CHAPTER XXVIII THE AIR SUPPLY OF THE HOUSE. VENTILATION
Besides the relatively permanent furnishings and fixtures of the house there are other necessaries of civilized domestic life, such as air, water, oil, gas, coal, and provisions, which come into the house only to be consumed, their waste ma- terials being cast out again. These are commonly called the domestic supplies, — air supply, water supply, gas sup- ply, etc., — and they are usually derived from much larger public supplies. which are used in common by many fami- lies. All such public supplies, although convenient, may, under certain circumstances, become dangerous to human life and health.
- The Air Supply of the house is probably more neg- lected than any other. Water, gas, coal, and provisions are costly and often difficult to get, but air is always abundant and cheap. The familiar saying, “as free as air,” applies best, however, to outdoor air; for, as we shall see, good air in houses is not always very abundant, nor always cheap and easy to provide.
Inasmuch as the adult human body requires for its regular uses about five hundred cubic inches of air per minute, the air in the immediate vicinity of the nose is quickly used up; and as an equal amount of exhausted or vitiated air is discharged per minute at the same place, the need is obvious of a constant streaming of air about the body which shall remove vitiated air and supply fresh air. This circulation or flow of air is just as necessary as is the circulation of the blood; but, as the movement always
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goes on unseen, through the diffusion of gases and by other natural and invisible agencies, it is harder to realize the need. Out of doors the air supply is ordinarily suffi- cient and of good quality, especially while the body is in motion, in walking, driving, riding, wheeling, skating, sailing, rowing, or in doing much of the manual work on farms, forests, ships, in fishing, etc.
Stagnant Air. — Indoors, conditions are very different. Life is more sedentary, the body is more quiet, and nat- ural wind currents or drafts are intentionally prevented ; the air of houses tends to become stationary and even stagnant, and with it the air supply about the bodies of the house dwellers. Since it is this stagnant air which is steadily exhausted or vitiated by the air discharged from the nose and mouth, a blanket of increasingly stagnant and impure air tends to accumulate about the body of a sitting or sleeping person. To prevent this stagnation, and the consequent impurity of the air supply, movement of the body or, better, movement of the air is a prime necessity.
Ventilation (Latin, ventus, wind) is the name usually given to any circulation or movement of the air of rooms or buildings by which fresh, pure air, preferably from out- doors, is introduced and vitiated air is removed, the move- ment of the air being rapid enough to meet all the needs of the body, but not so rapid as to cause dangerous cur- rents or drafts. This movement or circulation may be either intermittent and occasional, as when a window is opened for a little while and then shut, or more or less regular and constant, as in all efficient “systems” of ven- tilation or even in such primitive methods as that of the chimney above an open fire.
4, Natural Ventilation. — The walls of most houses are more or less porous and permeable for gases. Cracks and erevices around doors and windows also allow gases to
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leave and enter. In an experiment made by one of the authors, four ordinary gas jets in a small room were left open (but not lighted) all night, and after the gas had poured in for eight hours it was found that the room con- tained only three per cent of gas, the remainder having escaped by natural ventilation. It is largely because of the cracks, crevices, and pores in the walls that human beings get on as well as they do in rooms and houses seemingly wholly unventilated. Wood, brick, stone, and plaster are more porous than glass, iron, or glazed brick, and dry walls more porous than those wet ordamp. Painted and papered walls are less porous than those left bare, and accordingly the walls of summer houses are often loosely made, prefer- ably of “natural” woods.
- What do we mean by Air Good or Bad, Pure or Impure ? — Air is not a chemical compound of fixed com- position, but a mixture of gases containing, even when pure, varying amounts of nitrogen, oxygen, carbonic acid, ammonia, and water, — this last in the form of invisible (aqueous) vapor. Moreover, the density of the air varies not only at different places, but also at the same place at different times. Impure air contains all these gases, and Inay contain in addition any other gas capable of mixing with them, such as hydrogen sulphide, carbonic oxide, marsh gas, etc. The terms “good” and “bad” air, “moist,” “fine,” “dry,” “bracing,” “muggy,” “humid,” “heavy,” “foul,” “fetid,” “stagnant,” “dead,” “thick,” or “lifeless” air, and all similar terms, are popular de- scriptions of atmospheric conditions real or imaginary, testifying to the wonderful variety of this -part of the environment of mankind.
