Climate Adapted Building Design
West Elevation
by Vladimir Mikler and Christy Love
A building’s form and interaction with the local climate are critical to its overall environmental performance. Climate adapted buildings optimize the performance of “passive” building elements and employ smaller, more efficient “active” mechanical systems merely to complement what the building architecture cannot achieve on its own.
The remote location of the Hesquiaht First Nation community on the west coast of Vancouver Island makes its new school (now under construction) a valuable case study.
Hesquiaht is off-grid, with access by plane or boat only. The only source of energy is shipped-in diesel fuel, powering a small on-site generator. The site experiences strong prevailing winds from the Pacific, annual rainfall in excess of 3m, and very challenging topography.
The building form evolved as part of the Integrated Design Process during which the consultant team held three design charrettes, including an interactive energy performance workshop to assess impacts of different approaches. The architectural team from Marceau Evans Architects also spent a week in the community to present and discuss the project with the Hesquiaht First Nation.
There were two main questions posed. The first: how should we protect the building from the force of the prevailing winds from the Pacific and the enormous amount of annual rainfall? The second: how can we best harness these free forces and low-grade energies to reduce the building’s dependence on fossil fuels? For example, we could not simply open the windows to provide natural ventilation during the frequent storms. A more creative approach was required in which the relationship between the building and its environment was developed from first principles.
The building was shaped using aerodynamically sloping rooflines. Louvered air intakes were located below the roof overhang on the windward side of the building. The windward exterior wall was sloped away from the wind direction to form a wind scoop and to prevent entry of wind-driven rain into the air intake. On the inside, an intake air plenum was created between the exterior and interior walls. This plenum converts the kinetic force of the wind into static pressure. The plenum feeds into several ductwork rings buried under the slab that further equalize the air pressure and provide ventilation to individual spaces
The ventilation air is supplied at low level and low velocity in a uni-directional displacement flow pattern. The ventilation air is tempered in two stages: first as it passes through the underground tempering ducts, and again as it passes through final duct connections cast in the heated floor slab. Passive air exhaust openings are located at high-levels on the leeward side of the building just below the roof line.
The space heating is provided by a low-temperature radiant heating system integrated into the structural floor slabs. The heating capacity is provided by three water-to-water heat pumps tied into a pond-source geo-exchange system (integrated into the site’s storm-water retention pond). The low-grade heat available from the storm-water is a perfect match for the low temperature demand of the radiant heating system.
Comparing mechanical options
Although the integrated low-energy mechanical system concept was devised with the expectation that it would be the solution best meeting the overall project objectives, this needed to be proven by comparative analysis. Therefore, six different mechanical system options were evaluated and compared based on the following criteria:
- System performance in terms of thermal comfort and indoor air quality
- Energy efficiency
- Capital cost and life-cycle cost analysis
- Ease of operation and maintenance
The options were modelled using Tas simulation software, a design tool for dynamic hourly thermal simulation of a building, allowing accurate assessment of energy, comfort and environmental performance.
Three of the options were “forced-air” systems where the heating and ventilation requirement is provided simultaneously and the main mode of heat transfer is by forced convection. The other options provided space temperature control independently from ventilation, whereby space temperature control is supplied by low-intensity radiation from heated floor slabs and the ventilation function is provided by natural (wind and buoyancy driven) air flow.
In the past, design of passive building energy features and natural ventilation systems was typically based on intuition and simplified empirical formulas. With the help of an advanced simulation tool such as Tas, the effectiveness of the natural ventilation and low-intensity radiant heating systems could be accurately assessed.
The simulation confirmed that indeed the system could effectively provide the minimum required ventilation flows even during the infrequent low wind conditions. During these conditions, the open space geometry combined with air supply at low level and relief at high level below the sloping roof enables the system to be powered by the internal heat gains and natural buoyancy within the space.
The simulation also demonstrated that the “low-energy” radiant floor heating system in combination with natural displacement ventilation would provide the best space thermal comfort and indoor air quality conditions as well as the most energy efficient performance. This system performs better, is more robust and is less visually intrusive than the forced air option.
In spite of the extremely low efficiency of converting “primary” fossil fuel (diesel) energy into electricity, the electrically driven water-to-water heat pump system coupled to the pond-source geo-exchange system was demonstrated to provide the best efficiency and performance, and lowest operating and “primary” fuel cost.
The annual rainfall frequency and volumes were evaluated to ensure that the rainwater passing through the storm-water retention pond could provide enough low-grade energy for heating.
While the extraordinary nature of this project clearly lent itself to an integrated, climate adapted building approach, the same methodology can be effectively applied in any building in any climate.
The secrets to climate adapted building design can be summed up in a simple three-point methodology:
- Understand the specific climate and environmental conditions at the building site.
- Apply simple, passive design solutions that respect the laws of physics and harness free, natural energy flows.
- Apply efficient and “low energy” active technologies and integrate them with the rest of the building, carefully considering relationships among all parts of the building and local environment.
With the pressures of world population growth diminishing reserves of fossil fuels, the arguments for a climate adapted building approach to building become ever more compelling.
Vladimir Mikler MSc, P.Eng., LEED AP and Christy Love BA, BASc., LEED AP work with Cobalt Engineering, Vancouver.
Credits
- Architect: Marceau-Evans, Vancouver
- Structural Engineer: Equilibrium Consultants, Vancouver
- Mechanical Engineer: Cobalt Engineering, Vancouver
- Electrical Engineer: BLC Engineering Inc., North Vancouver
- Civil Engineer: Bullok Baur Associates, Victoria
- Geotechnical Engineer: Thurber Engineering Ltd., Victoria
- Energy Consultant: GeoTility Geothermal System, Kelowna
- Construction Manager: Newhaven Construction Mgt. Ltd., North Vancouver