Document ZBmLgm0o64kpg8xro9r8grvKp

610 CHAPTER 26 1955 Guide condensate from the cooling coil is sprayed over the condenser surface and vaporized, thus eliminating the need for drain connections. A simple dampering arrangement is generally provided for exhausting some air from the room, in addition to introducing outside air and recirculating required amounts of air. It is possible to remove the equipment for winter storage or utilize the ventilating features for winter operation. Controls for Room Cooling Units Control devices provided for self-contained cooling units generally will 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 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 Cooling* covering the selfcontained type. (ASRE Standard Methods of Rating and Testing Air Conditioners, ASRE Standard 16-R, 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 immaterial in the rating of a unit that in cludes 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 Unit Air Conditioners and Unit Air Coolers 611 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. Fan speeds should be selected accurately for the system resistance. Variable pitch motor pulleys are often provided in a unit for minor field Table 1. Standard Ratinq Basis fob Self-Contained Air Conditioning Units Functions All Tyres of Units Item Rating Condition Description All a Barometric Pressure Value 29.92 in. Hg. Cooling Heating Humidifying Air Circula tion Water-Cooled, Air' - Cooled and Evaporatively Cooled Con densers b c Unit Ambient and Air Entering Room--Air Inlet (1) Dry-Bulb (2) Wet-Bulb Ventilation Air 80 F 67 F See Note Water-Cooled d Water Temperature Entering Condensers Unit 75 F e Water Temperature Leaving Unit 95 F Air - Cooled f and EvaporCooled Con densers Air Entering Outside Air Inlet (1) Dry-Bulb (2) Wet-Bulb 95 F 75 F 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 70 F 16.7 lb per sq in. abs 180 F 160 F All Types Provided with Hu midifying Function i Unit Ambient j Total Air Entering Unit (1) Dry-Bulb (2) Wet-Bulb 70 F 70 F 53 F All k Filters New and Clean 67 Rating shall be based on both ventilation and recirculated room air entering at 80 F dry-bulb and j; wet-bulb temperature. (The Note as given in the code has been condensed in order to remove material t pertinent to this chapter). adj ustment of air volume. Any such field adjustment should be made when filters are dirty, to simulate average operating conditions. Because varying sizes of coils are used within the same casing, it is yery important that coil safing be carefully installed to prevent by-passing f 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 TMe need for careful installation of the various sections of sectionahzed