of time the different outdoor temperatures occur from the weather bureau reports. The 73% area represents the power recovery in pounds of steam at full vacuum or the saving is 73% of the heating steam.

The lines 26 in., 27 in., and 28 in., are the increases in steam due to apparatus design for the lower vacuums which show the more economical the power machine the less the saving in fuel by utilizing exhaust steam for heating. In this case, the cost of utilizing 75% of the heating in exhaust steam is 30% of the power, or live steam has to be added to utilize exhaust steam for the heating.

Note the actual variation of the power load is slight. It is constant for 57% of the time (lines 26 in., 27 in., 28 in. vacuum) and in the warmer periods above 45 deg. the increase in steam rate for proper heating temperature is not over 2 lb. per kw-hr. or less than 10%, so it is not serious. The degree of regulation obtained on the heating system, as a whole, reduces the total steam over ordinary methods so that in most cases less coal would be burned for heating and power than would be used where the apparatus receives no attention, when outside temperature changes occur. Under ordinary conditions when the temperature drops, it is several hours before the rooms or apparatus is affected and when the outdoor temperature rises, sometimes a day or two is needed before the system can be adjusted to the changed condition.

Where the heating medium is regulated by the outside temperature at a central point, these weather changes are met long before the buildings and rooms are affected, thus tending to the economical use of heat and greater comfort. The 46% area is the recovery of power by use of a bleeder turbine. This machine to operate successfully would have to be at least twice the capacity of the steam bled, this case 8000 to 10,000 kw., and might be larger than the maximum power requirements of the plant. The power recovery would be at the non-condensing steam rate.

If the steam were used on a non-condensing engine or turbine it is readily seen that the wide variation in load due to the constant steam rate would never be met with a single unit. If the average load were balanced, at 30-deg. F. outside, steam would pass to the atmosphere at temperatures above 30 deg. F. and live steam would be necessary at temperatures below 30 deg. F. The actual power recovery would not be more than 25%.

River or natural cooling water is not obligatory for the success of this system, as cooling towers may be used with equal economy and the savings are more than sufficient to warrant their adoption. They would operate 12 mo. and divide the condensing load with the heating system in winter.

In the middle west the industrial plant situation is in a deplorable condition as far as heating and power are concerned. Although the steam is generated from the fuel generally with good economy, the waste is criminal when applied to power and heating. The policy of the manufacturers is against spending any money for plant improvements that require a term of years to amortize the interest and principal with a saving in operation. The money makes a better showing with the stockholders distributed as dividends.

The fuel in some of these plants amounts to $250,000 per year, but the total expense of power and heating is only 3 or 4% of the total cost of the manufactured article.

One plant the writer investigated is using 10 lb. of coal in the plant for each kilowat hour generated at times and the average is 6 or 7 lb. A saving of 25,000 tons per year could be made in this plant on an investment of $500,000 It is in addition, exhausting 12,000 tons per year to the atmosphere from steam hammers, and purchasing $65,000 worth of current for a motor generator 20 ft. from the boilers and out board exhaust head. The 12,000 tons of coal on a low pressure turbine after leaving the hammers would exactly wipe out the $65,000 current expenditure with no fuel to purchase. This saving totals $250,000 a year conservatively calculated and would cut out the operation of 5 boilers or 2000 hp. in a separate plant with all attendant expense. The operation of this plant is notorious among engineers, but it is impossible to persuade the company to take action. Their yearly records showed a continuous increase in the kilowatt rate of about 1 lb. of coal per kw.-hr. per year with an increase in power load. It is with the idea that attention may be brought to manufacturers of the possibilities of remedying these wastes, that this section is given.

18. Comparison of Heating Systems.-The efficiency of any medium of transmission as steam, water, or air depends solely on the physical characteristics of the medium and not on any so-called trade name.

The universal question of "What is the best system" may be answered by stating that a building can be heated with equal satisfaction by any of the methods, and any system may prove unsatisfactory if it is designed, installed, or operated improperly.

