Page 47 - Zero Net Energy Case Study Buildings-Volume 1

STEVENS LIBRARY AT SACRED HEART SCHOOLS
CASE STUDY NO. 2
ing in this climate. This is due to its high efficiency combined with a level of occupant comfort at a wider range of temperature setpoints. Because this type of system has a higher first cost, however, and the fact that the client preferred a carpeted space, the decision was made to use a package unit utilizing an efficient air-air heat pump with both indirect and direct evaporative cooling sections. This solution works well in the warm but dry climate of this part of northern Cali- fornia. For potentially extreme temperature days, a compressor was added to the unit to provide mechanical cooling on those rare days.
The engineers decided to use the principle of displacement ventilation to move air through the large open space. Rather than using large energy-consuming fans to move the air, the system uses small fans and injects air via low velocity air nozzles at the perimeter windows and the air makes its way via natural pressure back to exhaust air openings. In addition, the ductwork is oversized to reduce pressure losses and no ducts are used on the return air side.
This type of system is unusual for buildings of this small size, but this application shows that high system energy efficiencies are possible at this scale of use.
The system has additional advantages of avoiding air drafts and system noise since the air moves at low velocity. In addition, the air can be injected at 65°F rather than 55°F, making the outside air economizer, or free cooling, available for more hours throughout the year. And, as a
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(Left) Diagram of low-energy design features (Courtesy of WRNS Studio)