Page 61 - Zero Net Energy Case Study Buildings-Volume 1

IDeAs OFFICE BUILDING
CASE STUDY NO. 3
to provide even daylight to the spaces below and were limited in number (17) to provide just the right thermal balance while meeting the overall optimum daylighting design.
The daylighting design is indicative of a common issue with ZNE buildings that utilize solar pho- tovoltaic (PV) panels for on-site renewable energy: the daylight collection features essentially compete with the PV panels in the harvesting of the sun’s energy. Not only must the balance of the two be carefully coordinated in the design, but the design has to respect the simple geometric requirement that one type of building feature will not cast shade on the other. For this building, where the PV panels are built integral to the roofing system, the roof framing is deliberately sloped enough to prevent this shading of the PV panels by the skylights and their curb framing.
The glazing for the building was selected generally for both high thermal performance and good visible light transmission. For the skylights, the glazing is clear but prismatic, which minimizes direct glare conditions, an important factor in good overall daylight design. The potential direct solar beam problem is also prevented by deep, flared skylight wells.
The window glazing is a spectrally selective glass with good visible light transmission (63%), low U-value (0.29, a low heat conduction value) and a low shading coefficient (0.31, a low fraction of solar heat gain and less than half that of regular double-glazing).
A continuous horizontal canopy made up of glass PV panels provides shading for the large new glazing area that is inserted into the cutout in the south wall. These particular PV panels are used in this location partly for demonstration purposes, justifying the extra cost. Operable windows are located in the exterior for local supply of fresh air.
Wall insulation levels were improved to approximately R-20 by adding fiberglass batt insulation to the inside of the concrete shell. The roof insulation was easily upgraded to R-30, while the roof membrane is white in color to provide high reflectance (80%) and a “cool roof”. It is interesting to note that the building envelope was not sealed to make a “tight” building, preventing leakage of temperate air; this is significant in how it affected the HVAC system design.
Zero Net Energy Case Study Buildings: Volume 1 45
PHOTO: DAVID WAKELY