Woodward's Graperies and Horticultural Buildings

by George E. Woodward; F. W. Woodward

HEATING.

The proper heating of Horticultural buildings being an important feature in their general management, and an essential condition of their success, we shall consider the subject at some length, availing ourselves of the practical experience of others, as well as of the knowledge we have acquired in our own experiments and practice.

Hot air stoves have been so generally condemned and discarded as a means of heating glass structures, that we shall not discuss their faults or merits, but confine ourselves to heating by flues, steam, and hot water in pipes and tanks.

Flues.—Flues have been generally used in heating for many years, and although the method is rude, imperfect and unsatisfactory, they possess certain advantages on the score of economy, which will prevent their total supercedure until some equally cheap and effective method shall be found, to take their place. It cannot be questioned that houses of moderate extent can be heated at much less expense for the original cost of apparatus by the flue system than by any other now before the public. Flues have the advantage over steam or hot water in their power to generate heat and supply it to the green or hot house in a very short space of time, and with this apparatus, the fires may be allowed to go out on mild and bright days in winter, with the certainty that heat can be easily and quickly commanded at nightfall. Steam cannot be generated quickly, and the hot water apparatus requires considerable time to get into full operation, with the usual amount of fuel.

Among the serious objections to the use of flues, is the unequal distribution of heat throughout the house; the parts near the furnace being overheated, while at the chimney it is scarcely warm. This difficulty can be partially obviated by the use of materials in the construction of the flues, of different thicknesses,—being made thick and heavy at the furnace, and gradually becoming thinner and lighter as it extends towards the chimney. Again, flues generally require more fuel than a hot water apparatus, and moreover, they are unsightly in an ornamental house, and with the best care in their construction and management, they do not give entirely satisfactory results.

Earthenware drain-pipe is frequently employed for flues, and when care is taken to prevent their cracking by the excessive heat near the furnace, they answer the purpose very well. When properly secured at their joints they prevent the escape of gaseous matter more perfectly than brick flues.

Flues should be elevated a few inches above the floor, and supported by bricks, to allow all the radiating surface to act upon the atmosphere of the house, and should have, in order to secure sufficient draft, a gradual rise through their whole length from the furnace to the entrance into the chimney.

The furnace should be built inside the house at one end, with the fire and ash-pit doors opening into a shed outside, to prevent any escape of gas into the house while replenishing the fire. It will be necessary to place the furnace low enough to allow a proper rise to the flue. If the flue be made to rise immediately from the furnace about one foot, it may then be carried fifty feet, with a rise of not more than six inches, and the draft will then be sufficient.

The dimensions of the flue may vary from 8 to 12 inches in width, and from 12 to 18 inches in height, according to the space required to be heated. The usual mode of construction, when bricks are used, is to lay them crosswise and flat for the bottom and top, and to set them edgewise for the sides. Tiles for the bottom and covering are an improvement upon bricks: being thinner, the heat passes through them more readily, while they still retain the heat sufficiently to equalize the temperature. Tiles used for the top covering are sometimes made with circular depressions for holding water for evaporation.

Steam.—The employment of steam for heating green houses, graperies, &c., is almost entirely superceded by the hot water method. It will, therefore, be necessary only to allude briefly to this part of our subject. It occasionally happens that a conservatory attached to a dwelling is heated by the same steam apparatus employed to heat the latter, but we believe that a person who should advocate, at the present day, the general adoption of steam as a means of heating horticultural structures, would be regarded as belonging to a generation which has now passed away.

Steam travels through pipes with great rapidity, and parting with its heat rapidly, it becomes quickly condensed, unless the boiler is of large capacity and capable of furnishing a full supply. It is, at best, an unsatisfactory mode of heating plant houses, for if from any cause the water in the boiler is reduced below the boiling point, the steam in the pipes is instantly condensed, and with it all heat, except that remaining in the iron of the pipes, and the condensed steam, is withdrawn.

Hood, an English author on heating, quoted by McIntosh in his valuable work the "Book of the Garden," thus compares the merits of steam and hot water. "The weight of steam at the temperature of 212° compared with the weight of water at 212°, is about as 1 to 1694, so that a pipe that is filled with water at 212°, contains 1694 times as much matter as one of equal size filled with steam. If the source of heat be withdrawn from the steam pipes, the temperature will soon fall below 212° and the steam immediately in contact with the pipes will condense: but in condensing, the steam parts with its latent heat and this heat in passing from the latent to the sensible state, will again raise the temperature of pipes. But as soon as they are a second time cooled down below 212° a further portion of steam will condense, and a further quantity of latent heat will pass into the state of heat of temperature, and so on until the whole quantity of latent heat has been abstracted and the whole of the steam condensed, in which state it will possess just as much heating power as a similar bulk of water at the like temperature; that is, the same as a quantity of water occupying 1-1694th part of the space that the steam originally did.

