METHODS OF VENTILATION.
In most houses no special means of ventilation are provided, windows,
doors and fire-places being trusted for ensuring a sufficient supply
of fresh air. These do not suffice in well-built houses, unless
the inhabitants train themselves into enduring the currents of air
necessarily associated with open windows and doors. They are, however,
aided in the majority of houses by the porosity of walls, by currents
of air through crevices of wood-work, and so on. It is desirable that
adequate special provision for ventilation should be made for every
house when it is built, and that as much care and forethought should
be exercised in this respect as in the laying on of a water-supply or
sanitary appliances connected with drainage.
Whatever the system of ventilation adopted, it is wise to _flush rooms
frequently with fresh air_. This is best effected by throwing the
windows wide open whenever a room is left unoccupied. In this way a
much more thorough and complete purification is effected than by any
other means. This is especially important in the case of bedrooms, in
which organic impurities are most prone to accumulate.
Not only should rooms be ventilated, but likewise _the furniture_ they
contain. This again is most important for bedrooms. Beds should not be
“made” till sometime after using; and in the interval, should be freely
exposed to the air. The same applies to night apparel.
It is well to allow _rooms to lie fallow_ at intervals. Organic matter
accumulates about a room, and devitalises any air which enters. If
the room is vacated, and flushed with air for a continuous period,
it becomes sweeter and purer. The importance of this is now well
recognised in the case of hospital wards. Such temporary disuse of
rooms must not, however, be regarded as sufficient without thorough
cleansing of every surface in them, in order effectively to remove all
organic and other dust.
=An Inlet and Outlet= for air should both be provided. According to
some an inlet only is required, while others would only provide an
outlet; but a perfect system of ventilation requires both. As heated
air expands, the outlets should theoretically be larger than the
inlets; but as the average difference of temperature is only 10°-15°
Fahr., the expansion is only slight, and may be practically neglected.
The necessity for both inlets and outlets may be illustrated by a
single apparatus like that shown in Fig. 11. A taper is burning at
the bottom of the jar, in the stopper of which two tubes, A and B,
are placed. So long as both tubes are kept open the candle will keep
alight, but if A be blocked, the candle goes out.
[Illustration: FIG. 11.
ILLUSTRATING NECESSITY OF INLET AND OUTLET.]
=Inlets= should bring air from a pure source, and should be arranged
at intervals in large rooms. Externally, inlets should be protected
from the wind; and the shorter the inlet tubes the better, as thus a
current is ensured, and they can be easily cleaned. The position of
inlets should not be too near the outlets, otherwise the fresh air
may escape immediately. The best position for inlets is at the floor,
but this necessitates warming the entering air, as otherwise it would
be intolerable, except in summer time. If the air cannot be warmed,
it should he admitted about seven feet above the floor, and directed
upwards. For size of inlets, see page 142.
=Outlets=, under ordinary circumstances, are best placed near the
ceiling. They should be enclosed as far as possible within walls, so as
to prevent the outgoing air being cooled; and should have smooth walls,
reducing friction to a minimum. Where artificial warmth increases the
temperature of the air, the discharge of outlets is much more certain
and constant. The chimney with an open fire forms one of the best
outlets. Gas, again, may be made to heat an outlet tube, which carries
off the products of combustion.
Two forms of ventilation are usually described—natural and artificial.
The former term is used to describe any plan not requiring heating
apparatus or the motive power of steam, or gas, or electricity, while
the latter implies the use of some such motive power or source of heat.
Obviously, however, there is no sharp line of demarcation between the
two. A lighted fire is strictly an artificial plan of ventilation, but
inasmuch as no apparatus intended for ventilating purposes is required,
it is hardly a means of artificial ventilation.
=Natural Ventilation.=—The most important means of natural ventilation
are the window and the chimney; but openings in outer walls and over
the door may form valuable adjuncts.
=The Window= is perhaps the most important agent in purifying a
room—both the light and air it admits being essential for health. The
window is invaluable (1) =for flushing the room= with fresh air at
intervals. Where possible, opposite windows should be opened, or window
and door. Cross-ventilation by opposite windows open at the top forms
one of the best means of natural ventilation, in large rooms, such as
school-rooms. This can, as a rule, be borne without discomfort, while
the room is occupied, unless the wind is very high.
