*2.4. Step 4: Integrate the Heat Pump with the Process*

At the next step, Pinch Analysis is used to integrate the HP with the process. The placement of the HP is configured following the outcomes from the previous step. When a HP is integrated with a process, the choice of a HP system depends on the operating temperature and the heat loads below and above the Pinch. In this part, the calculation results of the HPs are plotted against the GCC of the considered process, and the optimal results are linked to the GCC profiles, including the required duties and temperatures. In this way, engineers applying the method can get a better understanding of the optimal results.

The GCC of a HP and an illustrative process is shown in Figure 3. The appropriate placement of a HP means that the heat must be recovered from below the Pinch and released above the Pinch [34]. Improper placement on either side of the Pinch will result in lower energy efficiency. The figure has two lines representing each heat exchange between the HP and the process. The thick dashed lines represent the heat transfer taking place inside the HP block—absorbing and releasing heat. The thin dashed lines represent the heat exchange directly with the process. These form extra heat circuits for minimising the probability of contamination of the internal HP fluids. All other GCC figures in this paper follow the same convention.

**Figure 3.** Grand Composite Curve (GCC) construction of a process with an integrated heat pump: (**a**) JCHP, (**b**) VCHP and (**c**) TCHP.

The example GCC of the JCHP is shown in Figure 3a. In the JCHP cycle, the working fluid remains in a gaseous state during the whole cycle of heat exchange with the process source and sink as well as the compression and expansion. This results in certain variations of the JCHP working fluid temperature. The heat absorption curve (blue dashed line) and heat release curve (red dashed line) are both oblique straight lines, as shown in Figure 3a. The working fluid slope of a JCHP is relatively large in GCC.

The example GCC of the VCHP is presented in Figure 3b. The working fluid of a VCHP is evaporated during heat exchange with the source and is condensed during heat exchange with the sink, so the phase transition occurs. The temperature of the working fluid of VCHP almost unchanged in exchange heat with the source or sink. The evaporation curve (blue dashed line) and condensation curve (red dashed line) are horizontal straight lines (i.e., minimal temperature change).

The GCC of the TCHP is shown in Figure 3c. The working fluid of TCHP is evaporated when the heat is absorbed from the process source. The heat release to the process sink takes place at supercritical conditions of the working fluid. This is why the working fluid temperature of TCHP remains constant during heat absorption from the source but changes significantly during the heat release to the sink. The evaporation curve (blue dashed line) is a horizontal straight line, whereas the heat release curve (red dashed line) is an oblique curve, as shown in Figure 3c.
