Problem 2. For air at 75°F, 50% relative humidity, what will happen to relative

Question

Problem 2.

For air at 75°F, 50% relative humidity, what will happen to relative humidity if the air iscooled to 60°F? Cooled to 45°F?

Problem 3.
How much water (how many pounds) is present in 1 pound of air at 75°F, 50% relativehumidity? How much water is present in 1 pound of air at 95°F DB (dry bulb), 78°F WB(wet bulb)?

Problem 4.
Moist air at standard atmospheric conditions is at a dry bulb temperature of 50 °F and arelative humidity of 70%. It is sensibly heated (constant moisture) to 72 °F. Use thepsychrometric chart to determine the following properties of the air after it is heated:

a. The relative humidity:

b. The dew point temperature:

c. The specific volume:

d. The humidity ratio:

e. The enthalpy:

Problem 5.
Moist air at standard conditions in an indoor building space has a dry bulb temperature of70 °F and relative humidity of 50%. At what dry bulb temperature will condensation beginto occur on wall and window surfaces?

Problem 6.
A building owner is considering replacing singleglazed windows with doubleglazedwindows to eliminate condensation moisture problems during cold weather. Moist air atstandard conditions in the indoor building space reaches a maximum dry bulb temperatureof 72 °F and arelative humidity of 40%.

a. At what dry bulb temperature will condensation begin to occur on the window surfaces?

b. Will the doubleglazed windows prevent condensation under these indoor spaceconditions if the interior surface of the glass drops to 50 °F in cold weather? Why or whynot?

Explanation / Answer

1) Relative humidity doubles with each 20 degree (Fahrenheit) decrease, or halves with each 20 degree increase in temperature. Generally, as temperature goes up, relative humidity goes down and vice versa. So if relative humidty of air at 75oF is 50 %, then at 60oF it would be around 90-95% and at 45oF it would be 100%.

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