Document OzX2KK2JeMNzgY20BdJva7Drp

HEATING VENTILATINC AIR CONDITIONING GUIDE 1944 8. Determine pressure loss in duct system and select fail as also explained' in. the same> section. 9. Select cooling unit from manufacturer's data. Specify temperature and pressure of available cooling water, voltage and characteristics of electrical supply, and method of control of apparatus. 10. Select cooling coils from manufacturer's data to take care of latent heat load and togive required drop in air temperature with the weight ofair flowing. (See Chapter 26.) 11. If system is to be used for both winter heating and summer cooling, duct sizes must be checked to insure that velocities and friction losses are reasonable for both conditions of operation. Adjustable dampers will be necessary to make changes in air distribution for the two seasons. Provision must also be made for changing fan speeds for summer and winter operation. CHAPTER 21 (CentralSystems jor (Comfort sdir C^onditionin^ Types of Systems for Ventilating, Heating, Air Conditioning, Factors Involved in Use and Design of Systems, Design Procedure THE purpose of this chapter is to present a discussion of types of central systems usually encountered, together with a discussion of the factors involved in use and design and an outline of design procedure. Insofar as this chapter is concerned, a central system is defined as a field assembled apparatus, comprising such elements of equipment as are necessary to fulfill the purpose for which it is designed, and serving one or more conditioned spaces. It may be argued with justification that a factory produced unit, including all the essential items of equipment can be employed as a central system. Unitary equipment is discussed in Chapter 23. Further, this chapter is confined to comfort air conditioning . systems as such, and ventilating systems, warm air heating systems, together with central systems of a special nature, are excluded from the discussion. This chapter assumes a knowledge of all the component parts of a system and the reader is referred specifically to other chapters covering design conditions and physiological principles, cooling and heating load; spray equipment, heat transfer surface coils, cooling dehumidification and dehydration, fans, air cleaning devices, refrigeration, air distribution and. air duct design, automatic controls and instruments. In addition,' the engineer should refer to the Code of Minimum Requirements for Comfort Air Conditioning1 prepared by the joint committee of the American ! Society of Heating and Ventilating Engineers and the American Society of Refrigerating Engineers, and to national, state or local codes I that may apply. i i CLASSIFICATION OF SYSTEMS The generally accepted method of classifying systems is with regard to their function. A given type of system may be changed by the omission of certain of its functions or by the inclusion of others. As an example, a winter air conditioning system, by the omission of humidifying sprays, air cleaning devices, etc., will become a simple warm air heating system. 382 *Code of Minimum Requirements for Comfort Air Conditioning (A.S.H.V.E. Transactions, Vol. 44, I 1938. p. 27). Reprints of this code are available at S.10 a copy. 383