This section is from the book "The Gardener's Monthly And Horticulturist V22", by Thomas Meehan. See also: Four-Season Harvest: Organic Vegetables from Your Home Garden All Year Long.
W. D. Phillbrick, Newton Centre, Mass., says: "I notice in your February number an article by R. G. Parker & Co. on Heating Hothouses, in which the writer advocates heating by steam, and says he used five tons of coal to 1,000 feet of glass. I would like to hear what his average temperature was at night in severe weather, also height of house. I have used for several years hot water circulation, having 1,000 feet of pipe in a house of 5,100 feet surface of glass, average height of house 4 feet from beds to glass. In this I keep a temperature always above 40° with only 15 tons of coal to the season. I have a No. 16 Hitchings boiler with good draught. If anybody can show a better doing than this, let us hear from him. Shelter from winds has a good deal to do with this question".
[It would also help to understand the situation if the temperature of the severe weather were given. - Ed. G. M].
In looking through the Monthly for February, I read, with much attention, the article by Ft. G. Parker & Co., Boston, Mass., on heating greenhouses, etc., by steam; and being always deeply interested in anything pertaining to horticulture and floriculture, and especially in any efficient and economical method of heating horticultural buildings of any description, I thought perhaps for the purpose of eliciting further information, for my own, and, may be, the edification of others, I would venture a few remarks, and give you some of my ideas about the subject for what they are worth; you can publish such as you think is worth while, or not any, as you may deem best.
Mr. Parker says: "We have about 10,000 square feet of glass, which is heated by a twenty-eight horse power steam boiler," etc. I think Mr. Parker should state the number of cubic feet of air to be heated, rather than the square feet of glass, as one house covered with 10,000 square feet of glass may contain four, or forty times as many cubic feet of air to be heated, as another of the same superficial area.
" Being somewhat afraid of heating wholly by steam, we laid 4-inch pipes, the same as for hot water, and connected with cast iron heaters or boxes filled with steam pipes, which were connected with the boiler. The steam passes from the boiler through the pipes in the heaters and back to the boiler again. The 4-inch pipes are filled with water, as is also the space around the steam pipes in the heaters." So that the i house is really heated by hot water, and not by steam. But the water is heated by steam instead of the direct action of the fire. Again: "We obtain our heat much quicker than by the old method," If so, that is an advantage; because the same body of water contained in 4-inch pipes will contain and give off the same amount of heat whether absorbed from steam pipes or the direct action of the fire in a hot water boiler; and the quicker we get up the desired amount of heat, as a rule, the better, provided we do not make our heating medium over 180° in the effort to get up the heat.
Also: "As to economy, we burned last season five tons of coal to 1,000 square feet of glass, which is better by three tons than any have done in this vicinity." Three tons of coal saved for every 1,000 square feet of glass or 30 tons for the 10,000, and the labor of handling the coal would be a considerable item and well worth due consideration.
In order to enable us to judge of the comparative values of hot water and steam, I think Mr-Parker should state the number of feet of 4-inch pipe required to heat 10,000 square feet of glass, and number of cubic feet of air to be heated; or more easily perhaps, the size of the houses, in width, height and length and number of feet of pipe to each house, if double thick glass, etc., and whether the degree of heat to be maintained be merely to keep plants free from frost through the winter, say 35° to 50°, or whether a growing heat of 60° to 80°; all this makes a wonderful difference in the consumption of fuel. Also the cost of the twenty-eight horse power steam boiler with heaters and steam pipes as compared with the cost of a hot water boiler powerful enough to heat the water contained in the same number of feet of 4-iuch pipe to the same temperature, under the same circumstances, say 212°.
But it is not desirable to be obliged to heat hot water pipes to the boiling point. We should have heating surface enough to obtain the required amount of heat without ever heating the water over 160° to 180°. It is this slow soft warmth which makes them so preferable to overheated mediums like brick flues, hot air or steam pipes, etc. Mr. Parker quotes from Loudon's Encyclopaedia: " Steam affords a simple and effectual method of heating hothouses." Also, " The disadvantages of steam, as a vehicle for conveying heat to hothouses are few." The words, simple and effectual, I do not agree with, notwithstanding Mr. Loudon said so. Mr. Loudon wrote forty years ago, and more, and they did think something of steam for heating horticultural buildings at that time: but they had not then learned so much about hot water.
(To be continued).