Heat recovery

Condensation heat recovery of flue gas

For steam and hot water boiler rooms we make calculations and submit proposals to our customers concerning the energy saving (8-16 % in general) to be achieved by condensation heat recovery of generated flue gases.

The efficiency known in combustion technology can be determined as follows: Fuels are burned and based on the heat recovered in the boiler room efficiency is defined. The temperature of the flue gas can be calculated and measured according to chemical reactions. Considerable amount of water vapour in the flue gas is released as its temperature is far over 100 Co.

According to the reaction equation, the condensation to be extracted is about 15%. 

The summary of the special definitions is as follows:

  • Heat of combustion: heat released upon the complete combustion of normal unit gas if the water in the combustion product is of a liquid state.

  • Calorific value: a process under the before mentioned conditions, however, the water in the combustion product is of a vaporous state.

  • Consequently, the heat of combustion is higher by the heat of evaporation of the moisture content of the combustion product (flue gas).

Thus, a computer technology method can be applied where the efficiency calculated in consideration of the heat of evaporation is more than 100 %. Specialists have the responsibility of defining efficiency on the base of a single method that can be even 106 % for boilers equipped with condensation heat recovery unit when the same calculation is applied. Using the same calculation, such a value can be about 90 % for conventional boilers.

Operation of the system

The condensation heat recovery systems integrated in the boiler room are connected with the flues available in boilers. Flue gas is diverted by a ventilator with frequency regulation through a specially designed condensation heat recovery unit of stainless metal. Thus, the flue gas released can be cooled down even to 40-50 Co. The water vapour in the flue gas flowing through condenses on the surface of the heat recovery unit while the heat released therefrom is added to the water flowing in the ribbed pipes.

The operating efficiency of boilers increases, thus there is a less carbon-dioxide emission damaging the environment and energy is recovered, which otherwise would lose. The higher the performance of the condensation heat recovery unit is, the lower the temperature of the incoming water is and the higher its mass flow is.


Based on the experience gained so far, the return period of the equipment is 0,5-2 years depending on the utilization of the system.

Financing possibilities

We provide the possibility to our customers to achieve condensation heat recovery from the returns realized within the scope of a so-called agreement on flue gas energy utilization. In such a case, the investment is financed by our company and the customer agrees to have a bank guarantee relating to the investment value until the expiry date of the agreement. In accordance with the agreement on flue gas energy utilization, the amount of the energy recovery is measured by an integrated heat quantity measuring device on a permanent basis from the commissioning. The proportional part of the energy-saving value measured by such a device will be invoiced by our company each month. Thus, our customers purchase their rights concerning the heat recovery system from the actual saving or to its appropriate proportional part determined by measuring in accordance with the terms and conditions set forth in the contract.