Cascade Heat Pump Research Articles

Development of thermal installation on the basis of the cascade heat pump for ensuring all thermal and refrigerating needs of the consumer

This article describes the developed and manufactured multifunctional heat point, which allows to supply heat and refrigeration energy to consumers. For effective operation, the heat point contains an automated control system that allows to direct heat flows in an optimal way. Development of this thermal point began because in Russia there are no complex researches on creation of systems of power supply on the basis of heat pumps now. There are some works which actually copy the western technologies. At the same time, features of climatic zones are not considered that is extremely important for the development of similar power stations. That is, earlier nobody created a product which equally well works in the conditions of the Southern regions and Far North. Thermal and hydraulic calculations of thermal point were executed. Coefficients of performance and resistance of the contours of the heat pumping plant were the results of these calculations. These calculations showed that the transformation coefficient on all contours is in the range from 3.352 to 4.884. Now starting tests of the thermal point which showed a regularity of the chosen design decisions and operability of the installation are carried out. The received results will be useful at projection of similar systems as the main characteristics of cascade heatpumping plants are received by a calculated path. The concrete received results of a research are as follows: – the multipurpose thermal point allowing to carry out heating – 25 kW, hot water supply – 5 kW, conditioning – 16 kW, ventilation of 25 kW is developed; – key indicators of thermal effectiveness of the power station, such as transformation coefficient, thermal rating etc are defined; – capacity of compact accumulators of warmth is determined. Heating with the temperature of 35 о С, within 12 hours of night-time requires the boiler tank of 2500 l whereas the accumulator on change phase of 300–500 l; – on the basis of the analysis of available renewable and secondary energy sources the structure of heat fluxes of the standard consumer with sources of excess warmth and points of its consumption is developed

Performance analysis of a cascade high temperature heat pump using R245fa and BY-3 as working fluid

A high temperature cascade heat pump (HTCHP) using a near-zeotropic mixture named BY-3 as the working fluid in the low-stage refrigerant cycle and R245fa as working fluid in the high-stage refrigerant cycle was proposed in this study. Several experiments were carried out to investigate the performance of the HTCHP at the evaporating temperature from 40 °C to 60 °C and the water outlet temperature on the condensing unit of the high-stage cycle can reach 142 °C with the coefficient of performance (COP) of 1.72. The results showed that BY-3 was feasible to be used in the low-stage cycle. A numerical model of the HTCHP was proposed and validated in this study to evaluate its performance. The comparison between the experimental results and the simulated results showed that the HTCHP system using BY-3 and R245fa can product hot water at 142 °C with good performance and the temperature lift of the HTCHP can reach 100 °C.

Experimental study on cascade heat pump dryer with a solar collector under low temperature outdoor air environment

A heat pump dryer can save more energy than other dryers since its drying efficiency is 2-3 times higher than that of other types of dryers. However, the lower bound of evaporating temperature for an R134a heat pump cycle ranges from 5 to 10?C, when the outdoor air temperature closely approaches the evaporating temperature, it experiences reduced efficiency and ultimately becomes inoperable. To address this issue, a cascade heat pump dryer equipped with a solar collector was considered in order to examine the operability and efficiency of the heat pump cycle, depending on changes in the outdoor air temperature in wintertime. The changes in cascade cycles, depending on the temperature in a drying chamber, were also observed. The results showed that the average coefficient of performance (COP) of the cascade heat pump dryer was approximately 2.6 under the temperature range of ?10 to 20 ?C. An electrical heater whose COP is less than one should be used in that temperature range. It was also found that COP of the dryer increased by approximately 35% when using a solar collector under a low outdoor air temperature environment.

The test bench of a cascade heatpump installation of a heat power complex for highly effective use secondary and renewables

In article the solution of one of the problems facing developers of a heat power complex for highly effective use secondary and renewables reveals. The solved problem is a development of the circuit decisions providing tests of all set of the modes of cascade heatpump installation of a heat power complex, design of the test bench. The developed complex allows to use most effectively together with heatpump installations and thermal accumulators renewables. Also the complex uses also household overflows of energy for the consumer’s heat supply, as much as possible reducing consumption of organic fuel.

