The optimization of rotor profiles in screw compressors plays a crucial role in enhancing overall efficiency and performance under different operating conditions. Conventional rack generation methods serve as foundational tools for manipulating rotor profiles and ensuring the correct kinematics. However, to further explore the design space of screw profiles, machine learning (ML) can be leveraged and integrated to couple geometry manipulation and compressor performance estimation. To this end, the rack profile has been parametrized into segments based on normal and position vectors to allow the systematic generation of diverse profile geometries based on imposed constraints and/or objective functions. To conduct a global search, a genetic algorithm (GA) has been modified to include appropriate fitness criteria to automate the evolutionary profile generation process. Candidate profiles are evaluated using an ML model trained with a 1D compressor mechanistic model to predict performance metrics and both flow and mechanical losses. This integrated approach significantly reduces the computational time for completing a full GA optimization. The algorithm was trained and executed entirely on CPU due to the logic-intensive nature of geometry evaluation and performance prediction, which favor structured decision-making over the highly parallel workloads typically suited for GPU acceleration. An oil-injected screw compressor for industrial applications has been used as the case study. The results from the optimization runs are discussed and compared with higher-fidelity models such as CFD and a fully mechanistic compressor model.

The global phase-down of high-Global Warming Potential (GWP) refrigerants has created a need for compressors optimized for alternatives such as R-290 and R-454C. Although compressors using these refrigerants exist commercially, the open literature offers limited guidance on how their thermophysical properties, including vapor density, volumetric capacity, and leakage sensitivity, should inform geometric design. Additionally, it lacks a clear, systematic methodology for adapting existing compressor platforms to alternative refrigerants. This work addresses these gaps by building on a validated experimental and numerical framework that matched manufacturer and experimental data within +/- 5 % and incorporated detailed leakage correlations, a motor map, and a six-lump thermal network in the mechanistic model. Using this foundation, a soft optimization procedure is applied to redesign an R-410A scroll compressor for use with R-290 and R-454C. The optimization establishes clear relationship between geometry and performance, showing that the displacement volume governs capacity for low-density refrigerants, the built-in volume ratio controls over-/under-compression losses and strongly affects efficiency, scroll height primarily affects flank leakage and volumetric efficiency, and the base radius balances leakage reduction against higher frictional and thrust-bearing losses. Optimized R-290 design achieves 74.4 % peak overall isentropic efficiency, a seasonal COP of 5.11, and about 3.4 % lower annual power use than the R-410A baseline. Optimized R-454C design reaches 73.9 % peak efficiency at matched capacity, and the R-410A baseline delivers 74.4 % peak overall isentropic efficiency. Overall, this methodology provides a transferable pathway for adapting legacy HFC-based compressors to emerging next-generation refrigerants and to different compressor architectures.

The industrial sector is a major contributor to primary energy consumption and carbon emissions, with many processes relying on fossil fuels for heating and steam production. High-temperature heat pumps (HTHPs) have emerged as a promising alternative for decarbonizing industrial heating processes, particularly within certain temperature ranges. However, the limited availability of components that can safely and efficiently operate in a high-temperature environment over a long period of time is still a bottle-neck in the overall system and technology development. To address this challenge, a design study was conducted to develop a twin-screw compressor for HTHP applications targeting heat sink temperatures up to 200 ℃ with cyclopentane as the working fluid. An industrial refrigeration compressor has been used to establish a baseline geometry and to further manipulate the profiles to target HTHP boundary condition requirements. A thermodynamic model of the compressor has been used to investigate the design space and evaluate the impact of lubricant and economization of the discharge temperature, performance metrics, and losses. Furthermore, the dynamic behavior and thermal deformation during operation of the newly defined rotor pair was analyzed with a rotor dynamics simulation model to quantify the thermal–mechanical stresses and impact on sealing lines. Based on the findings, the 5/7 rotor configuration was further optimized to achieve a heating capacity of approximately 40 kW that will be used in an experimental setup. This study provides insights into advancing the design of compressors for high-temperature heat pump systems, addressing critical challenges in component performance and system reliability.

