| Energy has a great impact on the development of the world economy.With the progress of the 21 st century,the scale of economic development in countries around the world is getting larger and larger,so people’s demand for fossil energy is also increasing,making the world’s environmental pollution and energy crisis.The problem is also more serious.Building energy consumption has always been large,and winter heating accounts for most of the energy consumption of the entire building.Heat pump technology is one of the effective technologies that use low-temperature renewable energy.It can be used as a heat source for winter heating,but it is humid at low temperatures.The outdoor heat exchanger of the air source heat pump in the environment is prone to frost,which will affect its heat exchange energy efficiency.This paper studies the application of the air source heat pump heating system in low temperature and humid areas in winter,and conducts an experimental test analysis of its defrosting system and defrosting control strategy.First of all,combined with the meteorological data of Chongqing area,De ST software was used to analyze the outdoor climate characteristics of Chongqing.During the heating month,the average outdoor temperature is not more than 10 ° C,but not less than 5 ° C.The average outdoor air temperature in Chongqing during the winter heating season The temperature is 6-8 ° C.The minimum outdoor temperature can reach minus0.9 ° C,and the relative humidity of outdoor air is basically above 80%.Considering that,during the heating season,the outdoor air temperature in Chongqing is below 5 ° C for a total of 79 hours.The outdoor air in the area where the experimental bench built in this article is relatively Humidity is higher than 65% for a total of 1500 hours.If only the period from 9:00 to 18:00 during the day is calculated,the winter air source heat pump is in the frosting working area for 712 hours.Secondly,a physical model of the local frost layer on the surface of the outdoor heat exchanger fin is proposed and simplified.A mathematical model is established and its temperature distribution function is solved.The formation mechanism of the frost layer and the frost layer density and frost are explained in detail.Mathematical model of layer thickness.Based on the frost layer density,a new type of defrosting system is proposed.The structure of the defrosting system and the working steps of the system are introduced in detail,and its system diagram and system detection principle diagram are given.Based on the thickness of frost layer,the existing defrosting control strategy was optimized,its control logic was introduced in detail,and the defrost control logic diagram was given.Once again,an defrosting performance test bench for an air-source heat pump unit was set up to analyze the regularity between the indoor and outdoor air temperature and humidity changes and the frost layer of the outdoor unit.At the 15 th minute of the unit operation,the indoor air temperature and humidity were subjected to heat transfer from the outdoor In the 30 th minute,the humidity difference between indoor and outdoor air reached the minimum value.Subsequently,the unit started the defrost and completed the defrost in the 35 th minute.The unit current and unit power showed an overall increasing trend within 30 minutes before the unit operation,and the increasing rule was basically the same.At the 30 th minute,the frost layer growth reached the most serious level,hindering the air circulation in the outdoor unit.At this time,the unit current And unit power are increased to the maximum.Finally,comparing the calculated and experimental values of the frost on the outdoor heat exchanger fins,it is found that during a frosting period,the frost on the outdoor heat exchanger fins changes basically in a linear function.The experimental and calculated values The error does not exceed 10%.The frost area of the outdoor heat exchanger of the air source heat pump measured this time accounts for about 1/5 of the entire heat exchanger area.Taking into account the frost and defrosting factors of the unit,the change of the system COP with time is first increased and then decreased,and the average COP is 2.7,which has not reached 3.0.The "mis-defrosting" phenomenon that occurs when air-source heat pumps are used for heating in Chongqing is mainly premature defrosting and frost-free defrosting.In this paper,an experimental test of the air source heat pump defrosting system in Chongqing area was conducted,and the experimental data was processed to analyze the system performance and provide data support for the application of the system to actual projects. |
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