Online model-based framework for operation and fouling monitoring in a large-scale heat pump

Heat pump systems are a key technology towards the decarbonisation of district heating systems as they can leverage renewable energy sources and industrial excess heat. Large-scale heat pumps are prone to a variety of faults related to the heat source. Heat exchanger fouling is one of the most common types of faults, which corresponds to the undesired deposition of material on heat transfer surfaces. This fault can be mitigated by the use of different cleaning procedures such as cleaning-in-place. The optimization of the time interval between cleaning periods requires the estimation of the effects of fouling on the heat pump performance, which are often difficult to determine. The present study proposes a framework for online monitoring of a large-scale heat pump affected by evaporator fouling based on a quasi-steady-state simulation model. Model parameters related to the heat transfer coefficients and fouling were repeatedly adjusted by means of a dynamic calibration approach. The framework retrieved operational data from a cloud-based data management system and leveraged existing sensors and controllers in the heat pump. The results indicated that fouling had a larger effect on the thermal resistance than on the pressure drop in the evaporator. The framework also allowed to identify the extent to which a cleaning-in-place system enabled to reduce the evaporator thermal resistance caused by fouling. Overall, the results from the proposed framework showed its potential to describe the operation of the heat pump and to determine the effects of fouling on a real-time basis.