Question 24.1: Annual Savings from Window Replacement Find the annual savin......
Annual Savings from Window Replacement
Find the annual savings for the house of Figure 24.2 in Madison at a fuel price of $7/GJ if singlepane glazing with U = 5.713 W/(m² ·K) is replaced by double-pane glazing with U = 2.675 W/(m² ·K), the shading coefficient remaining the same at SC = 1.0. The area of the house is 143.06 m² and the total window is 8.65% of this value. Then total window area of 12.37 m² (= 0.0865 × 143.06 m²), i.e., primary window area = 0. Express the result as savings per window area.
Given: Figure 24.3b at A = 0, SC = 1.0
Find: Difference between curves for U = 5.713 and 2.675 W/(m² ·K)
Reading the curves, we find Q = 104 GJ with single glazing and Q = 86 GJ with double glazing, a difference of 18 GJ, or roughly one-fifth of the load. This is worth 18 GJ × $7/GJ = $126/year.
Dividing by 12.37 m², we obtain $10.19/m² of window per year.
Comments
Suppose the incremental cost of double glazing is $50/m². Then, the payback time is 50/10.19 = 4.9 years. Savings due to good glazing are very important!