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558 CHAPTER 24 1951 Guide from (his system. Many, states, however, have regulations that will not permit velocities as high as 800 fpm. If a vent opening at or near the floor is near a desk or place where a person is seated, a velocity of 800 fpm in the vent opening will produce an objectionable draft. In such a case the velocity in the vent opening should not exceed 400 to 450 fpm, although `duct velocities are maintained at 600 to 800 fpm if codes permit. In school buildings provided with wardrobes or cloakrooms, the vents may be so located that the air shall pass through these spaces, ventilating them with air which otherwise would be passed to the outside without being used to the best advantage. Many state, codes for ventilation of public buildings make this arrangement mandatory. Fio. 10. Ttpioal Window Ventilator WINDOW VENTILATORS A window ventilator illustrated in' Fig. 10 consists of filter and switch controlled motor driven fans enclosed in a cabinet to be mounted on the window sill. Such units accomplish ventilation, air Cleaning, and air cir culation, but have no means of heating the air. The direction of air dis charge is manually adjustable for seasonal operation. REFERENCES 1 See National Fan Manufacturers Association standard definitions in Chapter 32. Standard Code for Testing and Rating Steam Unit Heaters (A.S.H.V.E. Trans actions, Vol. 36, 1930, p. 165), prepared by a Joint Code Committee of the American Society or Heating and Ventilating Engineers and the Industrial Unit Heater Association and adopted 1930. Code revised 1950. Standard Code for Testing Hot Water Unit Heaters prepared by Engineering Committee of Industrial Unit Heater Association. Adopted by Industrial Unit Heater Association August 1942 and published September 1942. 4 A.S.H.V.E. Reseabch Report No. 958--Temperature Gradient Observations in a Large Heated Space, by G. L. Larson, D. W. Nelson and O. C. Cromer (A.S.H.V.E. Transactions, Vol. 39, 1933, p. 243). A.S.H.V.E. Reseabch Repobt No. 1011-- Tests of Three Heating Systems in an Industrial Type of Building, by G; L. Larson, D. W. Nelson and John James (A.S.H.V.E. Tbansactions, Vol. 41,1935, p: 185). . * A.S.H.V.E. Standard Code for Testing and Rating Steam Unit Ventilators (A.S.H.V.E. Tbansactions, Vol. 38, 1932, p. 25). A.S.H.V.E. Research Report No. 936--Investigation of Air Outlets in Class Room Ventilation, by G. L. Larson, D. W. Nelson and R. W. Eubasta (A.S.H.V.E. Tbansactions, Vol. 38,1932, p. 463). A.S.H.V.E.- Research Report No. 1017--Air Supply to Classrooms in Relation to Vent Flue Openings, by F. C. Houghten, Carl Gutberlet andM. F. Lichtenfels (A.S.H.V.E. Transactions, Voi. 41,1935, p. 279). CHAPTER 25 UNIT AIR CONDITIONERS AND UNIT AIR COOLERS Definitions, Classification of Unit Type Equipment, Component Parts of Unit Typo Equipment, Sound Isolation, Modifications of Remote Units, Ratings of Unit Air Conditioners, Application of Unitary Equipment, Unit Air Coolers THIS chapter presents the physical characteristics of air-cooling units and air conditioning units; a suggested procedure for selection of units; and some of the factors involved in the application of unitary equipment. In general, factory produced unit equipment can be obtained to accomplish all of the functions possible from field assemblies, but the advantages of unit equipment are most apparent in small and moderate capacities. Above 12,000 cfm capacity, or approximately 40 tons of refrigeration capacity, handling and assembly costs generally favor the use of field assembled units. Multiple application of unitary equipment is frequently justified for large gross tonnage installations where zoning or a minimum amount of air distributing ducts is desirable. DEFINITIONS The term air conditioning unit has been loosely used as a name for all types of factory produced air handling, cooling, or heating units. The code, Standard Method of Rating and Testing Air Conditioning Equip ment,1 defines the various types of unitary equipment: 1. A Cooling Unit is a specific air treating combination consisting of means for air circulation and cooling within prescribed temperature limits. 2. An Air Conditioning Unit is a specific air treating combination consisting of means for ventilation, air circulation, air cleaning, and heat transfer, with control means for maintaining temperature and humidity within prescribed limits. 3. A Cooling Air Conditioning Unit is a specific air treating combination consist ing of means for ventilation, air circulation, air cleaning, and heat transfer, with control means for cooling and maintaining temperature and humidity within pre scribed limits. 4. A Self-Contained Air Conditioning or Cooling Unit is one in which a condensing unit is combined in the same cabinet with the other functional elements. Self- contained air conditioning units are classified* according to the method of rejecting condenser heat (water cooled, air cooled, and evaporatively cooled), method of introducing ventilation air (no ventilation, ventilation by drawing air from outside, ventilation by exhausting room air to the outside, or ventilation by a combination of the last two methods), and method of discharging air to the room (free delivery or pressure type). 5. A Free Delivery Type Unit takes in air and discharges it directly to the space to be treated without external elements which impose air resistance. 6. A Pressure Type Unit is for use with one or more external elements which impose air resistance. 7. A Forced-Circulation Air Cooler is a factory encased assembly of elements by which heat is transferred from air to refrigerants.* CLASSIFICATION OF UNIT TYPE EQUIPMENT Field assembled apparatus as described in Chapter 29 can be designed in shape, size, and capacity for any application, with the refrigeration and 559