Greenhouse Thermal Screen Energy Saving
Builds the envelope area and UA for a gable house, applies the screen's UA reduction over the heating season.
Example
You enter
- House width (ft) 30
- House length (ft) 96
- Gutter height (ft) 12
- Ridge height (ft) 18
- Glazing U-factor (Btu/h-sq ft-deg F) 1.2
- Screen UA reduction (%) 35
- Heating-season nights 180
- Hours deployed per night 12
- Average night difference (deg F) 40
- Heating plant efficiency (%) 80
- Fuel price ($/therm) 1.2
- Installed screen cost ($/sq ft of floor) 4
You get
- Envelope area 6305.85
- Envelope to floor ratio 2.18953
- Roof share (%) 49.1901
- UA, screen open 7567 Btu/h-deg F
- UA, screen deployed 4919 Btu/h-deg F
- Seasonal heat saved 228827000
- Fuel saved 2860 therms
- Annual saving $3432 against an installed $11520
- Screen cost 11520
- Simple payback 3.36 years
Details, formula, and sources
Builds the envelope area and UA for a gable house, applies the screen's UA reduction over the heating season, and reports fuel saved and simple payback. The worked house saves $3,432 a year on a 3.36 year payback. The light the screen costs does not appear in that payback: open on a light level, not a clock.
UA = envelope area x glazing U-factor; seasonal saving = UA difference x average night temperature difference x deployed hours, divided by the heating plant efficiency.
The screen manufacturer's published UA reduction on the installed configuration, and the site's own fuel and weather records, govern.
Public envelope arithmetic; UA reductions are published by screen manufacturers.
Estimate. AHJ and licensed professional govern.
Field names used by the API: house_width_ft, house_length_ft, gutter_height_ft, ridge_height_ft, glazing_u_factor, screen_ua_reduction_pct, season_nights, night_hours, night_temp_difference_f, plant_efficiency_pct, fuel_price_per_therm, screen_cost_per_sqft, envelope_sqft, envelope_to_floor_ratio, roof_share_pct, base_ua, screened_ua, heat_saved_btu, therms_saved, annual_saving, screen_cost, payback_years
- Degree-days a single average night difference is used rather than binned weather datasite weather records
- Light cost not in the payback; holding the screen closed removes hours from a DLI already below targetspec-v1758 caveat