No_2_1960 — Page 46

(2) Cost as the tube gives over 100 uses. the material cost of forming the ducts is less than ld. per foot.

While the method at present finds its most extensive application in countries where there are difficulties either in producing or importing conduit, its use in the United King- dom is by no means unimportant. It has, since 1955, been recognized by the Institute of Electrical En- gineers in Regulation 223, Section F. of the Wiring Regulations.

Special concreting is not neces- sary and both single and multiple duct formation is possible. The method should not be used direct in foamslag concrete but can be ap plied if the tubes are covered with 3:1 cement mortar before the foam-

slag is laid. In other applications

the cement in the mix forms a slur.- ry round the tubing and becomes the internal face of the duct. It does not. therefore, matter if the concrete mix in general is coarse.

Fig. 2 illustrates a tube lay-out in the screed thickness of a hollow pot floor ready for concreting; the ducts, which are formed by the with- drawal of the tubing accommodate the lighting and power

circuit wiring for one of 76 flats erected by the Tottenham Borough Council.

The advantages of this system are such that it can be a means of reducing to £10 a dwelling the cost of electrical wiring installation in a housing scheme, without taking into account the saving in time, which is considerable.

Pneumatic rubber tubes can also be used to form ducts for several quite distinct uses related to the heating of buildings.

One is in the formation of closed heating grids in floors. Hot air s circulated through ducts in the floor to heat up the concrete floor and the ground beneath it, thus creating a store of heat which continues to radiate even when the heat supply is not in operation. This is. for instance, useful where electrical heat exchange is used and the power is taken from the mains supply at night when rates are reduced.

Two thousand years ago the Romans heated their buildings by means of hot air circulating in ducts under the floor. It is surprising

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that today, when rubber duct form- ers make this method SO much easier, so little attention is paid to this form of heating. in spite of the popularity of other methods of radiant heating.

It is interesting, therefore, to learn that a private house has recently been built that is heated by a warm air floor panel heating system. In this system, the warm. air is circulated in ducts which are formed in the floor concrete itself. the air in turn being heated by hot water from a large domestic boiler, The house is at Caversham, near Reading, and is the home of Mr.

Figure 4.

Figure 5.

Colin Allsebrook, A.M.I.Mech.E.. who designed the heating system himself. The architects were Booth and Ledeboer.

The house, which is built on one storey with basement, consists of a large living room facing south, a dining room. four bedrooms. a bathroom and kitchen. All these rooms are heated by the floor panel system, except the dining room where the structure would not per mit its use.

hard.

A high degree of insulation was aimed at in the construction of the building. The floor is a solid type. of concrete covered with invisibly nailed tongued-and-grooved wood, except in the kitchen. cloak- room. utility room and bathroom where a thermoplastic tile is laid. as a tile of this type is believed to be more suitable with floor heating than linoleum or cork. The depth of the concrete throughout was 6 in. and the duct diameter used through. out was 3 in. Beneath the floor con- crete is a moisture barrier consist- ing of a layer of reinforced water- proof paper, and the heat insulating layer, which consists of a 9-to 12-in. hard core fill of broken brick levelled off with concrete and paint. ed with a bitumen paint. The main ducts (18 in. x 12 in.) were formed with 4 in. clinker blocks painted outside and plastered inside.

In another heating system depend- ing on hot air ducts the hot air is circulated in the building and dis- charged through a series of grilles.

The illustration in Fig. 3 shows a progress photograph during the construction of the American Em- bassy in Sweden where the heating is by radial distribution from central rising hot-air duct.

a

These are fairly well-known uses of the duct heating method. A more recent idea is to make use of the ducts for electrical hot cables. The normal system of installing electrical hot cables is to insert them in the concrete floor, when, in the event of breakdown or burning-out, the floor must be broken up to assess the position of the fault. In the new method the mineral-insulated cable is housed in a small diameter duct so that if a fault occurs the wire can be withdrawn through the open end of the duct and a new section pulled into position.

THE HONG KONG & FAR EAST BUILDER

VOLUME 15, NUMBER 2