Principle
A greenhouse is « sealed » or « closed » when there is not any air exchange with outdoor air.
In order to maintain inner temperature and relative humidity of a closed greenhouse, heating, cooling and dehumidification systems have to be implemented, so that crop production can be realized in good conditions.
Cooling and dehumidification are usually done via heat-exchangers in the greenhouse. This enables higher CO2 concentrations in the greenhouse and consequently a higher crop production rate.
In some cases, a sealed greenhouse is linked to underground aquifer or very large buffer. During sunny or hot days, the surplus heat is stored in the short term (diurnal) buffers or long term (seasonal) storage in underground aquifers. During nightime or cloudy days, warm water from the aquifer or buffer heats the greenhouse.
What are the Hortinergy parameters ?
The maximum temperature and humidity settings, such as relative humidity and humidity deficit, have to be filled.
Once inner relative humidity is exceeded by relative humidity sets, latent cooling is engaged.
Cooling system will be activated so that inner temperature will not go above this set.
For instance, even though solar radiation is expected to rise the inside temperature significantly, the cooling temperature, set at 28°C during the day will prevent from exceeding this temperature.
Results
In turn, Hortinergy calculates the sensible and latent cooling needs to control the greenhouse inner climate (temperature and relative humidity).
Sensible cooling : it is the process in which only the sensible heat of the air is removed so as to reduce its temperature, without any change in the moisture content of the air.
Latent cooling : it is the capacity to remove the moisture from the air, without any change in the temperature of the air.
Based on the results, the engineer can design the best HVAC system and calculate energy consumption.
Hereunder a typical example from a report. Results are shown in three different ways.
First, as a monthly synthesis.
Then, as an hourly synthesis of a typical month.
Finally, hourly values during a typical year are referenced as OX-24h.
Sensible heat : it is the amount of heat exchanged, without any physical stage transition, between several bodies forming an isolated system.
Latent heat : it is the amount of energy exchanged between an object and its environment during a change of state, i.e. during solidification, fusion or boiling.
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