Hot Gas Bypass Research Articles

Hot gas bypass defrosting with auxiliary heat source in household refrigerators

Frost is inevitable in air-cooled household refrigerators. To maintain the performance of the refrigeration system and food storage quality, additional power input is required to melt the ice periodically. Hot gas bypass defrosting featured high defrosting efficiency, however, suffered insufficient defrosting power at low ambient temperatures, leading to rare application of this technology in household refrigerators. To mitigate this challenge, a novel cost-effective hot gas bypass defrosting system with an auxiliary heater wrapped along the hot gas bypass loop was proposed, and its performance was thoroughly investigated in this paper. Experimental results showed that the defrosting efficiency was 0.8 at an ambient temperature of 32 °C, which was much higher than that of baseline electric defrosting of 0.3. At 20 °C, the new defrosting system with 80 W additional power input in the auxiliary heater successfully melted all frost within 35 min, while the baseline hot gas bypass defrost system without additional heat input could not melt all frost even after 60 min. To further investigate the effects of ambient temperature, compressor speed, and auxiliary heating power, a mathematical model was established and validated by experimental data. The simulated results suggested that it was more efficient to supply more heat from the auxiliary heat source than from the compressor.

Heating and defrosting performance assessment of dual-source heat pump operational modes under various ambient conditions

Multifunctional dual-source heat pump systems, featuring two sets of heat exchangers (air-to-refrigerant and water-to-refrigerant) in series or parallel, aim to boost efficiency. However, these systems often require extensive piping, leading to power losses, higher energy consumption, and increased installation space requirements. Furthermore, few comparative studies have assessed the effectiveness of dual-source versus single-source heat pump systems under various ambient conditions. This study introduces a novel air-water dual-source evaporator design that enables efficient heat exchange using air, water, or both. With this design, the heat pump system can be tuned according to three distinct modes: pure water-source mode (WSHP), pure air-source mode (ASHP), and dual air-water-source mode (AWSHP). The heat pump's efficiency across these modes was evaluated under various weather conditions, adhering to the CNS15466 and GB/T21362 standards. The findings reveal a strong correlation between the operational modes and ambient temperatures, indicating that maximum efficiency is achieved with the WSHP mode below 7 °C, AWSHP mode between 10 °C and 35 °C, and ASHP mode above 35 °C. Moreover, three defrosting methods were evaluated: hot gas bypass, hot water bypass, and a combination of both. The hot water bypass, in conjunction with the proposed dual-source evaporator design, efficiently performed full defrosting, boosting system efficiency. The ability of the heat pump to switch between operating modes enhances the overall energy efficiency during space heating and defrosting, reduces installation space requirements and compressor oil loss, and facilitates hot water production. The proposed system is ideal for various industrial applications requiring efficient operation under diverse ambient conditions.

Study on various hot-gas defrosting configurations for CO2-NH3 cascade deep freezer

Four hot-gas bypass defrosting configurations for CO2-NH3 cascade blast freezer for application in fish processing firm are numerically investigated. Due to the high moisture content of fish, defrosting is necessary after every 4 to 5 h of batch operation. A thermodynamic model for the cascade system and defrosting was developed to study various defrosting configurations formulated by rearranging the existing compressor to operate as a defrosting compressor and with the addition of an external defrosting compressor. From the simulation findings, it can be summarized that the conventional hot-gas bypass defrosting without defrost compressor is suitable for a high-capacity cascade refrigeration system with more than three evaporators. For low cooling capacity refrigeration systems, a defrosting compressor is necessary to elevate the temperature above the cascade condensing temperature. A dedicated defrosting compressor with a power consumption of 3.1 kW and a modified refrigeration/defrosting compressor with a power consumption of 6.8 kW can deliver 33.3 kW of heating at a temperature of +10 °C (45 bar). Incorporating a desuperheater between the main and defrosting compressors reduces compressor temperature and maintains the lubricating oil stability, without change in defrosting energy consumption and less exergy loss. The defrosting efficiency is obtained in the range of 39.7–42% which is in agreement with published literature.

