CN107301276B - Method for calculating convection heat transfer load of large-space nozzle air supply layered air conditioner - Google Patents
Method for calculating convection heat transfer load of large-space nozzle air supply layered air conditioner Download PDFInfo
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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
Technical Field
The invention relates to an air conditioner load calculation technology, in particular to a method for calculating convection heat transfer load of a large-space nozzle air supply layered air conditioner.
Background
The large-space layered air-conditioning load is different from a common room calculation method due to the characteristics of a thermal environment under a layered air-conditioning of a large-space building, the vertical temperature layering and gradient of indoor air are obvious, the upper-lower temperature difference is large, and the temperature distribution of the wall surface of a roof is high. That is, the influence of complicated airflow organization in a large space and an indoor environment, outdoor environment change, indoor heat source distribution and the like can cause the change of indoor thermal environment state parameters and the change of convection heat transfer amount, so that the calculation of the convection heat transfer load is always a difficult problem for designers.
The method for calculating the layered air-conditioning load of the large-space building at present adopts a method mentioned in a practical heat supply air-conditioning design manual compiled by professor of Lu-dazang celebration, and indicates that the layered air-conditioning load comprises loads in a conventional air-conditioning area (such as heat transfer load of an enclosure structure, indoor heat source load, fresh air or infiltration wind load and the like) and loads formed by radiation transfer heat and convection transfer heat transferred from a non-air-conditioning area to the air-conditioning area, and factors influencing the heat transfer load and a calculation method are obtained through model experiments and on-site actual measurement contrast. The specific calculation method comprises the following steps: (1) the load of the conventional air conditioning area is calculated by adopting a traditional whole-room air conditioning load calculation method; (2) the radiation transfer heat load adopts a cold load coefficient method: firstly, calculating the radiation transfer heat from the non-air-conditioning area to the floor of the air-conditioning area, and then multiplying by the heat coefficient C1(generally 1.3) to obtain the radiation transfer heat from the non-air-conditioning area to the air-conditioning area. Then the heat is transferred by the radiation from the non-air-conditioning area to the air-conditioning area and multiplied by the cold load coefficient C2(the value range is 0.45-0.72, generally 0.5), and obtaining the radiation transfer load; (3) the calculation of the convection heat transfer load is realized by carrying out multiple tests and field actual measurement on a certain factory building, fitting the result regression into a calculation curve and popularizing and applying the calculation curve to a large-space building, simplifying the air flow movement between an air conditioning area and a non-air conditioning area and the energy transfer carried by the air flow movement, which is pushed by the action of nozzle air supply, internal heat source and air exhaust, which are key factors of the convection heat transfer load into the comparison relationship among the heat intensity of the air conditioning area, the heat intensity of the non-air conditioning area and the heat discharge amount, and obtaining the convection heat transfer load by checking a graph.
The method for calculating the convective heat transfer load is limited by the thermal environment of a large-space building at that time, wherein a plurality of experience values and measured data of a high and large plant of a steam turbine are adopted, and the experiment and the measured conditions are single. Based on the research degree of the indoor thermal environment of the current large-space building, the calculation method at that time has certain defects and shortcomings.
Disclosure of Invention
The invention provides a method for calculating convection heat transfer load of a large-space-nozzle air supply layered air conditioner, which aims at the problem that the current method for calculating load of the layered air conditioner of a large-space building is limited by current data. In the invention, the accuracy and reliability of the theoretical model are verified by using the result of the reduced scale model experiment, and then the main factors influencing the convection heat transfer load are analyzed by using a mathematical model. And obtaining a line calculation graph for calculating the convection heat transfer load, carrying out experimental verification and assisting with field actual measurement, researching the radiation transfer load of the layered air conditioner under the air supply of the nozzle by combining with a radiation transfer load theoretical calculation model at the later stage, and exploring a layered air conditioner calculation method of which the system is primarily suitable for the air supply at the nozzle side.
