Compression Heat Pump Research Articles

Visualization Study on Oil Return Characteristics of Vapor Compression Heat Pump System

Vapor compression heat pump technology is a widely utilized method for energy conversion. Lubricating oil plays a crucial role in the heat pump system cycle by effectively reducing wear on the compressor’s moving parts and preventing refrigerant leakage. However, it can also create an oil film in the heat exchange equipment, which increases thermal resistance and diminishes heat transfer efficiency. This study utilizes a vapor compression heat pump system test bench to investigate factors influencing the system’s oil circulation rate, the two-phase flow patterns of refrigerant and lubricating oil, and the impact of oil circulation on system performance. The findings reveal that as the compressor speed increases, the oil circulation rate initially decreases before increasing again. Additionally, a decrease in the evaporator’s heat load leads to a reduction in oil circulation at high temperatures, while it increases at low temperatures. Furthermore, increasing the opening of the electronic expansion valve results in a gradual decrease in the oil circulation rate, whereas an increase in the refrigerant charge correlates with a rise in the oil circulation rate. The oil return flow pattern can primarily be categorized into three states: slow oil return, oil film flow, and high-speed oil return. These patterns are closely related to the degree of superheat, with lower superheat levels intensifying oil return.

The Joint Use of a Phase Heat Accumulator and a Compressor Heat Pump

This article presents an example of the joint use of a compressor heat pump that uses propane as a natural, ecological thermodynamic medium and a phase heat accumulator that uses paraffin as a medium. Special attention has been paid to the solidification process of the phase change material, and a simple theoretical model of the solidification of this material has been proposed. Thermodynamic balance calculations were carried out for the compressor heat pump and the phase heat accumulator. This paper presents a theoretical analysis of two examples of heating using a compressor heat pump, implementing the Linde cycle for the refrigerant R290 (propane): high-temperature heating at a temperature of 80 °C and low-temperature (surface) heating at a temperature of 60 °C, with the same unit heat output of 0.376 kW taken from the lower-temperature heat source of each evaporator. This heat is generated by the solidification of the PCM. The compressor power is 77 W in the first case and 40 W in the second. The energy efficiency coefficients of the compressor heat pump for the proposed combination of a phase heat accumulator and compressor heat pump are 5.98 and 10.40. The joint use of a heat accumulator and a heat pump presented in this paper can be used in applications for the heating of domestic water or water for space heating.

Experimental and numerical study on transcritical CO2 air source heat pump water heater

As environmental problems become more and more serious, CO2 is widely used as a natural work material in heat pump water heaters. In order to better improve the performance of CO2 air-source heat pump water heater, a trans-critical CO2 quasi-two-stage compression heat pump system with ejector (TCIEJ) is proposed. And a transcritical CO2 air-source heat pump water heater experimental bench was built. The effects of parameters such as cooling water flow rate, high pressure and compressor frequency on the performance of the heat pump were tested. A simulation model of TCIEJ was also developed to simulate the system performance. The results show that when the cooling water flow rate is increased from 70 kg/h to 122.5 kg/h the COP is improved by 30 %, while the cooling water discharge temperature is reduced by 15.4 %. System performance can be enhanced by increasing the cooling water flow rate within the temperature range required to meet hot water demand. When the high-pressure pressure of the TCIEJ system was increased from 8.0 MPa to 10.4 MPa, the cooling water discharge temperature increased by 17.66 °C on average. Even in the ambient temperature of 0 °C high-pressure pressure of 10.4 MPa, the compressor discharge temperature is only 85.77 °C. It shows that the combination of make-up air technology and ejectors effectively reduces the compressor discharge temperature, which is conducive to improving the compressor’s service life.

