Ventilation shaft

“ In such a system of working the ventilation of the pit will be most powerfully aided or altogether effected by natural atmospheric currents. An upcast once determined by artificial means, it will thereafter proceed spontaneously,204 as the cold air of the downcast shaft will travel by a descending road to the workings, and then after becoming heated will simply obey the superior pressure of the heavy column behind, and proceed by an upward road to the upcast shaft. ”

“ When the temperature of outside and inside air becomes equal or nearly so natural ventilation ceases or becomes insignificant. In a mine with two shafts a ventilating current may result from other conditions creating a difference in the temperature of the air in either shaft—for example, the cooling effect of dropping water or the heating effect of steam pipes. Natural ventilation is impracticable in flat deposits worked by drifts and without shafts. ”

“ If they are deep, it becomes necessary to commence ventilation of the mere shafts themselves in the course of sinking. This is done344 by driving an air-way—a horizontal tunnel from one to the other, and then establishing an “upcast” in one of them by simply lighting a fire there. This destroys the balance between the two communicating columns of air; the cooler column in the shaft without a fire, being heavier, falls against the lighter column, and pushes it up just as the air is pushed up one leg of an U tube when we pour water down the other. ”

“ If, therefore, the inlets and outlets be properly proportioned and open, the ordinary atmospheric pressure will carry on the ventilation quite efficiently, and the whole hospital will be kept fresh and comfortable by the natural forces alone. There is no fear that the speed will not be enough to keep up efficient ventilation—it is more likely to be too great ; but there need be no fear of its being too great, because it is completely under control, and can be regulated to any rate desired by the valves at the ward inlets and outlets. ”

“ Artificial ventilation therefore becomes imperative. Natural ventilation by opening windows and doors can only be practised in intervals of work and as a rule only in small workrooms. During work time the draught and reduction of temperature so caused produce discomfort.
Artificial ventilation is effected by special openings and ducts placed at some suitable spot in the room to be ventilated and arranged so that either fresh air is introduced or air extracted from the room. The first method is called propulsion, the latter exhaust ventilation. ”

“ Filtration is a topic directly affecting ventilation; exhaust air laden with nanomaterials may need to be cleaned before being released into the environment.
General ventilation can be used to achieve several goals for workplace contaminant control. A properly designed supply air ventilation system can provide plant ventilation, building pressurization, and exhaust air replacement. As new local exhaust hoods are installed in the production area, it is important to consider the need for replacement air, the location of the hood installation, and the need to rebalance the ventilation system. ”

“ 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. ”

“ A few air-bricks connecting the inside by a hollow flue formed in the wall, with its outlet as far as possible from the inlet, should be sufficient to ventilate any strong-vault. But if other ventilation is necessary in the room, have a jet of gas always alight; and over the gas place a bell-shaped covering communicating with the outer air, or with a chimney flue in preference, by a two-inch iron pipe. ”

“ With downward ventilation by propulsion from three to four times the volume of air is required that is necessary with upward ventilation, the cost being proportionately increased.
Extraction by fans has not been more successful, and they have in many cases to be discarded owing to the unbearable draughts they create.
Hot-air aspirating shafts are a costly and unsatisfactory method of ventilation, and are now seldom employed.
Ventilation by dilution necessitates the supply of a very large volume of air to keep the air in a building in anything like a healthy state. ”

“ As stated in a previous chapter, in the opinion of the author the use of the direct-indirect radiator, which has been, up to this time, and is now, very limited, will be materially increased in the immediate future, as in connection with exhaust fans they form an effective means of introducing adequate ventilation into buildings which are not very densely populated but in which there is a decided need of ventilation. ”

“ 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. ”

“ A simple way to help out the ventilation without the expense and noise of a motor, would be to arrange the ventilating flue directly above the arc lamps so that heat rising from these would cause a draft. This can be further helped out by locating all resistances in this flue. They will then be out of the way in a safe place and assist in ventilating the room. The ventilating flue will need to be fitted with a damper for use in cold weather. ”

“ In these cases, if the outlet act at all as an outlet, it must obtain its supply down the chimney—hence a smoking chimney; but generally, instead of acting as an outlet, it becomes an inlet to supply the current up the chimney, and always so when the fire is burning—hence the cold draught so generally complained of from the ordinary ventilators, and hence the reason that ordinary ventilators are so generally closed up in disappointment and disgust, and ventilation decried as a nuisance, failure, and farce. ”

“ There are many different contrivances in use for washing, screening, and purifying the air, the majority of which answer their purpose fairly well, though the evidence would seem to indicate that they are found to be most effective when employed in conjunction with a ' natural ' system of ventilation where the air is not mechanically propelled, but is drawn through by extraction, the air being more thoroughly purified moving in at a low velocity than when forced in under pressure. ”

“ The present system of each man keeping up separate fires all over his house is as crude, and extravagant, and unnecessary as it would be for every man to make his own gas or have his own well for water.
Where a steam furnace is used, two-thirds of the heating surface should be put below the floor and fresh air brought into it, and from there conducted to the rooms through large pipes. This warmed air should be let into the room at the floor, and an opening into an exhaust flue, two-thirds the size of the inlet, should be provided at the floor for the escape of the foul air. ”

