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Heating Ventiuiting Air Conditioning Guide 1938 Fan Furnace System: See Warm Air Heating System. Force: The action on a body which tends to change its relative condition as to rest or motion. F = --W--V. - gt Fumes: Particles of solid matter resulting from such chemical pro cesses as combustion, explosion, and distillation, ranging from 0.1 to 1.0 micron in size. Furnace: That part of a boiler or warm air heating plant in which combustion takes place. Also, a firepot. Furnace Volume {total): The total furnace volume for horizontalreturn tubular boilers and water-tube boilers is the cubical contents of the furnace between the grate and the first plane of entry into or between tubes. It therefore includes the volume behind the bridge wall as in ordinary horizontal-return tubular boiler settings, unless manifestly in effective {i.e., no gas flow taking place through it), as in the case of wasteheat boilers with auxiliary coal furnaces, where one part of the furnace is out of action when the other is being used. For Scotch or other internally fired boilers it is the cubical contents of the furnace, flues and combustion chamber, up to the plane of first entry into the tubes. {A.S.M.E. Power Test Codes, Series 1929.) Cage Pressure: Pressure measured from atmospheric pressure as a base. Gage pressure may be indicated by a manometer which has one leg' connected to the pressure source and the other exposed to atmospheric pressure. Grate Area: The area of the grate surface, measured in square feet, to be used in estimating the rate of burning fuel. This area is construed to mean the area measured in the plane of the top surface of the grate, except that with special furnaces, such as those having magazine feed, or special shapes, the grate area shall be the mean area of the active part of the fuel bed taken perpendicular to the path of the gases through it. For furnaces having a secondary grate, such as those in double-grate down-draft boilers, the effective area shall be taken as the area of the upper grate plus one-eighth of the area of the lower grate, both areas being estimated as defined above. (A.S.H.V.E. Standard and Short Form Heat Balance Codes for Testing Low-Pressure Steam Heating Solid Fuel Boilers.) . Gravity Warm Air Heating System: See Warm Air Heating System. Grille: A perforated covering for an air inlet or outlet usually made of wire screen, pressed steel, cast-iron or plaster. Grilles may be plain or ornamental. Heat: A form of energy generated by the transformation of some other form of energy, as by combustion, chemical action, or friction. Accord ing to the molecular theory, heat consists of the kinetic and potential energy of the molecules of a substance. The addition of heat energy to a body increases the temperature or the kinetic energy of motion of its molecules {sensible heat) or increases their potential energy of position but does not increase the temperature, as when melting or boiling occurs {latent heat). 824 Chapter 45. Terminology Heat Capacity: The amount of heat (Btu or calories) required to raise the temperature of a body of any mass and variety of parts one degree (Fahrenheit or centigrade). This will depend on the masses and specific heats of the various parts of the body. Therefore S = mi Si + mt St + m, s,. ... etc. where S is the heat capacity and mu *,, m,, and Ji, s,, s, stand for the masses and cor responding specific heats of the parts, respectively. Heating Medium: A substance such as water, steam, air, electricity or furnace gas used to convey heat from the boiler, furnace or other source of heat or energy to the heating unit from which the heat is dissipated. Heating Surface: The exterior surface of a heating unit. Extended heating surface {or extended surface): Heating surface having air on both sides and heated by conduction from the prime surface. Prime Surface: Heating surface having the heating medium on one side and air (or extended surface) on the other. (See also Boiler Heating Surface.) Heat of the Liquid: The sensible heat of a mass of liquid above an arbitrary zero. Horsepower: A unit to indicate the time rate of doing work equal to 550 ft-lb per second or 33,000 ft-lb per minute. (One horsepower = 745.8 watts. In practice this is considered 746 watts.) Hot Water Heating System: A heating system in which water is used as the medium by which heat is carried through pipes from the boiler to the heating units. Humidify: To add water vapor to the atmosphere; to add water vapor or moisture to any material. Humidity: The water vapor mixed with dry air in the atmosphere. Ab solute humidity refers to the weight of water vapor per unit volume of space occupied, expressed in grains or pounds per cubic foot. Specific humidity refers to the weight of water vapor in pounds carried by one pound of dry air. Relative humidity is a ratio, usually expressed in per cent, used to indicate the degree of saturation existing in any given space resulting from the water vapor present in that space. Relative humidity is either the ratio of the actual partial pressure of the water vapor in the air to the saturation pressure at the dry-bulb temperature, or the ratio of the actual density of the vapor to the density of saturated vapor at the dry-bulb temperature. The presence of air or other gases in the same space at the same time has nothing to do with the relative humidity of the space. Humidistat: A regulatory device, actuated by changes in humidity, used for the control of humidity. Hygrostat: Same as Humidistat. Inch of Water: A measure of pressure which refers to the difference in the heights of the legs of a water-filled manometer. Insulation {heat): A material having a relatively high heat-resistance per unit of thickness. Isobaric: An adjective used to indicate a change taking place at con stant pressure. 825