The phase-down of high-global warming potential (GWP) refrigerants such as R-410 A, driven by the Kigali Amendment and regional regulations, has motivated the need for sustainable alternatives. Among alternative candidates, R-290 and R-454C offer favorable thermodynamic properties but lead to efficiency and capacity losses when used in compressors designed for hydrofluorocarbons (HFCs). This study establishes an experimental and numerical framework for developing compressors optimized for R-290 and R-454C but applicable for a range of alternative working fluids. Using experimental data collected in the scope of this project, a mechanistic compressor model was developed in the Positive Displacement Simulation (PDSim) environment to capture leakage, mechanical, and thermal losses. The model, featuring a multi-lump thermal network, achieved mean absolute percentage errors of 2.40%, 1.18% and 2.17% for mass flow rate, power consumption and overall isentropic efficiency, respectively, along with mean absolute error of 1.74 °C for discharge temperature. Energy distribution analysis showed that approximately 18% of electrical input power was lost through motor and mechanical frictional losses. The model-inferred energy distribution indicated that the scrolls, motor, and shell components are likely important heat-transfer regions, providing insights on internal thermal pathways. The developed framework provides an experimentally assessed foundation for compressor performance analysis and redesign studies. Future work will employ a soft-optimization approach to systematically adjust the displacement volume, built-in volume ratio, and leakage-sensitive parameters to enhance capacity and overall isentropic efficiency for R-290 and R-454C relative to the baseline R-410 A, and subsequently extend the analysis to other HFCs and their alternatives.

To enable smarter, more versatile, and more energy efficient domestic refrigerators, advanced cycle architectures and controllers are needed. Specifically, a multi-evaporator vapor-injected cycle architecture has been investigated in our previous work, and initial theoretical assessments estimated nearly 13

Residential buildings are increasingly integrating large devices that run natively on direct current (DC), such as solar photovoltaics, electric vehicles, stationary batteries, and DC motors that drive heat pumps and other major appliances. Today, these natively-DC devices typically connect within buildings through alternating current (AC) distribution systems, entailing significant energy losses due to conversions between AC and DC. This paper investigates the alternative of connecting DC devices through DC distribution. Specifically, this paper shows through laboratory and field experiments that an off-the-shelf residential heat pump designed for conventional AC systems can be powered directly on DC with few hardware modifications and little change in performance. Supporting simulations of a DC nanogrid including historical heat pump and rest-of-house load measurements, a solar photovoltaic array, and a stationary battery suggest that connecting these devices through DC distribution could decrease annual electricity bills by 12.5% with an aftermarket AC-to-DC heat pump retrofit and by 16.7% with a heat pump designed to run on DC. The associated savings in gross nanogrid energy are 8% and 9.2%, respectively.

This study experimentally investigates the impact of coil installation orientation on static pressure difference and airflow structure in HVAC&R duct systems, focusing on an A-coil evaporator heat exchanger. Tests were conducted in a controlled psychrometric wind tunnel at nine air velocity setpoints for three configurations: Acoil at 90 degrees, A-coil at 23 degrees (diagonal), and a MERV 8 filter at 90 degrees. Differential static pressure was measured using a high-accuracy differential pressure transducer, and downstream airflow patterns were captured via high-speed imaging for qualitative flow visualization. Results show a quadratic relationship between differential pressure and air velocity for all configurations, with orientation significantly influencing performance. The 90 degrees A-coil exhibited the highest pressure drop (100 +/- 2.5 Pa at 2.13 +/- 0.3 m/s), while the diagonal installation reduced the coil pressure drop by up to 57% relative to the perpendicular configuration. The MERV 8 filter demonstrated intermediate resistance. A corrected Forchheimer equation incorporating an angle-dependent factor is proposed, accurately reflecting observed reductions in viscous and inertial contributions for diagonal installations. Flow visualization revealed that diagonal placement promoted smoother flow redirection, reduced stagnation, and generated lower frequency shedding, more evenly distributed flow structures downstream, correlating with the measured lower inertial term. These findings highlight the potential for simple geometric modifications to reduce fan power demand, improve flow uniformity, and maintain thermal performance without major component redesigns. The dataset and correlations developed provide a benchmark for validating computational models of duct airflow and can inform energy-efficient design strategies.

