REDUCING TEMPERATURE OF FLUE

PRODUCTS.

Without considering yet any change in the assumed thermal efficiency of the coal heater, which efficiency represents that obtainable when operating the coal heater under the most favorable conditions, it will be well to see what saving could be effected in the gas installation by a reduction in the temperature of the flue products. We have already seen that a strong draft is not essential for the operation of the gas heater and as the draft is a function of the flue temperature, it will be perfectly safe to reduce this temperature to a relatively low point. Gas heater installations have been successfully operated with stack temperatures of 140°, this reduction having been obtained by the use of an economizer located in the uptake. If, in our problem, the flue temperature were reduced to 140° by the use of the accessory just noted, an hourly saving of 10,599 B.T.U. could be effected, which represents 3.96% of the total energy in the fuel. At 140° we are nearing the dewpoint of the products, which, it will be noted is 118°. If the water or gas entering the economizer is less than 118° some of the moisture may be condensed, the amount so condensed depending on the incoming temperature. Supposing that 50% of the water vapor could be condensed at 140°, then about 9,060 B.T.U. would be transferred to the economizer, the greater part of this heat resulting from the recovery of the internal energy of evaporation. This would represent a saving of about 3.4%.

An economizer could be usefully employed for preheating the return water in a hot water system or preheating the air in a hot air system. It would hardly be warranted in the steam system owing to the relatively high temperature of the returned condensation. It might be economically employed in any of the three systems for heating hot water for general household purposes.

In passing, it may be noted that at 140° and with 50% of the moisture condensed the potential draft would be 0.1 in. of water. The overall thermal efficiency of the installation would become equal to about 82%.

If now, the radiation loss, by the use of good lagging can be reduced to 6%, and the flue loss be maintained at 6% by the use of an economizer, as just noted, the saving effected by the economizer would increase to about 13% and the overall thermal efficiency to 88%.

The 55% thermal efficiency assumed for the coal heater, it must be remembered, is high, and as stated above represents the efficiency obtainable when operating the heater under the most favorable conditions. The average efficiency would be more nearly 40% and as low as 25% when operating the heater at low capacity. With a 40% efficiency the hourly fuel cost of the coal heater in our problem would increase from 8.4c to 11.6c, which, compared to the hourly fuel cost of the gas heater at 85% efficiency, would give the following ratios:

experience shows best, and that a committee on house heating design and installation be appointed by the Institute to co-ordinate the work of the members

and co-operate with the similar committee of the National Commercial Gas Association for the furtherance of this work.)

Notes on Warm Air Furnace Heating.

By Jesse M. McHenry.

This paper dealt with the moderatelysized gravity furnace system for heating the average home. Mr. McHenry stated that technically-trained heating and ventilating engineers have heretofore withheld approval of this system but he stated that there was a growing interest in this system being shown by engineering colleges. Mr. McHenry

endorsed the formula and rules for installation of warm air heating, issued by the National Warm Air Heating and Ventilating Association. He then presented the results of several furnace tests made to determine the efficiency and the causes of heat loss. Efficiencies were obtained running from 64% to 87%. The latter figure was obtained with a 25-in. diameter firepot, burning 5 lbs. of coal per hour. The tests demonstrated, said Mr. McHenry, the wisdom of using furnaces of generous proportions. Under forced circulation, the efficiency was 3% higher in one case, 2% in another and 5% in a third.

In the tests for radiation losses, the losses from the outer casing were found to be negligible, provided the cold air supply is adequate and a reasonably low rate of combustion is maintained. The chimney losses test showed that they may be reduced slightly by doubling the fire travel, with the requirement of only 0.01 in. (water) increased draft pressure.

Some notable results were obtained in tests on the use of extended surfaces to the fire pots. It was found that the frictional resistance due to the presence of the extensions restricted the air velocities, and lowered the efficiency, instead of increasing it. The extensions were

set radially, and in the opinion of the author, are of very doubtful value.

Windows.

By Dr. E. Vernon Hill.

In this paper Dr. Hill reviewed the history of window design and construction and showed that windows were in use in ancient Egypt, at least on the second floors of buildings, but without glass or other protection. That they

were also used by the Greeks and Romans is known to be a fact. Instead of glass it was customary to use pieces of colored glass. Dr. Hill then took up modern window construction from the standpoints of first cost, care and upkeep, loss of wall space, admission of flies and other insects, admission of dirt, weakening of walls and injury to building, entrance for burglars, increase of heat loss, interference with mechanical ventilation, increased liability to fire and fire panic and nuisance from noise. Under the last heading he showed that in office buildings in the congested districts of large cities, the noise from electric cars, passing trucks, etc., entirely prevent the use of windows for ventilation on the first, second or even third floors. This is also a serious objection in the cases of hospitals and schools. Dr. Hill spoke at length of the window requirements of factories and workshops, this part of the paper being accompanied by illustrations of typical designs. He stated that pending further development of artificial illumination, natural light for these buildings is to be preferred. He predicted that in the years to come all workrooms, salesrooms and rooms open to the public below the second story above grade would be compelled to be properly ventilated and the air washed and purified.

or 15 High

72-Methods of Heating Portable Build

ings.

QUESTION: Can you suggest a method of heating portable hospital units, such as are used in connection with military camps?

ANSWER: There are several methods that might be employed which are along the line of car-heating devices. One is the Baker hot water car heater, shown in Fig. 1. This has been used successfully for years in heating railroad coaches when they are left on sidings or on branch roads for long periods without connection to the locomotive. A notable example was in connection with the trains on the Brooklyn Bridge, when the cars were operated by cable. The boiler or heater is set on the same level as the coils and the supply pipe is carried through the roof, with a small expansion tank and pop safety valve set at 15 or 20 lbs. The supply pipe is taken from the expansion tank and these two pipes, A and B, give the difference in head

FIGS. I AND 3-BAKER HOT WATER CAR HEATING SYSTEM AND PETER SMITH CAR HEATING SYSTEM.

to circulate the water. The return is taken to the boiler which is nothing more than a coil of pipe in a stove.

O could be burned instead of coal, with burners similar to those used in the Detroit vapor stove. These burn either oil or kerosene. The firepot, when burning oil, should be filled with broken firebrick so that the high-temperature flame from the oil could be properly utilized. In the sketch a coil is shown, but if the weight were a considerable item in transportation, sheet metal radiators

temperature, up to 5 or 10 lbs. and a corresponding temperature of 227° to 250° F., so that the heating surface could be comparatively light in weight, especially if sheetmetal radiators were used.

Fig. 3 shows a scheme of heating used by the trolley cars in Detroit, made by the Peter Smith Heater Co., which is nothing more than a stove with a small motor and blower on top. The air is blown over the firepot and passed under the seats, recirculating the air of the car. As applied to the case in hand, firebrick could be placed in the firepot and gasolene or kerosene used with a Detroit vapor stove burner. The air-distributing pipes could be collapsible by making them of canvas or sheet metal, with the air distribution overhead.

Of course, this would require electrical current, but with the automobile engine available, a small portable plant could be rigged up to light the whole camp and take less bulk fuel than if torches or lamps were used. Such lighting plants are available in the trade.

The coils would probably be too bulky and weigh too much to transport. The Peter Smith, rig, however, should be very efficient and not of very great weight or bulk. Several of these rigs could be used, as desired.