CN107301276B - Method for calculating convection heat transfer load of large-space nozzle air supply layered air conditioner - Google Patents

Abstract

The invention relates to a method for calculating convection heat transfer load of a large-space-nozzle air supply layered air conditioner, which comprises the steps of establishing a Block-Gebhart model to calculate the convection heat transfer load of the large-space-nozzle air supply layered air conditioner, verifying the convection heat transfer load by using a reduced scale model experiment result, analyzing and discussing key factors influencing the convection heat transfer load, and making a line calculation chart. The invention can optimize the jet flow model, and the obtained optimized Block-Gebhart extended model can deeply analyze the change condition of the indoor thermal environment of the large-space layered air conditioner, and on the basis, the coupling calculation of the vertical air temperature and the wall surface temperature of the large space can be carried out, so that the calculation method of the convection heat transfer load of the layered air conditioner which is primarily suitable for air supply at the nozzle side is obtained by exploration.

Description

Calculation method of convective heat transfer load for large space nozzle air supply stratified air conditioner

technical field

The invention relates to an air-conditioning load calculation technology, in particular to a method for calculating the convective heat transfer load of a large-space spout air supply stratified air conditioner.

Background technique

In the thermal environment under stratified air conditioning in large space buildings, the vertical temperature stratification of indoor air, the obvious gradient and the large temperature difference between the upper and lower sides, as well as the characteristics of the temperature distribution on the roof and wall surface, lead to different calculation methods for large space stratified air conditioning load and ordinary rooms. That is, the influence of complex airflow organization, outdoor environment changes, and indoor heat source distribution in large spaces will lead to changes in indoor thermal environment state parameters and changes in convective heat transfer. Therefore, the calculation of convective heat transfer load has always been a problem for designers.

At present, the calculation method of layered air-conditioning load in large-space buildings adopts the method mentioned in the "Practical Heating and Air-conditioning Design Manual" edited by Professor Lu Yaoqing. , indoor heat source load, fresh air or infiltration wind load, etc.) and the load formed by the radiative transfer heat and convective transfer heat transferred from the non-air-conditioned area to the air-conditioned area. calculation method. The specific calculation methods are: (1) The conventional air-conditioning area load is calculated by the traditional whole-room air-conditioning load calculation method; (2) The radiation transfer heat load is calculated by the cooling load coefficient method: First, by calculating the radiative transfer heat from the non-air-conditioned area to the air-conditioned area floor, Then multiply by the heat gain coefficient C ₁ (usually 1.3) to obtain the radiation transfer heat from the non-air-conditioned area to the air-conditioned area. Then, the radiation transfer heat from the non-air-conditioned area to the air-conditioned area is multiplied by the cooling load coefficient C ₂ (the value range is 0.45 to 0.72, generally 0.5) to obtain the radiation transfer load; (3) The convective heat transfer load is calculated by calculating the load of a certain factory building. Repeated tests and field measurements, fitting the results into calculation curves and applying them to large-space buildings will form the key factor of convective heat transfer load - driven by the functions of vent air supply, internal heat source and exhaust air. The airflow movement in the air-conditioned area and the non-air-conditioned area and the energy transfer carried by it are simplified as the comparison between the heat intensity of the air-conditioned area, the heat intensity of the non-air-conditioned area and the heat exhausted. The convective heat transfer load can be obtained by looking at the graph.

It can be seen from the above that the convective heat transfer load is an important part of the cooling load of the stratified air conditioner. Since the calculation method of the above-mentioned convective heat transfer load is limited by the thermal environment of the large space building at that time, many empirical values and steam turbines are used. The measured data of the tall factory building, and the experimental and measured conditions are single. Based on the current research level of indoor thermal environment of large-space buildings, the calculation method at that time has certain defects and deficiencies.

SUMMARY OF THE INVENTION

Aiming at the problem that the current load calculation method of layered air conditioning in large space buildings is limited by the data at that time, the invention proposes a calculation method of convective heat transfer load of layered air conditioners with large space nozzles. On the basis of experiments, it proposes and establishes The Block-Gebhart model is used to obtain the theoretical calculation model of convective heat transfer load under stable heat transfer. In the invention, the results of the scale model experiment are used to verify the correctness and reliability of the theoretical model, and then the main factors affecting the convective heat transfer load are analyzed by using the mathematical model. The line calculation diagram for calculating the convective heat transfer load was obtained and verified by experiments and supplemented by on-site measurements. Later, combined with the theoretical calculation model of radiation transfer load, the radiation transfer load of stratified air conditioners under the air supply from the nozzle was studied, and it was found that the system is initially suitable for the nozzle side. Calculation method of stratified air conditioning for supply air.

