Document QMvM5vkgqX3LQJoLb59mEZjOL

- 414 Chapter 22 194S Guide the other hand, remote type room unite contain less mechanical ma chinery, avoid the operating cost penalty of an air-cooled condenser, as in the case of the self-contained, air-cooled room units, and seldom require heavy wiring to handle the fan load. In general, the smaller remote unite are more suitable for use with new construction;- where the unite will probably remain during, their useful life. This condition may change where larger, ceiling mounted units are compared with the floor mounted self-contained unite. Controls are essential in unit application and range from the simple snap switch of a room unit to elaborate means of control ling temperature, humidity and air movement in laboratory and testing room application. The criterion of a well controlled installation is. one which has neither too few nor too many controls. (See Chapter 33). With the expansion of cities during the past decade, the problem of water supply has become a costly and ever present problem5. Con sequently, laws are appearing designed to restrict the usage of water wherever possible, particularly when substitute means are available. Evaporative condensers and cooling towers (described in Chapters 24 and 26) are means devised to save large quantities of water in this connection. Most manufacturers furnish equipment designed for use in combination with these water savers. Municipal plumbing, heating, electrical and refrigeration codes,.as well as fire underwriter restrictions, are likewise having their effects on the application of unit air conditioners. Meeting municipal and national code requirements should be an important item in connection with the installation of any unit equipment. Ratings 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 Equipment8, covers'all types of air conditioning unite except - the self-contained type. The , latter is covered by the-second code, The Standard Method of Rating and Testing Self-Contained Air Conditioning Unite for Comfort Cooling7. The two codes are necessary because of the basic difference caused by the heat given up by the self-contained unite. 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 include 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. Concerning Conservation of Underground Water with Suggestions for Control, by Noel E. Porter (A.S.H.V.E. Transactions.. Vol. 47, 1941, p. 309). . `Loc. Cit. Note l TLoc. Cit, Note 2. * Unit Air Conditioners, Unit Air Coolers9 Attic Fans 41S Table 1. Standard Rating Basis for Self-Contained Air. Conditioning Units Functions Item Rating Condition Description Value All All a Barometric Pressure 29.92 in. Hg. ,b Water-Cooled, Air-Cooled and Evaporatively. Cooled Condensers c Unit Ambient and Air Entering* Room--Air Inlet (1) Dry-Bulb (2) Wet-Bulb 80 F 67 F Ventilation Air See Note Cooling Water-Cooled d Condensers e i_________ _____ J^ir- Cooled . f and Evaporatively Cooled Condensers , Water Temperature Entering Unit 75 F Water Temperature Leaving Unit 95 F Air Entering Outside Air Inlet (1) Dry-Bulb (2) Wet-Bulb 95 F ' 75 F Heating All Types. Provided with Heating Function g h Unit Ambient and Total Air Enter ing Unit 70 F Heating Medium, Pressure or Temperature (1) Dry Saturated Steam (2) Water In (3) Water Out 16.7 lb per sq in. abs. 180 F 160 F All Types i Unit Ambient Provided with Humidifying Humidifying j Total- Air Entering Unit Function (1) Dry-Bulb (2) Wet-Bulb Air Circulation All k Filters 70 F 70 F 53 F New and Clean Note: Rating shall be based on both ventilation and recirculated room air entering at 80 F dry-bulb and 67 F wet-bulb temperature. (The Note as given in the code has been condensed in order to remove material not pepinent to this chapter). UNIT AIR COOLERS This type of unit is primarily intended to perform the main function of cooling air, with humidity control a secondary function within the limita tions of the design. The main application of this equipment is in process and product refrigeration such as cold storage warehousing, fruit and vegetable packing, in breweries, and in wholesale and retail food markets; although some comfort cooling may be obtained by the use of a -unit similar in design to this type of unit as previously explained and as illustrated by Fig. 6. Application of the unit method of air cooling with mechanical circu lation is comparatively recent, being an improvement over the pipe or finned coil, which depended on gravity for circulation. Bunkers were sometimes constructed around the coils to direct the air flow and some times fans were used for forcing air over the coils. The location of the unit air cooler is usually within the refrigerated area, but the larger, blower type models may be remotely, located.