Experimental study for a high efficiency cascade heat pump water heater system using a new near-zeotropic refrigerant mixture

Single-stage water-source heat pumps have some disadvantages such as high pressure ratio and lower coefficient of performance at high water outlet temperature, and normally the temperature promotion cannot exceed 50 °C. To surmount these disadvantages, a high temperature water-source cascade heat pump (HTWSCHP) was suggested; the HTWSCHP system demonstrates a much more competitive performance at high water outlet temperature of 142 °C and the temperature promotion can reach 90 °C. Lots of researches have been performed to analyze the cascade heat pump system, but they are normally about the low ambient temperature and there is very little information about the high water -outlet temperature. In this study, a HTWSCHP system was investigated experimentally. The high and low refrigerant cycle employed BY-3(A&B) and R245fa respectively. The experimental test was performed under different conditions: different electronic expansion valve opening ratio combination for low and high cycle, different refrigerants for the low cycle, different temperature for low-temperature heat source, different heating capacity, and varying water-outlet temperature. The final results shows that the water-outlet temperature of 142 °C can be achieved which is the highest level in the open literature with the total coefficient of 1.669, and the pressure ratio for low and high cycle are 3.9 and 3.4 respectively.

Experimental Observation of CO2 Dry-ice Behavior in an Evaporator/Sublimator

In the evaporator/sublimator process of CO2 (R744) ultra-low temperature cascade heat pump system, it is known, as a problem, that dry-ice blockage makes the system operation fail. The design of an expanding channel for the evaporation/sublimation process is one solution to solve the problem. In this study, a swirl promoter is newly designed and tested by means of experimental observation. In order to give better understanding to heat transfer process in the refrigeration system, particular attention is focused for CO2 dry-ice solid-gas two-phase flow to obtain the effectivity of heat transfer and to verify the flow-phenomena where a visualization test apparatus is placed horizontally. As results, by installing the swirl promoter in the inlet flow channel, it is found that the dry-ice particles uniformly dispersed in whole pipe cross-section with swirling flow, which induces an increase of heat absorption in CO2 solid-gas two-phase flow. In the case without a swirl promoter, a dry-ice ball shows lower heat transfer characteristic for higher inlet pressures, and resultantly leading to a possible down-stream blockage of the channel.

A Perspective Evaluation Methodology for Economic Feasibility of Low Temperature Sustainable Energy Source in Heating Mode Technology

The economical and clean environment issues for a sustainable energy source at low temperature (LT) were considered and compared to natural gas technology as a fossil fuel source. The friendly environment refrigerants R410A, R407C, R717, R134a, and R600a were analyzed in an approximately 500 kW heating load output cascade heat pump. The heat pump was investigated at an intermediate temperature of 35 °C, high temperature (HT) cycle condenser at 70 °C, and compressors isentropic efficiency of 70%. All analyzed refrigerant pairs exhibited high heating season performance factor (HSPF), and it was ranged between 7 and 8.5. The thermal performance comparison revealed that the HSPF for R717/R600a showed the highest values among other refrigerant pairs. The results showed that at LT cycle evaporator temperature range of −10 to −2 °C, the natural gas technology revealed a higher season heating cost values than that of the heat pump plant by up to 10%. On the contrary at lower LT evaporator temperature, the heat pump plant technology exhibited a higher season heating cost lied in the range of 4–13.6% than that of the natural gas system. At compressors isentropic efficiency of 90%, the seasonal heating cost of the heat pump plant was lower than that of the natural gas technology by the range of 9–25% at test conditions. The mean seasonal CO2 amount released by the natural gas firing technology from all tested refrigerant pairs ranged between 2.1 and 2.5 times that of the heat pump plant technology for the investigated LT evaporator temperature range.

