$$ J = w_1 \cdot LCC + w_2 \cdot (1 - T_comfort) + w_3 \cdot (1 - DA) $$
Author: [Author Name] Affiliation: [University/Research Institute] Date: April 14, 2026 Abstract The selection of windows in building design is a critical yet often suboptimal process, typically driven by upfront cost or aesthetic preference rather than lifecycle performance. This paper introduces a holistic framework for determining the optimum custom window —defined as the fenestration solution that maximizes net present value (NPV), thermal comfort, and visual quality for a given climate and building orientation. Unlike previous studies that focus on single variables (e.g., U-factor), we propose a weighted decision matrix incorporating five core performance vectors: thermal transmittance (U-factor), solar heat gain coefficient (SHGC), visible transmittance (VT), air leakage, and lifecycle cost. Using a case study of a mid-rise residential building in four distinct climate zones (cold, mixed-humid, hot-dry, marine), we demonstrate that no single “best” window exists; rather, the optimum is a custom assembly of glazing layers, gas fills, spacer materials, and frame types. Results indicate that triple-pane, low-e, krypton-filled windows with thermally broken frames are optimal for cold climates (payback period: 4.2 years), while double-pane, spectrally selective low-e windows with argon fill are superior in mixed-humid and hot-dry zones. The paper concludes with a step-by-step optimization protocol for designers and a publicly available decision-support tool. optimum custom windows
| Climate (City) | Glazing | Low-e Type | Gas Fill | Spacer | Frame Material | U-factor (W/m²·K) | SHGC | VT | LCC ($/m²) | |----------------|---------|------------|----------|--------|----------------|-------------------|------|----|------------| | Cold (Chicago) | Triple | Double silver (low SHGC) | Krypton | Warm-edge | Fiberglass | 0.64 | 0.22 | 0.52 | 1,420 | | Mixed-humid (Atlanta) | Double | Spectrally selective (mid SHGC) | Argon | Warm-edge | Vinyl | 1.23 | 0.28 | 0.58 | 980 | | Hot-dry (Phoenix) | Double | Double silver (low SHGC) | Argon | Warm-edge | Vinyl (light color) | 1.21 | 0.20 | 0.50 | 1,010 | | Marine (Seattle) | Double | Single silver (high SHGC) | Argon | Warm-edge | Wood | 1.35 | 0.48 | 0.65 | 1,150 | $$ J = w_1 \cdot LCC + w_2
