• A Practical Approach to Natural Ventilation in Laboratory Buildings

    Tweet 2012 Feb 17

    Recently, Jacob Knowles of BR+A and I presented a workshop at the Labs21 2011 Annual Conference. An article about this workshop can be found in the latest issue of I2SL's Laboratory Design Newsletter or read it below.

    Natural ventilation has become a central strategy in sustainable buildings throughout Europe and is now becoming more prevalent within the United States. Natural ventilation, combined with climate-responsive design, allows spaces such as classrooms, offices, and common areas to operate without mechanical ventilation or conditioning during extended periods. Although typically overlooked, laboratory buildings need not be excluded; non-laboratory spaces can be designed to take advantage of natural ventilation, while still maintaining a controlled and healthy research environment.

    The benefits of natural ventilation in laboratory buildings include energy conservation, increased productivity, personal comfort control, improved indoor air quality, and connection to the outdoors. Strategies to consider at the beginning of the design process should include optimizing building orientation, program organization, fenestration, thermal mass, and controls such as automated windows, fan assist, and mix-mode ventilation. More advanced strategies such as night flush venting, wind scoops, and solar chimneys can also be considered. Successful natural ventilation implementation requires an integrated design process, including a clearly communicated set of goals and metrics. Using comfort, cost, carbon, and containment (the four Cs) as performance categories provides a framework for team members to readily understand and participate in the process.

    Comfort
    Comfort is used in a broad sense, and includes aural, respiratory, and thermal comfort. Aural (acoustic) comfort is often considered separately, and is primarily concerned with outdoor noise pollution entering through operable windows. Respiratory and thermal comfort are often addressed simultaneously, but it is important to recognize that natural ventilation and natural conditioning are individual concerns. For example, it is common in Europe to use a mixed-mode system, where hydronic systems provide supplemental heating or cooling, while an air-based mechanical or natural ventilation system provides fresh air. Adaptive Comfort, as outlined in ASHRAE 55, provides the primary guidelines for evaluating thermal comfort in naturally ventilated spaces.

    The Columbia University Gary C. Comer Geochemistry Building is organized into two distinct zones with different architecture and infrastructure. The laboratory side is designed as a high energy environment with complex mechanical and control systems, while the office side is designed as a low technology structure with operable windows and individual fan coil units.  

    Cost
    The cost of natural ventilation should be evaluated from a holistic perspective. For example, elimination of cooling in the atrium and reduction in peak loads throughout the offices and classrooms can offset the cost of fenestration upgrades, added control sequences, and other items such as variable-speed drives on the atrium smoke-evacuation exhaust to allow fan-assisted air movement. In addition, life-cycle cost should be considered as energy savings can also help offset first-costs. 

    Carbon
    Carbon is the metric of choice for environmental impact caused by energy consumption. Since mixed-mode systems often incorporate a changeover between mechanical operation and natural operation, it is critical to develop architectural, mechanical, and control-systems that work in concert to reduce energy consumption. The greatest concern lies in the introduction of large volumes of humid outdoor air that must be dehumidified when the mechanical conditioning system is engaged. To successfully reduce energy consumption, mixed-mode strategies to use may include occupant education and notification, supported by smart-controls that interpolate operational data and weather forecasts.

    The Center for Biotechnology and Life Sciences at the University of Rhode Island is organized around a five-story naturally ventilated atrium that connects the research and teaching wings. Motorized window operators and variable-speed fans designed for smoke exhaust also serve as the infrastructure for the building's natural ventilation strategy. 

    Containment
    One of the primary functions of a laboratory building is the ability to maintain occupant safety; the massive investment in proper laboratory planning, mechanical design, fume hood operation, and occupant education can easily be unraveled by a poorly planned natural ventilation approach. In addition, critical research may be impacted by fluctuations in temperature and humidity or contaminated by introduction of pollutants in unfiltered air.

    Typically, air is transferred from more positively pressurized spaces to less positively pressurized spaces at door undercuts. The transfer air is as little as 150 cubic feet per minute, so sensitive pressure relationships that ensure proper isolation can be overwhelmed by rapidly changing wind pressures that might drive hundreds of cfm in or out of a space. In addition, operable windows can allow exhaust to be reintroduced into the building.

    To mitigate these risks, each space needs to be properly categorized during the programming phase, listing pressure relationships and sensitivity to temperature, humidity, and contaminants such as pollen and dust. The level of control required by a given space, based on the potential risk of non-containment, will help determine where the space may be located and how air movement must be controlled. Sensitive areas that must be located adjacent to zones that are slated for natural ventilation often warrant a computational fluid dynamics study. Similarly, potential re-entrainment of exhaust must be evaluated by specialty engineering firms that perform wind-tunnel testing of scale models.

    The Science Research Building at the National University of Galway, Ireland, is organized so the atrium, office suites, technical work areas, and perimeter corridors are naturally ventilated, acting as a "thermal sweater" for the mechanically ventilated laboratory suites.

    As shown through the project examples, each situation merits a different solution, but one constant remains. To achieve holistic success, the integrated project team must approach natural ventilation in laboratory buildings with a clear set of goals and metrics, incorporating an iterative design process with timely analysis and feedback. Those who are up for the challenge will provide a healthier, more humane environment for building occupants, ultimately supporting the productive and creative community demanded by this critical and competitive industry.

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