Experimental investigation of heating performance of air source heat pump with stable heating capacity during defrosting

Traditional air source heat pumps with reverse defrosting and hot gas bypass defrosting methods significantly decrease the heating capacity and even extract heat from the user side, resulting in low indoor thermal comfort. In this study, an air source heat pump prototype was developed that used multiple air source heat exchangers linked with anti-icing fluid pipelines to extract heat from the outdoor air and alternately defrost one of the air source heat exchangers by transferring a small portion of the heat from the indoors, thus achieving stable heating to the user side during defrosting. Its performance was tested in an enthalpy difference chamber, and optimization was predicted based on the test results. The results showed that under the most severe frosting condition, with an outdoor temperature of 1 °C and a relative humidity of 95%, the heating capacity decay rate to the user side during defrosting was only 20%. After optimization, the heating capacity decay rate during defrosting could reach within 10%, and the coefficient of performance under nominal operating condition (outside temperature of −2 °C, supply water temperature of 35 °C) and the heating season performance factor were 3.38 and 4.05, respectively, when used for heating the radiation floor in hot summer and cold winter regions. The principles and results provided in this study can be applied to air source heat pumps with different heating capacity requirements during defrosting.

Evaluation and quantification of compressor model predictive capabilities under modulation and extrapolation scenarios

Testing and evaluation of select semi-empirical and black-box compressor models is carried out to quantify performance in modulation (variable speed), extrapolation, and additionally, variable superheat scenarios. Three representative literature models and an artificial neural network (ANN) model are benchmarked against the industry standard AHRI model. A methodology quantifying model performance, compared against experimental data, in said scenarios is presented. High-fidelity test data taken from either a hot-gas bypass load stand or compressor calorimeter. Scroll, screw, reciprocating, and spool compressor technologies were collected with R410A, R1234ze(E), R134a, and R32 refrigerants totaling 434 experimental points. Data is divided into training, extrapolation, variable speed, and variable superheat data splits to examine model performance. Mean Absolute Percentage Error (MAPE) is computed for mass flow rate and power after training models with training data and evaluating them against the other data splits. Two literature models are true semi-empirical formulations while the other, the ANN, and AHRI model are more empirical in nature. Neither semi-empirical model predicted all compressors. When the compressor type is predicted, the semi-empirical models yield MAPE’s less than 8%, 5%, and 4% for mass flow rate and power prediction in extrapolation, modulation, and variable superheat scenarios, respectively. The exception is the Popovic and Shapiro model performing at 21% MAPE in variable superheat power prediction for the spool compressor with R1234ze(E). The ANN showed highest errors of 9.3%, 12%, and 17% in extrapolation, modulation, and variable superheat scenarios, respectively. All models outperformed the AHRI model by several orders of magnitude in these scenarios.

An experimental study on improving defrosting performances of air source heat pump unit based on hot-gas bypass method

ABSTRACT A novel hot-gas bypass defrosting method for an air source heat pump (ASHP) unit has been presented in a previous work, which can satisfy defrosting and uninterrupted heating simultaneously. To further improve the novel hot-gas bypass defrosting performances, the effects of electronic expansion valve (EEV) on both the defrosting and uninterrupted heating performances are experimentally investigated. The results showed that the defrosting period and consumption decreased by 64.7% from 510 to 180 s and 19.7% from 1133.8 to 910.2 kJ when the opening of a 500-step EEV increased from 120-step to 480-step. Although the defrosting period for EEV opening of 480-step was the shortest, the period of blowing cold air was the longest which lasted for around 60 s. Besides, the percentage of consumed energy amount used for defrosting and the average heating capacity during defrosting period ranged from 65.2%~81.7% and 1178 ~ 903 W, respectively, with five EEV openings. The maximum average COP was 0.57 with EEV opening of 120-step, while the minimum value was 0.36 with EEV opening of 280-step. The results can help to optimize the defrosting control strategy of the ASHP units using the novel hot-gas bypass defrosting method and facilitate the development of ASHP technology.

Defrosting frequency optimization in a cooling system: Minimization of energy consumption vs reduction of the number of on/off cycles per hour. Definition of a methodology and assessment of commercial methods based on experiments

