Document bB6xKoREgEnoBzeX4LROZ098D

r American Society of Heating and Ventilating Engineers Guide, 1935 6 Make a rough approximation of the amount of coal required to heat a building located in Cleveland, Ohio, assuming that the calculated heating surface requirements are 500 sq ft of steam radiation based on design tem peratures of 70 F and O F. Using Fig. 1, the fuel consumption for a design temperature of 0 F is found to be 0.53 tons per thousand degree-days per hundred square feet of heating surface. Cleveland has a heating season equivalent to 6154 degree-days, therefore, 0.53 X 6.154 X 5 = 16.31 tons of coal. '7 Make a rough approximation of the gas required to heat a building located in Chicago, 111., assuming that the calculated heating surface requirements `are 1000 sq ft of hot water radiation based on design temperatures of O F and 70 F. Chicago has 800-Btu mixed gas, and 6315 degree-days. .Using Fig. 2, the fuel consumption for a design temperature of 0 F with 800-Btu gas is found to be 0.08 cu ft of*gas per degree-day per square foot of hot water radiation. 0.08 X 6315 X 1000 = 505,200 cu ft. 8 A certain building has a maximum heat loss of 250,000 Btu per hour in --15 F weather. How many tons of fuel will be required to maintain a temperature of 70 F during a 260-day heating season in which the average temperature is 39 F? The heating value of the fuel is 13,200 Btu per pound and the efficiency of com bustion is 60 per cent. 250,000 (70 - 39) 260 X 24 oc ,, ,, _ (70 + 15) 13,200 X 0.60 X , 2000 9 # Which item may be determined more closely, the heating value of a fuel or the efficiency of its combustion? The heating values of oil, gas, and solid fuels are closely determinable, whereas the efficiency of burning depends on the particular equipment chosen and the skill used in handling it. 10 In an office building, the thermostats are set to maintain 70 F from 7 a.m. to 5 p.m. and 50 F during the rest of the time. When the outside temperature is 30 F,' iiow much saving might be expected because the temperatures are lowered?. Under the above conditions the building becomes 50 F by 11 p.m. and 'warms:up-t6 70"F by 8 a.m. --____ A temperature of 70 F is maintained during 9 hours, and one of 50 F during 8 hours; the temperature would average about 60 F during the 7 hours required for cooling down and warming up: I. The average is 60.4 for the 24 hours. (The average temperature calculated wo.uld have been 58.3 F, had the warming and cooling periods been neglected.) The saving is ^ ~ ^ 100 = ^ Per cent' 11 How does'thei heat capacity of a structure influence the saving made by carrying lower temperatures during the night? The heat storage capacity of the walls prevents rapid dropping of temperatures at night time arid delays the warming up process in the morning. In an extreme case, the building would not reach the lowered temperature by the time the higher temperature is called for in the morning. But under any conditions, the saving made by lowering the tem perature can be correctly estimated by using the average temperature observed over the 24-hour period as a factor, as in Question 10. 12 What are some of the miscellaneous factors that may cause actual fuel consumption to vary from the theoretical fuel requirements as calculated by the! use of heat.Iosses,'<temperature difference, and fuel burning efficiency? The bpening of windows^abnormally high or low inside temperatures; other sources of heat/such as machinery or lights; sun effect; and unusual winds. 490 Chapter 30 RADIATORS AND GRAVITY CONVECTORS Heat Emission of Radiators and Convectors, Types of Radiators, Output of Radiators, Heating Effect, Heating Up the Radiator, Enclosed Radiators, Convectors, Code Tests, Gravity-Indirect Heating Systems THE general terms for heating units are: (1) radiators, for direct sur faces, either exposed, enclosed, or shielded; and (2) convectors, or concealed heaters, for extended surfaces that are built in as part of an enclosure or cabinet. Some heating units are also available that are a combination of radiators and convectors. HEAT EMISSION OF RADIATORS AND CONVECTORS All heating units emit heat by radiation and conduction. 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 built-in heating unit in a convector emits practically all of its heat by conduction to the air surrounding it and this heated air is in turn trans mitted by convection to the rooms or spaces to be warmed, the heat emitted by radiation being negligible. The small amount of heat trans mitted by radiation to the inside surface of the enclosure diminishes as the surface temperature of the enclosure approaches the surface temperature of the heating unit. 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 Coil Radiators 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 491