Heating is one of the fundamental requirements of greenhouses that directly impacts plant growth and production. As controlled environments designed for plant cultivation, greenhouses must maintain ideal growth conditions. Ensuring stable and sufficient greenhouse heating, particularly in colder months, is crucial. Well-designed greenhouse heating systems not only sustain optimal temperatures but also prevent excessive energy consumption and financial losses. Burners and boilers are key components of these systems, playing a vital role in improving efficiency and lowering operational expenses by supplying heat and carbon dioxide through CO₂ injection systems.
The project for equipping Bojaneh hydroponic greenhouse in Kurdistan was implemented using a Packman hot water boiler with a capacity of 5,000,000 kilocalories per hour, along with a Raadman dual-fuel burner (RLGB-M/M-805).
Significance of Greenhouse Heating
Maintaining an optimal temperature through greenhouse heating is crucial for plant growth, as inadequate heat can hinder growth and lower crop quality. An appropriate temperature not only enhances the taste, appearance, and shelf life of crops but also improves overall production efficiency. This is due to the fact that photosynthesis occurs more effectively at an optimal temperature, leading to higher productivity.
Moreover, carbon dioxide is essential for photosynthesis, and providing an adequate amount significantly improves this process. Low temperatures combined with high humidity create a favorable environment for pathogenic microorganisms, which can threaten plant health and reduce crop quality. Thus, effective heating and adequate CO₂ supplementation are crucial for maintaining greenhouse productivity and plant well-being.
Different Types of Greenhouse Heating Systems
Greenhouse heating systems can be broadly classified into central heating systems and local heating systems. Central heating systems are used for large greenhouses, where heat is distributed from a single source to different sections. In contrast, local heating is more suitable for smaller greenhouses, as it directly generates heat in special zones.
Central Heating System
A central heating system is a widely used method for greenhouse heating, relying on a hot water or steam boiler as the primary heat source. This system is centered around a dedicated boiler room, which houses essential components such as the boiler, burner, pumps, expansion tank, valves, and fittings—each playing a crucial role in ensuring efficient and reliable operation. The hot water or steam generated in the boiler is distributed through pipes to different sections of the greenhouse, providing the optimal temperature for plant growth by transferring heat to the environment. This central heating system is especially regarded as an efficient choice for larger greenhouses.
This greenhouse heating system can be divided into several categories: floor heating, bench heating, under-bench heating, and plant overhead heating.
Floor Heating
In this system, pipes carrying hot water or steam are positioned beneath the soil surface. This method transfers heat upward and is well-suited for greenhouses that require stable and uniform temperatures. Floor heating minimizes energy waste and is especially beneficial for keeping plant roots warm.
Bench Heating
In this method, pipes containing hot water or steam are laid horizontally on the surface of the benches or ground. The heat generated by these pipes is then transferred to the air around the plants, providing heat. This heating system is especially beneficial for plants that need gentle warmth, although it may incur heat loss due to the pipes being situated on the ground.
Under-bench Heating
It is a contemporary and effective technique within central heating systems. In this method, heating pipes are placed under the worktables or growing beds. Hot water or steam circulates through these pipes, directly transferring heat to the surface of the table or bed. This heat is delivered straight to the plants or crops without introducing additional heat into the greenhouse’s air.
Plant Overhead Heating
The overhead heating method is a type of central heating system in which heating pipes are placed above the plants or crops. This system allows heat to be released from the pipes into the air surrounding the plants. The advantage of this approach is the reduced risk of damage to the pipes, and it ensures an even distribution of heat across the upper section of the greenhouse. This method is ideal for greenhouses that require open working space.
Local Heating System
A local heating system is another type of greenhouse heating where heat is generated and distributed in a concentrated manner within a specific area. This system is mainly suitable for small greenhouses. Examples of this heating method include hot air furnaces and radiant heaters.
Hot Air Furnace or Greenhouse Heater
A hot air furnace, commonly known as a greenhouse heater, operates by drawing air from the greenhouse into the furnace using a fan. The air is then heated as it passes over the combustion chamber and heat exchange pipes before being released from the top of the heater back into the greenhouse. This cost-effective and straightforward heating method is particularly well-suited for small-scale and home greenhouses.
Radiant Heater
These heaters are usually mounted above the greenhouse, emitting heat waves that directly warm the plants, soil, and surfaces. Radiant heaters can operate using either gas or electricity. In gas-powered models, fuel and air mix within a steel tube, and the resulting combustion heats the tube’s surface. In electric versions, heating elements generate the heat waves. This method transfers energy directly to the targeted surfaces instead of heating the surrounding air, resulting in reduced heat loss, energy savings, and increased efficiency.
