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

HVAC Control in the New MillenniumSpecific HeatThis refers to the amount of Btus required to raise the temperatureof one pound of a substance one degree Fahrenheit. The specific heat ofa substance is the ratio of the quantity of heat required to raise its temperatureone degree Fahrenheit to the amount required to raise the temperatureof the same weight of water one degree Fahrenheit. This can beexpressed by the following formula:Specific heat =Btu to raise temperatureof substance 1°FBtu to raise temperatureof same weight water 1°FThe standard is water at 62°F to 63°F which has a rating of 1.00 onthe specific heat scale. Specific heat represents the Btu’s required to raisethe temperature of 1 pound of a substance 1°F.The specific heat of water is defined as 1.00, but the amount of heatrequired to raise the temperature of different substances through sometemperature range will differ. Water has a large heat capacity and it isused as a standard. Since 1 pound of water requires one Btu to raise itstemperature one degree Fahrenheit, it is rated on the specific heat scaleat 1.00. Iron has a lower specific heat with an average rating of 0.130, iceis 0.504 and air is 0.238. The more water a substance contains, the higherthe specific heat.Latent HeatLatent heat is that quantity of heat which disappears or becomesconcealed in a body while producing some change in it other than a riseof temperature.Latent heat means hidden heat and it is a form of heat that causes asubstance to change its physical state from a solid to liquid, a liquid tovapor, or the reverse. When a liquid is evaporated to a gas, the change ofphysical state is always accompanied by the absorption of heat. Evaporationprovides a cooling effect on the surroundings of the liquid since theliquid must obtain from its surroundings the required heat to change itsmolecular structure. This type of action takes place in the evaporator ofan air conditioner. All liquids tend to saturate the surrounding space withits vapor. This property is important in air conditioning.©2001 by The Fairmont Press, Inc. All rights reserved.