Methods of Air Conditioning Multi-Storey Buildings Jun 1963
BY W. SENNHAUSER*
IN seaking new lines of advance in
the design of office buildings, mo- dern architecture continually poses new problems in interior layout and comfort requirements. The desire for more light and air, leading in the extreme case to buildings consisting almost entirely of glass, raises difficulties in the disposal of unwanted radiant heat. Air condi- tioning thus becomes more imperative as architecture progressively abandons the hitherto accepted traditions. Some of the aspects of this development are dealt with here.
IF THE modern office building needs more complicated and expensive technical equipment, it is not be- cause our standards of comfort have risen, but rather because
the com- fort optimum was attainable with simple means in buildings of the traditional type.
The all-glass building lets in more light and so makes it possible to have rooms of greater depth; but it requires artificial cooling if it is to offer the same degree of comfort as an older building with much smaller window areas. Any com- pany which erects such a building must therefore accept in advance the fact that installation and run- ning costs for heating and air con- ditioning will be higher than in a conventional
structure; and any failure to realise this will inevitably lead to disappointments later on.
The higher costs, however, may well be regained in the long run on account of the better performance of the staff and the reduction of absences due to illness. Increases of production of the order of 10 per cent as a result of improved working conditions have repeatedly been confirmed by statistics.
Comfort Requirements
The ideal air conditions which the engineer must aim at are plea- sant, temperate and independent of weather and outside temperatures. A certain rhythmical fluctuation of the conditions is, however, desirable, since this has a stimulating effect, unlike an
absolutely constant in- ternal "climate." The temperatures may be a few degrees higher in summer than in winter, and for
Mr. Sennhauser, was chief engineer. Heating and Ventilating Department. Sulzer Bros., Ltd., Switzerland. until his recent retirement.
economic reasons the cooling capa- city is not calculated on the basis of a few extremely hot summer days, but on a fairly frequent sum- mer maximum.
In the temperature zones an in- side temperature of about 75°F will be chosen at an outside temperature of 85°F, and this difference will be maintained if the outside tempera- ture should rise higher. The relative humidity should lie between 45 and 60 per cent. Natural ventilation is not usually practicable, since noise, dust, exhaust
gases and draughts combine to make the opening of windows undesirable. On the other hand, a sufficient supply of hygienic- ally unexceptionable air must be provided.
Other requirements which the engineer must fulfil are the cooling and dehumidification of the air in rooms housing numerous occupants and office machines, the removal of used and contaminated air, and the intense renewal of the air in confer- ence rooms where many of the per- sons present may be smokers.
Technical Considerations
The demands made on the means of regulating_the air conditions will differ in different cases. In large offices overall temperature control may suffice, in private offices in- dividual control is often desired. The choice of the air-conditioning system will depend on this point, although it is often preferred for reasons of economy to control several private offices from one thermostat.
The supply of fresh air per per- son which is regarded as hygienical- ly desirable is about 1,000 to 1,400 cu. ft/h, or up to 1,750 cu. ft/h where heavy smokers are present.
The direction and intensity of sunlight vary with the position of the
which heats the sur-
sun,
Table 1:
on internal
faces of the building more or less according to orientation, angle of incidence, height above ground level and shading by other buildings. Between the time of maximum radiation and its effect air conditions, time lags of up to 12 hours may occur, according to the heat capacity of the outside walls. As the required cooling performance depends mainly on heat gains, the conditions must be calculated ac- curately in advance.
Table I shows window areas as a percentage of the whole facade, to- gether with the percentages of the cooling requirements due to trans- mission through the building struc- ture, occupants, lighting and win- dow gains, for various types of buildings. It is clear from this table that the cooling requirements are chiefly dictated
window by the Building 6 appears to be an exception to this rule, but the dis- crepancy is explained by the fact that the principal windows here face north.
areas.
In buildings with large window areas it must be remembered that considerable increases in the in- ternal temperature may be caused by sunlight even in winter, when outside temperatures are such that heating is still needed.
Control Zones
It may
These situations are often dif- ficult to deal with, and must be al- lowed for both in the choice of air- conditioning systems and in the selection of control zones. even happen that some zones require cooling while others still have to be heated. Air movements on hot summer days are felt to be pleasant, the movements of well-heated air in winter will worry nobody, but the movements of cool air are con- sidered as draughts and are there-
WINDOW Area as Percentage of Whole FacADE
Percentage of cooling requirements due to transmission, occupants, lighting and window gains Building
2
1
3
4
5
6
Percentage window area Air-conditioned space. cu. ft
69
500,000
60 400,000
55
310.000
34-7 880,000
34-7
31
350,000
230,000
Refrigeration output. B.t.u./
cu. ft h
5-0
2-0
1-7
2-3
2-9
2-0
due to:-
10 10
.15
14
6
6
12
20
18
8
8
51
80
65
68
86
86
37
Inside
Inside
Outside
Inside
Inside
Outside
Percentages of this figure
1. Transmission
Occupants.
2.
lighting
3. Window heat gains Blinds or shutters
Far East Architect & Builder February, 1965
BAN
57
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