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Five major issues in the technical standards for heat pump water heaters
In recent years, the market for heat pump water heaters has developed rapidly. For a new product, scientific and reasonable technical standards can provide a strong impetus to product development and industry development; conversely, defects in technical standards may have a negative impact on the development of the entire industry. This article will list some of the problems I found in the current standards for heat pump water heaters. Air inlet temperature for rated operation GB / T23137-2008 "Household and similar heat pump water heaters" Use 20 ° C as the inlet air temperature for rated operation of air source heat pump water heaters. This temperature is 5 ° C higher than the inlet air temperature recommended by the International Electrotechnical Commission (IEC) and 4 ° C higher than the inlet air temperature specified by the Japan Refrigeration Industry Association (JRA) standard. However, this seemingly small difference has far-reaching implications. Operating parameters under rated operating conditions are representative indicators of product performance. For market competition considerations, manufacturing enterprises are required to maintain a high evaporation temperature under rated operating conditions as much as possible in order to improve heating capacity and efficiency. However, the condensing temperature of an existing air conditioner compressor is usually set to 65 ° C. Generally, when the hot water temperature reaches 55 ° C, the condensing temperature is already close to the upper limit. Taking into account the distribution of performance parameters have a certain degree of dispersion and the technical and economical efficiency of the condenser and other factors, it is difficult for heat pump manufacturers to adopt measures similar to maintaining temperature margin in air conditioning design to ensure product reliability. Therefore, the heat pump water heater manufacturers to adopt a variety of solutions, such as the use of high temperature operating pressure switch, the compressor in the short term higher than the upper limit of the condensing temperature operation; to take a higher condensation temperature T3 climate type Compressor, allowing condensing temperature up to 70 ℃ and so on. Among them, the most striking is the development of heat pump water heater dedicated compressor. However, due to the air-source heat pump heating capacity is greatly affected by the inlet air temperature, when used in residential areas, when the inlet air temperature is low, there will be insufficient hot water situation. Under normal circumstances, the air temperature reaches 15 ℃, the air-source heat pump water heater heating capacity can reach a higher level, there will be no shortage of hot water. If 15 ° C is used as the rated inlet air temperature, the overheat protection function of the heat pump water heater will work when the inlet air temperature exceeds 15 ° C. The usual measures are to reduce the evaporator air flow, lower the evaporation temperature and lower the system temperature Heat load, which limits condensation temperature. This measure is simple and effective to prevent over-temperature operation of the system. Therefore, I believe that, for heat pump water heaters, the condensing temperature limit of 65 ℃ conventional air conditioner compressor enough to be competent heat pump system requirements. I can not be sure, in the preparation of GB / T23137-2008, the drafters whether the rated operation of the heat pump water heater inlet temperature in the over-temperature protection has been fully demonstrated, and perhaps in other respects there are more sufficient reasons to support the standard Set the inlet air temperature to 20 ° C. The steady and reliable operation of the compressor at higher water temperatures is an important topic in the heat pump water heater industry in recent years. What is puzzling is that, in most cases, manufacturers are more willing to adopt high condensing temperature solutions, including the use of expensive R417A refrigerants; even in disregard of the relevant CCC certification requirements and standards, the deployment of mixed refrigerants. In fact, as long as the standard is revised to 15 ℃ inlet air temperature as the air source heat pump rated operating parameters, you can solve the existing problems. R134a refrigerant embarrassment GB / T provides higher energy efficiency indicators, the use of R134a refrigerant system is usually difficult to meet the standard requirements. As a result, heat pump water heaters using R134a refrigerant are virtually eliminated in the domestic market, however, R134a refrigerant is still commonly used in air-source heat pump water heaters in Europe, North America and Australia. As R22 refrigerants have been discontinued in these areas, R134a refrigerants have the following ozone depleting potential (ODP) and greenhouse effect potential (GWP) relative to other commonly used refrigerants (such as R407C, R410A and R417A) Advantage. The R134a compressor has a lower exhaust temperature when operating at high condensing temperatures; the R134a compressor maintains operational stability and reliability at higher water temperatures. The most obvious drawback to the R134a system is its lower thermal efficiency than comparable systems using the R407C, R410A, and R417A. In addition, the operating range of some of the high backpressure piston compressors used in the R134a system is significantly larger