This section is from the book "A Treatise On Architecture And Building Construction Vol4: Plumbing And Gas-Fitting, Heating And Ventilation, Painting And Decorating, Estimating And Calculating Quantities", by The Colliery Engineer Co. Also available from Amazon: A Treatise On Architecture And Building Construction.
Arrangement Of Flues. The general method to be adopted in arranging the main distributing flues (or ducts) and branches in the basement of a building depends upon the system of ventilation to be employed, and upon the arrangement of the heating apparatus-whether concentrated or distributed.
With the plenum system, there are several methods in common use, as follows:
1. The main flue,-or duct, is carried along the center line of the building, and lateral branches are extended right and left to the vertical ducts in the side walls. If these are numerous, the aggregate length of the branches is liable to become excessive, causing too much frictional resistance, and entailing unnecessary expense.
2. The main flue is divided into two branches, one of which extends along each side of the building and supplies all the vertical flues on that side. The connections to the wall ducts are then made direct, or nearly so. In many cases this plan is more economical, in the matter of piping, than the previous one.
3. An air chamber is located in the central part of the basement, and the air is conveyed to the various vertical ducts by means of pipes extending radially from the central chamber to the points desired. This plan is suitable only for small buildings. If the pipes are very long, or are numerous, it is likely to prove an expensive and cumbersome arrangement.
4. The entire basement, or a large part of it, is made airtight, and is employed as a reservoir for fresh air. This plan is suitable for all classes of buildings where the basement is not required for storage purposes. Where this system is adopted, great care must be taken to make the floor or bottom perfectly water and gas tight, so as to prevent the entrance of moisture or earth gases; all drain and soil pipes must also be rigorously excluded from the rooms used for air storage.
5. A vertical air-shaft, extending from the basement to the top floor, is located in the central part of the building, horizontal branches, more or less subdivided, being taken off at each story. In buildings of three or more stories in height, this plan is usually an advantageous one.
6. The fan delivers the air into a chamber which is divided into two parts, one for hot and the other for cold air. Each wall flue is connected to this chamber by a separate and independent pipe, and each pipe is provided with a mixing valve which delivers air from either the hot or cold chamber, as desired.
Improper Outlet For Foul Air. The practice of using the attic of a building for a foul-air receiver, as frequently done in schoolhouses and similar buildings, is highly objectionable. The usual arrangement is to terminate the foul-air flues at the attic floor and permit them to discharge freely into the space above. Sometimes an aspirating shaft is attached to the roof to aid in discharging the foul air, but usually it finds its way out through slatted windows and similar openings. The wind has comparatively free access to the whole space, and while it blows, an increase of pressure is likely to exist, which is liable to cause a blow-down in the flues. This trouble could be prevented by connecting each flue to an aspirating shaft. The force of the draft would then be greatly augmented throughout the entire building.