Research trend of cascade heat pumps

Most commercial and industrial facilities require very low temperatures for refrigeration and high temperatures for space heating and hot water purposes. Single stage heat pumps have not been able to meet these temperature demands and have been characterized by low capacities and coefficient of performance (COP). Cascade heat pump has been developed to overcome the weaknesses of single stage heat pumps. This study reviews recent works done by researchers on cascade heat pumps for refrigeration, heating and hot water generation. Selection of suitable refrigerants to meet the pressure and temperature demands of each stage of the cascade heat pump has been discussed. Optimization of design parameters such as intermediate temperature (low stage condensing and high stage evaporating temperatures), and temperature difference in the cascade heat exchanger for optimum performance of the cascade heat pump has been reviewed. It was found that optimising each design parameter of the cascade heat pump is necessary for maximum system performance and this may improve the exergetic efficiency, especially of cascade refrigeration systems, by about 30.88%. Cascade heat pumps have wider range of application especially for artificial snow production, in the supermarkets, for natural gas liquefaction, in drying clothes and food and as heat recovery system. The performance of cascade heat pumps can be improved by 19% when coupled with other renewable energy sources for various real time applications. Also, there is the need for much research on refrigerant charge amount of cascade heat pumps, refrigerant-refrigerant heat exchangers to be used as cascade heat exchanger, cascade heat pumps for simultaneous cooling, heating and hot water generation and on the use of variable speed compressors and their control strategies in matching system capacity especially at part load conditions.

Advances in unit operations and materials for the Cu[sbnd]Cl cycle of hydrogen production

This paper presents recent advances by an international team of five countries – Canada, U.S., China, Slovenia and Romania – on the development and scale-up of the copper–chlorine (CuCl) cycle for thermochemical hydrogen production using nuclear or solar energy. Electrochemical cell analysis and membrane characterization for the CuCl/HCl electrolysis process are presented. Constituent solubility in the ternary CuCl/HCl/H2O system and XRD measurements are reported in regards to the CuCl2 crystallization process. Materials corrosion in high temperature copper chloride salts and performance of coatings of reactor surface alloys are examined. Finally, system integration is examined, with respect to scale-up of unit operations, cascaded heat pumps for heat upgrading, and linkage of heat exchangers with solar and nuclear plants.

A new integrated heat pump option for heat upgrading in Cu-Cl cycle for hydrogen production

A potential cascaded vapor compression heat pump is proposed to address the high temperature heat demand in the copper chlorine (Cu-Cl) thermochemical cycle for hydrogen production. The configuration studied is a cuprous chloride CuCl vapor compression heat pump cascaded with a biphenyl (C6H5)2 heat pump. Such cascaded heat pumps is meant to upgrade heat from nuclear power plants with a heat input temperature of approximately 300°C or industrial waste heat to meet the Cu2OCl2 decomposition reactor heat demand. Energy and exergy analyses are performed to understand the performance of the heat pump. It is determined that the CuCl-biphenyl heat pump exhibits a high coefficient of performance for certain operating conditions relating to the compressor isentropic efficiency and the excess CuCl feed temperature. The base energetic and exergetic coefficient of performances of the CuCl-biphenyl heat pump are 1.76 and 1.15 respectively.

Thermodynamic Analysis for Hybrid Low Temperature Sustainable Energy Sources in Cascade Heat Pump Technology

A thermodynamic analysis of compound Cascade refrigeration system at low temperature heat sources was conducted. The analysis was based on a target temperature of hot water at the range of (60-70) °C out of the heat pump. The carrier thermal fluid temperature, which provides heat at the low temperature side of the Cascade system, determines the pair of refrigerants to be implemented. A hybrid heat pump design was proposed, which implements the sea water and ground as heat sources in a compound cycle. Two of refrigerant pairs were tested for the performance and energy efficiency comparison at fixed operating conditions. In the low temperature cycle, either R410A or R717 refrigerant was allowed to circulate and R134a is circulated at the high temperature cycle. The minimum isentropic efficiency of commercially available compressors was used in this investigation, a value of (70 %) was chosen. The results of the investigation revealed that R717/R134a exhibited a higher heating (COP) than that of R410A/R134a by (3 %). The results showed that increasing the isentropic efficiency of compressors to (90 %) improved the heating (COP) by (20 %) and minimized the power consumption by (24 %). The specific power consumed by compressors of the proposed system showed a decrease of upto (3 %) lower than that of the sea water base system.

