Abstract
The present work conducts an evaluation of the feasibility and the overall performance and consequent optimization of a direct expansion solar assisted heat pump (DXSAHP) employed for domestic water heating. For the study conducted R134a, R404A, R407C and R410A working fluids were evaluated as well as the use of four, six and eight flat-plate solar collectors and a worktime ranging from 1 to 6 h. The case study is based in Mexico City with a 300 L container and a hot water outlet temperature of 51 °C. The paper introduces a new evaluation criterion based on the thermal capacity and all the evaluations conducted throughout this research revolve around this performance metric. The results show that, the system would require at least 4 h of operation to achieve the outlet temperature. Additionally, it was found that the R410A refrigerant has the best heat transfer properties; with an average condensation heat rate of 6.31 kW, followed by the R407C with 5.72 kW, the R404A with 5.42 kW and the R134a with 5.18 kW. Diversely, the R134a refrigerant requires 0.402 kW of compression work, 62% less than the R410A, which requires 1.06 kW. Consequently, R134a delivers the highest COP, which ranges from 7 to 14, followed by the R407C and R404A refrigerants, which present a similar behaviour between them, with COP ranging from 5 to 9 and 4 to 8, respectively, and finally the R410A, achieving the lowest COP, ranging from 3.5 to 6.5. Moreover, it was found that the R134a presents a higher dispersion regarding the energy exchange rate, which reveals that it is the fluid most susceptible to external factors, such as the weather. Contrarily, the remaining refrigerants present a more consistent performance. Finally, the optimization revealed that the R407C refrigerant is the most suitable given that it requires 20% less compression work than the R404A. This provides the heat pump system with a steadier behaviour, a COP ranging from 7 to 8, 30% higher than R410A, a worktime decrease of 1.5 h and heat transfer area of 5.5 flat-plate solar collectors, equivalent to a 31% reduction, both compared to R134a.
Highlights
In the last decades, the subject of efficient use of energy has become of great interest, for economic as well as environmental reasons
Obtain With the desired output conditions, while maintaining an acceptable performance, it is necessary to this objective in mind, an inferential statistical analysis is employed, an evaluate the existent connection between the coefficient of performance, COP, andPDE, the thermal capacity interpolation method known as estimation of the probability density function, to deduce the ofunderlying the heat pump, τ properties of the population, in order to identify the concentration areas of the datasets
The R404A refrigerant has a worktime range of 2.5 to 3 hours and, compared to R134a, a reduction in both the ranges of the heat transfer area and of the COP, with magnitudes reaching between 1.4 to 1.6 m2 and 5.5 to 8, respectively. This behaviour is relatively analogous for the R407C refrigerant, for which the concentration of data indicates a range in both heat transfer area and COP of 1.3 to 1.6 m2 and 6 to 9 respectively, with the advantage that the work time is concentrated around 2.5 hours
Summary
The subject of efficient use of energy has become of great interest, for economic as well as environmental reasons. The increasing demand of petroleum-based products and the consequent increase in fuel prices in the global market and issues caused by overexploitation of natural resources, have led to an increase in research and development of new technologies or alternatives to harness renewable energies, as well as new policies regarding energy savings and its efficient use [1,2]. The result of these policies is represented by the progressive measures implemented around the world, where the government and a variety of institutions and associations offer subsidies or economic. Characterized by the variety of the existing options and the satisfactory results yielded, their availability and utilization has proliferated [11,12,13,14]
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