High Performing Buildings - Spring 2009 - (Page 23) Control systems A fully centralized direct digital control system monitors all of the HVAC systems’ performance to ensure proper operation with minimal Photo © marc Cramer thermal energy storage. The perimeter of the excavated section was insulated with rigid insulation, and PEX piping was laid in multiple layers throughout the backfill. Sand was used to backfill the space to allow optimal contact with the piping and proper diffusion throughout the mass while protecting the pipes from damage. Literature on thermal storage almost exclusively covers tanks filled with liquid (using phase change or not); very little information exists on solid thermal storage. A simplified heat transfer model, based on finitedifference nodal networks, was used to establish the transitional behavior when charging and discharging the mass. This model allowed observation of the distribution throughout the mass and the conclusion that two important phenomas occur related to the rather slow thermal diffusion in the solid mass. First, the heat is not evenly distributed along the pipes but follows the water temperature profile in the pipes during the charging. Consequently, for an optimal thermal exchange, the flows should be reversed in the two modes, creating the effect of a counter-flow exchanger. Furthermore, penetration of heat for the anticipated operating condition was limited to a radius of 4 in. around the pipes. Therefore, a 2-D spacing of 9 in. between the pipes was chosen to limit the thermal interference between the charging and discharging cycles. Photo © Pageau morel The interior design maximizes open and airy spaces. Top: A second-level balcony overlooks the gymnasium and provides access to other office spaces. Above: The smaller northern atrium serves as the main entrance to the building. The weight room/fitness center is completely open to the atrium. The top floor is a typical office space, before fitup. spring 2009 HigH Performing Buildings 23
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