Document 5kJjdaXpEpyEdyErQBpEEpyVe

American Society'0/ Heating and Ventilating Engineers Guide, 1937~~~~ borne pollens will have their troubles increased with attic type coolers Some typical data on an attic fan installation in an average six-room house of frame construction containing 14,000 cu ft and located in the southern part of this country are: Installation cost.. Fan .data.:______ Operating period____ Power consumption__ $75 to $400, average $250 9000 cfm average, 280 rpm if belt driven, 570 rpm if direcl connected, 500 watts input April 15 to October 15, intermittently as weather con ditions demand 500 kwh per year for 8 months' operation Humidifiers Humidifying units may be installed as part of an air conditioning unit system, or may be installed individually to furnish additional humidity. Fig. 21 illustrates a humidifying unit for installation in connection with a warm air heating system, and as such it is located at the intake of the furnace. The air passes through a lint filter, then through the fans and finally through an air washer or spray system. Surplus spray is eliminated and the air delivered to the air distribution system. In other cases, similar spray type apparatus is used to deliver humidified air through ducts to openings beneath existing radiators in a steam heated residence. For other steam'heated homes, there is a humidifying unit as illustrated in Fig. 22. This unit is normally placed at some central location on the first floor, and receives the air from the floor into fans, delivering it through a heating coil and up through a target spray atomizer. Surplus moisture is removed by means of an eliminator filter and the humidified INTAKE Fig. 21. Humidifying Unit forWarm Air Furnace 272 Fig. 22. ' Humidifying Unit for Radiator Heated Homes 13--Unit Heaters, Ventilators, Air Conditioning, Cooling Units is delivered upward through the other half of the floor grille. Since a Tree percentage of the heater capacity is transformed inter the latent hat of humidification, this unit does not eliminate any existing steam diation. It may also be used with hot water systems but its capacity ^considerably reduced. AUTOMATIC CONTROLS The controls of all unitary equipment represent a vital part of their successful operation. This is particularly true in the case of conditioning equipment where a close inter-relationship exists between the thermo static room controls and the refrigerating unit controls. The proper selection of controls and the proper-adjustment is extremely important to prevent short cycling of compressors. Furthermore, the proper adjustment of direct expansion valve controls is likewise extremely Important. A detailed discussion of control problems is contained in Chapter 14. . PROBLEMS IN PRACTICE 1 f Distinguish between a unit and a.central-type of air conditioning system. In a unit system, the .air treating apparatus consists of factory assembled equipment which is shipped substantially complete or in sections and is installed without field fabrication except for the duct connections between the equipment and the point of delivery of the air. Usually.the air treating equipment is located closely adjacent to the conditioned space and serves a limited area. A central type of air conditioning system localizes the air treating equipment for the entire area at one point and involves the field assembly of a large number of individual elements. Manufacturer of the unit.is responsible for the output and performance of the unit under-rated conditions, whereas, the contractor installing the completely unitary or central type equipment is held re sponsible for the complete performance of the system. - 2 Is it satisfactory to use superheated steam in unit heaters? Superheated steam can be satisfactorily used in unit heaters provided the capacity is based on the saturated steam temperature and not on the total -temperature. If un usually high superheat is used, trouble may be experienced from the excessive expansion and contraction of the heating elements. 3 # Is it satisfactory to install one unit heater as the total load on a coal fired boiler? . Such an arrangement is impractical if the unit heater is started and stopped in keeping with the room temperature. However, if the room temperature controls the steam pres sure and the unit heater is arranged to start when there is steam in the mains and to stop when there is no steam in the mains, such an installation will be satisfactory. 4 Will a unit heater with a slow speed fan .be more quiet than one with a high speed fan? Quietness is a function of the type, diameter, blade form, and location of the fan, as well as the speed. For a given fan, slower speeds mean less noise. 5 Is it satisfactory to use steam at pressures less than atmospheric for unit heaters or unit ventilators? the air inlet temperature is above freezing, steam at any pressure may be used.in the . heating element of the unit heater or unit ventilator. If'the inlet temperature is below freezing the heating element should be filled with steam of at least 5 lb pressure (or with 273