Imágenes de páginas
[graphic][merged small][graphic][ocr errors]

heated by hot air from one grating, and some idea of the difficulty of dealing with buildings heated in this manner may be formed from the experience gained in this. By carefully closing the excessive outlet spaces in the roof, the down draughts were cured, and there was no apparent leakage from the ceiling when the outside temperature was at 4oo F. This arrangement, however, by adding to the ventilating power of the building, caused the sun-burners to place the air inside under considerable tension, the consequence being that much cold air came in around the doors and windows as well as a largely increased proportion of fresh air through the inlet to the hot air apparatus. The grating through which the hot air ascended was of small area for so large a building, the result being that the heated air shot upwards with considerable velocity in the direction of one of the sunburners which was nearly overhead. This upward movement of the air caused the gas flames of the sun-bumer to flare and flicker so considerably as to divert the attention of the audience. As the authorities did not see their way to furnish a more suitable heating arrangement at that time, and this flaring of the gas flames must be prevented, there was no alternative but to reduce the ventilating pressure on the building, and this was done by allowing more cold air to fall from the ceiling, but at the same time so distribute it as not to give rise to unpleasant down draughts. This sort of compromise equalised matters, because the air rose from the grating with less velocity; but there was, obviously, less fresh air coming into the building. This is another illustration of the necessity for warmed air being introduced through a number of small apertures in the floor of a building, and not to come in one volume at one point. If due provision were made for fresh warm air, the ventilating power of this building could be used to fair advantage.

Fig. 16 is a church seating 7oo persons, and over 4o feet high from the floor to the top of the roof. The roof was open

[graphic][merged small][graphic][ocr errors][merged small]

to within two feet of the ridge, and was carefully plastered between the main rafters. The building was lit by electricity, but jets of gas were fixed at intervals above the lower bond of each principal. There were two ventilators upon the roof of a "self-acting" type, and these, at their lower ends, were shut off by lifting plates about two feet square. Owing to the large area of these plates, and to the considerable spaces around them, much air leaked in; and, in cold weather, when the temperature of the air outside was 4oo F., a severe down draught, at intervals, was experienced from the one shown in Fig. 16, although the valves of both ventilators were closed. It was evident that the cracks and fissures in the plaster, or between the plaster and the rafters, were of considerable area in the aggregate. This is the church referred to on p. 65 as having a large volume of fresh air coming in through the inlet of the hot air apparatus, shooting up in a nearly perpendicular current.

This large volume of heated air escaped around the ventilator almost directly above it, and through the crevices, leaving so much ventilating power upon the building that the velocity through the outlets was considerable at the time when the other ventilator acted as an inlet. To illustrate the large volume of fresh air warmed which came into the building, it may be mentioned that when a very delicate anemometer was held above the grating down which the cold air in the church ought to circulate so as to be warmed before re-entering the building, little or no movement was perceptible. It was noticed, however, that there were two currents in the warm air grating, namely, a warm up current of high velocity and a lesser down current of cooler air. In consequence of the warmed air from the grating ascending so rapidly, it was not possible to open the plates of the ventilator, No. 2, throughout the winter and spring seasons when the heater was at work. If the temperature of the outside air was 5oo F. or less, powerful intermittent air currents were at once formed if the valves were opened very little. The caretaker had moved the lever which was supposed to close the valve and cut off the fresh air inlet, but the valve did not act, and he was not aware of the huge volume of fresh air which was coming in. This instance may be unique, perhaps, and in considering the effects which resulted, it is necessary to remember that the three-fourths of the ventilating power of a building which is generally used up in forcing air around the doors and windows was not wasted in this case, so that much of the total ventilating pressure was available for further ventilation. Under these circumstances, the velocity of the air in the outlets was considerable at one end of the church, whilst at the other end cold air streamed in to partly equalise and reduce the appreciable ventilating pressure which remained. Had the warmed air been introduced through a considerable number of small inlets in the floor instead of through one large opening, the ventilation would have been much improved. The ventilators required valves which would perfectly close the apertures.

Fig. 17 is a lecture hall, ceiled just above the centre bond of the principals, and there were three openings through the ceiling having gratings as shown. The three tubes from the gratings joined into one at a point some five feet from the top of the roof, and there were silk valves inserted with a view to prevent down draughts. When the hall was examined the silk valves did not act, because down draughts were more or less continuous, and very unpleasant in cold weather. The hall was heated by a large stove in the corner of one end, and as the heat from the stove was generally very insufficient when the temperature was low, jets of gas were lit which were fixed at intervals upon the iron ties forming the lower bond of the principals. Much cold air entered from the doors and from a high grating at the back, sweeping along the floor to the stove. The stove itself admitted a little warmed fresh air, but this simply rose with the air warmed by

« AnteriorContinuar »