Enter Window Service Data
Formula Used
Area: A = width × height
Effective solar load: S = irradiance × orientation factor × unshaded ratio × absorptance
Center rise: Tc rise = 0.020S × blind factor × airflow factor + 0.012E
Edge rise: Te rise = 0.45 × center rise − frame cooling allowance
Temperature difference: ΔT = center-edge rise + shade gradient + indoor-outdoor gradient
Thermal stress: σ = 0.62 × ΔT × restraint factor × pane factor × edge stress factor
Safety factor: SF = allowable glass stress ÷ calculated thermal stress
This is a screening method. Use professional review for final glazing approval.
How to Use This Calculator
Enter the window size, glass thickness, and glass type. Add solar load, shade, temperature, edge condition, and electrical heating load. Choose pane type, airflow, blind condition, and frame restraint. Press calculate. The service result appears above the form. Use CSV or PDF buttons to keep records.
Example Data Table
| Case | Glass | Solar W/m² | Shade | Edge | Electrical Heat | Expected Risk |
|---|---|---|---|---|---|---|
| Office facade | Annealed | 700 | 35% | Minor chips | 0 W/m² | Moderate to high |
| Heated display glass | Heat-strengthened | 500 | 10% | Excellent | 180 W/m² | Moderate |
| Tempered skylight | Tempered | 900 | 20% | Excellent | 0 W/m² | Low |
Window Thermal Breakage Calculation Guide
What This Service Checks
Thermal breakage happens when one part of a glass pane becomes much hotter than another part. The hot area expands. The cooler edge does not expand at the same rate. Stress then builds inside the pane. If that stress exceeds the practical strength of the glass edge, cracking can start from a chip or cut mark.
Why Solar And Electrical Heat Matter
This calculator treats solar heat and electrical heating as service loads. Solar energy can warm tinted or absorbing glass very quickly. Electrical heat can come from heated glazing, display lighting, radiant panels, or nearby equipment. These loads are converted into a heat index. The heat index helps estimate center temperature rise and edge temperature difference.
Important Field Inputs
Edge condition is very important. A perfect edge can carry more stress. A damaged edge needs a larger safety reserve. Partial shade is also important. It creates hot and cool bands across the same pane. Close blinds can trap air and raise the glass temperature. Deep frame bite can keep the edge cooler. That increases the center-edge difference.
Understanding The Result
The safety factor compares allowable stress with calculated stress. A higher safety factor means better reserve. A low safety factor means the pane may need a stronger glass type, lower absorptance, less shading contrast, improved ventilation, or a different frame detail. The risk score gives a quick service view, but it should not replace engineering judgment.
Best Service Practice
Use measured site data whenever possible. Record orientation, shade pattern, blind position, heating equipment, and edge defects. For high risk results, recommend heat-strengthened or tempered glass. Also review film use, internal blinds, nearby heaters, and frame restraint. Keep the downloaded report with inspection notes. This creates a clearer decision trail for installers, designers, and service teams.
FAQs
What is window thermal breakage?
It is cracking caused by uneven glass temperature. The center may heat faster than the edge. That difference creates stress. Cracks often start from weak or damaged edges.
Can electrical heating affect glass breakage risk?
Yes. Heated glass, radiant panels, display lights, and nearby electrical equipment can raise glass temperature. The calculator includes electrical heating load as watts per square meter.
Is this calculator suitable for final engineering approval?
No. It is a service screening tool. Use it for early risk review, field notes, and comparison. Final approval should follow project standards and professional engineering checks.
Why does partial shade increase risk?
Partial shade creates hot and cool areas on the same pane. The hot zone expands more. The cooler shaded zone restrains it. This difference can increase thermal stress.
Which glass type has lower breakage risk?
Tempered glass usually has the highest thermal stress resistance. Heat-strengthened glass also performs better than annealed glass. The best choice depends on project safety rules.
Why is edge condition included?
Thermal cracks often start at the edge. Chips, scratches, and poor cutting reduce practical strength. A damaged edge lowers the allowable stress used by the calculator.
What does safety factor mean?
Safety factor compares allowable stress with calculated stress. A value above one means reserve remains. Higher values show better tolerance against the entered heat and edge conditions.
Can I export the calculation?
Yes. Use the CSV button for spreadsheet records. Use the PDF button for a simple service report. Both exports use the current form values.