A+ for IAQ IQ
Many engineers are predisposed to the notion that a high-performance building simply can't deliver ideal indoor air quality because of the costs associated with conditioning lots of outside air. To that, the engineers from Lentz Engineering Assocs., Avon, Conn., say, "Nuts."
WWII buffs know that's the famed response of General Tony McAuliffe to a request by the advancing German Army for him to surrender at Bastogne. That bit of American vernacular confused the German officers. They didn't understand what the response meant, and very likely some readers now are also scratching their heads at the idea that high-performance buildings and good IAQ are not mutually exclusive.
If you were to ask Mike Sherber, vice president of LEA, he'd tell you that's because most HVAC systems are predicated on the concept that cooling is the dominant design parameter and that ventilation is not a controlled parameter, but a subordinate function of cooling. However, he maintains that by addressing ventilation directly and efficiently, HVAC systems can become much smaller, more efficient, more flexible and less expensive.
But this is not an academic debate. LEA, in completing and operating Wassau East High School, in Wassau, Wis., has put theory into practice this past year and with amazing results. The firm was fortunate enough to be in a position to benchmark the performance of Wassau East to a mirror-image school near Green Bay that employed a more conventional HVAC system. Actual energy performance is quite amazing: a net energy cost savings of $164,000. But more notable are the metrics typically more difficult to quantify—lower rates of student and staff absenteeism and a dramatic reduction in the incidence of communicable illnesses as seen in other schools.
For this outstanding achievement, LEA has won this year's inaugural ARC Award for HVAC. But how, exactly, did they do it?
Wassau East's HVAC system is based on an LEA-trademarked regenerative dual-duct air-handling system that was pioneered in the retrofit of Wassau East's sister school. For the record, RGDD is a full-range energy-recovery system that provides 100% outdoor air to occupied spaces through dual-duct VAV boxes. As part of the system, ventilation air is also measured and metered to document positive conformance with at least the requirements of the 1999 edition of ASHRAE 62.1.
According to Sherber, heat from lights, equipment and people, including latent heat, becomes a recoverable asset instead of a waste product. Since 100% outdoor air can be used in any application, he explains, the scheme maximizes overall system turn-down with respect to the types of spaces served. Furthermore, ventilation energy can be managed down to individual room levels.
OK, so how does it work? First, the system is based on plate-type heat exchangers and air is delivered in a displacement pattern to every space before it is exhausted completely from the building. The air-handling system itself uses multi-stage energy-recovery to efficiently process outdoor air, displacing approximately 80% of the annual cooling energy by extending the range of free cooling through enhanced evaporative processes. This almost completely eliminates the need for refrigeration, says Sherber, except where dehumidification is required. When refrigeration is necessary, the process utilizes energy recovery to synergistically eliminate the need for terminal reheat while amplifying the recoverability of cooling. At full loads, Scherber says, this permits 100% outside air systems to recover nearly 65% of the total cooling energy from building exhaust. At part load, this increases to 80%.
Although the building is air-conditioned, no cooling coils are used. Instead, chilled water is used to wash, dehumidify and scrub air of particulates and contaminants. Ozone and a daily sump purge are used to sterilize the water and prevent odor. Heat, when required, is provided through the direct combustion of fuel in the exhaust side of the system, permitting one source to provide heat, preheat and frost control functions. It is supplemented by hot water hydronic radiation.