Page 69 - Zero Net Energy Case Study Buildings-Volume 2

An example is the decision to use electrochromic or dynamic glass2 instead of insulated glass combined with exterior shades or interior blinds. Athough electrochromic glass outperforms the blinds/shading solution because of its fine-tuned operation with respect to solar impact, this fact alone would not have led to its selection based only on energy savings because of the premium initial cost. However, this product provides a greater connection to the outdoors during the day due to its operating characteristics and it was deemed to have an intrinsic appeal to user-tenants in this geographic market area. Because of these additional benefits, the holistic process showed that the overall ZNE design including the electrochromic glass would still be more profitable than the code-minimum design.
The project team chose a passive approach for its low-energy design concept. Even though the site is in a relatively warm microclimate where buildings can have a significant cooling load in the warm months, the night temperatures during that time fall into a range where “free cooling” can be used to pre-cool the large thermal mass of concrete walls. Also, for a good part of the year, natural ventilation near the exterior walls can provide cooling air during the day. The design strategies for the building envelope and the HVAC system, therefore, are aimed at optimizing the use of these aspects of building and microclimate in a passive way.
Building Envelope
The existing building was a standard one-story concrete tilt-up construction with uninsulated walls and minimally insulated roof. As with Case Study No, 8, the lightweight roof structure would have to be strengthened to support a new solar photovoltaic system; because of the daylighting design solution in this case (see below), the roof structural strengthening had to be done.
The passive design concept for the building called for insulating the exterior walls on the outside surfaces so that the mass of the concrete was available for heat exchange with the cool night air. At the same time, the BMS (Building Management System) controls the building fans to operate at night if the outdoor air temperature is low enough and if a cooling load is anticipated for the following day.
The team settled on 5-5/8” thick polystyrene retrofitted to the exterior wall surface. EIFS (Exterior Insulation Finishing System) was used to provide a finish over the thick layer of insulation. There is no foundation insulation primarily for cost reasons; the polystyrene ends at the level of the concrete floor slab. The concrete floor slab and the layer of ground beneath it act as additional thermal storage mass and, for this reason, the use of carpet is discouraged as part of tenant improvements3.
All existing single glazed windows were replaced by double-glazing. The electrochromic glass was used on all but the north side of the building, where a lightly tinted low-e insulated glass was used. Since many of the windows were converted to openable casement windows, a method had to be developed for using the electrochromic glass units in the openable sash, i.e., a method to ensure that the electric wiring connection functioned flawlessly for the life of the windows. This issue was one of many that was successfully researched and solved by the contractor.
2 Dynamic glass or electrochromic glass is electronically tintable glass units, setting solar heat gain and light transmission of the glass at a pre-programmed level or through instant control via portable device. A light sensor reading outside the glass panel is compared to the desired interior condition; the glass system then sets the tint based on the preferred interior light condition for minimal glare and best daylight levels. The glass is therefore tuned to the space.
3 Per the terms of the lease agreement, the tenant must pay for any energy charges in excess of the ZNE baseline.
Zero Net Energy Case Study Buildings, Volume 2
Replacement windows using electrochromic glazing.
SPECULATIVE OFFICE BUILDING AT 435 INDIO WAY
CASE STUDY NO. 9
Retrofitted polystyrene insula- tion at exterior wall surfaces.
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