Chris Flint Chatto, Associate AIA, LEED® AP, ZGF Architects LLP
University of Washington's Phase 1 Molecular Engineering Building (MEB) is a 90,000-square-foot research facility housing experimental laboratories and offices for interdisciplinary researchers in the fields of bioengineering, chemical engineering, nanotechnology, electrical engineering, mechanical engineering, and materials science engineering. From past experience, the design team, which included ZGF Architects LLP and Affiliated Engineers for mechanical and electrical systems, knew that providing adequate ventilation for researcher safety in laboratories would significantly drive energy use in this facility. Consequently, a set of comprehensive strategies were devised early on in the design process to reduce energy use associated with ventilation systems, including optimizing air changes, heat recovery, chilled beams and radiant cooling in computational spaces, and zoning the HVAC system for the offices separately from the laboratories. A number of factors, including opportunities presented by the site, the climate, and the client, enabled the design team to transform this last strategy into employing full natural ventilation (with no mechanical cooling) in the offices, a highly unusual and technically challenging strategy for a research laboratory building.
The University of Washington (UW) is a leading public research and educational institution, with its largest of three campuses located in Seattle and adjacent to Lake Washington. With over 40,000 students, 5,500 faculty, and over $1 billion annually in academic and research funding, the UW is one of the nation's largest public research universities. In addition, it is recognized as a leader in sustainability, as evidenced by its top ranking by the Sustainable Endowments Institute's 2008 College Sustainability Report Card. The Seattle campus has over 3.1 million square feet in faculty and staff offices, some of which was built over fifty years ago without mechanical conditioning. However, much of the office space built since then has included mechanical conditioning, and the university has expressed interest in investigating whether these new research offices could deviate from this de facto standard.
The Seattle climate is almost unparalleled in the United States for its suitability for natural ventilation. A typical year (as documented by the Seattle Boeing Field TMY3 climate data file) has less than 85 hours over 80°F. In addition, summers days are typically dry, with rare rain showers and relative humidity typically less than 60 percent. Analysis of site-specific climate data, provided by UW's Department of Atmospheric Sciences located adjacent to the MEB site, confirmed these conclusions and also suggested another opportunity for natural ventilation: when temperatures did exceed 78°F, wind speeds surpassed 2 mph over 95 percent of the time, and were virtually always from the NW, providing the necessary air movement to remove accumulated heat and provide additional occupant comfort through evapotranspiration.
Using ASHRAE's adaptive comfort analysis for the Seattle TMY3 field, the team found that maintaining interior temperatures within 3°F of exterior ambient temperatures would result in occupant comfort for over 97 percent of occupied hours. This analysis suggested that natural ventilation was a viable approach, should architectural and mechanical systems be developed to support it.
Figure 1: Annual temperature and humidity analysis for Seattle Boeing TMY3
One initial challenge was the designated site of the MEB. For funding and development purposes, the project was split into two phases, which would meet at right angles and complete an academic courtyard on the UW campus. Consequently, siting and construction phasing issues necessitated that the first phase's primary façades orient to the east and west (actually ENE and WSW, as the quadrangle is rotated 26 degrees from true north). As this dedicated research facility required a tight adjacency between researchers' offices and their laboratories (separated only by a glass partition), cross ventilation though the offices could not be employed. Instead, a strategy of stack ventilation allows air to be pulled through the offices without interfering with the mechanical ventilation and operations of the laboratories. Initial schemes located the laboratories on the east side of the building, facing the quieter courtyard, while the associated faculty offices would face west, enjoying the longer views to the west. However, practical considerations related to natural ventilation necessitated a reversal of this scheme. Stevens Way, a campus arterial that served bus and truck traffic, was located immediately to the west, and associated noise and pollution from this traffic would interfere with natural ventilation. The scheme reversal had another advantage: a western orientation would mean that peak solar load would coincide with peak afternoon temperatures, making occupant comfort more difficult to achieve. The laboratories, with their required high air changes, were much better equipped to deal with this condition.
At the beginning of design development, a full day charrette was held in order to focus the development of this strategy. The workshop was led my Michael Hatten of Solarc Architecture and Engineering, a mechanical engineer with an expertise in building simulation, climate responsive design, and passive design. An initial baseline energy model (DOE2 Quest) permitted the team to understand peak cooling loads and iteratively test basic façade concepts. Ultimately, an overall peak hourly cooling load of 12.5 Btu/square food (SF) was targeted, as a level that natural ventilation could remove heat from the space without requiring so much air flow as to be disruptive in the work environment. Two key strategies were identified to reduce the baseline peak cooling loads from 26.7 Kbtu/SF/hr to the target: reducing peak solar insolation through better façade shading and reducing electric lights through daylighting. With the employment of a single-zone bulk air flow equation, this target peak load also provided rough sizing of the stack chimneys (44 SF of cross sectional area on the upper floor, the worst case scenario as the shorter vertical distance provides less draw).
The architecture team explored numerous design alternatives to reduce peak solar loading by over 80 percent. Ultimately, three strategies were adopted that resulted in a combined 81.1 percent reduction: decreasing the glazed area of the façade by 40.8 percent, selecting better performing glazing that reduced insolation by 34.1 percent, and integrating external horizontal shades that reduced insolation by 51.6 percent during peak late morning hours.
Figure 2: Peak load target reductions and associated solar shading strategy
At the same time, iterative daylight studies quantified expected savings from the reduction of daylight use. An early baseline radiance model was calibrated with a physical daylight model tested at the University of Washington's BetterBricks Integrated Design Laboratory; this radiance model could then be quickly adapted to test the effect on daylighting from various façade configurations. It was found that the selected façade configuration reduced electric lighting use during peak summer morning hours by 67 percent, if a high performance daylight redirecting blind was employed to eliminate glare while redirecting daylight to the ceiling. The blind had the additional benefit of permitting airflow into the office (compared to a fabric shade).
