The design of a low-energy or carbon neutral building requires a specific design process that differs from standard practice. It requires an integrated design team that includes engineers, architects, owners and energy experts from the very outset to find the most optimized way to reduce emissions for the specific conditions of each project. Every building is unique and thus the sustainable design response is shaped by the unique climate, building size, typology and site conditions.
To take all these constraints into account, the design process for holistic carbon neutral buildings involves the following steps:
Utilize passive design strategies to reduce the heating and cooling demand the active mechanical and lighting systems need to provide. Examples include daylighting to offset electric lights, passive ventilation to reduce fans and air conditioning, and passive heating to use the sun to provide heating and cooling directly into a space (this is not to be confused with Photovoltaic and Solar Thermal collectors which are active systems). The building should be oriented on the site to maximally support passive design strategies. For the climate of Cambridge, Ontario, this means elongating the building east/west to maximize exposure for daylight, to reduce east/west exposure to excessive solar gain and take advantage of prevailing winds when passive ventilation is able to operate. Lastly, the building envelope should be designed to provide the insulating capacity to reduce heating in the winter and cooling in the summer. In the Cambridge climate, this means super-insulating the assembly.
When the building heating, cooling and lighting loads are reduced as much as possible through passive means, building orientation and a super-insulating envelope, the mechanical and lighting systems can be smaller than buildings that do not use these techniques. The Mechanical, Electrical and Plumbing systems, sized for smaller loads, should be of a high efficiency type to reduce teh amount of energy needed to power them. Sensors, building automation systems, smart controls adn the ability to tie into renewable energy systems should be included. For carbon neutral buildings, it is important that systems that use on-site combustion, such as natural gas water heaters and roof-top units, are not permitted due to the emission of carbon. Electrically based systems such as heat pumps, photovoltaic and solar thermal arrays and micro-wind turbines are applicable.
With a smaller Mechanical, Electrical and Plumbing system that needs to meet drastically reduced heating and cooling loads, affordable renewable energy systems that can easily fit onto the building are able to provide 100% of the annual energy demand. Choosing a renewable energy array for a building that is not low-energy has a marginal impact on reducing the total amount of energy required from the grid.
Increasing the amount of vegetation can increase the amount of carbon that a site can absorb. Because materials always come with carbon associated with their manufacture, transportation, and construction, and grid-tied buildings may draw from the grid from time-to-time, there is some residual carbon that must be addressed. Increasing vegetation that is more than just sod, reducing hard surface paving adn using green roofs can address a portion of the residual carbon. Transforming previously developed and brownfield sites is particularly effective as teh development of greenfield sites typically result in a loss of sequestration potential compared to the condition of the virgin, un-built site.
On-site sequestration typically cannot address the total amount of residual carbon from a building project over its life. The current mechanism available to a project is the purchase of carbon offsets. Although not perfect, they offer an interim solution to addressing the balance of residual greenhouse gas emissions until the global carbon balance can be reduced.