A method for calculating unsteady heat transfer of a non-steady property envelope

Abstract

This invention relates to the field of building load calculation and building envelope optimization technology, specifically disclosing a method for calculating unsteady heat transfer in unsteady building envelopes with unsteady physical properties. The method includes the following steps: first, calculating the dynamic transfer matrix of the building envelope based on the variation law of the heat transfer coefficient of the unsteady physical property medium layer; then, obtaining the corresponding periodic response coefficient of the building envelope based on the hourly changes in outdoor conditions; finally, calculating the unsteady heat transfer when the heat transfer coefficient of the building envelope changes. This invention employs the above-mentioned method for calculating unsteady heat transfer in unsteady building envelopes with unsteady physical properties. By utilizing the variation law of the heat transfer coefficient of the unsteady physical property medium layer in the building envelope, the transfer matrix and periodic response coefficient of the building envelope can be optimized in real time, thereby matching the actual outdoor conditions and accurately quantifying the unsteady heat transfer of the building envelope.

Description

Technical Field

[0001] This invention relates to the field of building load calculation and building envelope optimization technology, and in particular to a method for calculating unsteady heat transfer in unsteady building envelopes with unsteady physical properties. Background Technology

[0002] Actual building heat transfer is a complex process. Under the periodic influence of outdoor air temperature and solar radiation, the heat transfer process often exhibits non-steady-state characteristics. Not all the heat (or cold) transferred to the interior through the building envelope becomes the building's cooling (heating) load. The portion that enters the interior through heat conduction immediately becomes the building load at that time, while the heat transferred through convection and radiation has a certain lag.

[0003] The heat transfer of building envelopes is typically calculated using unsteady-state methods such as the reaction coefficient method and the transfer function method. However, existing unsteady-state heat transfer calculation methods usually assume that the thermal parameters of the building envelope are constant and only consider the periodic changes in environmental parameters. For building envelopes with air gaps or phase change structures, which are novel unsteady structures, the heat transfer coefficient of the building envelope also changes periodically with the environment when environmental parameters change. This makes it difficult to accurately quantify the hourly heat transfer of the building envelope, resulting in inaccurate load calculations for this type of building envelope and a lack of reference for selecting air conditioning equipment.

[0004] Therefore, there is an urgent need for a method that can accurately calculate the unsteady heat transfer of unsteady building envelopes with unsteady physical properties. Summary of the Invention

[0005] The purpose of this invention is to provide a method for calculating unsteady heat transfer in unsteady building envelopes with unsteady physical properties, in order to solve the problem of low accuracy in calculating unsteady heat transfer when the heat transfer coefficient of unsteady building envelopes changes continuously during actual heat transfer, and the difficulty in accurately quantifying the selection of air conditioning equipment.

[0006] To achieve the above objectives, this invention provides a method for calculating unsteady heat transfer in unsteady building envelopes with unsteady physical properties, comprising the following steps: S1. Determine the composition and physical property parameters of the medium layer of the unsteady physical property enclosure structure. The unsteady physical property enclosure structure includes at least one constant physical property medium layer and at least one unsteady physical property medium layer. S2. Calculate the sub-transfer matrix of each constant-property medium layer based on its physical property parameters; S3. Calculate the sub-transfer matrix of the unsteady physical property medium layer based on the variation law of heat transfer coefficient; S4. Calculated based on the sub-transfer matrices of each constant-property-value medium layer and each sub-transfer matrix of each unsteady-property-value-value medium layer. The total transfer matrix of an unsteady enclosure structure; S5. Solve for each total transfer matrix using the Heaviside expansion theorem. The root value of an element; S6, according to The root values ​​of elements are used to calculate the periodic heat transfer response coefficient and periodic endothermic response coefficient of unsteady building envelopes. S7. Calculate the hourly unsteady heat transfer of the unsteady building envelope based on the outdoor temperature and the indoor design temperature.

