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Net Zero Energy Buildings
The need for sustainable living may have been a matter of choice some years ago, but in present times, with Global warming and Climate change, it is no longer a choice but a necessity. Even though some of our world leaders have not yet accepted climate change as a reality, multiple researches and our own personal experiences prove otherwise. Hence, the onus of doing something about it lies on the shoulders of the people, until the leaders join in and extend support.
Buildings have always been built to respond to the local climate. With the dawn of the artificial cooling and heating equipment, this has changed. Any building can be fitted to provide the required thermal comfort to the inhabitants. But this became highly energy consuming. With the energy costs rising and their negative effects on the climate, new ways of thinking emerged leading to the concept of Net or Nearly Zero Energy Buildings (NZEB).The principle behind NZEB is to sharply bring down the energy demand of the building by using energy efficient building technologies and use of renewable energy sources for any balance energy requirements. The buildings are also fitted with the most energy efficient lighting systems and other gadgets. Sometimes these buildings produce more energy than they consume and supply excess energy to the grid.
Some important points to remember while designing Zero Energy Buildings are:
While looking for a place to build, it’s important to avoid greenfield sites or sites which have never been built upon. It is always best to pick a brownfield site, a site that has been built upon previously and is no longer in use. This not only reduces the environmental impact but also saves on infrastructure costs.
Also, avoid picking sites which fall in natural flood plane areas. This can lead to flooding during rains.
The selected site should be easily approachable as cost of transporting building materials can be significant.
A properly oriented building can save up to 25% of energy costs. The following points need to be kept in mind while orienting the house on the site:
- Minimise the east/west side walls as they have the maximum sun exposure due to low sun angles
- Maximise north and south exposures, less direct sun exposure on the north side, direct sun exposure on the south but high sun angle.
- Minimise east and west facing windows.
The location of the site and the climate makes a difference to the orientation of the building. The main principle of building orientation is to maximise the amount of solar radiation in winters and minimising it in summers. Wind direction also needs to be considered when orienting the building.
Building form determines the space enclosed by the buildings. The more the space, the more heating and cooling it requires. A compact shape means less waste in gaining or losing energy.
P/A or perimeter/floor area ratio. For the same volume of enclosed space, lesser building perimeter means lesser solar exposure.
The roof is one part of the building that is constantly exposed to sunlight. Hence, reducing heat gain from the roof makes a significant impact in the heat gain of the building.
A cool roof is one that has been designed to reflect more sunlight and absorb less heat than a standard roof. This can be done by using a highly reflective type of paint, a sheet covering, or highly reflective tiles or shingles. Traditional dark roofs reach temperatures of 66ºC (150ºF) or more in the summer sun, in contrast a cool roof under the same conditions could stay more than 28ºC (50°F) cooler.
Fenestrations are openings in a building (windows, skylights, ventilators etc.) which allow daylight and prevailing winds to enter the building when needed. These need to be carefully designed to reduce heat gain while not compromising on daylight, wind, views and aesthetics.
Here are some general guidelines
Methods to reduce heat gain through windows are:
- Orientation and size: North side has the least exposure to direct intense sunlight whereas on the south side the Sun is higher in the sky, and does not directly penetrate through the windows. A small sunshade can help in keeping direct sunlight out on the south. The east and west directions are most exposed to direct solar heat radiation hence should have least number of openings.
- Glazing: Glass allows short wave infra-red radiation from the Sun to pass through easily, but is very resistant to the passage of long wave radiations emitted from objects inside the building that are heated from solar radiation. Hence, the resultant temperature inside the building can be even greater than outside temperature due to the trapping of heat inside. Fenestrations, when using glass, have to be designed carefully.
- Internal shading devices: Internal shading devices like curtains and blinds are helpful in temporarily cutting sunlight. But efficacy of internal shading devices is limited as they absorb the heat once it has been transmitted inside the space and heat up themselves. This can lead to higher mean radiant temperatures inside the building.
- External shading devices: Orientation of an opening and solar radiation incident on it, is the single most important factor in the design of its external shading devices. These factors change with the season and time of the day. A variety of shading devices are possible depending on these factors.
Fresh air in a building brings health benefits and increased comfort to its occupants. Fresh air provision is considered as an efficient and healthy solution as it reduces the need for mechanical means to ventilate a building. The natural ventilation of a space is largely designed on the concepts of
-hot air rising and cold air settling down and
-small inlets increasing the speed of air and if the inlets are very small like a jaali, the air coming in will also be cooler.
Based on the above concepts, a number of natural ventilation techniques are possible.
The above passive energy technology guidelines are applicable to all kinds of buildings. Building performance simulation or BPS is nowadays being used for large projects to access the building performance with respect to energy usage
Hence, Net Zero Energy Buildings is the right and sustainable way forward in designing new buildings where traditional knowledge and latest technology join hands in creating new and better buildings and hence a better and sustainable world.
Image source: https://www.energy.gov/energysaver/energy-efficient-home-design
Image source: https://rahmblings.wordpress.com/
Image source: https://jaikeshavmishra.wordpress.com/2014/06/05/when-your-house-breathes-through-the-courtyard/
Image source: https://indiansustainability.wordpress.com/2015/08/04/importance-of-cross-ventilation/