Short answer: there is no fixed temperature difference between a greenhouse and the outside air. The gap changes with solar radiation, time of day, covering, air leakage, vent opening, wind, crop canopy, thermal mass and active heating or cooling. A useful answer needs the hour, weather, operating state and sensor locations.
Separate passive temperature rise from active control
An unheated closed greenhouse can warm quickly in sunlight because incoming solar energy heats the crop, floor and equipment while the enclosure limits air exchange. At night or under cloud, that solar input falls. The inside temperature can approach the outdoor temperature unless stored heat, insulation or active heating supplies the loss.
An actively controlled greenhouse is a different problem. Heating, vents, fans, shade, evaporative cooling and screens respond to setpoints and weather limits. The design question is whether those systems have enough capacity and a workable sequence to keep the crop within its allowed range.
Five inputs explain most of the temperature gap
| Input | Why it changes temperature | What to record |
|---|---|---|
| Solar gain | Shortwave radiation absorbed inside becomes heat | Outdoor radiation, shade position, covering condition and time |
| Air exchange | Vents, fans, leakage and wind replace indoor air with outdoor air | Opening position, fan stage, wind speed, wind direction and pressure state |
| Envelope heat loss | Covering, joints, perimeter details and screens affect heat transfer | Installed assembly, leakage condition and screen position |
| Crop and water | Transpiration and evaporation convert sensible heat into latent heat | Crop area, growth stage, irrigation event and humidity |
| Active equipment | Heating, cooling and circulation add or remove heat and moisture | Equipment stage, capacity, setpoints, alarms and measured output |
A single average can hide the dangerous hours
Daily averages can look acceptable while the crop experiences a short midday heat peak or an early morning cold event. Record at a consistent interval and review the maximum, minimum, duration outside the crop range and the system state during each event.
The University of Georgia gives ventilation examples in which changing the air exchange rate changes the temperature rise. Those figures describe a stated greenhouse and ventilation condition. They are useful for understanding the relationship, not as a universal promise for every structure.
Measure before changing equipment
Use calibrated sensors at representative crop height, not only near the controller or above the canopy. A large connected house may need several zones because sun, wind, crop stage and equipment distance vary across the floor. Place a shielded outdoor reference sensor where it is not heated by the wall or direct sun.
For each temperature event, save the outdoor condition, vent and screen positions, fan or heater stages, irrigation events and alarm history. That record shows whether the limit came from equipment capacity, control logic, sensor placement or an operating decision.
Turn crop ranges into a load and control brief
Start with crop-specific day, night, humidity and light ranges, plus the allowed duration outside them. Add an hourly weather file, project elevation, covering assembly, leakage assumption, crop area and equipment schedule. The designer can then estimate peak heating and cooling loads and test control stages.
Coordinate the greenhouse environmental control system with the automation and alarm scope. Ask for a written control narrative that covers normal weather, high wind, rain, sensor failure, power loss and manual operation.
Temperature-control RFQ inputs
- Project coordinates, elevation and the weather data or design conditions to use.
- Crop, growing method, production months and allowed temperature and humidity ranges.
- Covering, screen, vent, fan, cooling, heating and circulation selections.
- Sensor types, locations, calibration method, logging interval and alarm delivery.
- Control stages, deadbands, weather interlocks, manual overrides and safe states.
- Available power, fuel, water and backup duration for critical equipment.
- Required calculations, commissioning tests and operator training records.
Engineering boundary: this article does not state a fixed inside-outside temperature difference or size heating and cooling equipment. A project calculation must use local weather, crop limits, installed materials, ventilation, system capacity and applicable codes.
Technical references
- University of Georgia: Greenhouses, Heating, Ventilation and Cooling
- Washington State University: Greenhouse Construction and Management
- UMass Amherst: Natural Ventilation in Greenhouses
Need a temperature-control quotation? Send the weather basis, crop ranges, covering, vent plan, utilities and backup requirement to info@cfgreenhouse.com. The proposal can then state its load assumptions and control boundary.