Defrosting Method Research Articles

Feasibility analysis of thermal storage defrosting method for air source heat pump: From energetic and economic viewpoints

Frosting issue of air source heat pump (ASHP) is a continuing concern. The conventional reverse cycle defrosting (RCD) method absorbs heat from indoor heat exchanger, thus greatly impacts the indoor thermal comfort. To solve the problem of insufficient defrosting heat supply for RCD method, thermal energy storage (TES) based defrosting method has gained increasing attention over the past years. Yet existing studies have only focused on specific prototype tests. There lacks general analysis on system characteristics and design considerations. To better address application concerns of TES-based defrosting method, this study carried out feasibility analysis for the TES-based ASHP system from both energetic and economic aspects. The energetic analysis reveals that the stable operation of TES-based ASHP relies on proper system design and control. Feasibility conditions concerned with key operating parameters are defined and deduced. Impact factors on average heating efficiency are also analyzed. Theoretical and numerical results indicate that energy saving potential of TES-based ASHP over conventional ASHP is conditional on the defrosting discount factor of conventional RCD method. TES-based ASHP enhances heating efficiency of conventional ASHP by 3.0% to 19.5% at ambient from −2°C to 2 °C due to relatively large defrosting discount factor of conventional RCD method. With respect to the economic aspects, the capital cost of TES-based ASHP is 26% higher than that of the conventional ASHP. But the total life cycle cost can be reduced by higher heating efficiency. The condensing heat storage ASHP exhibits cost advantages to the conventional ASHP when defrosting discount factor of conventional ASHP is higher than 1.13. Further prototype test with the TES-based ASHP could shed more light on the feasibility characteristics as revealed by the theoretical analysis.

Efficiency comparison between defrosting methods: A laboratory study on reverse-cycle defrosting, electric heating defrosting, and warm brine defrosting

Frost on the evaporator of a cold storage refrigeration system reduces cooling capacity and COP (Coefficient of Performance). Hence an energy-efficient defrosting process is crucial for economical operation. Various defrosting methods have been proposed in literature and their defrosting efficiency has been assessed. However, differing experimental conditions, e.g., variations in evaporator geometry and diverse air conditions, hinder accurate comparison across literature. Further, while electric heating defrosting (EHD) and reversed cycle defrosting (RCD) methods are widely studied, warm brine defrosting (WBD) method is rarely investigated. Despite this, WBD offers the potential to use low-temperature waste heat for defrosting, which reduces energy consumption drastically. Therefore, this study experimentally assesses the defrosting efficiency for EHD, RCD, and WBD on a single experimental setup, thus ensuring comparability. For the first time, low brine supply temperatures (10 °C/20 °C/30 °C) for WBD are investigated. Our results show that RCD reaches the highest defrosting speeds and has the highest defrosting efficiency between 56% and 61%, depending on air conditions. WBD at10 °C and 20 °C exhibit low efficiencies of 16–29%. However, WBD at 30 °C has comparable efficiency to EHD (40–45%). The reported results can serve as a decision criterion in the design process of refrigeration systems.

Assessment of a novel defrost method for PV/T system assisted sustainable refrigeration system

Energy consumption has continuously increased depending on the rapidly growing human population, enlarging economies, advancing technologies, and improving living standards. A noteworthy share of the energy consumption has been arising from the buildings all across the world. Refrigeration, heating, and air conditioning systems have accounted for a significant portion of the energy consumption in the buildings. Therefore, it is possible to both reduce energy consumption, and mitigate the carbon footprints by efficiently designing, constructing, and operating these systems. In this framework, the present research has centered on the refrigeration systems, and aimed to develop a novel defrost method for photovoltaic thermal (PV/T) assisted sustainable refrigeration systems. In the conventional refrigeration systems, the frost process occurs when air condenses on the evaporator surface as a result of the evaporator surface temperature being below the freezing point of water or the dew point temperature of the air in the conditioned space. Differently in the present work, PV/T system is used to prevent the frost process in the refrigeration system, unlike the conventional systems. Accordingly, the efficiency loss caused by the temperature increment will be prevented by cooling the PV module, and it is aimed to be more efficient by reducing the daily power consumption as an alternative solution method to the frost that occurred on the evaporator in refrigeration systems. On this purpose, a novel evaporator design is developed, and used for defrosting in this study. Accordingly, this novel design includes a refrigerant line inside the evaporator and a hot water line from the PV/T in this design. In the results, it is noticed that the system designed for winter conditions could be used for defrosting. While an average of 605 W for heat energy was used for each defrost process, the average defrost duration was recorded to be approximately 4 min. While the average electrical efficiency of the PV module was found to be 13.6%, the average total efficiency was found to be 38%. Besides, Average PV module surface temperature was determined as 36.4 °C, average water storage tank temperature was determined as 26.4 °C. In addition, the coefficient of performance (COP) of the refrigeration system is calculated to be 4.18. COP increased by an average of 9% during defrosting. Furthermore, the environmental economic cost was calculated to be 14.6 $/h. In the conclusion, it is proven that the novel defrost method proposed in the present work can be used for refrigeration systems, and contribute to both the reduction of energy consumption and mitigation of carbon emissions arising from the buildings.

