Natural Ventilation
- Kshiti Mishra (Deactivated)
- Gert-Jan Swinkels
The greenhouse can be passively cooled by opening the ventilation windows, or vents, to exchange air between the inside and outside of the greenhouse. (Note: natural ventilation means no use of fans - air is exchanged solely due to the buoyancy of the lighter, warmer air in the greenhouse which rises to the vents, and due to wind flow).
The vents are divided into leeward (facing away from the wind direction) and windward (facing towards the wind direction) vents : natural ventilation starts by opening the leeward ventilation windows first, and if they don’t provide enough cooling, the windward ventilation windows will open afterwards.
The energy removed by natural ventilation depends on :
Ventilation capacity (depends on amount, size, form and position of the vents), and
the prevailing conditions (wind speed and direction, and temperature and humidity differences between inside and outside of greenhouse)
Contribution to energy balance and resource use of greenhouses:
Provides a way to discharge excess energy out of the greenhouse by exchanging hot and humid air from inside the greenhouse with the colder, drier air from outside.
Along with releasing energy, vents also remove water vapour from the greenhouse, reducing the humidity. This may be undesirable in regions with water scarcity.
Vents also affect the CO2 balance :
In greenhouses with no additional CO2 dosing, opening the vents replenishes CO2 consumed by plants
In actively dosed greenhouses, venting leads to a loss of CO2 to the outside air
Possible steps towards sustainable, energy-efficient greenhouses
Venting helps to lower the greenhouse temperature by ‘throwing’ heat away to the outside air - if stored, this heat could instead be utilized, especially for temperate climates, during night/cold winter days, when fossil fuels have to burned to provide heating for the greenhouse.
Several Dutch greenhouses adapt a ‘semi-closed’ greenhouse model: here, active cooling and dehumidification are used to reduce excess energy in the greenhouse instead of solely using vents; Only on the warmest days, vents are opened on top of the cooling. Active cooling and dehumidification still require energy, which could be supplied by more sustainable sources than fossil fuels.
Additionally, heat-exchangers, heat pumps, and novel long-term seasonal heat storage options could be explored so that the energy removed from the greenhouse on warm days can be utilized to meet the heat demand during colder periods.