(2) =The Upper Segment= of a window may be made to work inwards on a
hinge, and turned so that the current of air may be upwards. Where this
plan is adopted, triangular pieces of glass should be placed at the two
sides to prevent cold air from falling directly down at the sides of
the opening.
(3) =A Block of Wood=, two or three inches wide, may be inserted at
the bottom of the window sash at =A= (Fig. 12), and then the window
pulled down on this. The consequence is that air is admitted between
the two sashes at =B=, its current being necessarily directed upwards
(Fig. 12). This plan answers admirably in admitting pure air; but it
possesses a disadvantage common to all the plans in which external air
much colder than the internal is admitted into a room. The current of
cold air passes upwards for some distance, but may then fall down on
the heads of those occupying the room.
[Illustration: FIG. 12.
WINDOW VENTILATION.]
(4) The top sash of the window may be opened, and some =zinc gauze=
fastened across the open part. This is practically the same as the last
arrangement, except that the air is admitted through the apertures of
the zinc, and the amount admitted is greatly diminished (page 136).
(5) In =Louvre Ventilators=, a number of parallel pieces of glass,
each directed upwards, are substituted for a pane of glass. They may
be fixed or made movable, as in Moore’s ventilator. The incoming
current of air may be similarly directed upwards, in an open window, by
arranging Venetian blinds with the laths inclined upwards.
(6) In windows that will not open, =Cooper’s Ventilators= are often
used. Each of these consists of a circular disc of glass, having five
oval apertures in it, which works on a pivot through its centre, close
in front of one of the panes of a window, which has five similar holes
pierced in it. Consequently, when the disc is turned, so that its holes
are opposite those of the window, fresh air is admitted. The amount
thus admitted is necessarily small.
=The Chimney= forms the best means of escape of foul air. No room ought
to be built without a fire-place, which should never subsequently be
boarded up. In bedrooms the chimney forms a most important means of
ventilation. If there is no fire, the chimney occasionally furnishes
an undesirable source of air; but as a rule the current is upwards,
owing to the aspirating action of winds at the top of the chimney.
The downfall of air from a chimney chiefly occurs when there is an
insufficient inlet for pure air. This is the explanation of =smoky
chimneys= in nine cases out of ten; then the cure is easy by laying
on a pipe from the outside of the house to the hearth. When the smoky
chimney is due to the contiguity of higher buildings, the chimney must
be raised, or a cowl placed over it.
(1) The action of the chimney in carrying impure air away from the room
may be considerably increased by =narrowing the two ends=, so as to
produce a more rapid current at the entrance and exit of air.
(2) The heat of the chimney may be utilised by having a =separate
smaller flue= alongside it, with openings from the rooms on each floor.
The air in this being heated aspirates the air from each room in
succession.
Openings may be made into the chimney-flue at a higher point than
the fire-place. These are very valuable for carrying off the heated
and impure air resulting from the combustion of gas, as well as
for carrying off the respiratory products, which, in their warmed
condition, tend to rise towards the ceiling.
(3) =Dr. Neil Arnott= first devised a valve for this purpose. An
opening being made through the upper part of the wall into the chimney,
an iron box was inserted, in which was placed a light metal valve
capable of swinging towards the chimney flue, but not towards the room.
The objections to this apparatus are that it is apt to make irregular
clicking noises, and to admit blacks from the chimney when out of order.
(3) In =Boyle’s Valve= these objections are partially obviated. It
consists of an iron frame, across which lie iron rods; and from these
are suspended thin talc plates, only capable of moving in the direction
of the chimney (Fig. 13). Even this apparatus is rather noisy when
there is a strong wind.
[Illustration: View from room. View from chimney.
FIG. 13.
BOYLE’S MICA FLAP VENTILATOR.]
Neither of these plans answers so well as a second flue alongside the
chimney flue, communicating with each room near its ceiling; but the
latter can only be arranged for when the house is built, while the
valves may be inserted at any time.
