Design - Operating Energy
At the outset of design, an Energy Use Intensity (EUI) was set as a target for operating energy consumption that would allow an on-site renewable energy system that could annually provide 100% of the energy needs. Currently retail buildings have an annual EUI of 475 kWhr/m2/yr (44 kWhr/ft2/yr) while, in comparison, a survey of net-zero energy and carbon neutral buildings reveals that an EUI of 80-90 kWhr/m2/yr (7.4-8.4 kWhr/ft2/yr) is needed. The CN-SBS project aimed for an EUI of 90 and energy simulations using eQuest and VE Ware suggest that an EUI of 86 was achieved.
The CN-SBS project aimed for an EUI of 90 and energy simulations using eQuest and VE Ware suggest that an EUI of 86 was achieved.
Following the design process for low-energy and carbon neutral buildings, the CN-SBS retail building proposes the following passive design techniques and systems to achieve this level of performance:
- A daylight factor of 3% was achieved for the entire floor area, allowing it to be fully daylit and eliminate the need for electric lights during daylit hours. Daylight factors of less than 3% do not provide measurable daylight, only brightness. Daylight factors over 5% result in glare and too much glazing, reducing the overall insulating value of the building envelope that results in too much heat loss. This required a large north facing clerestory running the length of the building east-west, glazing on the house with integrated photovoltaic cells to both generate energy and avoid overheating, and strip glazing along the north facade. Non-regularly occupied spaces such as washrooms and storage rooms are located in the core of teh building and are fitted with occupancy sensors. Light coloured paint ensures a brighter interior and reflection of daylight throughout the space.
- The shelving is oriented north-south, perpendicular to the daylighting devices to ensure daylight penetration to the floor. Rotating the shelving to be parallel to the daylight devices would have created shadows throughout and thus electric lighting would be required.
- The building is elongated east-west and is perpendicular to prevailing winds in summer and shoulder seasons to allow for passive ventilation.
- Operable windows on the south facade, north facade and clerestory permit natural ventilation during shoulder seasons and summer when outdoor temperature is within the interior comfort parameters, between 18C and 24C. Natural ventilation also operates at night if excess heat is accumulated during the day. This eliminates the need for the ventilation system to operate.
- The Window to Wall ratio is 32%, and balances the area of glazing required for daylighting and view with the insulating value of the building envelope.
- The roof is air-tight and super insulated to R63, using 9.5" thick Structural Insulated Panels to avoid thermal bridging of structure and to facilitate disassembly.
- The walls are air-tight and super insulated to R43.2, using 6" thick Structural Insulated Panels to avoid thermal bridging of structure and to facilitate disassembly.
- Glazing is a high-performance triple glazing with thermally broken aluminum frames, non-conductive edge-spacers, low-e coatings and inert gas fill.
- All glazing that does not face north and does not feature integrated photovoltaic cells is fully shaded to avoid heat gain.
- Passive solar heating was not selected as a strategy for several reasons specifically related to retail, namely the protection of merchandise from UV exposure. Direct sunlight can damage and fade merchandise so the design team did not incorporate passive solar heating as a strategy. Instead, a super-insulated and air-tight envelope was used to reduce the amount of heating required.
- The concrete slab-on-grade acts as a thermal mass. It absorbs any spikes in heat gain to reduce cooling loads. Any heat absorbed is re-released when the temperature drops inside to also offset heating loads.
- The mechanical system uses in-floor hydronic heating to provide the most efficient kind of heating. Fed by a ground-source heat pump, conbustion sources of heating are avoided and heat and cold are provided from the earth. This required the heating and cooling loads to be relatively balanced, another factor that drove the design of the project. Retail buildings, unlike office buildings and residential projects, are not subject to the same pressures of individual comfort. Most staff are continuously occupied and shoppers are dressed for the outdoor conditions. Thus, a heating and cooling system that must quickly respond to small changes throughout the day is not needed, making an in-floor radiant system appropriate as its long lag times to change temperature is not an issue.
- The mechanical systems are electrically based to allow them to plug into a renewable energy array and not involve combustion sources of energy that would lead to carbon emissions.
- Over a year, energy simulation suggests that annually the building will need 51,438 kWhr (86 kWhr/m2/yr or 8 kWhr/ft2/yr). This is met by a 37.8 kW roof-top photovoltaic array.
- The landscape incorporates a large bioswale with a diversity of plantings including trees, shrubs and natural vegetation and a grass-paver parking lot. These landscape devices not only manage on-site water, but also increase on-site biomass to increase the ability for the site to sequester carbon.