Document J3MoxGL1dvYqOvB0M2wmgbqO2

508 __________________ . ... ........ . CHAPTER 26 ^V . 1943 Guide wall or partially recessed into' the wall to save; space without materially affecting.the results.. The air. inlet.may ,en.tei;.the .cabinet at .the.back at any point from top to bottom. ....... ; .. : : . ; : . .. . Air Exhaust Vents and Flues The size and location of the-air exhaust vent outlet is important. In many cases the sizes for public buildings are regulated by law. In cases where no codes govern, the location and size of vents are left to the discretion of the engineer., ;. Best - results have been obtained with a velocity through the vent openings nearly equal to that at which the air is introduced into the room, thus maintaining a slight pressure in the room. Calculate*! velocities at the vent openings of from 600 to .800 fpm produce the best diffusion results from this system. Many states, however, have, regulations that will not permit velocities as high as 800 fpm. If a vent opening at or near the floor is near a desk or place where a person is seated, a velocity of 800 fpm in the vent opening will produce ah objectionabledraft. In such a case the velocity in the vent opening should not exceed 400 . to 450 fpm, although duct velocities are maintained at 600 to 800 fpm if . codes permit. , In school buildings provided with wardrobes or cloakrooms the vents may be so located that the air shall pass through these spaces, ventilating them with air which otherwise would be passed to the outside-without being used to the best advantage. Many state codes for ventilation of public buildings.make thisarrangement mandatory. : WINDOW VENTILATORS A window, ventilator illustrated in Fig. TO consists of filter and switch controlled motor driven fans enclosed in'a cabinet to be mounted .on; the windowsill.. Such units accomplish ventilation, air cleaning,-and air cir culation, but have no'means -of heating the air. The- direction 'of air discharge is manually-adjustable 'for seasonal operation. V -- - - UNIT HUMIDIFIERS '... Unit humidifiers fall into four general classifications,- depending on the method of causing .evaporation.. Theseare as.follows:- {\)Nozzle Type, (2) Rotary TypeCascade Type, and (4) Healer-Typo. Unit Heaters, Unit Ventilators, Unit'Humidifiers 509 . In the- nozzle type of ;humidifier water is sprayed into the air and evaporation: is effected by adiabatic exchange of energy. - Units of this type in simplest form, spray a -fine mist of-.water directly into theair in a space. They are used to a great extent in.the textile industry. . * . .. To ;.the: simple: type of;Jiozzle unit-, ipay; be added the. following acces sories: a water heater whose function is to increase the vapor pressure, an air heater to heat the air either, before oi^-after humidification takes place, a screen or air filter over which the Water is sprayed and through which the'air is drawn for intimate contact'with--the water, a-fan to create an air stream: and to deliver air to the space to be humidified, and a housing to enclose all the elements'. . Thistype-pfunit has been made in practically all of the variations mentioned. It has the disadvantage of clogging the nozzles and must be serviced.continually.: Fig. 11 illustrates a nozzle unit having a humidifying capacity sufficient for a residence or small building. ' These units, usually include air filters and in some cases provide ventilation air by means of an outside air duct connection to the unit. The units are constructed for either floor or ceiling mounting and are usually placed in a central location in the basement with short supply and return duct connections from the first floor. Room air is brought into the-iiiiit through the return duct connection, is passed over a tempering coil heated by.steam or hot water, and is then humidified by passing through some, type of spray humidifier. Surplus moisture is removed by an eliminator and the humidified air is delivered to the room through a duct connection. Since a large percentage of the tempering coil capacity is transformed into latent heat during the humidifying pro cess, the unit does not generally eliminate any existing steam radiation but does tend to improve comfort conditions by supplying heat during the off-period of furnace operation7. In the rotary type of humidifier the spray is created by rotating vanes . or discs which throw the water by centrifugal force and in so doing break it up into a fine mist. In all other respects, this type of humidifier is similar to the nozzle type. It has the advantage over the nozzle type of being less liable to become clogged. In the cascade type the humidification takes place by water falling in sheets over a series of baffles or trays. This type is usually furnished with a fan, air heater, and air filter all enclosed in a housing. In the heater type of humidifier the water is heated either to the boiling point or to a temperature at which the water vapor readily passes into the. air stream. There are many variations of this type of humidifier. In the simplest form the heating element using steam, hot water, gas, oil, or electricity is placed in a pan or vessel of water and the vapor passes from,the surface of the water to the stream of air. Fig. 10. Typical Window Ventilator Fig. -11. Typical Unit Humidifier of the Spray Type with Steam Coil to Preheat the Air for Residences