Question

1.a/ A house is heated at 22oC and has an average outdoor air infiltration rate of 0.15 ACH at standard operating conditions. If the average temperature outside over three months (91 days) is 2oC what would be the approximate energy consumption due to natural air infiltration? The house is 250 m2 in area and has 8 foot high ceilings throughout.

b/If the house is being heated by a 100% efficient electric baseboard heater, what would be the savings due to infiltration losses over that three month period if you decided to heat the house to 18oC instead of 22oC. Electricity costs are $0.13/kWh?

Answer 1

Given:

Troom = 22 degree C = 295 K

Toutside = 2 degree C = 275 K

Vroom = Areaheight of ceiling = 25080.3048 = 609.6 m^3

Now,

Infiltration rate = 0.15 ACH = 0.15Vroom = 0.15609.6 = 91.44 m^3/hour

Now,

Mass of Supply Air entering = (pressurevolume of air entering) / (RTemperature)

= (10132591.44) / (287295)

= 109.43 kg/hour

= 109.43/3600 kg/s

Cooling load due to infiltrated air = mCp(Troom - Toutside)

= (109.43/3600)1.0216(22-2)

= 0.62107 kW

Hence, Total Energy consumption due to infiltrated air for 3 month period

= 0.62107 kW ( 3 months 30 days/month 24 hours/day )

= 1341.5 kWhr

If House is heated to 18 degree C instead of 22 degree C:

Troom = 18 degree C = 291 K

Mass of Supply Air entering = (pressurevolume of air entering) / (RTemperature)

= (10132591.44) / (287291)

= 110.93 kg/hour

= 110.93/3600 kg/s

Cooling load due to infiltrated air = mCp(Troom - Toutside)

= (110.93/3600)1.0216(18-2)

= 0.5037 kW

Hence, Total Energy consumption due to infiltrated air for 3 month period

= 0.5037 kW ( 3 months 30 days/month 24 hours/day )

= 1088 kWhr

Total Savings in electricity cost for 3 months = (1341.5 - 1088) kWhr 0.13 $/kWhr = 32.95 $

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