Popular Science Monthly/Volume 3/July 1873/Domestic Economy of Fuel II
By Captain DOUGLAS GALTON, C. B., F. R. S.
THE question of saving fuel for cooking purposes is even more important than economy in warming; because cooking is an operation required every day in the year, and the waste of fuel in cooking is even more considerable than in warming.
An ordinary cooking-range in houses, which, for convenience, may be designated middle-class houses, is derived from the time when the same fire was used for cooking and for warming. It is interesting to consider Count Rumford's remarks on this question. He largely developed the use of steam for cooking in large establishments, but, in considering private kitchens, he showed that nine-tenths of the heat produced in cooking operations were wasted, and only one-tenth utilized in cooking, by the use of open fireplaces. He laid down the following principles on fireplace construction:
1. Each fireplace should have its grate on which the fuel must be placed, and its separate ash-pit, which must be closed by a door well fitted in its frame and furnished with a register for regulating the quantity of air admitted into the fireplace through the grate. It should also have its separate canal for carrying off the smoke into the chimney, which canal should be furnished with a damper or register. By means of this damper and of the ash-pit door, the rapidity of combustion and generation of heat is regulated, and on the proper use of the two registers the economy of fuel will much depend.
3. In fireplaces for all boilers which are too heavy to be easily lifted with the hand, an opening just above the level of the grate should be made for introducing fuel to the fire, which opening must be closed by a close-fitting stopper or door. In fireplaces constructed for small stew-pans this opening may be omitted, and the fuel be introduced through the opening into which the stew-pan is fitted, by removing the stew-pan occasionally for the purpose.
4. All portable stew-pans should be circular, and suspended in their fireplace from the circular rim. The best form for large fixed boilers is an oblong square, broad and shallow rather than narrow, and deep, and it should be of thin metal.
5. All boilers and stew-pans should be fitted with covers to render them well adapted for confining the heat. The best arrangement is to make the covers of thin sheets of tinned iron, and double, that is, with an air space between the outer and inner cover.
We have, during the last twenty years, introduced, as a rule, close ranges. They are certainly cleaner and more convenient for cooking, and, if great care is exercised in the use of the dampers, they will be found more economical than open fires. But, as a rule, they are based on the principle of making one fire perform a variety of operations. Independently of the question of a combined fire, as compared with the separate fires advocated by Count Rumford, a consideration of the form of modern kitchen-ranges will show that most of the principles laid down by him have been entirely neglected. The doors of the fireplace and ash-pit seldom fit close; the boilers are rather deep and narrow than broad and shallow; the use of the hot-plate prevents the stew-pans from being suspended from the rims for the fire to play round them; the use of double covers for saucepans and boilers is rather a rarity than a usual arrangement.
To realize the question of economy of fuel, it is necessary to consider, in the first place, what a given quantity of fuel is capable of doing. As regards hot water, if water is kept at a temperature of 200°, or from that to 210°, the gases from the fire can, after communicating the heat to the boiler, pass off into the chimney at a temperature of little beyond that point; but, if the water be allowed to boil, in the first place a large amount of latent heat is absorbed by the steam, which is lost if the steam passes off into the air or the chimney, and, in the second place, it will be found that the gases, after they pass off from the boiler, will have a temperature of as much as 300°, 400°, and even 500°. Unless, therefore, water is required to be actually boiling for use, if the water is permitted to boil, a great quantity of heat is wasted up the chimney. For household purposes it is never necessary that the water in the boiler should exceed 200°. Tea, to be good, should be made (as clearly shown by Mr. Francis Galton in his "Art of Travel") with water of a temperature of from 180° to 200°. Very few culinary operations require the water really to boil, and, when boiling water is wanted, it is required in a saucepan standing on the fire. All operations of cleaning, etc. (except washing clothes), require water at a very much lower temperature than 212°. If, however, water at a higher temperature is wanted, it can be supplied up to about 230° without the generation of steam, by heating it under pressure; this can be attained by having a close boiler fed from a cistern placed at the top of the house. For the preparation of preserves and some other cooking operations, such a system is most convenient.
One pound of coal should raise from fifty to sixty gallons of water from 45° to 212°, and, when raised, very little fuel is required to maintain it, in a properly-constructed boiler, at that temperature. The total amount of water, at such a temperature, used daily, in an ordinary middle-class house, does not exceed thirty or forty gallons, and, therefore, if the boiler were made so as to absorb as much heat as possible, the hot water used in an ordinary middle-class house, with a family of ten or twelve persons, ought not, with thorough economy, to consume more than one-sixth of a ton of coals in the year. Count Rumford shows in his treatise that 25 lbs. of bread ought to be baked with one pound of coal, and that 100 lbs. of meat should be cooked with 2¼ lbs. of coal. If, therefore, we fully utilized our fuel, it is clear that, in the preparation of our food and hot water for domestic purposes, ½ lb. of coal per head of the population ought to be a sufficient daily allowance, which would be equivalent to one-twelfth of a ton per annum, and in large households even less than that quantity ought to suffice. I do not suppose that we should ever attain to this minimum of consumption, but it is well to consider what the standard is, so that we may not rest satisfied till it has been much more nearly approached than hitherto.
