## 2 Methodology
### Refrigeration Cycle Measurement Method
* _Step 3._ Show the isenthalpy and isentropy lines on the pressure-enthalpy diagram. The point 4 found in Step 2 is the suction point of the evaporator and the discharge point of the expansion valve. The expansion process of the air source heat pump system is an isenthalpy process, so the isenthalpy line is taken through point 4. The point 1 is the discharge point of the evaporator and the suction point of the compressor. The compression process of the air source heat pump system is an isentropic process, so the isentropy line is taken through point 1. * _Step 4._ Show the condensation process on a pressure-enthalpy diagram. The condensation process in an air source heat pump system is isobaric, the same as the evaporation process. The discharge point of the condenser is the same as the suction point of the expansion valve, and the suction point of the condenser is the same as the the discharge point of the compressor. Therefore, the condensation process must cross both the isenthalpy line and the isentropy line in Step 3. In addition, it must be parallel to the evaporation process. Calculate the enthalpy change in the condenser side refrigerant using Equation (9) using the measurement data on the air side of the condenser. Show the discharge point (point 3) and suction point (point 2) of the condenser where the calculated enthalpy change fulfills the above conditions. The condensation process of the air source heat pump system can be shown on the pressure-enthalpy diagram by connecting points 3 and 2. * _Step 5._ Show the expansion and compression processes on the pressure-enthalpy diagram. The expansion process of the air source heat pump system can be shown on the pressure-enthalpy diagram by connecting points 3 and 4. Moreover, the compression process of the air source heat pump system can be shown on the pressure-enthalpy diagram by connecting points 1 and 2. Finally, the air-side measurement data can be used to measure the refrigeration cycle of the air source heat pump system. The measurement variables and design data were selected to estimate the air-side enthalpy change in the air-source heat pump system. For the refrigeration cycle measurement method, air-side measured data, evaporator air intake temperature and humidity, discharge temperature and humidity, discharge airflow rate, refrigerant temperature, and condenser-side air intake temperature and discharge temperature were selected as measured variables. Generally, the condenser-side airflow in air-source heat pump systems is controlled at constant airflow, so design data were used rather than measurements. A refrigeration cycle measurement method using design data was developed for the refrigerant flow rate required to calculate the enthalpy change on the refrigerant side. Table 1 lists the input and measurement variables of the measurement method, and Figure 4 shows a conceptual diagram of the measurement points of the input and measurement variables. The inlet and outlet air temperature, humidity, and airflow were measured with twenty-five node, T-type thermocouple grids and thermopile. Evaporator refrigerant temperature was collected by measuring the refrigerant surface temperature. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Measurement** & **Symbols** & **Unit** \\ \hline Evaporator inlet air temperature & \(t_{Equ,in}\) & \({}^{\circ}\)C \\ Evaporator outlet air temperature & \(t_{Equ,out}\) & \({}^{\circ}\)C \\ Evaporator refrigerant temperature & \(t_{Equ,ref}\) & \({}^{\circ}\)C \\ Evaporator inlet air relative humidity & \(\varphi_{Equ,in}\) & \({}^{\circ}\) \\ Evaporator outlet air relative humidity & \(\varphi_{Equ,out}\) & \({}^{\circ}\) \\ Evaporator outlet airflow rate & \(t_{Equ,out}\) & \({}^{\circ}\)M\({}^{3}\)/s \\ Condenser inlet air temperature & \(t_{Cand,in}\) & \({}^{\circ}\)C \\ Condenser outlet air temperature & \(t_{Cond,out}\) & \({}^{\circ}\)C \\ Condenser outlet airflow rate & \(\varphi_{Cand,air}\) & \({}^{\circ}\)M\({}^{3}\)/s \\ Refrigerant flow rate & \(m_{ref}\) & kg/s \\ \hline \hline \end{tabular}
\end{table}