Imágenes de páginas
PDF
EPUB

these movements many Sundays in a place of worship where much fresh air passed through a heater, and the results were most unsatisfactory. In the case referred to, the means for shutting off the fresh air would not act, and the caretaker not knowing what was wrong, did his best under the circumstances.

Arrangements have been made in many buildings to heat fresh air by passing it through coils or over heated pipes fixed above the floor. If there is a wide aisle or space between the outer walls and the seats, it is possible to have coils, radiators, or simply rows of hot water pipes so arranged that fresh air can be wanned by them before it gets into the building. The colder the air outside the denser it is, and tends to flow in from the air inlets at the bottom of the coils, being only partially and imperfectly warmed. This behaviour of the inlet air is accelerated by the portion which is superheated, for this ascends quickly and gives rise to an upward movement which is fed very largely by the inside air. In many instances, much the greater portion of the inlet air flows in near the floor level in an unwarmed condition to supply the place o( what has moved upward; and if air is more evenly heated before it gets into the structure, it ascends and rarely gets into the lungs of the audience.

Space will not permit, nor would it serve a useful purpose, to detail the attempts made to heat inlet air by the various hot water and steam coils and radiators used, but until recently no great effort was made to devise a satisfactory way of heating fresh air by coils fixed to the walls of the building. Radiators are now made which enable air to be heated by passing through tubes inside the radiator, and much more attention is given to inlets in association with radiators generally. It is not the radiators, however, which are so much at fault as the introduction of warm air in the wrong portion of the building. It has been foreshadowed already how the heated air ascends, and, although a cold current from the walls and windows flows downward, still a powerful current of hot air ascends a foot or two away from the walls, and in the portion of the building where cool air would be more beneficial because it would flow towards the centre and seated portion of the structure. The larger and higher the building the more diffusion takes place, and the air currents are less perceptible generally, but to bring fresh air through radiators standing against the outer walls must always tend to create down draughts in the centre, especially if the roof has many interstices, and the outlet space renders the building top heavy.

Where fresh air inlets exist, the gratings in the outer walls should be protected from being aspirated by the wind, and they ought to be capable of being removed easily, so that the ducts might be cleansed from dust. In those structures where coils are fixed against the outer walls, attention should be given to the condition of the outlet spaces in the roof so as to make sure that the warmed air is caused to circulate as much as possible in the centre of the building.

The internal structure of large buildings is so variable— some having galleries, some side transepts with separate roofs, some being low, some very high, some being ceiled, some being open almost to the apex of the roof—that it is impossible to lay down any rule whether much cold air can be admitted without causing draughts. Each structure will have to be taken upon its merits or demerits, and the best provision for inlet air, either cold or heated, must be made according to circumstances.

There is no doubt whatever that the only satisfactory method of ventilating new buildings is to introduce warmed air through a large number of small openings in or just above the floor of the structure, and then make sure by the careful laying of felt upon the roof, and rendering the joints of the felt air-tight, that the outlet spaces, in the aggregate, are not of too great an area. The building should be high, and unceiled to near the apex of the roof, then the ventilating power of the structure will be sufficient to give fair results even during the warmer weather of spring and autumn. Now that the electric current is provided in most towns, it will be neither difficult nor expensive to fix a fan which may be used to assist the ventilation of churches and halls when the temperature of the air outside approaches that of the air inside—that is from 53o to 63o F.

CHAPTER V.

CHURCHES AND PUBLIC BUILDINGS AS THEY ARE.

As the ventilation of churches and public buildings must necessarily depend upon their form and architecture, it will tend to make a very difficult subject more clear if a number of illustrations are given showing the types of buildings erected and what is wrong with the ventilation and heating.

Reference will be made chiefly to buildings erected some years back, and attention will be given at first to those which have no induced ventilation other than the heated air by which they are warmed, the gas or other illuminant by which they are lit, and the heat evolved in the breath and from the bodies of the audience. With a view to show the movements of the air in public buildings, a rough outline of each type of structure is given, and in all cases the cold currents of air are shown by dark shading, and the direction of the currents, whether circular or otherwise, by the manner in which the shading is executed. The direction of the warm air currents is indicated by arrows. In some cases the buildings have galleries which are not shown in the drawings, and, when that is the case, they are omitted for simplicity's sake.

Fig. 12 and Fig. 13 indicate the movements of air in numerous churches, chapels, and halls which have no fixed ventilators on the roof and where the foul air escapes through cracks and interstices between the rafters and ceiling, or in the match-boarding as the case may be. This class of building is not ceiled, but is open practically to the apex of the roof, and boarded or plastered between the rafters. Fig. 12 represents a church where a certain volume of air leaked from the roof, R, but not enough to give rise to very perceptible down draughts even when the temperature of the air outside was at 35o F., whilst the tension of the air in the building was so relieved by the leakage falling from the roof that the air which got in around the doors and windows did not give rise to unreasonable draughts or discomfort. The dotted line shows the level of the wall plate upon which the roof rests, and the height from the floor, F2 to the roof, R, is 38 feet. When the temperature of the air outside was at 450 F., there was a strong pull upon the air in the building, and much air was drawn around the doors and windows as well as from the fresh air supply to the stoves, of which there were two. When the air outside was at 550 F. the ventilation of the building was at its worst point, and if the openings in the tops of the windows were kept shut it was very bad after an audience had been seated for an hour. The large stoves heated the air inside the building, but the volume of fresh air admitted through them was very inadequate. The building was lit by two ring burners. The church wanted much more warmed fresh air, and two roof ventilators which could be closed completely by suitable valves when the temperature of the air outside was 4o0 F. or less.

Fig. 13 is a section through the apex of the roof of a church, and the dotted line shows the level of the wall plate. S represents the seats, and P the pulpit. From the depth of the shading it will be seen that more air fell from the crevices in the roof when the temperature outside was at 350 F. than was the case in Fig. 12, and the movements of the air inside and the down draughts were decidedly unpleasant. It was quite possible to notice how the air circulated so that the coldest portion might be heated by passing down the . gratings under which hot air pipes were fixed. There were

« AnteriorContinuar »