With the deployment of variable-speed compressors in unitary air conditioning (AC) systems as well as the future implementation of newer HFO refrigerants, there is a need to upgrade line sizing guidelines to account for the effects of oil retention (OR). These new guidelines can be facilitated through developing and applying a predictive model for OR in vapor lines for commonly used refrigerant-lubricant combinations in the heating, ventilation, air conditioning, and refrigeration (HVAC&R) industry. This work aims to evaluate the prediction accuracy of machine learning (ML), physics-based (PB), and hybrid models trained using OR data obtained for horizontal and vertical lines of different diameters (11, 17, and 20 mm). The data include different refrigerants (R134a, R410A, R32, and R1234ze(E)) used with POE32 lubricant under various flow conditions. The ML models were trained and tested using data obtained from over 230 experimental tests. The input parameters for each model were refrigerant conditions (type, temperature, pressure, and mass flow rate), pipeline dimensions and orientation, injected oil mass flow rate, and oil viscosity, with OR as the predicted output. Various model types were investigated and compared, including a purely physics-based (PB) model, two standalone ML models, and two physics-based machine learning-aided (PBMLA) algorithms. A sensitivity analysis was performed to assess the effect of input parameters on the prediction errors. In addition, an extrapolation study was conducted using different refrigerants and various oil grades and types to evaluate the models’ ability to predict OR with acceptable accuracy. The results showed that the standalone ML algorithms exhibited lower accuracy in predicting OR compared to the PB model. Furthermore, the PBMLA models demonstrated a modest improvement in OR prediction accuracy over the purely PB model (improved R2 by up to 10.8%, and reduced RMSE by up to 4.5%). Moreover, the parametric analysis revealed that the PBMLA models could address variations of the feature inputs relatively better than the PB model, leading to their higher prediction accuracy compared to all other models. Finally, the extrapolation analysis showed that both the PB and PBMLA models were not limited to specific oil types or grades, suggesting their potential for general applicability in OR prediction and system design.

With growing environmental concerns and stricter regulations on high global warming potential (GWP) refrigerants, as well as the potential ban on per- and polyfluoroalkyl substances (PFAS), the quest for sustainable alternatives has intensified. Due to its low GWP and excellent properties, propane (R290) is considered a promising long-term solution. However, safety concerns surrounding its flammability have hindered its widespread adoption in residential settings. This work adopts a critical review framework to evaluate recent advancements in residential heat pump and air conditioning systems utilizing R290 as a refrigerant, offering deeper insights to enhance our understanding of these technologies. It includes aspects such as thermophysical properties, system design and performance, current regulations, and safety concerns. The paper examines the key advantages of R290 that contribute to its superior system performance and summarizes best design practices. It also addresses challenges, such as reducing the refrigerant charge to meet safety standards requirements. Studies have demonstrated that a specific charge of as low as 30 g/kW is attainable. The findings of this review were utilized to evaluate the feasibility of incorporating R290 into various residential systems. This study suggests that employing R290 in small-sized systems such as mini-split and window air conditioners should not pose significant challenges. However, its adaptation into larger unitary systems remains uncertain, prompting the need for further safety assessments and potential updates to safety standards. Furthermore, this review provides a summary of existing research gaps in the current literature and future research directions.

