Greening an Office Tower; An Architect's Advice

The following is excerpted from an article by Dermot Sweeny (Sweeny Sterling Finlayson & Co) in the May 2010 issue of Sustainable Architecture and Building Magazine:

Natural light

There is lots of anecdotal evidence, and some empirical evidence, to support our contention that natural light and views to the outside are critical contributors to stimulation, human comfort and well being. Effective daylight harvesting depends on capitalizing fully on daylight penetration into the space while controlling direct sunlight and glare.

We achieve this by maximizing ceiling heights, arguing successfully with our clients that the best compromise between economy and performance is achieved with a 13ft. floor-to-floor height incorporating 18in. of raised floor, a 10in. slab, and ceiling heights approaching 11ft., with full height glazing for excellent natural light penetration.

ASHRAE has tended to discourage this fully-glazed approach in order to increase insulation levels and reduce solar heat gain or conversely heat loss. This resulted in a reduction of glazed surface from somewhere between 80% and 90% in Mies’ day, to about 40% in the 1990s. What ASHRAE fails to recognize is that over the same period, the relative importance of solar gain through windows has been reduced both by advancements in glazing technology, and by the dramatic increase in internal heat loads noted above.

While it is still important to work on reducing the amount of excess heat in buildings, we believe that the environmental and psychological benefits of natural light far outweigh the disadvantages of any additional solar heat gain. We do, however, work to control heat gain, and the negative effects of glare while maximizing the positive attributes of daylight.

Typically, an external solar shading device at a height of approximately nine feet creates a clerestory and shades the glass curtain wall below. At the same time, an internal light shelf aligned with the exterior solar shade reflects sunlight penetrating the clerestory off the concrete slab and deep into the building. The light shelf is coupled with a roller blind that lowers automatically [while the light shelf rotates upward] in response to solar intensity and potential glare. The blind never comes to the floor so some views are always maintained.

The additional ceiling height enables us to suspend indirect lighting fixtures fitted with T5 or T8 fluorescent lamps. The goal is to achieve even, ambient lighting. Experience has demonstrated that where there is too much variation the natural tendency is to enhance the dark spots by introducing more light. This of course uses more energy and costs more money.

We find that if we can achieve savings by designing for lower overall lighting levels, it is easier to convince clients to invest money in control systems that further improve energy efficiency. Maximizing indirect lighting also dramatically reduces glare which further increases human comfort.

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