=The Ceiling= may be utilised for removing foul air; and thus serve to
diminish the draught which is often produced by the currents of air
towards the chimney, when this forms the only means of outlet.
In large rooms (1) a sunlight gas-burner forms an important means of
ventilation. It causes a strong up-current from every part of the room.
If there is a fire in the room, the burner is apt to become an inlet
for air, or the chimney to smoke, according to the relative strength of
the two currents.
(2) Benham’s and other forms of =Ventilating Gas Burners= serve the
same purpose. In each of them the products of combustion are conveyed
by special ducts above the ceiling to the outer air.
(3) =McKinnell’s Ventilator= is useful in single-storied buildings,
like certain barracks. It consists of two tubes encircling one another,
the inner forming an outlet tube, because the casing of the outer tube
maintains the temperature of the air in it. It is made higher than the
outer tube, and is protected by a hood. The outer tube forms the inlet
for fresh air. The entering air is thrown up towards the ceiling and
then to the walls by a flange placed at the bottom of the inner tube.
The air after traversing the room, and becoming heated, passes upwards
to the inner tube. When doors and windows are open, both tubes become
outlets; if there is a fire in the room, they may both become inlets;
but this may be prevented by closing the outlet tube.
[Illustration: FIG. 14.
MCKINNELL’S ROOF VENTILATOR.]
(4) Various other means have been devised for carrying foul air from
the ceiling through channels between the ceiling and the floor of the
room above. All share the disadvantage that the channels become dirty
and are difficult or impossible of access for cleaning.
(5) Various cowls connected by metal tubes with the ceilings of
rooms have been placed on roofs, and their aspirating effect
used in ventilating these rooms. When a room is furnished with a
chimney such cowls are most undesirable. In large rooms without a
fire-place they are helpful, but much more confidence can be placed
in cross-ventilation by hinged windows. It is doubtful if any of the
advertised fixed cowls produce materially greater aspiration of air
from rooms than a simple open tube of the same size. It is desirable
that the tube should be protected at its upper end against the entry of
rain, and that a grating should be provided to prevent birds building
their nests in the tube.
In the preceding plans of ventilation, the ceiling serves almost
entirely as an outlet for impure air. In the following plan, it is used
as an inlet for pure air.
(6) In =Sylvester’s Method of Ventilation=, the perflating force of the
wind is employed to produce an abundant entry of fresh air. A cowl is
placed, always turning towards the wind; the air received is conducted
to the basement, where it is warmed by a stove or hot-water pipes,
and then passed through tubes into the upper rooms. From these it is
carried by tubes above the roof, these tubes being covered with cowls
turning from the wind, so that in this way the aspirating power of the
wind is likewise used.
Ships are often ventilated in a somewhat similar manner. The tube to
which a windward cowl is attached above, ought to be bent at right
angles, so as to lessen the velocity of the entering air. By covering
other air-shafts with movable cowls, turning from the wind, the
aspirating action of the wind is brought into action to aid the escape
of foul air.
=The Walls= of a room, unless covered with an impervious material, are
constantly traversed by gentle currents of air, which play an important
part in the ventilation of rooms. Special apertures may be made to
furnish a freer supply, and these may be in various forms.
(1) =A Simple Grating=, may be inserted; but this is apt to become
blocked with dirt, and does not allow a large amount of air to enter.
Louvred openings in the walls are objectionable, except for very large
rooms.
(2) =Sheringham’s Valve= is the most convenient means of ventilating
through the wall. An opening in the external wall is made by a
ventilating brick or grating; into the wall is fixed an iron box, which
has in front of it an iron valve hinged along its lower edge, so that
it can open towards the room. On the sides of the valve cheeks are
attached, which fit into the box when the valve is shut. A heavy piece
of iron pressing against the valve from within the box, tends to keep
it constantly open. By means of a string and pulley, the valve can be
opened or closed at will, or fixed in any intermediate position.
[Illustration: FIG 15.
SHERINGHAM’S VENTILATOR.]
