The total volume of air to be dis- tributed and in circulation is thus greater than with the convector sys- tem and amounts to about 75 per cent of that of the conventional sys- tem. For this reason the dual-duct system takes up rather more floor area of each storey for the vertical distribution of the air than the con- vector system, a point which is of some importance in multi-storey buildings,
However, the ducts can be placed in the interior of the building, so that the narrow wall areas between the windows remain free. With the dual-duct system there is, further- more, no difficulty in conditioning deep rooms or interior zones of the building just as evenly and effectively as the offices on the outside.
Kinetic Energy
Here too a base-load heating sys- tem is provided under the windows, either a hot-water or an independent warm-air installation being used. With this latter method warmed (or cooled) air is blown vertically up- wards, which offers the advantage over radiators that sufficient kinetic energy is always available, to coun- teract the downward flow of cold air at the windows, whereas with radia- tors or convectors this energy de- pends on temperature and thus may not always be sufficient. The air thus expelled can also be used for cooling the windows.
The mixed air is introduced into the rooms through perforated ceilings, anemostats or window units. Instal- lation costs can be reduced consider- ably if several similarly located rooms can be connected to a common mix- ing unit, as shown in Fig. 5.
In an installation of the type shown in Fig. 4 fresh-air treatment takes place in two units, one of them in- tended for the minimum constant volume of fresh air demanded by considerations of hygiene, and the other, larger unit for return air as well as fresh air, and dimensioned for the extra supply of heat or refrigera- tion. The air supply fan conveys the treated and mixed air to the final heaters and coolers, and from here
60
K W B
the cold- and warm-air distribution ducts lead to the mixing units.
The used air leaves through col- lecting ducts and is either expelled to the atmosphere or returned to the second treatment plant. In winter the percentage of recirculated air is increased as the outside temperature falls, so as to save heat; in summer the percentage of recirculated air again rises, this time with rising tem- perature, since the return air is now cooler than the outside air and per- mits savings of refrigeration.
Synopsis
The first question which arises in the treatment of any air-conditioning project is that of the most suitable system. In the multi-storey buildings which we are considering here, the conventional low-pressure system is hardly used to-day, as the air ducts take up too much floor area in the various storeys.
The dual-duct system may be at a disadvantage for the same reason, as compared with the air-conditioning convector system, when the building concerned is very tall and the ground area comparatively small, and when it is not possible to provide special floors for technical equipment.
One air-conditioning convector is placed below each window. This leaves the full room space free, while a few standard types of convector are sufficient to meet all capacity require- ments. With the dual-duct system it is an advantage to place the mixing chambers in false ceilings in the cor- ridors, where they do not take up valuable floor space. The air ducts, however, are bulkier than those re- quired for convectors. With the dual- duct system, numbers of window modules, if the rooms are used for similar purposes, can be connected to the same mixing chamber. This of course reduces the price of the instal- lation.
The two systems are roughly equal in respect of noise, provided care is taken with the installations; the general noise level of the surround- ings will of course also affect the situation. Often it will be necessary to compromise between desired air
Fig. 5. Typical floor plan of a multi-storey office building with a dual duct air-conditioning installation. (B) Window air duct; (K) Cold air duct; (W) Warm air duct; (M) Mixing units.
flow for a given space and admissible noise at the given noise level of the surroundings.
The cooling of the condensers of the refrigerating plant is frequently a problem, as the municipal water supply may be unable to provide water, or at any rate sufficient water, for this purpose. Recourse can then be had to evaporative coolers in which the condenser heat is given up to the air and only 5 to 10 per cent of the normal cooling-water flow is required.
Where so many factors have to be considered, it is impossible to lay down any general rules as to the best or most economical method of air conditioning. Every concrete case calls for careful study by qualified engineers, who must take both tech- nical and financial factors into con- sideration.
Books
The Architect in the Nuclear Age The Design of Buildings to House Radio-activity by James F. Munce, FRIBA. (Iliffe Books, Ltd., London, £6 7s. 6d. by post).
MR. MUNCE has made a specialised study of his subject having spent a year in the USA looking at the in- fluence of radioactivity on architec- tural design. He has been actively concerned in a number of projects in which the applications of atomic energy were involved
The book starts with brief, clear account of the behaviour of the atom and its nucleus, what is meant by fission and the ways of bringing it about, and the nature of the activated particles and rays which result.
A chapter is devoted to power reactors, then follows an account of various types of accelerators.
Three chapters in turn then, cover radioactivity in laboratories; in me- dicine; and in industry and agricul- ture. The first deals with site selec- tion and overall planning; the de- velopment of radio-active labora- tories; interior arrangement and de- sign; decontamination and waste dis- posal; finishes and working surfaces; furniture and equipment; services; safety; structural peculiarities; and architectural character.
The important subjects of health hazards, safety precautions and pro- tection are next discussed. This leads on to a chapter on structural ma- terials and methods which discusses choice of site; planning and pro- gramming: foundations: biological shields; ancillary buildings; ventila- tion: erection problems: cooling water; and radioactive waste disposal.
The whole book is lavishly illustra- ed, the specially prepared line draw- ings have been adapted from material obtained from international sources. There are 30 architect's drawings of plans and structures.
Far East Architect & Builder February, 1965