Role of Boiler and Burner in Carbon Dioxide Supply System
Boilers, in addition to providing the necessary heat for greenhouses, can supply the carbon dioxide required by plants. In other words, hot water or steam boilers are a source of carbon dioxide. Fuel or air is mixed in the burner, and after combustion, carbon dioxide is produced. If this combustion meets the standards for carbon monoxide (CO) and nitrogen oxides (NOx) emissions, it becomes a rich source of carbon dioxide. As shown in the diagram, increasing carbon dioxide concentration to an optimal level enhances the growth rate of plants, but excessive concentration can lead to plant toxicity.
Carbon Dioxide Injection System
Today, modern greenhouses utilize carbon dioxide packages to provide the necessary CO2 for plant growth. These packages draw from warm air rich in carbon dioxide, which is released from the boiler’s stack. The Planta system, developed by raadman group of Packman Company, is one such carbon dioxide injection system. In this system, the flue gas from combustion products must be cooled to a temperature of 60 degrees Celsius. When using condensing boilers, the flue gas temperature approaches 60 degrees Celsius, enabling the direct introduction of the exhaust into the greenhouse via a mixing tee.
The article titled “A Comprehensive Review of Condensing Boilers: Advantages and Applications” provides comprehensive information about condensing boilers. It is suggested to read this article for further insights.
In the case of using three-pass boilers, it is necessary to use a condenser to cool the flue gas temperature. After the flue gas passes through the condenser and is cooled to 60 degrees, it enters the mixing tee. The condenser used in greenhouse systems is the Rico condenser, produced by Packman Company.
To decrease the concentration of carbon dioxide and reduce the gas temperature to the desired level, fresh air is drawn into the mixing box on the air damper side. The suction of the flow into the package and the final mixing of gas and air are facilitated by the indicated fan. Ultimately, a mass of hot air with the desired temperature (around 50 degrees Celsius), containing carbon dioxide gas at a concentration set by the user, is released into the greenhouse space. It is clear that the system continually evaluates the levels of carbon monoxide and nitrogen oxides pollutants and keeps them below permissible levels within the greenhouse.
The Planta system features two advanced sensors designed to accurately monitor the quality of combustion products. If an excessive increase in CO or NOx levels occurs, the sensors promptly respond by shutting down the burner and the entire system to protect the greenhouse and plants from harm.
With an innovative design, low-NOx burners prevent high-temperature spots that contribute to the generation of NOx (thermal NOx) emissions. Designed for consistent flame patterns and precise temperature control, these burners effectively minimize harmful gas emissions. Their advanced combustion technology ensures an optimal fuel-air distribution, keeping flame temperatures within a safe range to prevent excessive thermal NOx formation.
In raadman low-NOx burners, these features have been enhanced to meet the demands of industrial heating systems. Precise engineering and high-quality materials improve thermal efficiency, reduce pollutant emissions, and ensure optimal and stable performance.
Hot Water Storage Tank (Buffer Tank)
When the greenhouse demands CO₂ but does not require immediate heating, the hot water from the boiler is stored in a buffer tank rather than being circulated into the system. Acting as a thermal reservoir, this tank ensures heat availability when necessary, enhancing energy efficiency and enabling the coordinated use of CO₂ and heat at optimal times.
Reasons for Using Modulating Burners in Greenhouse Heating
Modulating burners are considered an optimal and efficient choice for greenhouse heating due to their unique design and advanced features. They are particularly useful in large-scale and industrial greenhouses where precise temperature regulation and energy efficiency are critical. Raadman modulating burners, with a focus on high efficiency and precise temperature control, provide an advanced solution for greenhouse heating. By reducing energy consumption and producing fewer pollutants, these burners create a sustainable and optimized environment.
Primary reasons for implementing modulating burners in greenhouse heating are as follows:
Precise Temperature Control: The ability to adjust heating power according to the greenhouse needs, ensuring a consistent and stable temperature.
Energy Consumption Reduction: Optimized performance and deactivation of unnecessary components to save fuel.
Lower Emissions: Minimum production of NOx and CO to protect plant health and the environment.
Extended System Lifespan: Reduced wear and tear due to staging operation.
Flexibility: Compatibility with varying greenhouse needs and environmental changes.
Cutting-edge Strategies for Sustainable Greenhouse Heating
Greenhouse heating systems and CO₂ injection systems are essential for the successful operation of greenhouses. Providing appropriate greenhouse heating through central and local heating systems creates optimal conditions for plant growth and increases productivity. The use of raadman industrial burners coupled with Packman hot water or steam boilers ensures reliable and efficient operation while reducing energy use and emissions, thus promoting a healthy environment for plants.
Furthermore, the Planta CO₂ injection system by raadman industrial group uses the CO₂ generated in the boilers to improve the photosynthesis process, significantly contributing to plant growth optimization. This system ensures precise CO₂ concentration control while monitoring environmental pollutants like carbon monoxide and NOx, thus fulfilling the plants’ CO₂ requirements and maintaining the health of the greenhouse environment. In summary, the integration of raadman modulating burners, Packman boilers, and the Planta carbon dioxide injection system developed by the raadman Industrial Group offers a complete solution that boosts greenhouse efficiency and productivity, while simultaneously reducing costs and emissions.