The same building was used as a problem to work out different methods and types of apparatus and these principles apply to all cases regardlesss of size or type. The same boiler and chimney capacity is required in all the cases and the accompanying table gives the results based on the different assumptions. However, the greater the rapidity of the movement of the fluid through the boiler, the less heating surface required for the same capacity. The conclusions drawn from the table and problem may be stated as follows:

1. Radiation has nothing to do with the size of the boiler unless accompanied by the temperature of the room and the medium. The heat loss of the building is the actual work to be accomplished.

2. The cost of the plant depends on the amount of radiation which in turn is determined by the average temperature of the steam or water. The lower the working temperature, the more costly the plant.

3. There is practically no difference in the use of steam or water as far as temperatures are concerned and the limits of their application, except that water has a lower and wider temperature range than steam.

4. Raising the pressure on a steam system increases the carrying capacity very rapidly due to the increased density of the steam (from atmospheric pressure to 10 lb., it is increased about 30%).

5. Size and lack of capacity (in the chimney) are more often the cause of unsatisfactory heating than the type of system (see chimney, boiler, radiation).

6. In all mechanically circulated water systems the rapidity of circulation is independent of the temperatures of the medium. This is not true of gravity circulation, as the height of system and drop in temperature are factors in the determination of the velocity. The average heating temperature is effected as the drop is increased.

7. All mechanically circulated water systems are independent of all grades or distances, as the power is applied externally.

8. The wider the possible range in average temperature of the heating medium, the better regulation and possible economy. Moderate temperatures below 210 deg. F. are the most desirable working temperatures for both steam and water.

9. Air removal is necessary for all steam systems, either through the return with the condensation or through a separate air line. Mechanical methods by pumps are the most satisfactory.

10. The thermostatic traps required on all vacuum systems require cleaning periodically. This is a considerable item in the upkeep of this type of system. Their initial cost should be an item of comparison as they are absent

on hot water systems.

11. Due to the constant temperature of the medium on steam systems, risers and mains necessitate the use of covering. This is unnecessary on water systems where the medium for the entire system may be changed in temperature to suit outdoor requirements thereby lowering the required temperature of the circulating medium. Covering is sometimes used to prevent the discoloration of plaster due to dirt collecting along the line of pipe due to convection and movement of air caused by the heated pipe.

19. Selection of a Heating System.-The selection of a system of heating for a building or group resolves itself into two parts:

1. The type of heating surface whether direct, indirect, or a combination of the two. 2. The medium of transmission-water or steam.

As either medium may be used with any or all types of heating surface, the latter being determined by the utilitarian purpose of the building, or arbitrarily by the desires of the owner, the engineer is mainly concerned with the type of transmission system.

This should be decided entirely on the basis of comparative first cost of installation and operating expense. Where the items are nearly balanced the choice may hinge on other minor disadvantages or advantages of water or steam (liability to damage from bursting or freezing) concerning possible accidental damage which occurs seldom and is generally due to ignorance or careless manipulation.

The reductions in opera

Consideration of this type of objection should be from the viewpoint of the actuary. ting or first cost should be weighed against the probability of the amount of damage occurring over a term of years. In small plants where the boiler is in direct circuit, either vapor steam or gravity will work out about equally advantageous, until the plant reaches about 3000 sq. ft. capacity. Then forced hot water with a pump and boiler directly in the circuit deserve consideration. The larger the capacity of the plant, the greater the advantage in the first cost of the forced hot water system.

The vacuum valves and their upkeep should be balanced against the pump and cost of current in arriving at a decision.

TABLE 20A.-APPROXIMATE RELATIONS OF OPERATING AND INSTALLATION COSTS OF DIFFERENT METHODS OF HEATING BUILDINGS

In all plants of this character where there is only live steam operation and no exhaust, the operating expense will be about the same, the difference being in the lower first cost of the mechanically circulated water arrangement over the vacuum steam arrangement.

When it is desirous to use exhaust steam for heating at atmosphere up to about 300 hp., and there are no long distances, the vacuum steam is available, without change. Steam boilers have to be substituted for water boilers and additional heaters for exhaust steam added to the forced hot water arrangement.

There is no limit to the size of the building or its purpose that will weigh one way or the other in the decision between water or steam, as these matters are covered in the type of heating surface which would be common to either. First cost and operating expense will determine the best selection.

