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
- Whole-house UA reduction from the screen (%; not the fabric rating -- UW Extension's 52% curtain saved 32% of a house) 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 7,567 Btu/h-deg F
- UA, screen deployed 4,919 Btu/h-deg F
- Seasonal heat saved 228827000
- Fuel saved 2,860 therms
- Annual saving $3,432 against an installed $11,520
- Screen cost 11520
- Simple payback 3.36 years
No published worked example is on file for this calculation. It is checked against a hand-worked derivation of its method and an independent reference test.
Details, formula, and sources
ScopeBuilds 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.
Formula or tableUA = envelope area x glazing U-factor; seasonal saving = UA difference x average night temperature difference x deployed hours, divided by the heating plant efficiency.
Source and editionThe screen manufacturer's published UA reduction on the installed configuration, and the site's own fuel and weather records, govern.
Free accessPublic envelope arithmetic; UA reductions are published by screen manufacturers.
What governsEstimate. AHJ and licensed professional govern.
API field nameshouse_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