Anderson Anderson Net Zero Energy Classroom

Anderson Anderson Architecture has designed a modular, portable, energy neutral classroom that can be customized to suit a variety of climates. The first classroom is being built for a location in Ewa Beach, Hawaii. This building maximizes passive strategies and high-performance design principles to produce up to four times the energy that it uses by harnessing on site solar and wind power.

Project Title: 
Net Zero Energy Classroom
Project Designers: 
Anderson Anderson Architecture
Project Date: 
Aug 2011

This project is part of the ZEBRA Series of Zero Energy Buildings by Anderson Anderson Architecture.

The building system itself is highly flexible and includes a range of optional components and configurations so that it’s performance characteristics can be optimized for a variey of environmental conditions, from subtropical Hawaii, to desert locations in the American Southwest, and the cold winter climates of New England.

This portable classroom system is designed to provide an optimized educational environment for students and teachers at an affordable cost while advancing sustainable design principles. Natural forces and resources are highlighted and exposed throughout the structure, which allows the building system to act as a learning tool for occupants, other schools and the general public. Its web-based performance monitoring system allows for real-time remote observation and data analysis by researchers and the general public from any location in the world.

The seemingly ideal climate of Hawaii leads many to believe that it would take little effort to provide an indoor environment similarly comfortable year around. However, classrooms need to be enclosed spaces so as to minimize noise and visual distractions, which can also leave the cooling breezes out, reduce illumination and trap stale air. The designer is then challenged to reintegrate the comfortable outdoor conditions into the indoor environment., while optimizing its function as a teaching and learning space.


Software and the Design

  • Autodesk Revit Architecture parametric modeling software is utilized to allow rapid analysis, design and manufacturing customization for the site conditions in Honolulu, Hawai'i, using site data retrieved from Autodesk Ecotect Analysis to drive design.
  • Primary analysis was performed in Ecotect software and Radiance software, based on the BIM model created in Revit Architecture.
  • Due to the parametric and flexible nature of the software, the advantages of modular construction can be optimized to suit the needs of each unique school site.


Building Energy Loads and Climate - Learn More


Autodesk Revit Architecture parametric modeling software is utilized to allow rapid analysis, desigClimate data retrieved from Ecotect Analysis and compiled here shows that the dominant winds on the site come consistently from the Northeast. Further analysis of the psychrometric chart shows that the outside climate is rarely comfortable, typically it is hotter and more humid than most people would prefer.

Taking those two conditions, the design team planned to passively ventilate the classroom using stack effect (the natural bouyancy of air) operable windows and the dominant winds from the North East.

Passive Heating, Cooling, and Ventilation - Learn More


A variety of strategies were used to maximize the performance of the building system for the site in Hawaii. Care is taken throughout the design process to keep the project as affordable as possible while selecting the appropriate materials to optimize the efficiency of the building system and ensure that the occupants have a delightful and comfortable environment for work and play.

Heating and Cooling:

  • The building modules are configured to allow either transverse or longitudinal application of roof clerestories. this gives the building orientation greater flexibility, so it can take advantage of varying sun and wind conditions.
  • Steel frame and steel and rigid foam sandwich panel floor and roof system minimize material use, maximize insulation, convection and radiant heat reflection, and deter pests and mold in the cavity-free structure.
  • This double wall cladding, along with the 24 gauge standing seam metal roofing shaded by solar panels above a 3” ventilated airspace, creates a chimney-effect ventilated double-skin shading and cooling the majority of the building surfaces, greatly reducing heat gain.
  • Additional modulation of the sun and wind effects on the building is achieved with a series of strategically placed external steel fins, which redirect and take advantage of naturally occurring air flows, and block harsh light from certain angles at specific times of the day.
  • Windows are clear anodized aluminum, thermally broken frames, with insulated, low-E glazing.


  • Natural ventilation provides a healthy indoor environment by providing an ample air change rate per hour (ACH). A minimum ACH of 2.0  was calculated from ASHRAE 62.1-2004 table 6.1 for indoor air quality within classroom spaces. The CFD Simulation shows the minimum ACH is achieved and surpassed for the times that the classroom will be typically occupied.


Computational Fluid Dynamic (CFD) studies were done on the prototype using the WinAir software.

  • Ventilation analysis predicts that hourly ACH values for the hottest day of the year  (September 3) achieve a maximum ACH of 133 with all clerestory windows and the lowest side windows open.
  • The wind speed was set to 5 m/s coming from an ENE direction as determined from climatic averages. The airflow across the occupants was calculated to range from 0.40 m/s at the north (back) wall down to 0.25 m/s near the south (front) teaching wall. These values provide comfortable air movement without moving paper around.


Thermal Comfort - Learn More

  • A script was written to extract the results from the CFD Simulation software into a spreadsheet. All analysis was performed using natural ventilation only.
  • The average PMV of .53 corresponds to a comfort level deemed appropriate for more than 90% of the population.
  • The analysis calculated just 345 hours (21%) out of a total of 1600 hours of occupancy to be above a PMV value of +1.5. This corresponds to a comfort level deemed appropriate for 50% of the general population. Note that this value assumes an air speed of 50 fpm (0.25 m/s), which is similar to a barely noticeable breeze.

Lighting and Daylighting - Learn More

The clerestory windows have north facing windows that are naturally shaded and provide excellent working light levels throughout the typical school day without electrical lighting. Electrical lighting back up is provided by efficient fluorescent tubes and a reflective ceiling surface which provides optimized work lighting conditions for use outside of daylight hours..

