Efficient use of waste heat from a refrigeration unit by means of a heat pump
Industrial heat pumps promise the efficient use of waste heat in industry and manufacturing. But can this promise be kept? In many cases, yes! But the use of a heat pump does not always make sense.
A necessary prerequisite is the existence of a heat source and a heat demand at the right temperature levels. But it is just as important to make sure that the heat demand cannot be met from other, cheaper sources. Otherwise, a significantly more expensive heat pump may be used instead of a simple heat exchanger.
The planning of a industrial heat pump starts with the assessment and analysis of the existing process flows in the production plant. By means of a pinch analysis, the best possible integration of the process flows can be determined.
In this case, the situation was very favorable for the integration of a heat pump. On the one hand, there was a lot of waste heat from a refrigeration plant at approx. 55°C and, on the other hand, a large heat demand for hot water heating to 80°C. The other process flows for heating the building, production processes and cold rooms, can be integrated using heat exchangers so that only a small external heating requirement remains.
A completely different situation would have arisen, for example, with a larger heat requirement at 40°C (e.g. building heating). In this case, it would have been possible to use the waste heat from the refrigeration systems without using a heat pump.
For the best possible efficiency and utilization, the right choice of working fluid and sizing of the industrial heat pump is crucial. With the help of our log-ph-diagram, an initial comparison of working fluids can be made quickly.
For ammonia, this results in a theoretical COP of 4.83 at a temperature difference of 10K each for heat transfer at the condenser and evaporator. Furthermore, it can be seen that the outlet temperature of the working fluid after the compressor with approx. 150°C is high enough to also achieve higher usable temperatures, if the heat pump is correctly sizing .
Different operating cases also play an important role for the sizing. Depending on the relevance and frequency of the operating cases (e.g. due to shift operation, weekends, seasonal influences) and existing backup systems (e.g. boilers), an economically and technically reasonable decision has to be made.
In the case of complex systems, it may well make sense to investigate the control and operating strategy of the heat pump in a dynamic system model. Ideally, time-resolved load profiles are available for this purpose. Then control algorithms can also be tested and all the advantages and disadvantages of integrating a heat pump into the existing system can be investigated.
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