## 2 Heat Recovery System
Assuming the process is isentropic, the process is carried out with the following Equations: Work performed by the compressor: \[W_{c}=\dot{m}\cdot(h_{2}-h_{1})\] where \(\dot{m}\) is the mass flow rate of the refrigerant; \(h_{2}\) and \(h_{1}\) are the specific enthalpies at points 1 and 2, respectively. Relationship between pressure and temperature (isentropic process): \[\frac{T_{2}}{T_{1}}=(\frac{P_{2}}{P_{1}})^{\frac{k-1}{2}}\] where: \(\text{T}_{1}\), \(\text{T}_{2}\): Temperatures at points 1 and 2 \(\text{P}_{1}\), \(\text{P}_{2}\): Pressures at points 1 and 2 \(\text{k}\): Ratio of specific heats. * **Condensation Process** In the condenser, the high-pressure refrigerant releases heat to the surroundings and condenses into a liquid at constant pressure. Heat released in the condenser: \[Q_{cond}=\dot{m}\cdot(h_{2}-h_{3})\] Pressure relationship: \(P_{2}=P_{3}\) (Since it is an isobaric process)
* **Expansion Process** The refrigerant undergoes isenthalpic expansion through the expansion valve (manufactured by Danfoss, Nordborg, Denmark), thereby reducing its pressure and temperature. Specific enthalpy remains constant: \(h_{3}=h_{4}\) Temperature drop due to pressure reduction: \(T_{4}<T_{3}\) (depends on refrigerant properties and phase diagram). * **Evaporation Process** In the evaporator, the refrigerant evaporates at constant pressure by taking heat from the cooler or the environment. Heat absorbed in the evaporator: \[Q_{eugy}=\dot{m}\cdot(h_{1}-h_{4})\] Pressure relationship: \(P_{4}=P_{1}\) (Since it is an isobaric process)
* **Coefficient of Performance (COP)** For heating: \[\text{COP}_{\text{heating}}=\frac{Q_{\text{cond}}}{\text{W}_{c}}\]For cooling:  
\[\mathrm{COP_{cooling}}=\frac{\mathrm{Q_{evap}}}{\mathrm{W_{c}}}\]  
The heat taken from the cooling liquid (coolant) is sent to the fan heater to be used in heating the workshop and to the boiler (manufactured by Mertsan Heat Systems, Istanbul, Turkey) to obtain hot water. The photograph of the cooling and recovery system produced according to the diagram in Figure 2 has been shown in Figure 2.  
The developed system consists of one compressor with a capacity of 12,350 BTU, two heat exchangers (As Evaporator and condenser manufactured by MIT, Istanbul, Turkey) with a capacity of 5 kW, one fancoil (manufactured by Danfoss, Nordborg, Denmark) with a capacity of 5 kW, a boiler with a capacity of 100 L, one expansion valve, one four-way valve, one three-way valve, and measurement and control equipment. A data logger (specially produced for the Recovery System) was used to collect data obtained from temperature sensors and flow meters placed in critical areas of the system. Additionally, the energy consumption of both the system and the CNC drilling machine was measured for each experiment using serially connected power meters. The data measured through the system are continuously recorded with the help of the data logger at short time intervals, such as 1 min. Photographs of the data logger and machine tool (vertical machining center) used in the experiments are presented in Figures 3 and 4, respectively. The heat recovery system is integrated into the machine tool to carry out the experiments. Figure 1:0 Photo of the developed cooling and recovery system.