The technical scheme of the invention is as follows: a method for calculating convection heat transfer load of a large-space nozzle air supply layered air conditioner specifically comprises the following steps:
1) analyzing convection heat transfer load, and establishing a Block-Gebhart model: under the large-space indoor nozzle air supply system, the nozzle installation height is a layering height, the height is an interface between a non-air-conditioning area and an air-conditioning area, the upper part is the non-air-conditioning area, the lower part is the air-conditioning area, the convection heat transfer load comprises heat brought by the flow of the non-air-conditioning area to the air-conditioning area and temperature difference heat exchange on the interface, a Block model divides an indoor environment into a plurality of control areas in the vertical direction, the indoor vertical temperature distribution of a large-space building is predicted and calculated, a Gebhart is adopted, the heat conduction, convection and radiation coupling heat exchange which are jointly influenced by outdoor environment heat transfer, indoor inner surface radiation heat exchange and indoor heat source radiation are comprehensively considered, the indoor wall temperature distribution is solved, the indoor wall temperature distribution is used as a boundary condition for the Block model calculation, and a Block-Gebhart model is used for;
2) and (3) solving a convection heat transfer load experiment verification by a Block-Gebhart model: the method is characterized in that a large-space indoor temperature field and convection transfer heat load experiment is carried out under a jet air supply system of a gaseous scale model experiment table, a model is verified, key factors influencing the convection heat transfer load are analyzed, an online calculation chart is made by utilizing the relation among a non-air-conditioning area, an air-conditioning area, a heat intensity ratio, a heat discharge ratio and a dimensionless convection heat transfer load, and the convection heat transfer load is simplified and calculated and is used practically.
The Block model in the step 1) adopts a multi-region thermal mass balance based Block model and is used for predicting indoor vertical temperature distribution of the large-space building;
assuming that the indoor environment is uniformly distributed in the horizontal direction except for the air conditioner jet flow influence area, analyzing the mass flow and energy transfer conditions of each control main flow area by utilizing the concept of a lumped parameter method, respectively establishing a mass and energy balance equation, then initially setting the air temperature and the wall surface temperature of the main flow area of each control area, and finally calculating the temperature of each control area within an allowable error through a series of iterative operations, thereby obtaining the indoor vertical temperature distribution (T)1，T2，T3···Tn) N is the total number of the control areas divided in the vertical direction; taking the mounting height of the nozzle as the layering height, wherein the height is the interface of a non-air-conditioning area and an air-conditioning area, namely, a 1-F layer is the air-conditioning area, and a non-air-conditioning area is above the F layer, and the convection heat transfer load calculation formula is as follows:
qd＝CpMcF(TF+1-TF)+CBFABF(TF+1-TF)
in the formula: q. q.sdThe unit is the convection heat transfer load of the non-air-conditioning area to the air-conditioning area, and the unit is W; cPThe air constant-pressure specific heat in kJ/(kg. DEG C.) can be taken as a value of 1.01 for air; mCFThe unit kg/s is the air mass net flow of the non-air-conditioning area to the air-conditioning area; t isF+1,TFRespectively the air temperature of the lowest layer of a non-air-conditioning area and the air temperature of the highest layer of an air-conditioning area in unit ℃; cBFThe heat exchange coefficient of the temperature difference of the non-air-conditioning area to the air-conditioning area is unit W/(m)2·℃)；ABFIs a layered boundary between a non-air-conditioning area and an air-conditioning areaArea per unit m2。
The step 1) of synchronously solving the convective heat transfer load by using a Block-Gebhart model specifically comprises the following steps:
optimizing a nozzle multi-strand jet flow calculation model, and establishing a wall surface flow model and a multi-region heat and mass exchange model;
b, solving convection radiation coupling heat exchange by using Block boundary conditions-wall surface temperature: dividing the building into wall surfaces according to the geometric conditions of the building, solving the angle coefficient and Gebhart absorption coefficient between the wall surfaces, calculating heat conduction quantity and radiation quantity by assuming the initial temperature distribution of the wall surfaces and taking indoor air temperature distribution, outdoor environment parameters, thermal engineering parameters of the building enclosure and an indoor heat source as boundary conditions, and finally simultaneously solving the distribution of the wall surface temperature according to a coupled heat balance equation;
c, establishing an air quantity and energy balance equation according to a Block-Gebhart model; after the calculation of each region submodel is completed, establishing a mass balance and energy balance equation of each Block region, then performing iterative calculation by a simultaneous equation set, solving the vertical temperature distribution of indoor air, the wall surface temperature distribution and the convection heat transfer load, and establishing an equation for any Block mainstream region;
synchronously solving a Block-Gebhart model:
(1) assuming initial temperature, assuming initial air vertical temperature distribution and wall temperature distribution, inputting the initial wall temperature distribution into a Gebhart model wall heat conduction, convection and radiation coupling heat exchange equation, taking an air vertical temperature result calculated by a Block model as a boundary condition, inputting the initial air vertical temperature distribution into a Block heat mass balance equation, taking a wall temperature result calculated by the Gebhart model as a calculated boundary condition, and inputting two model parameters mutually;
(2) iterative calculation, comparing the indoor air temperature and wall temperature distribution obtained in the second step with the initial values in the first step, and if the errors between the two are not satisfied<10-6Then, assigning the value to the initial value, returning to the first step and starting to repeat calculation;
(3) iterative solution of wall temperature distribution and indoor verticality in such a loopStraight temperature distribution, and relative error of two calculation results at the same time<10-6When the temperature of the indoor air is higher than the temperature of the wall surface, calculating the net flow on the layered interface by taking the net flow on the layered interface as a result of the calculation of the balance equation set to calculate the convection heat transfer load of the non-air-conditioning area to the air-conditioning area; and according to the obtained inner wall surface temperature, the indoor vertical temperature and the air net flow on the layered interface of the non-air-conditioning area and the air-conditioning area, and according to a convection heat transfer load calculation formula, obtaining the convection heat transfer load of the layered air conditioner.
