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662 CHAPTER 47 1959 Guide levels of unit conditioners are generally somewhat greater than those of unit ventilators. Unit conditioners are described in Chapter 16, Unitary Air-Conditioning Equipment. automatic control Discussion of automatic control in this chapter will be limited to general factors peculiar to school systems, and their effect on control or the need for it. Chapter 43, Auto matic Control, provides a detailed discussion of the proper application of mitomatie control to the various system dements normally encountered. Automatic temperature control equipment is justified in school systems because manual control will not maintain the temperature or environment within desirable limits. Automatic control, marie an integral part of the system design, can reduce the initial cost of the mechanical in stallation. EgonjJea of this type of control include warm up clocks or low-limit thermostats, which prevent the use of outdoor air until the building has been heated for a set period of time, or until a minimum space temperature is reached. Such controls permit selection of the minimum sue of equipment such as boilers, furnaces, burners, coils, piping, etc., having the least excess capacity for warm-up purpose. Controls to prevent the heating of service water in large storage tanks during the warm-up period accom plish a similar result. Controls which reduce the man-hours of attendance at the heating plant or reduce fuel costs, can reduce operating costs. Time clocks, relays, temperature and pressure con trol, which allow the starting of the heating plant without the presence of supervising personnel, are included in this category, together with controls to reduce the use of out door air during warm-up periods. Where fans and extended surface coils are used to main tain the temperature in an occupied space having outside exposure, it is not possible to control the capacity of the equipment manually without producing alternately high and low space temperatures because of the rapid changes in load due to shifting occupancy, variation in solar intensity, and wind variation in speed or direction, and the relatively high capacity of this type of equipment. Where occupancy is particularly dense, the changes in load due to changes in occupancy alone are enough to make proper automatic control necessary in order to maintain space temperatures within acceptable limits. This applies to a large percentage of the spaces in a school building. There are many other factors or conditions that proper automatic control necessary in order to achieve ac ceptable environmental conditions. Those already discussed illustrate some basic considerations in applying tempera- ture control to mechanical systems lor schools. OPERATION The proper method of operation of a system depends upon its design and the automatic control applied to it and will vary with each individual system. To insure good operation throughout the life of a system, it is essential that adequate written instructions be prepared and made readily available to the operating personnel. There should be at least two copes of the instructions, one of which should be placed in a secure depository to insure its pres ervation in good condition during the life of the building. The operating personnel should be thoroughly instructed regarding proper operation of the equipment upon com pletion of the installation. Someone having authority in the school administration, in addition to the operating person nel, should be instructed in the operating characteristics of the system, not only to insure that a change in the operating personnel does not result in the loss of knowledge required for the proper operation of the system, but also to insure that the operating personnel adheres to the in structions. It is seldom that the personnel in charge of the operation of a school system has training particularly applicable to the characteristics of mechanical equipment or the auto matic control applied to it. Therefore, it is essential that this type of operating personnel be made to understand the exact limits that must be observed in adjustment and opera tion of the system. Where temperature control is applied to a system, it must be realized that any instrument used for control purpose is of necessity very sensitive to any change or adjustment made in the setting of the instrument. Therefore, It is necessary that only personnel fully trained in the proper handling of the instruments should make adjust ments other than those expressly designated as proper for the operating personnel. It is common practice for officials in large school districts where there are many buildings to employ specialists ac quainted with the adjustment of critical items of equip ment such as temperature and automatic control. Where in dividual schools do not have such personnel available, it is necessary that the operating personnel be instructed to communicate with qualified service agencies to make changes in automatic control settings and instrument characteristics when they are found to be necessary by experience in the operation of the system. Continuing service contracts for proper maintenance of equipment can be had from compa nies in tins field. When systems are installed and designed on the basis of natural or gravity ventilation, the teacher or person in charge of the individual room or space must perform the functions of adjusting window openings or ventilator settings to provide the conditions of comfort and proper environ ment in the space. To accomplish efficient operation of the system and maintain a suitable environment, it is necessary that these people be instructed in detail regarding the techniques necessary to achieve the proper environment. It is necessary that the administrative authorities super vise the maintenance of such conditions by periodic checks on the efficiency of the people responsible for the spaces. MAINTB4ANCE OF MECHANICAL SYSTEMS The proper maintenance of a mechanical system will re sult in a minimum of repair and the extended life of