This section is from the book "The Gardener V1", by William Thomson. Also available from Amazon: The New Organic Grower: A Master's Manual of Tools and Techniques for the Home and Market Gardener.
The annexed figure will show how to heat a lean-to range of any number of compartments without sinking the boiler more than 1 foot below the floor on which the main body of the piping is laid.
A, Boiler; B, Main flow-pipe, rising above the door-tops against the back wall, enclosed in a wooden case filled with sawdust; C, Branch pipe, carried over door-top from main flow and attached in the usual way to the pipes D for heating the compartment; E, Main return-pipe, running the full length of the range a few inches below the floor-level. The dotted line is the supposed ground-level. The branch pipes over doorways to be covered with ornamental grating, or otherwise ornamented to correspond with the woodwork of the houses.
In this form of the hot-water apparatus Mr Pearson thinks air would be troublesome. Well, I do not underrate the resistance offered by air to the circulation of the water through the pipes; but in this form the heated air will get to the highest point by a shorter route than it does in the form in general practice. In the latter form the air finds its way to the highest points, and provision is there made for its escape.
In the form represented by the accompanying figure the air will also find its way to the highest points, and the usual means for its exit from the pipes will be provided. And if Mr Pearson has nothing of a more solid nature than air bubbles to offer in opposition to this form, I have no doubt of being able to prevent any obstruction that they, through their aerial nature, may be disposed to offer to the free circulation of the water through the apparatus.
Mr Pearson next says: "If the houses were built for the pipes, and not the pipes for the houses, he would let the water rise the whole way until it is about to re-enter the boiler." In reference to this statement, might I presume to ask Mr Pearson if he is ready to stake his reputation as a hot-water engineer that the circulation of the water will be as rapid in an apparatus having the pipes fixed on a continuous ascent their whole length, and with a vertical return as the water re-enters the boiler, as if the heated water ascended by a vertical rise to the highest point at first, and then descended the whole way until it re-enters the boiler? - the conditions, with the exception of the mode of arranging the piping, to be exactly the same in both cases.
I have repeatedly put this matter to the test - with a miniature apparatus, consisting of a saddle-boiler 9 inches by 3 inches, having 50 feet of half-inch pipe attached thereto - and always with the same result, - that is, when the heated volumes of water rise vertically to the highest point, the 50 feet of pipe becomes hot the whole length in less than half the time it takes to become hot when the heated volumes have to reach the highest point by a slow gradient and re-enter the boiler by a vertical descent. Let it be understood that in both cases the elevation is the same, the source of heat the same, the only difference being the different way of fixing the pipes.
I would also remark that when the pipe is fixed on the former method the boiler keeps cool compared with what is the case when the pipe is fixed on the latter. When fixed on the former, the heat is carried quickly away from the source, and is distributed where it is of use. When fixed on the latter, the heated water cannot get away quickly, and therefore remains and heats the stoke-hole.
Mr Pearson asks if I "intend to state that water in the return-pipe will fail to fill the vacuum caused in boiler by the rise of the heated water in the same time, if it have only an inclination of 1 foot in 100, as if it had 10 feet to fall in the same length?" And he answered this question by saying: "If so, all rivers would flow at the same speed." When Mr Pearson wrote the foregoing question and answer he appears to have forgotten that the water in the hot-water apparatus has to ascend as well as descend, and that the ascent is equal to the descent; whereas the water of a river flows downhill from the fountainhead until it finds its level in the sea. There is no analogy between a running stream and the circulation of the water in the hot-water heating apparatus.
C. M. having agreed with me that a continuous ascent of the flow-pipes is not essential to rapid circulation, I have little more to say to him. I would remark, however, that C. M.'s ideas on the subject of heating by hot-water are of such a "mixed" nature from beginning to end that I find it rather difficult to "equalise" them, and it strikes me he has been attempting to deal with a subject of which he has had very little practical experience. In one of his papers he "reminded " me of some things and "informed" me of others, for which I now thank him. And in return I beg to "remind" and "inform" him that he has missed (seeing the discussion is closed) a grand chance of becoming famous as a hot-water engineer, through his not having the courage to back his opinions by appending his name and address to his papers. J. Hammond.
[When we stopped the discussion last month it did not occur to us that Mr Hammond, as the originator of the discussion, had a right to the closing article, hence the insertion of this paper. - Ed].
Although the hot-water question has received notice to quit your columns, we trust we may be permitted space to correct a typographical error in your September issue. In stating the number of feet of piping attached to our Twin Climax boilers, we wrote "about 5800 feet." Your compositor, by reversing the two first figures, made it read 8500 feet. We repeat, that these boilers are computed to heat 4000 feet each; and we believe this statement is based on calculations of high authorities on the subject of hot-water heating - yet Mr Makenzie says, that in our case he would "never think of loading them with above 2500 feet each".
Since your last issue we have been visited by one of your correspondents, a practical and "qualified" hot-water engineer, who, after a most careful examination of the whole apparatus, failed to find anything materially wrong with the arrangement of the pipes with regard to circulation (according to the principles mentioned and followed by Mr Hammond's opponents), and he arrived at the conclusion that the boilers were too weak for the work they have to do. Since then we have thoroughly tested the power of these boilers. A mild day was chosen - fires put out, pipes allowed to get cold, one boiler shut off, fire re-lighted under the remaining one, heated water turned on to house after house, beginning at the lowest level nearest the boiler, until we had, and still have, 4216 feet of 4" piping heated to hothouse temperature by one boiler: it is only when we require heat in the houses on the higher levels that our real troubles begin. Joseph Hamilton & Sons.
Wellington Place, Carlisle.
I did not intend to have anything more to say on this matter, for reasons which I previously stated; but my apology for having to do so is, that I find Mr Makenzie in his last has shown a remarkable disregard for facts, and has, whether intentionally or not, misrepresented and placed me in quite a false position before your readers. This is in reference to what he alleges I stated as to "pressure or gravitation" having nothing to do with the circulation of the water in the pipes. How Mr Makenzie could draw such an inference from the sentence referred to is certainly beyond my comprehension. If Mr Makenzie will take the trouble to refer to p. 327 (July), he will there see that I do think pressure has to do with it, but it is only as a secondary agent; and how it can be made out to be the "sole and only cause" of circulation, I cannot see. Withdraw the primary cause, the heat - which, rightly or wrongly, we assume to be the motive power - and how long would circulation go on? Only until the pipes got filled and the water found its level. I think Mr Makenzie should be careful as well as clear in his writings, as in another sentence he says Mr Hammond and some others asserted that a continuous or vertical rise is a hindrance to circulation.
What is to be inferred from this? 80 far as I understand, the whole discussion arose from the statement that the continuous rise was a hindrance, not the vertical; and that the latter, rising at once to the highest point from the boiler, was the better system (see p. 421). And this is the reason why I drew a distinction between this and a body of water of a uniform temperature throughout - as in this case I assume we have a different motive power to that we have in a body of, say, cold water, raised by pressure or gravitation, of which I have had ample experience in works it was my duty to see carried out. Robert Stevens.
[These papers are positively the last we can insert on the heating question for the present. - Ed].