Abstract This study reviews the current state of the art and the current research activities of high temperature heat pumps (HTHPs) with heat sink temperatures in the range of 90 to 160 °C. The focus is on the analysis of the heat pump cycles and the suitable refrigerants. More than 20 HTHPs from 13 manufacturers have been identified on the market that are able to provide heat sink temperatures of at least 90 °C. Large application potentials have been recognized particularly in the food, paper, metal and chemical industries. The heating capacities range from about 20 kW to 20 MW. Most cycles are single-stage and differ primarily in the refrigerant (e.g. R245fa, R717, R744, R134a or R1234ze(E)) and compressor type used. The COPs range from 2.4 to 5.8 at a temperature lift of 95 to 40 K. Several research projects push the limits of the achievable COPs and heat sink temperatures to higher levels. COPs of about 5.7 to 6.5 (at 30 K lift) and 2.2 and 2.8 (70 K) are achieved at a sink temperature of 120 °C. The refrigerants investigated are mainly R1336mzz(Z), R718, R245fa, R1234ze(Z), R600, and R601. R1336mzz(Z) enables to achieve exceptionally high heat sink temperatures of up to 160 °C.

High Temperature Heat Pumps: Market Overview, Stateof the Art, Research Status, Refrigerants, and Application Potentials

The EU Regulation No 517/2014 is going to phase-out most of the refrigerants commonly used in refrigeration and air conditioning systems (R134a, R404A and R410A) because of their extended use and their high GWP values. There are very different options to replace them; however, no refrigerant has yet imposed. In this paper we review and analyze the different mixtures proposed by the AHRI as alternative refrigerants to those employed currently. These mixtures are composed by HFC refrigerants: R32, R125, R152a and R134a; and HFO refrigerants: R1234yf and R1234ze(E). It is concluded, from the theoretical analysis, that most of the new HFO/HFC mixtures perform under the HFC analyzed (although some experimental studies show the contrary) and, in most cases, do not meet the GWP restrictions approved by the European normative. Furthermore, some of the mixtures proposed would have problems due to their flammability.

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Analysis based on EU Regulation No 517/2014 of new HFC/HFO mixtures as alternatives of high GWP refrigerants in refrigeration and HVAC systems

A review of refrigerant R1234ze(E) recent investigations

In the present work, a large number of compounds described in the publicly available literature have been reviewed with the aim to identify possible substitutes for high-GWP HFCs in HVAC&R and organic Rankine cycle (ORC) applications. Taking into account various criteria (particularly low toxicity, low flammability, low GWP, and high energy efficiency), only a few single-component compounds are suitable for many of the relevant applications. In particular, in addition to natural fluids, studies have shown that there are only a few HFCs and a dozen or so HFOs, i.e. halogenated olefins characterized by the presence of a C C double bond in the molecule, that are potentially suitable for a number of relevant applications. Here, a review of the present state-of-the-art of experimentally-determined thermophysical properties of a number of HFOs working fluids and their mixtures also with other categories of refrigerants is presented, with particular emphasis placed on saturation and critical properties, vapor phase PVT data, liquid density, specific heat capacity, thermal conductivity, viscosity, and surface tension.