the system equipment. As is the case with operating instruc tions, it is essential that written instructions for the main tenance of the system be prepared and given to the owner when the system is completed and placed in his charge. These instructions should include detailed information on the lubrication and care of each item of equipment. A schedule showing items of maintenance to be performed for each month of the year should be prepared. Name plates and identification for each valve and item of equipment should be prepared. Manufacturers' catalogs and parts lists for the equipment should be obtained. One copy of each of these items should be placed in a secure depository, together with the operating instructions. A list of-the proper service agencies should be prepared and placed in the hands of the operating personnel. Any changes in service agencies should be recorded for the benefit of the administration as well as the operating personnel. CHAPTER 48 TRANSPORTATION AIR CONDITIONING Railway Passenger Car Air Conditioning; Passenger Bus Air Conditioning; Automobile Air Conditioning; Aircraft Air Conditioning; Ship Air Conditioning, Heating and Ventilating, Air-Conditioned Space Treatment, Systems and Controls HE principles of air conditioning applying to stores, panel duct increases air flow and improves heating surface Trestaurants, hospitals, theaters, and homes are - ap effectiveness. plicable to railway passenger cars, passenger buses, auto- Floor beat is supplied by introducing steam into an inner - mobiles, streetcars, trolley coaches, airplanes, and ships. tube within a finned tube or by means of a separate steam- However, equipment used for mobile applications differs to-Uquid heat exchanger. The liquid (usually an antifreeze) from that used for stationary purposes in that it must is mechanically circulated through plain finned tubing. meet additional requirements. Equipment must be compact, When steam is used directly, the tube-within-a-tube con accessible for quick inspection and servicing, light-weight struction makes it possible to obtain uniform distribution &nd unaffected by vibration and impact. Freedom from throughout the length of the car. It is achieved by means vibration which could be transmitted to supporting vehicle of beat transfer between the steam within the inner tube and thus to passengers, is essential. and the condensate returning in the annular space between RAILWAY PASSENGER CAR AIR CONDITIONING the tubes. The finned tubing at the floor must have sufficient ca The railway passenger car represents a very difficult airconditioning problem. Space is strictly limited so that all equipment and ducts must be reduced to minimum size. Electric power supply and water supply also are limited. All equipment must withstand severe vibration and shock, and must be very reliable since servicing points are fre quently far apart. During the heating season it is necessary to heat con ventional cars with steam from the locomotive at pressures that may vary from 250 peig to only 5 or 10 prig on the last car in long trains. Passengers in window seats sit' only a few inches from cold outride walls and windows, and are close to heating surfaces installed along sides of cars. Sudden changes in load-may be caused by changes in sun, wind, or train movement. Even in coldest weather, outride doors must be opened frequently. During the cooling season, the problem is further com plicated by a highly concentrated internal load due to the passengers. Air distribution problems are. increased by low ceilings and short air throws. Heating pacity to offset effects of cold walls and windows during normal operation, and to heat the entire car to a minimum temperature of 60 - during standby when the overhead system is not operating. The maximum capacity required (determined by standby requirements) varies with car construction and design temperatures, but is approximately 90.000 Btu per hour. This requires a heating capacity in finned tube of approximately 650 Btu per linear foot. The overhead air heating coil must have sufficient ca pacity to. heat the outdoor air brought into the car for ventilation, and to supply approximately 20 percent of the internal heat loss of the car so as to permit supply of floor heat at all times at an output that will not be objectionable to passengers sitting near it. The usual ca pacity of the overhead heating coil is approximately 100.000 Btu based on 2400 cfm of circulated air, with 600 cfm of this being outdoor air for ventilation. All Btu values are approximations of actual heating requirements, and do not include heat losses in the trainline (or leakage) or losses in the undercar piping. Present car designs have enabled the car builder to run the steam supply lines in recesses within the car body; thus greatly diminishing The heating of passenger cars is accomplished by using under-car losses. a split system consisting of an overhead air-circulating system with heating and cooling coils, and hating surfaces Refrigeration (floor heat) along car rides. The floor heaters, which usually For cooling and dehumidification during summer, re consist of finned tubing, may be made more effective by frigeration may be obtained from ice bunkers, steam-jet addition of covers designed to increase gravity air circula tion, and to direct the warm air from finnad heating sur systems, or mechanical compressors (driven directly from car axle by electric motors or by gas engines). Refrigera face along cold outride walls and car windows. In some new cars, wall convector panels are used and extend the tion required varies with load conditions, but 7Vfe tons per car is one capacity frequently used. Evaporative-type full length of the car, with air intakes along the floor and condensers are sometimes used in combination with the outlets at window sill height and at window head height usual air condenser on either steam-jet or maahaninal re in dead-light panels. The heated panel protects passengers frigeration. from cold outride walls, and the chimney - effect of the When an electric motor (approx. -10 hp) is used to 663