• design criteria

designing professional greenhouses

agrimec designs professional greenhouses: our experience allows us to analyse our customers’ needs so as to recommend the most suitable greenhouse, guaranteeing that it maintains the right temperature, humidity and light for your crops.

the climatic parameters
A good greenhouse must be able to limit the sudden and excessive climatic variations (air and soil temperature, relative humidity) in relation to the ideal values.

A greenhouse which mostly uses solar energy to meet its energy demand, must:
  • Have a low summer and winter thermal load
  • Keep soil temperature constant
  • Use electric and thermal energy efficiently
  • Monitor the main environmental parameters which regulate plant growth: ambient temperature, relative humidity, light and CO2.
holding heat
To be able to meet the energy demand, a greenhouse needs to keep the soil temperature constant, lukewarm in the winter and cool in the summer, minimising heat losses from the ground. The soil in a greenhouse is the ideal place to store precious heat, even when not cultivated.
the main environmental parameters
ambient temperature
The ambient temperature can be monitored through an efficient ventilation system and, when possible, an adequate air conditioning system, avoiding values harmful for the crops.
how to limit heat loss
The greenhouse exchanges heat with the external environment in several ways:
By conduction through the ground
Entità: 10% delle perdite complessive.
Per serre di dimensioni più contenute, gli effetti di bordo possono essere alquanto significativi. Il suolo stesso perde calore cedendolo all’ambiente esterno perimetrale. Intervento consigliato: isolamento perimetrale e/o sotterraneo.
By upwards radiation
Entità: 25% delle perdite complessive.
La serra dispone di un soffitto trasparente e pertanto una certa quantità di energia accumulata dal terreno e dalle piante viene irraggiata verso il cielo. Il manto di copertura deve essere quindi trasparente rispetto alla luce d’ingresso e il più opaco possibile nei confronti della radiazione infrarossa emessa dal suolo. I teli di polietilene sono poco opachi alla radiazione IR e quindi è un intervento consigliato installare un telo riflettente (schermo termico).
Through air exchange
Entità: 25% delle perdite complessive.
Il ricambio dell’aria è necessario per il controllo della temperatura e dell'umidità. Ricambiando l’aria viene espulsa aria umida dalla serra, sostituita con aria più secca. E’ bene precisare che un ricambio d’aria effettuato aprendo le finestre o mediante estrattori d’aria comporta la perdita di una consistente quantità di energia termica.

Interventi consigliati:
- ricambi d’aria più efficienti quando necessario;
- ridurre al minimo le perdite di calore dovute a sfiltrazioni involontarie, agendo sull’ermeticità della serra
By conduction and convection through the walls
Entità: 40% delle perdite complessive.

Interventi consigliati:
  • Porre attenzione agli aspetti dimensionali che incidono sulle dispersioni di calore: meglio un’unica serra di grandi dimensioni piuttosto che frammentata in numerose piccole serre;
  • Con un corretto orientamento: il suo asse deve essere nord-sud;
  • Limitare le superfici disperdenti agendo sul profilo dell’arco e sulla planimetria;
    Scopri la soluzione adottata da Agrimec
  • La giusta altezza per controllare l’effetto serra e il conseguente innalzamento delle temperature, senza esagerare: una serra troppo alta è un investimento inutile;

    Altezza ottimale (H) consigliata: tra 3 e 4 m Una serra alta è in grado di creare un ambiente più fresco, uno spazio meglio fruibile. Comporta inoltre costi di riscaldamento poco più elevati. Studi effettuati su serre (T. Foulard and H. Fatnassi, INRA-Unité URIH (France), “New models help optimise greenhouse design”, in FlowerTECH 2006, vol. 9/n.6) hanno dimostrato che la temperatura interna dell’aria decresce all’aumentare dell’altezza fino a 4 metri e che dopo tale quota i miglioramenti diventano poco significativi.
  • Limitare le discontinuità dei materiali di copertura al fine di ridurre l’incidenza dei ponti termici;
  • Ricorrendo ad un manto di copertura che garantisca un ottimo isolamento: materiali che dispongano di intercapedine; Agrimec consiglia l’uso del doppio telo gonfiato.
relative humidity
This is a source of the main diseases, obliging greenhouse growers to intervene with fungicides and pesticides, often systemic, or else to resort to abundant air exchanges, which nullify the benefit of the greenhouse or heating effect, wasting a considerable amount of heat to the outside. Relative humidity in the air must exceed 60% to allow the stomates of the leaves to open up enough, for maximum absorption of CO2; too high RH values are detrimental as they restrict the transpiration capacity of the plant.
how to facilitate control of relative humidity
Managing humidity is a key factor in the fight against parasites. This is crucial to keeping branches and leaves dry during the night, when humidity and lower temperatures can form condensation on the plants and the onset of diseases.
air circulation
The use of anti-air-stratification appliances prevents the build-up of heat in the greenhouse vault and thus the formation of humidity pockets in the lower areas. Condensation can be limited to the simple movement of air to keep the leaves dry.
It is not easy to create a well-insulated environment and at the same time to attenuate the entry of light as much as possible. Light is essential for photosynthesis. A precise illuminance corresponds to a precise ideal temperature. This means that indiscriminately keeping high temperatures in the greenhouse is totally unwarranted. Too high of a temperature also leads to a drop in relative humidity and the consequent closing of stomates, namely suffocating the photosynthesis reaction. Day and night therefore have different illuminance levels and also different setpoint temperatures;
ideal growth of the plant (a bit of chemistry)
The plant develops properly when the two processes are balanced:respiration (absorbing O2 from the environment and releasing CO2) and photosynthesis (synthesis of sugar with the absorption of H2O e CO2 in the presence of light and release O2):

6H2O + 6CO2 + light energy -> C6H12O6 + 6O2
how to maximise brightness levels
Sodium-vapour lamps (HPS) were used in the past as lighting to grow plants: low cost, rather efficient, but without selection and therefore with high consumption and high power engaged.
Keep in mind that in winter the concentration of carbon dioxide inside greenhouses is constantly much lower than the outside atmosphere (300 ppm) due to limited ventilation. Photosynthesis is limited with too low a concentration. Most plants stop growing below 150 ppm. An artificially induced increase in CO2 percentage (carbon fertilisation) rising concentration to 1000 ppm, can promote growth up to 40%, affecting both quality (more strength, greater uniformity and resistance to diseases) and quantity (better yield, more luxuriant plants, greater size, number and weight of the products).
the greenhouse arc
agrimec structures are designed and built with a semicircular arc vault.
This choice, widely developed and tested through the years, carried the following advantages:
  • Response to wind: vertical lift and not cross thrust
  • Less dispersing surface
  • Greater service height at the same maximum height
  • Improved film inflation
  • Less film wear
  • Still good snow discharge
Agrimec recommends, when possible, to build a square greenhouse, which, for the same volume reduces dispersing surfaces to a minimum.
Agrimec S.N.C. di Spelgatti & C.
Via Fratelli Calvi, 1
24060 Casazza (BG)

tel. +39 035 810747
fax. +39 035 812679
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