Research On Theory And Technology Of Frosting Suppression Based On The Constitutive Configuration Optimization Of ASHP Unit

Air source heat pump（ASHP）,as a kind of high-efficiency and energy-saving renewable energy technology,has been widely used in different regions of China,and has broad development prospects.Frosting is one of the operating problems commonly encountered for space heating ASHPs in winter.When the surface temperature of the outdoor coil in a space heating ASHP is below both the freezing point of water and the dew point of ambient air,frosting on the outdoor coil surface would take place.Frosting would result in a reduction in the heating performance by30%to 60%for an ASHP,and even its shut down.Frosting for ASHP was particularly severe in high humidity regions.As seen,frosting suppression was of great significance to ensure the efficient operation and stable heat supply of ASHP.However,the existing frosting suppression technology mainly optimized the constitutive characteristics of the outdoor heat exchanger and its internal and external operating conditions,resulting in insufficient frosting suppression capacity,which was difficult to meet the frosting suppression demand in severe frosting regions.These methods also had the problem of poor engineering practicality.On the other hand,the traditional design-development method for ASHPs failed to comprehensively take into account the differences in frost formation in different regions.Consequently,it severely restricts the efficient application and healthy development for ASHPs in different regions of China.This study explored a new theory and technology of ASHP for frosting suppression from the perspective of optimizing the constitutive configuration of the key components of ASHP（compressor,outdoor heat exchanger and outdoor fan）to improve the applicability of ASHP in different regions.The main work is as follows:Firstly,a field study on frosting suppression from the constitutive configuration of ASHPs was carried out to understand the feasibility of the constitutive configuration for frosting suppression.The results showed that when the constitutive configuration of the outdoor fan and the outdoor heat exchanger in ASHPs was doubled at the same time,the average frosting rate and the frosting-defrosting loss coefficient could be reduced by 37.2%～39.6%and 31%～34.2%,resulting in the improvement of the heating capacity and COP up to 11%～15%and 5%～14%.Secondly,the theoretical study on frosting suppression of constitutive configuration for ASHP was carried out to explore the influence laws of the constitutive configuration on frosting suppression for ASHPs,propose the characteristic parameter of frosting suppression characterizing the constitutive configuration relationships,establish a semi-empirical frost suppression model and verify it.Research results indicate:（1）The temperature difference of the heat transfer between outdoor coil and ambient airis the key influencing factor of frosting suppression for ASHP,and the outdoor heat exchanger area,outdoor fan air flow rate,compressor speed and compressor displacement as the constitutive of each key components were the key to affectΔT.By increasing F_c,G,and reducing n and V₀,could help to reduceΔT and achieve frosting suppression.（2）The proposed characteristic parameter of frosting suppression（CICO）clearly expressed the constitutive configuration relationships among the outdoor heat exchanger,outdoor fan and compressor.（3）The developed semi-empirical model of frosting suppression in this study comprehensively taked into account the differences between types and constitutive configurations of ASHPs,which could effectively characterize the joint effect of the constitutive configuration on frosting suppression for ASHPs.Thirdly,based on the semi-empirical model of frosting suppression and the design-development concept of“heating priority and taking into account frosting suppression”,a design-development method used in severe frosting climate regions for ASHPs considering output heating capacity and frosting suppression was developed,and its applicability and economy were verified.The results showed that COP of the frost-suppressed ASHP was 22%～27%higher than the specified value in the standard under rated condition.Furthermore,the field application comparison results showed that COP of the frost-suppressed ASHP could be increased by 21%to54%under typical frost conditions and by 22%to 45%under long-term operation.The annual cost of the frost-suppressed ASHP could be reduced 13%～19%,and the additional investment could be recovered in about 1 year.Finally,the suitable regions of ASHPs in China were analyzed,and the degree of frosting in different regions was determined,then the regionalization of frosting suppression technology in different regions of China had been completed.The results showed that the suitable regions of ASHPs in China included 261 prefecture-level administrative regions and 4 municipalities.The effects from frost for these 265 cities generally showed a decreasing trend from south to north and from east to west.Based on the energy efficiency rating reduction coefficient,and about 124 cities with strong frost suppression technology were identified.In summary,this topic developed the theory of frosting suppression based on the key constitutive configuration relationships of ASHPs,developed the design and development method for ASHPs considering output heating capacity and frosting suppression,and completed the division of technology application for frosting suppression in different regions in China.The study will help break through the technology bottleneck of local optimization for the existing frost suppression technology,make up for the lack of traditional development of ASHPs without considering the differences of frosting in different regions,promote the transformation of ASHPs from traditional standard configuration to personalized configuration in specific regions,and provide theoretical and technical support for the efficient application and benign development of ASHPs in China.