Blocked force characterization and transposition at secondary connections of a compressor

Applications in sustainable energy systems, like heat pumps, are encountering emerging challenges, among which acoustic comfort stands out as a critical factor in shaping the end-user experience. Early integration of vibroacoustic into each industrial design phase ensures the prevention and prediction of potential noise issues, thus avoid costly design modification loops. BDR Thermea and CETIM, in a collaborative project, have implemented new methodologies for designing acoustically optimized products, highlighting the importance of considering vibroacoustic design at each design stage of new products developments. In this study, structure-borne noise characterization methods are applied to a heat pump compressor using the ISO 21955 and ISO 20270 standards. The forces transmitted at its suction and discharge ports were studied through component based TPA for the intrinsic characterization of the compressor. Once obtained, these forces were transposed to a new receiving structure. The results allowed a comparison of the outcomes from both approaches and highlighted the importance of considering the influence of the stiffness of the connections at the compressor ports.

Water heater storage heat pump cycle for higher operating range

Heat pumps for water heating have become increasingly attractive. However, the achievable water temperature using a vapor compression heat pump water heater (HPWH) is often constrained by the compressor operating envelope. To address this challenge, HPWHs typically employ two-stage compression with complex system architecture or rely on back-up electric heating. This work introduces an alternate storage heat pump concept to improve the operating temperature range of an R134a HPWH system. The developed system operates in two modes: Mode I functions as a typical wrap-around condenser HPWH, while Mode II splits the wrap-around coil to use the top portion as a condenser and the bottom portion as evaporator. System modeling consisting of a vapor compression cycle and water tank sub-models was conducted to study the performance. The model was validated experimentally. The storage heat pump system could achieve an additional increase of 12 °C beyond the maximum possible water temperature of 46 °C which was achieved using the baseline conventional HPWH system. In Mode II, the system exhibits a 20 % higher average heating capacity and a 15 % lower average pressure ratio compared to the conventional system operating at a 27 °C ambient temperature. Compared to usage of electric heating elements, our system showed a longer recovery time with a 50 % lower energy consumption for a similar increase in water temperature.

Fast-airflow tumble clothes dryer with small thermoelectric heat pump: Experimental evaluation

Residential clothes drying accounts for about 5 % of the total residential-sector energy consumption in the United States. Most dryers use electric resistance heaters to dry clothes and have low efficiencies. Higher-efficiency dryers that use vapor compression heat pumps are expensive and complex and have not gained a large market share in the United States. A novel tumble clothes dryer using a small thermoelectric heat pump with faster airflow than typical dryers is presented in this work. The benchtop performance of the thermoelectric heat pump and high-speed blower are presented, and the development of the prototype dryer is described. The dryer was tested for efficiency and dry time for a range of airflow rates and applied currents to the thermoelectric heat pump. The combined efficiency factor was 5.09–6.29 lbBDW/kWh (specific moisture extraction rate of 1.23–1.53 kgw/kWh) with 100–138 min dry times for these tests. The measured efficiency was 36 %–68 % greater than the minimum efficiency standard in the United States, and compared with vapor compression heat pump–based clothes dryers, the prototype dryer had less expensive, less complex components and did not use refrigerants. The performance of this small thermoelectric heat pump clothes dryer is also compared with previous iterations of the thermoelectric tumble clothes dryer described in the literature.

A mass-coupled hybrid absorption-compression heat pump with output temperature of 200 °C

Heat pump technology is a promising solution for energy saving and emission reduction in industry. However, current technologies with limited temperature lift are not sufficient to meet the industrial heat demands. Aiming at efficient heat supply over 200 °C, this work proposes a hybrid absorption-compression heat pump cycle with mass coupling between LiBr-water type II absorption heat pump and water vapor compression heat pump, which could reduce the working pressure of compressor. Water injection is applied in the compressor for performance improvement. Detailed performance analysis is carried out for the hybrid heat pump cycle, showing an optimized COP of 3.01 under the temperature lift from 150 °C to 200 °C. Besides, the proposed system is capable of achieving temperature lift of 50 °C for heat source between 100 °C and 164 °C. Greater application superiority occurs at higher temperature output. The proposed cycle broadens the working domain of heat pump.

