Operational challenges in large-scale ammonia heat pump systems

The implementation of large-scale heat pumps in district heating systems is expected to play an important role in future integrated energy systems. District heating systems with large-scale heat pumps can benefit from using renewable energy sources and recovered excess heat. Improving the operation of heat pump systems may lead to cost and energy savings and increase the possibilities for providing ancillary services.

This study presents an overview of operational challenges that occur in large-scale ammonia heat pump systems based on information provided by their owners and operators. A survey was conducted, where twenty-five Danish and Norwegian district heating and industrial companies were asked about the characteristics of the heat pumps they operate and for a description of faults and operational challenges that they have experienced.

Moreover, their current monitoring and control possibilities were inquired including the possibility of providing frequency regulation services to the power grid using the existing heat-pump systems. Three companies that manufacture and provide maintenance services to ammonia heat pump systems were also asked about common faults that occur in such systems as well as strategies they use for fault detection and prevention.

The results of the study highlight the potential for improvement in current strategies to monitor and control heat pump systems. Most of the critical faults described by operators were identified in the compressor, evaporator as well as source heat exchangers and intake filters. Faults that led to a shutdown of the system like compressor breakdown were often identified after the incident occurred.

Further, the predictive maintenance for recurring faults, such as frosting of air-source evaporators or fouling has been found to have an improvement potential.