| There is a shortage of fossil energy nowadays,and energy saving and emission reduction as well as efficient use of energy received high attention.Energy consumption of building energy consumption accounts for a large proportion of the total energy consumption,so it is necessary to reduce the energy consumption of air conditioning by means of advanced technology improvement or optimization.Air source heat pump is a kind of high efficiency energy saving heat exchange equipment,which uses air as the low heat source to absorb heat or cold from the air,in order to achieve the purpose of heating or cooling.However,in the cold areas of northern China,the use of air source heat pump is limited.When the outdoor temperature is low in winter,and due to the impact of low temperature,a series of problems will appear,such as evaporator evaporative temperature decreases,the compressor exhaust temperature increases,the compression ratio increases and so the heat pump can not run normally or even can not start.But at this time,the heat load of the building increases with the outdoor temperature decreases,so that the heating energy consumption of air conditioning is increased.Multi energy comprehensive utilization is an effective way to solve the above problems,for example,a new heat pump can be constituted with the solar energy or biomass energy in order to auxiliary heat transfer on the basis of air source heat pump.In this paper,a new type of solar air source heat pump is used,and optimizing the structure of outdoor heat exchanger.The first row of heat exchanger tubes in the heat exchanger are connected with the solar hot water,and the low temperature air entering the evaporator is preheated to improve the evaporation temperature.In this paper,a brand 60kw-V air source heat pump is optimized and improved.First of all,the flow path is optimized in the outdoor part,and then the numerical model is built for the outdoor heat exchanger without solar hot water.The calculation unit is a layer of fins of the heat exchanger.The influence of air flow on heat transfer is simulated under the nominal operating condition of air source heat pump,which the fan volume is increased from 9000m3/h to 18000m3/h.The results show that the heat exchange quantity increases with the increase of wind quantity,and then the tends to be stable.When the outdoor temperature is high,the single heat source air source heat pump can be used for heating.In addition,the larger the air pressure,the greater the pressure loss on the air side.A numerical model was established for the composite heat exchanger of the composite heat pump.The outdoor temperature was simulated respectively under the nominal working conditions(7℃),the standard working conditions(0℃)and outdoor air conditioning temperature(-7.7℃),which takes Ji’nan as an example.TheDifferent fan air volume,the solar hot water to 5℃ for the step,from 15℃ to 30℃ when the composite heat pump heating performance.And simulating the composite heat pump performance in different fan air volume,solar hot water temperature,which increased from 15℃ to 30℃.The results show that the heat transfer capacity and COP of the composite heat pump are higher than those of the air source heat pump,which with no solar hot water.The lower the outdoor working temperature,the more obvious the advantages of the composite heat pump.Under the nominal operating conditions,the maximum heat transfer in the nominal working condition is 71.66 kw at the temperature of 30℃,18.21% higher than that of the air source heat pump,but the outlet temperature of the evaporator is higher than the ambient temperature when the solar hot water temperature is 30℃,and the heat transfer also decreases with the increase in the airflow of the fan.It is means that the air is additionally heated,and the water temperature of 30℃ is high.Under standard operating conditions,when the hot water temperature is 25℃,the air outlet temperature of the evaporator is higher than0℃,and the air outlet temperature of the evaporator is close to-7.7℃ when the airand solar temperature is-7.7℃ and 20℃.Nu increase with decreases of fan air volume and outdoor temperature.Finally,it is considered that the hot water temperature is more suitable for 15~20℃.The air pressure of the different fans has a great influence on the pressure loss on the air side of the fin,and the pressure drop increases exponentially with the increase of the velocity.According to air side drop and resistance characteristics of air source heat pump and composite heat pump,and combined with the corresponding heat transfer and COP,and so that the air flow15000m3 / h is more appropriate,equivalent wind speed 2.07 m / s.According to the variation trend of the evaporator outlet air temperature in different working conditions,when the outdoor temperature is lower,the inlet water temperature of the solar hot water can be appropriately reduced. |
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