A novel Temperature–Humidity–Time defrosting control method based on a frosting map for air-source heat pumps

To improve the defrosting accuracy and the energy efficiency of the air-source heat pump (ASHP) under frosting and defrosting conditions, a novel Temperature–Humidity–Time (T–H–T) defrosting control method, based on a frosting map for the ASHP unit, is proposed in this paper. A field test was conducted for two heating seasons, to verify the feasibility and applicability of the T–H–T method. The advantages of the T–H–T method, compared to the conventional Temperature–Time (T–T) defrosting control method, are presented. In total, eight cases are shown in this paper. Cases 1 to 4 were chosen to reveal the T–H–T performance under different frosting conditions. It was found that no matter what kind of frosting conditions, defrosting was always initiated in a similar situation: ∼90% of the outdoor coil surface was covered by frost; the temperature difference between the compressor suction and discharge increased by ∼20%; and the heating capacity decreased by ∼30%. These results indicate that the T–H–T method can make an accurate decision under different frosting conditions. Cases 5a, 5b and Cases 6a, 6b were two groups of cases to compare the advantages of the T–H–T method against the conventional T–T method. Cases 5a and 5b were chosen for the non-frosting condition. It was found that the T–T method initiated the defrosting operation 31 times within 24 h. However, none of the defrosting operations was conducted for the T–H–T method. Cases 6a and 6b were chosen to compare these two methods under consecutive and variable frosting conditions. For the T–T method, 63% of the defrosting processes were found to be executed under conditions where defrosting was not necessary. However, for the T–H–T method, all the defrosting controls were found to be accurate and reasonable. These results indicated that the novel T–H–T method is suitable for the defrosting control of the ASHP, and has a more competitive performance than the conventional T–T method.     

Defrost improvement by heat pump refrigerant charge compensating

During winters, the air-source heat pump often operates with substantial frost formation on the outdoor heat exchanger, and the frost layer has to be melted away periodically to keep a high heat pump coefficient of performance (COP). Otherwise, the unmelted frost layer and water will become high density frost or ice layer in heating mode. However, it is difficult to melt the frost layer in the defrosting cycle, where the effective defrosting time plays an important role in improving the defrosting ability. Generally, the defrosting time can be decreased by the following ways: increasing the refrigerant flow rate effectively, and rapidly establishing the suction pressure, discharge pressure, and the compressor power. A new heat pump defrost system with a refrigerant charge compensator, instead of the accumulator which is a key component for the frosting cycle performance, is developed in this paper. Furthermore, test results showed that the improved frost system with the compensator worked as expected, and its suction and discharge pressures and the power of the compressor during the defrosting were much larger than before.     

最大平均制热量控制除霜方法的实验研究

通过空气源热泵空调器冬季运行制热量不足的原因分析,在此基础上介绍了最大平均供热量除霜控制方法的定义,并通过实验对比验证了该方法的优势,同时也提出该方法能够实际应用还需要继续开展的工作.     

Effect of different treatments on the quality of cuttlefish (Sepia officinalis L.) viscera

The effects of different preservation times (cuttlefish auction), transformation factory treatments, different times of frozen storage at −20 °C and various defrosting temperatures were investigated with respect to the chemical changes of the viscera of cuttlefish (Sepia officinalis). During auction storage, pH and TCA (trichloroacetic acid)-soluble protein concentration decreased, whereas intracellular (cathepsins, total acid proteases and acid phosphatases) and extracellular (amylase, chymotrypsin, trypsin and total alkaline proteases) enzymatic activities increased. In cuttlefish transformation factories, pH value and TCA-soluble protein concentration increased. In transformation factory conditions, lipase and amylase levels varied, while other assayed enzymes were stable. Moreover, during transformation factory treatment, the molecular weight of proteins/peptides decreased and the oil composition evolution reflected hydrolysis of cuttlefish viscera. Thus, cuttlefish viscera fatty acid composition differed between fresh viscera and factory viscera. Despite changes in the fatty acid chain composition during factory transformation, the percentage of poly-unsaturated fatty acids remained high. Frozen storage implied major changes in viscera quality such as an increase in pH and a decrease in the quantity of high molecular weight protein. Moreover, the higher the defrosting temperature, the higher was the pH. During storage at −20 °C the quantities of proteins, carbohydrates and lipids decreased slightly.     