Low GWP halocarbon refrigerants: A review of thermophysical properties

Refrigeration systems, air-conditioning units and heat pumps have been recognized as indispensable machines in human life, and are used for e.g. food storage, provision of thermal comfort. These machines are dominated by the vapor compression refrigeration system and consume a large percentage of world-wide electricity output. Moreover, CO2 emissions related to the heating and cooling processes contribute significantly to the total amount of CO2 emission from energy use. The ejector refrigeration system (ERS) has been considered as a quite interesting system that can be driven by sustainable and renewable thermal energy, like solar energy, and low-grade waste heat, consequently, reducing the electricity use. The system has some other remarkable merits, such as being simple and reliable, having low initial and running cost with long lifetime, and providing the possibility of using environmentally-friendly refrigerants, which make it very attractive. The ERS has received extensive attention theoretically and experimentally.This thesis describes in-depth investigations of vapor ejectors in the ERS to discover more details. An ejector model is proposed to determine the system performance and obtain the required area ratio of the ejector by introducing three ejector efficiencies. Based on this ejector model, the characteristics of the vapor ejector and the ERS are investigated from different perspectives.The working fluid significantly influences the ejector behavior and system performance as well as the ejector design. No perfect working fluid that satisfies all the criteria of the ERS can be found. The performance of nine refrigerants has been parametrically compared in the ERS. Based on the slope of the vapor saturation curve in a T-s diagram, the working fluids can be divided into three categories: wet, dry and isentropic. A wet fluid has a negative slope of the vapor saturation curve in the T-s diagram. An isentropic expansion process from a saturated vapor state will make the state after the expansion to fall inside the liquid-vapor area of the T-s diagram which will result in droplet formation. Generally, an isentropic expansion for a dry fluid will not occur inside the liquid-vapor area, and consequently no droplets will form. An isentropic fluid has a vertical slope of the vapor saturation curve in the T-s diagram and an isentropic expansion process will hence follow the vapor saturation curve in the T-s diagram, ideally without any droplet formation. However, when the saturation condition is close to the critical point, it is possible that the isentropic expansion process of a dry fluid and an isentropic fluid occurs inside the liquid-vapor area of the T-s diagram, resulting in formation of droplets. In order to avoid droplet formation during the expansion, a minimum required superheat of the primary flow has been introduced before the nozzle inlet. Results show that the dry fluids have generally better performance than the wet fluids and the isentropic fluid. Hence the thesis mostly focuses on the features of vapor ejectors and the ERS using dry fluids.Exergy analysis has been proven to be very useful to identify the location, magnitude, and sources of exergy destruction and exergy loss, and to determine the possibilities of system performance improvement. This method is applied to the ejector and the ERS. The ejector parameters are closely interacting. The operating condition and the ejector area ratio have a great impact on the ejector overall efficiency and system COP. The ejector efficiencies are sensitive to the operating conditions, and they significantly influence the system performance. A so-called advanced exergy analysis is adopted to quantify the interactions among the ERS components and to evaluate the realistic potential of improvement. The results indicate that, at the studied operating condition, the ejector should have the highest priority to be improved, followed by the condenser, and then the generator.Thermoeconomics, which combines the thermodynamic analysis and economic principles, is applied to reveal new terms of interest of the ERS. The economic costs of the brine side fluids (fluids that supply heat to the generator and evaporator and remove heat from the condenser) play very essential roles in the thermoeconomic optimization of the ERS. Depending on different economic conditions, the system improvement from a thermodynamic point of view could be quite different from the thermoeconomic optimization. The ERS is economically sound when using free heat sources and heat sink.An ejector test bench has been built to test the entrainment ratio of different ejectors. Although the experiments do not achieve the desired results, they could still be discussed. The insignificant effect of the superheat of the secondary flow found in the theoretical study is validated. The assumption of neglecting the velocities at the ejector inlets and outlet are confirmed. The quantification of the ejector efficiencies shows that they largely depend on the operating conditions and the ejector dimensions.

Conventional and advanced exergyanalysis of an ejector refrigeration system

Performance analysis of a modified subcritical zeotropic mixture recuperative high-temperature heat pump

Measurements of isothermal (vapour + liquid) equilibria data for {1,1,2,2-Tetrafluoroethane (R134) + trans-1,3,3,3-tetrafluoropropene (R1234ze(E))} at T = (258.150 to 288.150) K

Phase equilibrium for the binary mixture of {1,1-difluoroethane (R152a)+trans-1,3,3,3-tetrafluoropropene (R1234ze (E))} at various temperatures from 258.150 to 288.150K

(Vapour + liquid) equilibrium data for the binary system of {trifluoroiodomethane (R13I1) + trans-1, 3, 3, 3-tetrafluoropropene (R1234ze (E))} at various temperatures from (258.150 to 298.150) K

Thermodynamic analysis of a volatile organic compounds (VOCs) condensation recovery system combined with mixed-refrigerant J-T (MRJT) refrigeration is illustrated in this paper, which provides an effective and economical choice for petroleum plants. VOCs is compressed, cooled by its recuperation process and separated in two simple rectification columns with 3–5 stages. The cooling powers for condensers at column top are provided by a high efficiency dual MRJT refrigerator at 100 K and 232 K, respectively. The cooling and separation characteristics of petroleum VOCs are also analyzed comprehensively. It is indicated that most of VOCs condensation load locates in high temperature region (≥ 235 K approximately). It might be feasible to cool VOCs from 235 K to 110 K by cold purified air through recuperation. For a typical petroleum VOCs, non-methane hydrocarbon residual of 56 mg Nm−3 is achieved with specific power consumption (SPC) of 0.1289 kWh Nm−3, free of additional purifying units. According to the analysis on the effects of variable VOCs composition and pressure, the cooing loads of top condensers are close related to the performance of VOCs recuperation. C1 and C2 are key components to enhance recuperation at low temperatures and reduce SPC. Exceed C3 could enlarge cold stage condenser load and SPC due degraded cold stage recuperation; while exceed C4-C6 could reduce condenser loads and SPC. Higher VOCs pressure could also decrease SPC.

Hao Guo

Papers

Performance analysis of a modified subcritical zeotropic mixture recuperative high-temperature heat pump

Measurements of isothermal (vapour + liquid) equilibria data for {1,1,2,2-Tetrafluoroethane (R134) + trans-1,3,3,3-tetrafluoropropene (R1234ze(E))} at T = (258.150 to 288.150) K

Phase equilibrium for the binary mixture of {1,1-difluoroethane (R152a)+trans-1,3,3,3-tetrafluoropropene (R1234ze (E))} at various temperatures from 258.150 to 288.150K

(Vapour + liquid) equilibrium data for the binary system of {trifluoroiodomethane (R13I1) + trans-1, 3, 3, 3-tetrafluoropropene (R1234ze (E))} at various temperatures from (258.150 to 298.150) K

Thermodynamic analysis of a petroleum volatile organic compounds (VOCs) condensation recovery system combined with mixed-refrigerant refrigeration