GREEN: Net-Zero Energy Buildings - a Worthwhile Sustainability Goal
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However, in the pursuit of the goal of greater efficiency and improved sustainability, creating green buildings is simply a step along the path towards the ultimate goal - net-zero energy buildings (ZEB).
A ZEB is a residential or commercial building that consumes a net total of zero energy from non-renewable sources, including utility electricity, natural gas and oil, all of which are created using fossil fuels and which are now considered to be unsustainable in the long term. These buildings have such a high level of energy efficiency that they can rely for the most part on renewable energy generated onsite and will only use non-renewable sources to supplement this during times of high demand. During times of lower demand any excess energy created can be exported back onto the utility grid, thereby offsetting any energy usage from this source. Non-renewable energy usage is thereby cancelled out, or offset, by excess renewable energy, and the net energy consumption of the building can therefore be considered to be zero.
Exporting excess renewable energy created back onto the grid is the ideal scenario for businesses wishing to develop ZEB. However within the current South African context this is not easily achievable and renewable energy technologies themselves may not yet have the financial payback periods that building owners require. For this reason the ZEB is not yet a reality in the country, however as technology improves and Eskom continue investigating smart metering this scenario is likely to change, and so the goal of creating ZEBs should be the end goal of any sustainability and energy efficiency programme.
On the journey towards creating ZEBs improving efficiency is the first step, as every bit of energy saved contributes towards lower energy demand and lower investment in renewable technologies. Energy saved is energy that does not have to be produced, and this applies to any building, not only ZEBs.
To achieve maximum building efficiency there are four stages that can be followed. The first of these is load reduction, which involves reducing every energy consuming load to the minimum and eliminating unnecessary loads. This can be done in any building no matter how old, but in the case of new buildings involves starting with a design that includes only the energy services that are necessary. The second stage is systems efficiency.
This step is designed to enable buildings to meet the remaining required loads as effectively as possible, by optimising the efficiency of the system as a whole in addition to individual components and ensuring that components such as pumps, motors, fans and insulation are optimally specified for the facility.
In order to achieve these first two stages an energy audit of current energy usage can be conducted to highlight areas where immediate and future improvements can be made. An energy audit encompasses all areas where energy is being consumed in a building or operation, such as light fixtures, the entire HVAC environment including air handlers, boilers, chillers, controls, air conditioners, heat pumps and so on, load controls, insulation and glazing, compressed air, backup power and many more areas. A thorough energy audit will not only show areas that can be improved with the upgrading of technology, but also through improved configuration of existing technology, helping to improve the overall energy system rather than focusing on individual components.
The third stage in the journey towards creating ZEBs is the implementation of regenerative systems, which use waste energy for useful purposes, such as Heat Recovery Systems which use excess energy from air conditioners to heat water for bathroom and kitchen use. The fourth and final stage is to implement renewable systems, which generate power on-site using sources such as solar and wind power.
South Africa in particular is well suited to the use of solar energy as a renewable source, since a building's size and shape significantly affect the building's ability to generate enough solar power to meet a ZEB goal.
Buildings of more than three storeys may have difficulty producing enough solar energy due to the relatively low ratio of roof footprint compared to the load density of the building. However since a large number of commercial buildings in South Africa generally consist of one or two storeys and are spread out, they create a large roof area that is perfect for photo-voltaic solar energy systems, making them ideal candidates for this renewable energy source.
While not yet a viable option in South Africa, net-zero energy commercial buildings do exist today. In some cases they have been shown to be cost-effective when compared to traditionally constructed buildings, and in others, building owners have invested in ZEBs to demonstrate their commitment to renewable energy, the climate, and other nonmonetary values.
The proof of concept provided by these buildings, combined with the increasing efficiency and lower costs of renewable energy technologies, should lead to the growing adoption of ZEB techniques and technologies within the commercial building marketplace. More experience with zero energy buildings will also lead to an awareness of best practices that will drive the cost lower and reduce the perception of risk associated with the concept.
Net-zero and near-zero commercial buildings offer exciting and rewarding opportunities for economic development and new jobs, and the advancement of climate and energy security goals. The aspiration for the creation of ZEBs offers a clear and inspiring goal for building owners, and a significant way to improve building energy sustainability and to reduce their environmental impact.
Business News Sector Tags: Environment|