Economy has, as I before observed, latterly been sought in combined apparatus. Where large numbers of persons have to be cooked for, and where, consequently, a carefully-constructed apparatus is always worked to its full extent, the results which have been obtained show a very moderate consumption of fuel; but the same apparatus, when used for smaller numbers of persons, gives results not favorable to economy.
The boilers in use in barracks, when I first took up the question, required from 16 ozs. to 20 ozs. of coal per head to supply water for breakfast and tea, and washing up, and to make soup for dinner for fifty or sixty men. The boilers I introduced would perform the same duty with from 3 to 4 ozs. of coal for each person cooked for, provided the number amounted to fifty or sixty persons. The ovens for roasting, which I introduced into barracks, would roast and bake with 1 oz. of coal for each person cooked for, when cooking for the full number for which the oven was designed, and for such numbers as 200 to 400 persons; smaller ovens would require 2 ozs. per head when cooking for 50 men. Of course, to produce these effects, great care was required.
Messrs. Benham introduced cooking apparatus which, when cooking for the full number of 300 soldiers, would perform the total daily cooking and supply of hot water in barracks, with from two to three ounces of coal per person cooked for.
Captain Warren constructed an apparatus to boil, bake, steam, roast, and fry, and provide hot water, which, when cooking for about 100 men, required somewhere about 2¾ ozs. for each person cooked for, but, when cooking for forty men, required 6 oz. per head, and when cooking for sixteen men the average of several days amounted to 9 ozs. or 10 ozs. per man cooked for, but on one or two of these days the consumption did not exceed 5 ozs. for each person cooked for.
These apparatus supplied to the men all the cooking and hot water necessary. The results show what degree of economy has been reached in ordinary practice with soldiers, who are not proverbial for care, and what, therefore, should be the standard of economy to which we have a right to expect to attain. No doubt, private houses containing sixteen persons might require more hot water or more cooking, but according to these facts, as to ascertained consumption of fuel, the expenditure of fuel in the kitchen for a family consisting of sixteen persons might easily be reduced to 1½ or 2 tons per year, and in all these apparatus further elements of economy remain to be developed.
The conclusions, however, to which I have been led in my consideration of this question, are, that with these apparatus, and, indeed, with all kitchen-ranges in use, the waste of heat lies in the number of functions the fire has to perform. It must warm water, it must heat the oven, it must stew, and grill, or toast, and sometimes roast at the open fire, and each of these processes requires a different condition of heat. Hot water requires a temperature of 200° to 210°, a roasting-oven of about 450°, a baking-oven probably 350°; grilling is performed on a clear flame, the temperature of which is probably 1,300°. Now, when the fire is in an efficient condition to perform one of these functions, it is also in an efficient condition to perform the others, and, although, by means of dampers, it may be somewhat checked in the performance of its full functions in certain directions, there is no doubt that an enormous amount of heat is wasted through the agency of those parts which are not wanted to be in operation. When the oven is not wanted, it is affording a means for the heat to escape rapidly, especially if ventilated as a roasting-oven. The boiler is supplied with heat beyond its requirements, and generally abstracts a large quantity of spare heat, which passes off in the shape of steam. I assume that the cook closes the dampers in order, as far as possible, to limit the action of the fire when cooking is not going on, but in practice this is difficult to insure. With these combined apparatus, the fuel consumed will be in proportion to the various operations which the fire is arranged to perform, and not in proportion to the limited work required when only one or other of the operations is wanted. When, for instance, the fire is only wanted to heat water, a great waste of heat will be going on, from the heat passing off from the oven, hot-plate, and front of the fire. For this reason, the combined apparatus can never be so economical in fuel as separate apparatus; while, however, apparatus of this class, if not very carefully worked, waste fuel, they, to some extent, save trouble to the cook.
I have already mentioned several points of detail where fuel could be saved in our kitchen-ranges, viz., by great attention to the close fitting of the ash-pit and fire-grate doors, the use of double covers to saucepans and boilers, the use of sand on the hot-plate to prevent the escape of so much heat from that part; and, beyond these, an important point in securing economy is the separation of those culinary processes which require different gradations of heat. The three main parts of the ordinary cooking apparatus are the oven for baking and roasting, and the boiler, and the hot-plate. If the boiler is to be of the form most effectual in saving fuel, the flame and gases from the fire should play under and round every part of it; the water should be kept at something under 212°, so that the gases, after leaving the boiler, may not enter the flue much above that temperature, and, inasmuch as that is a higher temperature than is necessary for the purpose of producing a sufficient draught in an ordinary chimney, the heat in these gases should be still further utilized. In the first place, they should be used to warm the water which will be required to replace what is drawn off from the boiler; and, in the second place, an economy can be obtained by employing the gases, which pass off into the chimney at a temperature above what is required for creating an efficient draught, to warm the air supplied to the fire for purposes of combustion. The experiments which I have made on the supply of warmed air to feed the fire have, unfortunately, not been worked out sufficiently to enable me to give them in a clear form with exact results; but an economy of from six to nine per cent, might be obtained from this source.
