Adopting Low-cost Alternative for Energy Saving
Case Study

General Information:

City: Chennai
Climate: Warm & Humid
Operational schedule – 8 hours, 5 working days in a week
Area of the building: 10800m² (out of which 9417 m² - conditioned area, 1383 m² - non-conditioned area)

Function: Office Space

Existing Building Design Features

Building Envelope


230mm brick wall with 30mm plaster on exterior side
and 20mm on interior side


The U- Value is higher than that of ECBC recommended (0.409W/m2K).
This results in high external solar heat gains and increased cooling loads


6mm clear single glazed window in thermally unbroken aluminium frames

(SC – 0.81,
U-value of Glass – 6.14 W/m2K)
WWR – 50%

Clear single glazed window and
WWR which is more than that of ECBC recommended (40%) increases the external solar heat gains and the cooling loads

Building Lighting

Lighting system
  • 17 % of the total connected load
  • 2 x 36W CFL lamps for work station areas, 11W CFL, 13W CFL and 18W CFL for corridors, 40W fluorescent tube lights for other locations
  • The CFL lamps have electronic ballast
  • Manual controls are used
  • The LPD 20 W/m2 is double than that of max ECBC recommended (10.8 W/m2) for office space which has high energy consuming potential
  • Lighting energy consumption: 7%
HVAC system Design
  • 3 roof top air cooled screw chillers of 340TR each
  • The COP of the chillers is 3.2 (rated) / ECBC recommended is 3.05
  • Rated Sqft/TR – 99
HVAC controls

  • Temperature of AC space maintained by variable air volumes and 2-way valve controls in the chilled water line
  • All the work station AHUs provided with manual variable speed drives
Energy Performance of the Building

Lighting Energy Performance of the Building

  • Annual Consumption (lighting) – 21%
  • Lighting Performance Index – 37 KWh/Sqmt/annum

Space Conditioning Energy Performance of the Building

  • Annual Consumption (A/C) – 79% of the total
  • HVAC Performance Index – 263 KWh/Sqmt/annum

Annual energy consumption due to lighting & air conditioning (kWh): 3618504

Energy Performance Index of the building (KWh/sq.mts of built up area/annum): 335

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