Document d01oKYdOw2ge7RVVBLQB26y9

616 CHAPTER 26 1956 Guide units are not generally equipped with controls. Control systems for remote units, and auxiliary controls for self-contained .units, are covered in the general treatment of Controls in Chapter 39. RATINGS OF UNIT AIR CONDITIONERS Two standards have been used for rating and testing of unit air con ditioners: (1) Standard Method of Rating and Testing Air Conditioning Equipment,1 covering all types of air conditioning units except the selfcontained type and (2) Standard Method of Rating and Testing SelfContained Air Conditioning Units for Comfort Cooling5 covering the selfcontained type. (ASRE Standard Methods of Rating and Testing Air Conditioners, ASRE Standard 16-53, covers rating and testing of all types which operate non-frosting when cooling and dehumidifying at standard rating conditions.) The standard rating of a self-contained unit for the conditions specified in Table 1, includes all items which apply to -the function of a unit as: (1) name of unit, (2) functions which unit performs, (3) data on cooling, (4) data on heating, (5) data on air flow, and (6) data on humidification. The standard rating conditions for unit air conditioners, other than the self-contained type, are identical with those in Table 1, except that entering wet-bulb temperature for cooling is expressed as 50 percent relative humidity (66.7 F wet-bulb) instead of 67 F wet-bulb temperature. In addition, the saturated suction refrigerant temperature for comfort cooling is specified at 40 F. This condition is omitted from Table 1 for self-contained units because it is not separately controlable in the testing of a unit that includes the evaporator and condensing unit. APPLICATION OF UNITARY EQUIPMENT One of the chief advantages resulting from use of factory produced units is the saving in installation and field assembly labor, a factor that should always be kept in mind when selecting a location for these units. Because of their compactness, the tendency exists to put them in closets, storage rooms, and other inaccessible places, where installation is so difficult that much of this cost advantage is lost. Access panels are provided on units for the proper servicing and main tenance of the equipment. Adequate outside clearance at these panels is essential. Wherever there is danger of freezing of coils or clogging with dirt, sufficient clearance should be available for replacing them without removing parts of the building. The outstanding source of difficulties in unitary systems is usually dirty filters. The characteristics of the light weight fans used are such that air volume drops off rapidly with increase in static resistance. Since changing of filters is an unpleasant duty likely to be neglected unless it can be done easily, the operator should be at the same level as the filters, rather than under them, when they are being removed. Variable-pitch motor pulleys are usually provided for adjustment of the air quantity. The fans and motors of most conditioners are selected for the usual range of external resistances commonly used with the specific size of conditioner. The larger conditioners are capable of serving larger areas and therefore require fan and motor capacity for the greater external duct resistances that may be imposed on such conditioners. Where varying sizes of coils are used within the same casing, it is very important that coil safing be carefully installed to prevent bypassing of unconditioned air. If coils are not equipped with individual casings, Unit Air Conditioners and Unit Air Coolers 617 Table 1. Standabd Ratino Basis fon Self-Contained Aib Conditioning Units Functions All Types op Units Item Rating Condition Description All a Barometric Pressure Value 29.92 in. Hg. > Cooling Water-Cooled, Air - Coolec and Evaporatively Cooled Con densers b c Unit Ambient and Air Entering Room--Air Inlet (1) Dry-Bulb (2) Wet-Bulb Ventilation Air Water-Cooled d Water Temperature Entering Condensers Unit e Water Temperature Leaving Unit Air - Cooled _ andEvapor- atively Cooled Con densers f Air Entering Outside Air Inlet (1) Dry-Bulb (2) Wet-Bulb 80 F 67 F See Note 75 F 95 F 95 F 75 F Heating Humidifying Air Circula tion g All Types Pro- vided with h Heating Function Unit Ambient and Total Air . Entering Unit Heating Medium, Pressure or Temperature (1) Dry Saturated Steam (2) Water In (3) Water Out A11 Types i Unit Ambient Provided with Hu j Total Air Entering Unit midifying (1) Dry-Bulb Function (2) Wet-Bulb AH k Filters 70 F 16.7 lb per sq in. abs 180 F 160 F 70 F 70 F 53 F New and Clean not pertinent to this chapter). 3 remove material additional safing may be required on top to prevent short circuiting air down through the upper edges of the fins. In this same category is the need for careful installation of the various sections of sectionalized units, using a sealing compound if necessary to prevent air leakage into the fan section of the unit. Since the drain connection is usually made on the exit side of the coil, it is important that the drain line be properly sealed. This seal should he at least twice as deep as the suction on the fan in inches of water, to prevent gurgling sounds, and to insure a positive seal against infiltration of odors and moisture laden air. Drain pans should not be used to sup port the coils, unless they are designed to hold this weight without sagging. As the movement of air draws the condensate or excess humidification water toward the fan, drain connections are usually placed on the exit