We may define “ pure” air as any portion of the atmos- phere free from noxious gases or vapors and from infec- tious microérganisms. Such air may, however, be unfit for breathing, as is the case with those higher portions
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of our atmospheric ocean into which aéronauts have some- times ventured. At the height of three miles above the sea the air no doubt is very “pure,” but yet too thin to support human life readily.
Air may be considered as polluted or “impure” when it contains noxious gases, or floating particles in large numbers (as in smoke), or disease-producing germs or microorganisms (perhaps derived from dust).
- The Sources of Discomfort and Danger in Air. — We must be careful to discriminate between discomfort and danger in atmospheric conditions. Positive danger comes chiefly from deficiency of oxygen, excess of carbonic acid, admixture of poisonous gases, or from infectious micro- organisms. Aéronauts, explorers on high mountains, and persons living at great altitudes are apt to suffer from oxygen deficiency. Miners, charcoal burners, and well cleaners sometimes suffer from carbonic acid excess. Laborers in gas works and consumers of illuminating gas may be poisoned by carbon monoxide; and workers in sewers, by various gases, especially by illuminating gas which may have leaked in. Air may also contain, and thus convey, germs. of infectious diseases such as smallpox, scarlet fever, measles, etc.
On the other BOs air that is not dangerous, and even perfectly “pure” air, may be a source of great discomfort, simply because of its temperature or moisture, or its tem- perature and moisture taken together. The air in the “dog days” of August is no less pure than that of June or October; yet it is often oppressive because it is both too warm and too moist. It has been shown in Chapter XII how greatly the regulation of the temperature of the body depends upon the capacity of the atmosphere to take up moisture, and it is plain that any atmosphere saturated or nearly saturated with aqueous vapor must seriously inter- fere with the cooling of the body. A careful review of that
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chapter will greatly help the student to an understanding of the sources of discomfort in the atmosphere of houses or rooms.
A shut and uninhabited room often becomes “ musty” or “damp,” because of a want of circulation to remove air containing traces of odoriferous gases and excess of mois- ture; the former perhaps derived from carpets or furniture, the latter from the basement or cellar.
The air of an inhabited room may prove a source of dis- comfort to its inmates, and therefore deserve to be called bad for any or all of the following reasons: (1) the air may be overheated or underheated; (2) it may contain an excess of moisture due either to its dampness of location or to the breath of its inmates; (8) it may be both over- heated and overmoist; (4) it may contain odoriferous gases which cause displeasure or discomfort.
What such rooms do not often suffer from is oxygen defi- ctency or carbonic acid excess ; for experiments have proved that unless the oxygen falls below twelve per cent, or the carbonic acid rises above three per cent (conditions which are very rarely met with in ordinary human habitations), no marked discomfort ensues. _
- Ventilation replaces Bad Air with Good Air and causes Aérial Movement or Circulation. —It is now easy to see precisely how ventilation aids us in securing comfortable and agreeable atmospheric conditions. It removes bad air and supplies good (that is fresh) air and, by causing move- ment, favors evaporation from the skin and consequent cooling on muggy days. It is also easy to see why ventila- tion is at times ineffective. No system of ventilation can wholly overcome the “mugginess” of a “close” room in August, because the pure outer air is itself unpleasant and uncomfortable ; but active ventilation, by producing a breeze, can do more than anything else to make the con- ditions tolerable (see Part I, p. 208).
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Fans and Fanning. —It is an old point of dispute whether or not a person who “fans” himself grows cooler or warmer. However this may be, there can be no question that persons who use fans feel cooler, and there is no doubt that any one fanned by another or by a breeze not only feels, but actually is, cooled thereby. The great and grow- ing use of electric fans in | hotels, houses, etc., testifies to the same fact.
A Room may be well Ventilated but Oppressive from Overheating.— This fact, though perfectly obvious, and fa- miliar to all who have been in well-ventilated boiler rooms, or who have lived in the tropics, is too little attended to. Many public halls, Pullman and other railway cars, steam- boats, and private houses, especially in the northern United States, are rendered almost intolerable and very unhygienic by simple overheating. Elderly people and infants require higher room temperatures than do active persons in youth and middle life, but in general any temperature above 70°F. must be regarded as excessive, and 65°F. to 68°F. is a better temperature (pp. 201, 390). Housekeepers, at least in the northern United States, would do well to try to keep the mercury in their houses between these lower limits. When the outdoor air is moist, as in rainy weather, a somewhat higher temperature is often required than when it is dry.