The technical scheme of the present invention is: a method for calculating the convective heat transfer load of a large space spout air supply layered air conditioner, which specifically includes the following steps:

1) Analyze the convective heat transfer load and establish the Block-Gebhart model: under the large-space indoor nozzle air supply system, the nozzle installation height is the layer height, which is the interface between the non-air-conditioned area and the air-conditioned area, and the upper is the non-air-conditioned area, The lower part is the air-conditioning area. The convective heat transfer load includes the heat from the non-air-conditioned area to the air-conditioned area and the temperature difference heat transfer on the interface. The Block model divides the indoor environment into several control areas in the vertical direction, and the prediction calculation is large. For the indoor vertical temperature distribution of the space building, the Gebhart absorption coefficient method is used to comprehensively consider the heat conduction, convection and radiation coupled heat transfer jointly affected by the outdoor environmental heat transfer, the indoor inner surface radiative heat transfer and the indoor heat source radiation to solve the indoor wall temperature distribution. Taking this as the boundary condition of the Block model calculation, the Block-Gebhart model is used to solve the convective heat transfer load simultaneously;

2) Experiment verification of block-Gebhart model solving convective heat transfer load: Under the gaseous scale model test bench nozzle air supply system, experiments on indoor temperature field and convective transfer heat load in a large space are carried out to verify the model and analyze the influence of convective heat. The key factor of the transfer load is to use the relationship between the heat intensity ratio, heat rejection ratio and dimensionless convective heat transfer load of the non-air-conditioned area and the air-conditioned area to make a line calculation diagram to simplify the calculation of the convective heat transfer load for practical use.

In the described step 1), the Block model adopts the Block model based on multi-zone heat and mass balance, for predicting the indoor vertical temperature distribution of large-space buildings;

Assuming that the indoor environment is uniformly distributed in the horizontal direction except for the air-conditioning jet affected area, the concept of lumped parameter method is used to analyze the mass flow and energy transfer for each control mainstream area, and the mass and energy balance equations are established respectively, and then The air temperature and wall temperature of the mainstream area of each control area are initially set. After a series of iterative operations, the temperature of each control area within the allowable error is finally calculated, so as to obtain the indoor vertical temperature distribution (T ₁ , T ₂ , T ₃ . . . . ·T _n ), n is the total number of control areas divided in the vertical direction; take the installation height of the nozzle as the layer height, which is the interface between the non-air-conditioned area and the air-conditioned area, that is, floors 1-F are the air-conditioned area, Above the F floor is the non-air-conditioned area, and the calculation formula of convective heat transfer load is as follows:

q _d =C _p M _cF (T _F+1 -T _F )+C _BF A _BF (T _F+1 -T _F )

In the formula: q _d is the convective heat transfer load from the non-air-conditioned area to the air-conditioned area, in W; C _P is the specific heat of air at constant pressure, in kJ/(kg °C), which can be _1.01 for air; Air quality net flow from air-conditioned area to air-conditioned area, unit kg/s; TF ₊₁ , TF are the air temperature of the lowest floor of non-air-conditioned area and the highest floor of air-conditioned area, unit ℃; _{C BF} is non-air-conditioned area to air-conditioned area Temperature difference heat transfer coefficient, unit W/(m ² ·°C); A _BF is the layered interface area between non-air-conditioning area and air-conditioning area, unit m ² .

Described step 1) uses Block-Gebhart model to solve the convective heat transfer load synchronously and specifically comprises the steps as follows:

A: Optimize the multi-jet calculation model of the nozzle, and establish the wall flow model and the heat and mass exchange model between multiple regions;

B: Solve convective radiation coupled heat transfer using Block boundary condition - wall temperature: According to the geometric conditions of the building, it is divided into walls, and the angle coefficient between the walls and the Gebhart absorption coefficient are solved. By assuming the initial temperature distribution of the walls, according to the indoor air The temperature distribution, outdoor environmental parameters, thermal parameters of the envelope structure and indoor heat source are used as boundary conditions to calculate the thermal conductivity and radiation.

