Transient modeling of an ambient temperature source centrifugal compressor steam generating heat pump

Abstract

As the US electricity grid transitions to renewable power generation, electrifying end-uses that are currently fossil fuel fired presents a promising path towards deeper decarbonization, and next generation high temperature heat pumps are a viable solution for decarbonizing fossil fuel fired steam boilers. These next-gen systems require a higher degree of design complexity and more finely tuned control strategies than existing systems, and therefore can benefit from complex transient modeling that has not been previously implemented for these types of systems. A transient study of a novel steam-generating heat pump with steam delivery temperature of 150°C was conducted using physics-based simulation software. The model used manufacturer supplied performance data to calibrate each competent, providing reliable preliminary validation to the model. The model was set up to match the configuration of a prototype system constructed at Colorado State University. It was found that the results of the transient model agreed well with the steady state model of the heat pump at the design point. Transient conditions including cold startup to full load operation, full load operation to part load operation, and part load operation back to full load operation were modeled and the system was found to operate with stability. Compressor and expansion valve performance was investigated. Compressors were found to operate within their performance maps for both steady and transient operation. A control strategy was developed for the expansion valves to prevent liquid ingestion when transitioning to turndown operation. The system COP was predicted for both full and part load operation and in transition between them.