Numerical modeling of heat transfer mechanism in remote sensing bulb of thermal expansion valves

Thermal management of automotive systems has garnered a lot of focus in recent times to improve the energy efficiency of vehicles and address the challenge of global warming. In combustible fuel vehicles, the heat pump compressor is driven by the engine power which leads to changes in operating condition of the cycle while the vehicle is in motion. In electric vehicles, a combined thermal management strategy handles both cabin and battery pack cooling/heating depending on the ambient conditions and power requirements by adjusting refrigerant flow rates and flow directions with sophisticated valves. Irrespective of the vehicle type, effective variable refrigerant flow control is prerequisite to ensure optimum thermal comfort with minimum energy. Thermal expansion valves (TXV) are the most widely used method for regulating mass flow rate of refrigerant during the expansion step of the vapor compression cycle based on the principle of trying to maintain a fixed degree of superheat at the evaporator outlet. Conventional models of the thermal expansion valve ignore the time lag between fluctuation of temperature at the evaporator outlet and the corresponding change in pressure of the TXV remote sensing bulb, treating the valve as an instantaneous element during transient operation. This paper presents a novel method for determining the temperature profile and time constant of the remote sensing bulb response using numerical methods, in an attempt to capture the dynamics of thermal expansion valve in active heat pump cycle. Finite difference method was used to solve for the conduction heat transfer between the bulb and the heat exchanger outlet tube in perfect thermal contact applying the necessary boundary conditions. This improved modeling approach will be helpful in better prediction of the dynamic behavior of thermal expansion valves and how it influences the evaporative heat exchanger performance during transient operations to determine control algorithm and strategies.

Biogas Heat Pump Power Supply Based on Smart Grid Functioning Solar Electric System Network

A comprehensive integrated solar power plant system has been developed to support the operation of a biogas plant based on a heat pump, for which fermented wort is a low-potential energy source. The change in the power factor of the solar power system connected to the grid and the temperature of the coolant entering the heat exchanger built into the methane tank are predicted. Promising solutions include changing the power of the heat pump compressor to maintain biogas production, unloading fermented wort and loading fresh material while maintaining the power factor of the grid solar system and changing the level of electricity transmission to the grid. The voltage at the input of the hybrid inverter, the voltage at the output of the frequency converter to assess their ratio and the voltage frequency are constantly measured. When changing the voltage at the input of the hybrid inverter from 240 V to 600 V, promising solutions were adopted to reduce the power of the heat pump from 3.14 kW to 1.58 kW in the production of biogas 352.5 m3/day to maintain the temperature of the heating coolant entering the heat exchanger built into the methane tank at 55° C - 45 °C in order to obtain biogas, unload fermented wort and load fresh raw materials. There is an increase in the power of electricity transmission to the grid from 0.27 to 1 and an increase in the power factor by 40% from 0.58 to 0.98. The use of the developed Smart Grid technology allows preventing peak loads of the power system, reducing electricity consumption from the grid by up to 30%.

Developing a novel anticipated inherent risk assessment approach applicable in early stages of process design

Inherently Safer Design (ISD), as one of the most fundamental approaches to process safety, focuses on the innate design features. Numerous tools have been developed to assess ISD and risk-based indices are one of the most elevated of them. Existing indices are limited in modelling consequences or are challenging to adapt in terms of probability. This study introduces the Anticipated Inherent Risk Index (AIRI), a robust tool for rapid risk assessment of the worst anticipated scenarios. It incorporates Furthest Effect Distance of the release from the largest connection, by software, and Representative Failure frequency, which is a relative dataset calculated from renown databases. This presents a relative risk map upon major consequences and their likelihood. AIRI applied to a PDH Fractionation Subunits shows that Heat Pump Compressor Suction Drum (AIRI≈3399) in PP Splitter Section, followed by Propylene Trim Condenser (AIRI≈1931) and PP Splitter Reboiler/Condenser (AIRI≈1798) are the equipment with the highest risk. AIRI is a competent tool for early high-level analysis of equipment risk, which gives useful indications on design and how to improve it. This tool also has the potential to be equipped with vaster frequency datasets and effects analysis and to be incorporated into other process safety studies.

