B
E
2
3
6 7
8 4
σ
10
14
12
13
Fig. 3.--Diagram of a convector air- conditioning installation with central fresh air treatment plant. A Supply 100 per cent; B Recirculated air 80 per cent; C Exhaust air 20 per cent; D Primary air 20 per cent; E Fresh air 20 per cent.
supply, each window module ог transverse section including one win- dow, is treated as a unit, so that it is quite possible to insert or move room partitions at any time.
The central treatment station for fresh air, with an air intake about 20 ft. above ground level, is located in the second basement and comprises electrostatic precipitator, mechanical filter, preheater, washer, precooler and supply-air fan. Four rising ducts, one in each corner of the rectangular ground plan shown in Fig. 2, supply the air to the substations on the vari- ous floors.
These consist of standardised sup- ply-air units with filters, supplemen- tary heaters and coolers and fans; by mixing fresh air and return air from their own zone, they automa- tically regulate its atmospheric condi- tions. Part of the return air corres- ponding to the volume of fresh air is expelled to the atmosphere through a special exhaust-air system.
The supply air enters the rooms through perforated ceilings, a method which has given very satisfactory re- sults, as it makes for even air distri- bution and permits very cool air to be introduced into the rooms in sum- mer without causing draughts. This is particularly useful when sudden sunshine sends the cooling require- ments up to a peak.
In addition, the perforated ceiling facilitates the damping of noise in the room
as well as that caused by the substations.
The cooling requirements for the building, for an inside temperature of 80° F at 86 F outside tempera- ture, work out at 460,000 B.t.u./h. A "Freon" refrigerating unit installed is connected to a refrigeration ac- cumulator or "ice bank.'
Convector System
a
Fig. 4. Diagram of dual-duct system. (1) Minimum air supply; (2) Additional air supply; (3) Recirculated air; (4) Used air; (5) Exhaust air; (6) Electrostatic precipitator; (7) Mechanical filter; (8) Preheater; (9) Humidifier; (10) Air cooler; (11) Air heater; (12) Cold-air duct; (13) Hot-air duct; (14) Mixing units.
conditioning station for recirculation. The only function of this recircul- ated air is to furnish heat or refriger- ation. The remaining 20 per cent leaves the building as exhaust air and is replaced by fresh.
When it became necessary to pro- vide full air conditioning and not merely heating for American sky- scrapers, great difficulty was encoun- tered in finding room for the air ducts, and a system was therefore de- veloped which made the return of air for recirculation unnecessary, so that only the 20 per cent of fresh air re- quired for hygienic reasons had to be distributed through the ducting (see Fig. 3).
The air-conditioning convector is usually placed under the window and consists of a system of ejector nozzles in which the primary air, supplied at fairly high pressure, is expanded, with the result that it entrains about three to five times as much room air (see Fig. 3). The air is then heated or cooled while passing over the con- vector's exchanger surface and em- erges at the top of the unit.
In winter the curtain of cold air descending at the windows can in this way be drawn in and warmed by mix- ing with the supply air, so that the window area is pleasantly air condi tioned. The situation is also favour- able for cooling in summer, as the stream of cool air blown vertically upwards cools the blinds inside the window and reduces their heat radia- tion. This method of cooling, as al- ready mentioned, is preferable for human comfort to an additional re- duction of the air temperature in the room in order to compensate for ra- diation from the blinds.
The depth of action of the air- conditioning convector placed at the window is limited to about 20 ft. Rooms of greater depth and those lying nearer the centre of the build- ing must have a supplementary air supply. Conventional or special high-pressure installations are often used for this purpose. necessary.
One of the principal features of the conventional system just described is the large volume of air which has to be conveyed and which makes a bulky ducting system
About 80 per cent of the air supplied to the rooms goes back to the air-
The conditions in every room can be regulated by controlling the flow
Far East Architect & Builder February, 1965
of heating or cooling medium with the aid of the convector, and а maximum of adaptability to individu- al comfort requirements is thus ob- tained.
The fully automatic regula- tors for air-conditioning convectors at present available on the market are rather expensive, and wide use is consequently made of the cheaper semi-automatic types.
In sultry weather it is more im- portant to reduce the relative hu- midity in the room than to lower the room temperature. The convector system here offers two possible ex- pedients: dew-point regulation of the primary air, and water separation in the cooled convector itself, which is provided with a drip pan and a water discharge pipe. Experience shows that this second method of dehumidi- fication comes into operation only on days of high relative humidity.
are
Air-conditioning convectors built either to stand freely in the room or to be fitted encased below the windows. Good convectors are practically noiseless provided that there are no sources of noise in the high-pressure air distribution system, i.e. that sufficient and correctly placed sound dampers are fitted.
Dual-duct System
An intermediate position between conventional air conditioning and the convector system is held by the high- pressure installation, in which cold and warm air are led in parallel through the building and every room or group of rooms receives the neces- sary amount of fresh air and the re- quisite heat or refrigeration through an automatically controlled mixing unit. In addition to its temperature control system, this mixing unit also incorporates a regulator for keeping the amount of mixed air constant. Fig. 4 shows the basic diagram of a plant of this type, as installed in a multi-storey glass-walled, office build- ing.
Part of the used air is returned to the air treatment station for recircula- tion and provides heat or refrigera- tion, as in the conventional system.
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