By experiments made by the above authority, it has been proved that a given bulk of steam will lose as much of its heat in one minute as the same bulk of hot water would in three hours and three quarters. And further admitting that the heat of cast iron is nearly the same as that of water, if two pipes of the the same calibre and thickness be filled, the one with water and the other with steam each at 212° of temperature, the former will contain 4.68 times as much heat as the latter; therefore if the steam pipe cools down to 60° in one hour, the water pipe will take four hours and a half to cool down to the same point. In a hot water apparatus we have in addition to the above, the heat from the water in the boiler, and of the heated material in and about the furnace, which continues to give out heat for a long time after the fire is totally extinguished; whereas in a steam apparatus, under the same circumstances we have no source of heat except the pipes by which it is conveyed—giving an advantage in favor of hot water over steam as regards its power of heating hot houses, and maintaining heat after the fire ceased to burn, in nearly the proportion of 1 to 7—that is, hot water will circulate from six to eight times longer than steam under the above circumstances."

Tanks.—This mode of heating horticultural buildings has been used in England for some years, and has, of late, obtained considerable popularity in this country; mainly, however, for the purpose of obtaining bottom heat. The tank method is more steady and reliable in its operations in this respect, than heating by flues or pipes, but even its most strenuous advocates must admit that for atmospheric heat hot water pipes or flues must be employed in some shape or other, where the tanks are covered with earth or sand beds for propagating purposes. With slate or metallic covering they are sometimes used solely for atmospheric heat, and are found to answer well. But if tanks are constructed of substantial and enduring materials, they possess little if any advantage, on the score of expense, over hot water pipes, while they occupy much more room and are unsightly objects in a well ordered green-house.

Wooden tanks are frequently used where the heat is required to rise perpendicularly from them. If constructed of good pine plank, well put together with white lead, and thoroughly painted inside and out, they will last for several years. Scarcely any heat will be radiated from the sides and bottom of a wooden tank. Tanks of brick and cement would answer better than those made of wood, if it were possible to make them water-tight when supported by piers above the ground, as they are usually built. But however carefully constructed, these materials are so unyielding to the expansion and contraction they are subjected to, that it is nearly impossible to prevent leakage for any length of time. A large number of brick and cement tanks have come under our notice, and we cannot call to mind a single one of them all that has not been a continual source of vexation and expense to its owner, since its first construction.

The principle objections to tank heating, as usually employed, are an excess of bottom heat and a deficiency of atmospheric heat, with a superabundance of moisture when the vapor from the tank is not properly excluded from the house. Tanks should be covered with some good radiating material, as slate or metal. If slate is employed, the joints should be carefully and effectually cemented. Boards are sometimes used as a covering, but their radiating power is slight, and their decay rapid.

Soil or sand, to the depth of six to ten inches, is usually placed upon the tanks, and used as a plunging bed for pots containing cuttings; or the cuttings are sometimes inserted in the bed itself.

Any arrangement by which vapor from the tanks is admitted to the roots of plants is to be avoided, for however desirable a moist bottom heat may be, it is found from experience that the soil is frequently rendered a mass of puddle, in which no living roots can exist.

A portion of the covering of the tank may be made moveable to allow moisture to escape into the house when required.

By means of the tank, bottom heat for propagating or other purposes, can be very steadily and uniformly maintained, more so than by other modes, and the changes of temperature of the outer air do not materially affect it. But the case is different with regard to the air of the house, which is frequently reduced below the freezing point, in severe weather. If the bottom heat is of the required temperature, any attempt to counteract the coldness of the air of the house by increasing the fire, would produce an injurious excess of bottom heat. It is evident that while the required supply of heat for the bottom is uniform, and that for the top exceedingly irregular, both objects cannot be properly secured except by a separate supply of heat for each. For these reasons we would employ a hot water pipe or pipes, passing around the house, on the same level with the tanks, supplied with a valve to regulate the heat at pleasure, or a brick smoke flue constructed in the usual manner.