The Electrochemical Looping Heat Pump (ELHP) introduces an innovative heat pump technology by replacing the traditional compressor with a reversible chemical reaction between a refrigerant pair. Prior research has highlighted the isopropanol/acetone pair as a highly promising candidate for this system, owing to its low Global Warming Potential (GWP) and high Coefficient of Performance (COP). This study presents a comprehensive simulation model of the electrochemical cell, the core component of the ELHP cycle, developed using COMSOL Multiphysics. The model integrates multiple physical fields, including electric potential, fluid dynamics, temperature, and mass transport, enabling a comprehensive simulation of the electrochemical cell. The study highlights the critical role of diffusivity in mass transport, demonstrating that a 10% increase in diffusivity can enhance system performance by 9.05%. These findings offer valuable guidance for optimizing the ELHP design and operation in the future.

As the United States transitions to greener power generation, the ability for the grid to handle complex daily demand profiles is becoming an increasingly hard problem to solve. Solar and wind power is intermittent, and often greatly out of sync with demand curves. Demand for electrified services (space heating/cooling, and electric vehicles) is also increasing, which the distribution grid is currently not able to support. Energy storage can help to smooth out these demand curves, especially for residential building energy systems with a high penetration of renewable energy generation. Being able to self-consume or store renewable energy generated can therefore help aid grid decarbonization. Typically, most energy storage applications for residential use are electrical. However, there is still an opportunity for the integration of Thermal Energy Storage (TES) since it can directly supply heating or cooling without an electrical conversion. However, TES hasn't achieved practicality for residential use from a techno-economic perspective since the return on investment is often noted as anywhere from 10-30 years depending on the technology chosen. This paper will present a convex model of a fully electrified residential building, the DC Nanogrid House, with PV production and electric storage to optimally size a TES-integrated HP system. Simulation results from several climate zones across the US are presented. A techno-economic assessment of multiple different TES technologies is performed to help unlock the design space of residential TES systems, to highlight their contribution in net zero energy operation, and to understand the context in which they are a viable option. This study concludes that a key benefit to TES utilization in residential buildings is grid flexibility, allowing for more complex day-ahead grid signals to be used by space conditioning systems.

The stringent regulatory shift towards low-global warming potential (GWP) refrigerants has necessitated the development of alternatives to existing high-GWP working fluids used in residential heat pumps and air conditioning systems. The scarcity of single-component refrigerants that are safe, efficient, environmentally sustainable, and cost-effective has driven increased interest in refrigerant mixtures as a viable solution. This study presents a theoretical screening of refrigerant mixtures to identify drop-in replacements for R410A that demonstrate ultra-low GWP and reduced flammability, designed for cold-climate applications. Binary and ternary blends were systematically evaluated using fifteen pure refrigerants, which included hydrocarbons (HC), hydrofluorocarbons (HFC), hydrofluoroolefins ( HFO), and CO2. The mixtures were investigated in 0.04-mole fraction increments, optimizing thermodynamic performance, environmental impact, and flammability characteristics. The analysis identified four promising mixtures incorporating R1123, complemented by R1234yf and an HC such as R290. This work highlights the potential of carefully engineered refrigerant blends to achieve regulatory compliance while meeting operational performance requirements. The findings contribute to developing sustainable refrigerants and offer valuable insights for future experimental validation and practical implementation.

