From it, she followed the horizontal line left—dew point, 60°F. That was the temperature at which the air would surrender, sweating moisture onto cold pipes like a guilty confession. She followed the vertical line down from the dot to the bottom—humidity ratio: 0.011 pounds of water per pound of dry air. And the specific volume, the tilted lines running from upper left to lower right—14.2 cubic feet per pound. The air was bloated, lazy.
She needed a 25-ton unit with a hot gas reheat. The chart had just saved the developer a million dollars in lawsuits and the future residents a lifetime of allergies. psychrometric chart
She measured the dry bulb: 94°F, straight up from the bottom axis. She measured the wet bulb from a sling psychrometer she’d spun outside: 72°F, following that diagonal down. Where the two lines crossed, she placed a dot. From it, she followed the horizontal line left—dew