CHAPTER IV THE BuILpINGc—Its VENTILATION (Part 2)

air space over a height of 12 feet should be ignored. Suppose, for example, that the space required for a certain room is 7200 cubic feet and that , d 72 the room is to be 14 feet high. A floor area of ~ , or 515 square feet, would give this capacity but would not be satisfactory from the point of view of ventilation. The usable height is 12 feet, THE BUILDING—ITS VENTILATION 49 - 2 so that the area should be ua or 600 square feet. A room 30 feet by 20 feet would meet the case. Customary Allowances. The following figures will give an idea of the customary allowances of cubic space per head: common lodging-houses*: rooms occupied at night only, 300 cubic feet; rooms occupied by day as well as at night, 400 cubic feet; Metro- politan police officers’ quarters, 450—cells, 800; army barracks, 600; factories, 400; hospitals for adults, 2000; ditto for children, 1500; bakehouses, 500. Figures such as these are not a satisfactory guide to good ventilation without a second figure of the number of air changes per hour to be given. For this reason certain licensing authorities, the London County Council among them, require ventilating arrangements capable of providing 1000 cubic feet of fresh air to each occupant (counting seating accommodation) of cinemas, theatres, music halls and similar public buildings, before granting the licence. Conditions of Satisfactory Ventilation. There are certain con- ditions which any really satisfactory system of ventilation should fulfil. They may be stated briefly as follows: 1. Fresh air must be admitted or injected and the vitiated air allowed to escape, be extracted, or expelled. 2. The quantity of air supplied and the velocity of its admission should be under control. 3. The change of air should be thorough, no stagnant corners being left. 4, There should be no draughts. 5. The incoming air should be clean and humid and not scorched or deprived of its moisture by defective methods of warming it before admission. 6. The temperature of the air should be uniform and under control. Probably there is no system which absolutely fulfils all these conditions at all times, but the principal systems in use and their respective advantages and disadvantages will be fully described. Natural Principles of Ventilation. There are certain natural principles which greatly assist the ventilating engineer, namely: * The term “common lodging-house”’ is rather vague. There is no English statutory definition of it, but from legal decisions it may be taken to be that class of lodging-house in which persons of the poorer class are received for short periods, and, although strangers to one another, are allowed to sleep in a common dormitory. 50 THE BUILDING—ITS VENTILATION 1. The fact that warm air is lighter than cool and tends to rise. 2. Moist air is lighter than dry air and also tends to rise. 3. Air in motion is less dense than still air. 4, Gases at different density tend to diffuse. Main Classification of Ventilation Schemes. There are three principal schemes of ventilation in common use: (a) The natural scheme, (b) The vacuum (or extraction) scheme. (c) The plenum (or propulsion) scheme. Schemes (b) and (c) are sometimes described as “mechanical” schemes. A natural scheme is one in which inlets and outlets are placed in suitable positions and nature is allowed to do the rest. This system is simple and economical. It will generally give reasonably good results in a building which provides approximately 1000 cubic feet of air space per person, but there is very little control. A vacuum or extraction scheme is one where the vitiated air is drawn out artificially—usually at outlets near the ceiling or roof— and the fresh air is allowed to make its own way in through inlets at a lower level. Air Conditioning. In a plenum or propulsion scheme the fresh air is pumped in and the vitiated air is allowed to make its own way out, or is drawn out by a fan or pump of smaller power than that at the inlet, when it is usually described as a “balanced scheme”. The plenum scheme usually combines air warming and ‘“con- ditioning” and is therefore a much more complex and expensive system both to install and to maintain. The vacuum scheme is to be reeommended, in preference to the natural, for buildings in which there is some reduction in the allow- ance of cubic air space per person. It usually entails merely the hurrying up of the air currents caused by the natural principles. It requires but little initial outlay, while running expenses also are low. Downward and Upward Plenum Ventilation. The plenum scheme, on the other hand, is usually arranged to provide down- ward ventilation, and the natural principles have then to be over- come before the fresh air (introduced at ceiling level) reaches the occupants, The plenum system is sometimes adapted to upward ventilation (which enables the natural principles to be utilised), but not every building is suitable to its use, while the expense of installation is usually greater. The Council Chamber of the London County Council provides an excellent example of upward plenum ventilation, the inlets THE BUILDING—ITS VENTILATION a1 being well-spaced low down around the walls and across the floor, by making use of fixed furniture to mask the inlets. The plenum scheme, either upward or downward, is essentially the scheme to be recommended for a closely packed building such as a theatre or cinema. Owing to its complexity it would be un- wise to advise its installation unless it can be done on thoroughly sound lines, and there will be an income sufficient to guarantee efficient maintenance. Disadvantages of Natural Schemes. The objections to the natural system are (1) the source