Rooms With a View

Nov. 1, 2006
With careful design, an atrium can maximize energy efficiency and provide beautiful, natural light-filled spaces

When well-designed and integrated into a campus living or learning space, an atrium can function as the heart and spirit of a building, connecting interior rooms and public spaces with the outside environment. But schools and universities should seek technological and HVAC solutions that maximize energy efficiency.

Atriums can achieve sustainable-design objectives by harvesting daylight and reducing heat loss. They can be designed to create a naturally ventilated thermal buffer between the occupied interior and outdoor environment. Transparent double-glazed, low-E coated glass can create views to the outdoor environment while minimizing heat gain and loss. By incorporating an automated control system, temperature sensors at the top of the atrium can control louvers and fans to allow outside air to ventilate the atrium, optimizing internal temperatures. In cool weather, the ventilation system can take advantage of outdoor temperatures to use filtered, unconditioned outside air for cooling.

Upper-level glazing that incorporates integral shading can reduce radiant heat penetration in hot weather. In cold weather, the atrium can act as an effective solar collector. It requires mechanical heating and cooling only at the occupied space, and when it does, energy-recovery measures transfer heating and cooling energy from the building's exhausted air to the fresh air supply.

Studying energy

When incorporating an atrium, it is helpful to make detailed comparisons. Daylight studies, including sun shots and radiance analysis, can measure solar access and interior atrium room illumination, which can be targeted to reduce lighting needs by a particular amount. It is reasonable to target a reduction of 50 percent or more.

Comparison studies of glazing systems, glass types and shading systems can optimize view, shading coefficient, thermal resistance and shading.

Natural and mechanical ventilation studies are essential to optimize indoor air quality with mechanical/heat-recovery systems, as well as temperature- and damper-controlled natural ventilation in the atrium. Mechanical system selection and control studies also are required to balance individual room control needs with overall building energy management. Other studies include exterior envelope comparisons, which can be used to identify materials with thermal performance that exceed code requirements.

Energy modeling can be used to estimate a building's annual energy consumption for various design and building system “what-if” scenarios. Calculations should consider adjusting heating, cooling and ventilation demand for unoccupied periods, which can be managed by a building's computerized automation system. These can be compared with energy consumption of a similar code-compliant building with conventional HVAC systems.

Integration is key

It is essential to integrate the design of the overall building, including the atrium, with the mechanical system. This does not mean that an atrium building requires a custom HVAC system; in fact, the system can be designed to use “standard components” in a way that provides economy of both first cost and energy use.

A one-year follow-up for energy analysis can determine if the building is performing as designed.

Hourihan is a principal with Cannon Design, Boston, and a member of the firm's higher-education practice. Berry, PE, LEED, is a principal and director of Cannon's engineering practice.

Location, location, location

Housing 345 students, Suffolk University's Nathan Miller Residence Hall, Boston, complements the character of its historic Beacon Hill neighborhood. It renews an undeveloped 8,700-square-foot lot on a pivotal block between the dense, low-rise neighborhood of historic Beacon Hill and the urban high-rise financial district and government center area. The site is a former parking lot surrounded on three sides by 12-story buildings. Historic classical-revival stone and brick buildings frame the street front on the east. The building is zoned vertically; public, building-wide common functions are situated in the basement and on the first three floors, and the fourth to the 19th floors have student housing. The basic organization of the building's plan, section and elevation is related directly to the site constraints and context, the building program and sustainable-design strategy.

In the residence hall, daylighting, ventilation and mechanical systems are interdependent, harvesting natural light and reducing heat loss and gain. The atrium ventilates itself when the temperature reaches 85°F, and vents automatically open so the building can cool itself. Working in concert with energy-efficient air-handling systems, chillers and a heat-recovery system, the building is one of the most green in Boston:

  • The upper-level curtainwall and skylight are glazed, and integral shading reduces radiant heat penetration by 40 percent in the atrium and in an outer, glass-enclosed stairway.

  • Exterior envelope comparisons resulted in a composite assembly with a thermal performance more than 20 percent more efficient than code requirements.

  • Energy-consumption estimates drawn from energy modeling of a similar code-compliant building with conventional HVAC systems and without an atrium show an energy savings of about 27 percent. A comparison of the building's estimated energy consumption to that of other buildings of this type in the Northeast shows an energy savings of about 38 percent.

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