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1010 CHAPTER 47 1952 Guide class, are usually air conditioned. This includes staterooms for ship's personnel and offices within conditioned passenger. areas. Third class' staterooms are air conditioned on some ships, depending on the particular trade. Theaters, lounges, smoking rooms, beauty'shops, barber shops and similar closed public spacesare usually air conditioned. All messrooms, recreation rooms, officers' offices, crew's inboard rooms, and those having fixed portlights are usually air conditioned on passenger vesgels. The treatment depends on the requirements of the operator and the proposed itinerary of the vessel. SHIP SYSTEMS AND CONTROLS The types of Comfort conditioning systems used to date generally have followed conventional lines, except for those serving staterooms, offices, and similar small spaces. Large public spaces are fitted with individual systems which supply dehumidified and cooled air during the cooling cycle, and warm air during the heating cycle. In many cases these rooms are fitted with large glass windows and doors, and require direct radiation to offset the downdraft which would occur in cold weather. Finned-tube radiation running the full length of the glass area is commonly used for this purpose: Introduction of warm air at the sill, in lieu of direct radi ation, is also used. Systems serving most public spaces are designed to provide all outside air as long as the refrigeration load is less than the capacity of the cooling equipment. Many central systems are' simplified by using 100 percent outside air all-year-round. The important problem in ship air conditioning concerns the treatment of the small spaces such as passenger staterooms, offices, and crew quarters. Low headroom, congested quarters, double berths, and unsymmetric arrangements make each space a problem in air distribution and treatment. The simplest system used f6r small spaces consists of a central filter bank, supply fan, preheater, and cooling and dehumidifying coil. The preheater steam valve and cooling coil water valve are controlled in sequence by a duct thermostat, in the fan discharge, set to maintain a constant outlet air temperature. Zone .reheaters are provided to take care of variations in heating loads. The reheater steam valve is controlled by a sub-master thermostat at the reheater outlet. Control of room tem perature is obtained by operating manual dampers in the air supply to the space. A recirculation exhaust fan is frequently provided, and operates in conjunction with automatic dampers to utilize the maximum quantity of outside air consistent with capacity of the cooling coils. One system utilizes the same central supply equipment and recirculation exhaust system as the one just described, except that zone reheaters are replaced by individual space hot water reheaters. Each reheater is pro vided with a control valve, controlled by room thermostat. Generally, a forced circulation single pipe hot water system is used. Fig. 1 shows a diagrammatic arrangement of this system. It should be noted that reheat is used to eliminate overcooling of the individual spaces during mild cooling conditions. This system is generally used for staterooms and small spaces devoted to first and second class passengers. The average total air per person is about 60 cfm, and average outside air per person is about 18 cfm. A third system, used to a limited extent, is similar to the system just described, except that each room is provided with an induction unit (floor type where possible) which reheats the primary air supply. Control of Transportation Air Conditioning 101i Fig. 1. .Arrangement of Aib Conditioning System with Central Supply Equipment and Individual Hot Wateb Room Reheatebs .' heating coil in the induction uhit is the same as noted for the system de scribed in the previous paragraph. The average primary air supply is about 40 cfm per person. Recirculation is not always used. The amount of induced air varies with unit design: A fourth less common arrangement is similar, but makes use of hot water in the induction unit in winter and cold water in the induction unit in summer.. Control of the valve on the unit is obtained by use of a summerwinter type thermostat. The unit is provided with drip pan and drain piping to remove condensation. No recirculation is used. On cargo ships, tankers and vessels not carrying passengers or not having air conditioning, heating of crews' spaces and officers' staterooms is usually obtained through a central system having filters, preheaters and reheaters. A minimum temperature of air leaving the preheater is controlled by a duct thermostat. The reheater is controlled by a sub-master discharge-duct thermostat, reset by outside master control. Relationship between sub master and master control (wherein discharge temperature, is raised, as outdoor temperature drops), is set according to a schedule based on the ship's itinerary.. Duct work for all systems described is designed for conventional velocity. However, if power is available, and suitably strong duct construction and adequate sound absorbing facilities are provided, high velocity systems may be used. BIBLIOGRAPHY Railway Passenger Cars . Report on Performance and Coat of Operation of 1037 Internal Combustion Engine Mechanical Compresemn Equipment for Air Conditioning Railroad Passenger'Care, by Division of Equipment Research, Aw cxatum of American Railroads, May 1,1937.