C: According to the Block-Gebhart model, establish the air volume and energy balance equation; after completing the calculation of each area sub-model, establish the mass balance and energy balance equation of each Block area, then iteratively calculate and solve the indoor air vertical temperature of the simultaneous equations Distribution, wall temperature distribution and convective heat transfer load, establish equations for any block mainstream area;

D: Block-Gebhart model is solved simultaneously:

(1) Assuming the initial temperature, assuming the initial vertical air temperature distribution and wall temperature distribution, the initial wall temperature distribution is input into the Gebhart model wall heat conduction, convection and radiation coupled heat transfer equations, and the air vertical temperature results calculated by the Block model are used as boundary conditions, The initial air vertical temperature distribution is input into the Block heat-mass balance equation. The model uses the wall temperature calculated by the Gebhart model as the boundary condition for the calculation, and the two model parameters are input to each other;

(2) Iterative calculation: compare the indoor air temperature and wall temperature distribution obtained in the second step with the initial value of the first step, when the error between the two does not satisfy <10 ^-6 , assign it to the initial value, and return The first step starts to repeat the calculation;

(3) Iteratively solve the wall temperature distribution and the indoor vertical temperature distribution in this way. When the relative errors of the first and last two calculation results are <10 ^-6 at the same time, it is considered that the last two calculation results of the indoor air temperature distribution and the wall temperature distribution is the solution of the problem, and the net flow at the layered interface calculated by the equilibrium equations is used to calculate the convective heat transfer load from the non-air-conditioned area to the air-conditioned area; according to the obtained inner wall temperature, indoor vertical temperature and non-air-conditioned area The net air flow at the interface with the air conditioner is calculated, and then the convective heat transfer load of the stratified air conditioner is obtained according to the calculation formula of the convective heat transfer load.

The beneficial effects of the present invention are as follows: the method for calculating the convection heat transfer load of the large space spout air supply stratified air conditioner of the present invention can optimize the jet model, and the optimized Block-Gebhart extended model can deeply analyze the indoor heat of the large space stratified air conditioner. Based on the environmental changes, the coupled calculation of the vertical air temperature and the wall temperature in the large space can be carried out, and the calculation method of the convective heat transfer load of the stratified air conditioner initially suitable for the air supply from the nozzle side can be obtained.

Description of drawings

Fig. 1 is the technical roadmap of the method for calculating the convective heat transfer load of the large-space spout air supply stratified air conditioner of the present invention;

Fig. 2 is a wall flow model diagram of the present invention;

3 is a schematic diagram of an indoor Block model of the present invention;

4 is a graph showing the relationship between the heat intensity ratio of the non-air-conditioned area and the air-conditioned area and the convective heat transfer load of the present invention;

FIG. 5 is a verification diagram of a line calculation diagram of a scaled model of the present invention.

Detailed ways

As shown in Figure 1, the technical roadmap of the calculation method for the convection heat transfer load of the large space nozzle air supply stratified air conditioner, the method specifically includes the following steps:

Step 1: Analyze the cause of the convective heat transfer load;

Under the large-space indoor nozzle air supply system, the nozzle installation height is the layered height, which is the interface between the non-air-conditioned area and the air-conditioned area, and the upper part is the non-air-conditioned area. Part of the heat in the area is transferred to the air-conditioned area, which immediately becomes the cooling load of the air-conditioned area. The root cause of convective heat transfer is mainly attributed to the following two points between the non-air-conditioned area and the air-conditioned area: one is the temperature difference between the two areas, and the other is the airflow between the two areas, both of which are indispensable. According to the above analysis, the convective heat transfer load includes the heat flow from the non-air-conditioned area to the air-conditioned area and the temperature difference heat transfer on the interface. Therefore, the flow and temperature difference of indoor air flow determine the occurrence of convective heat transfer and the size of convective heat transfer heat, and the factors that usually affect air flow and temperature difference mainly include the following: air supply and return air volume in the air-conditioning area, and air supply in the air-conditioning area Temperature, exhaust air volume in non-air-conditioned area, heat gain ratio between non-air-conditioned area and air-conditioned area. In addition, in some architectural forms, air inlets in non-air-conditioned areas and air outlets in other areas will also affect the flow of indoor air flow. The present invention only analyzes the four main factors listed above.

