Sustainable by BIM: Two Case Studies
In addition, ArchiCAD was useful in determining the location of the photovoltaic (PV) panels located on the detached garage. The home was modeled at various times throughout the year to minimize the amount of time the panels would be shaded.
A large bank of windows faces due south. Light is controlled through a fixed exterior brise-soleil, designed to be indexed to the site latitude. At the summer solstice, no direct sunlight penetrates the space. At noon on the winter solstice, sunlight penetrates through to the rear of the open floor plan. There is limited exposure to the west and east; however, three round windows facing west are located in the open stairwell. These "portholes" activate the space. Carefully placed ribbon windows to the east provide the dining area and main bedroom with morning light.
The building form is simple — the two-story open-plan "light box" volume contains the primary living spaces, while support spaces are contained in an adjacent one-story volume. The entire house is about 1,700 square feet (160 square meters), excluding the basement. (Wisconsin foundations must be deep in order to penetrate the frost line, so a basement is an economical additional space.) Provisions for a future elevator in this retirement home allowed placement of the main bedroom on the upper level.
The resulting building is scaled to be in harmony with the neighborhood. Materials, such as the six-inch (150-millimeter) tongue-and-groove cedar siding and metal roof, were chosen carefully to be sustainable and durable, but also to blend with the neighboring houses. Adjacent homes along with the designed home were computer-modeled early in the design to ensure contextual compatibility.
Numerous green strategies were employed. The landscape is entirely composed of native perennials and no turf grass. All rainwater falling on the site is either collected in cisterns or directed via bioswales to a rain garden.
The photovoltaic panels located on the detached garage generate approximately 58 percent of annual demand, less than the 3,045-kilowatt-hour prediction of the PVWatts calculator (from the National Renewable Energy Laboratory) by about 16 percent. The collectors are fixed panels and it takes some time for snow to melt clear of the PV array.
The well-insulated, leak-tight house envelope (less than one air change per hour) requires an energy-recovery forced ventilation system that works in harmony with a three-stage high-efficiency furnace. The Ross Street project received a Home Energy Rating System (HERS) rating of 42, meaning that project energy use was projected to be 42 percent of that of a similarly sized Wisconsin house built in accordance with the 2006 energy code. At the end of the first year, actual usage corresponded to a HERS rating of approximately 23.
The project met the goals of the program with a simple, well-considered, and integrated design solution. The result was a comfortable, livable home with the play of sunlight on interior surfaces providing passive heating as well as visual excitement throughout the year.
Hadlow College Rural Regeneration Centre
by James Anwyl
Location: Tonbridge, England, United Kingdom
Design firm: Eurobuild
Client: Hadlow College
James Anwyl, founding partner at Eurobuild, a company specializing in Passivhaus architecture and construction, designed and built the Rural Regeneration Centre for Hadlow College, which is one of the top three agricultural colleges in the UK. The Rural Regeneration Centre is the first certified Passivhaus educational building in the UK.
The 3,770-square-foot (350-square-meter) building includes two teaching spaces, a kitchen, offices, showers, and toilet rooms. Partially funded by the South East England Development Agency (SEEDA), the building was intended as a new teaching facility for the agriculture students and for occasional local community use.
Upon discussion with the Kent planning department, Eurobuild changed the location of the new building, which was originally destined for a virgin greenfield to the south of the current location. Instead, the planners approved Eurobuild's intention to use the footprint (and some existing walls!) from a number of redundant cow sheds on the college's fully operational dairy farm. Over 95 percent of the original shed structure was retained on site and used for non-structural backfill, and a significant proportion was reclad to match the new lumber.
The building's main purpose is to enable seminar-based teaching — it houses a staff office and meeting space, alongside a significant exhibition area used to display the college's expansive land-based study program. One of the college's requirements was a "wet working area," a semi-outdoor space for machinery and livestock demonstrations. A sliding window from the main seminar room allows students to watch these demonstrations as part of their studies. This space made use of the preserved brick and block work at the northeast corner of the former calf shed; the original walls are concealed behind a continuation of the larch cladding.