[0007] Preferably, in S1, the physical property parameters include the thermal conductivity of each dielectric layer. Heat capacity ,density and equivalent thickness And the variation law of heat transfer coefficient of unsteady physical property medium layer. .

[0008] Preferably, in S2, the sub-transfer matrix of each constant-property-value medium layer is calculated based on the physical property parameters of the constant-property-value medium layer. , No. The subtransfer matrix of a layer with constant physical properties is calculated using the following formula: ; in, , Let be the hyperbolic sine function and the hyperbolic cosine function. For complex frequency variables, For the heat capacity of each dielectric layer, Thermal conductivity, Equivalent thickness.

[0009] Preferably, in S3, the variation law of the heat transfer coefficient based on the unsteady physical property medium layer is... ,by The variation pattern of heat transfer coefficient with a period of hours Discrete by A sequence of numbers Then the subtransfer matrix of the unsteady physical property medium layer Calculate according to the following formula to obtain : ; in, The element is closely related to the change in heat transfer coefficient. This study investigates the variation of the heat transfer coefficient in unsteady media layers.

[0010] Preferably, in S4, the sub-transfer matrices of each constant-property-value medium layer and each sub-transfer matrix of each unsteady-property-value medium layer are calculated to obtain... The total transfer matrix of an unsteady enclosure structure Specifically: The matrix of the steady medium layer in the unsteady material property enclosure structure Matrix of unsteady physical properties of the medium layer Multiplying in order from the outdoor side to the indoor side yields the total transfer matrix of the unsteady enclosure structure. ; Among them, since the heat transfer matrix of the unsteady material properties medium layer changes with time, the matrices of other steady material properties medium layers are respectively compared with... Multiply, we get Total transfer matrix : ; in, It is the first A steady-state medium layer transfer matrix.

[0011] Preferably, in S5, the Heaviside expansion theorem is used to solve for each total transfer matrix. Elements in Root values ​​within the range: ; in, It is a hyperbolic sine function. For complex frequency variables, For the heat capacity of each dielectric layer, Thermal conductivity, Equivalent thickness.

[0012] Preferably, in S6, according to Calculation of the root value of elements for the periodic heat transfer response coefficient of unsteady building envelope and periodic endothermic reaction coefficient The calculation formula is as follows: ; ; in, It is the baseline value for the overall heat transfer coefficient of the building envelope. It is the total number of cycles in which the heat transfer coefficient changes. In the total transfer matrix The element's first One root value, It is a continuous-time variable. The time step for discretizing the heat transfer coefficient yes function at root value The first derivative at that point, In the total transfer matrix element at root value The value at that location.

[0013] Preferably, in S7, based on the outdoor temperature as The indoor design temperature is constant. When calculating unsteady physical properties of the enclosure structure Unsteady heat transfer at time t_t : .

[0014] Preferably, in S1, the unsteady physical property enclosure structure is the enclosure structure of an air-supported membrane structure building, and each medium layer consists of an outer membrane, an air gap layer, an insulation layer, and an inner membrane, wherein the air gap layer is an unsteady physical property medium layer.

[0015] Therefore, the present invention employs the above-mentioned method for calculating unsteady heat transfer in unsteady enclosure structures, and the beneficial effects are as follows: (1) The method of the present invention can dynamically optimize the total transfer matrix and periodic reaction coefficient of the enclosure structure according to the change law of the heat transfer coefficient of the unsteady physical property medium layer. Compared with the logical method of calculating the fixed transfer matrix and reaction coefficient in the traditional reaction coefficient method, the method uses a dynamic transfer matrix and multiple sets of reaction coefficients to calculate the heat transfer, thereby improving the accuracy of the calculation of the unsteady heat transfer of the enclosure structure.

[0016] (2) The method of the present invention can accurately quantify the air conditioning cooling load of unsteady building envelope under summer operating conditions, providing a basis for the selection of air conditioning system equipment for this type of building envelope.

