Design method for chimney structures inside buildings

Abstract

To provide a chimney structure in a building capable of preventing the temperature of a building from rising due to the heat of flue gas.SOLUTION: When an in-building chimney structure 3 including a chimney 20 erected to form a ventilation layer 13 inside a cylindrical shaft 10 of a building 1 is designed, design heat transfer conditions a to i related to the degree of steady heat transfer in an inward / outward direction at a predetermined height hs of the in-building chimney structure 3 are set. The expected temperature t13 of the outer surface of the shaft 10 at the predetermined height hs is calculated based on the assumed temperature tg of the flue gas g passing through the flue gas duct 29 and the design heat transfer conditions a to i. The optimum value of the thermal conductivity or the thickness of the chimney 20 among the design heat transfer conditions a to i is obtained such that the expected temperature t13 is equal to or lower than a predetermined temperature t13s.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for designing a chimney structure, and more particularly to a method for designing an in-building chimney structure to be installed in a building such as a commercial building. [Background technology]

[0002] Generally, commercial buildings, factories, and other buildings are equipped with boilers, generators, and other equipment that releases gas, as well as chimneys to exhaust the released gas (flue gas) to the outside. The chimneys run vertically through the building and protrude upward from the roof. The chimneys within the building are housed inside a vertical, open-ceiling shaft. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. WO2015 / 101751 Summary of the Invention [Problem to be solved by the invention]

[0004] The temperature of the flue gas passing through the chimney flue is high, for example, at about 200°C to 650°C. This heat may be transferred into the building, causing the temperature inside the building to rise. In view of the above circumstances, the present invention aims to provide an in-building chimney structure that can prevent the building from becoming too hot due to the heat of exhaust gas. [Means for solving the problem]

[0005] In order to solve the above problems, the present invention provides A design method for a chimney structure in a building, comprising: a cylindrical shaft provided so as to extend vertically in a building; a chimney provided inside the shaft to form an air layer between the shaft and the chimney; an air intake port connected to a lower end of the air layer; and an air exhaust port connected to an upper end of the air layer, A process of setting design heat transfer conditions related to the degree of steady heat transfer in and outward directions at a predetermined height of the chimney structure inside the building; calculating a predicted temperature of the outer or inner surface of the shaft at the predetermined height based on an assumed temperature of the flue gas passing through the flue and the design heat transfer conditions; and determining an optimum value of the thermal conductivity or thickness of the chimney among the design heat transfer conditions so that the predicted temperature is equal to or lower than a predetermined temperature.

[0006] Preferably, in the setting step, the design heat transfer conditions are set to at least some of the heat transfer coefficient between the exhaust gas passing through the flue inside the chimney and the inner surface of the chimney, the thermal conductivity of the chimney, the thickness of the chimney, the heat transfer coefficient between the outer surface of the chimney and the air in the ventilation layer, the required ventilation flow rate of the ventilation layer, the heat transfer coefficient between the air in the ventilation layer and the inner surface of the shaft, the cross-sectional shape and dimensions of the chimney and the shaft, the thermal conductivity of the shaft, and the thickness of the shaft.

[0007] Preferably, in the setting step, the required ventilation flow rate of the ventilation layer is set as one of the design heat transfer conditions, the predicted temperature difference between the air intake and the air exhaust when the thermal conductivity or thickness of the chimney is set to the optimal value is calculated, the ventilation flow rate of the ventilation layer is calculated based on the elevation difference and predicted temperature difference between the air intake and the air exhaust, and the opening areas of the air intake and the air exhaust, and it is determined whether the calculated ventilation flow rate is equal to or greater than the required ventilation flow rate.

[0008] Preferably, the opening area of ​​at least one of the air intake port and the air exhaust port is set so that the calculated ventilation flow rate is equal to or greater than the required ventilation flow rate.

[0009] Preferably, the flow path cross-sectional area of ​​the intermediate narrow portion of the ventilation layer is set so that the calculated ventilation flow rate is equal to or greater than the required ventilation flow rate. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide an in-building chimney structure that can prevent the building from becoming too hot due to the heat of exhaust gas. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a front cross-sectional view showing a simplified model of an in-building chimney structure set in a design method for an in-building chimney structure according to one embodiment of the present invention. [Figure 2] FIG. 2 is a flowchart showing the steps of the design method. [Figure 3] FIG. 3 is a front cross-sectional view showing a realistic model of a chimney structure in a building that is set in the design method. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. As shown in Figure 1, a building 1, such as a commercial building or a factory, is equipped with a flue gas emission facility 2 that emits flue gas g from a boiler, generator, etc., and an internal chimney structure 3 for discharging the flue gas g to the outside.

