Document 0qwEvrNE9q1mzD8b78bjyDqMV

American Society of Heating and Ventilating Engineers Guide, 1937 Smokeless Arch: An inverted baffle placed in an up-draft furnac toward the rear to aid in mixing the gases of combustion and thereby / reduce the smoke produced. y0 Specific Gravity: The ratio of the weight of a body to the weight of an equal volume of water at some standard temperature, usually 39.2 p Specific Heat: The quantity of heat, expressed in Btu, required to raise the temperature of 1 lb of a substance 1 F. Specific Volume: The volume, expressed in cubic feet, of one pound nf , IV a substance, v -- --7- = aW Split System: A system in which the heating and ventilating are accomplished by means of radiators or convectors supplemented by mechanical circulation of air (heated or unheated) from a central point Square Foot of Heating Surface (equivalent): Equivalent direct radiation (EDR). By definition, that amount of heating surface which will give off 240 Btu per hour. The equivalent square feet of heating surface may have no direct relation to the actual surface area. Stack Height: The height of a gravity convector between the bottom of the heating unit and the top of the outlet opening. Standard Air: As defined by A.S.H.V.E. codes, standard air is air weighing 0.07488 lb per cubic foot, which is air at 68 F dry-bulb and 50 per cent relative humidity with a barometric pressure of 29.92 in. of mercury. (Most engineering tables and formulae involving the weight of air are based on air weighing 0.07492 lb per cubic foot, which is dry air at 70 F dry-bulb with a barometric pressure of 29.921 in. of mercury. The error involved in disregarding the difference between the above two weights is very slight and in most instances may be neglected.) 1 Static Pressure: The compressive pressure existing in a fluid. It is a measure of the potential energy of the fluid. Steam: Steam is water vapor which exists in the vaporous condition because sufficient heat has been added to the water to supply the latent heat of evaporation and change the liquid into vapor. Steam in contact with the water from which it has been generated may be dry saturated steam or wet saturated steam. The latter contains more or less actual water in the form of mist. If steam is heated, and the pressure main tained the same as when it was vaporized, its temperature will increase and it will become superheated. Steam Heating System: A heating system in which heat is trans ferred from the boiler or other source of steam to the heating units by means of steam at, above, or below atmospheric pressure. Steam Trap: A device for allowing the passage of condensate and preventing the passage of steam, or for allowing the passage of air as well as condensate. Superheated Steam: See Steam. Supply Mains {steam): The pipes through which the steam flows from the boiler or source of supply to the run-outs and risers leading to the heating units. . 796 Chapter 44--Terminology Surface Conductance: The amount of heat (Btu) transmitted by diation, conduction, and convection from a surface to the air or liquid rarrounding it, or vice versa, in one hour per square foot of the surface for ^difference in temperature of 1 deg between the surface and the sur rounding air or liquid. Synthetic Air Chart: A chart for evaluating the air conditions maintained in a room. Therm: Symbol used in the gas industry representing 100,000 Btu. Thermal Resistance: The reciprocal of conductance. Thermal Resistivity: The reciprocal of conductivity. Thermodynamics: The science which treats of the mechanical actions or relations of heat. Thermostat: An instrument which responds to changes in tempera ture and which directly or indirectly controls the source of heat supply. Ton of Refrigeration: The extraction of 12,000 Btu per hour. Ton Day of Refrigeration: The heat removed by a ton of refriger ation operating for one day; 288,000 Btu. Total Heat: A thermodynamic quantity, variously called heat con tent, thermal potential, enthalpy. It is the heat required per unit mass (Btu per pound) to raise a given substance to a given point from an arbi trary datum point. It is the sum of the heat of the liquid, the latent heat, and any miscellaneous heat which may be present. Total Pressure: The sum of the static and velocity pressures in a fluid. It is a measure of the total energy of the fluid. Tube (or Tubular) Radiator: A cast-iron heating unit used as a radiator and having small v ertical tubes. Two-Pipe System {steam or water): A heating system in which one pipe is used for the supply of the heating medium to the heating unit and another for the return of the heating medium to the source of heat supply. The essential feature of a two-pipe system is that each heating unit receives a direct supply of the heating medium which medium cannot have served a preceding heating unit. Underfeed Distribution System {hot water): A hot water heating system in which the main flow pipe is below the heating units. Underfeed Stoker: A stoker which feeds the coal underneath the fuel bed. Unit: As applied to heating, ventilating and air conditioning equip ment this word means a factory-built and assembled equipment with apparatus for accomplishing some specified function or combination of ' functions. It is loosely applied to a great variety of equipment. Usually ..the function is included in the name, and hence come terms like Unit Heater, . Unit Ventilator, Humidifying Unit, and Air Conditioning Unit. Units are said to be direct, or room, when intended for location, or .located in, the treated space; indirect, or remote, when outside or adjacent "`to the treated space. They are ceiling units when suspended from above, 797