Tanks are usually divided in the centre, thus forming channels for the flow and return circulation side by side, equalizing the temperature throughout their whole length. This form is sometimes departed from by carrying the tank around the house, and connecting each end with the boiler, but in this case, except in small houses, a uniform temperature cannot be maintained, as the water will have lost several degrees of heat before it has accomplished its circuit. Another arrangement is to connect the remote end of the tank by an iron pipe for the return circulation, passing under the tank the whole distance to the boiler. This is not as perfect and effective an arrangement of pipes and tanks as that before referred to, as in this case we do not have the heat from the pipe under control.

A writer in a late number of the "Gardeners' Monthly," gives the following description of tanks erected by him to obviate excessive moisture and radiate a portion of their heat into the atmosphere of the house.

"In the winter of 1863-4, I finished two span-roof houses, each 60 feet in length, with water tanks three feet in width, running entirely around on both sides of each house, and heated by a single furnace. The tanks were made with wooden bottoms and sides, and covered with slate carefully cemented. My design was to heat the houses entirely by the tanks, by far the larger portion of the heat being given off from the slate covering, and as a bottom heat for plants. As I understand the various writers upon this subject, this is the approved plan. But I have found considerable difficulty, and have been obliged to modify my plan in various respects:

In the first place, wooden tanks, with the top covered with sand, will not give off heat sufficiently to keep up growth in houses of this size during extremely cold weather. By protecting the houses with shutters, this difficulty may be obviated. Crowding the fire, and raising the water in the tanks to a high temperature, is a more objectionable remedy. In this way the bottom heat is too strong. But my most serious difficulty has arisen from excessive humidity. I put three inches of sand over the whole slate surface of the tanks, using a part for cuttings, and the rest, (say 100 running feet of the three feet wide table), for standing pot plants upon the surface of the sand. The plants dried rapidly, and required watering every morning. The result was, that in watering the plants, and of course the sand on which they stood, to some extent, it was like pouring water upon a flue, or upon hot pipes: a constant steam was given off; all the moisture in the sand was rapidly converted into steam; so, also the water in the pots was quickly expelled. In order to heat the house sufficiently, the bottom heat became too strong, and the plants were in too direct contact with it. In cold days the house was in a perfect fog. It was ruinous to the plants. The remedy was simple: more heat must be allowed to escape from the tank into the house, without coming in contact with the sand-bed, and the moist earth of the plants. Another slate floor was laid, an inch above the tank slate, on which to put the sand and stand the plants. This hot air chamber opens into the house on the back and front side of the tank. Thus the whole radiating surface of the top of the tank may be directed into the house, or may be confined as bottom heat, as may be found necessary. By this plan, excessive humidity may be entirely obviated, and the heat completely controlled, as wanted."

Hot Water Pipes.—It is generally conceded, among practical men, that the circulation of hot water in iron pipes is the best known method of heating plant houses. The property which heated water possesses of retaining for a considerable length of time its heat and transmitting it to the pipes at long distances from the boiler, renders it a most effective agency for such purposes: A perfect control of the moisture of the atmosphere, by means of evaporating pans attached to the pipes; entire freedom from deleterious gases, sometimes escaping from flues, and the substantial character and enduring qualities of the apparatus, are important considerations in favor of this method of heating which are not to be overlooked or underrated.

It is true that a house of a given size cannot as soon be brought to the required temperature after the fire is first lighted, as by other modes of heating, but when once in full operation greater regularity is maintained, and if the fire should by any neglect go out, heat is still radiated, often for several hours, before the pipes become entirely cold.

For heating ornamental houses of glass, pipes are also to be recommended on account of the little room they occupy and the neatness of their appearance compared with the unsightly flues or tank. If properly put up, the pipes never leak at the joints, as is the case frequently with tanks, and scarcely need any repairs for years. The first cost of apparatus for heating by hot water pipes exceeds that of the other methods which we have named, but when we take into account its great durability, economy of fuel, and the satisfactory results produced in the growth of plants in houses heated in this manner, it must be evident that this method is the cheapest in the end.