The invention has the beneficial effects that: the method for calculating the convection heat transfer load of the large-space nozzle air supply layered air conditioner can optimize a jet flow model, and the obtained optimized Block-Gebhart expansion model can deeply analyze the change condition of the indoor thermal environment of the large-space layered air conditioner, and can perform coupling calculation of the vertical air temperature and the wall surface temperature of the large space on the basis, so as to obtain a calculation method for preliminarily suitable for the convection heat transfer load of the layered air conditioner for air supply at the nozzle side.
Drawings
FIG. 1 is a technical route diagram of a method for calculating convection heat transfer load of a large-space nozzle air supply layered air conditioner according to the present invention;
FIG. 2 is a wall flow model diagram of the present invention;
FIG. 3 is a schematic diagram of an indoor Block model of the present invention;
FIG. 4 is a graph of the heat intensity ratio of the non-conditioned area to the conditioned area versus the convective heat transfer load of the present invention;
FIG. 5 is a verification diagram of a scaled model linear arithmetic diagram according to the present invention.
Detailed Description
As shown in fig. 1, a technical route diagram of a method for calculating convection heat transfer load of a large-space nozzle blowing layered air conditioner specifically comprises the following steps:
step 1: analyzing the formation reason of the convection heat transfer load;
under the indoor spout air supply system in big space, the spout mounting height is the layering height, and this height is the interface in non-air conditioning district and air conditioning district, and it is the non-air conditioning district to go up, under the entrainment effect of spout air supply efflux for the regional part heat of non-air conditioning shifts to the air conditioning region, all becomes the regional cold load of air conditioning immediately. The root cause of the convection heat transfer is mainly attributed to the following two points of the non-air-conditioning area and the air-conditioning area: the temperature difference between the two areas is the first, and the airflow between the two areas flows, but the temperature difference between the two areas is not enough. According to the above analysis, the convective heat transfer load includes the heat from the non-conditioned zone to the conditioned zone and the differential heat transfer across the interface. Therefore, the flow and temperature difference of the indoor air flow determine the occurrence of convection heat transfer and the magnitude of the heat transferred by the convection heat, and the factors generally influencing the flow and temperature difference of the air flow mainly include the following points: the air supply and return air quantity of the air conditioning area, the air supply temperature of the air conditioning area, the air exhaust quantity of the non-air conditioning area and the heat gain ratio of the non-air conditioning area to the air conditioning area. In addition, in some building forms, the air inlets in the non-air-conditioning area and the air outlets in other areas can influence the indoor airflow flow, and the invention only analyzes the 4 main factors listed above.
Step 2: a multi-region thermal mass balance based Block model is adopted for predicting indoor vertical temperature distribution of the large-space building;
when the Block model is used to determine the indoor air temperature distribution, the wall temperature distribution affects the air temperature distribution, so the wall temperature determination method is very important. The heat conduction, convection and radiation coupling heat exchange method which comprehensively considers the common influence of outdoor environment heat transfer, indoor inner surface radiation heat exchange and indoor heat source radiation, namely a Gebhart absorption coefficient method, is adopted to solve the temperature distribution of the indoor wall surface, the temperature distribution is used as a boundary condition for Block model calculation, and a Block-Gebhart model synchronous solving method is used for researching the indoor thermal environment of the large-space building. Because the inner surface temperature and the indoor air temperature are in a coupling relation of mutual influence, iterative calculation is needed respectively, and the following parameters are calculated by synchronous solving, so that the convection heat transfer load is calculated:
(1) the temperature of the inner wall surface of each indoor area;
(2) air temperature distribution of each indoor area;
(3) mass flow between the zones.
