Extending the range and performance of R-744.

This research presents the R438A refrigerant that non-flammable refrigerant and develop for retrofit to R404A. The hydrofluorocarbons/hydrocarbon (HFCs/HCs) R463A (GWP=2,265) was zeotropic mixture of R125 (45%), R134a (44.2%), R32 (8.5%), R600 (1.7%) and R600a (0.6%). The R463A refrigerants is no frame propagation class A1 and lower toxicity and used polyol ester oil (POE). The results will investigation and analysis of the environmentally friendly refrigerant for R22 replacement. All refrigerant properties in this research were based on results from the REFPROP and CYCLE_D-HX software of NIST under CAN/ANSI/AHRI540. The results of this work show that HCs R170, R290, R600, R600a, R601, R601a, R1150 and R1270 can be mixed in HFCs R417A, R417B, R422A, R422B, R422C, R422D, R424A, R437A, R438A and R453A and able to be further developed in the future. All refrigerants are non-flammable refrigerants, non-toxic and zero ODP. The R438A mixed with HCs R600 (1.7%) and R601a (0.6%) and is the refrigerant cooling coefficient of performance close to that of R22 refrigerant. In conclusion, it can be used as an environmentally friendly and energy efficiency replacement for R22. The result of R438A normal boiling was lower than R404A 4% that high cooling capacity and zero ODP. All refrigerants are also refrigerants that are matched with the 4th generation refrigerants with the use of natural refrigerants.

In the European Union (EU), buildings are responsible for about 40% of the total final energy consumption, and 36% of the European global CO2 emissions. The European Commission released directives to push for the enhancement of the buildings energy performance and identified, beside the retrofit of the current building stock, Heating, Ventilation, and Air Conditioning (HVAC) systems as the other main way to increase renewable energy sharing and overall building energy efficiency. For this purpose, Ground Source Heat Pumps (GSHPs) represent one of the most interesting technologies to provide energy for heating, cooling, and domestic water production in residential applications, ensuring a significant reduction (e.g., up to 44% compared with air-source heat pumps) of energy consumption and the corresponding emissions. At present, GSHPs mainly employ the refrigerant R410A as the working fluid, which has a Global Warming Potential (GWP) of 2087. However, following the EU Regulation No. 517/2014 on fluorinated greenhouse gases, this high GWP refrigerant will have to be substituted for residential applications in the next years. Thus, to increase the sustainability of GSHPs, it is necessary to identify short time alternative fluids with lower GWP, before finding medium-long term solutions characterized by very low GWP. This is one of the tasks of the UE project "Most Easy, Efficient, and Low-Cost Geothermal Systems for Retrofitting Civil and Historical Buildings" (acronym GEO4CIVHIC). Here, a thorough thermodynamic analysis, based on both energy and exergy analysis, will be presented to perform a comparison between different fluids as substitutes for R410A, considered as the benchmark for GSHP applications. These fluids have been selected considering their lower flammability with respect to hydrocarbons (mainly R290), that is one of the main concerns for the companies. A parametric analysis has been performed, for a reversible GSHP cycle, at various heat source and sink conditions, with the aim to identify the fluid giving the best energetic performance and to evaluate the distribution of the irreversibilities along the cycle. Considering all these factors, R454B turned out to be the most suitable fluid to use in a ground source heat pump, working at given conditions. Special attention has been paid to the compression phase and the heat transfer in evaporator and condenser.

In recent years, an increased focus has been given to replacing high Global Warming Potential (GWP) refrigerants with relatively low GWP alternatives. Energy efficiency, carbon reduction and HFC phase-down will push the heat pump market towards natural refrigerants. Propane (R-290) is a type of hydrocarbon refrigerant with zero ozone depletion potential and very low GWP (< 4). R-290 is a pure refrigerant and has excellent thermodynamic properties. The research presented in this project is a study of the refrigerant side of an ASHP to analyze the thermodynamic performance of the propane refrigerant under different operating conditions. For this purpose, a test rig was designed and constructed in a single packaged air source heat pump unit. In addition, the air side of the tested heat pump was designed for energy recovery in cooling and heating modes. The compactness of the system and installation of air dampers allows its placement for coupling to the building renewable air sources, such as a building integrated photovoltaic/thermal (BIPV/T) system.