Operable exterior windows were developed to achieve the required aperture area for adequate airflow. Two sets of hopper windows were included. The upper half were sized to provide the required airflow and opened by mechanized actuators to provide controlled airflow as necessary. A lower set provided equal area, but were designed to be opened and controlled by occupants as needed.
In order to ensure that the natural ventilation scheme would not compromise researcher safety, computational fluid dynamic models (built originally to validate reducing the required laboratory air changes from the university standard of 10 to a more optimized value of 6) were adapted to test the effect of office air flow on laboratory ventilation. Among many probable variations, a key worst case configuration was tested that included a 35 mph wind blowing directly into the laboratory façade, worst case-infiltration simulated by a 1 inch crack running the entire length of the laboratory wall, and a laboratory door that was propped open against established procedures. In this case (and all others), neither pollutants were found to be leaving the laboratory environment, nor was laboratory exhaust compromised in any way.
Figure 3: Sectional CFD test of worst-case exfilitration situation. Image courtesy of AEI Engineering.
By the end of design development, it was confirmed that the amount of stack area that could be dedicated per floor was only about 75 percent of that required to provide completely passive air movement during peak load conditions. For that reason, and to provide greater assurance of the system's viability, additional cooling features were identified and developed within the office environment, and air movement assists were designed into the chimney stacks. A night ventilation control scheme was developed to provide night cooling of exposed thermal mass when temperatures in the past 24 hours exceeded set thresholds (78°F interior, or 72°F exterior). In the office, concrete mass was left exposed in circulation areas, structural columns, and beyond a handing acoustic ceiling cloud. In addition, a bio-based phase change material was integrated into the ceiling cloud as well as behind walls in private offices. Ceiling fans supply additional air movement during still conditions, providing additional human cooling through increased evapotranspiration during occupied hours, as well as increased air movement during night ventilation. Finally, two sources of additional cooling were recognized by virtue of the laboratory conditioning and ventilation requirements. The glass wall separating the office would effectively function as "thermal mass", as the laboratory air would be conditioned to approximately 72°F at all times. Secondly, in order to ensure consistent negative pressure in the laboratory, 500 cubic feet per minute (cfm) of its (conditioned) makeup air was provided on the office side of the partition, also providing bonus cooling to the office.
Chimney exhaust stacks incorporate several elements to ensure adequate air flow. Turbine ventilators induce air exhaust with wind from any direction, and additional operable louvers and an electric motor backup in the turbines ensures air flow in all conditions. In addition, a glazed panel was incorporated in the west-southwest orientation of the stack, inducing a solar assist to airflow by increasing the buoyancy of exhaust air during peak summer months.
Figure 4: 3D section showing airflow pathway from windows through stack turbine ventilators
Cost analysis showed that additional expenses and savings associated with natural ventilation resulted in a minor overall increase of $130,000 to the project cost, after accounting for reductions in the building cooling and ventilation system. The analysis also showed that in-slab radiant floor heating (with integrated insulation) provided the most cost-effective heating system in conjunction with natural ventilation. Thermal models showed that this scheme would provide occupant comfort in the office for over 97 percent of operating hours, and should save an estimated 68,000 annual kilowatt-hours over a mechanical conditioning baseline case.
Providing natural ventilation in a technical environment is not easy,
but requires a dedicated team and integrated design. In addition, natural
ventilation is quite possible in the Pacific Northwest climate, and presents
a significant overall campus strategy for the University of Washington's
climate neutrality plan to re-establish the precedent of not using mechanical
cooling in faculty and staff offices. At the same time, it must be recognized
that given the energy intensity of the research environment, natural ventilation
represents a minor portion of the overall building's energy efficiency.
In addition, as a building targeting LEED® Gold certification, it
must be also recognized that natural ventilation is not necessarily encouraged
by the LEED system and the ASHRAE 90.1 energy modeling guidelines. Ultimately,
the reasons to pursue this strategy have to do with creating quality,
comfortable environments, and the potential energy savings represented
by pursuing natural ventilation on a larger basis through the built environment.
Chris Flint Chatto, Associate AIA, LEED AP, is a sustainable designer at ZGF Architects LLP. With a depth of expertise on projects for both public and private sector clients, Mr. Flint Chatto focuses on optimizing building efficiencies through energy and daylighting studies in early project development and tracking those building efficiencies in completed projects. Specializing in energy use and environmental studies, he is responsible for researching and facilitating the design of efficient and healthy buildings through the innovative use of materials, technology, and design techniques, the results of which have been presented at numerous conferences, lectures, and seminars throughout the country. He has led numerous project teams through the eco-charrette process, translating technical performance goals into tangible strategies. His most recent laboratory projects include the University of Washington Molecular Engineering Building; the University of Minnesota Physics and Nanotechnology Building; and the University of Texas at Arlington, Engineering Science and Research Building. Mr. Flint Chatto has developed and taught courses focusing on sustainable, climate responsive, and energy efficient design at the University of Washington and the University of Oregon; was founding chair of the Seattle Emerging Green Builders; and is active on educational and advocacy issues for both the Seattle and Portland AIA Committee on the Environment (COTE). Mr. Flint Chatto holds a Master of Architecture degree from the University of Oregon, a Bachelor of Science degree in economics from the Wharton School of Business at the University of Pennsylvania; and a Bachelor of Arts degree in literature from the University of Pennsylvania.