What is hot gas reheat?
During mechanical cooling and dehumidification, a refrigeration system absorbs heat from the return airstream and rejects heat on the high side of the cycle. A hot gas reheat HVACD system redirects an engineered portion of that available heat to a downstream reheat coil after the evaporator.
The evaporator cools the air below its dew point so water condenses and drains away. The reheat coil then raises the temperature of the dried air before it returns to the room. Modulation allows the PLC to match reheat output to room demand instead of operating as a simple on/off function.
Sense
Read room temperature, relative humidity, and dew point.
Condense
Cool the airstream below dew point to remove latent moisture.
Reheat
Redirect available compressor heat to temper the dried air.
Control
Modulate refrigeration, reheat, and airflow around the room strategy.
Why hot gas reheat matters in cannabis cultivation
Cannabis rooms frequently need dehumidification when they do not need additional cooling. This occurs during lights-off, late flower, cool outside conditions, and other low-sensible-load modes. A conventional cooling coil may remove moisture but deliver air that is too cold, causing the room temperature to fall or forcing a separate heater to operate.
Integrated hot gas reheat coordinates those functions inside one HVACD platform. The control system can continue latent removal while using reclaimed refrigeration heat to maintain the supply-air and room-temperature strategy.
Hot gas reheat compared with electric or gas reheat
Reclaimed heat is not literally unlimited or universally “free.” Compressor power is still required, and available reheat capacity varies with operating conditions. The project load model must confirm the required dehumidification and reheat duty. When properly applied, hot gas reheat can reduce or avoid separately purchased electric or gas reheat energy for the modeled operating modes.
Modulation and dew-point-priority control
Equipment hardware alone does not create a stable environment. The internal PLC coordinates cooling, moisture removal, hot gas reheat, airflow, staging, setpoints, and alarms. Dew point provides a direct indication of air moisture content, helping the system distinguish a moisture problem from a temperature-only problem.
That sequence supports tighter control of temperature and humidity and provides a clearer path to the grower’s VPD strategy. Final control points, sensor locations, integration, and redundancy are configured for the room and facility.
Engineering inputs for a hot gas reheat HVACD design
- Room dimensions, envelope, location, and outside design conditions
- Lighting wattage, schedule, and sensible heat load
- Canopy area, irrigation basis, and latent moisture generation
- Temperature, RH, dew-point, and VPD targets by operating mode
- Airflow, supply and return layout, filtration, and pressure requirements
- Electrical service, utilities, access, redundancy, controls, and service strategy
Hot gas reheat questions
Does hot gas reheat use waste heat from the compressor?
It reclaims available heat from the refrigeration cycle that would otherwise be rejected. The usable amount depends on system operation and must be evaluated against the room’s reheat requirement.
Can hot gas reheat control humidity without overcooling?
Yes. Air can be cooled below dew point for moisture removal and then tempered before returning to the room. Proper coil selection, modulation, airflow, and controls are essential.
Is hot gas reheat only for cannabis grow rooms?
No. The same principle can serve vertical farms, controlled-environment agriculture, dry and cure rooms, research spaces, and other facilities with simultaneous temperature and humidity-control requirements.
Engineer hot gas reheat around the room
Request a custom load review, HVACD concept, and quote using your actual room, lighting, moisture, climate, and operating targets.
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