When a Block-Gebhart model is used for analyzing an indoor thermal environment under the condition of large-space nozzle air supply, assuming that the indoor environment is uniformly distributed in the horizontal direction except an air conditioner jet flow influence area, analyzing mass flow and energy transfer conditions aiming at each control main flow area by utilizing the concept of a lumped parameter method, and respectively establishing a mass and energy balance equation. Then, the air temperature and the wall surface temperature of the main flow area of each control area are initially set, and the temperature of each control area within the allowable error is finally calculated through a series of iterative operations, so that the indoor vertical temperature distribution (T) is obtained1，T2，T3···Tn)。
According to the above analysis, the convection heat transfer load includes heat brought by the flow of the non-air-conditioning area to the air-conditioning area and the heat transfer by temperature difference at the interface, as shown in fig. 2, the nozzle mounting height is taken as the layered height, which is the interface between the non-air-conditioning area and the air-conditioning area, i.e., 1-4 layers are air-conditioning areas, and 5 or more layers are non-air-conditioning areas. The convective heat transfer load calculation formula is therefore as follows:
qd＝CpMc5-4(T5-T4)+CB5-4AB5-4(T5-T4) (1)
in the formula: q. q.sdThe convection heat transfer load of the non-air-conditioning area to the air-conditioning area is in units of W;
CPthe specific heat at constant pressure of air, in kJ/(kg. DEG C), for air, can take a value of 1.01;
MC5-4the net flow of air quality of the non-air-conditioning area to the air-conditioning area is unit kg/s;
T5,T4-air temperature in unit of lowest floor of non-air-conditioning area and highest floor of air-conditioning area;
CB5-4-heat transfer coefficient of temperature difference of non-air-conditioning area to air-conditioning area in unit W/(m)2·℃)；
AB5-4The area of the boundary between the non-conditioned zone and the conditioned zone, in m2。
In order to calculate the indoor vertical temperature distribution of a large-space building, a Block model divides an indoor environment into a plurality of control areas in the vertical direction. If the influence of natural ventilation and indoor heat sources is not considered, the indoor airflow organization can be summarized into 3 airflows: wall surface flow, air conditioning jet flow and indoor main body airflow formed by temperature difference in the vertical direction are the result of combined action of heat and mass exchange between 3 jet flows under the assumption of indoor thermal environment. For these 3 streams, 3 sub-models were included in the Block model for thermal mass motion description: wall surface flow model, air conditioner jet flow model and inter-area heat and mass exchange model. According to the regional thermal mass balance analysis method, the Block model divides the indoor vertical direction into several regions, as shown in fig. 2. And establishing a mass balance equation and an energy balance equation by describing the air heat and mass transfer process among the Block areas, and solving the temperature of each Block area to obtain the indoor vertical temperature distribution.
And step 3: optimizing a nozzle multi-strand jet flow calculation model; the jet flow generating device comprises a single-strand jet flow motion track, a non-isothermal jet flow axis speed and temperature attenuation formula, superposition of multiple jet flows, entrainment characteristics and the like.
And 4, step 4: establishing a wall surface flow model and a multi-region heat and mass exchange model; the inner wall surface of the enclosure structure is comprehensively influenced by the outdoor environment temperature and the indoor environment, and airflow which flows upwards or downwards along the wall surface can be generated in the area near the inner surface. When the wall surface is a hot wall surface relative to the temperature of indoor air, the airflow flowing direction is upward, and the calculation is started by taking the Block at the bottommost layer in the room as a starting point when the wall surface air flow is calculated; when the wall surface is a cold wall surface relative to the indoor air temperature, the airflow flowing direction is downward, and the calculation is carried out from the Block of the highest layer to the downward layer by layer. The space enclosing structure can cause different temperatures of the inner wall surface according to different thermal parameters such as the orientation and the material of the wall surface around the space enclosing structure, so that 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. Fig. 3 shows a wall flow model diagram, which takes summer as an example. The wall surface is a hot wall surface, the temperature of the wall surface is higher than the temperature of the nearby air, and the convection heat exchange between the wall surface and the indoor air causes the outflow M of each layer (Block I) of airOUT(I, K) converge into a wall flow, the air flows upwards along the wall flow direction, and the wall flow takes the lowest Block 1 as the flowAnd starting to calculate upwards layer by layer. Mass outflow air (flow M) generated by any middle layer of Block IOUT(I, K) temperature T (I) and air (flow rate M) of the mixed air flow from the lower layer Block (I-1)MD(I-1, K) at a temperature TM(I-1, K-1)) meet and synthesize to form a mass flow rate MM(I, K) temperature TM(I, K). The rising composite stream continues to flow upwardly along the hot wall and then follows the composite stream temperature TMAnd (I, K) and the air temperature of Block I and Block (I +1) are partially or completely judged to flow back to Block I, and the rest flows flow into the upper layer Block (I +1) until all flows flow into the topmost layer Block N.
