Engineered Systems - August 2008 - (Page 38)

Looking Radiant in place at 6-in. centers. End loops are rounded to maintain 8 to 9 in. dia, thereby preventing buckling. Bolt anchors were fixed to the base slab in between tube rows to allow flexible exhibit ties. The topping pour provided a nominal 2-in. cover, which is necessary to prevent the concrete from cracking. Approximately 100,000 linear ft of tubing runs in the 38,000 sq ft of concrete slab. Manifolds are located at high level at Level B1. The system is broken into nine independent temperature control zones, so nine sets of valves, pumps, and accessories have been located in the Level B1 mechanical rooms. Each system is a tertiary, constant flow chilled water loop connected to the secondary chilled water loop. Many of these construction details began on paper but were further developed through on-site mock-ups and close observation of first-inplace assemblies. The snap-in tube rails and 1 in. insulation “spacers” were developed in this manner, as was the method of tying down the loop ends to prevent deflection while the workers walked over the tubes during the topping pour, as it was originally assumed that the topping pour would be worked by machines instead of workers in heavy boots. California Academy of Sciences Team FIGURE 3. The California Academy of Sciences building is hoping for a LEED® Platinum designation and is also a City of San Francisco Department of the Environment green building pilot project. Executive architect: Renzo Piano Building Workshop – Genoa, Italy Design architect: Stantec Architects – San Francisco Engineers and sustainability consultants: Arup – San Francisco Project manager: DR Young & Associates – San Rafael, CA General contractor: Webcor Builders – San Mateo, CA Mechanical contractor: Marelich Mechanical – Hayward, CA Hydronic subcontractor: O’Brien – San Francisco comfort is maintained. Sun shades on the east and west glass walls and on the north canopy will be activated when the solar intensity high, unless wind speed is excessive. High and low level ventilation openings are located in the glass walls surrounding the exhibit areas. In the colder months, high-level openings are used for background ventilation and avoiding low-level drafts. In the warmer months, both high- and low-level openings are used to maximize airflow and limit space temperatures. Roof vent hatches are also provided at the high points above the rainforest and planetarium. All openings are automatically controlled to adjust airflow and temperature. On a still day, airflow is generated by stack-effect (warm air rising), due to the height difference between inlet openings in the elevations and roof vents above the rainforest and planetarium. On a day where some wind is present, regardless of the wind direction, a negative pressure is generated at the roof vents and drives the airflow. Exhibit space temperatures and wind conditions drive the ventilation sequence. Wind direction determines which banks of dampers operate and the space temperature dictates damper position. Vent operation can be overridden by several means. They will move to a more fully open position if CO2 concentration exceeds the space setpoint or if high-level humidity exceeds its allowed limit. Some or all the vents will close if conditions are right for floor condensation, if wind speeds are excessive, or if rain or fog is present. High-level vents are kept open at night if the previous day’s temperature was high, the nighttime air is cool, and the slab is warm. Powerful exhibit lighting is located above the coral reef and rainforest. When the vents cannot be opened due to one of the aforementioned override conditions, high-level temperatures will rise and trigger the lighting control system to shut off lights, thereby preventing overheating of the space and nearby glass. The radiant floor is based on an Uponor system built up over a base concrete slab covered by an inch of rigid insulation. Support rails rest on 1 in. strips of insulation and hold 5/8 in. dia hePEX™ plus tubing 38 En gi neer ed S y stem s August 2008 The floor operates in cooling mode only when the exhibit area temperature is above setpoint or when the outdoor air temperature is above 77° and rising. In cooling mode, the return water temperature is fixed at 68°. When the outdoor air temperature falls below 64° the radiant floor switches into heating mode. Water temperature is modulates between 75° and 90° as the outdoor temperature drops to the winter design condition. The system changes over from heating to cooling via simple modulation of two-way valves — one at the tertiary chilled water (radiant) loop and one at the associated hot water heat exchanger. ES Switenki is a mechanical engineer with Arup (San Francisco), a global engineering and consulting firm. He has served as the mechanical project engineer throughout the construction phase of the new California Academy of Sciences, and has applied his strengths in low-energy HVAC system design and multi-discipline coordination to health care and arts and culture projects. He also has experience with all types of commercial, educational, and institutional facilities. He is also a member of both ASHRAE and ASHE.

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Engineered Systems - August 2008 Contents Editor's Note Back2Basics HVAC Challenge Case In Point Commissioning Building Automation Efficiency Incentives HVACR Designer Tips Glass Box to Grand Casino Looking Radiant In Green Mechanical Products Sourcebook Q&A: Dehumidification In Schools Building Oversight Management: M&V And More Products Classifieds Advertiser Index Tomorrow's Environment

Engineered Systems - August 2008

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