## 3 Case Study  
### Data Setup  
There are difficulties in collecting air-source heat pump system operation data [33]. Therefore, the NIST [34] data on the refrigeration operating behavior of air-source heat pump systems were used to evaluate the refrigeration cycle measurement method developed in this study. The data were collected by operating a system using R410A [35; 36; 37], a refrigerant commonly used in domestic air-source heat pump systems. Table 2 lists the specifications of the air-source heat pump system and the system with a cooling capacity of 8.8 kW and a COP of 3.81.  
The data were collected by attaching pressure transducers and T-type thermocouple probes to the inlet and outlet of all system components to measure the actual refrigerant pressure and temperature on the refrigerant side. The temperature was measured with an uncertainty of \(\pm\)0.3 \({}^{\circ}\)C and the pressure with an uncertainty of \(\pm\)1.0 Pa. The dew point and dry bulb temperatures were collected with an uncertainty of \(\pm\)0.4 \({}^{\circ}\)C. The refrigerant mass flow rate was measured using a flow meter with an uncertainty of \(\pm\)1.0%. The COP was calculated using the cooling capacity calculated from the refrigerant side measurement data, and the compressor power was measured using a watt-hour meter. The cooling capacity has an uncertainty of 4.0%, and the COP has an uncertainty of 5.5%. Table 3 lists the measurement ranges and uncertainties of the measurement devices used to measure the data.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Category** & **Specification** \\ \hline Used refrigerant & R410A \\ Cooling capacity & 8.8 kW \\ COP & 3.81 \\ \hline \hline \end{tabular}
\end{table}
Table 2: System descriptions for air source heat pump.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Measurement** & **Range** & **Uncertainty** \\ \hline Temperature Difference & 0 \({}^{\circ}\)C to 28 \({}^{\circ}\)C & \(\pm\)0.3 \({}^{\circ}\)C \\ Air Nozzle Pressure & 0 Pa to 1245 Pa & \(\pm\)1.0 Pa \\ Refrigerant Mass Flow Rate & 0 kg/h to 544 kg/h & \(\pm\)1.0\% \\ Dew point Temperature & 0 \({}^{\circ}\)C to 37.8 \({}^{\circ}\)C & \(\pm\)0.4 \({}^{\circ}\)C \\ Dry-Bulp Temperature & 0 \({}^{\circ}\)C to 37.8 \({}^{\circ}\)C & \(\pm\)0.4 \({}^{\circ}\)C \\ Total Cooling Capacity & 4.4 kW to 10.5 kW & 4.0\% \\ COP & 2.5 to 6.0 & 5.5\% \\ \hline \hline \end{tabular}
\end{table}
Table 3: Measurement uncertainties.  
Data were collected at indoor temperatures of 21.1 \({}^{\circ}\)C to 26.7 \({}^{\circ}\)C and an indoor humidity of 50%, with outdoor temperatures ranging from 21.1 \({}^{\circ}\)C to 37.8 \({}^{\circ}\)C and outdoor humidity ranging from 40 to 60%. The data collection conditions were selected based on ASHRAE Standard 37 [38] and ARI 210/240 Standards [39]. For the evaluation of the proposed refrigeration cycle measurement method, NIST data were used to evaluate the normal operation data in an environment that meets the conditions of indoor temperature 24.1 \({}^{\circ}\)C to 26.5 \({}^{\circ}\)C and outdoor temperature 26.0 \({}^{\circ}\)C to 36.6 \({}^{\circ}\)C, and Table 4 lists the environmental conditions of the data used for the evaluation.