Document 4v2VVQpLr4GLmQbMa05EYD8NG

HEATING VENTILATING AIR CONDITIONING GUIDE 1943 and economical operation, all automatically-fired gas burners ;should be equipped with pressure regulators on the gas supply line. Stoker Controls Domestic stokers are normally placed under command of a room thermostat for primary operation subject also to the command of a limit control to prevent their operation when conditions in the boiler or furnace exceed predetermined safe, maximums. Utilizing coal as fuel, automatic ignition is not provided and the stokers, once ignited, maintain their fire, merely changing the rate ,of combustion by changing the draft and the rate at which the coal is fed. Thus, at the command of the room ther mostat the stoker motor is started', driving a forced draft, fan and fuel feeding mechanism. The rate of combustion is thus increased and this operation continues until the thermostat has been satisfied when the motor is stopped and the fuel in the combustion chamber continues to burn at a slow rate with reduced draft. At certain seasons of the year, the. operation of the stoker under the ` requirements of the thermostat may be so infrequent that there is a possibility of the' fuel in' the combustion chamber burning out or the fire going out between operations. To prevent this occurrence, automatic controls may be utilized to operate the stoker independently of ther mostat requirements, sufficiently to sustain the fire either through a timing device functioning for. short periods at predetermined intervals or through a temperature control device reacting to minimum stack or boiler temperatures. Control may also be utilized to prevent stoker operation and the delivery of coal into the combustion chamber in the event that the fire has gone completely out. This control is governed normally, by the stack temperature and shuts down the stoker after a predetermined minimum stack temperature is. reached. RESIDENTIAL CONTROL SYSTEMS . The control installation in a residence may vary from the simple regulation of a coal-fired heating plant to the completely automatic all year air conditioning system. Residential installations with automatic fuel, burning appliances, such as oil. burners, gas burners or stokers, are . normally equipped with single rbom thermostat, limit and safety controls as outlined previously under Control of Automatic Fuel Appliances. Coal-Fired Heating Plant N . Control in the normal coal-fired domesticcheating plant consists of regulating the combustion rate in accordance with requirements. This function is accomplished by a.'spring or electric-driven damper motor .which, under'the command of a room thermostat and through chain . linkage, operates the draft and check dampers of a boiler or warm air furnace. Such installation should, be protected against excessive tem perature or pressure by means of a limit control serving to check the fire when conditions at the boiler or furnace reach a predetermined maximum. All Year Domestic. Hot Water Supply Hot water or steam heating boilers with automatic fuel burning ap- pliances can be used for all year heating of domestic water supply. The 666 CHAPTER 34. AUTOMATIC CONTROL fuel burning appliance in. this case is controlled from the temperature of water or pressure, of steam in the boiler to maintain uniform boiler-Con ditions and domestic hot.water is heated by means of an indirect heater.. The heating of the residence-is normally governed by means of a ther mostat which operates a control valve in the flow line of a gravity hot water or a steam system. Air Conditioning Systems Residential air conditioning systems normally include a heating source and a motor-driven fan for circulating air. In addition, such installations may involve spray-head equipment to supply humidity. Such instab lations distribute suitably heated and humidified air during the heating cycle, and during the summer or cooling cycle may be used effectively as conditioners if equipped with refrigeration means. Regulation of the humidity during the heating cycle is normally accom plished by opening and closing a solenoid water valve supplying water to the spray-heads, the solenoid valve being under control of a room type humidity control. In the average installation the fan is permitted to run only during such intervals as the thermostat is calling for heat or at the command of a limit control to prevent the overheating of the bonnet of a warm air. furnace. The limit control should also prevent'the operation of the fan at the command of the thermostat until the circulating air tem perature has increased to a predetermined point. For the cooling equipment provided in such installations, control- during the cooling cycle will be an adaptation of the control principles described for central fan systems selected for the type of cooling equip ment utilized. :. The selection of automatic control equipment for.residential air-con ditioning systems is just as important as for commercial installations. Fewer controls are generally used and systems are usually less, comr plicated except in the case of a very large residence installation when the control system may become as complete as the commercial installation. CONTROL OF REFRIGERATION EQUIPMENT The most common means of providing cooling for air conditioning may be divided into four general classifications as follows: Compressor Type Refrigeration Refrigeration compressors may furnish refrigerant to direct expansion cooling coils through which air is being passed, or to coils in cooling tanks through which water is passed which is then pumped to air. washers or cooling coils through which the air is passed. In either case the compressor motor may be started and stopped in order to meet the demand for refrigeration or a pressure controller may be used to regulate the low side or suction pressure of the compressor. When the flatter .method is used, the flow of refrigerant to cooling coils may be regulated by the opening and closing of a solenoid refrigerant valve at the command of a temperature controller or thermostat. A high pressure cutout as an individual unit or in combination with 667