A design method of a household air conditioner evaporator

Abstract

A kind of domestic air conditioner evaporator design method, comprising the following steps: S1: determining evaporator parameter;S2: by the heat and mass transfer correlation of air side of corresponding flat finned tube evaporator in different evaporator parameter range and different working condition, establish evaporator steady-state distribution parameter model;S3: in combination with the evaporator steady-state distribution parameter model of S2, solve the steady-state physical model of air conditioning prototype refrigeration system in frequency conversion domain;S4: draw air conditioning output cold quantity characteristic plane;S5: air conditioning output cold quantity characteristic plane is matched with building heat and humidity load characteristic plane, determine the optimal evaporator parameter combination of matching degree;The air conditioner evaporator design method of the application can design domestic air conditioner evaporator based on different temperature and humidity climate conditions, to maximize the matching of different regions heat and humidity load, improve the control of indoor temperature and humidity, improve indoor thermal comfort and reduce system energy consumption.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of household air conditioners, and in particular to a design method of a household air conditioner evaporator. BACKGROUND

[0002] Due to the vast territory and different climates in China, there is a large difference in the indoor thermal and moisture loads of buildings in different climate zones. In order to meet the needs of human thermal comfort, the indoor temperature and humidity need to be better controlled, so that the cooling and dehumidifying capacity of the air conditioner matches the thermal and moisture loads of the building. For household direct expansion air conditioning equipment with rated cooling capacity, the evaporator plays a decisive role in the distribution of sensible heat and latent heat. During actual operation, the surface temperature and humidity of the evaporator change coupled, which simultaneously affects human thermal comfort. The finned tube heat exchanger is widely used as an evaporator in household air conditioners due to its simple structure, high heat exchange efficiency, and advantages in heat transfer enhancement.

[0003] However, in order to facilitate mass production, the design method and test standard of the evaporator for the direct expansion air conditioning system widely used in small and medium-sized residential buildings are usually developed for a single fixed thermal and moisture condition.

[0004] According to the outdoor design calculation parameters specified in the "Code for Design of Heating Ventilation and Air Conditioning of Civil Buildings" (GB 50376-2012), the test conditions for refrigeration conditions are set as an outdoor temperature of 35℃ and a relative humidity of 40%. However, the average relative humidity in most areas of the southeast coast of China in summer is far more than 40%, and the average outdoor temperature in the northwest region in summer is always lower than 35℃. There is a large difference between the design condition and the actual operating condition, which leads to the fact that the household air conditioner designed and manufactured according to the standard condition cannot effectively coordinate the temperature and humidity treatment, affecting human thermal comfort, and causing energy waste to some extent.

[0005] Specifically, within the standard evaporator test condition range, the compressor speed and fan speed can be changed through operation control, thereby affecting the evaporating temperature, refrigerant flow rate, and air-side heat transfer coefficient, and then realizing accurate control of indoor temperature and humidity. When deviating from the test condition point, if the cooling demand is prioritized, the effective treatment of the moisture load cannot be guaranteed, and there will be obvious temperature and humidity fluctuations within a certain period of time, which will destroy the indoor thermal comfort environment and cause energy waste.

[0006] However, there is currently no method for designing and customizing household air conditioner evaporators based on different temperature and humidity climate conditions to maximize the matching of thermal and moisture loads in different regions, thereby expanding the control range of indoor temperature and humidity, improving human thermal comfort, and reducing system energy consumption. SUMMARY

[0007] The application aims to provide a design method for a household air conditioner evaporator which can match the climate.

[0008] The design method for a household air conditioner evaporator comprises the following steps: S1, determining the evaporator parameters; S2, establishing the evaporator steady-state distribution parameter model by the heat and mass transfer correlation of the air side of the flat finned tube evaporator corresponding to different evaporator parameter ranges and different working conditions; S3, solving the steady-state physical model of the air conditioner prototype refrigeration system in the variable frequency domain in combination with the evaporator steady-state distribution parameter model in S2; S4, drawing the air conditioner output cooling capacity characteristic plane; S5, matching the air conditioner output cooling capacity characteristic plane with the building heat and humidity load characteristic plane to determine the evaporator parameter combination with the optimal matching degree; in S5, the building heat and humidity load characteristic plane is drawn according to the building heat and humidity load in different temperature and humidity climate zones; and the matching degree is defined as the percentage of the building heat and humidity load points falling in the cooling capacity output characteristic plane.