Although CO 2 as refrigerant is well known for having the lowest global warming potential (GWP), and commercial domestic heat pump water heater systems exist, its long expected wide spread use has not fully unfolded. Indeed, CO 2 poses some technological difficulties with respect to conventional refrigerants, but currently, these difficulties have been largely overcome. Numerous studies show that CO 2 heat pump water heaters can improve the coefficient of performance (COP) of conventional ones in the given conditions. In this study, the performances of transcritical CO 2 and R410A heat pump water heaters were compared for an integrated nearly zero-energy building (NZEB) application. The thermodynamic cycle of two commercial systems were modelled integrating experimental data, and these models were then used to analyse both heat pumps receiving and producing hot water at equal temperatures, operating at the same ambient temperature. Within the range of operation of the system, it is unclear which would achieve the better COP, as it depends critically on the conditions of operation, which in turn depend on the ambient conditions and especially on the actual use of the water. Technology changes on each side of the line of equal performance conditions of operation (EPOC), a useful design tool developed in the study. The transcritical CO 2 is more sensitive to operating conditions, and thus offers greater flexibility to the designer, as it allows improving performance by optimising the global system design.

Domestic hot water heating of multifamily buildings accounts for a substantial portion of the energy load of existing buildings. This load is made up of both the energy required to produce hot water and the energy needed to maintain the temperature of the heated water within a building’s distribution piping so that heat can be promptly delivered to building occupants as needed. Properly designed heat pump water heater (HPWH) systems have the ability to improve efficiency in both water heating and temperature control operations. Further, CO2 heat pump technology reflects a shift away from traditional refrigerants and toward refrigerants with low global warming potential (GWP). In this paper’s case study, a design consisting of multiple CO2 heat pump water heaters (commonly used in single-family homes) with a novel “swing tank” was proposed to meet the demand for domestic hot water heating and recirculation loop temperature maintenance. The proposed design was applied to the retrofit of a 60-unit, low-rise, multi-family building located in the Pacific Northwest of the United States. The purpose of this paper is to verify the performance of the system including the proposed “swing tank” in a centralized SHW system using CO2 HPWH. It also provides practical information and lessons learned from the retrofit project. Long-term monitoring data showed that the system had a coefficient of performance (COP) of three or greater and provided an average of 20 gallons of hot water per day per apartment. The results of this work indicate that residential-scale CO2 HPWH equipment and a “swing tank” design can efficiently provide domestic hot water heating and temperature maintenance for mid-sized multifamily buildings.

Vehicle air conditioning is often blamed for its 20 to 40% overconsumption of fuel and its contribution to the greenhouse effect. This is largely due to the poor energy and environmental performances of the refrigerants used. Natural refrigerants as carbon dioxide (CO2) or hydrocarbon (HC) can contribute to contain the problem. But Carbon dioxide, as a refrigerant, does not liquefy at the high pressure heat exchanger of the refrigeration loop within tropical outside temperature, due to its low critical temperature (31°C), and HC are flammable. An alternative solution appears to be the use of the mixture of carbon dioxide (CO2) and hydrocarbon (HC) which is a less flammable or non-flammable refrigerant with low global warming potential. Thus the study reviewed the state of the art concerning the use of CO2 for vehicle air conditioning and focused on mixtures of CO2 and HC which are condensable at room temperature. The investigations were carried out on mixtures of CO2 and HC with different molar fractions of CO2 (from 0 to 100%). The equation of Van Poolen et al. made it possible to predict the critical points of the different mixtures. MATLAB software was used to compute the coordinates of the critical points of the mixtures and to deduce the eligible best mixtures candidate. The investigations showed that CO2/R600a mixtures are more suitable for hot and tropical areas.

Low global warming potential (GWP) refrigerants for the next-generation air conditioning systems have been investigated with target domestic applications. High-GWP refrigerants are mostly used in climate control applications such as heating, ventilation and air conditioning (HVAC) and refrigeration systems. The majority of refrigerants are responsible for significant environmental issues such as ozone layer depletion and global warming. The Montreal Protocol and the Kyoto Protocol have been implemented to address such issues. In the meantime, authorities in many countries have taken the initiative to phase out the usage of environmentally harmful refrigerants in vapor compression refrigeration systems. Following the global warming mitigation scheme by many signatory countries, research interest has been focused on finding alternative refrigerants with low or ultra-low GWP. This study considered the research trend and development of low-GWP refrigerants while examining system performance, safety issues, and the equivalent environmental impact as the critical assessment parameters. Here, the focus is primarily set on the potential of refrigerant blends (HFCs + HFOs) where the GWP value of 300 is set as the threshold value. Targeted for domestic heat pump systems, the performance of such systems using various refrigerant blends is collated and discussed. Many blends offer innovative drop-in replacements for R410A-conforming F-gas regulations. The technical difficulties and realistic remedies for the existing refrigerants are also discussed.

