Document 1g33974bLOXmq9jjV8drDkvdE

American Society of Heating rand Ventilating, Engineers Guide, 1934 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. Extendedheating surface (or extended surface): Heating surface havingair 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). 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. Humidity: The water.vapor (either saturated or super-heated steam) occupying any space, which may or may not contain other vapors and gases at the same time. Relative Humidity: A ratio, although 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. '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, which depends merely on the temperature and partial pressure of the vapor. Absolute Humidity: The actual weight of water vapor contained in a given volume of a mixture of air and water vapor at the observed temperature. Humidistat: A regulatory device, actuated by changes in humidity, used for the control of humidity. Hygrostat: Same as humidistat. Insulation (heat): A material having a relatively high heat-resistance per unit of thickness. Latent Heat: See heat. 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. W m = ------- . 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 apd the weight of a cubic foot is 0.002788 m lb). Neutral Zone: The level within a room or building at which the pressure is exactly equal to the outside barometric pressure. I 'These symbols-were approved by the A.S.H.V. K.. June, 1933. 592 Chapter 42:--Heating, and Ventilating Standard Terms 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. One-Pipe System (Steam): A steam heating system consisting of a main circuit in which the steam and condensate flow in the same pipe and usually in opposite directions. Ordinarily to each heating unit there is but one connection which must serve as both the supply and, the return, although separate supply and return connections may be used. Overhead System: Any steam or hot water system, in which the supply main is above the heating units. (With a steam system the return must be below the heating units; with a water system, the return may be above the heating units). Panel Radiator: A heating unit placed on or flush: with a flat wall surface and' intended to function essentially as a radiator. Panel Warming: A method of heating involving the installation of the heating units (pipe coils) within the wall, floor or ceiling of the room, so .that the heating process talfes place mainly by radiation from the wall, floor or ceiling surfaces to the objects in the room. Plenum Chamber: An air compartment maintained under pressure and connected to one or more distributing ducts. Prime Surface: See heating surface. Power: The rate of performing work, expressed in units of horse power, one of which is equal to 550 ft-lb of work per second, or 33,000 ft-lb per minute. Psychrometer: An instrument for ascertaining the humidity or hygrometric state of the atmosphere..- Psychrometric: Pertaining to psychrometry or the state of the atmosphere as to moisture. Psychrometry: The branch of physics that treats of the measurement of degree of moisture, especially. the moisture mixed with the air. Pyrometer: An instrument for measuring high temperatures. Radiation: The.transmission of heat through space by wave motion. Radiator: A heating unit located within the room or space to be heated and exposed to view. (A radjator transfers heat by radiation to objects "it can see" and by conduction to the surrounding air which in turn is circulated by natural convection; a so-called radiator is also a convector but the single term radiator has been established by long usage). Concealed Radiator: See convector. Recessed Radiator : A heating unit set back into a wall recess but not enclosed. .. Register: A grille with a built-in damper or shutter. Relative Humidity: See humidity: see also discussion of relative humidity in Chapter I. __ Return Mains:-The pipes which return the heating medium from the heating units to the source of heat supply. 593 %i