192 GREENHOUSE AND WINDOW-GARDEN WORK 



The Heating of Greenhouses (R. C. Carpenter) 

 Methods of proportioning radiating surface for heating of greenhouses. 



Radiating surface, whether from steam or hot-water pipes, is esti- 

 mated in square feet of exterior surface. All projections, ornaments, 

 etc., on the exterior of pipes or radiators are counted as efficient surface. 

 Formerly, cast-iron pipe of about 4 inches in diameter was used almost 

 altogether for greenhouse work ; it is still used to some extent for hot- 

 water heating, but the great majority of houses are now piped with 

 wrought iron or steel pipe, which is made of standard size and 

 thickness, and is a regular article of trade. 



The heating surface in a boiler or hot water heater is that portion of 

 the boiler, or heater, which is exposed to the direct heat of the fire or of 

 the heated gases. 



Grate surface is the number of square feet of grate in the boiler or 

 heater. 



In estimating the heat required for greenhouses, the area expressed in 

 square feet of glass in the roof and walls is taken as the basis from which 

 computations are made. Certain rules of practice have been adopted, 

 and appear to give fa : rly good results in proportioning radiating sur- 

 face, grate surface, and heating surface. The ratio of heating surface 

 to grate surface in heaters will depend upon the kind of coal to be 

 burned and the economy desired. The more heating surface provided 

 per unit of grate surface, the higher the economy, but the greater the 

 first cost of the heater. The usual practice in large boilers is 

 to employ 40 square feet of heating surface to 1 of grate surface 

 for hard coal, and 80 feet of heating surface to 1 of grate surface for 

 soft coal. 



In small cast-iron heaters the proportion of heating surface to 

 grate is frequently one-third to one-fourth that given above. 



If the greenhouse is maintained at 70 when the outside tempera- 

 ture is zero, one square foot of radiation will supply 5 square feet of 

 glass surface, if steam is used at 5 pounds pressure, or 4 square feet 

 of glass surface if water at a temperature of 180 F. is used. The 

 following table gives the ratio of radiation to glass surface for various 

 temperatures : 



