Mechanics of the Household / A Course of Study Devoted to Domestic Machinery and Household Mechanical Appliances

by E. S. Keene

The prevailing impression that impure air is heavy and settles to the floor is erroneous. Impurities in the form of gases and vapors (principally carbonic acid gas and odors) diffuse throughout the entire space, and the entering fresh air tends to dilute the entire volume.

As a quantative problem, ventilation consists in admitting pure air into an impure atmosphere in amount to give a definite degree of purity. This is accomplished by admitting sufficient air to completely change the atmosphere at stated intervals, or to provide a definite quantity for each inhabitant.

The methods by which ventilation may be accomplished will depend on the type of building to be ventilated and the apparatus it is possible to use. When the use of mechanical ventilation appliances are permissible, any desired degree of atmospheric purity may be maintained at all times, under any condition of climate or change of weather.

In buildings where mechanical ventilation cannot be considered as that of the average dwelling, the problem is one of producing an average condition of reasonably pure air by natural convection. In the average dwelling, ventilation is accomplished by the natural draft produced in chimneys or air flues, by partially opened windows and by the force produced by the movement of the outside air. In some buildings a better condition of ventilation is attained by ordinary means than at first sight seems possible.

The fact that it is difficult to keep a house at the desired temperature during cold weather indicates that a considerable quantity of outside air is constantly entering and heated air is leaving the building. It may be, however, that the ventilation under such condition is unsatisfactory, even though the amount of air which enters the building is sufficient in quantity to produce a desirable atmosphere. If the places of entrance and exit are so located that the entering air has no opportunity to mix with the air of the building, the advantage of its presence is lost.

In the burning of fuel in stoves and furnaces, the amount of oxygen necessary for combustion is supplied by the air which is first taken into the house and thus forms its atmosphere before it can enter the heater. Theoretically, about 12 pounds of air are required for the combustion of a pound of coal, but in practice a much larger amount actually passes through the heater. As given by Suplee, from 18 to 24 pounds of air are actually used in burning 1 pound of coal. If 20 pounds of air per pound of fuel is taken as an average, there will be required 198 cubic feet of air per pound of coal consumed. In a building that requires 10 tons of coal to be used during the winter months, this would necessitate the average use of 1977 cubic feet of air per hour, which must be drawn into the house before it can enter the stoves. This air acts as a means of ventilation and if it is used to advantage would furnish a supply sufficient in amount to produce excellent ventilation, considerably more than enough for two people. The amount of air drawn into the house in this way is further increased by that which passes into the chimney flue through the check-draft dampers, when the fires are burning low.

Fig. 162.—A simple expedient for the prevention of drafts and improving ventilation.

The aim of architects is to construct buildings as completely windproof as possible, but that such construction is attained in only a slight degree is sometimes very evident during cold weather. No matter how tightly constructed buildings may be, most of the contained air filters through the cracks and crevices of the walls or through the joints of the windows and door frames, because there is seldom any special provision made for its entrance. During extremely cold and windy weather the amount of air that enters the house in this way—because of the air pressure on the windward side—is sometimes sufficient to keep the temperature at an uncomfortably low degree. Under such conditions, the air drifts through the building faster than it can be raised to the desired temperature and the rooms on the windward side of the building cannot be kept comfortably warm.

The common method of ventilation in dwellings is that of partially open windows. The air thus admitted, being colder and consequently heavier than that at the temperature of the room, sinks to the lowest level. In so doing it creates drafts that produce discomfort and act only in the smallest degree to produce the desired effect of ventilation. The effect of window ventilation may be greatly improved by a simple expedient illustrated in Fig. 162. In this, the entering air meets a deflector in the form of a board or pane of glass that directs the cold air upward where it mingles with the heated air with the least production of a noticeable draft. This is the most efficient method of house ventilating where no special provision is made for the admission of fresh air.