Document OoX3V2LdzOG6br0BOY9jnGjQ

6 CHAPTER 1 1951 Guide Insulation (Thermal): A material having a relatively high resistance to heat flow, and used principally to retard the flow of heat. - Isobarlc: An adjective used to indicate a change taking place at constant pressure. Isothermal: An adjective used to indicate a change taking place at constant temperature. Load, Estimated Design: In a heating or cooling system, the sum of the useful heat transfer, plus heat transfer from or to the connected piping, plus heat transfer occurring in any auxiliary apparatus connected to the system. The units are Btu per hour or, in heating, equivalent direct radiation (EDR). Load, Estimated Maximum: In a heating or cooling system, the calculated maxi mum heat transfer that the system will be called upon to provide. 1 Manometer: An instrument for measuring pressures; essentially a U-tube partially filled with a liquid, usually water, mercury, or a light oil, so constructed that the amount of displacement of the liquid indicates the pressure being exerted on the instrument. Mass: A measure of the inertia of a body. It also measures the quantity of matter in a body. Since the only general property of a given portion of matter that cannot be changed is its inertia, it is this property by which quantities of matter are defined. Two bodies which have equal inertias are Baid to have equal masses, or to contain equal quantities of matter. (This definition fails at velocities approaching the veloc ity of light.) The mass of a body is numerically equal to the ratio of the force re quired to give the body a given acceleration, to the acceleration, m -- F/a. The common units of mass are the gram and the pound. Mechanical Equivalent of Heat: The quantity of mechanical energy equal to one unit of heat. J = 778.3 ft-lb per Btu -- 4.187 X 107 ergs per gram-calorie. Medium, Heating: A substance such as water, steam, air 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. Micron: A unit of length, the thousandth part of 1 mm or the millionth of a meter Millimeter of Mercury: A unit of pressure equal to the pressure exerted j>y a column of mercury 1 mm high at a temperature of 0 C. One millimeter of mercury', at 0 C ~ 1.934 X KT* psi. Mol: A weight of a substance numerically equal to its molecular weight. If the weight is in pounds the unit is a Pound Mol, in grams the unit is a Gram Mol. For . perfect gases the volume of 1 mol is constant for all gases at the same temperature and pressure. For real gases this is approximately true at moderate pressures. At 32 F and zero-pressure the value of the product, pressure times specific volume, is 359.045 0.006 atmosphere cubic feet (atm ft'),/or 1 mol of any gas. For dry air at 32 F and standard atmospheric pressure, the specific volume is 358.83 cu ft per mol (ft* per mol). One-Pipe Supply Riser--{Steam): A pipe which carries steam vertically to a heat ing unit, and which also carries the condensate from the heating Unit. In an up-feed system, steam and condensate flow in opposite directions; in an overhead or down-feed system, they flow in the same direction. One-Pipe System--{Steam): A steam heating system in which a single main serves the dual purpose of supplying steam to the heating unit and conveying condensate from it. 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. (Hot Water)--A hot water system in which the cooled water from the heating units is returned to the supply main. Consequently, the heating units far thest from the boiler are supplied with cooler water than those near the boilerin the same circuit. ^Overhead System: Any steam or hot water system in which the supply main is above the heating unit. In a steam system the return must be below- the heating units; in a water system the return may be above or below the heating units. Panel Heating: A heating system in which heat is transmitted by both radiation ' . and convection from panel surfaces to both air and surrounding surfaces. Panel Radiator: A heating unit placed on or flush with a flat wall surface, and in tended to function essentially as a radiator. _ Plenum Chamber: An air compartment maintained under pressure, and connected to one or more distributing ducts. Potentiometer: An instrument for comparing small electromotive forces, or for measuring small electromotive forces by comparison with a known electromotivo force. Itsprincipal advantage is that during the measurement, no current.flows through the source of electromotive force. Terminology 7 Power: The rate of performing work. Common units are horsepower, Btu per hour, and watts. Pressure: Force per unit area. Common units are pounds per square inch, gram ner square centimeter, inch of water, millimeter of mercury. Pressure, Absolute: The sum of the gage pressure and the barometric pressure. Pressure, Dynamic: Same as Total Pressure. Pressure, Gage: Pressure measured from atmospherio pressure as a base. Gage oressure may be indicated by a manometer which has one leg connected to the pres sure source and the other exposed to atmospheric pressure. Pressure, Saturation: The saturation pressure for a pure substance for any given temperature is that pressure at which vapor and liquid, or vaporand solid, can co-exist in stable equilibrium. Pressure, Static: The normal force per unit area that would be exerted by a moving fluid on a small body immersed in it if the body were carried along with the fluid. Practically, it is the normal force per unit area at a small hole in a wall of the duct through winch the fluid flows (piezometer) or on the surface of a stationary tube at a point where the disturbances, created by inserting the tube, cancel. It is supposed that the thermo-dynamic properties of a moving fluid depend on static pressure in exactly the same manner as those of the same fluid at rest depend upon its uniform hydrostatic pressure. Pressure, Total: In the theory of the flow of fluids; the sum of the static pressure and the velocity pressure at the point of measurement. Pressure, Vapor: The pressure exerted by a vapor. If a vapor is kept in confine ment over its liquid so that the vapor can accumulate above the liquid, the tempera ture being held constant, the vapor pressure approaches a fixed limit called the maxi mum, or saturated, vapor pressure, dependent only on the temperature and the liquid. The term vapor pressure is sometimes used as synonymous with eaturaied vapor pressure. Pressure, Velocity: In a moving fluid, the pressure capable of causing an equivalent velocity, if applied to move the same fluid through an orifice such that all pressure energy expended is converted into kinetic energy. Psychrometer: An instrument for ascertaining the humidity or hygrometric Btate of the atmosphere. Psychrometric: Pertaining to psychrometry or the state of the atmosphere with reference to moisture. ,. Psychrometry: The branch of physics relating to the measurement or determination of atmospheric conditions, particularly regarding the moisture mixed with the air. Pyrometer: An instrument for measuring high temperatures. Radiant Heating: A heating system in which only the heat radiated from panels is effective in providing the heating requirements. The term Radiant Heating is fre quently used to include both Panel and Radiant Herding. Radiation: The transmission of energy by means of electromagnetic waves. Radiation, Thermal (Heat) Radiation: The transmission of energy by means of electromagnetic waves of very long wave length. Radiant energy of any wave length may, when absorbed, become thermal energy and result in an increase in the tempera ture of the absorbing body. Radiation, Equivalent Direct (EDR): A unit of heat delivery of 240 Btu {Steam) or 150 Btu {Water) per hr. It does not imply 144 sq in. of surface. Radiator: A heating unit exposed to view within the room or space to be heated. A radiator transfers heat by radiation to objects within visible range, and by conduc tion to the surrounding air which in turn is circulated by natural convection; a so- called radiator is also a convector, but the term radiator has been established by long usage. Radiator, Concealed: A heating device located within, adjacent to, or exterior to the room being heated, but so covered or enclosed or concealed that the heat transfer surface of the device, which may be either a radiator or a convector, is not visible from the room. Such a device transfers its heat to the room largely by convection air currents. . Radiator, Direct: Same as Radiator. Radiator, Recessed: A heating unit set back into a wall recess, but not enclosed. Radiator, Tube or Tubular: A heating unit used as a radiator in which the heat transfer surfaces are principally tubes.