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.
- Shaw, Napier, 1854-1945.
- Date:
- 1902
Licence: In copyright
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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![\ tht‘ head for ventilation ip ])roduced ])v a single agent—a fan or a cliiiiiney—this is genenilly j)laced in one of the narrow channels. The energy necessiiry to get uj) the velocity in the second channel lias to be “ transmitted ” from the source of power, the fan or chimney as the case may he. Now there are special considerations attaching to this pneumatic trans- mission of ])Ower: for one tiling, it is transmitted to all openings, whether intended for the juirpose or not ; and, secondly, the low jiressure fans in genenil use for ventilation ])iirposes, are very uneconomical agents for transmitting energy ; a good deal of power is apt to go to waste in the attempt. I conclude from tliis that where it is necessary to have consider- able velocity in two sejiarate iiortions of an air circuit, as in inlets and in outlets, it is better to have also separate means of }>roducing the velocity. For jiroducing velocity in outlets, chimneys as well as fans are available : for jirodueing velocity in inlets without transmission of power, chimneys are not avail- able : hot air may be so in a few special cases, but as a rule a fan is the only resource. A special advantage of avoiding the pneumatic transmission of power here spoken of, is that the air i)ressure in the room itself need not be either above or below that of the outside, so that open windows or doors need not disturb the regular course of the ventilation. This is a very important matter. in.—Thermal Convection. The third ])oint to which 1 wish to direct j’oiir attention is concerned with the admission of air to a room, and its relation to the tem])erature of the room. 1 think the tendency, or rather the determination, of warm air to rise to the ceiling, and cold air to sink to the lloor, is only imi)erfectly realised, as a rule. A few experiments would convince you that if jmu admit cold air to a room you may seek it successfully at the floor, no matter where you i)ut your inlets ; if, on the other hand, your air is admitted warm—warmer than the air alread}' in the room—you must get a stei)-ladder if you want to find it. No mechanical arrangements that 1 know of will induce relatively warm air to reach persons near tlio floor until it has exhausted all the possibilities o])en to it at the ceiling; and, on the other hand, no arrangement of Tobin tubes or fine jets will induce cold air to float in warmer air for the benefit of the occuj)ants of the i-oom. The wonderful j)ersistence with wliich cold air in crowded churches manages to reach one’s feet—hidden away inaccessible to everything but cold air—is a striking indication of tlie inexorable laws of convection. Many important con- st fpu*nces follow from the recognition of these facts. To intiM (luce wai'in air for tin* jmrposes of ventilation in a room](https://iiif.wellcomecollection.org/image/b22449474_0008.jp2/full/800%2C/0/default.jpg)