of supply of fresh air is not under control; (2) the incoming air is not so readily cleansed and humidi- fied; (3) the volume, temperature, and velocity of incoming air are not under control; and (4) it is apt to prove a draughty system. On the other hand, it is simple and inexpensive, costing very little for maintenance, and doors and windows may be freely opened without disorganising the system. Disadvantage of Vacuum or Extraction Schemes. Few objec- tions are raised against the vacuum scheme, except that, if in- stalled in a closely packed public building, it does not give sufficient control to the “‘condition” of the air and is apt to cause draughts. Disadvantages of Plenum or Propulsion Schemes. The objec- tions often put forward against the plenum scheme are as follows: (1) the downward system is opposed to natural laws and necessi- tates vitiated air being re-breathed; (2) the flues and ducts are very difficult to keep clean, and become foul from dust and germs; (8) the air is apt to be delivered overheated, causing great dis- comfort about the head, while the extraction of vitiated air near the floor level is apt to cause coldness to the feet; (4) the incoming air is liable to be fouled by the roasting of dust on the heating batteries; (5) the doors and windows must be kept closed; and (6) the system requires skilled supervision, On the other hand, the system is under control as to quantity of air supplied, its temperature, and its humidity; it is claimed to keep out fog and to keep rooms more free from dust than the natural system, though it is doubtful if this claim can be fully substantiated. It is argued that pure air is conducted down to the nostrils, and so to the lungs, before passing over contaminating bodies, but this is also a matter of serious contention owing to the natural tendency of warmed vitiated air to rise. Natural Ventilation. Having dealt broadly with the principles of systems, let us next consider their details, starting with the natural system. In doing so, it will be well to have regard first to the ordinary 52 THE BUILDING—ITS VENTILATION dwelling-house, in which there should be three essential considera- tions: (1) the rooms containing sanitary fittings should be grouped together floor over floor and isolated from the rest of the house, so far as possible, by approaching them through a ventilated lobby. If circumstances permit, this lobby should have a good window on each of two opposite sides so as to ensure its through ventila- tion; failing this, one large window should be provided. The grouping together of the sanitary fittings in this way also greatly simplifies the drainage. (2) The building should be ventilated as a whole by providing a staircase as central as possible. If there be a fireplace in the hall, the upward current will be assisted. The outlet at the top may be in either of the following forms: (a) a lantern light having side lights to open, (b) an opening skylight, or (c) a good-sized window with opening sashes or casements. The ground-floor air inlet to this central air stream may be a special louvred panel (Fig. 69) or other inlet or may be an openable fanlight (similar to Fig. 52), over the hall door or just an ordinary openable window. (38) Each room opening out from this central shaft or air stream can then be separately ventilated by one or other of the methods which follow, into this central duct or may be dealt with independently. In either case the central air stream will be a valuable aid to the ventilation of the individual rooms. Nature helps to purify air through the medium of wind, rain, oxidation of organic impurities, diffusion, and the interaction, before referred to, between the vegetable and animal kingdoms. Inlet and Outlet Controls. In a natural system, no mechanical appliances are used except controls for the inlets and outlets and simple aids to nature, such as revolving cowls worked by the wind. It should be stated at once that a good deal of ventilation takes place in a well-arranged building with no special provision for ventilation whatever. This applies particularly to the com- paratively small rooms of dwelling-houses, as fresh air enters, and vitiated air leaves, via badly fitting doors and windows, even when kept shut, while a certain amount of air percolates through walls, ceiling, ete. This unintentional ventilation becomes less in pro- portion as the room or building becomes larger, as of course a door 24 feet by 6 feet will admit a man equally well into a large ball- room as into the smallest room in the house, while even window space is usually based not on eubie capacity but a proportion of the floor area. It is uncommon to find any systematic method of ventilation adopted for the rooms of private houses when they are provided with the conventional 9-inch x 9-inch flue of an THE BUILDING—ITS VENTILATION 53 ALT ASPHALT FELT srt pm GRATING GRATING UNDERLAY ‘CONCRETE VERTICAL FOR /NTERI/OR SIDE OUTLET FOR R.WP, EXTERIOR R.WP. ——————— 54 THE BUILDING—ITS VENTILATION open fire-place. If, however, special ventilation is introduced, it will almost certainly be the natural system. In this system, the outlets for vitiated air are put as high as possible and inlets for fresh air reasonably low, though not so low as to cause discomfort by draught or by the diffusion of the in- coming air with that of the room. The incoming air is sometimes filtered and warmed. The forms of inlet are not very numerous. The windows may be either intentional or unintentional inlets. Indeed, even if closed, it is probable that a good deal of vitiated air from a warm room will pass out through badly fitting joimery at the top while fresh air will enter at the crevices of the bottom half. Of