Determination of defrost efficiency and energy efficiency index value using different defrost methods and refrigerants: An experimental study

In this study, open-type refrigeration cabinets were designed and manufactured using hot gas and electrical resistance defrost methods and R290, R449A and R404A refrigerants. The aim of this study is to determine the temperature increase of the products during the process, CO2 emission amount, defrost efficiency, and energy efficiency index (EEI) value with different defrost methods and refrigerants for commercial refrigeration systems. The increase in package temperatures during the defrosting process was determined as 1.33 °C in the electrical method. The results showed that the hot gas method was 7.15% more efficient in terms of defrosting efficiency. The EEI value was calculated as 78.76 with the use of R290 in the hot gas method and the energy class was determined as F and the hot gas emit 5.9% less CO2 than in the resistance experiments. In the hot gas defrost method, it was seen that 20.3% less energy was consumed compared to the total consumption. It was observed that R290 refrigerant and the hot gas defrost method were the most suitable for commercial systems in terms of defrosting process losses, total energy consumption, and temperature rise of the cooled product during defrosting.

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.

Review regarding defrosting methods for refrigeration and heat pump systems

The paper presents a literature review regarding defrosting methods for household refrigeration and heat pumps. The literature review covers the period between 2008 and 2020. A number of 61 papers have been studied. The literature review was conducted by dividing the defrost methods into passive and active. Passive methods involve surface coating and off-cycle. The active defrost methods involve reverse cycle, ultrasonic vibration, hot–gas defrost, electric heating and hot fluid. Surface coating and ultrasonic vibration are recent defrost methods proposed in the literature. Also, recently, phase change materials have been used in household refrigerators to improve their efficiency. This is a topic that needs further investigation and is a subject of interest as it can lead to lower energy consumption during defrost cycles. From the present study, the research direction regarding the use of PCMs in defrost cycles can be highlighted.

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.

Effects of Cooking and Defrost Methods on Retinol Concentration of Chicken Liver

This study aimed to analyze the retinol concentration of chicken livers in various brands, batches and types of both organic and free range by HPLC. In addition, the effects of different cooking and defrosting methods on the retinol levels of chicken livers were also determined. Chicken livers samples were roasted for 35 minutes at 200°C, cooked for 40 minutes at (26 to 100)°C, fried for 5 minutes at 180°C. Other samples were frozen for 72 hours and divided to be defrosted by fridge for 8 hours at 3°C, at ambient temperature for 2 hours at 23°C, submersed in water for 35 minutes at 25°C, and microwaved on defrost function for 1 minute, where all methods were compared to its natural state (3°C). The mean retinol concentrations in brands A, B, C and organic and free-ranged were 9152, 4673, 5943, 3401, 30094 µg/100 g (P < 0.001). Significant losses of 39.9 % (P < 0.05), and 26.2 % (P < 0.01) were found when compared to natural state (raw) to roasting and microwave, respectively. This study showed a significant difference between brands and types of chicken livers, and a significant loss of retinol in chicken liver, in food processes commonly used. Otherwise, vitamin A values in chicken liver suggest that consumption could be recommended to prevent vitamin A deficiency.

Adaptive defrost methods for improving defrosting efficiency of household refrigerator

The defrosting method of the conventional household refrigerator increases freezer temperature during the defrosting operation, and defrosting efficiency reduces because the heater consumes more power than the amount of frost on the surface of the heat exchanger. To solve this problem, three defrost heater control methods, applicable to refrigerators equipped with conduction and radiation heaters, are being proposed. The control methods were classified as a method of simultaneously pulsating two heaters, method of individually pulsating two heaters, and method of step-by-step reduction of radiation heater power. The operation effect of each heater on freezer temperature was analyzed. For the three methods, a heater control optimization process was performed to reduce the temperature increase in the freezer. The power consumed by the heater was minimized and defrosting efficiency improved. The Best performance was observed when two heaters pulsated individually. For this method, the variation in freezer temperature, between before and after the defrost process, was reduced from approximately 11 °C to 5 °C. Additionally, the defrosting efficiency improved by 15%.

