Mechanics of the Household. E. S. Keene
href="#fb3_img_img_ecb8b7a1-9902-5784-930d-31fce780b68d.jpg" alt=""/>
Fig. 28.—Dining-room radiator containing a warming oven.
In the use of the direct or the direct-indirect method of heating the principal object to be attained is that of ventilation, but quite generally the passages are so arranged that the air may be taken from outdoors or, if desired, the air of the house may be sent through the radiators to be reheated. In extremely cold and windy weather it is sometimes difficult to keep the house at the desired temperature when all of the air supply comes from the outside. Under such conditions the outside air is used only occasionally. In mild weather it is common to use the outdoor air most of the time. The cost of heating, when these methods are used, is higher than by direct radiation, because the air is being constantly changed in temperature from that of the outside to 70°.
Fig. 29.—Ventilation by the indirect method of heating.
Fig. 30.—Ventilation by the direct-indirect method of heating.
Radiator Finishings.
—In steam and hot-water heating the decoration of the radiators is a much more important item than that of a good-looking surface or one which will harmonize with the setting. Until recently radiator finishing has been considered a minor detail and the familiar bronze has been looked upon as a standard covering, while painted radiators were considered only a matter of taste. The character of the surface is, however, the determining factor in the quantity of heat given out by radiators. This has been determined in the experimental laboratory of the University of Michigan by Professor John A. Allen. Comparison was made of bare cast-iron radiators with the same forms painted as indicated in the following table. The bare radiator was taken at 100 per cent.; the other finishes are expressed in per cent. above or below that of the bare radiator.
| Condensing capacity, per cent. | |
| No. 1, a cast-iron radiator, bare as received from the foundry | 100 |
| No. 2, a cast-iron radiator, coated with aluminum bronze | 78 |
| No. 3, a cast-iron radiator, three coats of white enamel paint | 102 |
| No. 4, a cast-iron radiator, coated with copper bronze | 80 |
| No. 5, a cast-iron radiator, three coats of green enamel paint | 101 |
| No. 6, a cast-iron radiator, three coats of black enamel paint | 101 |
The author has stated further that, “It might be said in general that all bronzes reduce the heating effect of the radiator about 25 per cent. while lead paints and enamels give off the same amount of heat as bare iron. The number of coats of paint on the radiator makes no difference. The last coat is always the determining factor in heat transmission.”
PIPE COVERINGS
All hot-water or steam pipes in the basement and in other places not intended to be used for heating should be covered with some form of insulating material. At ordinary working temperature a square foot of hot pipe surface will radiate about 15 B.t.u. of heat per minute. To prevent this loss of heat and the consequent waste of fuel the pipes should be covered with some form of insulating material.
Pipe coverings are made of many kinds of material and some possess insulating properties that may reduce the loss to as low a point as 15 per cent. of the amount radiated by a bare pipe. Many good insulating materials do not give satisfactory results as pipe coverings because they do not keep their shape, some cannot be considered in the average plant because of high cost.
Wood-pulp paper is extensively used as a cheap covering; it is a good insulator and under ordinary conditions makes a satisfactory covering. A more efficient and also a more expensive covering that is extensively used is that made of magnesia carbonate and known as magnesia covering. Aside from these, other forms made of cork, hair-felt, asbestos and composition coverings are sometimes used in house-heating plants.
In selecting a pipe covering, there should be taken into account not only its insulating properties but its ability to resist fire, dampness or breeding places for vermin. It rests entirely with the owner whether he covers the pipes with a combustible or an incombustible material when the insulating properties are about the same. Coverings made of animal or vegetable materials under some conditions furnish a breeding place for vermin.
Pipe coverings are made in sections about 3 feet in length and from 1 to 13⁄8 inches in thickness. The sections are usually cut in halves lengthwise to permit being put in place. The sections are covered with common muslin to keep the material in place and sometimes are painted after being installed. Painting has nothing to do with their insulating capabilities, but it preserves the cloth and makes a neat appearance. The sections when put in place are secured by pasting one of the loose edges of the cloth to the surface. The ends of the sections are bound together with strips of metal. Fig. 31 shows the appearance of the pipe when the covering is in place.
Fig. 31.—Pipe covering.
Irregular surfaces like the body of the furnace, pipe connections, etc., are insulated by coverings made from a plaster that is made expressly for such work. It is known as asbestus plaster. The plaster may be purchased in bulk and put in place with a trowel. As it is found in the market the plaster requires only the addition of water to put into working form.
The value of a pipe covering is not in proportion to its thickness. Experiments with pipe coverings have shown that a thickness of 13⁄8 inches will reduce the radiation 90 per cent., but doubling the thickness reduces the loss only 5 per cent. It, therefore, does not pay to make a covering more than 13⁄8 inches thick.
Vapor-system Heating.
—This system of heating is not greatly different from the steam plants already described but it is operated under conditions which do not permit the steam in the boiler to rise beyond a few ounces of pressure. Since the plant is intended to work at a pressure that is scarcely indicated by an ordinary steam gage, it has been termed a vapor system to distinguish it from the pressure systems which employ steam, up to 5 pounds or more to the square inch. The heat is transmitted to the radiators in the same manner as in the pressure systems. The heat of vaporization of steam is somewhat greater at the boiling point of water than at higher pressures, and the lack of pressure, therefore, increases its heating capacity. This is shown in the table, properties of steam, on page 3. The successful operation of such a plant rests in the delivery of the vapor to the radiators at only the slightest pressure and the return of the condensate to the boiler without noise or obstruction to the circulation at the same time ejecting the contained air.
The excellence of the system depends in the greatest measure on good design and the employment of special facilities that allow all water to be discharged from the radiators and returned to the boiler without accumulation at any part of the circulating system. It requires, further, the discharge of the air from the system at atmospheric pressure. The system is, therefore, practically pressureless.
Various systems of vapor heating are sold under the names