Support documentation

Principle

Supplementary lighting is used to increase the total daily light.  Light intensity, spectrum and duration affect several plant growth and processes. There are several reasons for providing supplementary lighting:

• When natural light is scarce, it helps to increase yield and production quality such as tomato …
• Supplementary lighting is also applied for day length control in ornamental crops.

With Hortinergy, you have two types of lighting systems : the first one is called “High Pressure Sodium” (HPS) and the second one “Light Emitting Diode” (LED).

LED light :

Pros :

-long life expectancy

-almost no excess heat, which allows it to be placed very close to plants

-low operating/maintenance cost

-high yield per Watt

Cons :

-high initial cost

HPS light :

Pros :

-low initial cost

Cons :

-the high intensity of light from this lighting system generates a lot of heat

-additional cooling system is needed

-high operating cost

Input parameters with Hortinergy

Input parameters are:

• LED and HPS specification: lighting intensity, efficiency…
• Regulation setpoints:
  • Day Light Integral (DLI) and minimum hours of ‘’night’’ per day,
  • or fixed monthly schedule above which solar radiation intensity lighting is switched off.

You first define you lighting system:

Then you define the regulation settings:

Results

Hortinergy simulates your project during one year like a virtual greenhouse. Outputs are :

• Solar radiation transmitted by the transparent cover and reaching canopy,
• Assimilation lighting required according to regulation setpoints (mol/m²/day):
• Electricity consumption,
• Impact on the inner climate and energy consumption: heating, cooling, dehumidification.

The reports are:

• a pdf document with typical days and monthly summary tables
• an Excel file with hourly data for deeper analysis.

Solar radiation reaching canopy and additional assimilation lighting required

Hortinergy simulates on hourly basis the solar radiation reaching canopy and the additional assimilation lighting required to reach the DLI.

The example below shows a monthly summary.

Impact on the inner climate and energy consumption (heating, cooling, dehumidification)

Hortinergy models the impact of assimilation lighting on the inner climate and energy consumption (heating, cooling, dehumidification).

The example below shows the crop transpiration and a higher inner temperature when HPS assimilation lighting is switched on from to 9 to 11 AM and 4 to 9 PM to reach DLI.

Electricity consumption and expenditures

Hortinergy shows also the electricity consumption and expenditures.

Hortinergy offers two heat production settings :

– Hortinergy’s estimate

– User defined (advanced parameters)

On the one hand, Hortinergy’s estimate takes into account one energy system, accompanied by its type and cost, considering also an efficiency of 95% of the boiler. Max power of the boiler is also calculated by the software. With it, you might choose one main energy and its cost, followed by its currency.

On the other hand, the option user defined puts forward two energy systems. Each of them can have different types of energy and advanced parameters : heating period, the maximum power that will be used, the presence of a condenser or not and the boiler efficiency.

As said before, for each system, you have the choice between several types of energy. The most common ones are gas and biomass.

If there is not any open buffer and the demand is superior than the maximum energy power of the main system, the second type of energy is turned on. In case there is an open buffer, if the request is superior than the maximum energy power of the main system, then it will unload. Once it is void, the second energy is engaged to replace it.

Heat pump enters COP as an efficiency and chooses electricity. For instance, a COP that is equal to 4 represents an efficiency of 400%.

CHP is based on heat production efficiency, generally set at 44%. Besides, it also calculates overall gas consumption.

Regarding water buffer tank, there are two utilisations : the first one with gas boiler and the second one with biomass/waste heat boiler.

Gas boiler : the container stores the heat energy generated in the gas boiler during daytime CO2 supply, when heating demand is the lowest.

Waste heat boiler : it uses the heat in flue gases from combustion processes or hot waste air flows from industrial processes to generate hot water.

For more information about water buffer tank, you can have a look at our support documentation.

Distribution efficiency :

It represents the heat losses in the transport between the boiler and the greenhouse. By default value, these losses amount to 5%, which represents a distribution efficiency of 95%.

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.

Humid air is taken in from the greenhouse, through the side panels, and travels over the cooling coils, which circulate the cold refrigerant. Then, water vapor condenses as it comes into contact with the cold coil. The liquid water that forms is channeled out of the unit. This distilled water may be collected and reused.

The dry air is then transported over hot coils, made hot by compressed and heated refrigerant. Passing through this second coil heats the air back up to greenhouse temperature. The dry air is released through the top of the unit, hitting the canopy, which spreads the dry air above the plants.

