Greenhouse cooling
Pad-and-Fan vs Mechanical (HVAC) Greenhouse Cooling
Evaporative cooling is cheap and effective in dry heat but consumes water and cannot dehumidify. Mechanical cooling controls temperature and humidity independently at a much higher CAPEX and energy bill.
Direct answer
When does pad-and-fan stop working?
Effectiveness collapses as wet-bulb temperature rises. Above roughly 26–28 °C wet-bulb the achievable pull-down is only a few degrees, which is why humid coastal sites move to semi-closed or mechanical designs.
| Dimension | Evaporative pad-and-fan | Mechanical / HVAC cooling |
|---|---|---|
| CAPEX per hectare | USD 60K–140K | USD 350K–900K+ (depending on tonnage) |
| Connected load | 20–45 kW/ha (fans + pumps) | 250–700 kW/ha |
| Water use | 3–8 m³/ha/day evaporated | Minimal (closed loop / condensate) |
| Temperature pull-down | 6–12 °C in dry air; 2–4 °C in humid air | Setpoint control regardless of humidity |
| Humidity control | Raises humidity — no dehumidification | Full dehumidification possible |
| Climate fit | Arid and semi-arid (low wet-bulb) | Humid tropics, high-value or pharma-grade crops |
| Maintenance | Pad replacement, water treatment, algae control | Refrigeration service contract, higher skill level |
| Uniformity | Temperature gradient pad-to-fan across the house | Uniform with correct air distribution design |
Cost delta at a glance
- •Mechanical cooling typically adds USD 300K–800K per hectare of CAPEX over pad-and-fan.
- •Annual energy cost difference is commonly USD 60K–200K per hectare in a hot climate, before demand charges.
- •Pad-and-fan adds a water line: 1,000–2,500 m³/ha/season of evaporative losses that must exist in the water budget.
Planning-grade ranges for budgeting only. Actual pricing depends on site, specification, climate and supplier scope.
Choose Evaporative pad-and-fan when
- Dry-heat markets (Gulf interior, North Africa, inland Spain, arid India)
- Vegetable crops with tolerance for daytime humidity swings
- Projects where grid capacity or energy price caps the design
Choose Mechanical / HVAC cooling when
- Humid coastal or tropical sites where wet-bulb temperature is high
- High-value crops (berries, propagation, cannabis, seed production) needing tight VPD
- Facilities where water is scarcer or costlier than electricity
Frequently asked questions
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