VENTILATION BY THE INTRODUCTION OF WARMED AIR.
=Ventilation by the Burning of Coal.= In winter and at any time of the
year when the out-door temperature is below 50° Fahr., the warming and
ventilation of a room are necessarily combined. If air is admitted
unwarmed it will produce draughts, unless directed upwards by Tobin’s
tubes or otherwise. In dwelling-rooms such contrivances may suffice;
but in any larger building, in order to ensure sufficient ventilation,
it is necessary to warm the incoming air.
=The Open Fire-place= forms the most common means of ventilation by
heat (see also page 159). The ascent of warm air up the chimney, causes
cold air to rush along the floor to the fire-place from all parts of
the room, especially the door. Part of the air thus approaching the
fire is carried up the chimney with the smoke, while the remainder,
after having been warmed, flows upwards towards the ceiling near
the chimney-breast. It passes along the ceiling, and cooling in its
progress towards the opposite wall, descends, and is again drawn
towards the fire-place. Thus there is a continuous circulation of the
air in a room.
In the experiments of the Barrack Commissioners (1861), it was found
that the amount of air passing up the chimney while a fire was lit,
ranged from 5,300 to 16,000 cubic feet per hour, the mean of 25
experiments being 9,904 cubic feet. We may conclude, then, that with
an ordinary grate, a chimney provides outlet for impure air sufficient
for four or five persons. Its lack of economy as a heat-producer will
be considered later. Its efficiency as a ventilator within the above
limits is evident.
When a fire is burning in the grate, all other openings in the room,
except openings into the chimney, serve as inlets. If the room is
insufficiently supplied with openings, a double current may be
established in the chimney, with the result that occasional down-puffs
of smoke occur.
As a rule the chimney serves only as an outlet for impure air. It
may by appropriate means be made to serve as an _inlet for pure and
warmed air_, the heat which would otherwise escape up the chimney being
utilised for this purpose. =Galton’s stove= is one of the best for this
purpose. At the back of this stove is an air-chamber, communicating
with the external air, and in which the fresh air is heated before
it enters the room. On the back of the stove broad iron flanges are
cast, in order to present as large a heating surface as possible. They
project backwards into the air chamber; and their heating surface is
aided by the iron smoke-flue, which passes through the air-chamber.
The warmed fresh air enters the room by a louvred opening above the
mantel-piece, or by an opening in each side of the chimney breast. By
this stove one-third of the total heat of the fire is utilised, as
against one-eighth in an ordinary fire-place.
[Illustration: FIG. 16.
Vertical Section through Two Rooms, showing—A. Currents of cold air
with an ordinary fire; B. Direction of currents of warmed fresh air
with a Galton’s Ventilating Stove.]
Shorland’s Manchester and other stoves are constructed on the same
principle as Galton’s.
=The Ventilation of Mines= is effected by lighting a fire at the
bottom of a shaft. The air for the combustion comes down another shaft
(the intake shaft), or down another half of the same shaft separated
by a partition. The consequence is that constant up and down currents
of air are produced. The air from the intake shaft is made to traverse
the galleries of the mines, its course being directed by partitions,
before it is allowed to reach the fire and s be carried up out of the
mine.
In addition to, or instead of, an ordinary coal-fire, the power for
extracting impure air may be obtained from =Hot Water or Steam Pipes=.
There are various plans founded on this principle.
When hot-water pipes are used for baths, etc., they may also be
utilised for ventilation, in two ways:—1st. The hot-water pipe may
be made to coil round the tube by which fresh air is admitted into a
room, thus warming the air as it enters. 2nd. The hot-water pipe in
its course upwards may be enclosed in a shaft, which opens into the
external air above. The air in this shaft being heated, the impure
air may be collected and removed from the different rooms by tubes
connected with it. Thus, a hot-water apparatus, when well arranged and
complete, may furnish pure warm air, and carry away impure air. The
ventilation by this plan is found in practice to be somewhat irregular.
The plan proposed by Drs. Drysdale and Hayward of Liverpool is similar
in principle:—Fresh air is warmed by a coil of hot-water pipes in the
basement, and is admitted into the staircase and landings, when it is
supplied to the different rooms by openings provided with valves. From
the rooms, special outlets converge to a foul-air chamber under the
roof. This is connected with a shaft leading from the kitchen-fire,
the latter, therefore, acting as an extraction furnace.
=Lighted Gas= may be employed to produce a current for ventilating
purposes, as well as fire or hot-water.
=Sunlight and Benham’s Ventilating Gas-burners=, have already been
mentioned in this connection (page 149). They are extremely valuable
means of ventilation, producing powerful currents of air from all
quarters of the room unless they are specially enclosed.
In theatres and similar buildings the =Chandeliers= may be made to
extract vitiated air. Where a number of chandeliers exist, they may be
connected by tubes with a main shaft, and all made to contribute to
the same object. According to the experiments of General Morin, the
discharge of 1,000 cubic feet of air is produced by the combustion of
one cubic foot of gas.
Various forms of gas-stoves are now sold, which act as ventilators as
well as sources of heat. Among these is =George’s Calorigen Stove=
(Fig. 17). It can be obtained in various forms suitable for burning
coal-gas, or coal, or oil. Within its outer case is contained a special
iron tube, which communicates at its lower end with the outer air,
and opens at its upper end into the room. The heat generated in the
stove warms the air in the spiral tube, which accordingly ascends
into the room. The ascent of warm air causes a draught from below,
and the consequence is, that so long as the combustion is going on, a
current of warm air continues to ascend into the room. The products of
combustion are carried out of the room by the pipe =F=. This stove is
free from most of the objections appertaining to gas-stoves; it can be
fixed into an ordinary fire-place, and made to keep the temperature of
a room uniform.
[Illustration: FIG 17.
GEORGE’S CALORIGEN STOVE.
=A=—The interior of the room.
=B=—Exterior of building.
=C=—Wall.
=D=—The Calorigen.
=E=—A cylinder.
=FF=—Pipes communicating with stove and cylinder to supply air for
combustion, and to carry off the products of combustion.
=G=—Pipe for passage of fresh cold air to Calorigen. Can be carried
above the floor between the joists, as may be more convenient.
=H=—Outlet for air into the apartment after being made warm.]
=Bond’s Euthermic Stove= is similarly constructed to the above, but
is open below so that the air needed for the gas combustion is drawn
from the interior of the room, and the continuous change of air is thus
favoured.
=Objections to Ventilation by Heating Apparatus.=—When _warmed air_ is
admitted into a room, it is very apt to be _dry_ and irritating. This
can be usually avoided by having water standing in the room, so as to
allow evaporation. A more difficult problem is to ensure the complete
absence of all products of combustion, particularly of the products of
incomplete combustion.