Question 6.5: Consider a heated manufacturing shop with a total conditione...

To determine the energy savings due to the addition of insulation, we assume that the annual heating degree-days before and after the retrofit remain unchanged and are close to 18°C. For Seattle, the degree-days (with base 65°F or 18°C) are about 2,656°C-days.

The existing air infiltration has an equivalent UA-value of UA_{inf} = mc_{p,a} = 500 W/°C. From Eq. (6.21) with the new air infiltration the equivalent UA-value 250 W/°C and the heating system efficiency set to be 80 percent (gas-fired boiler), the energy savings are calculated to be:

DE_{H,R} =E_{H,E} -E_{H,R}=\frac{24.(BLC_{E}.DD_H (T_{B,E})-BLC_{R}.DD_H (T_{B,R}))}{h_{H}}         (6.21)

ΔE=\frac {24}{0.80}.[(500-250)W/°C]*2656°C.day/yr=19.920kWh/yr

The cost of caulking and weatherstripping is estimated to be about $1,500 (if only material costs are included). For a gas price of $0.05/kWh, the payback period for reducing the infiltration rate can be estimated to be:

Payback=\frac{\$1,500}{19.920kWh/yr*0.05\$/kWh}=1.5 years

Therefore, the caulking and weatherstripping can be justified based only on energy cost savings. Additional benefits of reducing infiltration are improved thermal comfort.