Quick answer: Freestanding or ceiling-hung dehumidifiers dry the zone around each unit; choose ducted units when dry air must reach every row evenly. "Freestanding" describes where the unit sits; "ducted" describes how air reaches the crop. Choose by how evenly dry air must reach the crop and where there’s room for equipment.
A freestanding or ceiling-hung unit in the growing space draws air in and blows dry air out locally. It is simple, quick to install and easy to service, but it covers only its own zone, it takes up floor or roof space, and it may shade the crop. A ducted unit sits outside or above the crop and delivers dry air through ducts or perforated tubes. Distribution can be even, under or along the crop, with no equipment in the growing area. The trade-offs are duct cost, fan power and a more complex design.
Quick answer
- Freestanding/hung: simple, local coverage, takes space in the house.
- Ducted: even distribution, equipment out of the crop, more design and fan power.
- Either way, check dry air reaches the canopy.
Comparison
| Freestanding or ceiling-hung | Ducted | |
|---|---|---|
| Air delivery | Local discharge; relies on HAF fans to spread | Ducts or perforated tubes to each row or zone |
| Coverage | One zone per unit | Even across a large area |
| Space | Uses floor, bench or roof space; may shade | Unit outside or above; ducts in the house |
| Installation | Fast; power and drain at each unit | Ducts, fan sizing, fewer units |
| Service | At the unit, in the house | At the plant, outside the crop |
| Fan power | Lower | Higher (duct pressure) |
| Best for | Retrofit, smaller houses, zone-by-zone control | Large or long houses, crops sensitive to uneven conditions |
Check the air path
- Where is the air taken in, and where does dry air go?
- Does dry air reach the canopy and the lowest leaves, not just the roof?
- In ducted designs, what are the outlet positions and the duct pressure drop?
- With freestanding units, do HAF fans carry the dry air along the house?
See greenhouse ventilation tubing and central vs distributed dehumidification.
Check circulation where the crop grows
- Measure RH and temperature at canopy height in several zones after installation.
- Compare the spread between zones.
- Look for wet spots at dawn: ends of the house, near walls, under gutters.
Practical notes
- Drains: freestanding units need a drain at each unit; ducted plant drains at one place.
- Shading: ceiling-hung units over high-light crops cast shadows; place over paths where possible.
- Heat: in both layouts the latent heat from condensation stays in the house; in ducted designs it arrives with the dry air.
Our greenhouse dehumidifiers include ceiling-mounted units and ducted units with RYDZ capacities from 26 to 960 L/day (at stated rating conditions).
FAQ
Frequently asked questions
Are ducted dehumidifiers better for greenhouses?
For large or long houses that need even conditions, often yes; for smaller houses and retrofits, freestanding or hung units are simpler.
Can a freestanding dehumidifier cover a whole greenhouse?
Only small ones; larger houses need several units or ducted distribution, plus HAF fans.
Do ducted dehumidifiers use more energy?
Their fans use more power because of duct pressure; the drying itself depends on the unit.
Sources
- ASHRAE Handbook—HVAC Systems and Equipment, Duct design and dehumidification.
