A Comprehensive Review of Condensing Boilers: Advantages and Applications

Condensing Boiler | raadman

As the demand for energy efficiency and reducing environmental impacts grows, the importance of employing advanced technologies in heating systems has become more important than ever. One of these advanced technologies is condensing boilers, which, by using energy optimization principles, provide much higher efficiency than conventional boilers. These boilers reduce fuel consumption by using the latent heat of water vapor in combustion gases, while providing greater efficiency. For an initial introduction to industrial boilers, it is recommended to review the article “A Comprehensive Overview of Industrial Boiler Types; Structures, Operations, and Applications “.

Condensing boilers, due to their unique design and high efficiency, are an ideal choice for a variety of heating systems, including residential heating, pools, and different industries. This article discusses the features, advantages, types, and uses of these boilers to illustrate how this technology can contribute to energy optimization and cost reduction.

What is a Condensing Boiler?

It is a type of advanced boiler that provides higher efficiency than traditional boilers by recovering the latent heat of water vapor found in the combustion gases. If the design of the boiler allows the temperature of the exhaust gases to drop below the dew point, the water vapor within these gases will condense and convert into liquid. If the temperature of the inlet water is lower than the dew point of the combustion products, the water vapor in these products condenses. During this process, the latent heat contained in the water vapor is released and transferred to the water inside the boiler.

By recovering this latent heat, the boiler can produce more heat with less fuel consumption, resulting in increased efficiency. The efficiency of condensing boilers can reach approximately 98%. Due to the direct contact of the condensed water vapor, which has acidic properties, with the pipes and chimney, it is necessary to use corrosion-resistant materials such as 316 stainless steel.

Operation of Condensing Boiler | raadman
A schematic of condensing boiler operation

Advantages of Condensing Boilers

Condensing boiler, due to its advanced design and use of energy optimization technology, offers several advantages, including:

Higher Thermal Efficiency: These boilers are more efficient than non-condensing ones due to the use of the latent heat of water vapor in exhaust gases.

Lower Fuel Consumption: This type of boiler leads to better energy utilization, resulting in reduced fuel consumption and lower energy costs.

Compact Design: Condensing boilers are typically compact and small, requiring less space in boiler rooms. They are particularly practical for limited spaces.

Lower Carbon Dioxide Emissions: The reduction in fuel consumption and enhanced energy efficiency result in lower carbon dioxide emissions. This characteristic helps reduce harmful environmental impacts and mitigates climate changes.

Types of Condensing Boilers

Condensing boilers can be structurally categorized into fire-tube and water-tube. Coil-type condensing boilers and compact condensing boilers fall under the water-tube category, which have been explained separately. The following sections focus on the fire-tube condensing boiler and its features.

Raika Condensing Boiler | raadman
Raika condensing boiler by Packman with raadman burner and AutoFlame control system

Coil-type Condensing Boiler

A coil-type condensing boiler is a water-tube type, where water flows inside the coils (tubes), and the combustion gases pass outside them. This boiler includes a configuration of spiral tubes through which the water flows. The water inside the coils is heated by absorbing energy from the burner flame and exits the boiler. Given the unique combustion chamber design, premixed burners are suggested for this type of boiler.

In these boilers, both premixed and nozzle mix burners can be used. Raadman modulating post mixed and premixed burners with premixed flames, along with Packman non-premixed nozzle mix burner, equipped with AutoFlame advanced controllers, help reduce fuel consumption. These burners prevent the flame from contacting the boiler tubes and reduce harmful pollutants.

Raika condensing boilers, manufactured by Packman, are of coil-type condensing boilers. Due to the design of combustion chamber, it is recommended to use gas burners for this type of boiler. Since the boiler tubes are in a direct contact with the low-temperature combustion products and have corrosive properties, it is necessary to use stainless steel tubes which are resistant to corrosion. Additionally, the stack of these boilers must be made from corrosion-resistant materials.

Raika Boiler | raadman
A schematic of Raika condensing boiler by Packman

Modern coil-type condensing boilers have a single chamber divided into two sections by a separator plate:

  • Combustion Chamber: The first section houses the burner, where the combustion process takes place. Hence, the first chamber is referred to as the combustion chamber.
  • Condensate Chamber: The second section, also referred to as the condensate chamber, is where the condensation process takes place. In this chamber, the latent heat of the steam is absorbed, which raises the temperature of the inlet water and ultimately improves the boiler’s efficiency.
Coil-type Boiler | raadman
A schematic of coil-type condensing boiler

Compact Condensing Boiler

These boilers, also known as condensing heat exchangers, are a type of water-tube condensing boiler with an advanced design. The premixed burner in these boilers is positioned at the top, creating uniform combustion. The hot gases resulting from combustion pass through a series of plates and finned chambers. These fins, arranged in sequential rows, expand the contact surface between the hot gases and the plates, significantly improving the heat transfer efficiency.

