CHAPTER IV
VENTILATION
Introduction
Ventilation as defined by Webster is, “To cause fresh air to circulate; to cause inside resident impure air to be removed and replaced with fresh, pure air, whether it be in building, streets, mines, or sewers.”
Shakespeare speaks of sleep as “Nature’s second course.” Fresh air may well be called “Nature’s tonic.” Everything else necessary for good health may be provided, but if there is not a sufficient amount of fresh air the tissues of the body can not perform their functions. It is quite as necessary to have plenty of fresh, pure air as it is to have a proper amount of wholesome food and pure water. Ordinarily not enough attention is given the subject of ventilation, especially of the average home.
The average adult breathes at the rate of seventeen or eighteen respirations per minute. At each respiration about thirty cubic inches of air passes in and out of the lungs. The air in the lungs loses 4% of oxygen and absorbs about 3.5% to 4% carbon dioxide. The nitrogen remains the same. The temperature of expired air is raised to about 98.4% F. and contains approximately 5% aqueous vapor.
This volume of air inspired and expired during gentle respiration, which is, as has been said, about thirty cubic inches, is known as tidal air. By forced inspiration another 100 cubic inches of air in addition to the tidal air may be taken into the lungs. This is known as complemental air. By forced expiration it is possible to expel from the lungs 100 cubic inches of air over and above the 30 cubic inches of tidal air; this is known as the supplemental air. There is another 100 cubic inches which can not be expelled by the most violent expiration; this is the residual air. The supplemental air can, by forced expiration, be expelled from the lungs, but the residual air can not. Altogether there is in the lungs during forced inspiration about 330 cubic inches of air. An average adult gives off about 0.71 cubic feet of carbon dioxide per hour.
Taking into consideration the amount of air breathed into the lungs per hour and the amount of impurities carried into the breathing zone by the expired air, it can readily be seen that the problem of supplying a sufficient volume of pure air in the house is no small problem.
The amount of fresh air needed for the average adult is estimated to be 3,000 cubic feet per hour. The ventilating system that does not provide this amount of air per hour without objectionable draughts does not meet the requirements of modern hygiene.
In a system of ventilation it is not only a question of providing a certain volume of air from the outside, but the great problem is to provide a sufficient volume of pure air of proper temperature and of proper humidity. Air that is laden with smoke, dust and suspended matter, or that which contains gas or foul odors, is objectionable and does not meet the requirements. Therefore, the source of the air becomes important. The ventilating system must also keep the air in proper circulation at a proper velocity.
The ventilating system of an ordinary building might seem a very simple proposition, but when considered carefully it is a very great problem and one that requires the careful attention of engineers trained in that particular line.
It is not the object of ventilation to provide an indoor condition identical with that outdoors, but it is to maintain a condition indoors conducive to a normal expression of indoor life. It is quite obvious that if indoor conditions were maintained identical with outdoor conditions the desired results could not possibly be obtained, for indoor life demands a much different environment. It is necessary to give any system of ventilation as much attention as is given a heating system in order to obtain the best results. No system will work itself.
Sources of Impurities in Air
There are many processes carried on within the house that add to the impurities of the air. Such sources may be classified as follows: respiration of persons, impurities from heating and illumination, and accidental sources from processes carried on within the house, such as house cleaning and laundering.
It will be observed from a study of the amount of air inspired and expired and the impurities carried from the body in the process that one of the most common sources of vitiation of the air in houses is respiration. That these expired poisons may be diluted or carried out of the breathing zone it becomes necessary to have an adequate ventilating system. If the room is heated by a stove impurities will be added from coal dust and the dust of ashes. When the iron is overheated it gives off carbon dioxide and other gases. Open fire or an open blaze for lighting purposes consumes oxygen, gives off carbon dioxide, raises the temperature and increases the amount of aqueous vapor.
Vitiation from accidental sources consists of dust particles of organic and inorganic detritus which are added to the air from walls, floors, furniture and hangings. Other processes such as laundering will add a certain amount of poisons and suspended matter to the air. All this reveals the necessity for exchanging the inside air for pure outside air.
Requirements of a Ventilating System
A ventilating system must not only bring about an exchange of air, but it must also keep the inside air in proper circulation during the time it is contained inside. Proper circulation of air is one of the most important functions of ventilating systems.
The value of air circulation will be appreciated when it is known that an aerial envelope is formed around the body when the air is not kept moving and the temperature and humidity of this air will resemble that of a very hot, humid summer day. The effects will also be similar to those of heat exhaustion. This shows the importance of keeping the air in circulation in order to carry away the poisons that are being constantly excreted from the skin and through the respiratory tract.
The effects of foul air are usually manifested as headache, fatigue, lassitude, vertigo, nausea, vomiting, collapse and even death. The chronic effects are anemia, debility, lowered vitality and disturbances in digestion. Prolonged exposure to vitiated air will necessitate increased adaptation on the part of Innate Intelligence. If this exposure is carried to an excess it will draw upon the adaptative forces of the body and make it more susceptible to the invasion of toxins and subject to changes which it would not be when under more natural environmental conditions.
It is now affirmed by the best hygienists that there is no great objection to rebreathing air if provision is made for diffusion of the carbon dioxide and if the bodily odors are eliminated. In this way air may be properly warmed and kept recirculating; thus there is a saving on fuel. If air is to be rebreathed it must first be washed. There is, of course, a limit to the length of time air can be recirculated. At no time is the recirculated air equal to outside air and because this method is not properly regulated and carefully controlled it is not considered safe for use.
