NO. 1 NORMAL TEMPERATURE BAROMETRIC PRESSURE: 29.921 INCHES OF MERCURY COPYRIGHT 1992 ASHRAE 0.0 0.5 0.4 1500 0.3 10 SEA LEVEL SENSIBLE HEAT TOTAL HEAT ENTHALPY HUMIDITY RATIO 15 1000 Q 0 Ah AW 25 20 8.0 40- 2.0 500 55 ENTHALPY BTU PER POUND OF DRY AIR 20 50 50 10 800 90 Prepared by: CENTER FOR APPLIED THERMODYNAMIC STUDIES, University of Idaho 8 SATURATION TEMPERATURE- 60 75 70 45 80 55 50 85 85 WET BULB TEMPERATURE 10% RELATIVE HUMIDITY 20 DRY BULB T 60 CU, FT. PER LB ORY AIR HUMIDITY RATIO-POUNDS MOISTURE PER POUND DRY 028 026 60 024 55 022 020 50 016 014 45 012 2010 40 008 006 35 004 002 30 25 ENTHALPY - BTU PER POUND OF DRY AIR