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Green design, underfloor air delivery and commissioning are key trends driving HVAC design in today's high-rise buildings
Forty years ago, when energy was plentiful and relatively inexpensive, the mechanical systems in high-rise commercial buildings were, in many ways, admirable by today's standards. They could utilize 100% outside air, taking advantage of the economy of free cooling whenever possible; they could completely purge the building with outside air; filtration was superb and noise problems were uncommon.
Of course, these systems weren't perfect. Energy consumption was astronomical and the easily alterable pneumatic controls could throw the overall system out of whack with any occupant adjustments. But, in general, those systems created interior environments that were clean, pleasant and healthy-one of the chief aims of today's sustainable or green approach to HVAC design.
Then, something happened. Or rather, a number of things happened in tandem to alter how high-rise office buildings-- and their mechanical systems-were designed. The energy crisis resulting from the OPEC oil embargo of the early 1970s not only sent energy costs spiraling, it also made Americans realize that fossil fuels were not inexhaustible. Next, the revolution in office electronics in the 1980s and 1990s enormously increased a typical office's electrical requirements. Office space became ever more expensive to build and lease, which meant that less room could be allotted for mechanical-- system components. Furthermore, the economy went global, lengthening the hours most office buildings operated.
The OPEC crisis spawned a horde of building codes designed to curb energy use sharply. New office buildings were sealed tight to restrict infiltration. During air-conditioning season, increases in space temperatures were mandated and the use of outside air was severely limited. The upshot was an entire generation of office buildings that were prone to the symptoms of what was soon dubbed sick building syndrome.
But there were other problems, too. As space increased in value, the size of ductwork shrank, creating noise problems that somehow had to be ameliorated. Cheaper, disposable filters came into widespread use, and when not maintained properly, contributed to indoor environmental difficulties such as bacteria build-up in ductwork and coils.
CORRECTING THE MISTAKES OF YESTERYEAR
All approaches to HVAC system design developed over the past decade are, in part, responses to the well-intentioned errors...