Then, as regards the oven. The baker's oven, of fire-brick, in which the fire is made inside the oven, and the whole heat retained in and reflected back from the sides and top and bottom, is a very economical instrument when in continual use. With iron ovens, attached to a kitchen range, the case is different. An oven which roasts requires a temperature of from 400° to 450° at least. Therefore, to maintain this temperature, the gases must pass off into the flue at a temperature even higher; when the oven is a roaster, a considerable volume of air is being continually passed through it to carry off the steam from the meat. This air, if admitted cold, as is the case with many ranges, acts so as to cool down the interior, and therefore additional fuel has to be consumed to counteract this cooling-down process. Now, however good may be the conducting power of the material used for ovens or boilers, a coating of soot diminishes the conducting power very rapidly, and consequently the temperature of the flue conveying heat to the oven will always exceed that of the inside of the oven. It is, therefore, of great importance to remove any causes which tend to lower the inside temperature. Hence it is desirable to utilize some of the heat which passes off, at above 450°, into the flue, for the purpose of raising the temperature of the air to be admitted into the oven. As a general rule, however, and except in some apparatus, under present arrangements all this heat is wasted, and it certainly cannot be utilized properly so long as one fire is retained to perform so many separate operations.
The hot-plate is the third important part of the modern close cooking-range. Count Rumford proposed that the top of a hot-plate should be covered with sand, and the sand cleared away only under the saucepans. In its present shape, the hot-plate wastes an enormous amount of heat. It is wasteful, because it radiates the heat largely; because the application of heat to the saucepans is only through the bottom of the saucepan, and the bottom of the saucepan is not always in immediate contact with the flame, but is frequently allowed to receive the heat through the medium of the cast-iron hot-plate, which is a very moderate conductor of heat. Just consider what the difference of effect is. The heat of the flame, if directly acting on the bottom of the saucepan, would be 1,200° Fahr., but, unless the hot-plate is red-hot, probably not above 450° will pass through, but the heat in the flue which heats the hot-plate will be at 1,200°, and the spare heat from the flame will be wasted up the chimney. The hot-plate should be dispensed with, if economy is to be made paramount, and charcoal burners substituted for it. Where gas is available, the hot-plate can be dispensed with without extra trouble to the cook. The gas-burners should be properly protected in sunken holes, with side of fire-clay, and the saucepans should be dropped into the holes, so that the full effect of the heat shall be concentrated on them and round their sides, and the gas should be only kept lighted so long as the operation to be performed is going on. It may be assumed that one pound of coal is equivalent to from 28 to 30 cubic feet of gas; hence, as permanent fuel, gas would not be economical; but the simplicity of its application makes it a very convenient fuel in cooking, and economy is obtained from its use, because the full effect of the combustion can be utilized as soon as the gas is lighted, the flame can be regulated to any required extent, and the gas be extinguished as soon as the required operation is performed.
I have endeavored to enumerate, briefly, the economical conditions which should regulate the consumption of fuel for domestic purposes. By economy it is meant that, while all necessary operations of warming and cooking continue to be performed, the fuel employed should be utilized to the utmost. In the kitchen, the daily consumption of fuel, in small establishments, should not exceed half a pound of coal for each person cooked for, and in large establishments the proportion should be smaller. In the consumption of fuel for warming, so many conditions have to be considered that no standard can be laid down beyond the broad fact already stated—that one-sixth of the coal we commonly now use would suffice for all our requirements if it were properly utilized. I do not, however, anticipate that much progress will be made in economy, unless the price of coals should remain at a figure which will induce the householder to make himself thoroughly acquainted with the principles on which the apparatus for warming and cooking should be constructed and worked; for there is no apparatus which can be invented which will not depend, to a considerable extent, on the manner in which it is attended to.
The principal conditions which I have enumerated have long been known. There is an old saying in South Staffordshire, that "he who lives longest must carry coal farthest," and, acting on this, we have, year after year, simply wasted millions of tons of coal in our domestic fireplaces, because the coal was provided at a small cost, and we have had no thought for posterity.
George Stephenson once said, very happily, that coal represented the accumulated rays of the sun laid up in store in by-gone days. When this store is gone, the world will have lost the most convenient and economical means of generating heat. It is, therefore, a duty, which every man owes to posterity, to do his utmost to husband this great store.
I have endeavored to do my part by explaining the conditions which should govern the arrangements devised for regulating the consumption of fuel for domestic purposes. It remains for the public to insist on having these principles applied to the various apparatus which they adopt.—Journal of the Society of Arts.