Price of Coal.
—The value of coal as a fuel will depend on the amount of heat it is capable of producing when burned; its price should therefore be determined by the heating value per pound of fuel as purchased. Secondary determining factors in price are those of convenience of handling and the difficulty in burning the fuel such as the size and uniformity of the pieces, the formation of clinkers, smoke and accumulation of soot. Soft coals, containing a large amount of volatile matter, usually produce much soot and smoke and as a consequence sell for a lower price than coals that produce little smoke.
The selection of fuels will depend on the type of heating plant in use, whether by stoves or by furnaces. If by stoves, whether it is possible to use soft coal as a fuel. The automatically fed stove, of the base-burner type, are usually designed for the use of hard coal and in such stoves the use of soft coal would not be possible. Other stoves and furnaces are usually capable of burning soft coal with varying degrees of satisfaction, depending on the design and surrounding conditions.
The following prices, from the local market, show the usual ratings of various fuels in common use. These prices vary with the locality and somewhat with the season. It is usually possible to purchase coal at some reduction in price during the summer months when the demand for coal is light.
| Hard coal—stove size | $10.25 per ton |
| Hard coal—nut size | 10.50 per ton |
| Semi-bituminous—run-of-the-mine | 9.00 per ton |
| Pennsylvania bituminous—run-of-the-mine | 7.50 per ton |
| Soft coal—Ohio—run-of-the-mine | 7.50 per ton |
| Soft coal—Illinois—bituminous—run-of-the-mine | 7.50 per ton |
| Soft coal—Iowa—bituminous—run-of-the-mine | 7.50 per ton |
| Briquettes-mixture semi-bituminous coal dust | 9.00 per ton |
| Wood (oak), sawed, stove length and split | 8.50 per cord |
The price of coal is determined in many localities by the distance from the sources of supply and the means of transportation. The fact that coals from all of the principal mining areas from Pennsylvania, west to Iowa, are sold at points in the Northwest for the same price, is due in greatest measure to transportation rates on the Great Lakes. The prices of Eastern coals at Duluth are such that in competition with Western coals they are sold at the same price as is shown by the table.
It is usually impossible for the average householder, or even the dealer, to determine definitely the exact locality from which his fuel is mined. Even when such information is obtainable, the quality is still in doubt, unless analysis is obtainable by sample. The data given in the following tables is such as will furnish a fair knowledge of the relative heating values of coals from the principal mining areas of the United States. The data was obtained from a considerable number of authorities but chiefly from the reports of the United States Geological Survey. The different items are not intended to be exact, they merely represent reliable average conditions.
The varying conditions of available heat and percentage of moisture given in the following table are such as to be of little use to those unaccustomed to problems of this kind, unless a systematic method of comparison is made of the different fuels.
Approximate Composition and Calorific Value of Typical American Coals
| 1 Locality | 2 Kind of coal | 3 Number, of samples examined | Moisture | 5 Volatile matter | 6 Fixed carbon | 7 B.t.u. pound per dry coal | 8 Ash |
| Pa. | Anthracite | 12 | 5.05 | 5.52 | 82.54 | 12,682 | 11.53 |
| Md. | Semi- bituminous | 5 | 2.39 | 17.73 | 75.44 | 14,530 | 7.40 |
| Pa. | Semi- bituminous | 15 | 3.60 | 19.26 | 74.46 | 14,211 | 8.32 |
