Document 3wnB5NZMGGX0OXx1Rnk3QgY6

Heating Ventilating Air Conditioning Guide 1939 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. 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). 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 Healing 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. Humidistat: A regulatory device, actuated by changes in humidity, used for the control of humidity. Humidity: Thewater 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 840 Chapter 45. Terminology 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. 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. Isothermal: An adjective used to indicate a change taking place at constant temperature. Latent Heat: See Heat. Laws of Thermodynamics: The first law states that the total energy . of an isolated system remains constant and cannot be increased or dimin- ished by any physical process whatever. The second law states that no change in a system of bodies that takes place of itself can increase the available energyof a system. Manometer: An instrument for measuring pressures; essentially a U-tube partially filled with a liquid, usually water, mercury, or a light oil, so the amount of displacement of the liquid indicates the pressure being exerted on the instrument. Mass: The quantity of matter, in pounds, to which the unit of force (one pound) will give an acceleration of one foot per second per second. m -- --W . g Mb, Mbh1: Symbols which represent, respectively, 1000 Btu and 1000 Btu per hour. Mechanical Equivalent of Heat: The mechanical energy necessary to produce 1 Btu of heat energy. J = 777.5 ft-lb. Micron: A unit of length, the thousandth part of one millimeter or the millionth of a meter. Mol: The unit of weight for gases. It is defined as m lb where m denotes the molecular weight of a gas. For any gas the volume of 1 mol at 32 F and standard atmospheric pressure is 358.65 cu ft and the . weight of a cubic foot is 0.002788 m lb. One-Pipe Supply Riser (steam): A pipe which carries steam upward to a heating unit and which also carries the condensation from the heating unit in a direction opposite to the steam flow. One-Pipe System (hot water): A hot water system in which the water flows through more than one heating unit before it returns to the boiler; consequently, the heating units farthest from the boiler are supplied with cooler water than those near the boiler in the same circuit. 1These symbols were approved by the A.S.H.V.E., June. 1933. 841 1