This system is more suitable in cold regions than hot ones.

For more details : http://www.drygair.com

How does it work ?

The corridor, located on the outer gable of the greenhouse, uses outside air for dehumidification and cooling. Thus, the corridor is used to mix inner air with external air. This phenomenon represents the air treatment of semi-closed greenhouses, mostly used for Venlo glass (Kubo, Van der Hoeven, Richel, CERTHON…) and plastic (CMF, Richel…) ones.

This system aims to :

-dehumidify the atmosphere of the greenhouse by renewing and drying out the air inside, due to outdoor air (during the night and in the morning)

-cool dry inner temperature with pad cooling system, on external side of the corridor

-reduce the amount of harmful insects, thanks to overpressure

-control the climate of the greenhouse avoiding the gap of temperatures

-optimize the use of energy and CO2

Heating system is composed of :

-air ducts below crops’ gutters for the diffusion of warm/cold air

-low temperature network (30-40°C) placed in vegetation

-high temperature network (70-80°C) placed on the ground to ensure heating

Cooling system could be composed of :

-pad and fan system using evaporative cooling

-fog system using evaporative cooling

Imagine a battery of energy that is ready to be distributed at any time.

There are two utilisations of a water buffer tank : the first one with gas boiler and the second one with biomass/waste heat boiler.

How does it work ?

Gas boiler : the container stores the heat energy generated in the gas boiler during daytime CO2 supply, when heating demand is the lowest.

Waste heat boiler : it uses the heat in flue gases from combustion processes or hot waste air flows from industrial processes to generate hot water.

What are the Hortinergy parameters ?

The volume of a buffer tank is generally around 300 m³ per hectare.

As regards temperature variation, it is calculated according to the difference between the heat production temperature and the heat emission temperature of the boiler.

For instance, if the heat production of the boiler is 85°C and the heat emission temperature is 60°C, the temperature variation equals 85-20=65°C.

Hereunder a case study of biomass boiler’s heating demand, the buffer tank running on 410 kW.

On the one hand, the periods during which heating demand is under the main energy allow the water buffer tank to warm up. For instance, in this graphic, the water buffer tank is storing heat energy from 10 am to 3.30 pm.

On the other hand, during the rest of the day, when heating demand is above the main energy, water buffer tank is providing continuously heat energy to the system in which it is installed.

As the pad and fan system, it uses evaporative cooling method to cool down greenhouse temperature.

How does it work ?

Clear water is pushed through a stainless steel nozzle. Then, the particles of this water are evaporated before they reach the crops. This system works with a pump unit fitted with a high pressure pump. Nevertheless, it has to be mounted at the right height, according to climate conditions. Lastly, nozzles should be mounted alternately for a homogeneous coverage.

What are the Hortinergy parameters ?

Pros :

-natural cooling (it regulates temperature to a very high extent in situations where ventilation is not enough, thereby decreasing inner temperature when needed + less C02 will get lost and a higher amount will be available for crops to grow)

-minimal water use (thanks to the regulation of temperature and humidification)

-optimal humidity

-small droplets (micron) lead to a higher droplet density

Cons :

-this technology hugely depends on climatologic conditions. Indeed, if it is too wet, the system does not work effectively.

How does it work ?

Pad and fan system cools down greenhouse temperature, using evaporative cooling (absorption of a large amount of heat, by the water, in order to evaporate). During hot summer days, it is an effective way, for small greenhouses, to cool, putting plants in the best climate conditions. Besides, this system uses exhaust fans to absorb air from outdoors into the greenhouse. Firstly, the air is blown through the pad, which constantly evaporates water, creating a cooling effect. Then, the fans blow the cool air into the greenhouse, leading to an overall drop in temperature.
Some greenhouses do require cooling at night, mostly in tropical regions. However, wet pad and fan system may not provide the desired results in tropical regions, where absolute humidity is often high during the night.
Indeed, when conditions outside are humid, pad and fan system loses effectivity and provides a much lower cooling capacity. This is because evaporative cooling relies on the difference between outdoor and indoor conditions.

What are the Hortinergy parameters ?

Pros :

-it keeps the greenhouse’s inner temperature cool permanently, providing lower temperature even during hot periods of the year

-it decreases temperature and increases humidity, thereby reducing transpiration of plants

Cons :

-the distance from pad to fan reflects uneven cooling pattern

-if the system operates unceasingly, the growth of crops will be probably uneven

-it is not effective in areas with high humidity (ex : coastal areas)