The Bayer eco-commercial building located in the clean and green Bayer Campus, Greater Noida, India and the ZEB building in bustling campus of Building Construction Authority, Singapore are thousands of miles apart, yet have a common connecting thread. Both are shining examples of buildings that produce equal or more energy on site than they consume, namely net zero energy building or net positive building. By definition, net zero energy building (NZEB) refers to a building that generates onsite energy sufficiently to be able to meet its own energy requirement and also generate surplus, in some cases. In an off- grid situation, the onsite renewable energy systems provide adequate energy to cater to its demand. In a grid tied situation the building generates onsite and exports to the grid an amount of electricity that equals or exceeds the amount of electricity drawn from grid plus any other form of energy that the building may be using (e.g. fuels for heating).
Net zero buildings are desirable options for built environment, given the current context of growing number of buildings and their associated impacts on energy and resource use. Buildings continue to dominate the discussion on rising emissions across the globe . Buildings also have significant potential for reducing emissions through various mitigation opportunities. The 5th assessment report of IPCC reinforces the fact that energy use by buildings and associated emissions are on the rise. Globally building sector accounted for 32% of final energy use and 8.8 gt Co2 emissions, in 2010 (direct and indirect emissions). The share of the building sector in global GHG emission was 19%, which is projected to increase by 50-150% by mid-century. Thus moving towards net zero energy buildings for both new and existing buildings is a desirable option. However, inspite of being technically and conceptually proven, there are only a handful of examples of NZEBs.
The reasons are many. As rightly stated in the Global Energy Assessment report (IIASA, 2012), very efficient residential or commercial buildings have a total energy intensity of 50-150 kwh/m2 annum, which corresponds to an annual average energy flow of 5.7-11.4 W/m2 p.a. Variation of annual average solar irradiance is from 160W/m2 in middle latitude to 250W/m2 in sunniest regions. Considering 80% of roof area with solar PV having net sunlight to AC electricity conversion efficiency 10% and balance 20% area installed with devices to capture solar thermal energy with an efficiency of 50%, about 30-45 W/m2 of solar energy can be captured. Thus, net zero building opportunity is restricted in low to mid rise buildings, even if the buildings are very efficient. Possibilities of generation through façade integrated solar PV may enhance the scope marginally. Moving towards net-zero buildings would essentially lead to urban sprawl and hence the trade-off between transportation energy and building energy is necessary prior to implementation at urban level.
Achievement of net zero energy status during building operation is feasible through combination of aggressive demand reduction, operational controls and management of energy demand vs supply. Efficiency and adequacy of onsite energy supply is also a key necessity. GRIHA, the indigenous rating system for green buildings in India, through its criteria promotes design, construction and operation of net zero energy buildings. Adoption of climate responsive techniques through proper siting, shading, orientation and application of efficient materials and electro-mechanical systems as per the ECBC leads to demand minimization in buildings. The office buildings for PCNTDA, Pune (Pimpri Chinchwad New Town Development Authority), the newly constructed Indira Paryavaran Bhawan, the headquarters of the Ministry of Environment and Forests, GoI and the HAREDA building in Chandigarh, are all examples of net zero buildings India that have been rated as GRIHA 5 star. Demand optimization has been the forte in all these projects. While the PCNTDA building has adopted extensive passive strategies to eliminate need for air conditioning and artificial lighting (during daytime), the IPB building has reduced its airconditioning loads to one fourth of conventional building by adopting low window wall ratio, efficient glazing systems and wall insulation, higher threshold for thermal comfort among many other measures. The HAREDA building has deployed several innovative techniques such as solar chimneys and courtyard misting strategies to optimize demand. The common theme in all these buildings are energy efficiency combined with utilization of renewable energy sources.
With a modest number of Net zero campuses and buildings on their anvil, the newly launched smart cities program that aims at pushing the limits of efficiency, the ambitious solar mission being implemented, India is poised to be a leader in implementation of net zero buildings in the globe. The PACE D program provides an unique platform where there is congregation of knowledge , expertise and knowhow, that can facilitate this opportunity.