Page 26 - Zero Net Energy Case Study Buildings-Volume 1

CASE STUDY NO. 1
PACKARD FOUNDATION HEADQUARTERS BUILDING
(Above) Overhang design for east-facing facade, allowing maximum daylight penetration while protecting against direct sun.
(Below) Daylighting via sky- lights at interior conference room. (Opposite page) Auto- matically operating exterior blinds on west-facing facade.
Building Envelope
The high perimeter building allows for good natural ventilation and effective daylighting of office space, but also increases thermal losses. Energy analysis indicated that the high perimeter en- velope would result in lower energy demand when all factors are considered.
The building envelope satisfies two general requirements for a low-energy building: a high level of continuous insulation and a good seal at joints and other air leakage locations.
To avoid the thermal bridging effect of intermittent structural elements, the wood framed walls locate studs every 24”, with a 1” thick layer of rigid mineral wool insulation applied continuously over the outside of the studs. The insulation between the studs is also mineral wool, which is preferred over fiberglass insulation for its higher insulating value, stiffness (avoiding loss of insu- lating value in handling at the construction site) and greater resistance to mold development. The net result is a wall with insulating value R-24.2, including the muted effect of thermal bridging.
The roof has a similar insulating approach, using a 2” thick layer of rigid mineral wool insulation over the structure and under the metal roof. Finally, for added insulating value, the concrete slab is placed on top of water-impervious insulation board to provide a high insulating value of R-23 in the floor. The 1” rigid wall insulation layer wrapping the wall continues below grade to provide perimeter insulation at the footing.
Windows make up almost 50% of the exterior wall area, which supports good daylighting of the largely perimeter spaces. To ensure good thermal characteristics of this part of the building en- velope, the window glazing consists of heat mirror glazing units—two layers of clear glass with a suspended heat mirror film. A financial analysis indicated that the specification of this type of window would result in cost savings from a reduced size heating system and, more significantly, the planned solar photovoltaic system, which would more than offset the added cost of this premium glazing. (It is generally true that energy efficiency measures incur less cost than the corresponding energy production systems.)
Daylighting and Shading
With a building wing width of approximately 45 feet, good daylighting is possible virtually through- out the space. To ensure daylight penetration to the center, light shelves are added to direct the incident skylight inward. Because of the predominant east and west orientation of the long fa- cades, the light shelves operate well for half the day, when the direct sunlight is incident on the opposite side of the building wing.
When direct sunlight is incident on the façade, exterior blinds are automatically operated to a po- sition in front of the window and the blind louvers adjusted to block direct sun and to pass through diffuse daylight. The operation of the blinds still allows windows to be opened by the room oc- cupant for natural ventilation purposes if the outdoor air temperature is appropriate. The occu- pant has control of an interior shade system, but the exterior blinds are operated by the building control system. Changes to the operation of the exterior blind system, which can be done on an individual basis, is carried out by reprogramming the control system. This is relatively easy to do given the sophistication and siimplicity of the control system interface. (See the discussion of the building control system on the following page.)
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Zero Net Energy Case Study Buildings: Volume 1