We pay heavily for the ever basic necessity short of which our life would otherwise got dragged to a standstill. Studies have been depicting close ties between energy and development. The more abundant and accessible modern energy is, the easier a society develops. No wonder then that development is notoriously snail-pacing in rural Tanzania.
It is estimated that only 15 per cent of the population in Tanzania has access to electricity including about only a third belonging to rural areas. The more electricity is produced in the country the more it is used in urban Tanzania.
Currently, households in urban centres use around half of all the electricity consumed in these centres. Add office buildings to the mix, the amount of electricity consumed becomes tremendous. Wouldn’t it be reasonable then if we could design buildings that produce their own amount of energy they consume?
Well, that is not only a possibility but a reality. A zero energy building (ZEB) also known as zero net energy (ZNE) building or sometimes referred to as net zero energy building (nZEB), is a building with net zero energy consumption. This means that the total amount of energy used by a building on an annual basis is roughly equal to the renewable energy created on the site.
A slight problem in this definition is the scope of the terms ‘on the site’ and ‘annual basis’ as the time frame set. Scholars have been arguing over the term ‘on the site,’ saying it is ambiguous and that it does not portray a clear boundary of the site area. They also believe that net energy consumption should be looked at on a monthly basis so as to understand the dynamics caused by the change in climatic conditions.
However, taking the general and broad meaning, nZEB is typical of East Africa’s reality. A UN-Habitat’s headquarters building in Nairobi proves the notion by virtue of its being an energy-plus building capable of producing more energy than it consumes.
What is the secret behind this huge achievement?
Referring to nZEB definition, designing of a zero energy building consists of two essential parts; integrating renewable energy sources in the building site to produce energy and the designing of the building itself to reduce consumed energy. While both are integrated to function together, we can look at them separately especially in the initial design phase.
It is widely misconceived among both common and professional circles that an energy efficient building is more expensive than a conventional building. However, studies show that the additional cost to build an energy conscious building can vary from 0 per cent to 30 per cent. More often than not, the additional cost is that of renewable energy technologies, such as solar water heaters, solar-PV and energy saving appliances.
The other reason why an eco-building incurs additional cost is because there are very few specialized architects. It is worth mentioning that the operation cost of a green building is very low and the environmental benefits are enormous since their carbon footprint is small.
The designing of the nZEB follows the same principles of passive designing to reduce energy consumption. Issues to be considered involve plot coverage – which should be less than 60 per cent to put allowance for air movement, drainage and day-lighting and building orientation that constitutes of arranging the building in the direction that is affected less by direct sunlight.
Others include a narrow building form and shape to make room for cross ventilation and day-lighting, window designing to reduce direct heat gain, shading devices that will act as a second skin to the building, buffer zones such as verandahs, courtyards and corridors, as well as other passive designing methods that reduce energy consumption.
Use of simulation models to compute the appropriate insulation material and thickness, for an instance, is one of the most important methods used to improve energy performance of buildings.
The other aspect to consider when realizing nZEB is integration of renewable energy sources on site. By considering where the building is located, the site itself can provide various options for renewable energy integration. Use of seawater and other forms of geothermal water/heat to cool off a building is an option that is readily available to buildings that are located along the costal lines and other areas within the country.
Integrating solar energy such as photovoltaic systems for electricity production and solar water heaters for hot water systems in buildings is an easy option in Tanzania due to the abundant solar radiation throughout the year. Integration of more than one source of renewable energy on site such as wind and biogas is also a viable option to many building sites in the country.
Once the building is designed and renewable energy sources are integrated, the building needs to be monitored on its performance so as to maintain the status of nZEB. Here is where building energy management systems come to play. Building energy management system (BEMS) is a computer based control system installed in buildings that controls and monitors the building’s mechanical and electrical equipment such as ventilation, lighting, and power systems.
A BEMS that will continuously monitor the status and patterns of energy use in the building as well as energy production from the renewable sources integrated will provide the support and the means to verify the building’s energy status. Sophisticated BEMS can also work as systems to diagnose discrepancies in energy consumption patterns and production and can lead to earlier diagnosis and consequently maintenance schedules.
Although robotic in nature, BEMS can serve as a tool to control human behaviour by providing cues to when certain human actions such as closing of windows and doors, decreasing the indoor air temperature, putting appliances to sleep mode and other human regulated actions should occur.
It should be noted that it is easier to realize nZEB in areas with somewhat uniform climatic conditions such as areas in East Africa than areas that experience extreme opposite climatic conditions during the year. Countries that have hot summers and cold winters are faced with a much more difficult challenge in balancing the production of energy from renewable sources to the energy consumed in a particular season.
With perfect climatic conditions for the realization of net zero energy buildings in Tanzania, it is up to developers to put architects and other construction professionals to task. The government has all the reasons and incentives to have this issue in its agenda.
The less energy used in buildings the faster the development to its people. People in need of that development, demand that the government should set up policies to shape the building trend to a more energy conscious one. Building codes and penalties to excessive energy users have been known to work in developed countries. The earlier we follow that path the better for all the parties involved.