Quick answer: A vertical farm's HVAC must remove two loads at once: the heat from lights, pumps and fans, and the water the crop transpires. The most efficient systems handle both with a single integrated design that cools, dehumidifies and reuses the rejected heat, rather than letting air conditioning and dehumidifiers fight each other. Compare options on the same duty with clear metrics: kWh per kg of water removed, kWh of HVAC per kWh of lighting, and ultimately HVAC kWh per kg of produce, across both lights-on and lights-off periods.
Quick answer
- Size for both heat (lighting) and water (transpiration), at lights-on and lights-off.
- Integrated cooling + dehumidification + heat reuse beats separate systems fighting each other.
- Compare on kWh per kg of water and kWh per kg of produce.
The two loads
- Heat: almost all LED, pump and fan power becomes heat in the room.
- Water: crop transpiration ≈ irrigation − drainage, which must be removed from the air.
See the worked balance in vertical farming equipment.
System options
| Option | How it works | Strengths | Weaknesses |
|---|---|---|---|
| DX or split AC + standalone dehumidifiers | AC handles heat; dehumidifiers handle water, especially at lights-off | Simple, modular, lower first cost | AC and dehumidifier heat interact; control coordination needed |
| Chilled-water air handlers with reheat | Chilled coil cools and dehumidifies; reheat restores temperature | Central plant efficiency; precise control | Reheat energy unless reclaimed heat is used |
| Heat-pump systems with heat recovery | Dehumidify on a cold coil and reuse condenser heat for reheat | Uses rejected heat; efficient dehumidification | Higher complexity and first cost |
| Ducted dehumidifiers with dedicated cooling | Dehumidifiers supply dry air through ducts per tier; cooling separate | Even air to each tier; flexible | Duct design and fan energy |
| Outdoor air economisers (where climate allows) | Free cooling with filtered outdoor air | Low energy in cool, dry climates | Brings in humidity, pests and pollutants; CO₂ loss |
Lights-off is the critical period
When lights switch off, the cooling load collapses but plants keep transpiring. AC that is controlled on temperature stops removing water. Dedicated dehumidification sized for the lights-off load prevents humidity spikes and condensation on cold surfaces.
Metrics for a fair comparison
| Metric | Use |
|---|---|
| kWh per kg (L) of water removed | Dehumidification efficiency at the room condition |
| HVAC kWh ÷ lighting kWh | Overall climate system efficiency |
| HVAC kWh per kg of produce | Business-level comparison |
| Hours outside target | Control quality |
Compare all options at the same room conditions, crop load and operating schedule.
Ways to save HVAC energy
- Use efficient LEDs (less heat per µmol of light).
- Raise cooling coil temperatures where dehumidification is handled separately.
- Reuse condenser heat for reheat or water heating.
- Recover condensate for irrigation.
- Seal rooms to cut infiltration and CO₂ loss.
- Control on VPD rather than fixed temperature and RH bands, within crop limits.
What a supplier comparison should contain
- Heat and moisture load for lights-on and lights-off.
- Equipment capacity at room conditions.
- Total power for all components.
- Control sequence for transitions.
- Air distribution to each tier.
- Expected kWh per kg of water and per kg of produce.
Our ceiling-mounted and ducted dehumidifiers handle the moisture side in multi-tier rooms; see grow room dehumidifier sizing.
FAQ
Frequently asked questions
What HVAC system is best for a vertical farm?
An integrated system that removes heat and water together and reuses rejected heat is usually most efficient; modular AC plus dehumidifiers is simpler and cheaper to start.
Why do vertical farms need dehumidifiers if they have air conditioning?
Because AC removes water only while cooling; at lights-off, cooling stops but transpiration continues.
How do I compare vertical farm HVAC efficiency?
On kWh per kg of water removed and HVAC kWh per kg of produce, at the same conditions.
Sources
- ASHRAE Handbook—HVAC Applications; HVAC Systems and Equipment.
- Wageningen University & Research, Plant factories: crop transpiration and energy balance.
