Grow-Room HVAC and Dehumidification Calculator

Cooling tons and moisture removal are different requirements. Hot-gas reheat can keep dehumidification from overcooling the room, but its BTU/h rating does not say how many pints of water the unit removes.

1. Enter fixture and room-equipment heat, outside air, known building load, and a sizing margin.
2. Choose the humidity-system type and enter the peak room moisture load plus manufacturer-rated removal at the actual room temperature and RH.
3. For hot-gas reheat, enter reheat BTU/h and airflow only to estimate supply-air temperature rise.
4. For power cost, use actual input kW when possible; otherwise use full-load EER/EER2, cooling COP, or kW/ton with measured runtime and dry output.

• Check both lights-on and lights-off conditions; plants can keep releasing moisture when lighting sensible load falls sharply.
• Do not remove standalone dehumidifiers merely because a unit has hot-gas reheat. First verify its rated moisture removal, turndown, controls, and redundancy.
• Use EER/EER2 only as a rough full-load electrical estimate. Below 65,000 BTU/h (about 5.4 tons), smaller equipment may also list SEER/SEER2; at and above that size, commercial equipment commonly lists EER and IEER. Seasonal SEER/SEER2 and weighted IEER are not exact grow-room design-point power.

This is a first-pass system comparison, not an HVACD design. Coincident sensible and latent loads, outside-air humidity, psychrometrics, duct losses, infiltration, defrost, controls, turndown, redundancy, and equipment performance at room conditions require a qualified designer.

Sources

• ASHRAE: What Controlled Environment Agriculture Demands of HVAC Systems
• U.S. DOE: Commercial unitary equipment efficiency metrics and size categories
• Desert Aire: Grow-room energy and hot-gas-reheat system behavior
• Desert Aire: Grow-room HVACD system selection guide