热气旁通化霜技术在空调机组上的应用

传统的化霜模式是通过改变四通换向阀的动作,使冷媒逆向流动,通过压缩机排出的高温制冷剂来化霜,相当于在化霜过程中从制热状态变成制冷,室内的房间温度会波动很大;本文研究的化霜方法是通过直接热气旁通的方式进行化霜,并将此技术可以实现产品化的应用。热气旁通化霜是：当进入化霜时,直接把排气侧的高温气态冷媒旁通到冷凝器实现化霜,室内机仍然是制热状态,在制热化霜的过程中对室内温度影响很小,大幅提高了室内的舒适性。     

汽车挡风玻璃用除霜,隔热薄膜的试验研究

提出了汽车挡风玻璃用除霜、隔热薄膜的设计方案。为检验其可靠性和实用性，进行了试验研究和理论分析。     

关于风冷热泵除霜问题的研究

本文通过对风冷热泵冷热水机组冬季制热运行时换热器结霜与除霜问题的研究，提出了一种“能量分析法”。具体针对一种常见的除霜方法-逆循环除霜，提出了相应的减少除霜损失的方法。     

Evaluation of the effect of defrosting practices of ground beef on the heat tolerance of Listeria monocytogenes and Salmonella Enteritidis

The effect of common defrosting practices of ground beef, including (i) defrosting in the refrigerator (5 °C for 15 h), (ii) defrosting at room temperature (25 °C for 12 h) and (iii) defrosting in the microwave, on the heat tolerance of artificially inoculated Listeria monocytogenes and Salmonella Enteritidis, was studied. The thermal inactivation of S. Enteritidis was not, overall, affected by defrosting practices. In contrast, defrosting at room temperature resulted, overall, in an increased heat tolerance of L. monocytogenes compared to the rest tested defrosting practices. Inactivation kinetics of the two pathogens for the different defrosting practices were determined by fitting the data to the Weibull model. The δ parameter of the Weibull model (heat challenge time (min) required for the first 1-log reduction) for S. Enteritidis and for defrosting at 25 °C, microwave defrosting, defrosting at 5 °C and for the control (fresh ground beef inoculated with the pathogens just before the heat challenge trials) was 1.13, 1.62, 1.60 and 0.96, respectively, while the corresponding values for L. monocytogenes were 20.13, 10.82, 9.95 and 9.47, respectively. The findings of this study should be useful in risk assessments and in developing food handling guidelines for the consumers.     

Energy demand and comparison of current defrosting technologies of frozen raw materials in defrosting tunnels

The optimization process of coal defrosting in defrosting tunnels is solved in this article. Individual technical solutions of defrosting tunnels, as well as energy demands, are dealt with in this report. Defrosting tunnels are used for the defrosting of deep-frozen substrates like coal, ore or powdery substances. There are two different ways of defrosting. The first one is based on convective heating and the second one on radiant heating. Nowadays, convective heating is used much more than radiant heating. However, theory and practice show that the radiant heating is much more efficient. The aim of this article is to describe the design and construction of a multifunctional method of a defrosting tunnel. In the second stage we make experimental measurements of convective and radiant methods of defrosting on a built model. Its third aim is to make energy and economy assessments of defrosting process on the model. Finally, to implement the acquired knowledge in the practice, determining the conditions, in which the change of present-day convective defrosting technology to the new radiant technology becomes effective.     

Experimental study of an air-source heat pump for simultaneous heating and cooling – Part 2: Dynamic behaviour and two-phase thermosiphon defrosting technique

This article presents the concepts of an air-source heat pump for simultaneous heating and cooling (HPS) designed for hotels and smaller residential, commercial and office buildings in which simultaneous needs in heating and cooling are frequent. The main advantage of the HPS is to carry out simultaneously space heating and space cooling with the same energy input. Ambient air is used as a balancing source to run a heating or a cooling mode. The second advantage is that, during winter, energy recovered by the subcooling of the refrigerant is stored at first in a water tank and used subsequently as a cold source at the water evaporator to improve the average performance and to carry out defrosting of the air evaporator using a two-phase thermosiphon. Unlike conventional air-source heat pumps, defrosting is carried out without stopping the heat production. A R407C HPS prototype was built and tested. The basic concepts of the HPS are detailed in part1 of this article [1]. Its performance on defined operating conditions corresponds to the data given by the selection software of the compressor manufacturer. In the present part of this article, the operation of the high pressure control system, the transitions between heating, cooling and simultaneous modes and the defrosting sequence are analysed and validated experimentally.