  • All glazing is north facing and/or shaded to prevent direct sunlight.
  • All glazing is operable to allow many different occupant-controlled options for natural ventilation and comfortable airflow.
  • Ceilings use daylight reflective and sound absorbent high-recycled-content acoustical tile.


  • Day lighting was calculated with the Radiance engine and displayed through the Ecotect software.
  • Day lighting analysis indicates that excellent working light levels will be achieved throughout the typical school day without electrical lighting.
  • A glazing visible transmission of 0.52 was used in the calculation. The simulation was done under a clear sky model for September 21 at 12 noon. Material reflectivity is set to 80/60/40 as a mean recommendation by the IESNA for classroom spaces.
  • The work plane upon which the analysis was done was set to 30 inches off the floor. An average illuminance of 56.76 footcandles was calculated over the work plane, which is well above the IESNA minimum recommended illumination for educational spaces.
  • The angle of the roof is determined by a combination of the desire to optimize the placement of the solar panels on the exterior for maximum solar gain, and the desire to bring in high quality ambient north light from the clerestory windows, which is then reflected down into the classroom space using the underside of the roof monitors.]


Efficient HVAC Design - Learn More


Thermal comfort analysis indicates that the Ewa Beach prototype should be comfortable without air conditioning back up. The modular system provides for an efficient mechanical air conditioning system as an important option that must be available for many school sites where thermal, air quality, or noise conditions preclude optimized natural ventilation in all conditions. The mechanical systems are configured either to reside in a mechanical room in each portable unit, or can be even more efficient if provided in external power modules supplying more than one unit.

  • A variety of different HVAC systems can be utilized with the building to adapt its design, and in-floor radiant heating and/or cooling, and forced air ducted heating and cooling systems have been configured where appropriate.
  • The building enclosure is similarly adaptable—highly insulated exterior wall and window systems are implemented for the version designed for northern climates like New England, while the Hawaii version uses a lighter and thinner wall assembly optimized for that climate.
  • The energy modeling done by the project design team has projected that the building as located in the Ewa Beach area of the island of Oahu can achieve the required comfort ratings without the need for mechanical air conditioning, relying on natural ventilation through controllable openings, and the typical wind flow patterns in the area.
  • A supplemental fan ventilation system is incorporated into the design as a backup for times when the natural wind patterns are disrupted by unusual weather patterns, to allow the building to produce its own air changes if needed. The system is designed to allow for the installation of a mechanical air conditioning system if the same building design were to be used in another location, for instance on a site with higher humidity.


Energy Generation:


The classroom harnesses the available solar energy to offset its energy use. Its modular construction system enables the photovoltaic roof surface to be oriented to best suit conditions on the site. For the Hawaii building, the energy production is handled by 72 x 135 Watts photovoltaic modules (Kyocera) oriented due south and tilted at a 21 degree angle, generating a total of AC 13,853 kWh / year. This energy system makes the prototype a net energy producer of 11,591 kWh / year. Note that this energy balance assumes the classroom operates with no air conditioning.

  • Options for wind generation will offset limited available sunlight in some locations.
  • Anderson Anderson Architects in collaboration with the University of Hawaii School of Architecture’s Environmental Research & Design Laboratory, will lead the post-occupancy evaluation studies of the building performance. Additionally,
  • The Rocky Mountain Institute has been a consultant to the project throughout, and will be involved in the validation studies once the building is occupied.

Controls & Performance Monitoring

  • Performance criteria are monitored and broadcast to the web.
  • The classroom will include a sustainability information system that enables the building to be used as a teaching/learning tool, describing the green features and demonstrating how they are working using live data and interactive displays.
  • Weather data, energy use, energy production, resource collection, indoor air-quality and thermal comfort can all be monitored using a full array of basic and optional recording data and comparative analysis published to the project web site.


  • Varying conditions and microclimates require extensive flexibility and adaptability built into the system. A variety of options available in the portable will allow the same structure for the classroom system while addressing these conditions.
  • Readily adapts to different sites and to a wide range of classroom functions
  • With the power of this design software, the advantages of modular construction can be optimized to suit the needs of every unique school site.

Constructability and Maintenance


  • In determining the success of the design, additional criteria of manufacturing and transport efficiency, functionality for classroom use, low operating costs and ease of maintenance are evaluated and addressed.
  • The adaptable building design was developed and is copyrighted by Anderson Anderson Architecture as part of their ZEBRA (Zero Energy Building, Relocatable Assemblies] series of high performance prefabricated buildings developed for multiple production. They are commencing to market and distribute region-specific versions throughout North America in partnership with a number of different modular building manufacturers and dealers through the Modular Building Institute trade group, of which Anderson Anderson is a member.
  • Efficiently packed and enclosed for safe land or ocean shipping, modular design sized for cost efficiency in transport, and to highly practical dimensions for negotiating tight urban streets and difficult rural locations.    
  • Does not require cranes for delivery and installation    
  • This design is intended as a true relocatable classroom. It is built on a steel chassis to which the wheel system may be easily re-attached, the modules are assembled and dismantled using bolts and the building is easily re-deployed to other sites     
  • Low maintenance systems minimize repetitive application of paints, cleaners and other potential environmental hazards.

Energy Modeling and Ecotect Analysis performed by Olivier Pennetier of Symphysis.