| Input | Example value | Notes |
|---|---|---|
| Window area | 80 ft² | Panels facing prevailing winds. |
| Coverage | 85% | Roll-up curtains on tracks. |
| Existing value | R 1.2 | Single layer poly with air gaps. |
| Curtain value | R 3.0 | Insulated fabric with reflective layer. |
| Heating cost | $650/yr | Propane or electric equivalent. |
| Cooling cost | $320/yr | Fans and evaporative cooling. |
| Leakage bonus | 5% | Better edge sealing reduces drafts. |
| Upfront cost | $330 | Material + installation. |
Heat transfer through windows is approximated using a U-value: U = 1 / R. Adding curtains increases total insulation: R_total = R_existing + R_curtain.
The conductive reduction is: (U_old − U_new) / U_old, applied to the covered window area. Degree days scale seasonal temperature difference.
Dollar savings are based on your annual heating and cooling costs, scaled by the reduction and your “load share” percentages. A leakage bonus adds a small draft-reduction uplift.
- Choose your unit system, then enter total window area.
- Enter coverage percent and insulation values for windows and curtains.
- Add your annual heating and cooling costs from bills.
- Set load share percentages to reflect window-driven energy use.
- Enter costs, service life, and optional discount rate.
- Press Calculate and export results to CSV or PDF.
Why thermal curtains matter in greenhouses
Greenhouse glazing loses heat quickly because its insulation value is low. Thermal curtains add an insulating air layer, reduce long‑wave radiation to cold surfaces, and limit drafts along frames. When deployed consistently at night, they stabilize root‑zone temperatures, improve crop uniformity, and reduce heater cycling that wastes fuel.
Key inputs that drive savings
This estimator focuses on window area, percent coverage, and insulation values before and after installation. Climate severity is represented by heating and cooling degree days, while your annual utility totals set the cost baseline. Load‑share percentages help separate window‑related energy use from other greenhouse demands. If you have multiple zones, estimate a weighted average cost for the covered zone.
How the calculation converts insulation to dollars
The model converts insulation values to U‑values using U = 1/R, then computes the fractional reduction from adding the curtain. That reduction is applied to your heating and cooling costs after adjusting for the window load share. A leakage bonus can be added to capture improved edge sealing and reduced infiltration around doors and vent openings. The report also shows a degree‑day cross‑check in energy units for sanity testing.
Interpreting payback and long‑term value
Payback is calculated as total upfront cost divided by estimated annual savings. Net present value extends the same annual benefit across the expected service life and optionally discounts future cashflows. Use the service life field to match your fabric durability, cleaning routine, and track hardware quality. If you expect rising energy prices, consider increasing the annual cost inputs.
Practical optimization tips
For best performance, close curtains before sunset and open after sunrise to prevent moisture issues. Seal perimeter gaps with brush strips or overlapping panels, and maintain smooth tracks so deployment is fast. If you heat only during propagation, reduce the heating load share to avoid overstating savings. Track interior temperatures before and after to validate savings. Document settings for repeatable comparisons later.
What insulation value should I enter for my greenhouse panels?
Use the manufacturer rating if available. For single layer film or glass, a value near one is common. For double wall polycarbonate, use the listed value. Enter an average if panels vary across walls.
How do I estimate heating and cooling degree days?
Use a local weather dataset, energy audit tool, or nearby station summary. Enter seasonal totals for your greenhouse base temperature if known. If you only heat during nights, focus on the cold season total.
Why are there load share percentages?
Utility bills include many loads besides windows. Load share lets you assign a realistic portion of heating or cooling to window losses. If you are unsure, start with 60 to 85 percent and adjust after monitoring.
Does the estimator include humidity or condensation effects?
It does not model moisture directly. Curtains can reduce radiant cooling and surface condensation when managed correctly. If humidity control requires extra ventilation, reduce your expected savings or shorten the time curtains stay closed.
How should I choose the leakage bonus?
Use zero if your curtains are loose or edges leak. Use five to ten percent for well sealed tracks and overlapping panels. Keep it conservative unless you have measured infiltration improvements with smoke tests.
What is the best way to validate results?
Track inside temperature, heater runtime, and energy use for one week before installation and one week after. Keep crop load and ventilation settings similar. Compare normalized costs using degree days for those weeks.