EXERCISE # 3
ENVELOPE PERFORMANCE FACTOR (EPF) CALCULATION
Where
EPF Roof: EPF for roofs, other subscripts include walls and fenestration
As, Aw: the area of a specific envelope component referenced by the subscript “s” or for windows the subscript “w”.
SHGCw: The solar heat gain coefficient for windows (w). SHGCs refers to skylights.
Mw: A multiplier for the window SHGC that depends on the projection factor of an overhang or side fin.
Us: The U-factor for the envelope component referenced by the subscript “s”.
cRoof: A coefficient for the “Roof” class of construction. Values of “c” are taken from Table 12 – 1 through Table 12 –
5 for each class of construction (As given in ECBC Code Page 59 onwards).
Calculation of Envelope Performance Factor (EPF)

Project Specifications
 Location: Jaipur
 Building Type: Office (Daytime use)
 Shape: Square
 Area: 500 m2 (22.36 X 22.36 m)
 Floor to Floor Height: 4.5 m
 No. of Floors: 1
 WWR: 50%
 Wall Construction: Double Brick Wall (U – value 1.23 W/m2K), 20mm Plaster (both interior and
exterior) (U – Value), Polyurethane 25mm (U- Value - )
 Roof Construction: ECBC compliant roof of U – Value 0.409 W/m2K
 Fenestration Type: Single Glazed Unit Clear Glass, U – value 7.1 W/m2K, SHGC 0.82, VLT 0.76 (all
direction)
 Step1: Calculate EPF Wall using below formula
Prepared By: Dr. Ing Jyotirmay Mathur, Sachin Sharma, Centre for Energy & Environment, Malaviya National Institute of Technology, Jaipur
Page 1





Step2: Calculate EPFRoof using below formula




Now go to table 12 – 1 (Annexure 1) and find cwall,mass (U – factor): ......................
Now calculate Us x As for all the four(4) sides of the wall and sum total the values ∑ UsAs (Insert U- Value of
Wall): ....................
Since, in this case there is only mass wall, hence c Wall,Other = 0.
Now calculate EPF Wall: .....................
Now go to table 12 – 1 (Annexure 1) and find c Roof (U – factor): ........................
Now calculate Us x As for all roof, in this case there only one roof structure, so calculate that value (take roof
area same as floor area): .....................
Now calculate EPF Roof: ........................
Step3: Calculate EPFFenestration using below formula







First go to table 12 – 1 (Annexure 1) and find c1 Fenest, North (SHGC): ..............................
Since, there are no overhangs and sidefins in this case, so assume Mw factor as 1
Assuming one window on each direction calculate c1Fenest,North ∑SHGCwMwAw (Here SHGC value of the
window need to be inserted) :............................
Now, go to table 12 – 1 (Annexure 1) and find c2 Fenest, North (U –factor): ...................................
Calculate c2 Fenest,North ∑UwAw : ...............................
Now repeat the above steps same for non north windows, assuming one window in each direction makes no.
of north windows as three (3). Repeat the above steps and find c1Fenest,Non North ∑SHGCwMwAw
...................................and c2 Fenest,Non North ∑UwAw .............................................
Now calculate EPF Fenestration: ...............................................................
 Step4: Calculate EPF Total = EPF Roof + EPF Wall + EPF Fenestration:........................................
 Step5: Now calculate EPF Wall using table 4.3.2 (Annexure 2) and table 12 – 1 (Annexure 1) :
....................................
 Step6: Now calculate EPF Roof using table 4.3.1 (Annexure 2) and table 12 – 1 (Annexure 1): .........................
 Step7: Calculate EPF Fenest using table 4.3.3-1 (Annexure 2) and table 12 – 1 (Annexure 1): ............................
 Step8: Compare the two values
ECBC EPF Total
As is case EPF Total
ANNEXURE 1
Prepared By: Dr. Ing Jyotirmay Mathur, Sachin Sharma, Centre for Energy & Environment, Malaviya National Institute of Technology, Jaipur
Page 2
Prepared By: Dr. Ing Jyotirmay Mathur, Sachin Sharma, Centre for Energy & Environment, Malaviya National Institute of Technology, Jaipur
Page 3
Figure 1 Excerpt from ECBC Code 2007
Prepared By: Dr. Ing Jyotirmay Mathur, Sachin Sharma, Centre for Energy & Environment, Malaviya National Institute of Technology, Jaipur
Page 4
ANNEXURE 2
Prepared By: Dr. Ing Jyotirmay Mathur, Sachin Sharma, Centre for Energy & Environment, Malaviya National Institute of Technology, Jaipur
Page 5
Figure 2 Excerpt from ECBC 2007
Prepared By: Dr. Ing Jyotirmay Mathur, Sachin Sharma, Centre for Energy & Environment, Malaviya National Institute of Technology, Jaipur
Page 6