*3.1. Uncertainty Analysis*

The measured values of various parameters deviated from their actual values. The deviation between the measured value and the actual value of any parameter is termed as uncertainty associated with that parameter [27]. The accuracies of measuring instruments and errors during the measurements are the primary reasons for the uncertainties in various measuring and manipulating parameters [28]. The uncertainty analysis was conducted to assure the accuracy and reliability of the experimental data associated to the heat pump system with a high-pressure side chiller. The temperature, pressure, humidity, flow rate, air velocity and compressor speed were the measuring parameters during the experiments on the heat pump system with a high-pressure side chiller. The accuracies of the measuring instruments for various measuring parameters were the uncertainties associated with them, whereas the cooling capacity, coefficient of performance, chiller heat transfer rate, compressor power consumption, system efficiency and heater core performance were the performance (manipulating) parameters which were deducted from the experimental data of measuring parameters. The uncertainties in the performance parameters were evaluated using the concept of linearized fractional approximation which was proposed by Holman and Gajda [27,28]. Using this concept, the uncertainties in various performance (dependent) parameters due to uncertainties of various measuring (independent) parameters are evaluated by Equation (1) [29,30].

$$\mathrm{d}\mathcal{U}\_{\mathrm{R}} = \left[ \left( \frac{\partial \mathcal{R}}{\partial \mathcal{X}\_{1}} \mathcal{U}\_{1} \right)^{2} + \left( \frac{\partial \mathcal{R}}{\partial \mathcal{X}\_{2}} \mathcal{U}\_{2} \right)^{2} + \left( \frac{\partial \mathcal{R}}{\partial \mathcal{X}\_{3}} \mathcal{U}\_{3} \right)^{2} \dots + \left( \frac{\partial \mathcal{R}}{\partial \mathcal{X}\_{n}} \mathcal{U}\_{n} \right)^{2} \right]^{\frac{1}{2}} \tag{1}$$

where, *X*1, *X*2, *X*3, . . . *X<sup>n</sup>* are the independent parameters, *R* is the dependent parameter, *U*1, *U*2, *U*3, . . . *U<sup>n</sup>* are the uncertainties associated with independent parameters and *U<sup>R</sup>* is the total uncertainty associated with dependent parameter.

The uncertainties associated with measuring parameters, temperature, pressure, humidity, coolant flow rate and air flow rate were 2.2%, 0.2%, 0.2%, 0.7% and 2.0%, respectively. Whereas, the uncertainties associated with performance (manipulating) parameters, cooling capacity, coefficient of performance, chiller heat transfer rate, compressor power consumption and heater core performance were 3.02%, 3.06%, 0.60%, 0.38% and 5.08%, respectively.