[0017] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0018] Figure 1 This is an overall flowchart of an embodiment of the unsteady heat transfer calculation method for unsteady building envelope structures according to the present invention; Figure 2 This is a diagram of an unsteady heat transfer calculation method for an unsteady enclosure structure according to an embodiment of the present invention, wherein (a) is an external view of the enclosure structure, (b) is an internal view of the enclosure structure, and (c) is a cross-sectional view of the enclosure structure. Detailed Implementation

[0019] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0020] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects.

[0021] To accurately quantify the unsteady heat transfer of unsteady-state building envelopes with unsteady physical properties, this invention calculates the total heat transfer matrix of each dielectric layer of the building envelope using the integral transform method, based on the variation law of the physical property parameters and heat transfer coefficient of the building envelope. The transfer matrix contains 、 , and Four elements, of which The change in the element and the heat transfer coefficient is closely related, and the transfer matrix is ​​used to... The function calculates the periodic reaction coefficient under dynamic changes in heat transfer coefficient, and finally accurately calculates the hourly heat transfer of the unsteady physical property enclosure structure by using the reaction coefficients of different groups.

[0022] like Figure 1 As shown, a method for calculating unsteady heat transfer in an unsteady building envelope includes the following steps: S1. Determine the composition and physical property parameters of the medium layer of the unsteady enclosure structure, such as... Figure 2 As shown, the unsteady physical property enclosure structure includes at least one layer of constant physical property medium and at least one layer of unsteady physical property medium.

[0023] Premise and Assumptions: It is assumed that the unsteady enclosure structure consists of multiple layers of media, wherein the first layer is... The first layer is a medium with normal physical properties. The layer is a non-steady medium (such as a fluid); the variation law of the heat transfer coefficient of the non-steady medium layer is known and follows a time function. Thermal conductivity of each dielectric layer Heat capacity ,density and equivalent thickness The physical properties are known.

[0024] S2. Calculate the sub-transfer matrix of each constant-property-value medium layer based on its physical property parameters. , with the first Taking the subtransfer matrix of a layered medium with constant physical properties as an example, the calculation formula is as follows: ; in, , Let be the hyperbolic sine function and the hyperbolic cosine function. For complex frequency variables, For the heat capacity of each dielectric layer, Thermal conductivity, Equivalent thickness.

[0025] S3. Calculate the sub-transfer matrix of the unsteady physical property medium layer based on the variation law of heat transfer coefficient.

[0026] Specifically, the variation law of heat transfer coefficient based on unsteady physical property medium layer ,by The variation pattern of heat transfer coefficient over a 24-hour period Discrete by A sequence of numbers Then the subtransfer matrix of the unsteady physical property medium layer Calculate according to the following formula to obtain : ; in, The element is closely related to the change in heat transfer coefficient. This study investigates the variation of the heat transfer coefficient in unsteady media layers.

[0027] S4. Based on the sub-transfer matrices of each constant-property-value medium layer and the sub-transfer matrices of each unsteady-property-value medium layer, the total transfer matrix of the 24 unsteady-property-value enclosure structures is calculated. Specifically: The matrix of the steady medium layer in the unsteady material property enclosure structure Matrix of unsteady physical properties of the medium layer Multiplying in order from the outdoor side to the indoor side yields the total transfer matrix of the unsteady enclosure structure. Since the heat transfer matrix of the unsteady dielectric layer changes with time, the matrices of other steady dielectric layers are respectively compared with... Multiply, we get 24 total transfer matrices : ; in, It is the first A steady-state medium layer transfer matrix.

[0028] S5. Solve for each total transfer matrix using the Heaviside expansion theorem. Elements in Root values ​​within the range: ; in, It is a hyperbolic sine function. For complex frequency variables, For the heat capacity of each dielectric layer, Thermal conductivity, Equivalent thickness.

[0029] S6, according to Calculation of the root value of elements for the periodic heat transfer response coefficient of unsteady building envelope and periodic endothermic reaction coefficient The calculation formula is as follows: ; ; in, It is the baseline value for the overall heat transfer coefficient of the building envelope. It is the total number of cycles in which the heat transfer coefficient changes. In the total transfer matrix The element's first One root value, It is a continuous-time variable. The time step for discretizing the heat transfer coefficient yes function at root value The first derivative at that point, In the total transfer matrix element at root value The value at that location.