Thermally integrated pumped thermal energy storage systems based on organic Rankine cycle: Comparative investigation and multi‐objective multiverse optimization

AbstractThis work introduces two new thermally integrated pumped thermal energy storage (TIPTES) systems, including thermally integrated vapor compression heat pump (TIHP) as a charging cycle and dual‐pressure organic Rankine cycle (DPORC) and dual‐loop organic Rankine cycle (DLORC) as discharging cycles to investigate their capability of improving roundtrip efficiency compared with the basic ORC (BORC). The thermodynamic and economic performance of the proposed TIHP‐DPORC and TIHP‐DLORC are analyzed and compared with TIHP‐BORC using various working fluids. The multi‐objective multiverse optimization algorithm is conducted to ascertain the systems' optimum roundtrip efficiency and cost rate. Results indicate that at the same storage temperature, the TIHP‐DLORC gives the highest roundtrip and exergy efficiencies of 219.9% and 43.53% with R1233zd(E), indicating 6.69% and 8.04% improvements compared with the optimum TIHP‐BORC. Moreover, it shows the lowest levelized cost of storage (LCOS) and payback period (PP) of 0.160 $/kWh and 4.5 years, respectively, with a maximum net present value of 1.973 M$. Although the cost rate of TIHP‐DLORC is high, its excellent thermodynamic and economic performance compared with the existing TIPTES systems in the literature indicates that DLORC is a more appropriate candidate to be applied in the TIPTES systems.

Evaluation and Improvement of the Flexibility of Biomass Blended Burning Units in a Virtual Power Plant

Aiming at the problems of small thermal power units and biomass mixed combustion units with small generation loads and insufficient primary frequency modulation capability, which cannot be connected to the virtual power plant, this paper adopts a variety of flexibility retrofit methods for the units and explores the peak load capability of the units. Then, multiple units are coupled, and the unit coupling scheme with better economy and environmental protection is screened using comprehensive evaluation indexes. While evaluating the peaking load space of multiple unit coupling, the units’ primary frequency regulation capability and new energy consumption capability are improved. According to the calculation results, the low-pressure cylinder zero-output retrofit has the largest peaking potential among different technical paths, in which unit #3 has 27.55 MW of peaking space. The compression heat pump decoupling retrofit has the best economy, in which the daily profit of unit #3 increases from 0.93 to 1.02 million CNY with an increase of 0.09 million CNY. After the unit has been retrofitted with steam extraction, the three units can be coupled to meet the national feed-in standards. The multiple unit coupling can accommodate up to 203.44 MW of other energy sources while meeting the standard.

Recent Advances in Ejector-Enhanced Vapor Compression Heat Pump and Refrigeration Systems—A Review

Recent Advances in Ejector-Enhanced Vapor Compression Heat Pump and Refrigeration Systems—A Review

Effect of thermoelectric subcooling on COP and energy consumption of a propane heat pump

The building sector has an important impact on the environment, being responsible for 30 % of the total greenhouse gas emissions. Knowing that the energy consumption devoted to HVAC systems accounts for 50 % of the total energy consumption of buildings, it is paramount to develop environmentally friendly technologies able to provide green space heating to the building sector. To that purpose, this manuscript presents a computational study on propane vapor compression heat pumps which include thermoelectric subcooling to boost their operation. The combination of these technologies has been proven in the past to be very beneficial for refrigeration systems and this study concludes for the first time that propane heat pumps can highly benefit from thermoelectric subcooling. The widely conducted research includes the following parameters: ambient temperatures from −20 to 15 °C, voltage supplies to the thermoelectric modules from 0.5 to 10 VDC, number of thermoelectric subcooling blocks from 1 to 8 and two water inlet temperatures, 40 and 55 °C to study their influence on heating capacity, compressor and thermoelectric power consumptions, subcooling degree, propane mass flow, compressor capacity, COP, energy consumption and SCOP of the combined heat pump. The obtained results are very conclusive, COP enhancements up to 12.29 % are achieved when a thermoelectric subcooler with 16 modules is included in a propane heat pump already provided with an internal heat exchanger for an ambient temperature of −20 °C and a water inlet temperature of 55 °C. Additionally, improvements in Seasonal COP up to 9.98 % are achieved if the above-mentioned technologies integration between a vapor compression heat pump and a thermoelectric subcooler substitutes a conventional propane heat pump with an internal heat exchanger for space heating a single-story two-family house.

