Traditions in the field of energy efficiency and the development of innovative products for ventilation, heating, and air conditioning have a history of over 20 years at „Tangra”. The manager of the company of „Tangra”, Eng. July Armianov, is among the pioneers in Bulgaria working on energy-saving solutions for ventilation systems. One of the first energy-efficient products he worked on, even before founding the company, were the “air-to-air” plate heat exchangers. The development and improvement of these products led to the creation of a series of energy-recovery units, successfully sold in several European countries. The experience gained in designing and manufacturing energy-saving equipment for ventilation and air-conditioning systems, combined with „Tangra’s” policy of developing energy-efficient and environmentally friendly products, inspired Eng. Plamen Zhelyazkov, a partner at „Tangra”, along with the company’s team, to begin creating biomass heating systems four years ago. For the past two and a half years, „Tangra” has been producing pellet boilers from the Tangra HP Aero series. Four years ago, „Tangra” conducted extensive market research across Europe and neighboring Balkan countries. Naturally, in addition to the huge potential regarding wood waste as raw material for pellets, the company also identified a significant market for these products in Europe. According to Eng. Zhelyazkov, this market is now beginning to emerge in Bulgaria as well.
Advantages of Tangra Boilers
By initiating the development of pellet boilers, „Tangra” aimed to achieve a simplified design, maximum efficiency and functionality, while meeting the needs of the majority of users in Bulgaria—primarily single- and two-family homes. Thus, the „Tangra” team began developing two boiler models: Tangra HP 25 Aero and Tangra HP 35 Aero, with maximum heating capacities of 25 kW and 35 kW, respectively.
The key factors in the design of „Tangra” boilers are:
- Ensuring a sufficiently large water volume in the boiler body, which eliminates the need for an additional buffer tank. Thanks to the boiler’s large water volume, the burner operates relatively infrequently over a long period, even under nominal operating conditions.
- A simplified and lightweight design that can be easily transported and installed. This saves time and effort for the installation company and reduces the installation cost for the client.
The Tangra HP 25 and Tangra HP 35 pellet boilers consist of two separate modules of identical dimensions – the boiler body and the pellet hopper. The method of heat exchange is an important feature of „Tangra”-produced boilers. Heat transfer occurs largely in the tube bundle, achieving a large heat exchange surface, thanks in part to the integrated turbulators. These turbulators ensure a high intensity of heat transfer between the water and the flue gases from the combustion bundles.
These spirals also serve as cleaning elements for the tube bundle. The complete self-cleaning of the boiler’s burner and tube bundle is performed automatically using a modern electro-pneumatic system, requiring no user intervention.
Working Principle
In the design of the boilers, the single-pass boiler principle was adopted due to its simplified construction and the absence of intermediate chambers.
The high quality of the combustion process in the boiler is ensured by additional ceramic elements installed in the combustion chamber. Few manufacturers choose to use ceramics in the combustion chamber due to the increased cost of the final product.
Their crucial role is to promote the complete combustion of unburned gases produced during the burning process. Upon heating to 700–800 °C, the ceramic elements emit heat that facilitates the combustion of all remaining unburned particles and oxides. As a result, the level of harmful gases is three times lower than the permissible European standards.
The burner of the Tangra HP Aero boilers was selected after a thorough review of numerous European burner manufacturers, with the company placing its trust in one of the most renowned—Effecta from Sweden. The burners in Tangra boilers use high-quality steel for the fuel tubes due to the high temperatures they reach (up to 900 °C). This creates optimal conditions for oxidation and the release of maximum oxygen to support combustion. One of the key design requirements for these boilers is that the burners can operate with pellets of any type and quality. This is extremely important for the performance of a pellet boiler because additional impurities or poor-quality pellets can hinder the combustion process and leave significant residues in many equivalent European boilers.
Today, the companies „Effecta” and „Tangra” are partners, and thanks to the trust they have built, they jointly implement improvements in the boiler control systems that „Effecta” manufactures and sells throughout Europe.
"Unfortunately, in Bulgaria, the quality of pellets as fuel is not very good," says Eng. Zhelyazkov. "When pellets are made purely from wood, they burn without forming clinker, producing only residual ash, which does not require additional cleaning of the burner. Unfortunately, in Bulgaria, it is more common for inert materials, stones, and other waste to enter the pellet production machines along with the wood residues. Because these materials do not burn properly, clinker forms, which, if the burner is not cleaned regularly, accumulates and causes the burner to stop working, leaving customers without heat."