Air source heat pump with water heater based on a bypass-cycle defrosting system using compressor casing thermal storage

In this study, the defrosting system of an air source heat pump utilizing compressor casing heat storage combined with a hot gas bypass cycle (ASHP-CCHS-HGBC) was designed. The phase change material for defrosting was selected, the phase change heat storage exchanger was devised, and the ASHP-CCHS-HGBC test system was established. The power consumption, defrosting time, and the influence of the indoor exchanger outlet on the air temperature in the ASHP-CCHS-HGBC method were then compared with those of the reverse-cycle defrosting (RCD) and electric heating defrosting (EHD) methods. Experimental results reveal that the total defrosting time and consumption of the ASHP-CCHS-HGBC method was 100s and 43.6kJ, respectively. These values were lower by 10s (9%) and 12.1kJ (21.7%) relative to those of RCD. Moreover, the compressor suction temperature was increased by 10.1°C during defrosting by ASHP-CCHS-HGBC. Under the normal heating operation for 2.5h, 10L hot water with a temperature of 30°C was obtained, the compressor casing temperature was reduced by 4.6°C. While defrosting, the air temperature of the indoor heat exchanger outlet declined to only 3.3°C and exerted the least influence on the indoor temperature among those of the three defrosting methods.

Experimental investigation on a novel cold storage defrosting device based on electric heater and reverse cycle

It is universally acknowledged that the accumulation of frost on the evaporator surface will reduce the cooling capacity and performance of the cold storage. Therefore defrosting must be periodically and effectively carried out to avoid the evaporator blockage. The electric heater defrosting (EHD) and reversed cycle defrosting (RCD) methods are usually used in cold storages. However, no matter what method is adopted, there will be extra thermal load distributed to the compartments which lead to an unfavorable storage temperature fluctuation and then cause quality loss of the stored food. In order to solve the above-mentioned problems, a novel cold storage defrosting device based on EHD and RCD was proposed in this paper. Experiment was performed on the device to investigate its effect on several aspects including energy saving, reduction of cold storage temperature fluctuation and improvement of compressor operational stability etc. The results showed that this novel device could remarkably increase energy utilization and reduce temperature fluctuation of the cold storage, which was beneficial for long-term storage of products in the cold storage. Moreover, it was able to increase the operational stability of the compressor.

노인들의 식품안전 위험요인 규명을 위한 식품위생 지식, 태도, 행동 조사

The purpose of this study was to investigate food safety knowledge, food safety attitudes, and handling behavior in the elderly. The survey was conducted on 358 individuals over 65 years old in urban and rural areas. Data were analyzed with descriptive analysis and χ2 test analysis of variance using SPSS. From the results on elderly’s food safety knowledge, the item ‘tangerines should be washed before eating’ was correctly answered by urban subjects (75.4%) than rural subjects (49.7%). ‘Is it okay to cook meat left on the sink since afternoon in the evening’ showed the lowest correct answer rate in both urban (23.1%) and rural (31.9%) subjects. For the item related to food keeping, ‘Bacterial cells do not multiply in Samgyetang when it is kept in a refrigerator right after boiling thoroughly’, 58.5% of urban and 54.6% of rural elderly answered correctly. Most elderly people showed a tendency to think that boiled foods might be safe to eat. Secondly, for food safety attitudes, urban elderly had more proper attitude regarding the item, ‘Namul is very tasty only when mixed with bare hands’ (disagree rate 34.9%) than rural elderly (P＜0.05)’. On the other hand, rural elderly had more positive attitudes regarding the store principle “first in, first out” compared to urban elderly (P＜0.001). Thirdly, regarding food safety behaviors, only 67.9% of urban and 58.7% of rural elderly responded that they washed their hands right after answering the telephone while cooking. Exactly 33.8% of urban and 39.6% of rural older people replied ‘defrost meat on top of sink or table’ as the defrost method for frozen foods, showing that elderly did not recognize the risk of foodborne illness during improper defrosting at room temperature.

