1406 



GREENHOUSE 



GREENHOUSE 



expansion of the pipe which with vertical wall coils may 

 be done by running them partly across the ends of the 

 nouses and the same means may be used in horizontal 

 coils, or the headers at the lower ends of the coils may 

 be connected with the ends of the pipes by means of 

 nipples and right and left ells. Whenever possible, 

 there should be at least two returns supplied by each 

 of the flow-pipes and the number may be increased 

 until the capacity of the flow is reached. In determining 

 just how many returns may be supplied by a given flow- 

 pipe, one should always make allowance for the radia- 

 tion furnished by the flow-pipe itself and, as the fric- 

 tion will be greater in a large number of short returns 

 than for the same radiation with long returns, this 

 should be considered in adjusting the ratio between the 

 flow- and return-pipes. 



Even greater attention should be given to the grading 

 of the small return-pipes than to the larger flow-pipes, 

 as the danger from pocketing of the air will be increased. 

 For the smaller sizes, it will be advisable to give them a 

 elope of at least 1 inch in 15 feet; but, if carefully 

 graded and securely supported at intervals of 10 feet, 

 good results can be obtained with 2-inch pipe with a 

 fall of 1 inch in 20 feet; and if no more than 1 inch in 

 30 feet is available even this light fall will generally 

 suffice to rid the pipes of air. This is really the main 

 object for which the pipes are eloped, as the circula- 

 tion would be fully as good, or better, if they 

 are run on a level from the highest point in 

 the system, provided the air did not .? ^ 

 pocket. 



By having the highest point in 

 the system near the boiler 

 and attaching the expan- 

 sion-tank at that point, 

 one secures a down- 

 hill arrangement 

 of the pipes 

 which not 

 only gives a 

 better circu- 

 lation than 

 when the 

 flow-pipes 

 run uphill, 

 but it does 

 away entirely 

 with a ir- 



1764. Carnation-house, 100 x 23 ft. 6 in., piped for hot water. 



valves which must be provided when the flow-pipe 

 runs uphill and which often give trouble. 



The method of piping which has been advocated, i.e. 

 running one or more pipes in each house to the farther 

 end and there connecting them with the returns, will 

 give a more even temperature than can be secured in 

 any other way. Formerly, it was the custom to con- 

 nect the supply-pipes with the coils at the end of the 

 house nearest the boiler. In some cases, one-half of 

 the pipes in the coils served as flows to feed an equal 

 number of return-pipes, or all of the pipes in the coil 

 were connected at the farther end of the house with a 

 main return-pipe, of the same size as the feed-pipe, 

 which was brought back underneath the coil, or all of 

 the coils in the house were connected into one main 

 return. When the latter arrangement is used, the heat- 

 ing of the house is less uniform than with an overhead 

 flow-pipe, the farther end of the house being cooler than 

 the one near the heater. 



Unless the heating system is connected directly with 

 the water-supply system, which is used as an expansion- 

 tank, a special tank must be provided and connected 

 with the highest part of the flow-pipe or with one of 

 the returns near the heater. While it would answer if 

 this tank is located at some point but slightly above 

 the heating system, it is always desirable to have it 

 somewhat elevated, as this will raise the boiling-point 

 of the water in the system and hence increase its effi- 



ciency, as well as lessening the danger of its boiling over. 

 The pipe connecting the expansion-tank with the heat- 

 ing-pipes should not be less than %inch and this should 

 be increased to 13^ to 2 inches in large systems. The 

 size of the expansion-tank should be sufficient to equal 

 the amount which the water in the system will increase 

 in volume when it is raised from a temperature of 40 

 to 200, with a margin of perhaps 50 per cent. By con- 

 necting the expansion-tank with the highest part of 

 the system, one not only does away with the necessity 

 of using air-valves but also lessens the tendency of the 

 water to boil over. 



When there are several houses in the range connected 

 with one system, it is always a good practice to have a 

 valve upon the supply-pipe leading to each house, 

 with other valves upon at least one-half of the coils. 

 It will thus be possible to reduce the radiation in each 

 house or to cut it out entirely if desired. 



Hot water under pressure. 



Especially in large ranges it is now becoming cus- 

 tomary to place the water under pressure, thus making 

 it possible to raise the temperature at which it will boil, 

 and in this way the circulation can be improved, and 

 instead of the water in the returns having an average 

 temperature of 150, it can be maintained several 

 degrees above the ordinary boiling-point of water. 

 The principal objection to this plan is that the 

 water in the boiler being hotter, the gases of 

 combustion are not cooled down to the 

 same extent as when the water is at 

 160 or less. This results in lessen- 

 ing the economy of coal-con- 

 sumption, placing it upon 

 about the same plane as 

 when steam is used. 

 On the other hand, 

 this system has 

 the merit of 

 reducing the 

 amount of 

 radiation re- 

 quired in the 

 heating - sys- 

 tem, and in 

 this way 

 lessening the 

 cost of piping 



the greenhouse fully twenty-five per cent. 



Various methods of placing the water in the heating- 

 system under pressure have been employed. Among 

 them is to use a safety-valve and a vacuum-valve, 

 either upon the expansion-tank, or if this is not closed, 

 upon the expansion-pipe within the tank. The safety- 

 valve allows either the air or the water, as the case may 

 be, to pass out of the system when the pressure desired 

 is reached, while the vacuum-valve permits the air or 

 water to re-enter the system when the pressure drops. 



What is known as the "mercury generator" or "cir- 

 culator" also serves the same purpose. In these a column 

 of mercury prevents the escape of the water in the 

 system until the pressure has reached the point desired, 

 when it allows a portion of the water to escape and, 

 later on, to re-enter the system when the pressure 

 decreases. It will be seen that this acts in exactly the 

 same way as the safety-valve and vacuum-valve 

 described above. By raising the boiling-point of water 

 and improving the circulation, it not only makes it pos- 

 sible to use smaller pipes both for flows and returns, 

 but the amount of radiation required will be consider- 

 bly reduced. In fact, although it is not advisable to 

 carry it to that extent, it is possible to reduce the 

 amount of radiation practically to that required for 

 steam-heating. 



This system is of value particularly in sections of the 

 country in which the usual winter temperature is well 