“ The defect in most plans for ventilation is in the air-supply. Many people suppose that they have made all necessary provision for ventilation if they have put in tubes or openings for the escape of foul air, forgetting that these outlets will have no effect if corresponding inlets are not provided. Examine, first of all, therefore, the ducts, flues, and openings proposed for the fresh-air supply, with reference to their size and position and the amount of air to be furnished by them. These will almost invariably be found to be too small. ”

“ The so-called ventilators which many hatters insert into the crowns of their hats, and which consist of a simple eyelet-hole covered with wire gauze, are perfectly useless. Ventilation is impossible unless the air can circulate, and for this to take place there must be at least one inlet and one outlet ventilator. ”

“ Wherever a building is occupied permanently with definite conditions it is far better to trust to the ventilation of Nature—natural ventilation—than to the artificial pumping in of air. During that part of the year when the windows can be opened, at least fifteen to twenty times as much fresh air would be admitted into the ward, per patient, than could be obtained if the air was pumped in, as in the Birmingham Hospital, and that was certainly much more beneficial to the patients. I visited the Victoria Hospital at Glasgow, and went through the wards. ”

“ Where the initial outlay on hospital construction is so compulsorily a matter of supreme importance, it would seem advisable to secure very convincing proofs of the advantages derived from the mechanical ventilation in force at Glasgow and Birmingham, before incurring the cost of installing the ' Plenum ' system in other hospitals. It must be borne in mind that with an allowance of 1,000 cubic feet of air space per bed, adequate ventilation by natural means is practically always possible. ”

“ With mechanical ventilation the air is propelled or drawn in at a high velocity ranging from 5 feet to 20 feet per second, destructive of diffusion, and fatal to the effective or comfortable ventilation of a building. As one authority says, "Engine-driving columns of air through a building is not ventilating it." ”

“ The notion that our common fireplaces and chimneys afford an efficient means of ventilation, is almost too absurd for serious discussion. Everybody who has thought at all on the subject is aware that in cold weather the exhalations of the skin and lungs, the products of gas-burning, etc., are so much heated when given off that they rise to the upper part of the room (especially if any cold outer air is admitted) , and should be removed from there before they cool again and descend. Now, our fireplace openings are just where they ought not to be for ventilation ”

“ It however must be recognized that no supply of a definite amount can be obtained by merely connecting a room with the outside air by opening a window, and that as a consequence a system of ventilation which depends alone on the opening of windows will be certain to fail and will be certain to give air which will differ largely from the external air surrounding the building. ”

“ In the days of our forefathers, when houses were built with large rooms and great, high-ceiling halls, and when people spent a large part of their time in the open, air, there was in reality but little need of artificial ventilation ”

“ When the inlet under the door is of considerable dimensions, there may be some escape of warmer upper air at the top of the windows, if their fitting is correspondingly defective. These, however, are mere accidents; they are not a part of the vaunted chimney-hole ventilation, but interferences with it.
There is another experiment that illustrates the absence of ventilation in such rooms where gas is burning. It is that of suspending a canary in a cage near the roof. But this is cruel; it kills the bird. ”

“ The vitiated air immediately rushes up the shaft connecting the ventilator with the apartment to be ventilated, extracting the air and producing a continuous upward current without the possibility of down draught. The partitions separating the chambers prevent the external air being drawn through the slits upon which the wind is not directly acting. The whole arrangement being a fixture, with no mechanical movement, it is never liable to get out of order, and the apparatus can be easily fixed over a wood base or frame covered with zinc or lead to secure a good water-tight connection. ”

“ Over-heated Air a Danger to Health.
" One of the latest examples of the failure of mechanical ventilation was described by Mr. Thomas Blashill, the Architect to the London County Council, in a paper read before the Royal Institute of British Architects, on the new Council Chamber of the L.C.C., which is mechanically ventilated by a fan and fresh air warming apparatus. Mr. Blashill was 'not sure that these were of any use,' it being necessary at times to resort to natural ventilation in its most primitive form, and 'open doors, windows, coves, &c.,' both in warm and cold weather. ”

“ A current of cold air may descend upon the head of the individual, whilst the warmer air takes some other opening to escape from. No doubt the movement of heated volumes of air is subject to definite laws, which apply themselves under every case, but are rather difficult to grasp when the subject of ventilation is concerned. The philosophical ventilator is often dreadfully teased by the inversion of all that he had [Pg 389] planned, or the total failure of his apparatus. No specific mode of ventilation can be found to suit all rooms and buildings ”

“ They constitute what is, in effect, the third factor in the phenomenon of a roaring draught, and also, therefore, ineffective ventilation. That is, the entering or induced current of air must always find its channel of progress and exit certain correct degrees larger than the opening by which it entered. Every one knows that a stove or chimney wide open admits of but little suction in connection with even the blaze of paper or shavings. ”