Idea of regulating comfort for energy efficiency

First-ever push for thermal comfort standard for buildings shifts focus from only energy efficiency of mechanical cooling systems to thermal comfort for all

By Anumita Roychowdhury
Last Updated: Saturday 09 March 2019
Photo: Getty Images

Let us not miss the big idea. With no buzz around the Environment Ministry’s announcement of the Cooling Action Plan — A 20-year roadmap to address cooling requirements in buildings, cold chain, transport and refrigeration — the first-ever push for adaptive thermal comfort standards for buildings to reduce energy guzzling has gone unnoticed.

This idea must get scripted as a regulation quickly to not let it fall by the wayside. This has broadened the regulatory ambit: From only quicker uptake of energy-efficient cooling technologies to adoption of passive architectural and bioclimatic options for reducing heat load on buildings and cutting down unnecessary energy intensive cooling for delivery of comfort for all.

Building operations and adaptive behaviour change to reduce demand for active cooling are now on the table. Design can improve indoor comfort and reduce operational hours or need of mechanical cooling in buildings. This can be a game changer in the way buildings get designed in the future.

This has to work for the poor. The new Plan has recommended thermal comfort strategies for affordable housing projects under the Pradhan Mantri Awas Yojana for the economically weaker section. This is important for affordable housing sector and low-income housing where the current focus is only on speed and ease of construction, disregarding comfort requirements of the poor.

Comfort delivery through design and system approach is necessary for lower-income groups. The United Nations has proposed comfort as a human rights issue. It is not necessary to pull down the standard for the poor people if design and material solutions are available.

It has taken a while to acknowledge 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 to provide thermal comfort in buildings was weak.

The revised version of ECBC has introduced Energy Performance Index (EPI) score for all designs to 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.

Another addition is the regulating indoor temperature threshold for Heating Ventilation and Air-conditioning design to prevent energy penalty. This refers to Indian Adaptive Comfort Model for better energy efficiency in thermal comfort delivery.

But this stops short of preventing unnecessary cooling or heating of indoors in disregard of outdoor weather conditions and realistic thermal comfort expectations of occupants. The new approach should help to address the gaps.


Taming the AC

The Cooling Action Plan has also asked for minimum temperature set points for operation of air conditioner to be based on adaptive thermal comfort. It states categorically that this is needed to shift behavioural and psychological change towards adaptive thermal comfort practices.

It proposes that ECBC and National Building Code (NBC), in their next revision cycles, should mandatorily be between 24 degree Celsius and 26 degree C with corresponding temperature guidelines. This is important as space cooling for buildings is already using up 60 per cent of total energy supply to buildings, with only 8 per cent of households using air conditioning.

Earlier the Ministry of Power had proposed to fix the starting temperature of room air conditioners at 24 degree C, as against the current popular practice or switch ON temperature at 18-20 degree C.

Set point control can make users more aware of energy penalty due to very low set points. With just one degree drop in operational AC temperature the energy penalty can be up to 6 per cent. The power ministry has estimated that this voluntary move by all can save 20 billion kilowatt hours of electricity in a year.

Even globally, there is growing interest in not binding solutions only to energy-efficient cooling or heating technologies but to allow richer bouquet of design solutions for indoor comfort. Japan has recommended 28 degree C and bush shirt rules for offices. China, Hong Kong, South Korea and UK are adopting similar approaches. California does not allow set points below 26 degree C for summer and heating above 20 for winter. Australia is more nuanced — 20 degree C to 28 degree C depending on local climate; buildings are designed to provide indoor temperature conditions of 28 degree C most of the time. Air conditioning comes on when indoor temperature conditions are breached — the systems can reduce or extend non-AC hours to meet comfortable conditions and promote acclimatisation abilities. Under the Cool UN programme, summer temperature set points have been changed from 22.2-25  degree C.


Demystify and act

Now that the idea of adaptive thermal comfort standards has been mooted it needs public support and action. The new plan has asked Bureau of Indian Standards to frame these standards. The NBC in its 2016 version has adopted adaptive or dynamic approach that models indoor temperature in relation to optimum range of outdoor temperature at which occupiers are expected to feel comfortable.

These ranges have been developed separately 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. They have worked out the comfort ranges for naturally ventilated, mixed mode buildings and air-conditioned buildings that have informed the NBC. For example when outside mean running temperature condition is 35 degree C, people in a mixed-mode building can have a comfort range of 24.2-1.1 degree C. But in an air-conditioned building the comfort range is much narrower — 24.5-27.5 degree C.  The mixed mode offers more opportunity for adaptive comfort and low energy solutions.

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. Experts talk about the “forgiveness factor”, when people can disregard or ignore actual physical discomfort recognising unique nature of their surroundings.

Designers can fix envelop, design, insulation, and orientation to improve air movement and cut down radiant heat and usage of air conditioning. In sensibly designed buildings one can open a window, draw a blind, use shading, allow air movement, use fans, and change clothes to feel comfortable and adapt.

Based on passive strategies and design, the sizing of cooling systems can be planned to meet thermal comfort goals. Designers can assess and 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.

This will allow wider adaptive comfort range and temperature for building operation as opposed to a very narrow temperature band maintained in fully controlled air-conditioned buildings. This will give people greater control and ability to adjust to indoor climate. People can play around with shade, wind speed and direction to maintain temperatures and comfort conditions. This makes way for low-energy solutions with bioclimatic strategies.

This is the way forward to moderate demand for highly energy intensive mechanical cooling. The new plan forecasts that cooling demand is expected to grow eight times by 2037-38, with space cooling in the building sector alone witnessing an 11-time increase.

If not tamed, this can incite massive energy guzzling, worsening overall wellbeing and health.

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