| In recent years,the research that focused on heat pump heating by air source has obtained several results and a certain scale of engineering practice.under the major trend of"coal-to-electricity",the air source heat pump system,as the energy-saving and environmental friendly heating equipment,is being widely used step by step.however,from the past research it can be seen that the researches on the influencing factors of the heating performance of the small cascade type air source heat pump were still minority relatively among several research results in the past,some individual factors that affect the performance of the heat pump system have been studied only under given working circumstance.based on the several factors that affect the heating performance of cascade type low-temperature air source heat pumps,a cascade type R404A air source heat pump heating laboratory bench was built during the winter heating period in hot summer and cold winter regions,so as to qualitatively and quantitatively study various factors on cascade type low-temperature air source heat pumps,which aims at providing reference for engineering applications in practice.Many experimental researches were conducted,which mainly include:experimental research an the influence of temperature parameters on the performance of the cascade type heat pump system,experimental research on the influence of water flowing on the performance of the cascade type heat pump system,experimental research on the influence of the shape of the heat-insulation water tank on the system performance,and research on other related improvement scheme.the experimental research on the influence of temperature parameters on the performance of the cascade type heat pump system mainly has two aspects,which include the influence of hot water temperature on the COP of system and heating capacity and the influence of environmental temperature on the system performance.the experimental research on the influence of water flowing on the performance of the cascade type heat pump system mainly has four aspects,which include the influence of circulating water flowing on the heating capacity of the heat pump,the influence of circulating water flowing on the temperature of compressor air exhaust,the relationship between heat transfer temperature difference of the intermediate evaporator condenser and hot water temperature,and the influence on hot water temperature with different circulating water flowing under high and low temperature degree when inhaling and exhausting.the experimental research and related improvement schemes on the influence of the shape of the heat-insulation water tank on the system performance have three aspects,which include:modeling construction analysis of the influence of different shapes of the heat-insulation water tank on the system performance,the influence of taking out efficiency of the hot water storage tank on the system performance,and the improved scheme analysis of the heat-insulation water tank,of which mainly includes the plan of built-in layered partition in the heat-insulation water tank,and the optimization scheme of the double water tank structure,etc.The experimental research results have shown that:under the test conditions where the hot water temperature has influence on the system performance,as the hot water temperature increases,the heating capacity and COP of the heat pump decrease gradually,and the input power P gradually increases.when the hot water temperature is set up to 28.4?,33.4? and 58.4?,the system cop value is generally higher than the specified cop value,so choosing the appropriate temperature of outlet water can optimize the stem performance as maximum as possible.under the test conditions where the circulating water flowing rate affects the system performance,as the the circulating flow rate increases,the heating capacity of the heat pump is increased,and the exhaust temperature of the high-temperature compressor gradually decreases,and the machine is working more stably.therefore,under a certain flow rate,the machine cop and the circulation flow rate are positively correlated.under the test conditions where the environmental dry bulb temperature affects the system performance,as the environmental dry bulb temperature increases,the heating capacity of the heat pump increases,and the system cop value is also increased.In the relevant experiments on the rationality of the water tank structure and the taking out efficiency,the heat leakage of the cube,cylinder,cuboid,and sphere tanks are compared under the same water storage volume.when the heat-insulation layer has the same thickness and different heat transfer temperature differences,it has shown that the leakage heat of cuboid water tank Q1>the leakage heat of cubic water tank Q2>the leakage heat of cylindrical water tank Q3>the leakage heat of spherical water tank Q-.When the heat-insulation layer has the same thickness and heat transfer temperature differences,the cuboid water tank is greater than the leakage heat of the cylindrical water tank after comparing the relationship between height-diameter ratio and leakage heat,and the daily heat leakage of the cylindrical water tank has minimum value when H/D=1 or so.according to the analysis of the experimental results,the optimization scheme of the water tank system is proposed,which are the plan of built-in layered partition in the heat-insulation water tank,and the optimization scheme of the double water tank structure.At the same time,in the experimental research process of the factors affecting the performance of the small cascade type R404A air source heat pump heating system in hot summer and cold winter areas,some places still need to be improved and studied more deeply in the aspects such as design of experimental schemes and data processing of experimental results,and the details are as follows:(1)the research direction is not comprehensive enough that only the side of evaporator's air flow(wind speed)on the system performance in hot summer and cold winter areas is discussed,but the machine working conditions,frosting and defrosting conditions below-20? has not been studied;(2)in this experiment,regarding the impact of environmental wet and dry bulb temperature on system performance,the environmental temperature only changed within a small range,and temperature span was small,which leads to not comprehensive experimental results.the experimental range of environmental temperature and humidity should be expanded in the later period;(3)when studying the temperature stratification of the water tank,it was only indicated by the taking out efficiency,which was not satisfying enough,and the simulation software such as FLUENT was not used to analyze the temperature field of the water tank temperature stratification;(4)the experimental results of heat output of the heat pump and the COP were both average values within the experimental range,which did not reflect the instantaneous values well during the experiment.Figure[22]table[16]reference[53]... |
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