[0009] Further, S2 comprises the following steps: S21, performing physical modeling, setting the main structural parameter variation range of the evaporator, including the tube spacing P t , the row spacing P l , the outer diameter of the circular tube D c and the fin spacing F p , selecting a representative heat exchange unit as the calculation domain by using the symmetry boundary and periodic arrangement of the heat exchanger, performing grid division and making corresponding assumptions; S22, according to the component conservation and mass conservation, energy conservation and momentum conservation equations, simulating the component concentration of the unit by using CFD, solving the convective heat transfer factor and the mass transfer factor; S23, according to the model solving results, obtaining the correlation of the convective heat transfer factor, the mass transfer factor and the heat and mass factor in the different structural parameter variation ranges by using the multivariate linear regression fitting method, and substituting the correlation into the evaporator two-zone distribution parameter steady-state model to calculate the corresponding heat transfer coefficient and mass transfer coefficient.

[0010] Further, S3 comprises the following steps: modeling the remaining components of the refrigeration system, combining the evaporator steady-state distribution parameter model in S2 to solve the steady-state model, and obtaining the sensible cooling capacity and latent cooling capacity that can be output by the evaporator under various control conditions by changing the rotation speed of the compressor and the evaporator supply fan within a certain range.

[0011] Further, S4 is to draw the air conditioner output cooling capacity characteristic plane according to the calculation results of S3, taking the sensible cooling capacity output under various control conditions as the horizontal coordinate and the latent heat as the vertical coordinate.

[0012] Further, the building heat and humidity load characteristic plane of S5 is drawn by the following steps: SS1: selecting a typical city in the climate division; SS2: counting a typical house type in the typical city; SS3: calculating the hourly heat and humidity load of the building; SS4: taking the hourly heat load as the horizontal coordinate and the hourly humidity load as the vertical coordinate, drawing the building heat and humidity load characteristic plane.

[0013] The present application draws the cooling capacity characteristic plane of the evaporator under different conditions by drawing the cooling capacity of the evaporator under different conditions, and draws the heat and humidity load characteristic plane according to the building heat and humidity load in different temperature climate divisions, and matches the two to determine the optimal matching parameters to realize the design of the evaporator, improve the human thermal comfort feeling and reduce the system energy consumption. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 is a flow chart of an embodiment of the household air conditioner evaporator design method of the present application.

[0015] Figure 2 is a schematic diagram of the geometric model and calculation area of the flat-fin tube evaporator in the specific embodiment of the present application, wherein (a) is a schematic diagram of the geometric model, (b) and (c) are respectively a top view and a side view of the calculation area.

[0016] Figure 3 is the output cooling capacity characteristic plane of the heat exchanger with different row spacings corresponding to the base case in the specific embodiment of the present application.

[0017] Figure 4 is the building heat and humidity load characteristic plane of two representative cities in the specific embodiment of the present application, wherein (a) corresponds to Shanghai, and (b) corresponds to Guangzhou.

[0018] Figure 5 is a schematic diagram of the matching of the characteristic planes corresponding to two representative cities in the specific embodiment of the present application, wherein (a) corresponds to Shanghai, and (b) corresponds to Guangzhou. DETAILED DESCRIPTION

[0019] The specific embodiments will now be described in detail with reference to the accompanying drawings.

[0020] Figure 1 A household air conditioner evaporator design method is illustrated, which is used for designing household air conditioners in different climate environments and has climate adaptability.

[0021] Figure 1 The household air conditioner evaporator design method illustrated includes the following steps:

[0022] S1: determining the evaporator parameters;

[0023] In the present embodiment, the main parameters of the flat-fin tube evaporator include material, tube row form, fin thickness, tube row number, tube spacing, row spacing, outer diameter of circular tube, fin spacing, etc. Some parameters are limited by system space and cost and other factors, and some parameters have the possibility of being designed within a certain range. The following table (Table 1) is for the present embodiment. The table gives the material, tube row form, fin thickness, tube row number, etc. which need to be fixed, and the tube spacing, row spacing, outer diameter of circular tube, fin spacing which are adjustable parameter variation range.

[0024] Table 1

[0025]

[0026]

[0027] S2: Establish an evaporator steady-state distribution parameter model through the heat and mass transfer correlation of the air side of the flat-fin tube evaporator corresponding to different evaporator parameter ranges and different working conditions; specifically including the following steps:

[0028] S21: According to the variation range of the main structure parameters of the evaporator, including tube spacing P t , row spacing P l , outer diameter of circular tube D c and fin spacing F p , use the symmetry boundary and periodic arrangement of the heat exchanger to select a representative heat exchange unit as the calculation domain, as shown in Figure 2 , perform meshing and make corresponding assumptions, and set the boundary conditions of the calculation region, as shown in the following table (Table 2).

[0029] Table 2

[0030] Boundary conditions Setpoint Inlet air relative humidity RH a，in / %]]> 50、60、70、80 Inlet air temperature t a，in / °C 18、26、35 Inlet air flow rate u in / m·s -1 ]]> 1.0、1.5、2.0、2.5、3.0 Tube wall temperature T wall / °C 7、12、18

[0031] S22: According to the component conservation and mass conservation, energy conservation, momentum conservation equations, use CFD to simulate the component concentration of the unit, and solve the convective heat transfer factor j h and mass transfer factor j m .

