Search

This work presents an experimental analysis of a non-flammable R1234ze(E)/R134a mixture (R450A) as R134a drop-in replacement. While R134a has a high GWP value (1430), the R450A GWP is only 547. The experimental tests are carried out in a vapour compression plant equipped with a variable-speed compressor. The replacement suitability has been studied combining different operating conditions: evaporation temperature, condensation temperature and the use of an internal heat exchanger (IHX). The drop-in cooling capacity of R450A compared with R134a is 6% lower as average. R450A COP is even higher to those resulting with R134a (approximately 1%). The discharge temperature of R450A is lower than that of R134a, 2K as average. The IHX has a similar positive influence on the energy performance of both fluids. In conclusion, R450A can be considered as a good candidate to replace R134a. [ABSTRACT FROM AUTHOR]

• Ejector and parallel compression configurations are proposed for high temperature heat pumps. • Internal heat exchanger analysis is included in the proposed configurations. • Alternative sustainable refrigerant assessment is performed to replace HFC-245fa. • Multi-objective analysis evaluates the compromise between volumetric heating capacity and COP. • Advanced high temperature heat pump configurations are promoted. Climate change evolution urges us to take action to reduce greenhouse gas emissions. As one of the main contributors, the industrial sector requires cleaner methods of heat production, such as high temperature heat pumps (HTHP) with the highest energy efficiency. Facing this challenge, this paper provides a performance comparison of the ejector and economizer with parallel compression configurations in HTHPs for low-grade waste heat recovery. A single-stage cycle has been used as a reference configuration to compare the proposed options. The internal heat exchanger (IHX) is included in all the configurations to extend the analysis and illustrate the influence of this component in high temperature applications. Moreover, alternative low-GWP refrigerants have been analyzed in order to replace the reference working fluid HFC-245fa. Ejector and economizer with parallel compression configurations with IHX provide a coefficient of performance (COP) improvement of up to 36% and 72.5%, respectively, using HFC-245fa for a heating temperature production of 140 °C. Moreover, the volumetric heating capacity (VHC) increases around 36% for the ejector cycle and 80% for the economizer with parallel compression cycle with IHX. HC-601, HFO-1336mzz(Z), and R-514 have the most significant COP improvement compared to HFC-245fa, along with the highest VHC drop. Multi-objective evaluation illustrates that single-stage and ejector configurations with IHX have similar results, whereas the economizer with parallel compression cycle with IHX presents a significant COP and VHC improvement. HCFO-1233zd(E) and HCFO-1224yd(Z) presents the proper trade-off between COP and VHC. [ABSTRACT FROM AUTHOR]

R1234yf and R1234ze(E) have been proposed as alternatives for R134a in order to work with low GWP refrigerants, but this replacement results generally in a decrease of the performance. For this reason, it is interesting to explore ways to improve the system performance using these refrigerants. In this paper, a comparative study in terms of energy performance of different single stage vapour compression configurations using R1234yf and R1234ze(E) as working fluids has been carried out. The most efficient configuration is the one which uses an expander or an ejector as expansion device. On the other hand, using an internal heat exchanger in a cycle which replaces the expansion valve by an expander or an ejector could produce a detrimental effect on the COP. However, for all the configurations the introduction of an internal heat exchanger produces a significant increment on the cooling capacity. [ABSTRACT FROM AUTHOR]