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s, hot water or steam pipes are used to facilitate the
imatarge of foul air through the outlets. It is too often
Si*-*tten that their effective value depends upon the column
J:a.rfT above the heater, and between it and the outer atmos
^iifcfe. Where the outlets enter near the ceiling of the
."C.i. and floor of a building two or more storeys high, heaters
/.. effective, and, where there is a high column of air above
..m, they can be made to aspirate powerfully; but they are
worth the expense of erecting and maintaining unless
t air column measures 2o feet or more. Small fans are
irh more effective, and, on the whole, less costly.
Where coke or common fuel is burnt in a furnace or
ranged so as to give the greatest heating surface for the fuel
■nsumed, and there is a tower or stack sufficiently high to
lord good ventilating power, it is possible to assist the
utlets of a building very effectively by connecting them with
le furnace. The upcast pits of coal mines used to be
entilated chiefly by furnaces in the first half of the
lineteenth century, but fans have taken their place since;
ind for ventilating buildings, furnaces are rarely employed
now. Furthermore, it is not probable that new buildings will
be erected in which furnaces will be used to remove the outlet
air. Not that the furnace is ineffective or unreliable, for
this is not the case. Where furnaces have not done what
was expected of them it was not their fault, but the want
of physical knowledge on the part of those who planned the
ventilation. Where the outlets are properly adjusted, and
shafts are so shielded as to be almost independent of
effects, excellent results can be obtained by furnace
on. The furnace has proved its value in the ventilation
J mines so conclusively that further comment is need
;ss. It is a fact, howev*- that the majority of ventilating
eers are in favou "an for coal mines, and, when
ntly driven, thf loubt the exhaust effects are
i well as more powerful. CHAPTER VIII.
HOW TO VENTILATE NEW BUILDINGS.
It rarely happens that the architect of a building has any lot in the selection of the site upon which the structure is to be erected. In the case of a church it is most probable that the site was purchased years before the plans were ordered, and the design may have been selected from a number sent in for competition, the architect himself not having seen the position at all. Under these circumstances, the architect knows nothing of the wind effects upon the ground in question, although it is possible for him to alter somewhat the sizes and positions of the air inlets and outlets. It often happens, however, the church authorities determine that a building shall be erected in strict accordance with the plans, or, as is not unfrequently the case, they conclude that certain spires or towers shall not be proceeded with until there are more funds forthcoming; the result being that the heating and ventilating arrangements are modified and changed to the detriment of the well working of the whole.
In the selection of other sites for assembly halls, town halls, schools and hospitals, the architect has rarely any choice in the matter, so it generally happens that he has to adapt his building to the site, rather than select a site for his building. If the architect aims at appearance chiefly, and this is the principal point in a competition, then everything else has to give way so that the building may be imposing and striking in design. The comfort of the audience ought to be the chief consideration, but if it has due prominence, the architect will be handicapped in his design. Architects, therefore, have not had much inducement to try and make the ventilation the chief consideration, hence it is, perhaps, that so little real progress has been made in supplying a reasonable volume of fresh air in every part of the building where the audience is seated.
The authorities who are responsible for the selection of a site for a church or any other public building ought to have some knowledge of what they are doing. If the ridge of the roof must run east and west, much will depend upon the side of the road or street where it is to be erected. If the church is to be built on a hill side, much care is necessary to make sure that the prevailing winds do not blow at right angles to it, and that the outlets on the roof shall not be subjected to greatly increased pressure every time a moderately strong wind is blowing.
The same precautions ought to be taken in the case of the sites for all public buildings, and if the authorities are in any dilemma as to the probable results of wind action, advice should be taken beforehand, as it is quite possible that a great mistake may be made for want of some knowledge in the matter. Those buildings which are erected in more or less open spaces are the most subject to the aspiration of the wind, and it is always well to know from what side the inlet air is best taken, and what parts of the building the winds will chiefly affect. Much more attention ought to be bestowed upon the probable action of the wind upon inlets near the ground level. Now that the effects have been described, it is not difficult to find a remedy, and, with the same consideration given to the outlets through the roof, the ventilation of a building and the movements of air in it ought to be much more under command.
One of the first considerations is the height of the building.
No question as to cost should stand in the way of its being high. If it were only the increased number of cubic feet of air per head which it will afford at the time the audience assembles, it is worth all the extra cost; but the increased ventilating power which 2o feet of headroom will afford is equal to about 2 ounces of pressure on the square foot during the cold months of the year. Then with 8 feet or more of basement underneath the church for the purpose of forming a heating and mixing chamber, it is possible to get a height of 5o feet from the basement to the apex of the roof: and for working a building by what is called natural ventilation such a height is excellent. Not that 4o feet is unworkable, for it is not, but a good height is in keeping with a bold design, and herein the architect and the ventilating engineer will be in agreement.
If it is intended to ventilate without mechanical aid, the height of the building is the first and chief point of importance, and it is much more necessary for natural ventilation than when mechanical aid is employed. But even where mechanical aid has been furnished it will be possible to do without during cold weather and dispense with the fan, if the building is high; and, as such a structure will afford so many thousand extra cubic feet of air by reason of the good height, it will be best that a church or hall shall be high although mechanical aid is to be supplied.
With regard to the ceiling, most modern buildings are now made without, and, for the sake of the extra cubic space, it is to be hoped that they will never come into fashion again. The first consideration is to make sure that the roof under the tiles is covered with felt which is joined air-tight alike between each width and between the last width and the wallplate. Then it will be possible to keep the area of the outlets in the roof under command.
With regard to ventilators, if the building is long it is not wise to expect all the foul air to travel to the centre and then through one opening. Such an opening would have to be large, and if the roof of the building were much higher than the roofs of the buildings around, the outlet would be subject to much suction, and it would be difficult to prevent alternating air currents being formed in windy weather. Two or three ventilators had better be used, and with a building 4o feet or more from the basement, if there is one, to the apex of the roof, the area of the inlets should be double that of the outlets for winter ventilation; and care should be taken to make provision for regulating the area of the outlets perfectly. During' very cold weather, the extra ventilating power which is then at command, should be used up in forcing the air through the outlets under great pressure, and, therefore, at a high velocity. Under these circumstances the outlets should be closed considerably, and the ventilators had better be closed altogether, probably, when the temperature is below 32o F., unless it should happen that the felting of the roof is so air-tight that the interstitial cracks and spaces are not large enough for the outlet air —a state of things which the author has never met with in an unceiled building.
Another point of considerable weight bearing upon the ventilation of a building if it is to be done without mechanical aid, is the arrangement of the window openings for summer use. It is thought that a study of Fig. 6, p. 31, will throw some new light upon this subject. The window openings should be high up, and as many in number as it is possible to accommodate in the design. Window openings have hitherto been designed with a view to cause the air as it passes inwards to take a vertical direction, so that they may be used for winter ventilation. It is full time that the folly as well as the impossibility of ventilating by cold air was recognised, and this chapter is not complete until the point is reached where sufficient air is introduced through the floor to supply all that is required. Under these circumstances, all attempts