Step 2: Use the Block model based on multi-zone heat and mass balance to predict the indoor vertical temperature distribution of large-space buildings;

When using the Block model to determine the indoor air temperature distribution, the wall temperature distribution will affect the air temperature distribution, so the method of determining the wall temperature is very important. In this paper, the thermal conduction, convection and radiation coupling heat transfer method, namely the Gebhart absorption coefficient method, which comprehensively considers the joint effects of outdoor environmental heat transfer, indoor inner surface radiative heat transfer and indoor heat source radiation, is used to solve the indoor wall temperature distribution, and use this as the The boundary conditions calculated by the Block model, and the Block-Gebhart model synchronous solution method is used to study the indoor thermal environment of large-space buildings. Since the inner surface temperature and the indoor air temperature are coupled with each other, iterative calculations are required, and the following parameters are calculated simultaneously to calculate the convective heat transfer load:

(1) The temperature of the inner wall in each area of the room;

(2) Air temperature distribution in each area of the room;

(3) Mass flow between regions.

When the Block-Gebhart model analyzes the indoor thermal environment under the air supply from the large space nozzle, it is assumed that the indoor environment is uniformly distributed in the horizontal direction except for the area affected by the air-conditioning jet, and the concept of the lumped parameter method is used to control each mainstream area. Analyze mass flow and energy transfer, and establish mass and energy balance equations, respectively. Then, the air temperature and wall temperature of the mainstream area of each control area are initially set, and after a series of iterative operations, the temperature of each control area within the allowable error is finally calculated, so as to obtain the indoor vertical temperature distribution (T ₁ , T ₂ , T ₃ · · · T _n ).

According to the above analysis, the convective heat transfer load includes the heat brought by the flow from the non-air-conditioned area to the air-conditioned area and the temperature difference heat transfer on the interface. As shown in Figure 2, the installation height of the nozzle is taken as the layer height, which is the non-air-conditioned area. The interface with the air-conditioned area, that is, floors 1-4 are air-conditioned areas, and floors 5 and above are non-air-conditioned areas. Therefore, the calculation formula of convective heat transfer load is as follows:

q _d =C _p M _c5-4 (T ₅ -T ₄ )+C _B5-4 A _B5-4 (T ₅ -T ₄ ) (1)

In the formula: q _d — the convective heat transfer load from the non-air-conditioned area to the air-conditioned area, in W;

C _P ——The specific heat of air at constant pressure, in kJ/(kg·℃), it can be taken as 1.01 for air;

M _C5-4 —— the air mass net flow from the non-air-conditioned area to the air-conditioned area, in kg/s;

T ₅ , T ₄ —— the air temperature of the lowest floor in the non-air-conditioned area and the highest floor in the air-conditioned area, in °C;

C _{B5-4 ——The} heat transfer coefficient of the temperature difference between the non-air-conditioned area and the air-conditioned area, in W/(m ² ·℃);

A _{B5-4 ——The} layered interface area between the non-air-conditioned area and the air-conditioned area, in m ² .

In order to calculate the indoor vertical temperature distribution of large-space buildings, the Block model divides the indoor environment into several control areas in the vertical direction. If the influence of natural ventilation and indoor heat source is not considered, the indoor airflow organization can be classified into three airflows: wall flow, air-conditioning jet and indoor main airflow formed by the temperature difference in the vertical direction. The exchange of heat and mass between them is the result of joint action. Corresponding to these three airflows, three sub-models are included in the Block model to describe the motion of heat and mass: the wall flow model, the air-conditioning jet model, and the inter-regional heat and mass exchange model. According to the regional heat and mass balance analysis method, the Block model divides the indoor vertical direction into several regions, as shown in Figure 2. By describing the air heat and mass transfer process between each block area, the mass balance and energy balance equations are established, and the temperature of each block area is solved to obtain the indoor vertical temperature distribution.

Step 3: Optimize the calculation model of multiple jets at the nozzle; including the trajectory of a single jet, the non-isothermal jet axial velocity, the temperature decay formula, the superposition of multiple jets, and the entrainment characteristics.