than existing rolling-rotor compressors and is better able to cope with a wider range of operating requirements than some newly developed or under development Heat pump water heater dedicated scroll compressor roughly the same. In summary, R134a system, the technical economy as much as the use of R22, R407C, R410A, R417A system. In my opinion, due to the high coefficient of performance index R134a exclude the domestic heat pump water heater market strategy is not appropriate. Heat pump water heaters with CO2 as a refrigerant Appendix A (informative) of "GB / T Heat pump water heaters with CO2" basically derives from JRA4050: 2007 "Domestic heat pump water heaters". If you compare the pressure safety features of a heat pump refrigeration system, you will notice that there is a difference between a heat pump water heater with CO2 as a refrigerant and a heat pump water heater with a conventional fluorocarbon refrigerant. The former uses a transcritical cycle resulting pressure safety characteristics and the latter there is a big difference, and the former system pressure is higher. At present, the applicable standards for such issues have not been released in China. Internationally, in addition to the JRA standard, the standard that has been officially released is the European Union EN378 series standard 2008 edition and the revised ISO5149 series standard. Due to the difference of standard system, there are some differences between JRA standard and EN standard and ISO standard about pressure safety requirements of refrigeration system, EN378 and ISO5149 belong to ISO / IEC system, and GB / T23137-2008 quoted safety standard is GB4706.32-2004 "Household and similar electrical appliances safety heat pumps, air conditioners and dehumidifiers special requirements", GB4706.32-2004 on the part of the pressure safety is quoted GB9237-2001 "refrigeration and heating mechanical refrigeration system safety requirements", and GB9237 -2001 Equivalent to ISO5149: 1993. In other words, according to the Chinese standard management system, the safety requirements of heat pump water heaters with CO2 as the refrigerant will be officially formulated in the future, and the corresponding standards in the IEC / ISO system will be adopted. Thus, among the standards to be developed, the pressure safety of CO2 transcritical cycle will be different from that of Appendix A of GB / T, which is the same as the forthcoming ISO5149 series standard and already released EN378 series standard. Against this background, the corresponding requirements of Appendix A of GB / T are not only inconsistent with the GB4706.32 safety standard system adopted in the main body of this standard, but also inconsistent with similar standards formulated in the future. Not difficult to see, GB / T23137-2008 appendix A as an informative appendix is ​​more harm than good. Commercial heat pump water heater standard safety requirements Domestic heat pump standard safety requirements than the commercial heat pump strict. At present, GB / T21362-2008 "commercial or industrial and similar uses of heat pump water heater" is often regarded as some manufacturers and GB / T equivalent standards. According to my understanding, there is such an understanding is due to GB / T21362-2008 in the "range" made it clear that commercial or industrial and other uses other than heat pump water heater can refer to the use of the standard. In contrast, GB / T21362-2008 safety requirements lower. Therefore, without supplementing the corresponding requirements, the direct use of GB / T21362-2008 production of household heat pump water heaters, some of the product safety indicators will not meet the relevant mandatory standards (such as GB4706.32-2004) requirements, the consequences are self-evident. At the same time, GB / T21362-2008 refers to JB8654-1997 Safety Requirements for Volumetric and Centrifugal Chilled Water (Heat Pump) Units in terms of safety requirements, while JB8654-1997 mainly refers to the American ANSI / ASHRAE15-1992 " Mechanical refrigeration safety regulations. " In general, pressure safety management usually includes the installation site classification, system classification, refrigerant selection, system design pressure determination, component strength requirements, protection device configuration and testing. However, JB8654-1997 basically did not make the above-mentioned content explicit, neither the reference standard nor the body mentions ANSI / ASHRAE15, and no reference to the main contents of ANSI / ASHRAE15. Visible, GB / T21362-2008 lack of pressure on the safety requirements. The pressure safety is the core of refrigeration system mechanical safety, the standard existence of such a problem some incredible. As the current compulsory safety standard, GB9237-2001 "refrigeration and heating mechanical refrigeration system safety requirements" for the scope of the refrigerant in the closed refrigeration circuit evaporation and condensation of various refrigeration systems. Refrigeration circuits include heat pumps and absorption systems, but are not suitable for systems that use water or air as a refrigerant. Obviously, as long as the appropriate reference GB9237-2001 as GB / T21362-2008 pressure safety requirements, we can solve this problem. GB / T18430.2-2008 "Household and similar uses of cold water (heat pump) unit" is often used as a heat pump water heater standard. As the standard is in accordance with the relevant requirements of the development of household appliances, there is no problem in the scope of application. However, GB / T18430.2-2008