Energy efficiency matters


Energy efficiency matters

Buildings account for 30-40 pc of energy use as well as 30 pc of the share of CO2 global emissions. Minimising the operation energy demand of the building sector through better design practices can provide enormous potential to reduce the demand for energy. The Fourth Assessment Report of the IPCC has concluded that there is a global potential to reduce about 29 pc of the projected baseline CO2 emissions from residential and commercial buildings by 2020 at a net negative cost. The potential is the highest and cheapest among all other sectors such as transportation, industry, forestry, agriculture, etc.

Attributes of an energy efficient building The design of an energy efficient building depends on the climate and location characteristics.

Minimising heat gain is of prime importance in most tropical climates. In the tropics, compact building forms (measured as a ratio of the surface area to the volume) are preferred in hot and dry climates, but a more open and spread out layout is preferred in warm humid climates to minimise heat gain. Optimising the orientation of the building can decrease the heat load by five per cent even as it maximises natural light in indoor spaces. 

Window sizes, opening orientations and properties of glazing materials of the building envelope can also significantly influence the heat load and the amount of light that penetrates indoors.

Large glass surfaces, particularly in commercial buildings, can become a thermal liability by increasing heat gain and thus air conditioning energy requirements by a significant amount. However, double glazed windows with air gaps can provide good insulation to lower the heat gain. Further reductions in heat gain are possible with low emissivity coatings and/or argon gas fill.

Towards thermal comfort

Choosing appropriate wall and roof assemblies can also reduce heat gain and moderate indoor thermal comfort for non-air conditioned buildings.

Cavity walls, fly-ash based concrete blocks, cellular concrete blocks have good insulating properties and may be considered for wall construction. Roofs receive maximum solar radiation and could be designed appropriately to maximise its insulation and reflective properties. 

The typical construction practice of using 9” brick walls and concrete roofs in Bangalore, particularly in residential buildings, tend to produce thermal discomfort during late evenings when the properties of the material cause the heat absorbed during the day to be released at a later time when temperatures outside are much cooler and comfortable. 

The Bureau of Energy Efficiency (BEE) has recommended maximum values for the shading coefficient and U-value (both of which determine the amount of heat that is transmitted) of glazing to minimise the heat gain within air conditioned spaces for various climatic zones in India.

These specifications are a part of the Energy Conservation Building Code 2007 that is mandatory for all new commercial buildings with a connected load of 500kW (or contract demand of 600 kVA) and above. 

In addition to similar specifications for wall and roof assemblies for such buildings, the ECBC also mandates minimum efficiencies for HVAC, lighting and electrical equipment without compromising on indoor comfort conditions. Smaller office buildings that are not mandated to follow the ECBC would do well to consider the long-term operational cost savings of following the code. 

Renewable energy can have its benefits

Integrating renewable energy systems into buildings can also have significant energy saving benefits. Most parts of India receive relatively high solar radiation and this could be harnessed at the individual building level to reduce the demand from the electricity grid. Solar thermal systems offer tremendous potential in dramatically reducing the energy demand. In Bangalore alone, it is estimated that 250MW of generation capacity is required to meet the hot water requirements of individual houses during the mornings. 
Energy audit could help

Existing commercial buildings, especially large buildings with significantly large air-conditioned spaces such as IT parks, hotels and shopping malls, can derive significant energy and cost savings from carrying out an energy audit of their service systems.
An energy audit is a professional service that makes use of energy measurements and monitoring to identify potential energy savings of lighting, HVAC and other electrical systems. 

Energy savings potential range from 10-25 per cent if recommendations from an energy audit are implemented and paybacks on investments for improving energy efficiency typically range from one to three years. Energy efficiency projects in large-scale commercial buildings are becoming more attractive.

This is because  they are also eligible for carbon credits that can be traded under the Clean Development Mechanism (CDM) of the Kyoto Protocol. 

Building automation systems are now available that lend ‘intelligence’ to buildings. These systems enable buildings to sense environmental conditions such as light levels, temperatures and occupancy, and accordingly control sub-systems of the building. 

Although the initial investment for such a system is very high, they have been shown to reduce energy and maintenance costs when compared to a non-controlled building. 

To summarise, energy efficiency in buildings can be made more effective if such considerations are taken at the design stage.

This requires greater time and attention by designers and developers but could prove beneficial in the long run in terms of operational cost savings.

Similarly, existing buildings, particularly large air conditioned buildings, could be retrofitted with more efficient equipment and systems to obtain significant energy and thus operation cost savings. 

(The writer is a senior consultant at an energy and environment consulting firm.)

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