Comparative analysis of solar-powered heat pump systems for decarbonization of process heating and cooling applications: Case of milk pasteurization

The dairy processing industry is heavily dependent on fossil fuels for heating applications at different temperature levels and contributes to greenhouse gas (GHG) emissions. Besides, process cooling, product refrigeration, and storage are mainly reliant on vapour compression refrigeration technologies. This study investigates the performance of solar photovoltaic (PV) and solar thermal (ST) powered heat pumping technologies for simultaneous heating (at 75 °C) and cooling (at 2 °C) applications in a selected typical thermal process in a dairy processing plant (milk pasteurization). An ammonia/water absorption heat pump (AHP) and a two-stage R717 vapour compression heat pump with an open intercooler (VCHP) are used in the present study. The VCHP and AHP are powered by market-available solar PV modules and ST collector technologies. The electrical COP and exergy COP of the VCHP were about 4.710 and 0.535, respectively. The AHP operates at a thermal COP and exergy COP of 0.979 and 0.301 when the driving hot water and absorber cooling water inlet temperatures are 160 °C and 30 °C. The grid-connected PV-VCHP system and ST-AHP with natural gas-fired auxiliary heater operate at an annual solar fraction of 0.533 and 0.572, respectively, for a typical weather condition in Barcelona (Spain).

Performance Analysis of an Ejector-Enhanced Heat Pump System for Low-Temperature Waste Heat Recovery Using UHVDC Converter Valves

This article proposes a heating method based on heat pump technology to address the large amount of low-grade waste heat generated by a certain type of ultra-high voltage direct current (UHVDC) converter valve. Thermal performance calculations for two systems, a basic vapor compression heat pump system (BVCHPS) based on thermal expansion valve throttling and an ejector-enhanced heat pump system (EEHPS) are analyzed. The research results show that the EEHPS exhibits superior COP and exergy efficiency when generating hot water above 80 °C using a heat source below 50 °C. Additionally, mathematical modeling analysis identifies optimal structural parameters such as nozzle throat diameter, throat area ratio, and nozzle outlet diameter for the ejector in its design state. The low-temperature waste heat recovered from the UHVDC converter valves can be further used in engineering applications such as heating, refrigeration, seawater desalination, and sewage treatment.

Vapor absorption, compression and cascade heat pumps for carbon capture plants: Multi-criteria analysis and techno-economic assessment with different working fluids

Post-combustion CO2 capture plants include high costs that are associated with intense energy consumption. Heat pumps can recover heat from the flue gas and other sources in the CO2 emitting plant and upgrade it to reduce the use of fossil-based steam. The few studies regarding heat pumps in CO2 capture systems include arbitrary selection among limited working fluids, without optimizing the underlying cycle. This work implements a multi-criteria investigation of the performance of 20 working fluids for vapor compression heat pumps (VCHP) and 21 refrigerant/absorber pairs for absorption heat transformers (AHT), considering the operating optimization of each cycle for each fluid. A cascade cycle combining the two configurations (AHT-VCHP) is proposed, using the optimum fluids cyclopentane and water/potassium nitrate identified for the VCHP and the AHT. The annual operating costs are higher than the annualized capital expenditures. The proposed fluids outperform the conventional options. The VCHP with cyclopentane covers 58 % (2.68 GJ/t CO2) of the reboiler duty with recovered heat and exhibits the lowest cost of $33.8/tCO2. This is $18.7/tCO2 lower than the cost of the conventional direct contact cooling unit that is used in capture plants. The VCHP remains competitive for up to 57 % increase in the electricity price.