This paper presents the definition of a new method to obtain the optimum defrosting start time for a medium temperature refrigeration system with hot-gas bypass defrosting technique. A series of experiments is performed for a monoblock prototype placed in a cold room with controlled temperature (from −4 °C to +2 °C) and relative humidity (from 70% to 90%), whereas the ambient temperature is set to 25 °C and monitored in a calorimetric chamber. Specific tests are carried out by leaving the machine in operating mode up to the complete blockage of the evaporator, measuring the corresponding defrosting phase period and frost accumulated mass. A new method for data reduction of experimental data is presented to calculate the average energy consumption of the whole cycle (on–off operation and defrosting). With these results from experiments, firstly, the average energy consumption is used as one of the decisional parameters together with the number of hourly on–off cycles of a multi-criteria optimization under constrained heating load versus cooling capacity ratio. Secondly, an assessment of the results achievable with commercial defrosting method is carried out. The new method for data reduction could be used to collect performance maps under lab conditions and then use it as multi-criteria decisional basis for a control system. The commercial methods monitoring air-evaporator temperature difference or pressure drop across the evaporator do not allow to keep the heating load versus cooling capacity below a desired threshold value under all operating conditions. Conversely, a control system based on a defined maximum allowable heating load versus cooling capacity ratio permits to control the temperature of the cabinet.

A pressure and temperature cycling test stand with hot-gas bypass control for evaluation of adhesive joints in HVAC&R applications

The formation of joints is critical to the long-term reliability with leak-free operation of heating, ventilation, air conditioning, and refrigeration (HVAC&R) systems. Leakages commonly occur due to fatigue failure developing in joined materials from continuous pressure and temperature cycling with mechanical vibration and refrigerant under pressure inside the system. In particular, rapid pressure and temperature changes happen frequently (e.g., multiple times per day) when the system is switched on and off. Therefore, it is important to have an automatically controlled fast-response pressure and temperature cycling (PTC) test stand available to test the performance of refrigeration joints to evaluate new bonding technologies. An innovative PTC test stand with hot-gas bypass control was designed, built, and demonstrated that eliminated the need for an evaporator and ensures rapid transition between different operating conditions. Tests were performed to demonstrate test stand functionality using R410A as the refrigerant to provide pressure and temperature cycles from 600 to 4500 kPa and 5 to 80 °C. A 50-cycle, 5-hour demonstration test was performed with both adhesively bonded and brazed joints following standardized joint testing guidelines. Both joint types survived the test without leaking, suggesting that the adhesive joints have sufficient thermal fatigue resistance along with the conventional brazed joints. Throughout the demonstration, the test stand accurately controlled the setpoint temperatures and pressures while switching the test section between these conditions. The test stand serves as a new approach for pressure and temperature cyclic fatigue testing of joints in HVAC&R systems.

Dynamic Evaluation: Centrifugal Compressor’s Operation in Determining Anti-Surge Controller

Anti-surging is developed for a compressor system consisting of a booster compressor and a high-pressure compressor in a serial circuit. This evaluation presented 6 options of anti-surge systems with variations of the number of Anti-surge Valve (ASV) and its combination with the addition of a Hot Gas Bypass Valve (HGBV) and Cold Gas Bypass Valve (CGBV). From the model evaluation, the option that involves a special ASV (dedicated) for each compressor and coupled with a dedicated CGBV or HGBV is the best because the compressor can be back to normal in less than 1 second (maximum time to return to normal condition is 3 seconds. Referring to these options, a dedicated ASV for each compressor provides more benefits to the security of compressor operation. However, the most appropriate option in the field will return to the issue of cost or ease of modification. For facilities that are running (brownfield), the use of tools that already exist in the field and do a little modification is the most appropriate option, while for the new facility (grassroots project), the single ASV for a compressor circuit is the most optimum as it only involves minimum equipment and configuration as simple as possible piping/instrumentation.

Experimental studies on hot gas bypass defrosting control strategies for air source heat pumps

The air source heat pump (ASHP) is commonly used for improving indoor thermal comfort with its traditional defrosting strategy based on reverse circulation, leading to a widely fluctuating range of indoor air temperatures, which can drop dramatically when the defrosting is in operation and increase sharply after it stops. Based on a theoretical analysis of the characteristics of a hot gas bypass defrosting system, this study proposes a novel intelligent control strategy based on the maximum heating capacity of the ASHP system with appropriate start and end points for defrosting designed to operate accurately under different outdoor temperature ranges. This defrosting method was verified in a well-structured environmental laboratory and the performance was compared to the conventional system through experiments. The results show that the heating capacity of the hot gas bypass defrosting is 10.17% higher and the overall energy efficiency is 4.06% higher. The indoor air temperature fluctuates in the range of 1°C–1.6 °C, which is about 84% less than that under conventional defrosting conditions. Moreover, the temperature of the outlet air is decreased by about 7 °C, with the fluctuation range being 56% less than that of conventional defrosting. The maximum outlet temperature remains stable at 35.2 °C and the rising rates of indoor air temperature and outlet temperature are significantly improved, ensuring a comfortable indoor thermal environment. The proposed hot gas bypass control strategy enables a high energy efficiency for the ASHP for winter heating to be achieved whilst avoiding sharp fluctuations in the indoor air temperature during defrosting.

