*4.2. Evaluation*

The results of the Heat Integration of the four industrial processes with HPs are compared. They are summarised in Table 7.


**Table 7.** The results of different industrial Processes Integration with heat pumps.

For the processes with steep source and sink slopes, such as the spray drying process of the milk powder in a dairy factory in Case Study 1, the average ΔT of working fluid and source/sink in JCHP is small, resulting in a small energy loss and high heat exchange efficiency. The COP of JCHP is large, so it is appropriate to choose the JCHP.

When the source and sink slope of process is gentle or (nearly) flat, for example, as in the dairy product processing of Case Study 2 and the candy processing and packaging in Case Study 3, the VCHP is most suitable because the average ΔT of the working fluid and source/sink are small, the energy loss is small resulting in high thermal efficiency and high COP values. In Case Study 2, the ΔTin is as low as 1.5 ◦C, and the COP of VCHP is as high as 13.07.

From Case Study 2 to Case Study 3, the ΔTin increased from 1.5 ◦C to 11.84 ◦C, and the COP of the VCHP decreased from 13.07 to 4.44. Therefore, the smaller the ΔTin between source and sink is, the larger is the COP of the VCHP. The COP of the VCHP decreased rapidly with the increase of ΔTin between source and sink. However, the COP of JCHP decreased less with the increase of ΔTin between source and sink.

The application scope of the TCHP is limited. The TCHP is more appropriate for a process with a relatively gentle source slope and a relatively steep sink slope. The best process is one which the inlet temperature of the source is less than or equal to 20 ◦C, and the ΔTin between the source and sink is less than 10 ◦C.
