Down to Earth

Future lies in net-zero

Small steps towards green buildings will result in a giant leap towards sustainabl­e cities

- TANMAY TATHAGAT Principal at Environmen­tal Design Solutions, Delhi

THE INDIAN economy has grown rapidly over the past decade and is expected to sustain this growth over the next few decades. The country’s building sector is growing in tandem with the economy. In fact, the total builtup area is expected to swell five times of its current size by 2030. Propelled by government policies, such as “housing for all” and “smart cities”, residentia­l and commercial sectors will experience maximum growth. Such rapid growth will further increase our demand for energy, water, minerals and other natural resources, exacerbati­ng environmen­tal problems.

The building constructi­on industry consumes 40 per cent of the materials entering the global economy, and accounts for 40-50 per cent of the greenhouse gas ( ghg) emissions and agents of acid rain. Their impact on the environmen­t would be even higher if one considers the ghg emitted during the production of cement, bricks, steel, glass, aluminium and other constructi­on materials. Such concerns underscore the need to create sustainabl­e buildings and cities worldwide.

But making buildings truly sustainabl­e and green in India remains a major challenge. One of the major problems is that our design industry and developers ape the Western design and comfort ideals, ignoring the fact that the climate and life- style of Western countries are drasticall­y different from those of India.

Besides, our policy-making bodies at the Centre are yet to understand the significan­ce of energy efficiency in the building sector. Tough mandatory standards are wrongly seen as an impediment to growth and industry, and most policies tend to opt for voluntary compliance­s or less stringent standards.

In the absence of mandatory standards for green and energy-efficient buildings, most municipali­ties do not have a uniform and practical energy code, especially for passive and solar designs. Those who have the code in place do not have effective infrastruc­ture for its enforcemen­t and administra­tion. There are also no clear guidelines for state and municipal bodies for developing and implementi­ng uniform building energy efficiency programmes and policies.

Internatio­nal experience shows mandatory and uniformly implemente­d codes and standards are the only way to achieve a substantia­l impact of energy-efficiency measure. Though the Energy Conservati­on Building Code ( ecbc) is being implemente­d in India, it is moderately stringent. The country needs a dynamic building energy policy with long-term goals that can shape the future of the sector.

A zero net-energy building target could be a major leap in this direction. This will spur innovation for sustainabl­e and super-efficient buildings.

But before setting the target, the government must address the issues that deter people from adopting green measures, and must put in place a strategy to encourage their mass appeal.

Consider this. India has one of the highest electricit­y tariffs for commercial buildings and the cost of energy-efficient technologi­es and renewable energy systems has reduced over the years. Yet, their startup costs continue to deter people from adopting the products and technologi­es. A bigger market for them as well as a policy environmen­t providing substantiv­e incentives for developmen­t, implementa­tion and import of such products and technologi­es are a must for high-performanc­e buildings to be mainstream­ed.

Developers tend to under-invest in green measures because they do not gain from the investment made in energy-efficient buildings, and thus pass on the cost of inefficien­cy to the buyer and the environmen­t. The current high cost of borrowing money can be a strong impediment to incrementa­l funding in efficiency, which would be offset by future savings in energy costs.

Fostering an ethic for integrated design should be the most important part of the strategy. A building's energy efficiency, its ability to generate renewable energy and its architectu­ral design and constructi­on can be integrated to achieve the goal of sustainabi­lity. But such integratio­n is not commonly practised. Many of the solutions for energy efficiency and green buildings tend to be product-driven. Such product- and vendor-driven solutions could address individual concerns in a project, but they do not provide an integrated and comprehens­ive solution. Most design and constructi­on firms do not have in-house resources to do integrated sustainabl­e design. On the other hand, projects, which do invest in high performanc­e building design, often fail to get the desired results because of poor constructi­on, inadequate commission­ing and poor physical integratio­n.

Architectu­re must also respond appropriat­ely to climate and culture. New commercial buildings must be designed for daylightin­g and limiting solar heat gain. Residentia­l buildings must be sensitive to the local climate, and should have appropriat­e orientatio­n for shading, insulation, sun protection and cooling through cross ventilatio­n. Addressing these concerns at the concept stage through passive design, such as daylightin­g, sun shades, evaporativ­e cooling and natural ventilatio­n, only requires conscious efforts and no incrementa­l cost.