Performance Analysis of a New Cogeneration System with Efficient Utilization of Waste Heat Resources and Energy Conversion Capabilities

This paper proposes a new type of cogeneration system coupled by Organic Rankine Cycle (ORC), Absorption Heat Pump (AHP), and Compression Heat Pump (CHP). The new system can meet the needs of different scenarios. Simulations were conducted to analyze the effect of different factors on the parameters and performance indexes of the new system and compared with the system of ORC, AHP, CHP. The results showed that the factors of flue gas temperature at evaporator1 outlet and CHP have the greatest effect on the parameters and performance indexes of the Organic Absorption-Compression Coupling Heat Power (OACCHP) system, and the effect of AHP on the parameters and performance indexes of the OACCHP system can be ignored. In the given range of flue gas temperature at evaporator1 outlet, the heat production of total and net work is reduced by 1.17% and 33.33%, respectively. In a given range of CHP evaporation temperature, the heat production of the total is reduced by 5.74%. In the given range of the outlet temperature of the gas cooler, the heat production of the total is increased by 10.58%. In a given working condition, compared with the single ORC system, the single CHP system, and the single AHP system, the thermal efficiency, COP, and energy earning rate of the OACCHP system are increased by up to 755.49%, 59.8%, 5.8%, respectively. Finally, the optimal operating conditions for different scenarios were determined.

Thermodynamic Analysis of Modelled and Simulated Heat Pump Drying System Using Azeotropic Mixture of Organic Working Fluids

It is well-known that the choice of working fluid significantly impacts the performance, cost estimation, and environmental effect of a heat pump. In this study, the performance of pure working fluids (dimethyl ether and ethanol) was compared with that of azeotropic mixture working fluids used in vapor compression heat pumps. The study also examined the effect of compression ratio and different compressor models on the performance of a vapor compression heat pump for heating processes and drying tomato slices at an air temperature of 40 °C and an air flow rate of 200 kg/hr. Using ethanol as the working fluid at evaporating and condensing temperatures of 10 °C and 15 °C, respectively, the specific moisture extraction rate was 0.2112 kg/kWh, and the Carnot coefficient of performance was 57.60. The study demonstrated a COP improvement of more than 15% for azeotropic mixtures compared to a pure working fluid. The maximum overall energy efficiency and exergy efficiency, achieved with Mixture II, were 5.68% and 27.32%, respectively. As suction pressure increased while maintaining constant discharge pressure, the compression ratio and work done by the compressor decreased, while the system's overall energy efficiency, and overall exergy efficiency improved under the given conditions.

Research on the lubricating oil leakage characteristics in the vapor compression heat pump system under refrigerant leaking

Refrigerant leakage is a situation that often occurs in refrigeration equipment such as heat pumps. However, certain alternative refrigerants, while exhibiting superior environmental performance, possess varying levels of flammability. The leakage of flammable refrigerants into confined spaces can pose a significant risk of explosion. The amount of lubricant in the leaking refrigerant will undoubtedly affect the flammability characteristics of the refrigerant. In this paper, the content of PVE32 oil in the leaking refrigerant during the operation of a heat pump was investigated. The results showed that, under the five leakage rate scenarios set up in the experiment, the oil concentration was highest when the leakage occurred at the condenser inlet and lowest when the leakage was at the evaporator outlet. During the leakage process of the experiment, as the mass flow rate of the leakage increased, the oil content in the early stage of the leakage increased, but the oil content in the late stage of the leakage decreased. The reasons for the change in oil content were analyzed by the oil circulation rate and the degree of phase separation. The decrease of the oil circulation rate and the change of the degree of phase separation were the key factors affecting the magnitude of the oil content as the leakage proceeded. The results of the study reveal the leakage characteristics of lubricating oil with refrigerant leakage.