Considerations and complications with "first principles" dynamic modelling of industrial compressors

Readily available processing hardware and "off-the-shelf" (OTS) simulation software has made "high fidelity" first principles models of both steady and transient states, for both axial and centrifugal industrial compressors, relatively easy to construct. These high-fidelity models are finding their way into "real-time. digital twin" performance monitors, front-end engineering design, and post-design – pre-construction compressor performance evaluation. The compressor models are useful for reliably demonstrating the compressor and – to some degree, based on the complexity of the model – process response to various operating conditions. Once the model is constructed, it is trivial to run a "what-if" analysis of compressor performance to answer questions related to (a) recommendations or validation of the recycle/vent valve size and actuation speed, (b) general piping layout and sizing around the compressor, (c) and hot gas bypass requirements, to name a few. This paper takes a practical approach in discussing the compressor and process parameters necessary for building these dynamic "high-fidelity" industrial-compressor models. We identify compressor inputs and compressor responses that are faithfully modeled by first-principle equations available in the simulation software and those that typically require a compromise between an "ab initio" and data-fitting approximation. We discuss the simulation's tendency to overstate pressure excursions during surge events and understate the compressor operation in the "stonewall" region. We also discuss using the simulator software's compressor-stage enthalpy calculations to predict and quantify the compressor train reverse rotation. We use our broad experience and understanding of the compressor operation and simulation and our experience with the AVEVA™ Dynamic-Simulation "OTS" simulation software as the basis for this discussion.

Comparison between reverse cycle and hot gas bypass defrosting methods in a transcritical CO2 heat pump water heater

• Reverse cycle defrosting method showed lower power consumption and shorter time. • System returned to steady heating faster with hot gas bypass defrosting method. • Averaged heating capacity with reverse cycle defrosting method was 8.24% lower. • Averaged COP with the reverse cycle defrosting method was 4.61% higher. Defrosting is an important issue that should be considered when an air source heat pump is operating in a cold climate. For the transcritical CO 2 heat pump (TCHP) water heater, the high operating pressure affects the application of defrosting methods. In this paper, the reverse cycle defrosting (RCD) and hot gas bypass defrosting (HGBD) methods were experimentally investigated in an air source TCHP water heater. The dynamic defrosting characteristics, influences on system operation and overall energy performances of the two methods were analyzed. The results suggested that the RCD method presented more complex parameter variations, lower power consumption, shorter defrosting time and larger influence on the system operation; while the HGBD method displayed less impact on the system heating capacity. The electric energy used for the RCD method was only 17.5% of that for the HGBD method. Moreover, the averaged COP with the RCD method was higher than that with the HGBD method by 4.61%. In summary, the RCD method showed evidently higher energy performance and could be a promising solution for the TCHP water heater, and the HGBD method demonstrated its robustness but had a limited energy performance.

A New Method of Regulating the Cooling Capacity of a Cooling System with CO2

New guidelines set by international organizations for refrigeration companies cause that natural working fluids such as carbon dioxide are increasingly used in new refrigeration systems. Carbon dioxide (R-744) is used in freezing, cooling, or air conditioning installations, in which the cooling load fluctuates hourly. To adapt the cooling capacity of the evaporator to the current cooling load of the cooled space, a number of control elements are used. The paper proposes a new method of regulating the cooling capacity for a one-stage refrigeration cycle with the R-744 refrigerant and an internal heat exchanger (IHX). The proposed method involves using an additional evaporator and combines the possibility of regulating the cooling capacity with the possibility of energy efficiency ratio (EER) improvement. The energy analysis of the proposed method of regulating the cooling capacity was performed and the results were compared with the control method. The control method was using the compressor hot gas bypass valve which allows the flow of hot vapor refrigerant to the suction side. The energy analysis was carried out for both subcritical and supercritical cycles using the energy equations. For each of the considered methods, the characteristics of the change in the EER as a function of the reduction of the cooling capacity in both supercritical and subcritical cycles were determined. It was found that when the cooling capacity decreased by 50%, the hot gas bypass regulating method was around 30% less efficient compared to the proposed additional evaporator regulating method.

