Slike strani
PDF
ePub

scribed as the ventilation in any room which has cold walls, any local source of heat, such as radiators, stoves or animals, and which has a comparatively small constant air supply and exhaust, whether above or below atmospheric pressure. Such ventilation results from every local contact of air with objects of different temperatures, which cause an upward or a downward current of considerable proportions, regardless of whether the air is fresh or contaminated.

We have built small toy windmills which will be caused to revolve by the rising current of air actuated by the heat of the human hand. The entering fresh air, if warmer than the air in the room, rises to the ceiling; if cooler, it falls to the floor. If the outlet is at the floor and convenient to a downward fresh and cool current, the fresh air will short circuit out, leaving the contaminated air in blissful occupation of the breathing zone. Under such conditions, of course, each warm thing in the room would be promoting the dilution by causing the fresh air to rise to replace the air warmed and so pumped up by contact, and each cool thing, such as the windows, would be causing the displacement from the floor into the breathing zone of fresh air, by the falling currents of cooled contaminated air.

VENTILATION BY DISPLACEMENT.

Ventilation by displacement may be described as the ventilation in any room when the windows are opened on each side so that the wind may cause a complete horizontal displacement. Where it is possible to introduce fresh warmed air through an opening under each seat, as in many theatres and churches, the ventilation is by displacement, if it rises directly to the ceiling and so passes out. Practically, ventilation by displacement is only possible under such conditions or where a very small difference in temperature may be obtained between the room and the entering air, without local or cold surfaces to cause vertical mixing

current. Some interior rooms of buildings having no heaters and no windows. or cold walls are satisfactorily ventilated by displacement with air movement from side to side at the breathing zone. Ventilation by displacement is not practical in the ordinary class-room as now constructed.

The Chicago Commission on Ventilation, however, has had an experimental class-room, using this principle, in use under observation, for several years. This class-room has inlets for fresh air under every desk, and is provided with special air chambers under the floor and over the ceiling.

STANDARD EQUIPMENT FOR CHICAGO SCHOOLS.

The Chicago schools are practically all equipped with mechanical ventilation, and the standard procedure is to arrange the ventilating systems so as to deliver a minimum of 30 cu. ft. per pupil per minute, under a slight pressure, occasioned entirely by the resistance of the duct systems. The pressure at the supply fans is depended upon to deliver the air to the rooms and gradually to force the contaminated air out of the rooms through flues to the roof ventilators. This pressure is seldom sufficient to overcome the inward leakage due to the wind and usually such is this leakage that rooms to windward show more air leaving the rooms through the exhaust flues than is entering through the supply flues, while the rooms on the leeside show very much less air leaving by the exhaust openings than is delivered by the fan. This leakage in and out through walls and windows is a wellknown phenomenon, and is not particularly objectionable, as it assists in the ventilation, when ventilation by dilution. must be used.

Experiments have been made which show that a ten mile per hour breeze is approximately sufficient to balance the static pressure ordinarily maintained in the Chicago schools.

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

PLAT PLAN, LEWIS CHAMPLIN SCHOOL, CHICAGO AND NEIGHBORING BUILDINGS.

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

THROUGH HEATING CHAMBER, LEWIS CHAMPLIN SCHOOL.

COURT OF LEWIS CHAMPLIN SCHOOL, SHOWING INTAKE AND VENTS ON ROOF.

DESCRIPTION OF SYSTEM.

Steam at about 90 lbs. pressure is supplied from a detached boiler-house through a tunnel. The heating is accomplished with exhaust steam, supplemented with live steam, introduced through an automatic pressure regulator, and is circulated at not exceeding 3 lbs. pressure. The returns are under the suction of a vacuum pump in the boilerhouse.

The fresh air supply is drawn from an interior court, paramount to taking. it from the third floor level. It passes through the engine-driven fan, then through heaters arranged so as to provide two temperatures of air, one at about 120° F., the other at about 60° F. The hot air (120°) is delivered into the upper part of a large plenum chamber, and the tempered air (60°) is delivered into the lower part of the chamber. There are two such chambers in the Lewis Champlin School. From these chambers chambers comparatively small horizontal metal ducts extend along the ceiling to the first floor rooms, and to the bases of the vertical flues leading to

« PrejšnjaNaprej »