We come now to groups of buildings heated from a central plant. There are three methods of transmission: (1) High pressure steam with vacuum steam in each building served through a reducing valve, (2) vacuum steam for mains and entire system, and (3) hot water forced circulation.

Institutions where the power load is much less in proportion than the heating requirements, may be handled according to (2) for the nearby buildings utilizing exhaust, and by (1) by those further away.

High pressure steam distribution due to small diameter of main required will prove the most economical method of heat transmission, and by regulating the pressure on a small main and utilizing the drop the steam may be transmitted with a minimum loss of condensed water from the pipe. Exhaust steam, however, cannot be used on a system of this kind.

Low pressure steam, due to the large diameter of pipe necessary and constant operating temperature of the steam, is the most expensive method both for operation and cost of installation. Exhaust steam can only be used at atmospheric pressure or slightly above, and when live steam is necessary at periods of no exhaust, the economy is reduced. Grades have to be carefully observed and traps and drips provided with possibly power pumps to handle the condensation.

Hot water forced circulation enables exhaust steam below atmosphere or live steam to be used with equal facility as no steam is taken outside the power house. The radiation loss from mains is greater than for high pressure steam but not as great as the vacuum steam system. All drips, traps, and vacuum traps are eliminated. Condensing turbines may be used and the power recovery from the heating steam for plants over 500 hp. will make this arrangement preferable over any other by a wide margin and the first cost will be no greater than the vacuum steam and possibly less.

The type of radiation effects the cost independent of the system of transmission as follows:

1. Direct radiation generally costs less for operation and installation than indirect.

2. The lower the temperature of the circulating medium, the more surface and greater cost of any type of radiation.

3. Blowers and direct radiation in conjunction cost somewhat more than either alone, but the flexibility is increased and lower temperatures and more satisfactory heating result, with greater economy in the use of heat.

4. The larger the building or plant, the greater the difference in favor of mechanically circulated systems, both from the standpoint of first cost and operating expense. Table 20A is an attempt to classify what is best and the order in which the combinations will work out both from an operating and installation standpoint. This is the writer's judgment from an experience of many years-the 1, 2, 3, etc., and the A, B, C, etc., respectively give the order of the combination as they increase in cost and operation. The experience and ability of the engineer and contractor have considerable to do with the results and in many cases the order will be reversed. The whole is subject to the foregoing discussion.

VENTILATION

20. Quantity of Air Necessary.-Ventilation consists briefly of all the artificial air conditioning necessary to maintain the air inside of a building in a condition desirable for certain purposes, such as for breathing or for making it suitable for given manufacturing processes, and at such standards as may be regarded as desirable.

The most common form of ventilation is that used to furnish an air supply or an air exhaust for the occupants of a building and to keep the interior air from becoming foul-also remove objectionable odors, such as in kitchens, restaurants, and toilet rooms.

In past years the amount of carbonic acid in the air has been used to determine the comparative degree of purity even though it has been understood that carbonic acid itself is not dangerous. This is because pure air seldom contains over 4 parts of carbonic acid in 10,000, while in exhaled air the number of parts rises rapidly and almost proportionately with the other impurities. Therefore, a statement of the amount of carbonic acid present in a given sample of air, a measurement comparatively easy to make, may also be taken as indicative of the amount of other impurities.

Each person gives off about 0.6 cu. ft. of carbonic acid per hour. If the fresh air entering a room has 4 parts of carbonic acid in 10,000, and the limit in the room is desired to be kept below a certain number of parts, the number of cubic feet per minute per occupant must be not less than as follows:

While these are the theoretical amounts of air required, some consideration must be given to the quantity of air contained in the room at the beginning of its occupancy, and also to the length of time the room is occupied. Thus, a church where the services are short and the volume of fresh air is large at the beginning requires less air for ventilation than a moving picture theater running continuously for 10 hr. a day and usually in more or less cramped quarters. The quantity of air necessary for ventilation is measured in cubic feet per minute per occupant or in changes of air per hour. Table 21 shows the cubic feet per minute (C.F.M.) per occupant or the number of changes of air per hour.