[0032] S23: According to the model solving results, use the method of multiple linear regression fitting to obtain the corresponding convective heat transfer factor j h and mass transfer factor j m correlation in the variation range of different structure parameters, and the calculation results are as follows:

[0033]

[0034] wherein, Re DC is the Reynolds number calculated from the inlet air flow rate.

[0035] The correlation is substituted into the two-zone distribution parameter steady-state model of the evaporator, where the convective heat transfer h s and mass transfer coefficient h m can be calculated by the convective heat transfer factor j h and mass transfer factor j m The correlation is calculated as follows:

[0036]

[0037] In the formula, G max is the mass flow rate of the wet air at the narrowest part between the fin flow channels, in kg / m 2 ·s -1 , c p，a is the specific heat capacity of the wet air, in J / kg·K -1 ; Pr and S c are the dimensionless Prandtl number and Schmidt number, respectively.

[0038] S3: combining the evaporator steady-state distribution parameter model of S2, solving the steady-state physical model of the air conditioning prototype refrigeration system in the variable frequency range;

[0039] S4: drawing the air conditioning output cooling capacity characteristic plane;

[0040] Based on the parameters of the components of a commercially available large 1-patch household variable frequency direct expansion air conditioner, a steady-state physical model of the air conditioning refrigeration system is established, and the state parameters of the refrigerant and air flowing through the main components are calculated. The condenser is modeled using a three-zone distribution parameter method, and a simulation program is developed using MATLAB software. According to the relevant provisions in the “Code for Design of Heating Ventilation and Air Conditioning of Civil Buildings” (GB50376-2012) for the rated refrigeration operating conditions, the return air temperature of the indoor side of the household air conditioner is set to 26℃, and the relative humidity is 50%. The outdoor inlet air temperature is 35℃, and the relative humidity is 40%. This condition is taken as the reference condition. The compressor speed varies from 1500 to 9000 rpm, and the evaporator fan speed varies from 600 to 1300 rpm. Within the speed variation range, 30 combinations are selected, i.e., the compressor speed starts from 30% of the maximum value, increases by 10% to 80%, and similarly, the evaporator supply fan speed also starts from 30% of the maximum speed, increases by 10% to 70%. The compressor and fan speeds are changed simultaneously, and the sensible and latent cooling capacities of the air conditioner under this structure can be calculated accordingly, so as to draw the characteristic plane of the air conditioning system output cooling capacity with the sensible cooling capacity as the horizontal coordinate and the latent cooling capacity as the vertical coordinate. Figure 3 As shown in the figure, for the same other structural parameters, the air conditioning output cooling capacity characteristic plane corresponding to different row spacing heat exchangers under the reference condition is shown. The air conditioning system using different structural flat finned tube heat exchangers is calculated, and the output cooling capacity under this structure is calculated.

[0041] S5: match the air conditioner output cooling capacity characteristic plane with the building heat and humidity load characteristic plane to determine the evaporator parameter combination that optimizes the matching degree.

[0042] The building heat and humidity load characteristic plane is drawn according to the building heat and humidity load in different temperature and humidity climate zones. Taking two climate zones as examples, both cooling and dehumidification need to be considered in the refrigeration season, but 1 representative city is selected in each of the two climate zones with different refrigeration requirements, such as Shanghai and Guangzhou. The representative house size with the highest proportion in the built and in-use buildings in each city is used to draw the corresponding building and structure model in SketchUp software. The thermal performance parameters of the building envelope are reasonably valued with reference to the national standards and the latest version of the residential building energy-saving design standard of each province and city. The indoor parameters and air conditioning temperature and humidity set values are referred to the relevant provisions of the Code for Design of Heating Ventilation and Air Conditioning of Civil Buildings (GB 50376-2012) for comfort air conditioning. The outdoor climate parameters are selected according to the data of the Chinese typical meteorological year obtained from the EnergyPlus website, and the calculation is performed according to the summer air conditioning refrigeration time (June 15 to August 31) specified in the Design Standard for Energy Efficiency of Residential Buildings in Hot Summer and Cold Winter Zones (JGJ 134-2010). The building hourly total load, hourly heat load and hourly humidity load of each city are obtained. It should be noted that in actual operation, the indoor temperature and humidity set point and the fresh air volume have a great influence on the building load, but they are irrelevant to the climate adaptability design of the air conditioner. In this embodiment, they are set as constant values, and only the differences in building heat and humidity load caused by different outdoor climate conditions, corresponding building envelope parameters, house types and room areas in different regions are considered. The building hourly heat and humidity load of the representative cities in different temperature and humidity climate zones is obtained by simulation with the EnergyPlus software. The building heat and humidity load characteristic plane is drawn with the hourly heat load as the horizontal coordinate and the hourly humidity load as the vertical coordinate, as shown in FIG. 1. Figure 4