Energy, economic and environmental assessment of transcritical carbon dioxide heat pump water heater in a typical Chinese city considering the defrosting

Considering the high demand for domestic hot water in China, the air source heat pump water heater is being popular due to higher energy efficiency. However, the heat pump is mainly studied from the energy perspective in the previous literature, and the influence of the frosting is also neglected. In this paper, with the presented domestic hot water load in a typical Chinese city, the carbon dioxide heat pump was tested at the varied ambient temperatures considering the different defrosting methods. With the proposed hot gas bypass defrosting method, a techno-economic analysis is required. To show the benefits of the proposed system, the unit is analyzed with the energy, economic and environmental analysis. The comparison with two traditional heating solutions is also presented. Results show that the seasonal performance factor is improved by 2.85%, and the annual fuel cost is decreased by 758.26 Chinese yuan in the proposed system compared with the baseline system. For the additional cost required by the proposed defrosting method, the proportion declines rapidly from 1.53% to 0.46% in the first 5 years. Compared with the direct electric heater, the life cycle cost is reduced by 2313.23 thousand Chinese yuan, and the carbon dioxide emission is declined by 266.46 tons in the proposed system. With the negligible direct emissions of 36.98 kg, the total equivalent warming impact is mainly determined by the indirect emissions. The primary energy consumption and CO2 pollutant emission is related with the domestic hot water load. The payback period is sensitive to the domestic hot water load, compressor cost and electricity price.

An experiment investigation of temperature control performance for machine tool oil coolers with hot-gas bypass temperature control scheme and inverter temperature control scheme

Following the machine tool with demands of high-speed, high-precision machining and multi-axis, the heat generation of machine tool will lead to thermo growth of spindle, thermal error, etc. Therefore, the machine tool oil cooler has been frequently adopted for thermal management of heat generation for machine tool. However, it will be quite challenging to develop high-precision machining without suitable temperature control scheme. And, the machine tool oil cooler with on-off control is difficult to control the oil temperature accurately. Therefore, in this paper, the machine tool oil cooler with hot-gas bypass temperature control scheme and inverter temperature control scheme based on the PID control logic have been proposed to solve the oil temperature control problem for machine tool oil cooler. Furthermore, the temperature control performance (i.e. thermo growth of spindle, oil temperature control accuracy, and EER) of hot-gas bypass temperature control scheme and inverter temperature control scheme has been compared by means of experiment. The experimental results shows that the inlet oil temperature control accuracy can be maintained ±0.2 °C during spindle operation by using the hot-gas bypass temperature control scheme (HGB cooler) and inverter temperature control scheme (INV cooler). Furthermore, the thermo growth of spindle of HGB cooler is about 14 % smaller than the INV cooler because of hot-gas bypass temperature control scheme with thermal compensation function. However, the total power consumption of HGB cooler is about 0.18 kW higher than the INV cooler. Hence, the energy efficiency ratio (EER) of INV cooler reveals about 10.9 % higher than the HGB cooler at steady state. Furthermore, when oil flow rate declined to about half, the temperature difference between initial and final steady state temperature of the spindle is increased around 94.3 %, and the thermo growth of spindle is increased 58.7 %.

Annual energy simulation for the air conditioning of Fuxing high speed trains

China ranks first in the world both for the operating mileage of high-speed railways and the quantity of high-speed trains. The energy consumption of air conditioning ranks second for the sub-systems of high-speed trains. In this paper, a simulation model is created to calculate annual thermal load and electricity consumption hour by hour for Fuxing high-speed train in Harbin, Beijing, Shanghai and Guangzhou. The simulation is validated in climate laboratory and shows 1.3%–13.2% deviation compared with the test results in different external temperatures. The simulation results show that the annual electricity consumption for a coach, the whole fleets of Fuxing trains and all high-speed trains in China are estimated as 60,050 kWh, 286.2 M kWh and 1.71G kWh respectively. Through analyzing the thermal load, electricity consumption and energy efficiency, six technical means are proposed to be implemented in the air conditioning of Fuxing trains considering both for energy saving and hygrothermal comfort. Heat pump and decreasing the inside setting temperature are the two methods to reduce the consumption in heating, and their saving will be 15.1% and 7.8% respectively. Replacing hot gas bypass by parallel compressors, removing reheating and reducing air flow of CFs in part-load are the three suggestions in cooling with saving of 9.6%, 4.9% and 5.4% respectively. Changing alternating current fans to electronically commutated fans will be one rich oil deposit where energy can be dug in all the working hours, and it will save 4.8% of total energy. Meanwhile, 131.0 M kWh and 781.8 M kWh (45.8%) electricity will be saved for Fuxing trains and all the high-speed trains in China respectively if all the six technical means can be implemented into the air conditioning system.