Constructed of super-insulated closed panels, the structure was designed using ArchiCAD and assembled in just three days. In under ten days overall, the structure was airtight to a very high standard: 0.34 air changes per hour (ACH). Prefabrication led to a high-quality finish with significant time savings.
A monitoring system has been installed to track the energy consumption of the building over the next two years and beyond, for Eurobuild to learn from the "as built" building performance in relation to weather and usage patterns. The information communications technology display, ventilation unit, and heat pump are monitored individually, in addition to a number of lighting and power circuits. The students and staff can see the results displayed on a very visible monitor in the exhibition area and via the online building user guide.
The building employs a number of sustainable technologies including a super-efficient Drexel & Weiss Aero Centro mechanical ventilation system with heat recovery; triple-glazed windows; and a ground-source heat pump for both heating and cooling.
Since carbon dioxide sensors (to measure occupancy and automatically control mechanical ventilation for appropriate fresh air) were not affordable, the seminar and demonstration spaces are ingeniously equipped with manual switches. When these spaces are occupied, the ventilation rate will increase above 16 cubic feet per minute (CFM) per person (8 liters per second per person).
The bathrooms all have waterless urinals, low-flush toilets, timed water-saving taps, and moderated-flow showers. Low-energy T5 fluorescent lamps are used throughout the building and the lighting was carefully planned using DiaLux software.
Natural slate laid on the screed gives a flooring depth of 2.75 inches (70 millimeters), while the medium-density concrete-block partition walls increase internal thermal mass and absorb the solar gain from the large south facade. Cooling is governed primarily by the ground-source heat exchanger in the ventilation unit and backed by the heat pump and underfloor pipework. In addition, the seminar room windows are time- and temperature-controlled to enable night flushing for free cooling at night.
Individual window pergolas and a colonnade across the south facade prevent overheating in summer. Solar geometry was modeled in 3D in ArchiCAD, and then verified with EDSL's Tas energy simulation software and backed up by PHPP (Passive House Planning Package) analysis.
All the lumber used in the project was derived from FSC-certified sources or from sustainably managed forests in Austria, and apart from two three-foot (one-meter) lengths of steel section (four by two inches, or 100 by 50 millimeters), there is no metal in the superstructure. This was a conscious decision to minimize lifecycle costs and embodied energy.
As a result of the careful planning, it seems from pre-assessment that the building might achieve the Building Research Establishment Environmental Assessment Method (BREEAM) "Excellent" rating. It has already achieved Passivhaus certification.
With an insulation value of over R-56, the wall and roof panels use 15.75 inches (400 millimeters) of recycled "blown" cellulose insulation. These panels were made in Eurobuild's partner factory in Austria and transported directly to the site near Tonbridge, Kent. The factory is ultra-compact and one of the most advanced timber frame facilities in the world.
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Carol Richard, AIA, LEED AP Homes, is cofounder and partner of Richard Wittschiebe Hand. She has directed a wide range of project types and sizes as principal, project manager, and designer within the architectural industry since 1980.
James Anwyl is a founding partner at Eurobuild, a company specializing in Passivhaus architecture and construction. He has 15 years of experience in building design and construction, and is an ardent practitioner and beta tester of Graphisoft's ArchiCAD software.
François Lévy, AIA, AIAA, is a registered Texas architect and researcher. He holds an MArch and an MS in architectural engineering from the University of Texas at Austin, where he has been lecturing since 1998. Lévy has been practicing architecture since 1993, and established his own firm in 1997. His areas of research interest are sustainable architecture, cooling through passive ventilation, and space architecture. He also leads CAD and BIM seminars for professionals.
This article is excerpted from BIM in Small-Scale Sustainable Design by François Lévy, copyright © 2012, with permission of the publisher, John Wiley & Sons.