Step 4: Establish a wall flow model and a multi-region heat and mass exchange model; the inner wall of the enclosure is affected by the outdoor ambient temperature and the indoor environment, and the area near the inner surface will generate upward or downward airflow along the wall. When the wall surface is a hot wall surface relative to the indoor air temperature, the airflow direction is upward, and the calculation of the air flow on the wall surface must start from the lowest block in the room; when the wall surface is a cold wall surface relative to the indoor air temperature, the airflow direction The flow direction is downward, and the calculation must start from the block at the highest level and calculate downwards layer by layer. According to the different thermal parameters such as the orientation and material of the surrounding walls of the enclosure structure, the temperature of the inner wall surface will be different. Therefore, the wall surface is divided into K different wall surfaces from the bottom layer to the top layer according to the corresponding Block for processing. As shown in Fig. 3, the wall flow model is taken as an example in summer. The wall is a hot wall, and the temperature of the wall is higher than the temperature of the nearby air. The convective heat exchange between the wall and the indoor air causes the outflow M _OUT (I, K) of each layer of (Block I) air to merge into an airflow along the wall, and the air flows along the wall. In the upward direction, the wall flow starts from the lowest Block 1 and starts to calculate upward layer by layer. The mass outflow air (flow rate M _OUT (I, K), temperature T(I)) generated by any block I in the middle layer and the mixed airflow from the lower block (I-1) (flow rate M _MD) (I-1,K), the temperature is T _M (I-1, K-1)) after meeting and synthesis, the mass flow rate is M _M (I, K), and the temperature is T _M (I, K). The rising synthetic flow continues to flow upward along the hot wall, and then according to the relationship between the synthetic flow temperature T _M (I, K) and the air temperature of Block I and Block (I+1), it is judged that part or all of it flows back to Block I, The rest of the traffic flows into the upper block (I+1) until all flows into the topmost BlockN.

The air temperature near the wall can be analyzed according to the boundary layer theory, and the air temperature of the boundary layer along the K wall of Block I is calculated as follows.

T _D (I,K)＝0.75T(I)+0.25T _W (I,K) (2)

In the formula, K is the wall serial number, T _D (I, K) is the average air temperature in the boundary layer along the K wall of Block I, T(I) is the air temperature of Block I in °C, and T _W (I, K) is the wall surface temperature in K °C.

The equilibrium formula of mass flow heat transfer and natural convection heat transfer near the wall is established as follows:

C _P M _OUT (I,K)[T _D (I,K)-T(I)]=α _C (I,K)A _W (I,K)[T _W (I,K)-T(I )] (3)

In the formula, M _OUT (I, K) is the mass outflow of Block I along the K wall, kg/s, α _C (I, K) is the convection heat release coefficient of the wall K, W/(m ² ·℃), A _W (I, K) is the area of the wall surface K of Block I, m ² , and C _P is the specific heat of air at constant pressure, W/(m ² ·°C).

The natural convection heat transfer between the wall and the air is equal to the energy carried by the boundary layer to process the flow.

When the airflow is synthesized, the air volume and heat balance equation of the synthesized upflow between the wall and the air are as follows:

M _OUT (I,K)T(I)+M _MD (I-1,K-1)T _M (I-1,K-1)＝M _M (I,K)T _M (I,K) ( 5)

M _M (I,K)＝M _OUT (I,K)+M _MD (I-1,K-1) (6)

Temperature _TM (I,K) of the mixed gas stream:

And the air flow rate M _MD (N, K) of the mixed air flow from the uppermost block (N) in the upflow of the hot wall surface is 0, and the air flow rate M _MD (0, K)=0. (When I=1, there is no flow from the previous layer I-1 to the I layer, so _MMD (0,K)=0; when I=N, there is no flow from the I layer to the next layer I+1 quantity, so M _MD (N,K)=0)

When each layer of synthetic upflow flows to the next layer for specific distribution, the mixed airflow distribution process:

M _M (I,K)=M _IN (I,K)+M _MD (I,K) (8)

When the mixed airflow is distributed, the specific flow direction and flow amount are determined by the average temperature of the mixed airflow T _M (I, K), the temperature T (I) of the air layer of this layer of Block I and the temperature of the air layer of the lower Block (I-1) T ( I+1) to judge by comparing the three, all or part of the flow into Block I and Block(I+1) in proportion, that is, the flow volume M _IN (I, K) flowing to the current layer and the flow volume M flowing to the next layer. The ratio and criterion of _MD (I, K) are shown in Table 3.

table 3

The large space is vertically divided into several areas. It is assumed that the temperature distribution in the mainstream area of each block is uniform. Due to the temperature difference between adjacent mainstream areas, air flow between areas will be caused. Heat exchange also occurs at the interface. When the temperature of the upper area is higher than that of the lower area, the air temperature distribution is stable, and the heat will be transferred from the upper area to the lower area; when the temperature of the upper area is lower than that of the lower area, the air temperature distribution is unstable at this time, and the air is floating Under the action of lift, it flows until the temperature of the upper and lower air is uniform. At this time, the heat exchange between the upper and lower temperature difference can be ignored.

When Block(I+1) is higher than the air temperature in the mainstream area of Block I, the heat exchange between the two is shown in the following formula (9).

