Document 3Jx3Qo3184gkKy45j1nx6DJ0D

American Society of Heating and Ventilating Engineers Guide, 1936 for partial recirculation is usually made. If a humidifier is included, such a filter-equipped device becomes a winter-type unit conditioner. Unit ventilators are used primarily for offices, schools, and places of public assembly. Up-Feed System {steam): A steam heating system in which the supply mains are below the level of the heating units which they serve. Vacuum Heating System: A' two-pipe steam heating system equip ped with the necessary accessory apparatus which will permit operating the system below atmospheric pressure when desired. Vapor: Any substance in the gaseous state. Vapor Heating System: A steam heating system which operates under pressures at or near atmospheric and which returns the condensa tion to the boiler or receiver by gravity. Vapor systems have thermo static traps or other means of resistance on the return ends of the heating units for preventing steam from entering the return mains; they also have a pressure-equalizing and air-eliminating device at the end of the dry return. Direct Vent Vapor System: A vapor heating system with air valves which do not permit re-entry of air. Vapor Pressure: The equilibrium pressure exerted by a vapor in contact with its liquid. Velocity: The time rate of motion of a body in a fixed direction. In s the fps system it is expressed in units of one foot per second. V = Velocity Pressure: The pressure corresponding to the velocity of flow. It is a measure of the kinetic energy of the fluid. Ventilation: The process of supplying or removing air by natural or mechanical means, to or from any space. Such air may or may not have been conditioned. (See Air Conditioning.) Warm Air Heating System: A warm air heating, plant consists of a heating unit (fuel-burning furnace) enclosed in a casing, from which the heated air is distributed to the various rooms of the building through ducts. If the motive head producing flow depends on the difference in weight between the heated air leaving the casing and the cooler air entering the bottom of the casing, it is termed a gravity system. A booster fan may, however, be used in conjunction with a gravity-designed system. If a fan is used to produce circulation and the system is designed especially for fan circulation, it is termed a fan furnace system or a centralfanfurnace system. A fan furnace system may include air washers and filters. Wet-Bulb Temperature: The lowest temperature which a water wetted body will attain when exposed to an air current. This is the temperature of adiabatic saturation. ' Wet Return: That part of a return main of a steam heating system which is filled with water, of condensation. The wet return usually is below the level of the water line in the boiler, although not necessarily so. See Dry Return. 782 Chapter 44--Terminology ABBREVIATIONS2 Absolute................................................................................................................................. abs Acceleration, due to gravity...................... g Acceleration, linear..... ...................... :.............................................................................. ...... a Air horsepower........................ ........................................................................................ air hp Alternating-current (as adjective)............................................ i_....................................... a-c Ampere.................................................. -............................................................................ amp Ampere-hour.-................................................................................................................ amp-hr Area................................................... -..................................... ............. .............................. --A Atmosphere...... .......................................................... atm Average............................................................................. -........... -................................... -avg Avoirdupois............................................................................ avdp Barometer...................................................................... bar. Boiler pressure....................................................................... -.............................. -............. ibp ' Boiling point..................................................-.......................... -.......................................... bp Brake horsepower................................................................................................ bhp Brake horsepower-hour.......................................... .bhp-hr British thermal unit............................................................................................................. Btu Calorie....................................................................................................................................cal Centigram............................................ eg Centimeter............................................................................................................................. cm Centimeter-gram-second (system)......... ~-- ....................................................................cgs Change in specific volume during vaporization...........................................-.................... rfg Cubic................................................ ............ .......................................-........................ -.......cu Cubic foot............. ...................................................,..........................................................cu ft Cubic feet per minute..........................................................................................................cfm Cubic feet per second.......................................................................... .cfs Decibel........... db Degree2...........................................................................................................................deg or Degree centigrade-...........................................;......................................................................C Degree Fahrenheit--.................................................................................................................F Degree Kelvin-............................................................ J..........................................................K Degree R&aumur......................................................... R Density, Weight per unit volume. Specific weight.!-..........................................d or p (rho) Diameter....................................................................................................................D or diam Direct-current (as adjective)......... .................... d-c Distance, linear--............................ s Dry saturated vapor. Dry saturated gas at saturation pressure and temperature, Vapor in contact with liquid_______________________________ _________Subscript g Entropy (The capital should be used for any weight, and the small letter for unit weight.)-........................................................................ ...................................... .... S or s Feet per minute....................................................................................................................fpm Feet per second......................................................................................................................fps Foot.......... .................................................................................................................................ft Foot-pound............................................................................................................... ft-lb Foot-pound-second (system)............... fps Force, total load............................................................ 1.................. .................................. ... F Freezing point............................................................... :.........................................................fp Gallon......................................... ..gal Gallons per minute. .-........ .......... ........... ....... :................. .............................................gpm Gallons per second.....................................l.................................. ...................................... gps Gram......................................................... :.....:...................... :........ J................................. ...... g Gram-calorie........................................................ !........................................................... -g-cal 5From compilations of abbreviations approved by the American Standards Association, X, 10 a, c, f, and i. As a general rule the period is omitted in all abbreviations except where the omission results in the formation of an English word. It is recommended that the abbreviation for the temperature scale.F, C, K, be included.in expressions for numerical temperatures but, wherever feasible, the abbreviation for degree be omitted; as 68 F. 783