VENTILATION AND WATER HEATING

Adequate ventilation of buildings has received increased attention during the last few years. Low ceilings, small window areas, back-to-back houses, and excessive densities are things of the past, and now every endeavor is made to ensure a free circulation of air about buildings for the purpose of efficient ventilation.

Natural Ventilation

Small domestic buildings, offices, hotels, and other places with small floor areas are ventilated by natural means depending largely upon the provision of suitable inlets and outlets. The fittings used are too well known to set down in detail, but briefly they comprise: windows, lantern lights with sides to open, fanlights, hopper sashes, revolving cowls, draught window boards, valves and vents, «hit and miss» ventilators, tobin tube inlets, fireplaces, doors, electric fans, etc.

With regard to the tobin tube (Fig.11) care should be taken to see that this fitting receives attention, otherwise after a number of years the receptacle may be found full of filth owing to misuse. It is not unusual for careless people to deposit cigarette-ends, waste paper, etc., into the open ends of the ventilator. The usual height of 5ft. to 6 ft. is convenient for this misuse, particularly as few people realise their real purpose.

This type of ventilator is used mostly in public buildings, church halls, billiard halls, etc., and can be quite efficient if given periodic attention.

Natural ventilation has the advantage of being cheap to install, and provides healthy and stimulating conditions, provided the inlets and outlets have been designed with skill.

Vacuum Ventilation. –This is a system of ventilation whereby the internal air is extracted by suitable fans. The ingoing air is induced through windows and other similar inlets already described for natural ventilation, and a steady flow of air is maintained by means of the extraction fans.

Various types of fans may be used. They are generally made of metal of a rotary design and housed in a convenient part of the ductwork. Care must be taken to see that the ducts are fairly straights, and with easy bends it necessary. Avoid right-angled bends, which impair the efficiency of the system owing to friction.

Fans are usually driven by electric motors, but other power may be utilised where electricity is not available.

With the vacuum ventilating system there is no control of the incoming air; therefore this system can only be employed successfully where the surrounding are not noisy and windows can be opened to admit clean air.

Plenum Ventilation.- Control over the incoming air is an important feature of this type of ventilation. Where the conditions are such that the surroundings are noisy and the air is fouled by smoke and dust, the plenum system can be contemplated to provide clean air at the correct temperature and humidity. The air is drawn into the building by a fan, and is discharged through ductwork at suitable positions; conveniently placed outlets abstract the vitiated air through ducts controlled by an extraction fan of a smaller power than the inlet fan. A slight pressure is created owning to a large rate of incoming air than that which is extracted, and consequently any leakage must be outwards.

The plenum system of ventilation is costly to install, owing to the necessity for expensive apparatus consisting of propulsion and extraction fans, air heaters, washers and filters (these vary according to circumstances), and distributing ductwork for the incoming air and outgoing air.

A typical arrangement of plenum heating suitable for a large auditorium is as follows: The air coming in is heated by a heater battery, led from an independent boiler, feeding wrought-iron gilled tubes which have a good radiating surface. In summer, however, the air can be cooled by passing through the same battery fed by an ammonia refrigerating plant supplying cold water instated of hot water from the boiler. The ductwork is liable to convey sound unless special care is taken with the placing of the fans. These should be well away from the most important rooms, and even then the fan and motor should have an anti-vibration base of rubber or similar material to minimize noise. Another good precaution is to provide flexible connections of leather between the ductwork and the inlets and outlets of the fan casing.

The ductwork may be of lights galvanized-iron sheeting, circular in section, or formed in brickwork or concrete. In new building it is possible to incorporate the various ducts in the general layout of the design, but where the ductwork has to be applied to an existing building, galvanized circular trunking is frequently used. Asbestos-cement conduits are also favoured. The main ductwork should have means of access for cleansing purposes.

In the cases of the inlet and outlet grilles, it is usual to make them decorative in the character and detachable.

From the foregoing description it will be seen that the plenum system is rather complicated and needs skilled attention for maintenance.

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