Q _B (I+1,I)=C _P M _C (I+1,I)[T(I+1)-T(I)]+C _B (I)A _B (I)[T(I+ 1)-T(I)] (9)

In the formula, A _B (I) is the adjacent interface area m ² between Block I and Block (I+1), C _B is the temperature difference heat transfer coefficient W/(m ² ·℃), and T(I) is the Air temperature ℃, M _C (I+1, I) is the air flow kg/s between Block I and Block (I+1), and the value of temperature difference heat transfer coefficient C _B means Block (I+1) to Block I The degree of heat transfer varies with factors such as the number of spatial layers. Measured by experiment, when T(I+1)>T(I), C _B =2.3W/(m ² ·℃); when T(I+1)<T(I), it is caused by density difference The intensity of the heat transfer flow increases, C _B =116W/(m ² ·°C).

Step 5: Use the block boundary condition - wall temperature to solve the convection radiation coupled heat transfer; according to the geometric conditions of the building, divide it into walls, and solve the angle coefficient between the walls and the Gebhart absorption coefficient. By assuming the initial temperature distribution of the wall, according to the indoor air temperature distribution, outdoor environmental parameters, thermal parameters of the enclosure structure, and indoor heat sources as boundary conditions, the thermal conductivity, radiation, etc. are calculated. Finally, according to the coupled heat balance equation, the temperature distribution of the wall can be obtained by solving simultaneously.

Step 6: Establish air volume and energy balance equations according to the Block-Gebhart model; after completing the calculations of the above sub-models, the mass balance and energy balance equations of each block area can be established, and then the simultaneous equations are iteratively calculated and solved to obtain the indoor air Vertical temperature distribution, wall temperature distribution, and convective heat transfer loads. For any block mainstream area, establish an equation.

Step 7: Simultaneous solution of the Block-Gebhart model; the calculation steps for the simultaneous solution of this model are as follows:

The calculation steps include: (1) Assume the initial temperature. Assuming the initial vertical air temperature distribution and wall temperature distribution, the initial wall temperature distribution is input into the Gebhart model wall heat conduction, convection, and radiation coupled heat transfer equations, the air vertical temperature results calculated by the Block model are used as boundary conditions, and the initial air vertical temperature distribution is input into Block In the heat-mass balance equation, the model takes the wall temperature calculated by the Gebhart model as the boundary condition for the calculation, and the two model parameters are mutually input; (2) Iterative calculation. Compare the indoor air temperature and wall temperature distribution obtained in the second step with the initial value of the first step. When the error between the two does not satisfy <10 ^-6 , assign it to the initial value, and return to the first step to repeat the calculation. . (3) Iteratively solve the wall temperature distribution and the indoor vertical temperature distribution in this way. When the relative errors of the first and last two calculation results are <10 ^-6 at the same time, it is considered that the last two calculation results of the indoor air temperature distribution and the wall temperature distribution is the solution of the problem, and the net flow on the layered interface calculated by the equilibrium equations at this time is used to calculate the convective heat transfer load from the non-air-conditioned area to the air-conditioned area. According to the obtained inner wall surface temperature, indoor vertical temperature and air net flow at the interface between the non-air-conditioned area and the air-conditioned area, according to q _d =C _p M _c5-4 (T ₅ -T ₄ )+C _B5-4 A _B5-4 (T ₅ -T ₄ ) calculation method to obtain the convective heat transfer load of stratified air conditioning, where q _d is the convective heat transfer load of the non-air-conditioned area to the air-conditioned area, C _P air constant pressure specific heat, M _C5-4 Air mass net flow from non-air-conditioned area to air-conditioned area, T ₅ , T ₄ air temperature in non-air-conditioned area and air-conditioned area, C _B5-4 temperature difference heat transfer coefficient, A _B5-4 stratified interface area between non-air-conditioned area and air-conditioned area .

Step 8: The block-Gebhart model solves the convective heat transfer load experimental verification; under the gas scale model test bench nozzle air supply system, the experimental research on the indoor temperature field and convective transfer heat load in a large space is carried out. According to the height of the laboratory and the nozzle At the location, the scaled model is divided into 4 regions in the vertical direction, and the mass and energy balance equations are established for these 4 block regions. Comparing the calculation results of the Block-Gebhart model with the experimental data results, it can be found that the maximum error between the experimental value and the theoretical value of the convective heat transfer load is 11.50%, and the average error of the six operating conditions is 6.60%, which can be explained Feasibility of calculating convective heat transfer loads using the Block-Gebhart model.