In a very large room, it is better to have several medium-sized
valves, than a few larger ones, the air being thus more completely
diffused. If there are two valves, they should not be opposite one
another, as the air may then simply pass from one to the other, without
becoming diffused through the room. If there is only one valve, it may
occasionally serve as an outlet when the wind is to leeward. By means
of this form of valve, the air is projected upwards in a diverging
current towards the ceiling. The valve should be placed above the
level of one’s head, but not too near the ceiling; as in the latter
case, the current of air is driven hard against the ceiling, and
falls thence with considerable force towards the floor. A combination
of Sheringham’s inlet and Boyle’s mica outlet into the chimney at
the opposite side of the room ensures efficient ventilation in a
dining-room. Better than the outlet into the chimney is an opening into
a special flue alongside the chimney-flue, if this be available.
(4) =Ellison’s Inlet= consists of a brick pierced with conical holes,
the apex of the cone being towards the external air. By this means
any great draught is avoided, and the air is distributed over a
considerable area. In order that this may prove an efficient means of
ventilation, a considerable number of bricks are required.
The =Floor= of a room is always the source of considerable currents of
air, even when well carpeted. Air mounts up through the crevices of the
wood-work, being aspirated into the room when its temperature is higher
than that of the rooms below. In the case of rooms on the ground floor,
air is often drawn from the subjacent soil, or through dust-bins, etc.
Theoretically, in all measures of ventilation, the floor would be the
best point for the entry of cold air. This, however, is intolerable
when the incoming air is cold, and the floor must therefore be
abandoned as a means of ventilation, apart from heating apparatus.
The floor may be used as a means of entry of fresh air in a modified
manner, by directing the air entering at the floor-level for some
distance up a tube at the side of the wall. This apparatus is known
as =Tobin’s tube=. It consists of a rectangular or cylindrical tube
from 4 to 6 feet high, which communicates at the lowest point with the
external air by means of a perforated brick or grating. The air enters
the room in an upward direction, and is consequently sent towards the
ceiling, where it becomes mixed with warmer air, before diffusing
itself throughout the room. But when the incoming air is very cold, it
may fall more rapidly, causing cold draughts on the heads of those in
the room.
As the air enters directly from outside the house, it often carries
with it particles of dirt, soot, etc. This may be remedied by placing
a pan containing _a shallow layer of water_ at the lowest part of the
tube, or by placing _cotton wool_ at the point of entry of the tube
into the room. The tray of water soon dries up and is rarely replaced,
while the cotton wool diminishes the amount of entering air. It is very
useful however in cold weather, or when fogs occur. A _gauze funnel_ is
sometimes inserted in the tube, or a sheet of gauze arranged diagonally
across the tube from its highest to its lowest point. The gauze does
not keep out minuter particles of dust, and requires occasional
cleaning. All Tobin’s tubes, like other ventilating openings, should be
made to open, so that their interior can be frequently cleaned.
_Summary as to Domestic Ventilation._—Open windows, doors, and
fire-places may be in most instances trusted. If gas is used as an
illuminant, they should be combined with special arrangements for
carrying off the products of combustion from the room. For delicate
people, and especially in small rooms, outlet ventilation into the
chimney breast combined with a Sheringham’s valve on the opposite wall
is desirable.
=Artificial Ventilation.=—Artificial ventilation may include two
important and very different measures. In one of them currents of air
and an exchange of pure for impure air are effected by means of various
forms of heating apparatus. In the other mechanical measures are used
for the same purpose,—the air being either driven out of the room or
drawn out of it. In this chapter we shall consider only the =mechanical
means of artificial ventilation=. There are two kinds, the first being
known as ventilation by aspiration, or the _vacuum_ system; and the
second as ventilation by propulsion, or the _plenum_ system.
In =Ventilation by Aspiration= the foul air is drawn out of the room by
machinery, its place being supplied by fresh air, which may be warmed
before entry or not. This plan and the next have been employed chiefly
in connection with large buildings, such as hospitals, etc., and in
mines.
The extraction of foul air may be effected by—(1) _a steam-jet_, which
is allowed to pass into a chimney, and sets in motion a body of air
more than 200 times its own bulk. Tubes from each room of the building
are connected with this chimney, and the strong upward current extracts
the air from them. This plan is useful in factories, where there is a
superfluous supply of steam.
