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.
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
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.
Yes. Many projects use pad-and-fan or high-pressure fogging as the base system and add mechanical cooling only to a propagation or post-harvest zone, which keeps the tonnage — and CAPEX — small.
Design ambient and wet-bulb conditions, target inside temperature and RH, air changes per hour, pad face velocity, fan static pressure, and who is responsible for water treatment and power supply to the fan wall.