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Heating Ventilating Air Conditioning Guide 1938 and adjacent piping be of non-combustible material.as even slow-burning insulation constitutes a dangerous fire hazard in case of low water in the boiler. PROBLEMS IN PRACTICE 1 What basic requirements of boiler design are to be accomplished with a combination boiler and oil burner unit? Combination units vary widely but in general, the basic requirements of design depends upon a combustion chamber of proper design and arranged for the flame shape with adequate heating surface for the complete combustion of the fuel. 2 What is the normal rating range of each type of boiler? ' 0. Cast-iron boilers are rated at from 200 to 18,000 sq ft EDR. b. Steel boilers are rated at from 300 to 50,000 sq ft EDR. 3 What factors contribute to economical fuel operation in low pressure boilers burning coal or oil? a. Proper furnace volume for complete combustion. b. Arrangement of heating surfaces in series to create a turbulent and scrubbing contact of gases against the convective surfaces. c. Rapid internal water circulation which will remove steam bubbles from the water side of heating surfaces and allow other steam bubbles to be formed. ' Rapid disen gagement of steam bubbles increases the steam generating efficiency of each unit area of heating surface, and thereby lowers flue gas temperatures. 4 What equipment is usually directly attached to a low pressure heating boiler? For coal.burning steam boilers: water column, water gage, tri-cocks, steam gage, lever pop safety valve, boiler damper regulator. ' For coal burning hot water boilers: damper regulator,- altitude gage, thermometer, relief valve. .. "' For oil burning boilers, the damper regulators are omitted and the following additional equipment is usually attached: automatic water feeder, low water cutout, a pressure control, and a water temperature control. These are generally furnished by the oil burner manufacturer and do not come with the boiler. 5 0 What general precautions regarding the boiler should be faken to make sure a proposed heating installation will work properly? - a. Select the right size and type of boiler. 1 b. Be sure the combustion space is proper for the type of fuel burned. c. Allow sufficient space around the boiler for cleaning. ' 1. Secure proper height and area.of chimney and connecting breeching. e. Clean the boiler thoroughly and provide surface blowoff connections and bottom blowoff connections for periodic cleaning after operation is begun. /. See that the boiler heating surface is cleaned at regular periods. g. Check flue gas temperatures and make a flue gas analysis at least once a month. h. Secure information and advice from boiler manufacturer. 5 What is the average heat transmission rate in heating boilers in Btu per sq ft of heating surface per hour? 3500 for coal burning boilers; 4200 for oil burning boilers. 262 Chapter 14 RADIATORS AND GRAVITY CONVECTORS Heat Emission of Radiators and Convectors, Types of Radi ators, Output of Radiators, Heating Effect, Heating Up the Radiator and Convector, Enclosed Radiators, Convectors, Selection, Code Tests, Gravity-Indirect Heating Systems THE accepted terms for heating units are: (1) radiators, for direct surface heating units, either exposed, enclosed, or shielded; which emit a large percentage of their heat by radiation: and (2) convectors, for heating units having a large percentage of extended fin surface and which emit heat principally by convection. Convectors are dependent' upon enclosures to provide the circulation by gravity of large volumes of air. HEAT EMISSION OF RADIATORS AND CONVECTORS All heating units emit heat by radiation and convection. The resultant heat from these processes depends upon whether or not the heating unit is exposed or enclosed and upon the contour and surface characteristics of the material in the units. An exposed radiator emits less than half of its heat by radiation, the amount depending upon the size and number of sections. When the radiator is enclosed or shielded, radiation is further reduced. The balance of the emission is by conduction to the air in contact with the heating surface, and the resulting circulation of the air warms by convection. A convector emits practically all of its heat by conduction to the air - surrounding it and this heated air is in turn transmitted by convection to the rooms or spaces to be warmed, the heat emitted by radiation being negligible. TYPES OF RADIATORS . Present day radiators may be classified as. tubular, wall, or window types, and are generally made of cast iron. Catalogs showing the many designs and patterns available now include a junior size which is more compact than the standard unit. Pipe Coils . Pipe coils are assemblies of standard pipe or tubing (1 in. to 2 in.) which are used as radiators. In older practice these coils were commonly used in factory buildings, but now wall type radiators are most frequently used for this service. When coils are used, the miter type assembly is to be 263