Surge analysis in a centrifugal compressor using a dimensionless surge number

Surge protection via the installation of an anti-surge control valve is indispensable in centrifugal compression systems, and the designs of such valves are often specified in the early design phase of centrifugal compression systems. However, additional recycle valve piping, such as hot or cold gas bypass valves, could be required in the case of emergency shutdowns. Furthermore, design verification via dynamic simulations is crucial in the engineering workflow. Because of the unavailability of design guidelines in the early design phase, only late verification is possible, necessitating system redesign when dynamic simulation results evidence the need for additional protection. This study presents a compressor surge distribution map by analyzing sensitivity parameters and establishing a new dimensionless number called the “surge number” (Ns). The surge distribution map is used to classify the safe and unsafe areas for surge protection using numerical threshold values. The map is to be used as a preliminary guideline for surge protection for engineers to quickly review the system and take additional protection measures in the early phase of design.

Experimental investigation on the hot gas bypass defrosting in air source transcritical CO2 heat pump water heater

The transcritical CO2 heat pump is widely used due to its higher efficiency. Frost is inevitable at low ambient temperature, resulting in a deteriorated coefficient of performance and heating capacity. Considering the disadvantages and limitations of other defrosting methods, the hot gas bypass defrosting method was experimentally investigated in this paper. The dynamic characteristics of pressure and temperature during the defrosting process are studied in detail and the pressure-enthalpy diagrams are depicted. In addition, energy analysis of the heat supply and energy consumption is presented to evaluate the defrosting efficiency. Furthermore, the influence of ambient temperature is also discussed. The results show that the measured parameters change gradually during the defrosting process except for the initial stage and defrosting time is within the defrosting regulations. The defrosting efficiency is evaluated to be 41.16%–50.84% with variation of ambient temperatures, which indicates that the hot gas bypass defrosting method is suitable for the air source transcritical CO2 heat pump.

Experimental analysis of defrosting and heating performance of a solar‐assisted heat pump integrated phase change energy storage

This thesis investigates a novel solar-assisted heat pump integrated phase change energy storage system. The defrosting performance of this system was studied experimentally and the results were compared with two traditionally used methods: reverse cycle defrosting (RCD) method and hot gas bypass defrosting (HGBD) method. The results show that the phase change energy storage system has superior performance compared with traditional defrosting methods. The indoor temperature drop recorded was relatively small and the defrosting time was 75% of the RCD system and 53% of HGBD system. The phase change energy storage system increased the condensation temperature which consequently increased the temperature difference of heat transfer resulting in higher conductivity in the defrosting progress. Compared with the method of RCD and the method of HGBD, the recovery time of the system was shortened by 90 and 160 seconds, respectively. The system works with low-temperature heat source and circulating water, which considerably reduces energy consumption, thereby improving the performance of the defrosting system. A further experimental study was also conducted on the heating performance and the results also indicated that the value of COP can reach up to 3.6 in daytime, and the indoor temperature can be stably maintained above 18°C throughout the day. Novelty Statement A new defrosting method for energy storage defrosting is proposed, and the defrosting performance is compared with two common defrosting methods. In addition, the performances of the heating system over the day were experimentally investigated. The experimental results show the system meets the heating needs of the building. Finally, the influence of the outdoor temperature on the exergy efficiency of the system was discussed. It shows that this system can improve the operational stability, the system economy and energy saving.

Intelligent control and energy efficiency analysis of the multi-functional freezing and refrigerated storage system

ABSTRACTTo improve the efficiency of specialized cold storage, a multi-functional freezing and refrigerated storage system was developed, of which quick-freezing, differential pressure precooling, freezing-point storage and intelligent defrosting could be performed. It involved parallel control system, hot-gas bypass adjustment, and variable speed control to meet the adjustment capacity under different evaporation temperatures. Results showed that the temperature of the refrigerated storage for frozen food was further steadier and the energy consumption decreased by about 9.7%. There are high control accuracies of temperature (±0.2°C) and relative humidity (±3%) during freezing-point storage. Furthermore, the energy consumption of defrosting decreased by about 30%.