Page 48 - Zero Net Energy Case Study Buildings-Volume 2

CASE STUDY NO. 8 IBEW-NECA JATC TRAINING FACILITY
(Above) Clerestory windows installed as part of the renova- tion.
Building Envelope
PHOTO: CHAD ZIEMENDORF
(Above) New roof monitors for daylighting, passive ventilaton and structural support of solar photovoltaic panels.
(Opposite) View of roof monitor array from classroom interior.
The existing building was a typical tilt-up structure with 10-foot deep “mansard”-type overhangs on all sides, single-glazed windows and no insulation on the concrete walls. A band of relatively small clerestory windows was located on all four sides of the perimeter—insufficient for any day- lighting given the overhangs but potentially capable of being repurposed for natural ventilation.
The early energy modeling and cost analysis indicated that insulating the walls or replacing the windows with double-glazed units would not improve energy performance enough to justify the cost. This is due in part to the fact that the largest portion of the exterior envelope is the roof; the wall and window area is simply a small fraction of the total.
The roof received a standard code-level of insulation (R-19) applied on the interior surface and a portion of an east-facing wall received an application of an exterior insulation and finishing sys- tem (EIFS) to repair the old concrete surface. Also, the natural ventilation strategy required the replacement of every second clerestory window with a system-operated double-glazed hopper window, thus upgrading the insulating value of some of the window system. (See “Natural Ven- tilation” discussion below.) Aside from these measures, the building was left in its original state of a relatively low level of thermal insulation. Other cost effective ZNE design strategies were adopted instead in order to bring the overall energy load down to a level that made ZNE perfor- mance realizable.
Daylighting and Electric Lighting
Daylighting was an important design strategy for this renovated building given the large amount of interior floor space, with most program spaces lacking adjacency to the limited number of exterior windows. The principal daylighting design approach is the use of roof monitor arrays, which were also designed to support the solar photovoltaic panels and to provide air outlets for the natural ventilation of these interior spaces. Solatubes are used as a secondary daylighting system, providing daylight principally in the corridor spaces and in those areas where roof moni- tors are not structurally possible.
The design of the roof monitors was dictated by the structural characteristics of the existing build- ing as well as the functional needs of the spaces below. The limited load-bearing capacity of the existing roof prevented the installation of a typical solar panel structural support system. Howev- er, the roof monitor system, which could be supported on existing beams, could also be utilized as the support system for these solar panels. In a manner similar to that of Case Study No. 7, the DPR Construction Office Building, the roofscape was carefully designed so that shading of solar panels from adjacent roof monitors is avoided, while maximizing the number of solar panels and providing a good distribution of daylight to the spaces below the right-sized roof monitor glazing.
In this case study building, the roof monitor glazing is vertical and faces the lower north portion of the sky. There is additional limitation on the view of the sky above due to the structural overhangs on the roof monitors, which are included for waterproofing reasons. The vertical glazing also “sees” the solar PV panels on the roof monitor to the north, which actually provides additional daylight that is reflected back off the panels.
The shape of the roof monitors creates diffuse daylight from these natural and structural exterior daylight sources for the classroom and workshop spaces below. Electrically-operated shades in the monitors are used to reduce the light level when required for A/V presentations.
An initial design idea was to turn one roof monitor in the central café space to face south, con- necting it to a large concrete wall for passive solar heating of that one space. The concrete wall proved to be impractical and was eliminated for cost reasons, but the one south-facing roof moni-
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Zero Net Energy Case Study Buildings: Volume 2