III. Second Report Upon Some of the Comparative 

 Merits of Steam and Hot Water for Greenhouse 

 Heating. 



In the winter of 1891-2, a series of tests was made to determine some 

 of the relative merits of steam and hot water for the economical and 

 efficient heating of forcing-houses. The conclusions of the experi- 

 ment — which are published in Bulletin 41 — were to the effect that 

 steam is perhaps better for large forcing-houses, for several reasons.* 

 Our experiments have been severely criticised, especially upon the 

 score that the hot-water boiler which we used is a poor machine for the 

 purpose. The experiment was repeated during the last winter with 

 great care, but in l^his instance one boiler was used for both steam and 

 hot water. That is, for a certain season it was run with water, and 

 then for a season with ste^^m. No change whatever was made in the 

 heater or the piping when these transfers were made except to shut 

 off the expansion tank when steam was used. This expansion tank 

 was a large pail standing about four feet above the heater and con- 

 nected with it by an inch pipe, which was closed by a valve. The 

 heater is a small portable machine designed exclusively for hot water; 

 and in order to make a shift for a steam dome, a piece of 4-inch gas 

 pipe 14 inches long was secured vertically to the top of the heater. 



* The conclusions were as follows : 



1. The temperature of steam pipes averaged higher than those of hot water 

 pipes, throughout the entire circuit for the entire period of test. 



2. The higher the inside temperature in steam pipes the less is the proportion- 

 ate warming power of the pipes at a given point. The heat is distributed over 

 a greater length of pipe, and as steam is ordinarily carried at a higher tempera- 

 ture than hot water, it has a distinct advantage for heating long runs. 



3. When no pressure is indicated by the steam gauge, the difference between 

 the temperatures of the riser and the return, is greater with steam than with 

 hot water. 



4. Under pressure, the difference is less with steam than with hot water. 



5. There is less loss of heat in the steam risers than in the hot water risers, 

 and this means that more heat, in the steam system, is carried to the farther 

 end of the house and more is spent in the returns as bottom heat. 



6. This relation is more uniform in the steam risers than in the liot water 

 risers, giving much more even results with steam than with hot water. 