| W. Va. | Semi- bituminous | 12 | 2.50 | 19.00 | 75.70 | 14,758 | 5.24 |
| Ala. | Bituminous | 6 | 3.55 | 29.99 | 59.24 | 13,522 | 10.73 |
| Ark. | Bituminous | 2 | 1.42 | 16.58 | 73.37 | 14,205 | 10.05 |
| Colo. | Bituminous | 6 | 9.89 | 37.34 | 52.53 | 12,325 | 10.32 |
| Ill. | Bituminous | 22 | 10.31 | 36.73 | 50.52 | 11,504 | 12.73 |
| Ia. | Bituminous | 8 | 7.72 | 39.15 | 50.54 | 12,656 | 10.33 |
| Kan. | Bituminous | 3 | 4.25 | 32.20 | 51.17 | 12,031 | 13.75 |
| Ky. | Bituminous | 9 | 5.99 | 34.58 | 56.56 | 13,341 | 8.86 |
| Mo. | Bituminous | 9 | 11.52 | 37.85 | 48.11 | 12,398 | 14.04 |
| Ohio. | Bituminous | 14 | 5.65 | 38.51 | 50.59 | 12,839 | 10.65 |
| Okla. | Bituminous | 3 | 5.72 | 34.83 | 52.76 | 12,648 | 12.41 |
| N.M. | Bituminous | 1 | 12.17 | 36.31 | 51.17 | 12,126 | 12.52 |
| Pa. | Bituminous | 15 | 2.44 | 33.41 | 58.31 | 13,732 | 8.40 |
| Tenn. | Bituminous | 4 | 2.53 | 36.58 | 58.21 | 14,098 | 5.47 |
| Tex. | Bituminous | 3 | 3.84 | 35.05 | 48.99 | 12,302 | 15.96 |
| Va. | Bituminous | 5 | 2.71 | 31.32 | 62.47 | 14,025 | 6.92 |
| W. Va. | Bituminous | 10 | 2.61 | 33.92 | 58.80 | 14,094 | 7.27 |
| Colo. | Lignite | 6 | 19.75 | 45.21 | 45.85 | 10,799 | 8.93 |
| N. D. | Lignite | 5 | 35.93 | 44.33 | 43.21 | 10,420 | 12.45 |
| Tex. | Lignite | 6 | 30.86 | 44.06 | 39.21 | 10,297 | 16.76 |
| Wyo. | Lignite | 4 | 14.71 | 48.47 | 44.49 | 11,608 | 7.035 |
The following table was prepared from the date of that preceding combined with the prices of various coals to be obtained in the local market. The table is intended to present a method of comparing the values of fuels from different coal areas. The consumer is interested to know the amount of heat purchased in the form of fuel. The table shows in the column headed “Heat per $1,” the number of B.t.u. purchased for $1 in coal; the number of available B.t.u. in the different kinds of coal may be taken as a relative comparison of their values as fuel.
The gas-coke in the table is that sold by the local gas company. The amount of moisture in this case is relatively high because of the fact that the coke is stored in a yard exposed to the weather, where it absorbs all precipitated moisture. A less amount of moisture would give a higher value for the same fuel.
| Kind of coal | Price per ton | Per cent., water | B.t.u. per 100 pounds | B.t.u. to evaporate water | B.t.u. per 100 ÷ cost per 100 pounds | Heat per $1 |
| Bituminous Pennsylvania | $7.50 | 2.44 | 1,340,000 - 3,439 = | 1,336,565 ———— $0.375 | = 3,564,000 B.t.u. | |
| Semi- bituminous West Virginia | $9.00 | 3.06 | 1,420,000 - 4,315 = | 1,415,685 ———— $0.45 | = 3,145,000 B.t.u. | |
| Gas-coke | $7.00 | 10.00 | 1,117,900 - 16,888 = | 1,101,012 ———— $0.35 | = 3,145,000 B.t.u. | |
| North Dakota lignite | $4.50 | 35.90 | 668,000 - 50,728 = | 607,282 ——— $0.225 | = 2,703,000 B.t.u. | |
| Bituminous Illinois | $7.50 | 10.31 | 1,032,000 - 14,398 = | 1,017,602 ———— $0.375 | = 2,980,000 B.t.u. | |
| Bituminous Iowa | $7.50 | 13.10 | 1,012,000 - 18,471 = | 994,529 ——— $0.375 | = 2,652,000 B.t.u. | |
| Hard coal Pennsylvania | $10.50 | 3.05 | 1,230,000 - 4,195 = | 1,225,905 ———— $0.525 | = 2,335,000 B.t.u. | |
Semi-bituminous coal commands considerable favor as a house-heating fuel, because of the fact that it burns with much less smoke than bituminous coal. In available heat it is considerably above the Western bituminous coal and it sells at a price $1.50 higher per ton. The reason for the difference in price is not so much on account of its heating value, as because of relatively small amount of smoke produced in combustion. Other coals capable of producing more heat are sold at less price because of smoke and soot produced in burning.