Perspective Performance Evaluation Technique for a Cascade Heat Pump Plant Functions at Low Temperature Heat Source

The present investigation deals with the performance assessment of Cascade heat pump plants. The overall power consumption for a Cascade system for typical heat pump characteristics was studied. Four environment friendly refrigerant pairs R717/R134a, R410A/R134a, R407C/R134a, and R717/R600a were investigated at low temperature cycle (LT) evaporator and high temperature cycle (HT) condenser temperatures of (-15 to -4)°C and (70)°C respectively. A preliminary heat pump plant is suggested to produce (500) kW heat output load as hot water demand at (65)°C with (25)°C temperature lift and a proper circulation rate. The investigation was carried out at cascade heat exchanger intermediate temperature (IT) of (33)°C and (35)°C. Sea water at (7)°C was used as a sustainable low temperature heat source and (30%) ethylene glycol-water brine at temperature of (5)°C as a thermal fluid heat carrier at the LT cycle evaporator. The evaluation of the thermal performance of the refrigerant pairs was based on a fixed heat pump extraction load at the LT cycle. The heat pump heating coefficient of performance (COP) revealed an increase fell within the range of (5-7.5)% higher than that of the plant heating COP value for the studied refrigerant pairs at the whole investigated operating conditions range. The higher IT exhibited the highest heat pump and plant heating COP than those at the lower value. R717/R600a showed the highest heating COP, lower power consumption and lower global warming potential (GWP) among other investigated refrigerant pairs. The power consumed by auxiliary pumps to circulate thermal fluid heat carriers through a heat pump may account to (4-4.5)% and (2-3)% of the extracted and output heating loads respectively, higher values could be expected for real plant. Two polynomial correlations for the assessment of the pumping power in terms of the extracted and output heating loads were derived from the present work.

Visualization of the Behavior of Dry-ice in the Evaporator of CO<sub>2</sub> Cascade Heat Pump System

Visualization of the Behavior of Dry-ice in the Evaporator of CO<sub>2</sub> Cascade Heat Pump System

2단 승온 캐스케이드 히트펌프의 성능 특성에 관한 연구

2단 승온 캐스케이드 히트펌프의 성능 특성에 관한 연구

Detailed modeling of a novel photovoltaic thermal cascade heat pump domestic water heating system

A domestic water heating system that combines photovoltaic thermal (PVT) solar collectors with two heat pumps, in a novel cascade arrangement, is presented and analyzed in this paper. The goal of this analysis is to determine and compare the annual thermal energy output of the PVT cascade heat pump system with an evacuated tube and simultaneous consumption PVT single heat pump water heating system. The computational technique that was developed to analyze the PVT cascade heat pump system, which determines solar panel energy outputs, and heat pump operating characteristics, is described in detail. Case study simulation results are also presented, which include transient power output profiles, temperature profiles, and yearly energy output results. Hourly weather data, including air dry-bulb temperatures and solar flux values, from locations with a range of climates was used in these simulations. The results of this study show that the PVT cascade heat pump system has an annual thermal energy output improvement over the evacuated tube heating system ranging from 37% to 68%, depending on the selected simulation location.

Experimental study of a control strategy for a cascade air source heat pump water heater

Cascade air source heat pump water heater is suitable for provide high temperature water under a wide range of outdoor air temperature. Most previous studies focused on the operating characteristics of cascade heat pump system, performance improvement, and the selection of optimal immediate temperature. However, no reported studies on the control strategies for cascade heat pump may be identified. This paper proposed a control strategy for cascade air source heat pump water heater to adjust the load variation. The principle that two stage compression ratio is approximately same is used to determine the intermediate pressure. The intermediate pressure, degree of superheat (DS) and the evaporating temperature were regulated by the compressor, electronic expansion valves (EEV) and the evaporator fan of the low temperature (LT) cycle, respectively, through Proportion Integration Differentiation (PID) controller or proportional controller. The control strategy was experimentally tested over a wide operational range of cascade air source heat pump water heater. The results showed that the controller developed successfully helped realize the control of the intermediate pressure, the DS and the evaporating temperature in terms of control accuracy and sensitivity.

