The optional as-needed switching of the economiser from boiler water pre-heating to circulation of the feed water may lead to energy savings of up to 1%. The steam boiler pump pumps continually. If the steam boiler does not need any boiler water, the feed water is pumped into the feed water container in the circuit. This increases the flow rate in the economiser, the water temperature drops and the efficiency of the economiser rises.
The second economiser is a heat exchanger that uses the residual energy of the flue gases for heating water, such as:
The second economiser is installed on the flue-gas side between the first economiser and the chimney. The water to be heated flows to the flue gases to be cooled in a counter flow. The lower the temperature of the flowing water, the higher the efficiency. The integration of the second economiser depends on the expected condensate return flow.
The reduced flue gas temperatures may cause the flue draught to be insufficient. The design of the chimney system should be re-calculated accordingly. For brick chimneys, i.e. without stainless steel lining, sooting must be expected.