Page 244 - Green Building Through Integrated Design

220 CONSTRUCTION DOCUMENTS PHASE

Figure 12.1 Enthalpy energy recovery wheel.

We did a number of computer models of each system that we were considering. Those
were based on the building program that we had at the time, which initially was about
120,000 square feet. We modeled the building and then we did “what if’” scenarios
for each of the systems we were considering. Then we did a life-cycle cost analysis,
a performance analysis and a LEED point analysis based on the number of points
each system would give us.
The decision was arrived at from several different considerations. One was, of course,
cost. The second was what we would get in terms of reduced operational costs for the
building. The third was what we would get in terms of the number of points from the
LEED perspective.
One of the considerations early on was that the faculty wanted us to consider having
operable windows. There’s a downside with operable windows: they allow in pollu-
tants, pollen, and dirt in some cases. Of course you can also have wind and other
weather [to deal with]. But from an energy and engineering perspective, if you run
air-conditioning or heating and you’ve got the windows open, then of course, you’re
consuming more energy, not less. As a compromise, since they wanted to have large
volumes of fresh air in the building, we proposed the enthalpy wheel [which takes
heat or cold from the exhaust air, depending on the season, and transfers most of it to
the incoming air, thus saving most of the energy to condition the supply air].
Because there’s little energy penalty for using this device, we almost tripled the amount
of outside air in the building. Instead of having the normal, minimum code-required
amount of air—and this is what got us another LEED point and helped us toward
Platinum—we actually were able to provide a lot more air into the building without
having operable windows. That air doesn’t contain pollutants from the outside because
it’s filtered. When you go into the building, you get the sense that the windows are
open but they’re actually closed—they’re not operable. You have a lot fresh air that
adds tremendously to the learning environment. The faculty likes it, and the students
like it even better, as it helps eliminate the complaint of wanting to snooze after lunch.
The enthalpy wheel can be very difficult to implement which is why you don’t see
these devices very often. They’re huge. We have two of them in this project, and