The 2019 conversation on sustainable buildings cannot ignore the 2018 discussion on the idea of codifying Adaptive Thermal Comfort Standard to create opportunities for design options for improving indoor comfort and reduce operational hours or need of mechanical cooling for energy efficient buildings.

This idea has been mooted in the India Cooling Action Plan (ICAP) that charts a 20 years roadmap to combat energy impacts of highly energy intensive cooling requirements. If implemented Adaptive Thermal Comfort Standard can be a game changer in the way buildings will be designed. This will be different from the current regulatory practice that gives primacy to uptake of energy efficient cooling technologies over passive and bioclimatic options for delivery of comfort. ICAP has only floated this potentially big idea. But this has not yet been scripted as a regulatory framework. This idea must not fall by the way side. Even globally, there is growing interest in not binding solutions only to energy efficient cooling or heating technologies but allow bouquet of design solutions for indoor thermal comfort. We adapt to seasonal temperature variation naturally but now we know how this works and can be codified based on adaptive comfort model. Link this knowledge and experience more explicitly with building design and operations. Energy regulations have neglected architectural design opportunities to reduce dependence on active mechanical cooling for sufficiency. It is important to push for spaces with mixed modes of cooling and comfort and not just air-conditioned spaces with efficient technologies.

Evolving Mandate

It has taken a while to acknowledge and evolve towards this idea. When the original Energy Conservation Building Code (ECBC) was scripted to govern energy efficiency in buildings, formal requirement of passive architectural systems for low energy solutions was almost non-existent.

The revised version of ECBC has taken a step forward to introduce Energy Performance Index (EPI) score for all designs that can be used as benchmark to track operational energy performance of buildings. But there is no mechanism to ensure that building operators continue to maintain EPI score awarded at the completion of the construction.

The ECBC has also added a section on regulating indoor temperature threshold for Heating Ventilation and Air-conditioning (HVAC) design to prevent energy penalty. This refers to Indian Adaptive Comfort Model for better energy efficiency in thermal comfort delivery. But this is not a binding requirement and stops short of banning unnecessary cooling or heating of indoor, disregarding outdoor weather conditions and realistic thermal comfort expectations of occupants.

In 2018, the government also woke up to the risk of uncontrolled consumer behaviour to operate room air-conditioners (RAC) at unnecessarily low temperature set points with huge energy penalty. The Ministry has proposed to fix the starting temperature of RACs at 24°C, as against the current switch ON temperature at 18-20°C. New RACs, when switched ON, will start at 24°C unless changed. Now, manufacturers are free to set the default temperature at any level and often this can be lower than 20 or 18°C. Set point control can make users more aware of energy penalty of very low set points. With just one degree drop the energy penalty can be up to 6 per cent.  The ministry has estimated that this voluntary move can save 20 billion kw hours of electricity a year if adopted by all consumers. This may be made mandatory later, which is one of the many moves planned. All these developments foreshadow the idea of adaptive thermal comfort standards. It is tacitly recognised that comfort needs can be met even at higher temperatures setting if several environmental and behavioural parameters are accounted for.

Towards Adaptive Thermal Comfort

It is not easy to regulate human thermal comfort as it involves indoor and ambient temperature along with environmental variables—temperature, humidity, heat radiation and air movement—and human variables—clothing and an individual’s metabolism rate. There is also the “forgiveness factor”, when people can disregard or ignore actual physical discomfort in recognition of unique nature of their surroundings. Combination of these variables can help to achieve comfort goals.

The 2016 version of National Building Code (NBC) has adopted adaptive or dynamic approach that models indoor temperature in relation to optimum range of outdoor temperature at which occupants are expected to feel comfortable. These ranges have been developed for naturally ventilated buildings, mixed mode buildings with different types of cooling systems, and air-conditioned buildings. Supported by the research of Centre for Advanced Research in Building Science and Energy, CEPT University, the concept of mixed mode building is gaining ground.

This can encourage designers to fix envelop, design, insulation, and orientation to improve air movement and cut down radiant heat and usage of air conditioning. Most of the problems stem from poorly designed buildings.  Sensibly designed mixed mode buildings with adaptive thermal comfort approach offer a range of ‘adaptive opportunity’ to improve thermal comfort. One can open a window, draw a blind, use shading, allow air movement, use fans, and change clothes as needed. Comfort delivery through design and system approach is necessary for lower income groups as well. The UN looks upon thermal comfort as a human rights issue. Therefore, it is not necessary to pull down the standard for poor people if design and material solutions are available.

Mandate Change

To influence mass construction, codifying some basic requirements can help to promote sustainable practices. This can allow planning for passive strategies and sizing of cooling systems dictated by design to meet thermal comfort goals. This will give people greater control and ability to adjust to indoor climate.  The standards and design guidelines will help architects to assess & forecast comfort range of indoor temperature through seasons (which they do) but now more deliberately to reduce operational time of air conditioning or the need of it. People can play around with shade, wind speed and direction to maintain temperatures and comfort conditions in buildings.

With wider adaptive comfort range, as against narrow temperature band maintained in fully controlled AC buildings, occupants will have more control over operation of buildings than the operators of HVAC systems of the building. Low energy solutions will become more viable including bioclimatic strategies.

India with its climatic advantages will have to work harder on this. Centre for Advanced Research in Building Science and Energy, CEPT University have worked out the comfort ranges for naturally ventilated, mixed mode buildings and air-conditioned buildings that have informed the NBC 2016. This, for instance, shows that when outside running mean temperature is 35°C, people in a mixed mode building can have a comfort range of 24.2-31.1°C. But in an AC building the comfort range is much narrower (24.5-27.5°C). This mixed mode offers more opportunity for adaptive comfort and low energy solutions.

Changes have happened even in ASHRAE Standards 55 in 2010. Even though it is meant for buildings without HVAC, this can be adapted and further improved for mixed mode buildings. It includes processes that consider operative temperature, radiant heat, humidity limits and higher air movement and air speeds etc to allow some control to occupants. They can use fans, window, and ventilation to reduce mechanical cooling and adapt.

No other option

Mixed mode buildings and bio climatic strategies based on adaptive comfort model that are now well understood backed by science need to inform regulations to moderate demand for mechanical cooling. According to the ICAP draft, cooling demand is expected to grow 8 times by 2037-38 with space cooling in building sector alone witnessing 11 times increase. If not tamed, this can incite massive energy guzzling affecting climate, wellbeing and health.

Other countries are responding to this concern. Japan has recommended 28°C and bush shirt rules for offices. China, Hong Kong, Korea and UK are adopting similar approaches. California does not allow set points below 26°C for summer and heating above 20 for winter. Australia is more nuanced–20°C to 28°C depending on local climate; buildings are designed to provide indoor temperature conditions of 28°C most of the time and air-conditioning comes on when upper limit of indoor temperature conditions are breached; systems can reduce or extend non-AC hours to meet comfortable conditions and promote acclimatisation. Under the Cool UN programme summer temperature set points have been changed from 22.2 to 25°C.

These regulations will also have to be defined right so as not to limit design choices. But these regulations are inevitable and should not be resisted on erroneous grounds of invasion of privacy and state dictating private comfort. This is about sensible holistic approach for public good and sustainability.


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