Page 98 - Designing for Zero Carbon - Case Studies of All-Electric Buildings

CASE STUDY NO. 4 REDFORD CONSERVANCY AT PITZER COLLEGE
(Opposite Page)
Arrays of operable windows throughout the building pro- vide fresh air and cooling via daytime natural ventilation and night purge ventilation. (Photos: Costea Photography Inc.)
Natural Ventilation
The seasonal air temperature ranges at the site are ideal for natural ventilation for fresh air and cooling: cool night temperatures for space pre-cooling and daytime air temperatures within the comfort range most of the year. In addition, the historic building was designed originally to maxi- mize natural ventilation through the large areas of openable windows and doors. Natural ventila- tion is an obvious design strategy to employ in the renovated building.
The designers used the existing crawl space beneath the wood joist floors combined with the operable skylights to create an air flow path through the main spaces, with the air intake at openings in the exterior wall of the crawl space and a connection to the occupied space above through floor grilles. The air flow is driven by the natural buoyancy of the air traveling vertically to the open skylights combined with the draft created by the prevailing breeze above the roof. Thus, the cooling air flow can be done entirely without fans for most of the year. Large ceiling- mounted, slow-moving room fans create comfort conditions on those days when there is little or no air movement due to lack of prevailing breezes.
This effect is enhanced by broken shards of the red hollow clay bricks that line the crawl space, which were placed there after the original interior walls were demolished and the bricks were broken into pieces. This effectively adds thermal mass to the crawl space, which is used to pre- cool the incoming outside air. This thermal mass is typically chilled during night purge ventilation3 of the building.
Heating, Ventilating and Cooling Systems
The renovated building employs a Mixed-Mode System to maintain comfortabe conditions
throughout the year.4
The natural ventilation system design described above is utilized when outside air temperatures are within the comfort zone. Outside of those comfort conditions, this natural ventilation is shut down by automatically closing the skylights and the air-intake dampers at the crawl space wall. In this case, either heating or cooling is required, which is provided by ductless fan coil units in each room, tied to a heat pump.
The operation of this mechanical heating and cooling system requires that all operable windows (and the skylights) are closed. Window contacts ensure that the system cannot operate if a win- dow is open. If outside air temperatures rise during the day such that cooling is desired by the occupants, closing the windows in the space will cause the thermostat-controlled fan coil unit to start operating. Since the windows are all manually operated, the occupants effectively control the temperature conditions in each space through their adjustment of these windows.
3 See: https://knowledge.autodesk.com/support/revit/learn-explore/caas/simplecontent/content/ night-purge-ventilation.html. See also: https://www.windowmaster.com/expertise/natural-venti- lation-and-mixed-mode-ventilation/night-cooling-ventilation/.
4 See: https://cbe.berkeley.edu/mixedmode/aboutmm.html.
See also: Zero Net Energy Case Study Buildings, Volume 2, “Case Study No. 10: West Berke- ley Library”, (2016), p. 88:http://online.flipbuilder.com/bernheimdean/yxkr/
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Designing for Zero Carbon: Volume 1