Cost of Opening a Door =7
Energy Calculation
E = m C ∆T
m : Mass of Air
C : Specific heat of Air at given Temperature
∆T : Temperature Difference
m = Density X Volume
Density of Air at 40˚C = 1.127 Kg/cu. meter
C = Specific Heat = 1.005 KJ / (Kg ˚C)
∆T = Temperature Difference = 15˚C
(assuming outside temperature is 40˚C and inside is 25˚C)
Volume = Area X Velocity of Air from Door X Time of Opening
(Say : Door Size = 8ft X 4 ft
Velocity = 1 m/s = 200 fpm
Time of Opening = 1 min
Volume = 32 X 200 X 1 = 6400 cu. ft. = 181.22 cu. meter)
m = Density X Volume
(from Above = 1.127 Kg/cu. meter X 181.22 cu. meter
= 204 Kgs)
E = m C ∆T
= 204 kgs X 1.005 KJ / (Kg ˚C) X 15˚C
= 3075.3 KJ = 0.85425 KWh
Thus –
India if Per KWH cost of Power is Rs 8.10
Cost of Opening the Door of Size 8ft X 4ft for 1 min is = Rs 6.92
Cost of Running an Air Curtain of 4 ft = 400W (Input Power) for 1 minute = 6 paise
Rate per Kwh X Time X Power Input
8.10 X 1/60 X 0.4 = 5.4 paisa
Net Saving = Rs 6.92 – 0.06 = Rs 6.86