Space cooling and heating systems in buildings use nearly 33% of the world's energy. To make heat pump (HP) systems more energy-efficient, especially during part-load operation, it is important to use variable-speed compressors. However, part-load conditions come with their own set of problems, primarily because the ideal amount of refrigerant varies based on both indoor and outdoor temperatures. Another difficulty is accurately controlling the expansion device when both operating conditions and refrigerant charge levels fluctuate. In this study, we examined an R-410A based 5-ton (17.6 kW) HP system that includes a variable-speed rolling piston compressor and an expander/separator replacing a traditional expansion valve. This expander/separator also recovers some energy during the expansion process. A validated steady-state HP model in cooling mode was used to simulate performance, with refrigerant charge gradually increased from 4.2 kg to 5.6 kg in steps of 0.01 kg across six different operating scenarios. The analysis revealed that the system achieved its highest coefficient of performance (COP) when the charge was around 5 kg, though this optimal point shifted slightly (+/- 0.03) based on operating parameters. While the cooling output rose steadily with added refrigerant, extra charge led to flooding in the expander/separator, which in turn lowered the energy recovery output. Furthermore, using the optimized refrigerant charge of 5 kg, the cycle was simulated to match the building loads for typical residential buildings in a mixed-humid climate (West Lafayette, IN, USA), and in an extreme hot-dry climate (Kuwait City, Kuwait) during summer months. Comparisons were made between an R-410A based 5-ton (17.6 kW) baseline-TXV cycle and the expander cycle. Similar overall hourly COPs were reported from these simulations. However, the cooling capacity from both locations was higher for the expander system than the TXV-system by 0.3 to 2 kW. As the HP was undersized for an extremely hot-dry climate zone, the expander was unable to generate power at peak temperature periods in Kuwait, given the expander over-flooded with refrigerant as opposed to the mixed-humid case. These results highlight the need for an effective system to manage refrigerant charge, as maintaining the right charge level under different environmental conditions is essential, especially with upcoming cooling technologies expected to use low-Global Warming Potential (GWP) refrigerants. In addition, there is a need to optimize the expander designs depending on the climate zones to achieve maximum COP improvements and power generation.

To reduce the direct global warming impact of refrigerants in HVAC&R applications, low-global warming potential (GWP) refrigerants, including natural refrigerants, have been extensively investigated as alternatives to hydrofluorocarbon (HFC) refrigerants. Among the natural refrigerants, Carbon Dioxide (CO2) offers several advantages, such as excellent transport and thermo-physical properties, being neither toxic nor flammable, and having a low price and high availability around the world. However, the high critical pressure and low critical temperature of CO2 often lead to transcritical operation, resulting in lower efficiency due to the additional compressor power necessary to achieve transcritical operation relative to subcritical HFC cycles. Therefore, a number of cycle modifications are used to enhance the coefficient of performance (COP) of transcritical CO2 cycles to meet or surpass those of HFC cycles. This paper provides a systematic experimental investigation of four such cycle architectures by employing the same multi-stage, two-evaporator CO2 refrigeration cycle test stand, 3 of these configurations in transcritical and 1 in subcritical conditions. The four cycles architectures included intercooling, open economization, an internal heat exchanger and two different ejector control approaches. Specifically, a variable-diameter motive nozzle and a variable-speed liquid CO2 pump located directly upstream of the ejector motive nozzle inlet were analyzed. Based on the experimental data, the maximum COP improvements are 4.64 % and 9.47 % when the ejector and the internal heat exchanger are used, respectively. The CO2 pump, once successfully stabilized, can control the ejector, increase its efficiency by up to 15% and increase the cooling capacity to a maximum of 6.2 %. Nevertheless, a reduction in COP is measured when the pump is in use; however, unlike the other three different configurations, it was only analyzed under subcritical conditions.