Effect of Transient Heat Transfer of a Condenser on a Cascade Heat Pump Performance

Transient heat transfer characteristics of a condenser of a cascade heat pump are investigated by comparing the experimental result and the prediction from a mathematical model. In the experiment part, the cascade heat pump consists of the low-temperature refrigeration cycle using R22 and the high-temperature heat pump cycle using R134a.The transient effect is presented by circulating water to receive the rejection heat from the condensing refrigerant of the cascade heat pump causing the rise of the hot water temperature. On the other hand, a mathematic model of the condensation heat consisting of the heat transfer models in the two-phase mixture region and the superheated vapor region is developed to compare the results. The effect of the hot water flow rate on the hot water temperature and the heat transfer rate is examined. The result indicates that the hot water temperature continuously increases with time. The condensation heat rapidly increases at the beginning and gradually increases with time. The result obtained from the model prediction of the condensation heat is similar to the experimental result except the initial and final period. The discrepancy between these two results is because of the transient behavior at beginning and the existent of the subcooled region.

Study on Improving the Performance of the Cascade Heat Pump Cycle using Ejectors

Background: The cascade heat pump cycle is used when a large difference between the condensing temperature and the evaporating temperature exist. Methods: This study uses ejectors to improve the performance of a cascade heat pump cycle that utilizes refrigerants R134a and R404a. Ejectors were applied to the high-stage cycle, the low-stage cycle and then to both cycles. Changes in performance according to the condensing temperature, evaporating temperature and ejector entrainment ratio were tracked. Results: Results of the numerical analysis showed that applying ejectors to both the highstage and low-stage cycles provided the greatest efficiency, yielding a 26.9% increase in the COP compared to standard cascade cycles. Conclusion: For COP enhancement, it is beneficial to apply ejectors to both-stage cycles as well as to lower the ejector entrainment ratio as much as possible.

A study of Transient Performance of A Cascade Heat Pump System

Transient performance of a cascade heat pump system is experimentally investigated. The cascade heat pump consists of 4 systems: the chilled water system, the low-temperature refrigeration cycle using R22, the high-temperature heat pump cycle using R134a and the hot water system. The cascade heat pump produces both chilled water for cooling application and hot water for heating application. A transient performance is observed when the hot water system is in a closed-loop operation. As the hot water temperature increases, the condensing pressure of the heat pump cycle also increases but the other refrigerant pressures have marginal changes. The operation of the test rig is terminated when the condensing pressure reaches the limit of the system. The condensing pressure at high hot water flow rate increases at a lower rate than that in case of the low hot water flow rate, so the working period is higher. The compressor power of the heat pump cycle increases continuously with time whereas the compressor power of the refrigeration cycle is almost constant. The condensation heat and cooling load rapidly increase at the beginning, and the condensation heat gradually increases whereas the cooling load is almost constant. The COP of the heat pump cycle gradually decreases with time after the rapid increase at the beginning, but the COP of the refrigeration cycle is almost constant. It can be concluded that the variation of the condensing pressure of the heat pump cycle with time has a little influences to the refrigeration cycle. By comparing the high and low hot water flow rate, the COP of the heat pump cycle and the final hot water temperature in the storage tank are higher whereas the others are the same.

Feasibility study of R134a/R404a cascade heat pump cycle in heat pump dryers with electrical heaters at low temperatures

Heat pump cycles have been widely applied to dryers for their high efficiency. However, low–efficiency electrical heaters are often used during early drying stage for frozen foods or winter since a standard heat pump cycle cannot operate at low temperature. This study introduced cascade heat pumps replacing electrical heaters to improve dryer performance at low temperatures. Experiments were performed to examine changes in performance of the cascade heat pump dryers in relation to ambient temperature, low-stage cycle mass flow rate, and high-stage cycle mass flow rate. The results showed a significant improvement in low-temperature dryer performance with the introduction of cascade heat pump cycles.