The air temperature near the wall surface can be analyzed according to the boundary layer theory, and the air temperature of the boundary layer at the position of the Block I along the K wall surface is calculated according to the following formula.
TD(I,K)＝0.75T(I)+0.25TW(I,K) (2)
Wherein K is the wall number, TD(I, K) is the average air temperature of Block I in the boundary layer along the wall surface of K, T (I) is the air temperature of Block I, TW(I, K) is the temperature of the wall K.
The following formula is established for the balance of mass flow heat transfer and natural convection heat transfer near the wall surface:
CPMOUT(I,K)[TD(I,K)-T(I)]＝αC(I,K)AW(I,K)[TW(I,K)-T(I)](3)
in the formula, MOUT(I, K) is the mass flux of Block I along the K wall surface, kg/s, αC(I, K) is the convective heat-release coefficient of wall K, W/(m)2·℃)，AW(I, K) is the area of wall K of Block I, m2，CPIs the specific heat of air at constant pressure, W/(m)2·℃)。
The natural convection heat exchange quantity between the wall surface and the air is equal to the energy carried by the processing flow of the boundary layer.
When the airflow is synthesized, the balance equation of the air quantity and the heat quantity of the synthesized upwelling flow between the wall surface and the air is as follows:
MOUT(I,K)T(I)+MMD(I-1,K-1)TM(I-1,K-1)＝MM(I,K)TM(I,K) (5)
MM(I,K)＝MOUT(I,K)+MMD(I-1,K-1) (6)
temperature T of the mixed gas streamM(I,K)：
And the air flow rate M of the mixed air flow from the uppermost block (N) in the upward flow of the hot wall surfaceMD(N, K) 0, and the air flow rate M of the mixed air flow from the bottom Block (0)MD(0, K) ═ 0. (when I is 1, there is no flow of the previous layer I-1 to I, so MMD(0, K) ═ 0; when I ═ N, there is no flow of I layers to the next layer I +1, so MMD(N,K)＝0)
When each layer of composite ascending current flows to the next layer for specific distribution, the mixed gas flow distribution process comprises the following steps:
MM(I,K)＝MIN(I,K)+MMD(I,K) (8)
when the mixed gas flow is distributed, the specific flow direction and flow quantity are determined by the average temperature T of the mixed gas flowM(I, K), the temperature T (I) of the air layer of the Block I of the present layer, and the temperature T (I +1) of the air layer of the lower layer Block (I-1), and the flow rate M to the present layer, which is the flow rate M to the Block I and Block (I +1) in proportion to the whole or part of the flowsIN(I, K) and the amount of flow M to the next layerMDThe proportions and criteria of (I, K) are shown in Table 3.
TABLE 3
The large space is divided into a plurality of areas in the vertical direction, the temperature distribution in the main flow area of each Block is assumed to be uniform, air flows among the areas can be caused due to the difference of the temperatures of the adjacent main flow areas, and heat exchange is also generated on the interface of the adjacent Block areas. When the temperature of the upper area is higher than that of the lower area, the air temperature distribution is stable, and heat can 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, the air flows under the action of the buoyancy lift force until the temperatures of the upper air and the lower air are uniform, and at the moment, the heat exchange of the upper temperature difference and the lower temperature difference can be disregarded.
When Block (I +1) has a higher air temperature than the mainstream region of Block I, the heat exchange amount between both is as shown in the following equation (9).
QB(I+1,I)＝CPMC(I+1,I)[T(I+1)-T(I)]+CB(I)AB(I)[T(I+1)-T(I)](9)
In the formula, AB(I) Is the adjacent interface area m of Block I and Block (I +1)2，CBIs the heat transfer coefficient W/(m) of the temperature difference2DEG C C.T (I) is the air temperature of Block I, MC(I +1, I) is the air flow kg/s between the Block I and the Block (I +1) region, and the heat exchange coefficient of temperature difference CBThe value size represents the degree of heat transfer from Block (I +1) to Block I, and varies with the number of spatial layers and other factors. When T (I +1)>When T (I), CB＝2.3W/(m2DEG C.); when T (I +1)<T (I), increased intensity of heat transfer flow due to density difference, CB＝116W/(m2·℃)。
And 5: solving convection radiation coupling heat exchange by using Block boundary conditions-wall surface temperature; and dividing the building into wall surfaces according to the geometrical conditions of the building, and solving the angle coefficient and the Gebhart absorption coefficient between the wall surfaces. The heat conduction quantity, the radiation quantity and the like are calculated by assuming the initial temperature distribution of the wall surface and taking the indoor air temperature distribution, the outdoor environment parameters, the thermal engineering parameters of the enclosure structure, the indoor heat source and the like as boundary conditions. And finally, simultaneously solving according to a coupling heat balance equation to obtain the distribution of the wall temperature.
