HVAC Control in the New Millennium.pdf - HVAC.Amickracing

HVAC Control in the New Millenniumtemperature. The relative humidity of air at any given temperature canbe found by dividing the amount of moisture actually in the air by theamount of moisture that the air can hold at that temperature and multiplyingthe result by 100.Relative Humidity MeasurementRelative humidity has been traditionally measured by sling psychrometers.This instrument has two thermometers fastened to a frame.The instrument is spun around on a chain so it comes in contact with themaximum amount of air.Around the bulb of one thermometer is a small piece of cloth,which is dampened with water before taking a reading. The evaporationof moisture from the bulb of the wet thermometer causes it to read lowerthat the one which is dry. The difference between the readings of the twothermometers provides the relative humidity.Dew PointThe saturation temperature for a given quantity of water vapor inthe atmosphere is called the dew point. At a given atmospheric pressure,the dew point is the temperature of saturation where the moisture beginsto change into the form of tiny water droplets or dew.Effective TemperatureEffective temperature provides an index of the degree of warmthor cold apparent to the human body. It takes into account the temperature,moisture content and motion of the surrounding air.The effective temperature is not strictly a measure of heat in thesame way that dry-bulb temperatures are. The effective temperature canbe lowered by increasing the rate of airflow even though the wet- anddry-bulb temperatures remain constant. If the air movement is constant,the effective temperature is determined by the wet- and dry-bulb thermometerreadings.©2001 by The Fairmont Press, Inc. All rights reserved.