Ejectors are used in various engineering systems, including steam and vapor compression cycles. Optimizing the performance of ejectors requires understanding and analysis of multiphase and turbulent flow structures associated with their internal flow fields. This approach yields higher fidelity but at a high computational cost. Lower-fidelity one-dimensional (1D) models offer lower computational costs; however, 1D models are often empirical and provide limited understanding of the internal flow fields, overlooking possibilities of optimization. Ejector flows can be categorized into four regimes: Regime 1 (R1), which is compressibility dominated; Regime 2 (R2), which is interface instability driven; Regime 3 (R3), which is buoyancy dominated; and Regime 4 (R4), which is a wall-bounded turbulent jet expansion. Among these, the buoyancy-dominated regime is the most complex and least understood. This work discusses an approach to develop a reduced-order model utilizing a selfsimilarity framework to capture the internal flow field of the jet within the buoyancy-dominated regime under quasi-steady, compressible, and isothermal flow conditions, where density variations arise only from mixing. The density variation is captured through the Favre-averaging approach. The model captures the expansion of a central jet influenced by momentum diffusivity and a constant streamwise pressure gradient. Interaction of the central jet with the cylindrical wall induces a counterflow annular wall jet due to the combined effects of negative radial density gradients and shear stress imposed by the wall. Initially, the discussion focuses on flow topology inside the ejector, followed by the self-similarity methodology and implementation of asymptotic analysis. Finally, the resemblance of the self-similar nature of the flow field and the existence of inner and outer regions in the flow field are discussed. The boundary conditions are derived from a validated high-fidelity three-dimensional (3D) numerical simulation of a subcritical liquid-gas carbon dioxide (CO2) ejector used in multi-stage refrigeration. The 3D simulations modeled turbulence via the Reynolds Averaging approach, incorporating a Reynolds Stress Model - Shear Stress Gradient (RSM-SSG) as the closure. The self-proposed similarity methodology developed from the knowledge gained from the 3D simulations enables the development of a low-order model that accurately predicts jet interface characteristics, providing a fast and efficient tool for optimizing ejector designs in cycle-level applications.

Residential electrification - replacing fossil-fueled appliances and vehicles with electric machines - can significantly reduce greenhouse gas emissions and air pollution. However, installing electric appliances or vehicle charging in a residential building can sharply increase its current draws. In older housing, high current draws can jeopardize electrical infrastructure, such as circuit breaker panels or electrical service (the wires that connect a building to the distribution grid). Upgrading electrical infrastructure can entail long delays and high costs, so poses a significant barrier to electrification. This paper develops and field-tests a control system that avoids the need for electrical upgrades by keeping an electrified home's total current draw within the safe limits of its panel and service. In the proposed control architecture, a high-level controller plans device set-points over a rolling prediction horizon. A low-level controller monitors real-time conditions and ramps down devices if necessary. The control system was tested in an occupied, electrified single-family house with code-minimum insulation, an air-to-air heat pump and backup resistance heat, a resistance water heater, and a plug-in hybrid electric vehicle with Level I charging. The field tests spanned 31 winter days with outdoor temperatures as low as -20 C. The control system maintained the whole-home current within the safe limits of electrical panels and service rated at 100 A, a common rating for older houses in North America, by adjusting only the temperature set-points of the heat pump and water heater. Simulations suggest that the same 100 A limit could accommodate a second electric vehicle with Level II charging. The proposed control system could allow older homes to safely electrify without upgrading electrical panels or service, saving a typical household on the order of $2,000 to $10,000.

The phasedown of hydrofluorocarbon (HFC) refrigerants with high global warming potential (GWP), alongside growing restrictions on PFAS compounds, has intensified the search for sustainable and efficient alternatives in residential space conditioning. Propane (R290) has emerged as an appealing environmentally friendly refrigerant, but its flammability requires the utilization of indirect system architectures. In parallel, electrification efforts demand highly efficient heat pumps to replace traditional fossil fuel-based heating systems. This study experimentally evaluates a novel two-stage, variable-speed, liquid-to-liquid heat pump with R290 refrigerant for cold climates. Unlike prior studies, it introduces independent speed control of the low-and high-stage compressors, providing the first experimental dataset for R290 in two-stage systems. The system achieved an 18.3% increase in heating capacity and a 5.8% improvement in the coefficient of performance (COP) at an ambient temperature of-8.3 degrees C in two-stage mode compared to single-stage operation, although with an 11% increase in refrigerant charge level. The study also highlights the critical role of the secondary fluid in system design, overall performance, and thermal comfort. Namely, a design mismatch was identified between hydrocarbon refrigerants and aqueous secondary fluids in the evaporators of indirect systems operating at low evaporation temperatures. These findings provide key insights for designing high-performance regulation-compliant heat pumps suitable for safe residential use in cold climates.