Step 6: establishing an air quantity and energy balance equation according to a Block-Gebhart model; after the calculation of each sub-model is completed, a mass balance equation and an energy balance equation of each Block region can be established, and then a simultaneous equation set is used for iterative calculation and solving the indoor air vertical temperature distribution, the wall surface temperature distribution and the convection heat transfer load. For any Block of Block mainstream region, an equation is established.
And 7: synchronously solving a Block-Gebhart model; the calculation steps for the model synchronous solution are as follows:
the calculation steps comprise: (1) an initial temperature is assumed. Assuming initial air vertical temperature distribution and wall surface temperature distribution, inputting the initial wall surface temperature distribution into a Gebhart model wall surface heat conduction, convection and radiation coupling heat exchange equation, taking an air vertical temperature result calculated by a Block model as a boundary condition, inputting the initial air vertical temperature distribution into a Block thermal mass balance equation, taking a wall surface temperature result calculated by the Gebhart model as a calculated boundary condition, and inputting two model parameters mutually; (2) and (5) performing iterative computation. Comparing the indoor air temperature and the wall temperature distribution obtained in the second step with the initial values obtained in the first step, and if the errors of the two are not satisfied<10-6And assigning the value to the initial value, returning to the first step and starting to repeat the calculation. (3) The wall surface temperature distribution and the indoor vertical temperature distribution are solved in a circulating iteration mode, and the relative errors of the current calculation result and the later calculation result are simultaneously obtained<10-6And then, considering the results of the last two times of calculation of the indoor air temperature distribution and the wall surface temperature distribution as the solution of the problem, and calculating the convection heat transfer load of the non-air-conditioning area to the air-conditioning area by taking the net flow on the layered interface calculated by the balance equation set at the moment. According to the obtained inner wall surface temperature, indoor vertical temperature and air net flow on the layer interface of the non-air-conditioning area and the air-conditioning area, and then according to qd＝CpMc5-4(T5-T4)+CB5-4AB5-4(T5-T4) Calculating a method to obtain a convective heat transfer load of the layered air conditioner, wherein qdConvective heat transfer load from non-conditioned to conditioned zones, CPSpecific heat at constant pressure of air, MC5-4Net air mass flow, T, from non-conditioned to conditioned zones5,T4Air temperature, C, of non-conditioned and conditioned areasB5-4Coefficient of heat transfer by temperature difference, AB5-4The area of the layered interface between the non-air-conditioning zone and the air-conditioning zone.
And 8: solving a convective heat transfer load experiment verification by a Block-Gebhart model; the experimental study of the large-space indoor temperature field and the convection transfer heat load is carried out under a nozzle air supply system of a gaseous scale model experiment table, the scale model is divided into 4 areas in the vertical direction according to the height of a laboratory and the position of a nozzle, and a mass and energy balance equation is established for the 4 Block areas. Comparing the Block-Gebhart model calculation result with the experimental data result, the maximum error between the experimental value and the theoretical value of the convection heat transfer load can be found to be 11.50%, and the average error of six working conditions is 6.60%, so that the feasibility of calculating the convection heat transfer load by using the Block-Gebhart model can be demonstrated.
And step 9: the mutual relationship between the convection heat transfer load and the key influence factors thereof is converted into the relationship among the dimensionless convection heat transfer load (convection heat transfer load relative to the heat gain of the non-air-conditioning area), the heat intensity ratio of the non-air-conditioning area to the air-conditioning area and the heat discharge ratio (heat discharge relative to the heat gain of the non-air-conditioning area) and is made into a linear calculation graph so as to be convenient for practical application.
