Document 3Nbr78Be4nGNwXL5VrbqYgaV6

Heating Ventilating Air Conditioning Guide 1939 One-Pipe System {steam): A steam heating system consisting of a main circuit in which the steam and condensate-flow in the same pipe, 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 thait.the heating process takes 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. - Potentiometer: An instrument for measuring or comparing small electromotive forces. . - 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. : . Prime Surface: See Heating Surface. 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. Psychror metry: 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 exposed to view within the room or space to be heated. A radiator 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. . Recessed Radiator: A heating unit set; back into a walk recess but not enclosed. Refrigerant: A substance which.produces a refrigerating effect by.its absorption of heat while expanding or vaporizing. , Relative Humidity: See,1 Humidity: see also discussion of'relative humidity in Chapter 1. Return Mains:. The pipes which return the heating medium from the heating units to the source of heat supply. Reversed-Return. System (hot water): A,hot water heating system in which the water from several hea.ting units is returned along paths arranged so that all circuits composing the system or composing a major sub-division of the system are practically of equal length. 842 Chapter 45. Terminology Roof Ventilator: A device placed on the roof of a building to facilitate egress of air. Saturated Air: Air containing as much water vapor as it can hold without any condensing out; in saturated air, the partial pressure of the water vapor is equal to the vapor pressure of water at the existing tem perature. Sensible Heat: See Heal. Smoke: Carbon or soot particles less than 0.1 micron in size which result from the incomplete combustion of carbonaceous materials such as coal, oil, tar, and tobacco. Smokeless Arch: An inverted baffle placed in an up-draft furnace toward the rear to aid in mixing the gases of combustion and thereby to reduce the smoke produced. 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 F. 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 of a substance, v = -- - d- w 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 above1 two weights is very slight and in most instances may be neglected);. . Static Pressure: The compressive pressure existing in a fluid. It is a measure of-the potential energy of the fluid. . Steain: Steam-is water vapor tvhich 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 yapor.^.:Steam in: contact with the waiter vffom : which it has ibe'en 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- taiped.-the same- as- when, it was vaporized, its-temperature will.inorease and it wi.lftbecoine superheated. v, V.' ^ Steam,Heating System: A. heating system:';in: whichj.heat is -trjans; 843