This section is from the book "The Principles And Practice Of Modern House-Construction", by G. Lister Sutcliffe. Also available from Amazon: How Your House Works: A Visual Guide to Understanding & Maintaining Your Home.
Tobin tubes will not be required. One or more openings may be made into this duct to permit the fresh air to descend into the room, or heated air to escape.
These ducts doubtless leave the direction of the air through them very much to chance; under some conditions they may be inlets and under others outlets, but movement in any direction is better than stagnation.
In common lodging-houses, rooms without chimney-flues should never be used for bedrooms, and the Inspector should see that fireplaces, where they exist, are not closed, for the keepers will often board them up when lodgers complain of draught, rather than provide screens for the beds nearest to them. In a bedroom occupied to the extent of one person to every 300 cubic feet of air-space, it is difficult to obtain sufficient ventilation without causing intolerable draughts. The air of such a room is often sickening to a person who enters from out-of-doors, soon after it has been used. But possibly for economic reasons a higher minimum of space could not have been successfully insisted upon, even had it been suggested by the Local Government Board. Seeing, however, that, to conserve heat, the poorer classes not only crowd into rooms, but make matters worse by closing door and windows, it would perhaps have been better had some such tubular ventilators as have already been mentioned, been provided for in the Model By-laws (which most towns copy), especially with respect to common lodging-houses.
A slight digression may here be allowed, to remind the Inspector that floor-space is of first importance in measuring up a sleeping-room. The Local Government Board, in their by-laws, are silent on this point, hence a mistake may be made if the total capacity of a high room is divided by the 300 cubic feet of space they suggest. In a common lodging-house, for instance, a bed for a single person (6 feet by 3 feet), with room for approach, cannot well occupy less floor-space than 32 square feet (8 feet by 4 feet); therefore in a room 12 feet high, 384 cubic feet would have to be allotted to each person in order to give him the necessary floor-space. Again, a room 24 feet long by 16 feet wide and 12 feet high has a cubic capacity of 4608 feet; if this sum be divided by 310 (the extra 10 feet being allowed for the cubic space occupied by the bed), it will appear to be suitable for 15 lodgers, whereas the floor-space only admits of 12 beds.
Fig. 676. - Plan of small Bedroom, showing Method of improving Ventilation.
In the older parts of most great towns are to be found streets of large and lofty houses, once the residences of the wealthy, but now let out in tenements. The stairway, which is the common means of access to the several rooms, is also the principal channel for ventilation. For this purpose a louvred opening in the roof above the staircase, and another over the front door, will be found useful. The one in the roof must be dormer-shaped, with louvred laths in front, or a small turret with laths on all sides.
It is often undesirable in a direct manner to supply copiously the smoke-and-soot laden air of some towns. In these cases, therefore, it is essential that openings for inlet-ventilation be small, numerous, and distributed about the room, and that all of them, so far as practicable, be inclosed in a muslin-covered wire cage, the area of the muslin surface being many times greater than that of the opening. Some ventilators have muslin or cotton-wool smut-screens in their interior, but these not only seriously reduce the air-passage, but are quickly choked, and - being hidden - their condition is not observed. Others provide that the air shall first impinge upon water, on the frequent renewal of which their efficiency as dirt-removers depends. Both these arrangements are sure to be neglected, and the cage method may also be, but with less likelihood, as the scree in this case is always in sight, and no effort of memory is demanded.
Even its dirty appearance will tend to induce the little trouble being token that renewal of the cover requires.
The size of the openings necessary to admit the required amount of air cannot, of course, be scientifically fixed, as the volume of air passing through them is dependent upon many atmospheric conditions. They should, however. be as large as convenient, and possess means of controlling their area. As some guide, it is usual to regard the velocity of air passing through an unobstructed opening a foot square as five feet a second, or 18,000 cubic feet an hour, and the amount of air neccessary to keep the permissible impurity as low as 2 volumes of CO, per 1000 volumes of air, as 3000 cubic feet per hour per person.1 In the calculation it will not be necessary to provide that the whole of this amount must pass through openiings specially provided, because the door and windows will take their share of the work. Therefore every ease must be judged upon its merits.
Three ordinary gas-burners are anally counted as equal to one person. This is under the mark, as it is estimated that one medium-sized gas-jet vitiates as much air as five or six persons.
DR. SCURFIELD'S VENTILATION INDICATOR.
The actual amount of air coming into a room from all sources can only be correctly ascertained by finding the area of the outlets, and the velocity with which the air is passing through them. The latter can be obtained with an anemometer.
The Inspector's nose is the only instrument required in the first place to detect insufficient ventilation, but a handy chemical "ventilation-indicator" has recently been invented by Dr. Scurtield. the Medical Officer of Health for Sunderland, which will undoubtedly prove very useful in detecting the approximate amount of CO2 in the air of rooms. In the doctor's own word-. "The object of the apparatus is to furnish a reliable comparison between the percentage of carbonic acid in the air of a room and the air outside. The apparatus when ready for use, consists of an aspirator filled with water and supplied with a gauge, surrounded by a number of tubes, all containing exactly the same quantity of the same pink solution of baryta and phenolphthalein. Each tube can be in turn connected with the aspirator, so that as the water is run off from the aspirator, an equivalent amount of air bubbles through the pink solution in the tube, which loses its colour quickly or slowly, according as there is much or little carbonic arid in the air. The apparatus is carried in a case, which is used for catching the water and refilling the aspirator when necessary.
The Apparatus (without case).
Enlarged Sections of Aspirator and Single Test-tube.
Fig. 677. - Dr. Scurfields Ventilation Indicator AA, metal tubes; b. rubber tubing; or, rubber stoppers; D. tap for lettting off water: B. tubing slipped over tap to increase suction power: F, ring for teat-tube; 0. socket for test-tube; HH. gauge.
When the decoloration is complete,.the tap is turned off, and the amount of air that has been necessary to effect the decoloration is shown by the amount of water that has been run off from the aspirator. For example: - One tube is decolorized in the outside air, and it is found that 1.8 cans of air are necessary to do this. A second tube is decolorized in the room under observation, and it is found that 1.2 cans of air are necessary to do this. Then - the amount of carbonic acid in the air of the room is to the amount in the outside air as 1.8 is to 1.2, or, in other words, the air of the room contains half as much again car-bonic acid as the outside air."