Adaptive control of radiator systems for a lowest possible district heating return temperature

• A new control method for radiator systems has been developed and tested in practice.
• A reduction of district heating return temperature in the order of 2 °C was reached.
• Both radiator supply temperature as well as flow rate are controlled.
• The method is adaptive and will constantly give lowest possible return temperature.

The present paper describes how the control of a radiator system connected to a district heating (DH) network via a heat exchanger can be optimized to provide the lowest possible DH return temperature. This can be achieved for each operating point by employing an optimal combination of radiator circuit supply temperature and circulation flow rate. The control algorithm gradually modifies the control curve for the radiator circuit, enabling it consistently to provide an optimal cooling of the DH water. Since the heat exchanger is dimensioned for very low outdoor temperatures, it is oversized for smaller heat loads. In addition, radiator systems are often oversized due to safety margins. Such facts render it possible to reduce the DH return temperature. The objective of the present study was to develop a control algorithm and to test it in practice. A description is here given of the algorithm, and, additionally, of field tests that were undertaken to practically verify it. The adaptive control method could be implemented in any modern radiator circuit control logics, and the achieved improvement was an added 2 °C district heating water cooling, resulting in a 3.5 per cent reduction in average district heating flow.