Ventilation as a dynamical problem : a paper read before the Annual Meeting of the Medical Officers of Schools Association, on February 6th, 1902 / by W.N. Shaw ; with the subsequent discussion.

Napier Shaw

Date:: 1902

Credit: Ventilation as a dynamical problem : a paper read before the Annual Meeting of the Medical Officers of Schools Association, on February 6th, 1902 / by W.N. Shaw ; with the subsequent discussion. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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$satisfactory circulation. The loss of momentum through friction and other causes must be made good by the provision of some mechanical aspirating power in connection with the main extract shaft. As a result of this opinion, she found small aspirating fans fixed in the extract shafts of the best schools to supplement the work of the large propelling fan. An excellent point in connection with this combination method of ventilation is that windows can be opened in any part of the building without interfering with the successful working of the system. This is not allowable where the Plenum system alone is installed, as the air must enter rooms under a slight pressure, with which the opening of even one window interferes. She found her own opinion shared, viz., that the effect on young people of attending schools where the windows are hermetically sealed is unsatisfactory. Teachers rarely take the trouble to explain how ventilation is secured, and the children, accustomed to the sight of closed windows, lose useful training in hygienic habits. Another objection is also raised to the adoption of the pure Plenum system: there are very few buildings which are not the better for free flushing at intervals by currents of air through open doors and windows, but this is an impossibility where windows are not made to open. A decided opinion is held by some U.S.A. experts that certain sensa- tions of draught experienced in mechanically ventilated buildings might be obviated if two or more smaller outlets were provided in each room, instead of one large one as is now usTial. This is a point she would very much like to hear discussed. She had had no opportunity of observing a building where this arrangement has l)een adopted, but she did know several mechanically ventilated schools in England where there is a very perceptible current of air experienced by the scholars sitting in line with the one outlet; especially does this appear to be the case in rooms where there is a considerable expanse of window on the opposite side from which the air enters. The air, being propelled into such rooms at a considerable velocity, impinges on tlie cold surfaces of the large windows and then passes in a very chilled state up the extract shaft, causing such discomfort to those sitting in its track, that, in order to mitigate the nuisance, the extract shaft is often temporarily closed up, thus, of course, defeating the principle of the system. Another development now ad\ocated in the United States is that of ha\ ing several small inlets as well as more than one outlet, in order to secure improved diffusion. It is thought that when air is admitted b}^ only one large opening, it passes too rapidly to the opposite side of the room, and suffers from unequal distribution, whereas if it be admitted at several small inlets, of course, all at the same level, it would be better diffused. The ultimate economy of mechanical systems of ventilation is thoroughly recognised in the United States, and that view is supported in the cities in the north of England where a suflicieut length of time had elapsed since installations had been made to enable authorities to strike averages. All evidence pointed to the fact that the working expenses of these systems are very reasonable indeed; it is the first installatio)! that is financially costly. She wished to ask if a portion of the draughts so often complained of by the occu])auts of mechanically ventilated rooms is jiot possibly attributable to the fact of the air entering without a sufficient admixture$