Adopting Low-cost Alternative for Energy Saving
Case Study


General Information:


Client: WIPRO Info Tech
City: Bangalore
Climate: Moderate
Operational schedule – 10 hours, 5 working days in a week for 10 floors, 24 hours for 2 floors
Area of the building: 32, 438 m² (out of which 24, 440m² - conditioned area, 7, 998m² - non-conditioned area)

Green Building Design Features:

Building Design

Orientation

1:3 rectangular with longer façade on N-S and shorter façade on E-W

  • Windows in N-S help in day night integration and reduced heat gain
  • E-W façade with service shafts and emergency stairs create a thermal buffer to the conditioned spaces

Building Envelope

 Walls

200mm concrete block with 30mm plaster on exterior
side and 20mm plaster on interior side

Roof

250mm of RCC concrete slab

 Windows
  • Double glazing window (6-12-6)mm
  • Glass on north orientation has a lighter light transmission
  • The glazing for the building has been designed to maximize the effect of natural light, largely eliminating the need for artificial light during day time
  • The high performance window glass, while allowing light inside, does not allow heat and also keeps office cool from inside during the day decreasing the load on HVAC systems
  • Optimum WWR which is less than ECBC standard (40%) helps in reducing external solar heat gain

Building Lighting

Lighting System
  • 9.4% of the (273 kW of indoor lighting, 30kW of outdoor lighting)
  • Luminaries used mostly –recess mounted direct-indirect down light luminaries with twin fitting 36 W CFL lamps and low loss copper ballast
  • LPD – 11.2-12.4 W/m2
  • The LPD (11.2 W/m2) is less than the max allowed LPD of ECBC (11.8 W/m2) for office space which is very good.
  • According to Energy Star, CFLs provide the same amount of light as ordinary bulb using 75% less energy.
  • It also generates 75% less heat, reducing cooling costs
Lighting Controls
  • Occupancy sensors have been integrated with luminaires in the office space
  • Reduce energy by turning the lights on when someone enters and switches off, when the room is empty
HVAC System Design

  • Central AC plant with two 815 TR and 400TR screw chil
  • The COP of the screw chillers is 64. (rated) / ECBC recommended is 6.3
  • Rated Sqmt/TR – 30
Energy performance of the building

Lighting Energy Performance of the Building

  • Annual Consumption (lighting) – 324754 KWh
  • Lighting Performance Index – 13 KWh/Sqmt/annum

Space Conditioning Energy Performance of the Building

  • Annual Consumption (A/C) – 24440 KWh
  • HVAC Performance Index – 137 KWh/Sqmt/annum

  

Annual energy consumption due to lighting & air conditioning (kWh): 3448073

Overall Energy Performance Index due to lighting & air conditioning (kWh/m2): 118

 
   

Comparison of various parameters for ECBC compliant Moderate (WIPRO) with conventional case

The table below summarizes the calibrated existing ECBC model case, conventional case generated over the existing building in moderate climate zone.

 
Parameters ECBC compliant case (Existing Building) features Conventional Case (Building features)
Building orientation Longer façade on N-S and shorter façade on E-W

Building orientation to longer facades facing East-West
windows shaded on E-W orientation Windows, Walls and Roof are not shaded
Building Envelope

Insulation on roof with air gap for walls
U value for Wall - 1.29 W/m2/K
U Value for Roof - 0.47 W/m2/K

No insulation on wall and roof.
U value for Wall -1.94 W/m2/K
U Value for Roof-1.5 W/m2/K


Double Glazed windows( U value of glass -2.64 W/m2/K and Shading coefficient-0.17)
WWR - 26%
Single Glazed windows( U value of glass -6.17 W/m2/K and Shading coefficient-0.61)
WWR – 26%
Building Lighting Power density Lighting power density is 11.8 W/m2 Lighting power density 20 W/m2
Controls Occupancy sensors No controls or sensors
Building Chiller 4 water cooled screw chillers with COP of 6.4 (rated) PTAC units having EER of 8.4 and Fan power as 0.000134 bhp/cfm
Energy performance Index (KWh/m2/yr) 118 167

Energy Saving Potential

The conventional case defined above was selected to run different energy saving options and to finally quantify the energy saving potential which can be realized in moderate climate by incorporating the low design strategies, ECBC envelope, and the best case (incorporating both low energy strategies and ECBC measures)


Impact of Low energy strategies

The conventional case was run by incorporating low energy solar passive design strategies on the annual electricity consumption (kWh), electric load (kW) and cooling demand (TR) of the building.

Parameter comparison Conventional case Existing case Low energy strategies)
Electrical load Base case 14.7% less than the conventional case
Cooling Load Base case 38.6% less than the conventional case
EPI Base case 25.4% less than the conventional case


Impact of ECBC Envelope

The conventional case was run by incorporating ECBC envelope on the annual electricity consumption (kWh), electric load (kW) and cooling demand (TR) of the building.

Parameter comparison Conventional case Existing case Low energy strategies)
Electrical load Base case 14.6% less than the conventional case
Cooling Load Base case 13.6% less than the conventional case
EPI Base case 12.6% less than the conventional case


Overall Impact of ECBC Envelope and low energy strategies

The conventional case was run by incorporating both the low energy solar passive design strategies and ECBC envelope on the annual electricity consumption (kWh), electric load (kW) and cooling demand (TR) of the building.

Parameter comparison Conventional case Existing case Low energy strategies)
Electrical load Base case 32.4% less than the conventional case
Cooling Load Base case 56.9% less than the conventional case
EPI Base case 26.4% less than the conventional case




The above graph shows the variation in the Electrical load (kW), Coil load (TR) and EPI (energy performance index) for all the cases.

The below table gives the comparison of the impact of ECBC, Low energy strategies, and ECBC + low energy strategies on conventional case for WIPRO building for a Moderate Climate

Parameter comparison Existing case Conventional case ECBC case Low energy strategy ECBC+Low energy strategy
Electrical load 35% less than the conventional case Base case 14.6% less than the conventional case 14.7% less than the conventional case 32.4% less than the conventional case
Coil Load 52% less than the conventional case Base case 13.6% less than the conventional case 38.6% less than the conventional case 56.9% less than the convention al case
EPI 28% less than the conventional case Base case 12.6% less than the conventional case 25.4% less than the conventional vase 26.9% less than the conventional case


   
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