Document 3JEdONGygZMgYXXObzB8mRjEJ

American Society of Heating and Ventilating Engineers Guide 1935 atmosphere, provided all units, drip points, and radiation are pra trapped to prevent steam entering the returns. - On vacuum or open vented systems the return from each unit shouij fitted with a large capacity trap to discharge the water of condense and with a thermostatic air valve for eliminating the air, or with>a hea duty trap for handling both the condensation and the air, provided* air finally can be eliminated at some other point in the return system] For high pressure systems the same kind of traps may be used as vacuum systems, except that they must be constructed for.the pr used. If the air is to be eliminated a!t the return header of the uni high pressure air valve can be used; otherwise the air may be passed the condensate through the -high-pressure return trap, with some d of return pipe corrosion and the problem of its elimination'at someo point in the system. The connections for steam and return piping to unit heaters ,, always be calculated on the basis of the high heat emission or condensa rate of such devicesf^-sThe pipe-size tables given in Chapter 32 mayi used for unit heater work by multiplying EDR values by 240 to get values. OTHER TYPES OF UNITS .All Electric The foregoing discussion relates generally to units in which steam c water is used as the heating medium. On rare occasions elecL resistances are used as the heating element. These are applied only w1 electric power is abundant and cheap and where other forms of fuel scarce and expensive. (See Chapter 39.) Direct 'Fired A recent development in gas burning, equipment is the direct- industrial unit heater. These heaters are of the warm air type and, equipped with fans which cause the air to pass over the heating surf at a fairly high velocity and then direct the warm air in to the space to, heated. As is the case with the steam fed .unit heaters, the gas ' appliances may be used for. heating, stores, shops, and warehouses, usually are suspended in the space to be heated and in most ins leave the entire floor and wall area free for commercial use. Partial complete automatic control also may be secured on appliances of this t]_ This type of heater is often used for temporary heat during buil" construction or where the installation of a steam or hot water plant i some reason not justified. Turbine Driven Where high pressure steam is available it is sometimes used to dn steam turbine direct-connected to the unit heater. The exhaust J this turbine, reduced in pressure, is then passed into the heating where it is condensed and returned to the boiler. INDUSTRIAL USES In addition to their prime function of heating buildings, unit I may be adapted to a number of industrial processes, such as 226 ^^jTER 13--Unit Heaters, Ventilators, and Coolers _r_,. wjth which the use of heated air in rapid circulation with ElP^dfetribution is of particular advantage. They may be used for KguggP? absorption, such as fog removal in dye-houses, or for the preBnpjQr6 , ^densation on ceilings or other cold surfaces of buildings in SStHsIbrocess moisture is given off. When such conditions are severe, it ESaSE^p. that the heaters draw air from outside in enough volume'to - rapid air change and that they operate in conjunction with iSKUnrs or fans for exhausting the moisture-laden air. (See discussion ImSation in Chapter 7.) . TjJJormation on the control of unit heaters will be found in Chapter 14. /____ UNIT VENTILATORS2 rmnlt ventilator must be pleasing in design because it is generally Pjfewghere it must harmonize with the furniture or with the decorative Baggie. It consists usually of a rectangular steel cabinet finished with, an IgBBlJed surface and containing the following necessary or optional fflgftitside air inlet'. EBniet damper for closing the opening to the outside air inlet .when the unit is not JncL; ... gMftdhesive or dry type filters for cleaning the air (optional). . fflTOheating element usually of special design and intended for low pressure steam. HWMptor and fan assembly. ;,0- ICTMbdng chamber where warm and cold air streams are brought together. - (No njmfTchatnber is normally provided .where sectional type convectors are used.) l7jtwtdo6r air inlet and recirculating air mixing.damper (optional). fgSDevice for ozonizing air (optional). IMDischarge grille or diffuser. HOUTemperature control arrangement. jFKKprimary functions.of a unit ventilator are: Jj^fisupply a given quantity of outdoor air for ventilation or to mix indoor and ^gjfigair. gjfiprarm the air to approximately the room temperature if the unit is intended for Sstjjatfon only, or to a higher temperature if it is intended to take care of all or a part MSRraeat.transmission losses from the room. JjKlgcontrol the temperature of the air delivered so as to prevent both cold drafts ItadByenjeating. . Pgg" a'r to the. room in such a .manner that .proper distribution is obtained IMffgfeecircuIate room air for the purpose of heating or promoting comfort when gjuaticra 19 unnecessary. B9^perform all its functions without objectionable noise. JBjpMtion to these functions, unit ventilators frequently are arranged jjjgajlthe air supplied may be cleaned by means of filters of either the l^^viscous type. If filters are used, the proper allowance must be EmSm. lncreased resistance offered to the air flow. Humidifiers in TM!&fler0rS arC rat^er d'cu^ to. control and are only furnished upon Sj. - Jpoiilator is sometimes termed a unit ventilator. For information on roof ventilators, see 227