The specific idea of constructing the first calculation graph is as follows: (1) the heat intensity ratios studied were determined to be 0.32, 0.4, 0.45, 0.52, 0.58, respectively; (2) respectively calculating the proportion of the total heat quantity occupied by each external peripheral structure of the non-air-conditioning area and the air-conditioning area, and redistributing the heat intensity of the non-air-conditioning area to the internal heat source of the non-air-conditioning area according to the proportion respectively as follows: 0, 100W, 200W, 300W, 400W; (3) respectively calculating dimensionless convective heat transfer loads according to the convective heat transfer loads calculated under different heat intensity ratios; (4) the heat rejection ratios were varied to 0%, 10%, and 20%, respectively, and calculated as described above to obtain the final plot, as shown in fig. 4. As is apparent from the graph, the convective heat transfer amount from the non-air-conditioning area to the air-conditioning area gradually increases as the heat intensity ratio increases at the same exhaust heat ratio. This is because the heat obtained directly acts on the non-air-conditioned area, so that the temperature of the non-air-conditioned area rises, and heat diffusion from the non-air-conditioned area to the air-conditioned area occurs. Thus, the amount of heat transfer from the non-air-conditioned area to the air-conditioned area is increased. Along with the increase of the heat extraction ratio, the heat of the non-air-conditioning area is gradually removed, the temperature difference between the non-air-conditioning area and the air-conditioning area is reduced, and the heat diffusion from the non-air-conditioning area to the air-conditioning area is weakened, so that the heat transfer amount from the non-air-conditioning area to the air-conditioning area is reduced.
Step 10: the reduced scale model of the line calculation graph is verified, and it can be seen from fig. 5 that the difference between the experimental data of 0% heat rejection ratio and 10% heat rejection ratio and the calculated curve value of the original manual is large, and the difference is basically consistent with the convective heat transfer load line calculation graph of the present study, so that the accuracy and the applicability of the application of the line calculation graph can be basically explained.
Finally, the line calculation graph prepared by the method starts from airflow flow, combines theories and experiments, and is assisted with a mode of actual measurement on site to obtain a simple method for calculating the convection heat transfer load. The invention analyzes the indoor heat environment such as temperature distribution, airflow flow and the like of a large-space building based on a Block-Gebhart theoretical model, calculates the convection heat transfer load according to the temperature difference and the flow quantity between the non-air-conditioning area and the air-conditioning area, then analyzes key factors influencing the convection heat transfer load, such as nozzle air supply parameters, heat distribution from the outdoor to the indoor, heat extraction and the like, and utilizes the relationship among the heat intensity ratio, the heat extraction ratio and the dimensionless convection heat transfer load of the non-air-conditioning area and the air-conditioning area to prepare an arithmetic graph so as to conveniently calculate the convection heat transfer load.
Claims (2)
1. A method for calculating convection heat transfer load of a large-space nozzle air supply layered air conditioner is characterized by comprising the following steps:
1) analyzing convection heat transfer load, and establishing a Block-Gebhart model: under the large-space indoor nozzle air supply system, the nozzle installation height is a layering height, the height is an interface between a non-air-conditioning area and an air-conditioning area, the upper part is the non-air-conditioning area, the lower part is the air-conditioning area, the convection heat transfer load comprises heat brought by the flow of the non-air-conditioning area to the air-conditioning area and temperature difference heat exchange on the interface, a Block model divides an indoor environment into a plurality of control areas in the vertical direction, the indoor vertical temperature distribution of a large-space building is predicted and calculated, a Gebhart is adopted, the heat conduction, convection and radiation coupling heat exchange which are jointly influenced by outdoor environment heat transfer, indoor inner surface radiation heat exchange and indoor heat source radiation are comprehensively considered, the indoor wall temperature distribution is solved, the indoor wall temperature distribution is used as a boundary condition for the Block model calculation, and a Block-Gebhart model is used for; the method for synchronously solving the convective heat transfer load by using the Block-Gebhart model specifically comprises the following steps:
optimizing a nozzle multi-strand jet flow calculation model, and establishing a wall surface flow model and a multi-region heat and mass exchange model;
b, solving convection radiation coupling heat exchange by using Block boundary conditions-wall surface temperature: dividing the building into wall surfaces according to the geometric conditions of the building, solving the angle coefficient and Gebhart absorption coefficient between the wall surfaces, calculating heat conduction quantity and radiation quantity by assuming the initial temperature distribution of the wall surfaces and taking indoor air temperature distribution, outdoor environment parameters, thermal engineering parameters of the building enclosure and an indoor heat source as boundary conditions, and finally simultaneously solving the distribution of the wall surface temperature according to a coupled heat balance equation;
