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desired effect. Tinted glass has become popular in the United States, particu- larly since its large-scale application in the Seagram Building. Its relatively high cost is less of a deterrent there.

The so-called photropic glass with its variable light transmission is as yet little more than a technical curiosity at the present. It functions as a result of the darkening effect of short wave light on sub-microscopic crystals of silver halide. The glass returns to full transparency when the source of light is removed. Heat transmission remains unaffected in the change so that to limit solar gain as well as sky glare it becomes necessary to apply a heat re- flecting coating.

Whether to double-glaze or not is not the straight-forward question it seems to some. The value of the sec- ond membrane depends on the extent of the interior heat load. If high, double glazing may in fact retard necessary heat dissipation from the building.

Artificial lighting

The Germans have standardised on 1,000 lux as the illumination value to be applied to landscaped offices (the recommended value for 'ordinary' of- fices is 500 lux). Asked to provide firm and detailed technical evidence in support of their choice they are in some difficulty.

This is not to suggest that the German recommendations are insecure or that those responsible are technical- ly unreliable. The fact is that illumina tion values the world over are an odd mixture of the technical, the economic and the politic. 1,000 lux is a nice round figure that satisfies all the cur- rent physiological considerations, provides a brightness which is a fair match with the average day as seen from indoors, and, most important, is economically attainable.

It appears not to create any prob- lems of excessive irradiance and the attendant heat load of about 4W per sq.ft. nicely satisfies the total thermal requirements of a reasonably well- insulated building. The automatic as- sumption these days is that the fluo- rescent lamp to be used would be one of the high efficiency types such as 'White' or 'Warm White'.

Regrettably, on very few occasions these days are specifiers prepared to opt for a lamp of good colour quality with its lower luminous efficiency.

The lamps, once chosen, might be introduced to the interior in a number

of ways, the more obvious of which are listed below.

1. Via ceiling-mounted fittings em- ploying louvers or prismatic panels. This treatment which can be so suc- cessful in the small office seldom comes off completely in the larger, fairly low-ceilinged area. The lighting fittings appear as a permanent re- minder of failure (whether this was so or not) to integrate them with the fabric of the interior.

2. Via louvers or prismatic panels set within the suspended ceiling. Al- most any louver will be satisfactory at illumination levels up to 1,000 lux and the parabolic wedge type can cope with any illumination value. Prismatic panels of good quality say Holo- phane injection moulded or K Lite Extruded will be satisfactory up to about 1,500 lux.

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lation for a landscaped office should not be too difficult. The logical choice is a central all-air system of the low or high velocity type. It will be necessary for the building to be zoned to take account of the varying nature of the heat gain, particularly from the moving sun in window areas. Further- more, heat or cooling requirements vary in different parts of the building and so does the influence of the gen- erating equipment.

A landscaped office permits the design of a simple layout of ductwork which can be fitted into the ceiling void. Both delivery and extract of the air is usually arranged through the ceil- ing, though some perimeter air input frequently takes place at cill level. This serves to prevent cold air draughts in winter.

Exhaustion of air through lighting 3. Via battens or simple troffers fittings is becoming a common techni- above large-scale baffles.

que and is likely to grow.

Which method one adopts is a matter of personal choice; one cannot argue in general terms that either is better than another. In addition to handling light the lighting system can be adapted to deal with air movement if so desired.

Air conditioning

Air conditioning with mechanical cooling is almost essential in land- scaped offices. Fortunately the land- scaped arrangement permits the easiest possible air conditioning layout.

The popular internal temperature in Europe lies in the range 68 deg. to 72 deg. F; females prefer the upper part of the range. Temperature re- quirements are 5 deg. or so more in the United States than they are here. A point to remember is that the demand for heat within the building increases with outside temperature. The 72 deg. upper limit referred to earlier is acceptable with outdoor tem- peratures up to 68 deg. F. At 85 deg. F outside, for comfort conditions, the temperature indoors must be 75 deg. F.

Air movement is necessary to main- tain the required temperature con- ditions and to remove such pollutions as body-odours and cigarette smoke. The speed of movement should vary with temperature the higher the temperature the greater can be the air movement, and 40ft. per min. has been suggested as a reasonable limit for sedentary work such as one gets in offices.

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Selecting an air conditioning instal.

It is very sensible to pick up light- ing heat before it gets into the interior since this can reduce air volume by as much as 30 per cent. An important side effect is that heat removal at the lighting fittings can enable lamps to be operated closer to their optimum temperature with a gain in luminous efficiency of up to 16 per cent.

If the space available is plentiful, a zoned low velocity conventional all-air system with simple radiant heating under the windows will be best. Large ducts enable air velocities to be kept down, thereby reducing operating costs. Where space is restricted an all- air single duct high velocity system should be considered, though it may transpire that its cost is approaching that of a more sophisticated dual duct system.

Conclusion

The evidence seems to indicate that the integrated approach to the design of engineering services is here to stay. Whether the same will apply to the landscaped treatment of office in- teriors which gave birth to the inte- grated approach remains to be seen. There are many people who appear to appreciate the benefits of the superior physical environment while remaining unconvinced about the value of open plan working.

However, there are some hard facts to support a claim for a retention of square plan forms as distinct from the conventional 'thin' office block with its central corridor.

One such example is a completed

Far East BUILDER, December 1970

service publicité g. e. 21

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