CHAPTER XXIII.

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.

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.

=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.