February_1965 — Page 26

fore usually found to be objectionable. The cooling plant is designed for a base load which permits sun gains to be disposed of as they occur, so that stationary conditions are main- tained. As already mentioned, ex- tremely hot days are excluded from the load diagram on grounds of

if Consequently, economy.

the blinds are not lowered when the sun first enters the room, the tempera- ture will rise quickly and it will not be possible to get rid of the ac- cumulated excess heat for some hours. The

of outside thermostats may help in switching on the cool- ing system in good time, but the attendants must still watch the weather and start the cooling sys- tem before sunlight falls on the facade if the heat stored in the building structure, and particularly in the false ceilings, is to be dispos- ed of quickly enough.

use

From the engineer's point of view, the blinds should be on the outside of the windows, for it is only there that they can effectively reduce the heating of the window-panes and give up part of the radiant heat they absorb to the outside air. A special window design which can be turned on a vertical axis is of considerable interest in this connection, allows the blinds to be turned outside on sunny days and inside in bad weather.

as it

Vertical radiation shields projecting from the facade also have their advantages, as they permit shading of the facade for part of the day at least. Metal shutter-type blinds turning on vertical axes have also proved valuable, as they are strong enough to stand up to winds, but unfortunately their heavy construc- tion will inevitably restrict their use.

Inside Blinds

Comparative

measurements were made with a Stoll-Hardy radiometer in two equally lighted rooms of a fully air-conditioned office building

with Venetian blinds inside the win- dows. The blinds in one case were of light-coloured enamelled alumin- ium, in the other of highly polished aluminium. In the first case the equivalent radiant temperature of the blinds was 98°F, in the second 80 ̊F. The reflective properties of blinds, even when these are placed inside the windows, consequently have a on the very pronounced influence comfort of the occupants of a room. The intensity of the thermal radia- tion of the blinds depends on their emissivity, and for the colours in commonest

including light colours, this is 90 to 95 per cent, whereas for polished aluminium it is only 8 per cent that of an ideal black body.

use,

Even when the room temperature is lowered, the radiation from intern- al blinds is felt to be unpleasant, whether they are light or dark in colour, because the heat is first re- ceived and sensed by the body before being given up to the cooler room air. It is therefore important to cool the blinds with cold air, and this can be done with systems in which the air is blown in wholly or in part at the windows.

Great hopes of reducing summer cooling requirements were entertain- ed in America when coloured glass was first used. The results fell far short of expectations, however, for although the direct entry of radiation was lessened, the glass was heated by absorption and thus itself gave off radiation in the infra-red range.

An improvement, however, is to be expected from the use of window glass vapour-coated with metals, which has a high reflectivity for thermal radiation while impairing light transmission only very slightly.

That part of a multi-storey build- ing which overtops surrounding buildings is much exposed to winds, and for this reason it is the custom in America to make the heating sur- faces up to 20 per cent larger on the windward sides. Great importance

also attaches for the same reason to good sealing of the windows.

As a result of the temperature outside the difference inside and building, the air inside tends to rise and produces a "chimney effect," with the result that cold outside air is aspirated in the lower storeys, while warm air escapes through im-

sealed perfectly

windows on the upper floors. The wind pressure on the exposed wall acts counter to this escape of air, but it is if anything intensified on the leeward side.

Where building regulations require fire partitions between horizontal floors, the upward flow of air is diminished or prevented. In any case it is useful to provide staircases with self-closing doors on the ground floor and to fit a tight-closing door after another five or six floors. Attention should also be paid to sealing be- tween lifts and lift shafts.

Conventional System

There are various methods of carrying out the air-conditioning programmes based on these various requirements.

In an office building having for the most part large rooms serving similar purposes and with roughly the same numbers of occupants, such as draw- ing, designing or big commercial offices, it will usually be sufficient to limit temperature control to zones constituted according to aspect and embracing groups of floors, without providing individual control for single rooms. Separate treatment is then necessary only for conference rooms, special departments with automatic office machines, duplicat- ing offices and the like.

The conventional air-conditioning system, which not only supplies the rooms with the necessary treated fresh air but also does most of the space heating by providing warm air, is very satisfactory for the require- ments just described.

An example is given in Fig. 1. For the purposes of the air and heat

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air-conditioning

(1)

Fig. 1.-Diagram of

a conventional installation with control zones for the various floors. Fresh air intake; (2) Electrostatic precipitator; (3) Cellular filter; (4) Air Heater; (5) Air Cooler; (6) Humidifier; (7) Fresh-air fan; (8) Floor substation; (9) Fresh Air; (10) Supply air; (11) Perforated ceiling; (12) Window heating: (13) Exhaust air; (14) Exhaust-air fan; (15) Exhaust-air outlet.

Fig. 2.-Ground plan showing four control zones. (1) Floor substations; (2) Supply-air distribution; (3) Return-air ducts; (4) Distribution of recirculated and exhaust air; (5) Heating under windows.

فرح

Far East Architect & Builder February, 1965