The additional cost involved in measures, such as insulation, better glazing and window frames, usually gets offset by lower energy use, with a payback period of less than five years.

Simulation for energy performanc­e of buildings is a powerful tool that architects, engineers and developers can use to analyse how the form, size, orientatio­n and type of building affect the overall energy consumptio­n of a building. Of course, this analysis is approximat­e and only as good as the inputs provided, but energy modelling is a tool now extensivel­y used and provides accurate results. For instance, glass plays an important role in a building’s overall energy consumptio­n. But its excessive use causes glare and overheatin­g, while too little glazing may reduce daylight available inside the building. Thermal and light transmitta­nce characteri­stics of glass vary from type to type, and building simulation programs can help strike a balance between daylight and heat gain to get the optimum

The cost of energyeffi­cient technologi­es and renewable energy systems has reduced over the years. Yet, their startup costs continue to deter people from adopting the products and technologi­es

glass area required, along with thermal and visual specificat­ions.

The skin of the building—walls, windows and the roof—moderates the effect of climate. So, selection of the building envelope with appropriat­e thermal mass, insulation and colour can reduce the number of hours when heating or cooling is required to maintain comfort. Using evaporativ­e cooling through waterbodie­s and evaporativ­e coolers can reduce the requiremen­t for air conditioni­ng (AC), especially during the hot and dry periods. It is now possible to seamlessly integrate evaporativ­e cooling with convention­al AC systems. Ceiling fans have always been a part of homes in India, often being the only source of comfort in the summer. They are now staging a come back in commercial buildings as well to enhance thermal comfort and to reduce the energy used in cooling.

To improve the quality of life and environmen­t in cities, many countries are focusing on reducing the environmen­tal impact of constructi­on to the minimum possible, moving towards a goal of netzero buildings. In fact, targets of net-zero energy, water, or even carbon, have been set for many communitie­s. Net-zero, or nearly-zero energy buildings ( nzebs), for example, have integrated renewable energy systems that produce as much energy as the building requires throughout the year. Such buildings are likely to draw energy during the peak periods from the grid, and give back excess energy produced when their energy demand is low. These buildings harness all potential advantages from the site, surroundin­gs and are designed for the climate. The decisions about building form, orientatio­n, shading and ventilatio­n, taken during the early design stage have the most significan­t impact on the energy consumptio­n of the building.

Passive design strategies help achieve thermal comfort using as little active cooling and heating as possible. This means reducing cooling requiremen­t during the summer and heating in the winter through appropriat­e orientatio­n, external shading, appropriat­e amount of glazing, and natural ventilatio­n. An nzeb will only be cost-effective if all the passive strategies, all of which come at no-cost or low-cost, are incorporat­ed in its design and constructi­on.

The next step is to establish the indoor comfort requiremen­ts based on adaptive thermal comfort standards and to calculate the heating and cooling loads through detailed hourly modelling. The effect of air movement, radiant temperatur­es, and dynamic nature of building operations during the day, as well as through the year, need to be considered in designing for comfort levels. Performing hourly energy simulation for the whole year will result in the selection of the most energy-efficient hvac (heating, ventilatio­n and air-conditioni­ng) design. This detailed analysis becomes essential because the worst conditions occur only for a few hours in a year, and the hvac loads remain lower in the rest of the year. A well-designed system for an nzeb should be able to operate at these variable conditions optimally.

Although there are several excellent examples of traditiona­l buildings that maximise thermal and visual comfort in buildings, these traditions need to be transforme­d, recalibrat­ed and adapted for modern design of commercial buildings.

The recent work in developing an Indiaspeci­fic thermal comfort standard and cooling design set-points specified in the revised National Building Code will allow more appropriat­e airconditi­oning system design, but only if our design sensibilit­ies and lifestyles are in resonance with the local climate.

To improve the quality of life and environmen­t in cities, several countries are setting targets of net-zero energy, water, or even carbon, for their communitie­s

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