Abstract
Exergy analysis has been widely used to assess refrigeration systems by evaluating exergy losses or exergy efficiency. The latter is mostly used as an indicator to determine the system performance, which requires the comparison of the actual system with its idealized reversible version, but not the practical achievable efficiency. Therefore, a practice-oriented evaluation method for refrigeration plants in free cooling operation is proposed, based on exergy analysis and technical standards as baseline. By considering the exergy input of auxiliary devices, the overall design of hydraulic circuits can be assessed on subsystem level. The achievable optimization potential compared to the state of the art in technology and the performance is revealed with the introduced optimization potential index (OPI). The application is demonstrated on a case study, where the analysis reveals an adequate operation of the field plant in general. Most cooling locations show potential for improvement, which is indicated by an OPI superior to zero. Moreover, the auxiliary electrical exergy input shows the same magnitude as the thermal exergy input, which emphasizes the importance of reducing the electrical energy usage of auxiliary devices in refrigeration plants to increase the performance.
Highlights
In order to evaluate and reduce the energy consumption in buildings, e.g. heating, ventilation and air-conditioning (HVAC) systems, different approaches were applied
With the optimization potential index (OPI), a comparison between different refrigeration systems is possible and the reference can vary depending on the technological requirements, which is of great importance in practice
A possible reason are the three additional cooling locations which were integrated at the end of April, and the actual exergy input of the subsystem is increased
Summary
In order to evaluate and reduce the energy consumption in buildings, e.g. heating, ventilation and air-conditioning (HVAC) systems, different approaches were applied. Exergy is destroyed in real (irreversible) thermodynamic processes, such as heat transfer in a heat exchanger. This represents a loss in energy potential to produce work. Such losses are the key for optimization, as their location and magnitude can be identified throughout systems and subsequently countermeasures may be initialized. Exergy analysis allows a deep insight in the different energy flows and the corresponding losses of thermodynamic systems which is not feasible with a purely energetic analysis
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