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Optimizing HVAC through Green design

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HVAC with its vast usage in most of the buildings and increased focus on thermal comfort for the occupants, has become the main contributor to building energy consumption. In a typical air-conditioned building, more than 50% of the electricity consumed will be from HVAC. Therefore, it is very critical to optimize this component to improve the energy performance of a building & reduce the operational costs.

The energy consumption from the HVAC is influenced by various factors which are both tangible and intangible. These factors are climatic conditions, heat loads in the building, efficiency of the HVAC system and building operation schedule. Understanding each can help in optimizing the building design and save energy in turn.

To further elaborate, the overall design of the building and its systems depend on the climatic conditions with respect to the location of the building. Hotter the climate, more is the cooling required, hence higher the electricity consumed and vice versa. The architectural and MEP design of the building should be in line with the climatic conditions of that location as the climatic condition directly influences the heat loads in the building.

Heat Loads

Heat loads are of two types, namely internal heat load and external heat load. The primary factors that contribute to external heat loads are climatic condition, location, building shape, building orientation, building materials and the interior layout. Also the façade design majorly contributes to the heat load. The secondary factors such as window to wall ratio, shading devices are all important parameters in determining the heat loads as well. The internal heat load comprises of heat generated from lights, equipment, human beings and other process and non-process loads.

Further, based on the heat loads & climate, the HVAC system type and the efficiency have to be chosen. The energy consumption of the HVAC system directly relates to its performance efficiency. Finally, the entire building operating hours also determine the energy usage.

Once the major contributors to the energy consumption in a building are identified, the areas of energy savings can be analysed. Factors like climatic conditions and operating schedules remain constant and no changes can be attributed to these parameters. Heat loads and HVAC system efficiency are the two main areas for improvement which can contribute greatly towards energy reduction.

Heat Load Reduction

M. SELVARASU, B.E., MBA LEED Accredited Professional & Faculty Of USGBC,Director-LEAD Consultancy & Engineering services(India) Pvt Ltd

External Heat loads in a building can be reduced with a good architectural design. A building in best orientation (longer façade in north and south orientation) with buffer spaces / no conditioned spaces in the west and east façade will reduce significant amount of heat ingress into the building. Reduced glazing in east and west, use of high efficient glazing system coupled with shading devices can be options for conditioned spaces in these orientations. Also, building shape which can contribute to self-shading should also be encouraged.

The choice of building materials is critical in curbing the heat ingress. Materials with low U values, use of insulation, double glazing with low solar heat gain, shading devices, landscape wall, double façade are all key features which can be part of the building design.

Internal loads can be reduced by using efficient light fixtures like CFL, T5, LEDs integrated with light shelves. Lighting controls like daylight and occupancy sensors can be integrated into the design along with use of efficient equipment with star ratings can be chosen.

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