A Room may be Comfortable in Temperature but Defective in Ventilation. — This fact is less obvious than that just considered, but nevertheless true. It may be because of excessive moisture, or because of odors, or for other reasons; but those entering such rooms from out of doors are often able to remark and deplore the fact. It is perhaps oftenest exemplified in warm countries or in warm seasons when people close and darken rooms to “ keep out the heat.” Such closing and darkening interferes with a good circulation of air and thus hinders ventilation. It also favors dampness by excluding sunshine.
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- Some Practical Hints about the Ventilation of Rooms. — We have already referred to the great value of chimneys and open fireplaces as ventilators, and to the “natural” ventilation by porous walls, and by cracks above and below doors and windows. The simplest and most usual artificial method of ventilation is the opening more or less widely of windows or doors, and this is a means which should never be disregarded. The great drawback associated with it is the fact that uncomfortable and frequently unwhole- some drafts are likely to ensue. It should be remem- bered, however, that the existence of a decided draft is usually an indication that the amount of ventilation is greater than is necessary. When the wind is blowing against a window it is enough to open this an inch or less; if the wind is blowing very hard, the natural ventila- tion may be sufficient. Moreover, the amount of natural
ventilation secured depends quite as much on the ease of ©
egress as of ingress of air. It often happens that if the window be closed or very slightly opened on the wind- ward side of the house, enough natural ventilation will be secured by opening other windows on the side away from the wind.
It is often possible, especially in warm or temperate weather, to secure satisfactory ventilation by opening win- dows both at the top and the bottom, the warm air passing out above, while cooler, fresh air comes in below. This, however, is not advisable when the temperature of the incoming air is too low, since the air then sinks at once to the floor and chills the feet. Another good plan is to raise the lower sash three or four inches and place under it a board made to fit the space. Air now enters between the sashes and, the air being directed upward, the occu- pants of the room are protected from drafts. Where elec- tricity is available, an electric fan placed in one of the upper sashes is frequently very effective in hastening the
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removal of vitiated air. Fans for this purpose are now read- ily obtainable, and have often proved to be serviceable.
In winter, fresh air and good ventilation cost something, as the air must be heated; but it is pgor economy to use stagnant air for the sake of saving fuel. The keen edge of capacity for good work is dulled by bad air, the vital resistance is lowered, and the susceptibility to disease in- creased. On the other hand, there is such a thing as too much ventilation; for if it causes dangerous drafts or leads to actual chilling of the body, it may do almost as much harm as too little ventilation. Here again each in- dividual must study and determine his own needs.
The hot-air furnace is capable of supplying fresh air in abundance and, if the air be not overheated or overdried, gives an admirable method of heating and ventilation, combined in a single device, — the jacketed stove, — pro- vided always that the air supplied to its heating chamber is unobjectionable.
- Mechanical Systems of Ventilation. — Buildings larger than dwelling houses, such as large schoolhouses or public halls, are, or should be, ventilated by some mechan- ical system. These are of two principal types, known as
the “ yacuum” and the “ plenum” systems. In the former
an attempt is made to effect good ventilation by sucking out the air from the building by an exhaust fan or blower attached to one main pipe or duct, to which are led tribu- tary ducts connected with the various rooms. To supply the air thus removed, fresh air is supposed to make its way in, either by “ natural” ventilation (p. 443) or through inlet ducts specially provided, in either case being pressed in by the outer atmospheric pressure. In the plenum system this arrangement is reversed, and air, previously warmed if need be, is driven by a fan into a main duct or space, from which smaller ducts carry it to the various rooms, circulation being favored by outlet ducts through
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which the air flows away. Sometimes an effective combi-
nation of the two systems is used, in which case the air is not only pumped in but also at the same time sucked out.
In favor of the, plenum system it may be said that, instead of currents of (often) cold air pressing in by the paths of natural ventilation, about doors, windows, etc., the direction of the aérial current at these places is re- versed, owing to the pressure to which the air is subjected, so that it is more often possible to sit very near such win- dows and doors.
The combination of the two systems offers many prac- tical advantages, but is obviously relatively costly. It is sometimes forgotten that air, quite as truly as water, pos- sesses inertia and moves along paths of least resistance ;
but experience has shown that in order to govern the
direction of flow of the aérial stream it is often necessary,
as well as advisable, to control the outgo as well as the —
income of air,