c, establishing an air quantity and energy balance equation according to a Block-Gebhart model; after the calculation of each region submodel is completed, establishing a mass balance and energy balance equation of each Block region, then performing iterative calculation by a simultaneous equation set, solving the vertical temperature distribution of indoor air, the wall surface temperature distribution and the convection heat transfer load, and establishing an equation for any Block mainstream region;
synchronously solving a Block-Gebhart model:
(1) assuming initial temperature, assuming initial air vertical temperature distribution and wall temperature distribution, inputting the initial wall temperature distribution into a Gebhart model wall heat conduction, convection and radiation coupling heat exchange equation, taking an air vertical temperature result calculated by a Block model as a boundary condition, inputting the initial air vertical temperature distribution into a Block heat mass balance equation, taking a wall temperature result calculated by the Gebhart model as a calculated boundary condition, and inputting two model parameters mutually;
(2) iterative calculation, namely, the indoor air temperature and the wall surface temperature distribution obtained in the second step and the initial temperature of the first stepSetting values and comparing, when the error between the two is not satisfied<10-6Then, assigning the value to the initial value, returning to the first step and starting to repeat calculation;
(3) the wall surface temperature distribution and the indoor vertical temperature distribution are solved in a circulating iteration mode, and the relative errors of the current calculation result and the later calculation result are simultaneously obtained<10-6When the temperature of the indoor air is higher than the temperature of the wall surface, calculating the net flow on the layered interface by taking the net flow on the layered interface as a result of the calculation of the balance equation set to calculate the convection heat transfer load of the non-air-conditioning area to the air-conditioning area; according to the obtained inner wall surface temperature, the indoor vertical temperature and the air net flow on the layered interface of the non-air-conditioning area and the air-conditioning area, and according to a convection heat transfer load calculation formula, the convection heat transfer load of the layered air-conditioner is obtained;
2) and (3) solving a convection heat transfer load experiment verification by a Block-Gebhart model: the method is characterized in that a large-space indoor temperature field and convection transfer heat load experiment is carried out under a jet air supply system of a gaseous scale model experiment table, a model is verified, key factors influencing the convection heat transfer load are analyzed, an online calculation chart is made by utilizing the relation among a non-air-conditioning area, an air-conditioning area, a heat intensity ratio, a heat discharge ratio and a dimensionless convection heat transfer load, and the convection heat transfer load is simplified and calculated and is used practically.
2. The method for calculating the convection heat transfer load of the large-space-nozzle air supply layered air conditioner according to claim 1, wherein a Block model in the step 1) is a multi-region thermal mass balance-based Block model and is used for predicting indoor vertical temperature distribution of a large-space building;
assuming that the indoor environment is uniformly distributed in the horizontal direction except for the air conditioner jet flow influence area, analyzing the mass flow and energy transfer conditions of each control main flow area by utilizing the concept of a lumped parameter method, respectively establishing a mass and energy balance equation, then initially setting the air temperature and the wall surface temperature of the main flow area of each control area, and finally calculating the temperature of each control area within an allowable error through a series of iterative operations, thereby obtaining the indoor vertical temperature distribution (T)1，T2，T3···Tn) N is the total number of the control areas divided in the vertical direction; taking the mounting height of the nozzle as the layering height, wherein the height is the interface of a non-air-conditioning area and an air-conditioning area, namely, a 1-F layer is the air-conditioning area, and a non-air-conditioning area is above the F layer, and the convection heat transfer load calculation formula is as follows:
qd＝CpMcF(TF+1-TF)+CBFABF(TF+1-TF)
in the formula: q. q.sdThe unit is the convection heat transfer load of the non-air-conditioning area to the air-conditioning area, and the unit is W; cPThe air constant-pressure specific heat in kJ/(kg. DEG C.) can be taken as a value of 1.01 for air; mCFThe unit kg/s is the air mass net flow of the non-air-conditioning area to the air-conditioning area; t isF+1,TFRespectively the air temperature of the lowest layer of a non-air-conditioning area and the air temperature of the highest layer of an air-conditioning area in unit ℃; cBFThe heat exchange coefficient of the temperature difference of the non-air-conditioning area to the air-conditioning area is unit W/(m)2·℃)；ABFIs the area of the layered interface between the non-air-conditioning area and the air-conditioning area, and has unit m2。
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Effective date of registration: 20220106 Address after: 200241 room 1502, building 2, Lane 39, Shangyi Road, Minhang District, Shanghai Patentee after: SHANGHAI SHINELONG AIR CONDITIONING Co.,Ltd. Address before: 200093 No. 516, military road, Shanghai, Yangpu District Patentee before: University of Shanghai for Science and Technology |
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