[0030] S7. Finally, based on the outdoor temperature... The indoor design temperature is constant. When calculating unsteady physical properties of the enclosure structure Unsteady heat transfer at time t_t : .

[0031] Ultimately, the time-by-time unsteady heat transfer of the unsteady enclosure structure can be obtained.

[0032] In the heat transfer calculation method of this invention, for a constant physical property medium layer, its thermal inertia parameter generally does not change, while the heat transfer coefficient of an unsteady physical property medium layer is in a state of constant fluctuation. Therefore, when the heat transfer coefficient of the building envelope is dynamically changing, its periodic response coefficient will inevitably change as well. The heat transfer coefficient of the building envelope under different operating conditions will correspond to different sets of periodic response coefficients. Therefore, when calculating the unsteady heat transfer of the building envelope, the periodic response coefficient under the corresponding operating condition should be used for calculation.

[0033] In the heat transfer calculation method of this invention, since the heat conduction process of the solid structure has a lag, when the outdoor disturbance changes, the heat transfer process affects the calculation of each subsequent moment according to the thermal property parameters of the solid envelope. Therefore, when calculating the unsteady heat transfer corresponding to the disturbance at a certain moment, the periodic response coefficient under the outdoor parameters at that moment should be used. For the next moment, the periodic response coefficient corresponding to the outdoor parameters at the next moment is used for calculation. The dynamic periodic response coefficient at each moment is determined by the total heat transfer coefficient of the unsteady envelope.

[0034] Example 1 In this embodiment, the research object is an air-supported membrane structure building envelope, which, from the outdoor side to the indoor side, includes: an outer membrane—an air gap—an insulation layer—an inner membrane, as shown in the attached figure. Figure 2 As shown, the membrane layer has a very small thickness and low thermal resistance; the air gap layer has a relatively large thickness, and its heat transfer coefficient varies with the temperature difference between the inside and outside of the membrane, the airflow organization, and the operating conditions. It is a typical unsteady physical property enclosure structure.

[0035] In this embodiment, the unsteady physical property enclosure structure is the enclosure structure of an air-supported membrane structure building. Each medium layer consists of an outer membrane, an air gap layer, an insulation layer, and an inner membrane, with thermal conductivity of 0.22 W / (m·K), 0.0267 W / (m·K), 0.028 W / (m·K), and 0.214 W / (m·K), respectively; specific heat capacities of 1360 J / (kg·℃), 1003 J / (kg·℃), 670 J / (kg·℃), and 1360 J / (kg·℃), respectively; and densities of 1250 kg / m³. 3 1.205kg / m 3 48kg / m 3 and 1208kg / m 3 .

[0036] The air gap is an unsteady medium with varying heat transfer coefficients. The daily variation range is 0.2-5 W / (m²). 2 • K). The outdoor meteorological parameters are the hourly calculated outdoor temperatures of air-conditioned buildings in a certain city during summer. In some cases, this range varies with outdoor meteorological parameters and building envelope design parameters, but this invention is not limited thereto.

[0037] I. Envelope Transfer Matrix: This embodiment determines the heat transfer matrix based on the physical properties of the air-supported membrane enclosure structure. The transfer matrices for each medium layer can be summarized into six types: 1) Heat transfer matrix of outdoor air and sunlight to the outer surface of the building envelope via convection and radiation : .

[0038] 2) Thermal conductivity matrix of the outer membrane : .

[0039] 3) Convective heat transfer matrix between the outer and inner membranes and the air gap : .

[0040] 4) Thermal conductivity matrix of the insulation layer : .

[0041] 5) Thermal conductivity matrix of the inner membrane : .

[0042] 6) Convection and radiation heat transfer matrix between the inner membrane and indoor air ; .

