*3.2. Data Reduction*

Based on the measured data, the refrigerant-side heat transfer rate of the chiller was calculated by Equation (2) using the refrigerant enthalpy method (ASHRAE Standard 116, 1983). The air-side heat transfer rate is calculated by Equation (3) using both the air flow rate and enthalpy difference. The compressor power consumption was calculated using voltage and current values as expressed by Equation (4). The coefficient of performance (COP) of the tested system was calculated by Equation (5) using the compressor power consumed by compressor work. The heat transfer rate of coolant in the chiller was calculated based on its volume flow rate, density, temperature gain and specific heat capacity of coolant, as presented by Equation (6). The pressure ratio in cooling and heating modes was calculated using Equation (7) as the ratio of high pressure to low pressure.

$$
\dot{Q}\_{ref} = \dot{\mathbf{m}}\_{ref} \Delta h\_{ref} \tag{2}
$$

$$
\dot{Q}\_{\rm air} = \dot{\mathbf{m}}\_{\rm air} \Delta h\_{\rm air} \tag{3}
$$

$$\mathcal{W}\_{comp} = VI\tag{4}$$

$$\text{COP} = \frac{\dot{Q}\_{air}}{W\_{comp}} \tag{5}$$

$$\dot{Q}\_{\text{coolant}} = \dot{V}\_{\text{coolant}} \cdot \rho\_{\text{coolant}} \cdot \mathbb{C}\_{p,\text{coolant}} \left( T\_{\text{coolant,in}} - T\_{\text{coolant,out}} \right) \tag{6}$$

$$\text{Pressure ratio } = \frac{P\_{\text{high}}}{P\_{\text{low}}} \tag{7}$$

where, . *<sup>Q</sup>re f* is the refrigerant side heat transfer rate of chiller (kW), . m*re f* is mass flow rate of refrigerant (kg/s), ∆*hre f* is the enthalpy difference for refrigerant (kJ/kg), . *Qair* is the air side heat transfer rate (kW), . m*air* is the mass flow rate of air (kg/s), ∆*hair* is the enthalpy difference for air (kJ/kg), *Wcomp* is the compressor work (kW), *V* is voltage (v), *I* is current (A), COP is the coefficient of performance of the tested system, . *Qcoolant* is coolant heat transfer rate in chiller, . V*coolant* is volume flow rate of coolant (L/min), ρ*coolant* is density of coolant (kg/m<sup>3</sup> ), *Cp*,*coolant* is specific heat capacity of coolant (kJ/kg·K), *<sup>T</sup>coolant*.*in* is coolant inlet temperature (◦C), *<sup>T</sup>coolant*.*out* is coolant outlet temperature (◦C), and *<sup>P</sup>high* and *Plow* are high pressure (MPa) and low pressure (MPa).