It is generally supposed that the heat obtained from steam or hot water pipes necessarily contains moisture. For those who have had any experience in the use of these methods of heating, it is needless to say that such is not the case. To obtain moisture evaporation of water in some manner in the atmosphere must be effected. This is provided for by attaching to the pipes evaporating pans filled with water, by which the moisture can be perfectly regulated and controlled. The capacity of the boiler and the length of the pipes should be in proportion to the size of the house to be heated, bearing in mind that it is better to have a reserve of heating power for extraordinary occasions. In such cases economy in fuel will be secured, as the fires will not be required to be kept constantly burning brightly.

Fault is sometimes found with the apparatus when it lies entirely with the proprietor of the establishment, who in his short-sighted economy, has restricted the builder in the amount of pipe put into the apparatus.

CONSTRUCTION, &c.

The general plan of Horticultural structures may be as perfect as possible, but if the details are not well carried out, and especially if the workmanship be not good, they will prove a source of never-ending vexation and expense. Insecure foundations, ill-fitting doors and ventilators, imperfect glazing, and inferior workmanship of every description, are evils that skillful gardeners have to contend with, and upon whom the consequences of such defects usually fall, when they should be placed upon the shoulders of the constructor.

Methods for building cheap Graperies and Green houses have often been described, and we find many of these imperfect and temporary structures scattered through the country. Such buildings may be cheap as respects their first cost, but their durability is a question which should enter into the calculations of their builders, as well as the consideration of the original outlay. After a year or two we find them with open joints, leaky roofs, and decaying foundations. The inferior and temporary character of materials and workmanship is often a source of serious loss to their owners, and every building of this description demonstrates the mistaken and short-sighted economy of its projector. It is much wiser and truer economy to expend at the outset, a sufficient amount of money and care to make the structure permanent, and to obviate the necessity of constant repairs. Experience has taught us that if they are well and substantially built, these structures will endure for twenty years with very few repairs except an occasional coat of paint. It need not be demonstrated that the profit and gratification to be derived from a well-built house far exceed those accruing from a cheap and imperfect one, with escapes for the heat in winter, and inlets for cold air and driving snow and rain.

The foundations of Horticultural buildings should be of stone or brick, both below and above the ground, if they are to be of a permanent character. The superstructure should be of the best white pine and thoroughly painted. In building curvilinear roofs the rafters and sash bars should be sawed out in pieces to the regular curve. The rafters being put together in sections, breaking joints are thus equally strong throughout their length. The advantages of sawed bars over those bent in the usual manner, are very great. The thrust of the roof is but slight, and the house always remains in shape. With the bent bars the strain is enormous, as may be seen in the settling of such houses at the ridge, and expansion at the sides, besides the liability of breaking the glass by the constantly varying strain of the bars.

Iron has been frequently and strongly recommended in the construction of horticultural buildings. It has been used, with very satisfactory results in England, and doubtless it may there be found to be the best and most economical material for such purposes. It has been tried also in this country, but the experiment has not resulted so favorably. The main difficulty is that, in this climate, the expansion and contraction of the iron rafters and bars are so great that the glass is continually and badly breaking, and it is very difficult to keep the joints tight enough to repel the rain and the cold air. There can be no doubt that in this country, wood is a better material than iron for these purposes.

Thick and double thick glass has heretofore been used almost exclusively for first class houses, but the high price of glass has of late, compelled the use of a thinner article. It is generally believed that thick glass will resist hail storms better than thin, but on this question practical men differ in their opinions. It is contended, on the other hand, that the elasticity of the thin panes resist a blow better than the unyielding thick one, also that the latter is more likely to be broken by the accumulation of water between the laps of the glass.

We have found that the 8 by 10 size of single thick French window glass, second or third quality, is sufficiently good for Horticultural buildings, and we do not use any other, unless especially called for by the proprietor.

Glazing is often badly executed, half an inch lap, and sometimes more, being often allowed to the glass, from the mistaken idea that rain, in a driving storm, will find its way through. A lap of one-eighth of an inch is amply sufficient in any case. The glass should be well "bedded" down to the sash bar, in putty containing a portion of white lead, and well secured with small iron nails or glaziers points. All putty should be removed from the outside when the work is finished, and the sash bars should then be painted with a heavy coat of thick paint which will close up the joints and render them water tight.

Ample ventilation should be provided both at the top and bottom of houses, so that large quantities of air may be supplied when necessary, as in ripening the wood of vines in graperies, and in "hardening off" plants in green houses before removal to the open air.

By reference to the numerous designs given in this work, the manner of arranging the interior details, such as shelving, tables, walks, hot water pipes, and the general features of construction and adaptation, will be understood.