[0043] The heat and humidity load characteristic plane and the air conditioner output cooling capacity characteristic plane are compared and analyzed in the same coordinate system. The percentage of the building heat and humidity load points falling within the cooling capacity output characteristic plane is defined as the matching degree, which is used as the criterion for the degree of climate adaptability. The orthogonal test table is designed as shown in Table 3, and the heat exchanger structure combination with the highest matching degree suitable for the two representative cities is selected. Figure 5 The compressor speed is 1500-9000 rpm, the evaporator fan speed is 600-1300 rpm, the representative cities of Shanghai and Guangzhou in different temperature and humidity climate zones, and the characteristic plane matching condition of the evaporator structure combination corresponding to the maximum matching degree.

[0044] ​It can be concluded that for Shanghai, the difference of the matching degree corresponding to different structures is 24.5%, compared with the minimum matching degree corresponding to the A1B2C1D2 structure, the best matching degree of the A2B1C3D3 combination is increased by 85%; for Guangzhou, the difference of the matching degree corresponding to different structures is 27.1%, compared with the minimum matching degree corresponding to the A3B1C3D3 structure, the best matching degree of the A2B2C1D2 combination is increased by 135%. It is proved that the climate adaptive design of the evaporator significantly increases the controllable range of temperature and humidity during air conditioning operation, thereby improving thermal comfort and reducing energy consumption.

[0045] Table 3

[0046]

Claims

1. A design method for a household air conditioner evaporator, characterized in that, Includes the following steps: S1: Determine the evaporator parameters; S2: Establish a steady-state distributed parameter model of the evaporator by using the heat and mass transfer correlations of the air side of the straight finned tube evaporator under different evaporator parameter ranges and different operating conditions. S3: Combining the evaporator steady-state distributed parameter model of S2, solve the steady-state physical model of the air conditioning prototype refrigeration system in the variable frequency domain; S4: Draw the characteristic plane of the air conditioner's output cooling capacity; S5: Match the air conditioning output cooling capacity characteristic plane with the building heat and humidity load characteristic plane to determine the evaporator parameter combination that achieves the optimal matching degree; Step S4 is to plot the characteristic plane of air conditioning output cooling capacity based on the calculation results of S3, with the sensible heat and cooling capacity that can be output under various control conditions as the horizontal axis and the latent heat and cooling capacity as the vertical axis. S5 In the middle, the building heat and humidity load characteristic plane is drawn according to the building heat and humidity load in different temperature and humidity climate zones. The building heat and humidity load characteristic plane is plotted with hourly heat load as the abscissa and hourly humidity load as the ordinate. The degree of matching is defined as the percentage of the building's heat and humidity load points that fall within the characteristic plane of cooling output.

2. The design method for a household air conditioner evaporator according to claim 1, characterized in that, S2 includes the following steps: S21: Perform physical modeling and set the variation range of the main structural parameters of the evaporator, including the tube spacing P. t Row spacing P l Outer diameter D of the circular tube c and fin spacing F p We select representative heat exchange units as the computational domain by utilizing the symmetry boundary and periodic arrangement of the heat exchanger, perform mesh generation, and make corresponding assumptions. S22: Based on the equations of conservation of components, mass, energy, and momentum, the component concentration of the unit is calculated using CFD simulation, and the convective heat transfer factor and mass transfer factor are solved. S23: Based on the model solution results, the correlation formulas of the convective heat transfer factor, mass transfer factor and heat-mass factor corresponding to different structural parameter variations are obtained by using the multiple linear regression fitting method. These formulas are then substituted into the steady-state model of the distributed parameters in the second zone of the evaporator to calculate the corresponding heat transfer coefficient and mass transfer coefficient.

3. The design method for a household air conditioner evaporator according to claim 2, characterized in that, S3 includes the following steps: Model the remaining components of the refrigeration system, and solve the steady-state model by combining the steady-state distributed parameter model of the evaporator in step S2. By changing the speed of the compressor and the evaporator blower within a certain range, obtain the sensible heat and latent heat that the evaporator can output under various control conditions.

4. The design method for a household air conditioner evaporator according to claim 1, characterized in that, The characteristic plane of building thermal and moisture load is drawn using the following steps: SS1: Select typical cities from climate zones; SS2: Statistics on typical apartment layouts in typical cities; SS3: Calculate the hourly heat and moisture load of a building; SS4: Plot the characteristic plane of building heat and moisture load with hourly heat load as the x-axis and hourly moisture load as the y-axis.

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