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Energy Consumption, Generation and Atmosphere for green building

Er. Parbhakar Dwivedi
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In order to earn green building rating, reduction energy consumption below the baseline, use of renewable energy resources, reducing dependence on fossil fuel based energy sources and protecting atmosphere from greenhouse gases and ozone depleting gases are important factors which earn maximum points. In the following articles, various techniques are listed which can save the energy consumption. Some of these techniques are utilized by various owners and occupants of the building, but the most important aspect of green building is the implementation of all the strategies in an integrated manner.

a. One of the foremost requirement before earning points under this head is to have a building system commissioning plan in place. This is to make sure that the systems are designed and installed as required. There shall be qualified professionals with high level of experience in energy calculations, installation, operation and commissioning procedures. They are well versed with automation controls which go a long way in achieving the desired savings in energy consumption. The owner can thus rest assured that all activities will achieve the desired goals and are being well documented for sub-mission to rating agency.

b. Achieving minimum energy performance levels as set in the beginning of a project. These levels shall be set as prescribed by ECBC code. Any further reduction in energy consumption fetches additional points. Some rating agencies, particularly those following USGBC norms, prefer to adopt the standards set by ASHRAE/ISHRAE.

Let's examine the methodology set by ECBC for various energy devices and their applicability.

i. The ECBC code is applicable to buildings with a connected load of 100 kW or more or a contract demand of 120 KVA or greater. Generally, buildings or complexes having conditioned area of 1000 m2 or more will fall under this category. This code is presently voluntary for adoption in India.

ii. The intent behind developing this code was to develop and prescribe various energy efficient practices which could reduce energy consumption requirements of a building. The provisions of this code applies to

• Building envelopes, except unconditioned storage spaces or ware houses.

• Mechanical systems and HVAC

• Service hot water heating

• Interior and exterior lighting

• Electrical power and motors

iii. The code prescribes mandatory and prescriptive approach to reduce energy consumption for new as well as existing buildings. The foremost requirement of the code is compliance with mandatory provisions. But to allow flexibility to designers while designing building components, code specifies specific levels for each individual component of the building stems called prescriptive requirements and if these individual components are achieved, compliance with the code is done.

Further flexibility has been allowed in the code by a Trade-off option that allows trading-off the efficiency in the thermal performance of one envelope element with another to achieve the overall efficiency level required by code. But this tradeoff option can be exercised only within building envelope components like roof, wall, fenestration, overhangs, etc. This trade-off is not against improvement in lighting and HVAC systems.

Next level of design flexibility allowed in the code is with "Whole Building Performance" (WBP) method which is more complex than prescriptive method in approach. In this method, whole building is analyzed as an integrated unit with the help of energy simulation software and the energy (like envelope, HVAC, lighting and other building systems) is optimized to achieve the most cost effective solution. In this method, a computer software prepares a "Proposed design", calculates its annual energy requirement and compares it with "standard design" which is based on the upper limits of energy use allowed by the code for the particular set of conditions. If the energy use in proposed design is lower or equal to the standard design, the compliance to the code is achieved.

From the above, it will be seen that building a model on prescriptive approach is the first step in any building design. The next is to demonstrate that the design complies with mandatory provisions and the final is to develop a model using simulation software and compare with the model prepared in the first step.

c. Halocarbon gases, popularly CFC gases used in air conditioning and fire suppression appliances are a great threat to ultraviolet protective layer of atmosphere called ozone layer. The depletion of ozone is causing global temperature rise resulting in melting of glaciers and increasing of sea levels. The green building norms prescribe zero use of CFC gases in the construction of new buildings or a comprehensive policy of a time based phase out of CFC gases in the existing HVAC equipments.

d. Methods which help to reduce dependency on fossil fuels and encourage renewable sources of energy like solar power, solar water heating, and wind and water turbines, geothermal and biomass power generators earn extra points for green building rating.

e. Once the building has been commissioned, it is important that it operates at the same efficiency levels for which it was designed and at which it was commissioned. Thus a comprehensive operation and maintenance plan must be put in place, ensure that contract guidelines and conditions are very clear and a protocol, to measure and verify the energy performance parameters, is put in place by installing necessary metering equipments providing training to engineers and operators and compare the performance to baseline performance at least for a period of one year.

f. To encourage investment in off-site renewable energy projects, additional points are allowed where such green power is exported to grid.

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