Document ZR5r0N1Q9RxgVRrNxYGgdYNL

,646 CHAPTER 36 1948 Guide Controls for Room Cooling Units Control devices for self-contained cooling units are generally provided to include all necessary means for automatic'operation. Provision is also made for adding auxiliary external controls when desired. Remote 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 34. RATINGS OF UNIT AIR CONDITIONERS There are two codes governing the rating and testing of unit air con ditioners. The first code, Standard Method of Rating and Testing Air Conditioning Equipment *, covers all types of air conditioning units except the self-contained type. The latter is covered by the second code, The Standard Method of Rating and Testing Self-Contained Air Conditioning Units for Comfort CoolingJ. The two codes are necessary because of the basic difference caused by the heat given up by the self-contained units. The standard rating conditions for self-contained unit air conditioners, as given in the code, are set forth in Table 1. 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 to those in Table 1 except the entering wet-bulb temperature for cooling is expressed as 50 per cent 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 as immaterial in the rating 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 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. Fan speeds should be selected accurately . .for the system resistance. Unit Air Conditioners, Unit Air Cooler's 647 Table 1. Standard Rating Basis for Self-Contained Air Conditioning Units Functions Types op Units Item Rating Condition Description Value All Cooling All a Barometric Pressure 29.92 in. Hg. b Unit Ambient and Air Entering Water-Cooled, Air-Cooled and Evapora- Room--Air Inlet (1) Dry-Bulb (2) Wet-Bulb 80 F 67 F tively- Cooled Condensers c Ventilation Air See Note Water-Cooled d Water Temperature Entering Unit Condensers e Water Temperature Leaving Unit 75 F 95 F Air-Cooled f Air Entering Outside Air Inlet and Evapora- (1) Dry-Bulb tively- Cooled (2) Wet-Bulb Condensers 95 F 75 F Heating g Unit Ambient and Total Air Enter ing Unit 70 F All Types Provided h Heating Medium, Pressure or with Heating Function Temperature (1) Dry Saturated Steam 16.7 lb per sq in. abs (2) Water In (3) Water Out 180 F 160 F All Types i Unit Ambient Provided with Humidifying Humidifying i Total Air Entering Unit Function (1) Dry-Bulb (2) Wet-Bulb 70 F 70 F 53 F Air Circulation All k Filters New and. Clean Note: Rating .ball be based on both ventilation and recirculated room air entering at80 F dry-bulb and 67 F wet-bulb temperature. (The Note as given in the code has been condensed m order to remove material not pertinent to this chapter). Variable pitch motor pulleys are often used for field adjustments which should be made when filters are slightly dirty to obtain average conditions. Because varying sizes of coils are used within the same casing, it is very important that coil safing be carefully installed to prevent by-passing of unconditioned air. If coils are not equipped with individual casings, 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 be 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 arid moisture laden air. Drain pans should not be used to sup port the coils unless they are designed to hold this weight without sagging.