Ventilator helps yield dividends for business school addition

Engineered Systems, July, 2001

The Tuck School of Business at Dartmouth College (Hanover, NH) was founded in 1900 as the first school of business management. Given this long-standing tradition of studying economics and business administration, it's no surprise that the design of its newest graduate student residence employs a state-of-the-art hvac system producing a healthy, comfortable living environment while delivering an annual return on investment that will eventually pay for itself.

Whittemore Hall is the focal point for residential and community life for both full-time M.B.A. students and executive program participants. The four-story, 45,000-sq-ft building consists of 60 private rooms; each with its own bath; 10 group study rooms; three conference rooms; and a distance learning suite (for tele- and video-conferences) all organized around a central, common living room to foster a sense of community and teamwork.

DESIGN DECISIONS

It was the college's intention to make the building as energy efficient as possible. To this end, the project was developed by Marc Rosenbaum, P.E. from Energysmiths and BR + A, a Boston MEP consulting firm. The overall concept called for an energy recovery ventilator using an enthalpy wheel to supply 100% outside air to the bedrooms, while a more traditional variable-air volume (vav) system serves the public areas of the building. The latter was selected because the team felt it would most efficiently address the occupancy fluctuations in the common areas.

The design of the hvac system was further complemented by an extremely tight building envelope to reduce energy losses through air leakage, and by the use of triple glaze, low-e glass on the building's many windows. Based on prescriptive ventilation requirements dictated by ASHRAE 62-1999, it was judged that 14,700 cfm of outside air would be required in order to maintain an acceptable level of indoor air quality for the students. The decision was also made to use the exhaust air coming from the bathrooms to maximize the latent recovery.

SIGNIFICANT SAVINGS

The energy recovery ventilator was supplied by Annexair, a Montreal-based air-handling unit manufacturer. Every aspect of the energy recovery unit was constructed in accordance with the school's overall design philosophy. "It was really nice to see a project like Whit-temore, because it indicated to us that designers and specifiers are finally starting to realize that a truly energy efficient design requires a manufacturer that specializes in the these types of packaged units. We provided 2-in, double-wall construction, backward-inclined fans with airfoil blades, premium-efficiency motors, a steam preheat coil, a chilled water coil and, of course, a high-performance energy recovery wheel," says Anthony Palucci, Annexair's national sales manager.

The benefit of this type of comfort-to-comfort application is that energy can be conserved during both the summer and winter months. Based on a bin analysis for Hanover, the use of the wheel results in significant savings of $ 10,050 in annual heating and cooling costs for the facility. One other important feature is the ability to significantly downsize the capacity of other hvac components. Greg Sifferlen at GreenTech, the manufacturer's representative, says, "In most cases when an enthalpy wheel is used, the client can really save on first costs. In our case, we were able to reduce the total cooling required by approximately 42 tons."

CONCLUSION

Since it was completed only this past December, the building has not yet experienced a full cooling season. However, results from the past heating season were above expectations. The college's mechanical engineer, Bo Petersson relates, "One winter morning, with an Outdoor ambient of 5[degrees]F, the unit supplied 55[degrees] air without opening the steam valve to the steam coil."