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.
[Illustration: _Window Ventilation._]
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.
[Illustration: _Window Mopper_]
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.
[Illustration: _Window Ventilation_]
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.
[Illustration: _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.