(2) _A fan or screw_ may also be used. The vanes of the fan, when set
in motion by electrical or some other motive power, produce a powerful
current of air, which can be regulated according to requirements. As in
the last plan, the aspirating influence of the fan may be exerted over
a system of rooms, by means of connecting tubes.
In =Ventilation by Propulsion= a fan is used as in the last plan, the
air being propelled along conduits leading from it into the room to
be ventilated. The size of the conduits being known, the amount of
air to be discharged can be regulated by timing the rapidity of the
revolutions of the fan.
This plan is suitable for crowded places, where a large amount of
air is required in a short time. It is excellent for large schools,
churches, and theatres. Its superiority for large elementary schools
has been proved at Dundee by the experiments of Drs. Carnelley,
Haldane, and Anderson, the results of which are summarised in the
following table:—
Column headings:
A No. of Schools. B No. of Rooms. C Cubic ft. allowed per person.
D Carbonic acid in 10,000 of air. E Micro-organisms per litre.
F Bacteria. G Moulds.
┌───────────────────────┬─────┬──────┬───────┬────────┬──────────────┐
│ │ A. │ B. │ C. │ D. │ E. │
│ │ │ │ │ ├────────┬─────┤
│ │ │ │ │ │ F. │ G. │
├───────────────────────┼─────┼──────┼───────┼────────┼────────┼─────┤
│_Mechanical ventilation│ │ │ │ │ │ │
│ by warmed air_ │ 6 │ 32 │ 160 │ 12·3 │ 17·5 │ 1·0 │
│_Natural ventilation │ │ │ │ │ │ │
│ and hot pipes_ │ 17 │ 43 │ 176 │ 16·3 │ 96·5 │ 1·1 │
│_Natural ventilation │ │ │ │ │ │ │
│ and open fires_ │ 33 │ 84 │ 145 │ 19·2 │ 153·2 │ 4·8 │
└───────────────────────┴─────┴──────┴───────┴────────┴────────┴─────┘
The air to be admitted may be warmed by passing it over hot-water or
steam-pipes. In large establishments, as in hospitals, theatres, etc.,
it has been arranged so that the incoming air is passed through a
screen of coarse cloth, which is kept wet by water trickling down each
cord. The air is thus kept moist and freed from dust.
The great advantage of the plan of propulsion, is its certainty. By
it the temperature, moisture, and freedom from suspended matters of
the incoming air can be exactly regulated and controlled. Its chief
disadvantages are that (1) it is somewhat costly, and (2) the apparatus
requires skilled supervision. On the other hand it maintains the air
in crowded rooms in a condition which cannot be secured by any other
method. When combined, as is done in the Houses of Parliament, with
the use of a flue for the extraction of foul air, this plan answers
admirably.
=The Relative Value of Artificial and Natural Ventilation= scarcely
needs to be discussed. They are both valuable, but under different
circumstances. In dwelling-rooms natural ventilation by doors, windows
and chimney usually suffices, especially if the products of combustion
of gas are removed through a special flue. Natural ventilation is
always occurring, and only needs a little aid in domestic life.
For large rooms occupied by many persons artificial ventilation is
necessary to maintain pure air.
Whatever method of ventilation is adopted, the atmosphere will remain
to some extent polluted, if the room and its occupants are dirty. In
certain experiments made by Carnelley in schools, it was found that
dirty children increased the number of micro-organisms per litre of air
more rapidly than dirty rooms. Thus:—
┌────────────────────────┬──────┬───────┬──────┐
│DEGREE OF CLEANLINESS OF│CLEAN.│MEDIUM.│DIRTY.│
├────────────────────────┼──────┼───────┼──────┤
│_Children_ │ 63 │ 99 │ 159 │
│_Rooms_ │ 85 │ 94 │ 139 │
└────────────────────────┴──────┴───────┴──────┘
_Number of micro-organisms per litre of air._
Hence cleanliness of rooms and of their occupants is quite as important
as a good system of ventilation.