Review of energy efficiency and system performance of residential heat pump water heaters

Experiments of advanced centrifugal heat pump with supply temperature up to 100 °C using low-GWP refrigerant R1233zd(E)

Absorption heat pump system using R1234ze(E)/ionic fluid is developed for cooling and heating application in Proton-Exchange Membrane Fuel Cells (PEMFC) vehicles. Waste heat from the PEMFC is utilized as the heat source of the absorption heat pump system. A low global warming potential (GWP) refrigerant of (R1234ze(E)) and an ionic fluid of [hmim][Tf2N] are used as refrigerant and absorbent, respectively. Additionally, the heat pump system is assisted by a compressor placed between evaporator and absorber. Cooling and heating performance of the absorption heat pump is evaluated under various generator and absorber temperatures and concentrations. The results show that the coefficient of performance of refrigeration (COPc) is up to 0.566 and the COP of heat pump(COPH) is up to 1.517.

A photovoltaic-thermal (PV-T) hybrid collector evaporator was designed and developed to produce electrical energy and extract thermal energy simultaneously from the panel using the refrigerant circulated the evaporator tubes. The refrigerant absorbs the heat from photovoltaic panels during its phase change from liquid to vapour. The PV-T evaporators deliver both electricity and heat outputs. An R-32 refrigerant-based solar-assisted heat pump water heating system with a rated heat output of  4 kW was developed and tested its performance for producing 150-200 litres of hot water at an average temperature of 60oC. The R-32 refrigerant is selected because it does not have any ozone depletion potential (ODP), and possess very low global warming potential (GWP). The heat pump evaporator was designed to absorb 3.25 kW heat from the panel and maintains the panel below 30oC. The average PV electricity output was 6 kWh, and the requirement was 3.5 kWh. The average excess power of 2.5 kWh has been supplied to the grid, and the average coefficient of performance (COP) of the system was 6.3. For a life span of 25 years, the total equivalent warming impact analysis (TEWI) resulted in a CO2 value of 15,543 kg, which is very much lower than that of conventional systems. The economic analysis performed was reported, and the system is found to be quite suitable for domestic applications and also economically feasible with a payback period of 2.5 years. Keywords: Solar PV-T Collectors, VFD Compressor, Domestic Water Heating.

Ground Source Heat Pumps (GSHPs) take advantage of the high thermal inertia of the ground to achieve a higher energy efficiency compared to Air Source Heat Pumps. GSHPs, therefore, have the potential to reduce heating, cooling, and domestic hot water costs, however the high installation cost of borehole heat exchangers (BHEs) limits the growth of such installations. Nevertheless, GSHPs can be profitable under certain conditions (climate, expensive fuels, subsidies, etc.), which can be identified using geo-referenced data and Geographical Information Systems (GIS). The proposed work investigates the economic and financial ability of GSHPs to cover the heat demand of the residential building stock of the Italian region Valle d’Aosta. To identify the opportunities offered by GSHPs in the Valle d’Aosta region, more than 40,000 residential buildings were analyzed using a GIS-based method. The return on the investment was then assessed based on the occurrence of two conditions—the Italian subsidies of the “Conto Termico” and the installation of rooftop photovoltaic (PV) systems—which contribute to the reduction of the initial and operation costs, respectively. The life-cycle costs of the four resulting combinations were compared with conventional systems composed of an oil/gas boiler and an air-source chiller. One of the main findings of this study is that subsidies exert a key role in the financial feasibility of GSHPs, especially for replacing gas boilers, whereas the presence of a PV system has a minor influence on the financial analysis carried out.

Evaluation of low-GWP and mildly flammable mixtures as new alternatives for R410A in air-conditioning and heat pump system

The use of electric vehicles is rapidly increasing, but their range remains limited due to battery capacity constraints. This paper presents the thermodynamic analysis results of a novel type ejector-assisted heat pump designed for air-conditioning cycle (AC) for electric vehicles. Ejectors are used in cars to reduce compressor energy consumption in AC systems, which is crucial for improving electric vehicle battery efficiency. A chiller unit and an ejector were added to the heat pump system to increase the system’s efficiency. In the proposed system, environmentally friendly fluids with low global warming potential (R290, R1234yf, R1234ze, R600, R717, R744) were tested as alternatives to the refrigerants that are being phased out due to their negative effects on the environment. After applying the first and second law analyses of thermodynamics to the proposed system, an average coefficient of performance (COP) increase of 32.75% was found. According to the analysis results, among the examined fluids, R290 has the maximum COP value of 2.81. At the specified temperature values, the system using R290 as the refrigerant achieved the highest exergy efficiency, with a value of 0.24.

Experimental study of propane heat pump system with secondary loop and vapor injection for electric vehicle application in cold climate