Optimum — Custom Windows Extra Quality

The concept of an "optimum custom window" is inherently local. This paper demonstrates that by jointly optimizing U-factor, SHGC, VT, frame, and gas fill against lifecycle cost and comfort, designers can achieve energy savings of 40–70% compared to code-minimum windows. The key findings are:

$$ J = w_1 \cdot LCC + w_2 \cdot (1 - T_comfort) + w_3 \cdot (1 - DA) $$ optimum custom windows