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Green building performance matters: measure it correctly!

Green buildings are environmentally responsible through their life cycle- design, construction, operation & after deconstruction. Energy efficiency, though a significant component/ aspect of any green building, is not the only determining factor of a green building.

Sustainable site planning, water and waste management, use of low energy and environment-friendly materials, use of renewable energy systems and several other aspects have significant importance in any green building rating system.

Therefore, hypothetically speaking, even if a building meets the threshold level of energy efficiency as determined by a rating system, can still be rated under green building rating systems. Of late there has been much hue and cry about energy performance of green buildings that are rated.

Energy performance index (EPI) is total energy consumed in a building over a year divided by total built up area in kWh/sq m/year and is considered as the simplest and most relevant indicator for qualifying a building as energy efficient or not. It forms one of the many indicators in the holistic definition of green buildings.

So, while the Star rating programme of the Bureau of Energy Efficiency rates a building based on its EPI and thus, energy efficiency only, a green building rating system such as GRIHA rates a building on multiple parameters including EPI. The GRIHA system has been developed based on Indian needs, recognizing the fact that performance, not only during operation, but through construction phase as well, is critical to determine how green a building is.

A minimum of three due diligence visits are carried out during construction and commissioning of a GRIHA registered project to ensure that all commitments made on paper are actually been implemented on site and also to facilitate handholding of project proponent to implement green measures with the right intent.

It is important to understand that the first principle of a high performance building is proper design and installation/ commissioning of the building and systems. Performance of a building through its life, much similar to any other system/machine, depends on its operation and maintenance.

Needless to say, if the building is not operated as designed, it will never perform as intended. To give an example, a daylit building is usually designed to save energy during daytime by switching off lights. However, if the user of building decides to put curtains, and switch on the lights, the desired savings shall not be achieved.

Similar analogy prevails for other inherent systems of green buildings such as rain water harvesting system or sewage treatment plants.

It must be noted, that when a green building gets rated, its energy performance or EPI gets calculated using energy simulation in specialized software. The assumptions on equipment efficiency, occupancy, weather and several other parameters determine the predicted/calculated energy performance.

The actual energy performance, when the building starts functioning, may have significant variation from the simulated performance due to climate variability, actual occupancy, operating efficiency of equipment, hours of operation, to name a few.

Thus it is very important that measured data is critically evaluated to ensure that the building is performing as intended. GRIHA has embraced this within its system and, proving performance of a provisionally rated building is the only way to get final rating under GRIHA.

Continuing the discussion on energy performance index and its sensitivity to various factors, it must be noted that EPI varies significantly with varying number of people, internal loads, percentage of air-conditioned space, surface to volume ratios and various other parameters. Thus the dialogue on EPI has to be contextualized and put in right perspective.

Concluding remarks:

  • Energy performance index, that is determined by total energy consumed upon total built up area should be understood in the right context and is not the only determinant of a green building.
  • Comparison across different systems should be done after data normalization to reflect identical assumptions.
  • Operation and maintenance is critical for maintaining "greenness".
  • Buildings undergoing green rating should be monitored through construction and operation.
  • All green parameters should be monitored and performance should be judged based on holistic performance. What's the point in having a building that consumes minimal energy but does not provide thermal and visual comfort, or if it does not have good indoor air quality?
  • Large construction projects undergoing environmental clearance are required to incorporate most of the green/sustainability parameters as required by green building rating systems. Who monitors the performance of the buildings that have received environmental clearance?

Finally, in benefit of the society it makes better sense to work collectively towards better managed service industry, building enhanced capacity amongst practitioners to deliver, produce scientifically analysed data and most importantly participate in the green building movement with enthusiasm, grit and HONESTY.

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