Document JvmoBv1ma3q5br58RO24wqNrB

Iy American Society of Heating and Ventilating Engineers Guide, 1936 412 Chapter 23--Mechanical Warm Air Furnace Systems where G = required grate area, square feet, H = total heat loss from building, Btu per hour, F = calorific value of.coal, Btu per pound: C = combustion rate in pounds of fuel per square foot of grate per hour, E = furnace efficiency based on heat available at register faces. In practice it is customary to use the following constants: F = 13,000 (For specific values, see Table 1, Chapter 27). C = 5 to 10 lb (Use 8 lb as maximum in residence work). E = 55 per cent to 65 per cent depending on fuel burned. be used with highly volatile solid fuel. Lower efficiency must . . .. , Where ratio of heating, surface to grate area is less or greater than 20 to 1, deduct or add 2 per cent from or to rating of furnace for each unit decrease or increase in ratio, as the case may be. The foregoing procedure' for determining the size of the furnace to be used applies to continuously heated buildings. Although intermittently heated buildings usually have their heat losses computed according to the standard rules for determining such losses, these rules do not take into account the heat which will be absorbed by the cold material of .the building after the air is raised in temperature. This heat absorption must be added to the normal heat loss of the building to determine the load which the heating plant must carry through the warming-up process. - It is customary to increase the normal heat loss figure by from 50 to 150 per cent depending upon the heat capacity of the construction material, the higher percentage applying to materials of high heat capacity such as concrete and brick. Fan furnace systems are well adapted for heating intermittently heated buildings as these systems do not require the warming of intermediate piping, radiators, or con vectors, the generation of steam, or the heating of hot water. Follow the same methods for an oil furnace as for coal where a con version unit is to be used,, making sure that the ratio of heating surface to grate area exceeds 20 to 1. If it does not, a size larger furnace should be selected. Use the manufacturers' Btu ratings, of furnaces designed for exclusive use with oil, and select a burner with liberal excess capacity. The selection of the proper size gas furnace for a constantly heated; building can be easily made by using the following American Gas Associa tion formula: where H = total heat loss from building in Btu per hour. R = official A.G.A. output rating of the furnace in Btu per hour. In the case of converted warm air furnaces a slightly different procedure is necessary, as the Btu input to the conversion burner must be selected rather than the furnace output, The proper sizing may be done by means of the following formula: I =4.56H (3)