Quick answer: Heat recovery tends to win in cold, dry climates with cheap fuel; dehumidifiers win on humid nights, in mild humid climates, and where CO₂ and screens must be kept closed. In a 2,000 m² greenhouse removing 30 kg/h at 18 °C / 85 % RH, 70 % sensible heat recovery cuts ventilation heating from about 16 kW to 5 kW.
Both cut the energy cost of drying a greenhouse at night, in different ways. Heat-recovery ventilation exchanges humid inside air for drier outside air and uses a heat exchanger to pre-warm the incoming air with heat from the outgoing air, so less heating is needed; it only removes water when outside air holds less water than inside air. A dehumidifier condenses the water inside the greenhouse and returns both the heat of condensation and its electrical input as heat; it works whatever the outdoor humidity.
Quick answer
- Heat-recovery ventilation: needs drier outside air; recovers much of the sensible heat.
- Dehumidifier: works in any weather; returns condensation heat plus its own power as heat.
- Choose by climate, energy prices and how often outside air is humid.
Where water and heat go
| Route | Where water leaves | Where heat goes |
|---|---|---|
| Plain ventilation + heating | With exhaust air (if outside air is drier) | Lost with exhaust; heating replaces it |
| Ventilation with sensible heat recovery | With exhaust air | Most sensible heat transferred to incoming air; latent heat leaves with the vapour |
| Mechanical dehumidifier | As liquid condensate to a drain | Latent heat of condensation + electrical input returned to the greenhouse |
Wageningen University & Research has studied energy-saving dehumidification techniques and heating with dehumidification in production greenhouses (WUR, Energy-saving dehumidification techniques; WUR, Dehumidification at northern latitudes).
Worked comparison (illustrative)
Remove 30 kg/h of water from a 2,000 m² house at 18 °C / 85 % RH; outside air 10 °C / 90 % RH (as in our greenhouse humidity control example).
Ventilation without recovery: about 7,300 kg/h of air exchanged; about 16 kW of heat to warm it.
Ventilation with 70 % sensible heat recovery: heating need drops to roughly 5 kW, plus fan power for two air streams. Latent heat in the exhausted vapour (about 20 kW) is still lost.
Dehumidifier: at the greenhouse's night condition, a refrigerant unit might remove around 2 litres per kWh (lower than its 30 °C / 80 % RH rating), so about 15 kW of electricity; it returns roughly 20 kW of condensation heat plus those 15 kW to the house, which offsets heating.
Which is cheaper depends on electricity vs heating fuel prices, how much of the returned heat is useful that night, and how often outside air is humid. On a humid night (outside 14 °C / 95 % RH), the ventilation airflow needed is almost three times larger, and the dehumidifier's case strengthens.
When each fits
| Situation | Better fit |
|---|---|
| Cold, dry winters; cheap gas or district heat | Heat-recovery ventilation |
| Mild, humid climates; frequent humid nights | Dehumidifiers |
| CO₂ enrichment or closed screens at night | Dehumidifiers |
| Large glasshouses with central air handling | Often both: recovery ventilation plus dehumidification for humid periods |
| Strict night humidity targets (cut flowers, tomatoes) | Dehumidifiers, or both |
What to check in a proposal
- Removal at your night conditions, not rated conditions.
- For heat recovery: exchanger effectiveness, fan power, frost protection, cleaning access.
- For dehumidifiers: L/kWh at night conditions, heat output, drainage.
- Operating hours per year with outside air humid enough that ventilation fails.
Our greenhouse dehumidifiers list power and capacity per model; see how to choose a greenhouse dehumidifier.
FAQ
Frequently asked questions
Is heat-recovery ventilation better than a dehumidifier for a greenhouse?
In cold, dry climates with cheap heat, often yes. In humid climates or when vents must stay closed, dehumidifiers usually work better.
Does a dehumidifier heat a greenhouse?
Yes. It returns the heat of condensation and its own electrical input to the house.
Can heat recovery remove humidity on humid nights?
Only if the outside air holds less water than the inside air; on humid nights it removes little.
Sources
- Wageningen University & Research, Energy-saving dehumidification techniques; Dehumidification of greenhouses at northern latitudes; Heating and dehumidification in production greenhouses.
- US DOE, Energy recovery ventilator core research.
- ASHRAE Handbook—Fundamentals, Psychrometrics.