When selecting a burner and seeking the best solution, the „Tangra” team chose burners manufactured by Effecta due to their unique compressed-air cleaning system. This system is controlled by the burner’s management unit and operates via specialized software. Parameters such as the number, frequency, and duration of the cleaning cycles can be programmed. The inclusion of all these features ensures the reliable operation of the burner with pellets of any type and quality. This is particularly important, considering that one of the most common complaints among pellet boiler customers in Bulgaria is burner shutdown caused by low-quality pellets.
The „Tangra” team further developed the electro-pneumatic burner cleaning system by integrating turbulators for cleaning the tube bundle, as mentioned earlier. In this way, both the burner and the boiler body are cleaned simultaneously. All of this provides the customer with the assurance that, under normal operation of the installation, their only responsibility is to supply pellets as fuel.
System Capabilities
The boilers are built on a modular principle – consisting of a boiler body and a pellet hopper. They are packaged separately and assembled on site, which greatly facilitates installation. According to Eng. Zhelyazkov, an average qualified technician can install a boiler into an existing heating system in no more than an hour and a half. Another advantage of the boilers is their compact dimensions, allowing them to occupy very little space. This makes it possible to install them directly against a wall or in the corner of a room without obstructing maintenance. The only requirement is a one-meter clearance in front to allow the doors to open.
In addition to the boiler and the hopper, various external devices can be added to the heating system as needed – such as circulation pumps, a three-way valve, a hot water boiler, and a buffer tank. The built-in controller in „TANGRA” boilers not only manages the combustion process but also controls all of these external devices. This means there is no need to build a separate control panel, since everything is fully operated and coordinated by the boiler’s controller.
Fuel Consumption and Operating Efficiency
The fuel consumption depends mainly on the heat losses of the building, as well as on each user’s preferences for their comfort temperature. Based on accumulated experience and monitoring of customer needs, Eng. Zhelyazkov shared that, under continuous boiler operation, the use of pellets for heating and domestic hot water averages between 3 and 5 tons. This includes heating for one heating season and year-round domestic hot water supply.
As for the efficiency of the combustion process, it varies from boiler to boiler. For the Tangra HP 25 Aero and Tangra HP 35 Aero pellet boilers, the actual efficiency reaches 94%, which can be demonstrated in real time. Moreover, the indicated outputs of 25 kW and 35 kW for „Tangra” boilers are maximum values and are capable of meeting the heating needs of almost all single- and two-family houses in our country.
The Next Generation of Pellet Boilers – Tangra CL 35
This year, at the Autumn Plovdiv Fair, the new Tangra CL 35 pellet boiler was presented for the first time, attracting significant interest. The reasons for this are its more competitive price and specific advantages of the equipment. In addition to the boiler body and the pellet hopper, both the burner and the control software are manufactured by „Tangra”, which substantially reduces the final cost. The complete development of the equipment and the software took the team about six months, but it incorporates numerous improvements based on the accumulated experience from the previous generation of „Tangra” pellet boilers.
The most significant differences are:
- Pneumatic burner cleaning system.
- An integrated flow meter in the burner measures the actual amount of air entering it and monitors combustion quality. It also enables automatic air regulation, independent of chimney draft or other external factors.
- The burner is set up once and operates with high efficiency in the same way, regardless of external conditions.
The new development by „Tangra” saves the customer approximately 25% of the equipment cost. As an additional option, the customer can choose an ash container for the pellet residue.
This is not the last innovation in „Tangra’s” development in this sector. In 2012, the company planned to develop a higher-capacity boiler, aiming to cover an additional segment and meet the requirements of clients with larger building installations, summarized Eng. Plamen Zhelyazkov.
„Tangra” offers the complete system of products and services for heating, covering the design and construction of a heating installation, as well as warranty and post-warranty service for each of these units. The company has an extensive distribution network of certified companies authorized to carry out installation and maintenance of the equipment.
Engineer Zhelyazkov’s recommendation to clients is to use the off-season for selecting a heating installation, although their services are sometimes used during the winter as well. Besides the crucial role of the system itself in ensuring comfort in the premises, he emphasized the importance of proper maintenance. Peace of mind in this regard can be guaranteed through a standard service contract with the installation company.
At the end of our conversation, he expressed his satisfaction with the work accomplished this year despite the economic and financial crisis, and he promised that „Tangra” will continue next year to develop more energy-efficient and environmentally friendly products in heating and ventilation.