Before considering methods for obtaining pure air it is interesting to look at Nature’s purifying system. The effect of vegetation upon the air is to consume carbon dioxide, especially in the sunlight. The purifying effects of the sun’s rays on the organic particles, the washing of the air by the rain which carries down the dissolved gases and suspended impurities, the natural constant diffusion of the air due to the wind, are all natural processes tending to keep the outside air in a state of purity.
Man so far has been unable to find any artificial means of purifying the air and therefore must provide means of admitting air from the outside in a state conducive to sustaining indoor life.
Natural Means of Ventilation
Outside air may be polluted with dust, smoke and suspended matter and it is then necessary to free the air of these impurities before it enters the house. Especially is this true in cities and where large buildings are to be ventilated. The most satisfactory methods of ventilating a large building is the plenum and the vacuum systems.
In the ordinary home, ventilation is through the natural openings such as windows and doors, although special openings may be provided which will admit fresh air and carry out the vitiated air. A great deal of air is admitted through the crevice and openings around windows and doors. A very simple method of airing a room in cold weather when a direct draught is objectionable is to place a board a few inches wide and as long as the width of the window beneath the lower sash. This prevents the air from coming through the open window, but permits it to enter between the upper and lower sashes. This also has the advantage of directing the air current toward the ceiling. This is very effective in the sick room and is so simple that any one can use it.
The size and shape of the room to be ventilated must be taken into consideration as well as the number of persons therein. The minimum amount of space allowed for each person has been placed by various authors at from 300 to 1,000 cubic feet, depending upon the nature of the work carried on, the size and shape of the room and the type of ventilation depended upon. In hospitals where fever cases are cared for 2,500 cubic feet are desired, while in government barracks each soldier is allowed 600 cubic feet.
The necessity for a sufficient supply of pure air can not be over-emphasized. When the windows and doors are used to ventilate the house they should be thrown open at different times so that the house air may be completely changed. We must not, however, go to the other extreme and jeopardize the health of the occupants by keeping the temperature too low, yet it has been proven that cool, fresh air is more easily heated than warm vitiated air.
When air is admitted by special ducts they should be so arranged that air may be evenly distributed over the room. The relative position of the inlets to the outlets is a question upon which the engineers are not exactly agreed. It is obvious, however, that their arrangement must admit of a complete change of air at proper intervals and that draughts will not be established directly between inlets and outlets. It is generally conceded that the best results are obtained when the inlet is placed above near the ceiling, and the outlet placed directly below near the floor. In this way there seems to be a more equitable distribution of the entering air and less likelihood of a direct draught between the inlet and outlet. The outlet should never be directly opposite the inlet, since the air will pass directly through the room and there will be very little mixing with the room air. If the room is crowded it is more desirable to admit the fresh air from beneath, but when this is done there must be a great number of inlets. In this way the fresh air is admitted more directly into the breathing zone and at the same time advantage is taken of the natural air currents in the room.
There are many patent devices on the market for ventilating through the windows. Such devices are very good and may be used to an advantage. Usually they are so built that the air is directed toward the ceiling as it is admitted. The same desired end is accomplished by placing a board under the lower sash as described above.
Mechanical Ventilation
By far the most satisfactory method of ventilating large buildings is the mechanical method. This is not practical for small buildings or homes because of the special devices that are required and the expense of operation. Mechanical ventilation may be accomplished by the plenum system, the vacuum system, or by the combined plenum and vacuum systems. The most desirable results are obtained when both systems are used and used in connection with the heating system. Heating and ventilating are so closely related that they must be considered one with the other. A poorly ventilated room is more difficult to heat and an improperly heated room is difficult to ventilate.
The plenum system consists of a fan to force the air into the rooms. These fans are run by water motors or electricity whereby the air is forced through ducts into the rooms. This system is made necessary by the great buildings, basements and large steamships, which could not be inhabited if natural ventilation was the only method employed.
The vacuum system consists of suction fans whereby the vitiated air is drawn out of the rooms and replaced by fresh air through the natural openings. In this way natural ventilation may be made more efficient, but this method in itself is not adequate for large buildings.
The two systems, vacuum and plenum, are commonly used together and when employed in connection with the heating device the very best results are obtained. The amount of air, the temperature and humidity, and the purity of the air may be regulated to a nicety in this way.
A complete system of vacuum and plenum consists of plenum fans for forcing the air into the rooms, vacuum or suction fans for the removal of vitiated air, the ducts for conducting the air to and from the rooms, the necessary machinery to run the fans, and a proper heating system whereby the air may be warmed in the winter and cooled by ice coils in the summer. It is also necessary to have a device for washing the air.
Washing the Air
As the air is drawn into the buildings by the plenum fan it is passed through a chamber where it is washed. This is done by forcing the air through a spray of water. A water curtain is formed by forcing water through perforated pipes placed across the chamber from each other and the water thus sprayed made to intercept. As the air passes through this curtain of water many of the impurities such as dust, cinders, bacteria, some of the gases, particles of decomposition, and epithelial cells, are removed. Washing does not remove carbon dioxide or bodily odors. Washing is one of Nature’s methods of cleaning the air as is seen in rain.
Central heating with washed air.
After the air is washed it is passed over tempering coils. In the winter the air is warmed and in the summer it is cooled in this way. The humidity is also controlled. It can thus be seen that this method, although rather expensive, is the only real method of ventilating large buildings satisfactorily.