[0043] Therefore, the total transfer matrix of the enclosure structure is : The convective heat transfer matrix between the outer membrane and the insulation layer and the air gap. The first term is a dynamic matrix, and its value varies with the convective heat transfer coefficient of the air layer. The other five terms are constant transfer matrices.

[0044] II. Periodic response coefficient of the building envelope: Calculate its based on the total transfer matrix of the building envelope. The root value of the element, when the heat transfer coefficient of the air layer is 0.2 W / (m²). 2 ·K), 1W / (m 2 ·K), 2W / (m 2 ·K), 3W / (m 2 ·K), 4W / (m 2 ·K), 5W / (m 2 When K), its The function can be represented as: ; The air-to-air heat transfer coefficient at time 0 0.2W / (m 2 For example, when K), The root values ​​of the function are -2.505 and -15.238.

[0045] Repeat the above steps to calculate the air-to-air heat transfer coefficient at time τ within a 24-hour period. time Root value of the function.

[0046] Then based on The root function is used to calculate the periodic response coefficient of the air-supported membrane enclosure structure. The periodic response coefficient can be expressed as: ; ; The air-to-air heat transfer coefficient at time 0 0.2W / (m 2 Taking K as an example, the periodic reaction coefficient =[0.0938, 0.0826, 0.0079, 0.0006, 0, ..., 0].

[0047] Repeat the above steps to calculate the air-to-air heat transfer coefficient at time τ within a 24-hour period. Periodic reaction coefficient and .

[0048] In traditional methods, the heat transfer coefficient of the air gap is calculated using the recommended value in the standard as a constant. In this example, however, the calculation is based on the standard. The value is 2.63 W / (m 2 The method of this invention uses only one set of periodic reaction coefficients (K). However, the method of this invention uses the above six sets of periodic reaction coefficients to calculate the unsteady heat transfer of the building envelope when the heat transfer coefficient changes.

[0049] III. Unsteady heat transfer in the building envelope: Based on the above six sets of periodic response coefficients, the hourly unsteady-state heat transfer of the building envelope can be calculated over a day. The unsteady-state heat transfer of the building envelope can be expressed as: .

[0050] The unsteady heat transfer of the air-supported membrane envelope in Zhengzhou City over a 24-hour period was calculated. =[0.01, 0.22, 0.35, 0.4, 0.8, 1.3, 1.9, 3.1, 5, 7.34, 9.3, 10.85, 11.45, 11.07, 9.9, 7.7, 5.42, 3.13, 1.35, 0.31, -0.55, -0.55, -0.36, -0.16], unit is W / (m 2 ·K).

[0051] Compared to traditional methods that use recommended values ​​from specifications for calculation, the present invention can improve the accuracy of hourly unsteady heat transfer by up to 18.1% by using dynamic response coefficient calculation.

[0052] Therefore, this invention adopts the above-mentioned method for calculating unsteady heat transfer in unsteady enclosure structures, which gives the dynamic heat transfer matrix of the enclosure structure by the variation law of the heat transfer coefficient of the unsteady medium layer, and then uses multiple sets of periodic reaction coefficients to express the unsteady heat transfer process of the enclosure structure under different working conditions, thereby improving the accuracy of the calculation of unsteady heat transfer in unsteady enclosure structures.

[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for calculating unsteady heat transfer in unsteady enclosure structures with unsteady physical properties, characterized in that, Includes the following steps: S1. Determine the composition and physical property parameters of the medium layer of the unsteady physical property enclosure structure. The unsteady physical property enclosure structure includes at least one constant physical property medium layer and at least one unsteady physical property medium layer. S2. Calculate the sub-transfer matrix of each constant-property medium layer based on its physical property parameters; S3. Calculate the sub-transfer matrix of the unsteady physical property medium layer based on the variation law of heat transfer coefficient; S4. Calculated based on the sub-transfer matrices of each constant-property-value medium layer and each sub-transfer matrix of each unsteady-property-value-value medium layer. The total transfer matrix of an unsteady enclosure structure; S5. Solve for each total transfer matrix using the Heaviside expansion theorem. The root value of an element; S6, according to The root values ​​of elements are used to calculate the periodic heat transfer response coefficient and periodic endothermic response coefficient of unsteady building envelopes. S7. Calculate the hourly unsteady heat transfer of the unsteady building envelope based on the outdoor temperature and the indoor design temperature.