Water flows through specially designed channels within the boiler. These channels are arranged in such a way that the water flow direction is perpendicular to the flow of the hot gases. This cross-flow design maximizes heat exchange, leading to a significant improvement in heat transfer efficiency and the overall performance of the boiler. Only premixed burners are used in these boilers. Raadman modulating premixed and post mixed burners, manufactured by Packman, are a suitable choice for these boilers, complying with the latest global standards.

Compact Condensing Boiler | raadman
Compact condensing boiler and its components

Fire-tube Condensing Boiler

These are another types of condensing boilers, where the hot gases from combustion pass through the flue tubes (or fire tubes) and heat the water surrounding these tubes. These boilers are equipped with premixed burners and nozzle mix burners. The combustion chamber in fire-tube condensing boilers is designed to accommodate dual-fuel burners which can use both gas and liquid fuels. After passing through the combustion chamber, the hot combustion products enter the smoke tubes. In the smoke tubes, water vapor in the combustion products condenses. The resulting condensed vapor is then directed through an outlet to the drainage system.

The material of the smoke tubes in these boilers must be carefully selected. Due to direct contact with the acidic condensed water vapor, the typical tubes are susceptible to corrosion. Therefore, the smoke tubes must be made of corrosion-resistant stainless steel. Additionally, due to the corrosive nature of the combustion products in these boilers, the chimney material must also be resistant to corrosion.

Firetube Condensing Boiler | raadman
Three-pass firetube condensing boiler

Condensing Boilers Efficiency

Boiler efficiency is defined as the ratio of the useful thermal energy produced to increase the water temperature to the energy consumed from the fuel. The energy consumed from the fuel is measured based on its calorific value, which has two definitions:

  • Lower Heating Value (LHV)
  • Higher Heating Value (HHV)

Higher Heating Value (HHV): This refers to the condition in which the water vapor formed from combustion products is treated as liquid, thereby including the latent heat of vaporization of water. Since these boilers operate by recovering this latent heat, their efficiency should be calculated based on the higher heating value for a precise and practical assessment. This is known as gross efficiency, and it is always less than 100%.

Lower Heating Value (LHV): The claim of efficiencies exceeding 100% (or net efficiency) for condensing boilers is largely promotional. This efficiency is calculated based on the lower heating value (LHV), which does not include the latent heat of vaporization of water. For a more accurate and realistic evaluation, it is recommended to calculate the efficiency of condensing boilers based on the higher heating value (HHV), which represents the true efficiency of these boilers and can reach up to 98%.

Condensing Boiler Applications

Two common applications of condensing boilers are underfloor heating and pool water heating. Additionally, they play a crucial role in laundries, supply hot water for healthcare facilities, support the food industry, and provide heating for greenhouses.

Underfloor Heating

Condensing boilers, known for their high efficiency and capability to operate at lower temperatures, are an ideal choice for underfloor heating systems in buildings. In such systems, hot water circulates through the pipes embedded in the floor, gradually transferring heat to the surrounding area. Since the heating temperature is lower than the dew point of the combustion products, condensing boilers provide a suitable solution.

Another major challenge when replacing heating systems in old buildings with newer systems, such as underfloor heating, is selecting the appropriate boiler size. Due to the compact design of condensing boilers, choosing a suitable condensing boiler can effectively address this issue.

Pool Water Heating

These boilers are frequently used in heating swimming pool water because of their superior efficiency. They recover latent heat from the combustion gases, making them an energy-efficient option for pool heating. Additionally, their capability to operate at lower temperatures ensures that pool water is heated effectively while minimizing energy usage.

Condensing Boilers: An Optimal Solution for Heat Supply

As one of the most advanced heating systems, condensing boilers stand out for their high efficiency and reduced fuel consumption, making them an ideal choice for various industries. By utilizing the latent heat of water vapor, these boilers help reduce fuel consumption, energy costs, and emissions of pollutants. Packman, a reputable manufacturer of condensing boilers, assists industrialists in achieving efficient and sustainable heating systems by offering high-quality products and innovative designs. With a long-standing reputation in design and production of condensing boilers, Packman company offers solutions tailored to the specific requirements of its customers.

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