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The engineering behind the greenhouses microclimate

The engineering behind the greenhouses microclimate

Heating and Cooling

Heating

Greenhouses create a protected environment for plants by using solar radiation to trap heat. This heating and air circulation system helps create an artificial environment in a greenhouse that can support plants when the outside temperature is too cold or changeable. The heat enters the greenhouse through its glass or plastic cover and begins to heat the objects, the soil and the plants inside. The warm air near the ground begins to rise and is immediately replaced by cooler air which begins to heat up. This cycle increases the temperature inside the greenhouse faster than the outside air, creating a warmer and more protected microclimate.

In temperate climates, the sun can heat the entire greenhouse, but when temperatures drop, artificial heat may be needed to keep temperatures above freezing. When some greenhouses have access to the central heat of the main building, others must use natural or bottled gas, heating coils or heating fans. Usually, these will work in conjunction with a thermostat. Because heat is one of the most important expenses for maintaining a greenhouse, other sources of energy are always explored, such as the use of solar or animal batteries as heat sources.

How greenhouse get warm?

There are also other processes that act in the air inside a greenhouse. Energy from the sun can easily travel through the glass in the greenhouse, but the radiation from plants and heat absorbing soil is not released as easily, which helps trap heat inside. .

This will keep a greenhouse warm, but it can also cause overheating problems. To prevent the plants from getting too hot, a method of heat control is necessary. The vents that allow lighter, warmer air to exit the greenhouse near the ceiling and cooler air closer to ground level act like air conditioning. Adequate ventilation keeps the air in a circulating greenhouse. This helps maintain a stable temperature and also circulates the carbon dioxide (CO2) that plants need for photosynthesis.

Greenhouses usually have at least two vents, one near the roof and one in the lower half of the structure. Mechanical fans can also help maintain good airflow and heat control by automatically opening and closing vents when the temperature in the greenhouse changes.

Cooling

Good ventilation = good air circulation.

And good air circulation means better gas exchange and temperature regulation. This is important in any greenhouse and is very easy to set up.

Most greenhouses are built with fans and windows already present. Otherwise, you may need to open a door and use your own fans. It doesn’t have to be a sophisticated configuration to work!

Using shade cloth

A thick shade cloth or an opaque structure on your aquariums will do you two favours:

  • First, it will minimize algae, which only needs a small amount of light for photosynthesis.
  • Second, it will help regulate the temperature of your aquariums. I cannot overstate the importance of this. Your aquariums have most of the thermal mass of your system.

Evaporation cooling

Greenhouse cooling pad

Evaporation is relatively inexpensive and is very effective in drier climates. This cooling method usually uses a cooling pad with fans. Water is pumped from the pads and evaporates into the air, cooling the surrounding area.

Fog cooling

Mist sprinklers

Fog is a method in which water is tarnished or tarnished from the roof of the greenhouse to your crops. As a rule, misting nozzles or sprinklers should be installed. This method can be useful in certain situations, but it is not main recommendation.

Excess moisture can encourage fungus and the mists are short-lived. However, if you have already installed sprinklers or nozzles, this can be a great tool in emergency situations as it quickly lowers the temperature.

Evaporation and misting will only work in dry climates. In wetter climates, air conditioning is one of the options available to you.

Low grade geothermal cooling

Low-grade geothermal heating and cooling is one way of storing and distributing the earth’s thermal energy. In hot climates, air flows through underground pipes, where water vapour condenses and the air cools. It is recirculated in the greenhouse, leaving behind heat and humidity.

How to calculate Cooling capacity of a product?

The “cooling power” of a product can be listed in two different ways:

A BTU calculator will tell you the cooling power you will need. Some products indicate the power in BTUs they have in the description. Other products give the degrees of cooling they are capable of.


For example, The description of the product of a certain cooling pad (see photo on the right) may say that it is capable of reducing the temperature of the greenhouse by 10 to 20 degrees if the cooling pad is spread over the entire length. sidewall.

However: the cooling effect of this buffer will be less for a greenhouse fifty feet wide than for a greenhouse ten feet wide. Do you know what I mean?

Another factor that will influence the effectiveness of evaporation pads, fogging, etc. is humidity. The drier the environment, the more efficient these types of coolers will be.

Carbon Dioxide enrichment (CO2)

The CO2 enrichment of greenhouses allows crops to respond to the photosynthesis potential. CO2 can be enriched in the air by burning natural gas or liquid CO2. Adding additional carbon dioxide is a method often used to increase the yield of greenhouse crops.

CO2 Generator
CO2 Generator

The amount of carbon dioxide in outdoor air is, depending on its location, 350 parts per million. This is enough for plants to grow, however, when many plants are placed together in a greenhouse, carbon dioxide levels decrease because all plants use carbon dioxide for photosynthesis. By adding CO2 (CO2 enrichment), it is possible to increase the photosynthetic potential of crops, especially on sunny days.

CO2 Enrichment can be achieved by Different Method

  • Intake of cigar (liquid CO2)
  • Combustion of fossil fuels with air heaters.
  • Combustion of fuels with a central burner, in combination with a heat storage tank.

The addition of CO2 can lead to local variations in the CO2 concentration throughout the greenhouse because the concentration decreases from the source to the sink. Horizontal and vertical gradients under ambient conditions are disadvantageous but inevitable. The most important thing is to avoid a decrease in the homogeneity of plant growth and agricultural production.

CO2 Generator
CO2 Generator

For example, with a distribution network, a high concentration of CO2 is found near the distribution pipes and a low level near the ridge or near open ventilation windows. In Dutch greenhouses, CO2 distribution lines are placed under the cultivation gutter, near the crops. With the natural diffusion of carbon dioxide to the top of the greenhouse, plants will certainly benefit from CO2 enrichment.

The most common method of CO2 enrichment for greenhouse applications is the burning of fossil fuels. The combustion gases used must not contain dangerous amounts of harmful components. Therefore, the most widely used gas for CO2 enrichment in Dutch greenhouses is natural gas. With the combustion of 1 m3 of natural gas, approximately 1.8 kg of CO2 is generated.

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