The difference between the places that heat significantly, versus places that do not is, obviously, quite dramatic. But the most challenging variation, according to Nall, is that some locations have higher than desirable humidity most of the year.

“It's not necessarily recognized, but when you're trying to do innovative, energy efficient HVAC systems there is no such thing as passive dehumidification,” said Nall. “There is passive cooling, such as night flushing, storage of cool overnight, and evaporative cooling. Or if you're in a high altitude you can do radiant night cooling whereby you can encourage the building to radiate heat into the night sky. But if you live in a humid place, those options for passive cooling are less available. Secondly, you're going to have to do some kind of active cooling anyway to dehumidify.”

According to Nall, LEED's emphasis on energy efficiency makes engineers think twice about their choices, even on non-LEED projects.

Another engineer who has come to depend on LEED is Kim Shinn, principal and director of sustainable design for TLC Engineering for Architecture in Orlando. Shinn's firm does lot of work in the Gulf Coast and Southeast Atlantic regions.

In these areas, the heating systems are designed for humidity control and reheat, not space heating. Shinn routinely works with clients who need help deciding if and where to locate vapor retarders in the wall and roof sections. The conventional wisdom is to locate vapor barriers so that moisture is kept inside the building, but this is an extremely bad idea in the hot and humid south, said Shinn.

“We don't even bother with economizers,” said Shinn. “There are just not enough hours where the outdoor wet-bulb temperatures are low enough, and the leakage through the economizer intake and exhaust dampers can often do more harm than good. And humidification, forget it. We don't even put humidifiers in surgery suites.”

The LEED model contributes to better planning and collaboration on non-LEED projects. According to Shinn, the main difference between working with a LEED system versus a traditional system is LEED's emphasis on “integrated” design. This fosters early cooperation and consultation between owner, architect, contractor, and other engineering disciplines, and leads directly to an approach that pays more attention to “rightsizing” of systems and greater emphasis on individual user/occupant control, Shinn said.

Many modern buildings are supposed to operate 24/7/365, like hospitals. Running systems continuously can overcome a lot of design shortfalls. One does not have to be particularly elegant in the system configuration and control philosophies when there isn't an OFF button. While the “turn it off if nobody's using it” strategy offers a lot of bang for the buck, designers need to be careful that they design ways to allow systems to be shut down properly.

“For instance, it can be really bad news if an air handling system shuts down the supply fans, but leaves the exhaust fans running, pulling the building negative and inducing a lot of infiltration through the building envelope,” says Shinn. “Understanding the thermal inertia of building construction is pretty important in taking advantage of occupancy cycles, especially in optimizing pre-cooling or pre-warming startup.”

To mitigate the risk of dealing with so many variables, many LEED project engineers use models and simulation programs to explore their systems. Shinn's firm simulates many different HVAC systems, particularly when they need to evaluate utility rate effects (time of day rates and demand management). Shinn also investigates the economic return of high efficiency systems and equipment. Many of these tools were introduced to the engineering community at large thanks to LEED.

Another practice used in LEED and now finding greater applicability is a system to replace peer evaluation when the project at hand is so unique that there are no peers with which to consult.

“When you're doing a fairly commonplace system, you can review it with your peers,” says Nall. “But if you're doing stuff that people haven't done before, you have to use a lot of design assistance, simulation, and full-scale mock ups.”

LEED has provided the tools needed to do this, and now many of these tools are being used on non-LEED projects.

For previous Engineering Green Buildings columns, visit www.hpac.com.

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Matt Stansberry is a commissioned staff writer for the USGBC. He has written extensively on the built environment and sustainability. Stansberry is the former managing editor of Today's Facility Manager magazine, and current News Editor of the Data Center Media Group . He can be reached at mstansberry@techtarget.com.

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