High-pressure liquid carbon dioxide (CO2) entering the converging motive throat of an ejector with a pin forms a jet that entrains low-pressure gas in the mixing zone, creating an annular wall-bounded jet. This study investigates the flow regimes and turbulence mechanisms of such jets using large eddy simulation for a CO2 ejector in a subcritical vapor compression cycle. The high-pressure liquid jet enters at a Reynolds number (Re) of 1.2 × 105, while the low-pressure gaseous CO2 enters at Re 9.8 × 104. The outlet pressure (Pd) is 1.2 times the suction inlet pressure (Ps). The jet inside the ejector is categorized into different regimes based on the dominant physics in the regime. The jet initially expands due to the pressure drop between the high-pressure nozzle and the low-pressure suction chamber in response to the isothermal expansivity of CO2(l) (regime 1) and thereafter behaves as an incompressible flow with an interface affected by Kelvin–Helmholtz instabilities (regime 2). The developing region of the jet (regime 3) is characterized by an adverse pressure gradient with reverse flow outside, similar to a negatively buoyant turbulent jet. The fully developed turbulent jet (regime 4) is a wall-bounded turbulent flow filling the mixing chamber. The design intent is to entrain vapor from the suction inlet. Our insight is that entrainment is maximized by design changes that extend regime 3, where entrainment occurs. This study advances the development of a reduced-order mixing zone model for an ejector, offering strategies to optimize ejector efficiency for any fluid and operating conditions.

The chemical looping heat pump (CLHP) is a promising electrochemical heat pump technology due to high system efficiency, scalability, and use of low-to-zero Global Warming Potential (GWP) fluids. However, similar to other emerging HVAC&R technologies, there is a lack of direct comparison and discussion of economics between CLHPs and conventional vapor compression (VC) heat pumps. In this work, a generalized modeling framework to estimate the levelized cost of energy (LCOE) for space conditioning applications is used to assess the early-stage economic feasibility of CLHP. The LCOE consists of two components: levelized operating expenditures and levelized capital expenditures. These clarify the influence of key factors such as annual cooling and heating delivered and price of electricity. The simulations show that the LCOE of CLHP could be less than that of VC in the case of unit utilization of >30,000 kWht yr(-1), operating current density of >0.4 A cm(-2), and 30% performance improvements. This is despite the projected capital cost of CLHP is nearly 1.6 times higher than that of VC system.

The development of advanced heat pump technologies is critical for reducing global energy consumption in the building sector, where space heating and cooling account for nearly 50% of energy use. Electrochemical heat pumps (EHPs) offer a promising alternative to vapor compression systems by enabling direct electrochemical-to-thermal energy conversion, often with environmentally benign working fluids that exhibit low or zero global warming potential (GWP). Prior literature has predominantly focused on chemically reactive heat pumps, while comprehensive assessments of electrochemical mechanisms remain limited. This review addresses this gap by systematically evaluating the underlying principles, architectures, and performance metrics of EHP systems. Compared to conventional vapor compression systems, EHPs can achieve 10%–30% higher energy efficiency, with reported cooling coefficients of performance (COPc) ranging from 3.5 to 14.3 under standard operating conditions. Despite these advantages, widespread adoption is hindered by challenges including membrane degradation, electrode fouling, sluggish redox kinetics, and elevated system-level capital costs. To address these limitations, the review outlines three research priorities: (i) the development of advanced membranes, catalysts, and electrode materials with enhanced chemical and mechanical stability; (ii) the application of molecular-level simulations for the rational design of high-performance redox-active working fluids; and (iii) the integration of advanced diagnostic techniques for real-time monitoring and sustained operation of EHPs. By consolidating recent advances and explicitly identifying technological and scientific gaps, this work uniquely contributes a comprehensive framework for guiding future electrochemical heat pump research and facilitating the transition to sustainable thermal management technologies.