course, the hygienically-minded householder will want to increase the flow of air in both directions when conditions warrant it and windows should be provided by the architect of such size and type that they can be opened without causing undue draught or letting in the weather during rain. When casement windows are adopted, there is much to be said in favour of putting part of the glass above the level of a transome, one or more of these transome lights (hinged at the top) opening outwards to allow for ventilation at night or during rain when the casements below will probably be closed, is shown in Figs. 71 and 72. During fine weather, if casements are hinged on alternate sides as in Figs. 72 and 78, they can be opened in such a way as to shield the effect of a stiff breeze or to catch the light air and bring it inside, according to the outside conditions. Figs. 52a and 52b show the effect of hinging a transome light at bottom and top respectively. The first type is used more in schools and semi-public buildings, and is often provided with hopper sides of glass or metal to cause incoming air to flow upwards and diffuse with the warm air in the room before reaching the person of occupants. The second form throws off most of the rain but does not control direction. It acts chiefly as an air outlet. Sash windows, illustrated in Fig. 53, allow the occupant excellent control of ventilation. Deep Bead or Hospital Type Ventilators on Sash Windows. Sash windows, illustrated in Fig. 58, allow the occupant excellent con- trol of ventilation, especially if a deep bead or draught-board about 8 inches wide is fitted on the inside of the bottom rail of the lower sash. This enables the lower sash to be raised so as to admit air in an upward direction between the meeting rails of the THE BUILDING—ITS VENTILATION 55 two sashes, without the liability to draught lower down. In the sketch the glass is shown in section by thick lines and the course of the incoming air indicated by arrows. This is the most con- venient type of inlet for a dwelling-house or ordinary office. This principle was introduced in the eighteenth century by Whitehurst, but the subject of ventilation was not then considered so important and it fell into disuse. Nearly a century later the system was reintroduced by Dr. Hinckes-Bird, and it is now usually known by his name, or as the “deep bead” or “ Hospital type” ventilator. Common modifications of this type are (a) to place the deep bead inside at the top of the upper sash. (b) The provision of a loose “draught board’’, which can be placed under the bottom sash when raised a few inches (instead of the deep bead). (c) The modification of the deep bead by constructing it in two members, the lower one clearing the sash and the upper one touching it for a width of perhaps 1 inch only. This is found to prevent draughts and to reduce the risk of the lower sash “binding” in damp weather. The Sheringham Valve. Another form of inlet is the Shering- ham valve, shown in section by Fig. 55. It consists of a small iron flap with fan-shaped ends to prevent draught, and is hinged at the lower edge A; it can be opened or closed to varying extents by means of cords and pulleys and is so shaped that the incoming air is given an upward direction. The outer face of the opening through the wall is protected by a grating. This form of inlet is often found in use in bedrooms. ““Cooper’s” Ventilator. Cooper’s ventilator is sometimes used as an inlet. Fig. 56 shows it to be a circular “hit and miss” ventilator in glass. A series of openings is shown by firm and ' dotted lines respectively. Those shown by firm lines are cut in a circular piece of glass fixed at its centre so that it can be made to rotate in the direction shown by the arrowhead. The openings shown by dotted lines are formed in the window pane. On rotat- ing the circular dise the openings can be made partially or entirely to coincide, thus providing a less or greater amount of air inlet. Fig. 54 shows a straight ventilator of the same type, capable of being opened or closed by means of cords and pulleys. ‘‘ Hit and miss” ventilators are almost always found over the doors of rail- way carriages, though there, of course, they are of wood. Louvred Panels. Another form of window inlet is the “louvred” pane; that is to say, an arrangement of strips of glass working like a Venetian blind and capable of being opened or closed. This 56 THE BUILDING—ITS VENTILATION arrangement is sometimes adapted as a wood or metal louvred panel in an outside wall instead of in a window. The Tobin Tube. A form of inlet found more often in a public building than in a private house, though sometimes met with in billiard rooms, is that known as the Tobin tube. It is often found in a neglected and dusty condition and is misused as a receptacle for litter, especially in schoolrooms. For this reason it is looked upon with disfavour by most present-day architects. It is of various forms and constructed of various materials. Thus it can extend from the floor level to a height of about 5 feet 6 inches or 6 feet above the floor, or it may be of a bracket form not reaching to the floor. Again, it may have a filter, a regulator, and a lid, or it may have neither of these accessories. Further, it can be of wood, zine or sheet-iron. At the top of Fig. 57 is shown a muslin bag filter. Sometimes an inclined sheet of tightly drawn muslin is used instead. The object in either case is to obtain a large area of filtering material; a piece of muslin across the top of the tube would be speedily clogged up owing to its affording such a small filtering surface. The main trouble with Tobin tubes is that the householder seldom makes use of the facilities provided for