Performance evaluation of a novel method of frost prevention and retardation for air source heat pumps using the orthogonal experiment design method

In this study, a novel technology of frost prevention and retardation for air source heat pump (ASHP), which reduces thermal discomfort, is introduced. It utilizes auxiliary electric heaters (AEH) on tubes before (B-AEH) and (or) after (A-AEH) the outdoor evaporator to retard frost formation or prevent frost from accumulating on the outdoor heat exchanger. This enables the supply of hot air into the interior space without interruption. This new method differs from the common high pressure hot gas bypass defrosting (HGBD) methods and the reverse cycle defrosting (RCD), both of which could result in significant temperature fluctuations and thermal discomfort. The orthogonal experiment design (OED) was applied in this study to evaluate the performance of the air source heat pump (ASHP) with different magnitudes of AEH power under a range of ambient frosting conditions. The L25(56) orthogonal array was selected for the experiment and data were analyzed by means of the analysis of range (ANORA) and the analysis of variance (ANOVA). The optimum parameter combination affecting the performance of the ASHP was determined and the most significant parameters were identified. It was demonstrated that the proposed ASHP design is effective for frost prevention and retardation in real applications.

Simulation based identification of the ideal defrost start time for a heat pump system for electric vehicles

Resistance heating with PTC elements to cover the heat demand of electric vehicles reduces significantly the cruising range at low outside temperatures. Reversible heat pump systems are one of the most promising solutions for this problem. However, in heat pump mode the frost formation on the exterior heat exchanger reduces the performance and efficiency of the system. Therefore, an efficient defrost method is crucial to benefit from the heat pump also under frosting conditions. In the present paper, a transient Modelica simulation model of a reversible CO2-heat pump system with hot gas defrost was set up in order to assess the impact of different defrost start times. The model is able to handle frost growth on the exterior heat exchanger as well as defrosting. The simulation results showed an optimal point of time to conduct defrost at chosen operating conditions in order to maximize the average COP including the frosting and defrost period.

Defrosting performances of a multi-split air source heat pump with phase change thermal storage

Recently, multi-split air source heat pumps (ASHPs) have been used increasingly for space heating in cold winter. When it operates in frosting environment, periodic defrosting is necessary to maintain a high system performance. However, researches on its defrosting were few due to its high capital and complicated controls. To solve its fundamental problem of insufficient heat available during defrosting, a novel reverse-cycle defrosting (NRCD) method based on the phase change thermal storage has been developed. In this paper, comparative experiments using both standard reverse-cycle defrosting (SRCD) method and NRCD method were carried out on a multi-split ASHP unit with a phase change material heat exchanger (PCM-HE) acting as energy accumulator during heating operation and heat source during defrosting operation. Experimental results suggested that when using the NRCD method, the system performances, such as suction pressure and temperature, defrosting and heat-resumption durations, COP during defrosting operation can be effectively improved.

A combined Dual Hot-Gas Bypass Defrosting method with accumulator heater for an air-to-air heat pump in cold region

Abstract The Dual Hot-Gas Bypass Defrosting (DHBD) cycle is an effective defrosting method compared to a Reverse Cycle Defrosting (RCD) method to remove frost from the outdoor heat exchanger (HEX) of an air-to-air heat pump, especially the outdoor temperature is above 0 °C. However, the DHBD method has a drawback when the heat pump operates in cold outdoor environment, below 0 °C due to rapid decrease in refrigerant temperature followed by lower hot-gas bypass temperature. In order to overcome lower discharge temperature of compressor, a combined defrosting cycle with DHBD and the accumulator heating method is developed. An induction heater (IH) is adopted as the accumulator heater. The dynamic performance and defrosting time are compared between the conventional RCD method and the combined DHBD–IH method using a medium size air-to-air heat pump of 16 kW under the condition of −5 °C outdoor temperature. Due to the additional heater, the combined DHBD–IH method sustained higher discharge temperature of the compressor and reduced 15% of the defrosting time than that of the RCD method with nonstop indoor heating operation. The overall heating capacity of the DHBD–IH cycle including defrosting mode was 2.5 kW higher than that of the RCD cycle.