Hard coal at $10.50 is the most expensive coal of all. The ratio of available heat units per $1 for hard coal, as compared with the best soft coal, is as 23 is to 35. This means that at the stated prices those who burn hard coal pay the additional price, because of the physical properties it possesses.
In constructing the above table, 100 pounds of coal was taken as a unit of comparison. The price per ton is that given in the table of local prices. The per cent. of moisture and the B.t.u. per pound of fuel was taken from table on [page 192].
In explaining the method by which the different items were obtained, it will be necessary to discuss briefly the condition of combustion and the heat losses that take place when fuel is burned.
The moisture in the fuel is the undesirable part, because it requires a large amount of heat to dispose of it. It is looked upon as so much water, that must be raised in temperature from that in which it is taken from the coal bin to the temperature and condition of vapor in which it passes into the chimney. When the fuel enters the furnace the water is heated to the boiling point. In changing temperature it absorbs 1 B.t.u. for each pound of water, through each degree of change. Suppose that, as in the case of Pennsylvania bituminous coal which contains 2.44 pounds of water to each 100 pounds of coal, the coal entering the furnace was at 50°F. To raise its temperature to the boiling point (212°F.) required a change of 162°. The 2.44 pounds of water raised this amount
162 × 2.44 = 395.28 B.t.u.
To change the 2.44 pounds of water, into steam at the atmospheric pressure requires 969.7 B.t.u. (heat of vaporization), practically 970 B.t.u. per pound of water. The heat required to vaporize 2.44 pounds of water is
2.44 × 970 = 2366.80 B.t.u.
The vapor is now raised in temperature, to that of the furnace, which we may assume is 1200°F. The furnace being at atmospheric pressure the vapor merely expands in volume as a gas. The specific heat of steam at atmospheric pressure is 0.464; that is, 1 pound of steam requires only 0.464 B.t.u. to raise it a degree, and 2.44 pounds of water will absorb
0.464 × 2.44 × 1200 = 1356.00 B.t.u.
Of this last amount of heat, approximately 50 per cent. is recovered as the gases pass through the furnace. The total loss of heat due to the evaporation of the water is
| Raising temperature from normal to 212° | 395 B.t.u. |
| Evaporation | 2,366 B.t.u. |
| Changing temperature of vapor, less 50 per cent. | 678 B.t.u. |
| ————— | |
| Total heat loss | 3,439 B.t.u. |
In the 100 pounds of coal under consideration, there is 100 pounds, less 2.44 pounds of water, or 97.56 of dry coal, each pound of which contains 13,732 B.t.u. as given by the table on [page 193]. This gives
97.56 × 12,682 = 1,339,753 = practically 1,340,000 B.t.u.
From this quantity is subtracted the loss of heat, 3439.
1,340,000 - 3439 = 1,336,561 B.t.u.
This represents the total available heat in 100 pounds of coal. If this quantity is now divided by the cost of 100 pounds of coal at $7.25 per ton, the result, 3,564,000 B.t.u., will be the available heat bought for $1 as given in column 7 of the table.
CHAPTER X
ATMOSPHERIC HUMIDITY
The physical effect of atmospheric humidity has come to be recognized by all who deal in problems of house heating, sanitation and hygiene. The difference in effect of dry atmosphere, from that of air containing a desirable degree of moisture, is very noticeable in all buildings that are artificially heated. The effect of dry air is made apparent in the average home during the winter months by the shrinking of the woodwork and furniture. The absorption of the moisture from the building which is usually termed “drying out,” causes the joints in the floors and casements to open, doors to shrink until they fail to latch and drawers that have opened with difficulty during the summer then work freely.
Winter time is the season of prevalent colds, chaps and roughness of the skin, not so much on account of cold weather as because of dry air. The skin which is normally moist is kept dry by constant evaporation with the attending discomfort of an irritated surface and the results which follow.
The humidity of the air in which we live and on which we depend for life has much to do with the bodily comfort we derive in existence, and is suspected of being the cause of many physical ailments. Ventilation engineers not only recognize this condition but have found means of controlling it. It is possible to so control atmosphere temperature and humidity of buildings as to produce any desired condition.