Referring to the illustrated psychrometric chart, if the measured dry bulb temperature is 80 °F and the measured wet bulb temperature is 70 °F, what is the determined relative humidity? Illustration GS-RA-22
• Use the dry bulb temperature (DBT) along the bottom axis to go straight up to 80 °F • Follow the wet bulb temperature (WBT) line for 70 °F (slanted line) until it meets the 80 °F dry bulb line • From that intersection, trace toward the percent relative humidity curves at the top of the chart
• How far above or below the 60% and 70% humidity curves is the intersection point of 80 °F DBT and 70 °F WBT? • Does the intersection fall closer to the 0.6 (60%) or 0.7 (70%) humidity band when you follow it up to the top scale? • Compare the spacing between the 60% and 70% curves in that region—where within that band does your point land?
• Confirm you are using 80 °F on the dry bulb (horizontal bottom) axis, not the wet bulb scale on the left • Make sure you are following the correct 70 °F wet bulb diagonal line, not an adjacent 65 °F or 75 °F line • When you reach the top, read the percent relative humidity and then convert it to a decimal form (e.g., 60% = 0.6) before choosing your answer
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