2. The method for calculating unsteady heat transfer in an unsteady building envelope according to claim 1, characterized in that, In S1, the physical properties include the thermal conductivity of each dielectric layer. Heat capacity ,density and equivalent thickness And the variation law of heat transfer coefficient of unsteady physical property medium layer. .

3. The method for calculating unsteady heat transfer in an unsteady building envelope according to claim 2, characterized in that, In S2, the sub-transfer matrix of each constant-property-value medium layer is calculated based on its physical property parameters. , No. The subtransfer matrix of a layer with constant physical properties is calculated using the following formula: ； in, , Let be the hyperbolic sine function and the hyperbolic cosine function. For complex frequency variables, For the heat capacity of each dielectric layer, Thermal conductivity, Equivalent thickness.

4. The method for calculating unsteady heat transfer in an unsteady building envelope according to claim 2, characterized in that, In S3, the variation law of heat transfer coefficient based on the unsteady physical property medium layer ,by The variation pattern of heat transfer coefficient with a period of hours Discrete by A sequence of numbers Then the subtransfer matrix of the unsteady physical property medium layer Calculate according to the following formula to obtain : ； in, The element is closely related to the change in heat transfer coefficient. This study investigates the variation of the heat transfer coefficient in unsteady media layers.

5. The method for calculating unsteady heat transfer in an unsteady building envelope according to claim 4, characterized in that, In S4, the sub-transfer matrices of each constant-property-value medium layer and each sub-transfer matrix of each unsteady-property-value-value medium layer are calculated. The total transfer matrix of an unsteady enclosure structure Specifically: The matrix of the steady medium layer in the unsteady material property enclosure structure Matrix of unsteady physical properties of the medium layer Multiplying in order from the outdoor side to the indoor side yields the total transfer matrix of the unsteady enclosure structure. ; Among them, since the heat transfer matrix of the unsteady material properties medium layer changes with time, the matrices of other steady material properties medium layers are respectively compared with... Multiply, we get Total transfer matrix : ； in, It is the first A steady-state medium layer transfer matrix.

6. The method for calculating unsteady heat transfer in an unsteady building envelope according to claim 5, characterized in that, In S5, the Heaviside expansion theorem is used to solve for each total transfer matrix. Elements in Root values ​​within the range: ； in, It is a hyperbolic sine function. For complex frequency variables, For the heat capacity of each dielectric layer, Thermal conductivity, Equivalent thickness.

7. The method for calculating unsteady heat transfer in an unsteady building envelope according to claim 6, characterized in that, In S6, according to Calculation of the root value of elements for the periodic heat transfer response coefficient of unsteady building envelope and periodic endothermic reaction coefficient The calculation formula is as follows: ； ； in, It is the baseline value for the overall heat transfer coefficient of the building envelope. It is the total number of cycles in which the heat transfer coefficient changes. In the total transfer matrix The element's first One root value, It is a continuous-time variable. The time step for discretizing the heat transfer coefficient yes function at root value The first derivative at that point, In the total transfer matrix element at root value The value at that location.

8. The method for calculating unsteady heat transfer in an unsteady building envelope according to claim 7, characterized in that, In S7, based on the outdoor temperature... The indoor design temperature is constant. When calculating unsteady physical properties of the enclosure structure Unsteady heat transfer at time t_t : 。 9. The method for calculating unsteady heat transfer in an unsteady building envelope according to claim 1, characterized in that, In S1, the unsteady physical property enclosure structure is the enclosure structure of the air-supported membrane structure building. Each medium layer consists of an outer membrane, an air gap layer, an insulation layer, and an inner membrane. Among them, the air gap layer is an unsteady physical property medium layer.

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