Hot gas defrosting method for air-source transcritical CO2 heat pump systems

When the air-source heat pump systems operate at low ambient temperatures in winter, frost forms on the coil surface of the outdoor evaporators. The frost substantially affects the operating performance and energy efficiency of heat pump systems, and hence periodic defrosting is essential. In this study, several defrost methods are presented to look for a candidate for air-source transcritical CO2 heat pump systems. The hot gas method proves to be more suitable among other defrosting methods for transcritical CO2 heat pump systems. To validate its reliability and rationality, an air-source transcritical CO2 heat pump water heater was built in a climatic laboratory. Through the experiments, the dynamic process of temperature and pressure were obtained to demonstrate the hot gas defrosting characteristics and system cycle. The hot gas defrosting cycle in the p–h diagram was also validated by experiment results. Meanwhile, instant defrosting images were captured to record the dynamic defrosting process. The defrosting process lasted 10min and defrosting efficiency was 34.8% for hot gas defrosting method. The effectiveness and applicability of hot gas defrosting method for CO2 heat pump water heater is validated by experiments.

온도차 감지 제상법과의 비교를 통한 광센서 제상법의 타당성 검증을 위한 연구

Abstract Experiments were performed to verify if performance and characteristic curves obtained from the temperature differential defrosting method, where surface temperature is measured to judge defrosting condition, can be reproduced bythe photoelectric technology where defrosting condition is judged by photoelectric sensors. The output voltage of a phototransistor and heating capacity, power consumption, and surface temperature of the outdoor heat exchanger are compared.The results showed that the photoelectric sensors can be used as a defrost control device. On-off control timings in temperaturedifferential defrosting method are in good agreement with those predicted by the high and low threshold output voltages of the photoelectric sensor. Key words Frost(서리), Temperature Differential Defrosting Method(온도차 제상 방법), Photoelectric Sensor(광센서), Mal-defrost Phenomena(오제상 현상)†Corresponding author, E-mail: dongseonkim@ut.ac.kr 기호설명 : 열전달률 [W] T : 온도 [K]  : 동력 [W]하첨자 cool : 냉각 DB : 건구 heat : 가열

AN EXPERIMENTAL STUDY ON PERFORMANCE IMPROVEMENT FOR AN AIR SOURCE HEAT PUMP BY ALTERNATE DEFROSTING OF OUTDOOR HEAT EXCHANGER

For a space heating air source heat pump (ASHP) in the condition of low temperature and high humidity, frost on the surface of heat exchanger becomes the major cause decreasing heating surface area and thus the performance of heat pump. In this study, we showed a method of delaying the implantation of frost using alternate defrost control. First, we acquired the performance data for conventional periodic reversed-cycle defrosting with a 5RT heat pump. After the experiment, the heat pump was modified to verify the effects of newly introduced alternate defrosting and compared with the conventional periodic reverse cycled method. It was found that heating coefficient of performance (COP) of heat pump using newly proposed alternate defrost method was about 17% higher than conventional heat pump using periodic reverse cycled defrosting.

A novel defrosting method using heat energy dissipated by the compressor of an air source heat pump

When an air source heat pump (ASHP) unit is used for space heating at low ambient temperatures in winter, frost may form on its outdoor coil surface. Since the accumulated frost adversely affects its performance and energy efficiency, periodic defrosting of the outdoor coil is necessary. Currently, the reverse-cycle defrosting (RCD) method is widely used for the defrosting of ASHP. However, this operation interrupts space heating during the defrosting process. A time lag occurs to resume heating at end of the defrosting cycle. Moreover, frequent reversing of the 4-way valve may cause mass leakage of the refrigerant, even make the system unsafe. Furthermore, some amount of heat is dissipated to the atmosphere through the compressor casing. To improve the defrosting process and use this waste heat, a novel ASHP unit is developed. The space is heated during the defrosting process using the heat dissipated by the compressor. Experiments using both the RCD method and the novel reverse cycle defrosting (NRCD) method developed in this study are conducted on an ASHP unit of 8.9kW nominal heating capacity. The experimental results indicated that in the NRCD method, the discharge and suction pressures are increased by 0.33MPa and 0.14MPa, respectively, the defrosting time is shortened by 65% while the resuming heating period vanished with the NRCD method, and that the total energy consumption in comparison to RCD method is reduced by 27.9% during the period which is composed of defrosting period and resuming heating period. Moreover, the NRCD method ensured continuous heating during defrosting. The mean temperature difference between the air entering and leaving the indoor coil reaches 4.1°C during defrosting. Over a test period of 125min, compared to RCD method, the total heating capacity and input power are increased by 14.2% and 12.6%, respectively. The increase in the system COP is 1.4%.