We also have to get very specific about the energy-using and energy-supply systems for the project. This activity is especially important as projects move toward "zero net energy" goals. A good example is an enthalpy wheel (Fig. 12.1) designed by Alfa Tech Cambridge Group of San Francisco, for the Ohlone College Newark Center for Sciences and Technology in Newark, California. Principal in charge Michael Lucas spoke about how this design element evolved.*
We presented a number of mechanical concepts. One, of course, was photovoltaic panels to offset some of the electricity consumption in the building. We also presented three or four mechanical system options. The two that turned out to be most the energy efficient and the ones that the client liked the most were the geothermal system and the enthalpy wheel energy recovery system. (We also evaluated thermal storage and ice storage.)
*Interview with Michael Lucas, Alfa Tech Cambridge Group, March 2008.
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 pollutants, 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 they're each 16 feet in diameter. They take up a lot of space and have a lot of associated ductwork. Architects, generally speaking, don't like to incorporate them in their buildings because they take up so much room. The architect, Perkins+Will, did a great job, making circular windows, like portholes, on two sides of the building so you can actually look through the windows and see the wheels rotating. Also there is a graphic display next to the window that shows how much energy is being saved real-time.
Because all of the air coming in and all of the air going out has to go through the system, it's got to be in a fairly central location unless you want miles of ductwork. The engineer has to work very closely with the architect to make sure you can locate them somewhere central in the building. It's perhaps 80 percent engineering and 20 percent architecture involved in getting these integrated correctly into the building.
Was this article helpful?