Green Building as a Tool for Natural Cooling Amidst the Climate Crisis
With burgeoning urbanization in cities, the demand for construction and infrastructural development in India is rapidly growing. The building sector consumes about 40% of the total energy produced globally. India’s building sector consumes about 31% of our total energy production, as per the 2013-14 figures of the Ministry of Statistics and Programme Implementation, Government of India. Therefore, energy conservation in the building sector has become the need of the hour. This necessitates the integration of the Green Building concept.
What has also been experienced in the recent past are more frequent occurrence of heat waves. Cities work as urban heat islands and are hotter than the nearby areas. There is thus a need to construct buildings in cities so that they have natural cooling mechanisms.
What is a Green Building?
Before we proceed, let us first understand as to what is a Green Building. These are structures that ensure efficient use of natural resources like water, energy, building materials and other resources. They also ensure minimal generation of non-biodegradable waste and minimize the demand of non-renewable resources during its construction and operation. There are several Codes for making buildings green.
Since different parameters are set out by different agencies for making a Green Building, the introduction of a Code that is standard for the whole country was required. Further, whether Green buildings are really green was to be decided against the pre-defined rating systems. Consequently in 2007, the Bureau of Energy Efficiency (BEE) launched Energy Conservation Building Code (ECBC) to establish minimum energy performance standards for buildings in India. It is an essential regulatory tool to curb their energy footprint.
ECBC 2017 has been revised to incorporate advanced technologies. There are now three levels of energy performance standards in the code. In ascending order of efficiency, these are ECBC, ECBC Plus and Super ECBC. The adherence to the minimum requirements stipulated for ECBC level of efficiency would demonstrate compliance with the code. The other two efficiency levels are of voluntary nature.
ECBC compliance include:
- Provisions for installation of renewable energy generation systems is mandatory in ECBC 2017.
- Passive designs strategies like daylight and shading are mandatory in ECBC 2017. Objective for this change is to encourage design with passive strategies to be the norm for buildings in India.
Natural Cooling of Buildings
A building constructed in a manner so that it remains cool during intense heat is the need of the hour. For better thermal insulation of buildings, various requirements have been mandated in the Green Building Code such as U-Factor, Solar Heat Gain Coefficient and Visible light transmittance of various building components.
Fenestration (arrangement of windows) Requirements
1. U-Factor: The rate of heat loss is determined by U-Value. The lower this factor, the greater is a window’s resistance to heat flow and the better its insulating properties. It is determined for the overall fenestration product in accordance with ISO 15099:2003 that specifies detailed calculation procedures for determining the thermal and optical transmission properties (e.g., thermal transmittance, total solar energy transmittance) of window and door systems.
2. Solar Heat Gain Coefficient: In accordance with ISO-15099 by an accredited independent laboratory, and labeled or certified by the manufacturer.
3. Visible Light Transmittance: In accordance with ISO-15099 by an accredited independent laboratory, and labeled or certified by the manufacturer.
Roofs shall comply with the maximum assembly U-factors as determined in the Green Building Code. The roof insulation is to be applied externally as part of the roof assembly and not as a part of false ceiling.
Vegetated and Cool Roof
All roofs that are not covered by solar photovoltaic, or solar hot water, or any other renewable energy system, or utilities and services that render it unsuitable for the purpose, shall be either cool roofs or vegetated roofs.
(a) For qualifying as a cool roof, roofs with slopes less than 20° shall have an initial solar reflectance of no less than 0.70 and an initial emittance no less than 0.75.
(b) For qualifying as a vegetated roof, roof areas shall be covered by living vegetation of >50 mm high.
Opaque External Wall
Opaque above grade external walls shall comply with the maximum assembly U-factors as determined in the Green Building Code.
For all climatic zones, vertical fenestration compliance requirements shall comply with the following:
(a) Maximum allowable Window Wall Ratio (WWR) is 40% (applicable to buildings showing compliance using the Prescriptive Method, including Building Envelope Trade-off Method)
(b) Minimum allowable Visible light transmittance (VLT) is 0.27.
(c) Assembly U-factor shall be determined for the overall fenestration product
Naturally ventilated buildings shall:
(a) Comply with guidelines provided for natural ventilation in NBC.
(b) Have minimum BEE 3-star rated ceiling fans, if provided with ceiling fans.
(c) Have exhaust fans complying with minimum efficiency requirements of fans as specified, if provided.
For Artificial Cooling of Buildings
(a) Install mechanical systems that provide outdoor air change rate as per National Building Code.
(b) Have a ventilation system controlled by CO sensors for basement carpark spaces with total car park space greater than or equal to 600 m2. All heating, ventilation, air conditioning equipment and systems, and their controls shall comply with the mandatory provisions and the prescriptive criteria for the respective building energy efficiency level.
The application of air-cooled chiller is allowed in all buildings with cooling load less than 530 kW. For buildings with cooling load equal to or greater than 530 kW, the capacity of air-cooled chiller shall be restricted to 33% of the total installed chilled water capacity unless the authority having jurisdiction mandates the application of air-cooled chillers.
Low-energy Comfort Systems
Alternative Heating, Ventilation, and Air Conditioning (HVAC) systems which have low energy use may be installed in place of (or in conjunction with) refrigerant-based cooling systems, such as:
- Evaporative cooling,
- Desiccant cooling system,
- Solar air conditioning,
- Tri-generation (waste-to-heat),
- Radiant cooling system,
- Source heat pump,
- Adiabatic cooling system etc.
However, ECBC needs to expand, made compulsory to comply. ECBC should throw more light on requirements and provisions on Natural Cooling systems, promotion of sustainable materials and processes of construction, the natural cooling techniques like Earth Air Tunnel, wind towers etc reducing the energy demand for cooling.
Till date, India does not have an effective and comprehensive Green Building Code. Green Building Laws and Codes in our country are voluntary. All states of India have not adopted ECBC yet. Till May 2017, ECBC norms were notified by nine states. The main reason of reluctance is the involvement of multiple stakeholders leading to the delay of the approval of construction of buildings.
We have Green Rating for evaluation and awarding the points once it fulfills the rating criteria but has become more like a business and too commercialized and everyone seems to be jumping onto the bandwagon. The policy should offer incentives to commercial builders in the form of tax benefits and quick permits. Penalties should also be imposed wherever required.
Living in an Eco-friendly building comes with its own benefits. Adoption of ECBC 2017 aims in achieving 50% reduction in energy use by 2030. Lets do better than that. Honest implementation of laws is the need of the day.
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