Passive Design as Integrated Design Practice

The following excerpt is taken from a white paper co-authored by Rod Kruse, FAIA (BNIM), Alfredo Fernández-González (University of Nevada, Las Vegas), Ulrike Passe (Iowa State University) and Jörg Rügemer (University of Utah). The paper will be presented at the World Renewable Energy Forum National Solar Energy Conference taking place next month in Denver.
Click here to read the complete paper.


An Integrated Design Practice (IDP) is essential for successful passive and net zero ready design on larger scale projects. This method of project delivery requires early and extensive creative and technical leadership in an integrated manner from the entire team comprised of the owner, architect, landscape architect, mechanical engineer, electrical engineer, structural engineer, civil engineer, energy modeler, daylight modeler, cost estimator and building product suppliers. This integrated process allows the team to analyze optimum passive strategies focused on orientation and massing, daylighting, and passive heating and cooling strategies prior to the integration of technical building systems design.

The State of Iowa, Iowa Utilities Board / Office of Consumer Advocate Building (IUB/OCA) is an example of Integrated Design Practice. From inception, the Owner established a commitment for a high performance building. Beginning with the Request for Proposals for this 44,500 gross square foot office facility, the State of Iowa established a goal for the building to consume 28.0 kBtus or less per square foot per year. This goal was equivalent to a 60% energy savings when compared to the baseline for a similar building established by ASHRAE 90.1 – 2004.

An integrated design process was employed to consider building placement and orientation, open office vs. enclosed office configurations, material selection and configuration, and the integration of all passive and active strategies and systems. Initially, the design team focused on building orientation and proportions to maximize daylighting and passive heating and cooling opportunities. Design of the mechanical building systems appropriate to support the passive design followed.

The site selected provided opportunities to maximize daylighting and reduce site development requirements by utilizing existing campus facilities. The building is sited with an East-West orientation which combined with the narrow North-South building configuration provides the most appropriate daylighting and natural ventilation opportunities. West and East elevations were designed with minimal glass to provide specific views toward the State Capitol Building and Capitol Complex while mitigating heat gain and glare. The Iowa climate includes hot and cold extremes. A white thermomass precast concrete with continuous insulation and non-thermally conductive ties, provides a simple yet high performance envelope that eliminates traditional thermal bridging at roof interfaces, foundation walls and wall openings.

Innovative details allow insulation to wrap uninterrupted from the roof into the thermal wythe of the wall panel, around the foundation system and across the underside of the slab on grade. This thermal mass captures free heating, modulates temperatures and reduces loads. The geothermal well field uses the earth’s constant temperature to offset heating and cooling loads. High performance glass is tuned to the characteristics of each elevation’s exposures.

The building automation system is tied to an onsite weather station which identifies favorable and unfavorable exterior conditions, sending an email to occupants to inform them when windows can be opened and when they should be closed. The automation system also disables the associated zone’s heat pumps when windows are open, ensuring energy is not wasted.

An ideal building footprint depth is employed to deliver daylighting throughout the facility. Louvered sunscreens, with horizontal blades and vertical fabric panels at the south elevation of each wing, reflect daylight deep into the office space during all seasons, block unwanted summertime heat gain and allow passive winter heating. The parabolic profile of the sunscreens reflects high elevation summer sun off of the curved portion and low winter sun angles off of the flat portion of the louvers. Zinc-clad office enclosures cantilever from the north elevations, taking advantage of diffuse northern light.

Daylight simulation resulted in the selection of open-office workstations, which demonstrated a significant performance increase by implementing low 36” high furniture panels with 16” translucent upper panels. At the core of the building, the selected furniture supported the required lighting levels at the work surface without electric lighting 70% of the time (vs. 30% of the time with owner’s existing 64” high furniture). Solar tube skylights at the core deliver additional daylighting. Over 95% of regularly occupied spaces have access to daylight and views provided by the glazing on the north and south elevations. All employees have access to operable windows.

Measurement and verification is integral to Integrated Design Practice and the continued development and success of high performance buildings. The metrics of the IUB/OCA Building are continuously being documented. Nearly every outlet can be monitored and real time data is analyzed to develop opportunities to improve building performance. Monitoring is being provided in partnership with the State of Iowa Department of Administration and the Iowa Energy Center. The Iowa Energy Center will further use results to support various research projects.

All outlets are designated as critical power, non-critical power or task lighting. Open office and enclosed offices outlets are tied to occupancy sensors that shut down all noncritical loads when not in use. Task lighting circuits are individually monitored as part of a larger daylighting study within the building to understand the extent of savings and total energy use assigned to artificial lighting.

The performance of the IUB/OCA Building has exceeded the targeted performance established by the owner. After twelve months of occupancy, the building is consuming 22.5 kBtus per square foot, a 67.9% energy savings below ASHRAE 90.1-2004 requirements, prior to consideration of on-site renewable energy production. The geothermal field tied to dual stage heat pumps accounts for 39% of total energy savings, while the total energy recovery unit provides 12% of the total energy savings. Additional strategies comprise the balance of the energy savings including: variable frequency drives; high-efficiency, low power density lighting; automated dimming for interior lighting; occupancy sensor for lighting and workstation plug loads; time-of-day control of office equipment plug loads; CO2 sensors for moderated control of ventilation air. In addition, a roofmounted 45 KW photovoltaic array provides an additional 13% renewable energy.