Step 9: Convert the relationship between the convective heat transfer load and its key influencing factors into dimensionless convective heat transfer load (convective heat transfer load relative to the heat gain in the non-air-conditioned area), heat in the non-air-conditioned area and the air-conditioned area. The relationship between the intensity ratio and the heat rejection ratio (relative to the heat rejection in the non-air-conditioned area) is made into a line graph for practical application.

The specific idea of constructing the first calculation map is as follows: (1) Determine the heat intensity ratios of the study to be 0.32, 0.4, 0.45, 0.52, 0.58; (2) Calculate the total heat gain of each outer protection structure in the non-air-conditioned area and the air-conditioned area. The heat intensity of the non-air-conditioned area is redistributed to the internal heat sources of the non-air-conditioned area according to this ratio: 0, 100W, 200W, 300W, 400W; (3) According to the convective transfer heat calculated by the model under different heat intensity ratios (4) Change the heat rejection ratio to 0%, 10%, and 20%, respectively, and calculate according to the above method to obtain the final line calculation curve, as shown in Figure 4. It can be seen from the figure that under the same heat rejection ratio, as the heat intensity ratio increases, the amount of convective heat transfer from the non-air-conditioned area to the air-conditioned area also increases gradually. This is because the heat gain directly acts on the non-air-conditioned area, causing the temperature of the non-air-conditioned area to rise, resulting in heat diffusion from the non-air-conditioned area to the air-conditioned area. In this way, the amount of heat transfer from the non-air-conditioned area to the air-conditioned area is increased. As the heat rejection ratio increases, the heat from the non-air-conditioned area is gradually removed, reducing the temperature difference between the non-air-conditioned area and the air-conditioned area, reducing the heat diffusion from the non-air-conditioned area to the air-conditioned area, thereby reducing the non-air-conditioned area to the air-conditioned area. amount of heat transfer.

Step 10: Verify the scaled model of the line calculation diagram. According to Figure 5, it can be seen that the experimental data of 0% heat rejection ratio and 10% heat rejection ratio are quite different from the calculated curve values in the original manual, which are different from the convection in this study. The heat transfer load line calculation diagram is basically consistent, which can basically explain the accuracy and applicability of the line calculation diagram.

Finally, the line calculation diagram of the present invention starts from the airflow flow, and uses a combination of theory and experiment, supplemented by field measurement, to obtain a simple method for calculating the convective heat transfer load. Based on the Block-Gebhart theoretical model, the present invention analyzes the indoor thermal environment such as temperature distribution and airflow flow of large-space buildings, calculates the convective heat transfer load according to the temperature difference and flow between the non-air-conditioned area and the air-conditioned interface area, and then analyzes the influence The key factors of the convective heat transfer load are the air supply parameters of the nozzle, the heat distribution from the outside to the room, and the heat removal, etc., using the relationship between the heat intensity ratio, heat rejection ratio, and dimensionless convective heat transfer load between the non-air-conditioned area and the air-conditioned area Draw a line diagram for easy calculation of convective heat transfer loads.

Claims (2)

1. a large space spout air supply layered air conditioning convection heat transfer load calculation method, is characterized in that, specifically comprises the steps: 1) Analyze the convective heat transfer load and establish the Block-Gebhart model: under the large-space indoor nozzle air supply system, the nozzle installation height is the layer height, which is the interface between the non-air-conditioned area and the air-conditioned area, and the upper is the non-air-conditioned area, The lower part is the air-conditioning area. The convective heat transfer load includes the heat from the non-air-conditioned area to the air-conditioned area and the temperature difference heat transfer on the interface. The Block model divides the indoor environment into several control areas in the vertical direction, and the prediction calculation is large. For the indoor vertical temperature distribution of the space building, the Gebhart absorption coefficient method is used to comprehensively consider the heat conduction, convection and radiation coupled heat transfer jointly affected by the outdoor environmental heat transfer, the indoor inner surface radiative heat transfer and the indoor heat source radiation to solve the indoor wall temperature distribution. Taking this as the boundary condition for the calculation of the Block model, the Block-Gebhart model is used to solve the convective heat transfer load simultaneously; the steps to solve the convective heat transfer load simultaneously using the Block-Gebhart model are as follows: A: Optimize the multi-jet calculation model of the nozzle, and establish the wall flow model and the heat and mass exchange model between multiple regions; B: Solve convective radiation coupled heat transfer using Block boundary condition - wall temperature: According to the geometric conditions of the building, it is divided into walls, and the angle coefficient between the walls and the Gebhart absorption coefficient are solved. By assuming the initial temperature distribution of the walls, according to the indoor air The temperature distribution, outdoor environmental parameters, thermal parameters of the envelope structure and indoor heat source are used as boundary conditions to calculate the thermal conductivity and radiation. C: According to the Block-Gebhart model, establish the air volume and energy balance equation; after completing the calculation of each area sub-model, establish the mass balance and energy balance equation of each Block area, then iteratively calculate and solve the indoor air vertical temperature of the simultaneous equations Distribution, wall temperature distribution and convective heat transfer load, establish equations for any block mainstream area; D: Block-Gebhart model is solved simultaneously: (1) Assuming the initial temperature, assuming the initial vertical air temperature distribution and wall temperature distribution, the initial wall temperature distribution is input into the Gebhart model wall heat conduction, convection and radiation coupled heat transfer equations, and the air vertical temperature results calculated by the Block model are used as boundary conditions, The initial air vertical temperature distribution is input into the Block heat-mass balance equation. The model uses the wall temperature calculated by the Gebhart model as the boundary condition for the calculation, and the two model parameters are input to each other; (2) Iterative calculation: compare the indoor air temperature and wall temperature distribution obtained in the second step with the initial value of the first step, when the error between the two does not satisfy <10 ^-6 , assign it to the initial value, and return The first step starts to repeat the calculation; (3) Iteratively solve the wall temperature distribution and the indoor vertical temperature distribution in this way. When the relative errors of the first and last two calculation results are <10 ^-6 at the same time, it is considered that the last two calculation results of the indoor air temperature distribution and the wall temperature distribution is the solution of the problem, and the net flow at the layered interface calculated by the equilibrium equations is used to calculate the convective heat transfer load from the non-air-conditioned area to the air-conditioned area; according to the obtained inner wall temperature, indoor vertical temperature and non-air-conditioned area The net air flow at the interface with the air conditioner, and then according to the convective heat transfer load calculation formula, the convective heat transfer load of the stratified air conditioner is obtained; 2) Experiment verification of block-Gebhart model solving convective heat transfer load: Under the gaseous scale model test bench nozzle air supply system, experiments on indoor temperature field and convective transfer heat load in a large space are carried out to verify the model and analyze the influence of convective heat. The key factor of the transfer load is to use the relationship between the heat intensity ratio, heat rejection ratio and dimensionless convective heat transfer load of the non-air-conditioned area and the air-conditioned area to make a line calculation diagram to simplify the calculation of the convective heat transfer load for practical use. 2. according to the described large space spout air supply layered air conditioner convection heat transfer load calculation method of claim 1, it is characterized in that, in described step 1), Block model adopts Block model based on multi-zone thermal mass balance, for predicting large space Building indoor vertical temperature distribution; Assuming that the indoor environment is uniformly distributed in the horizontal direction except for the air-conditioning jet affected area, the concept of lumped parameter method is used to analyze the mass flow and energy transfer for each control mainstream area, and the mass and energy balance equations are established respectively, and then The air temperature and wall temperature of the mainstream area of each control area are initially set. After a series of iterative operations, the temperature of each control area within the allowable error is finally calculated, so as to obtain the indoor vertical temperature distribution (T ₁ , T ₂ , T ₃ . . . . ·T _n ), n is the total number of control areas divided in the vertical direction; take the installation height of the nozzle as the layer height, which is the interface between the non-air-conditioned area and the air-conditioned area, that is, floors 1-F are the air-conditioned area, Above the F floor is the non-air-conditioned area, and the calculation formula of convective heat transfer load is as follows: q _d =C _p M _cF (T _F+1 -T _F )+C _BF A _BF (T _F+1 -T _F ) In the formula: q _d is the convective heat transfer load from the non-air-conditioned area to the air-conditioned area, in W; C _P is the specific heat of air at constant pressure, in kJ/(kg °C), which can be _1.01 for air; Air quality net flow from air-conditioned area to air-conditioned area, unit kg/s; TF ₊₁ , TF are the air temperature of the lowest floor of non-air-conditioned area and the highest floor of air-conditioned area, unit ℃; _{C BF} is non-air-conditioned area to air-conditioned area Temperature difference heat transfer coefficient, unit W/(m ² ·°C); A _BF is the layered interface area between non-air-conditioning area and air-conditioning area, unit m ² .

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