[0013] Figure 1 shows a simple model of an in-building chimney structure 3. The in-building chimney structure 3 includes a cylindrical shaft 10 and a chimney 20. The shaft 10 is integrated with the skeleton of the building 1 and extends vertically. The shaft 10 is made of reinforced concrete. In addition to ordinary concrete, autoclaved lightweight aerated concrete (hereinafter referred to as "ALC") is also used as the concrete for the shaft 10. The cross-sectional shape of the shaft 10 can be a rectangle, a circle, or a modified polygon with a corner at one corner of the rectangle.

[0014] As shown in Fig. 1, a chimney 20 is housed inside a shaft 10 so as to stand upright. A main wall material 21 of the chimney 20 is made of a heat insulating material such as calcium silicate. An inner surface material 22 such as a steel plate is provided on the inner surface of the main wall material 21, and an outer surface material 23 such as a steel plate is provided on the outer surface of the main wall material 21. A flue 29 is formed inside the chimney 20.

[0015] The cross-sectional shape of the chimney 20 may be rectangular, circular, or the like. The cross-sectional shapes of the shaft 10 and the chimney 20 do not necessarily have to be similar; for example, the cross-section of the shaft 10 may be rectangular, while the cross-section of the chimney 20 may be circular. A gas introduction pipe 4 from the equipment 2 is connected to the lower end of the chimney 20. The upper end of the chimney 20 protrudes further upward from the upper end of the shaft 10 and, therefore, from the roof of the building 1.

[0016] A ventilation layer 13 is formed between the inner surface of the shaft 10 and the outer surface of the chimney 20. An air intake port 14 made of a louver or the like is provided at the lower end of the shaft 10. The lower end of the ventilation layer 13 is connected to the air intake port 14. An air exhaust port 15 made of a louver or the like is provided at the upper end of the shaft 10. The upper end of the ventilation layer 13 is connected to the air exhaust port 15.

[0017] The flue gas g generated in the flue gas discharge equipment 2 is introduced into the lower end of the flue 29 through the gas inlet pipe 4, rises inside the flue 29, and is discharged to the outside from the upper end of the chimney 20. The heat of the flue gas g penetrates the chimney 20 in the thickness direction, is transferred to the air in the ventilation layer 13, and is then transferred to the shaft 10 via the air.

[0018] The main factors (heat transfer conditions) that affect the degree of heat transfer in the chimney structure 3 inside the building are as follows: a. Heat transfer coefficient between the flue gas g in the flue 29 and the inner surface of the chimney 20 b. Thermal conductivity of chimney 20 c.Thickness of chimney 20 d. Heat transfer coefficient between the outer surface of the chimney 20 and the air in the ventilation layer 13 e. Cross-sectional shape and dimensions of the chimney 20 and shaft 10 f. Ventilation flow rate of air in the ventilation layer 13 g. Heat transfer coefficient between the air in the ventilation layer 13 and the inner surface of the shaft 10 h. Thermal conductivity of shaft 10 i. Thickness of shaft 10

[0019] An ascending air current ac, i.e., the ventilation flow rate, is generated within the ventilation layer 13 due to the heating of the air. Along with the ascending air current, room temperature air from outside the building chimney structure 3 flows into the ventilation layer 13 through the air intake 14. The air that rises within the ventilation layer 13 is discharged to the outdoors through the air outlet 15. At the same time, some of the heat from the chimney 20 is discharged to the outside of the system. The greater the ventilation flow rate, the greater the amount of heat exhausted from the chimney 20.

[0020] The ventilation flow rate depends on the air temperature at the air intake port 14, the air temperature at the air exhaust port 15, and the ventilation conductance (degree of ease of air flow) of the ventilation layer 13. The subfactors that determine the ventilation conductance and thus "f. ventilation flow rate" are mainly f1 to f4 below. f1. Height difference h from the air intake 14 to the air exhaust 15 13 f2. Cross-sectional area of ​​the flow path of the ventilation layer 13 f3. Opening area of ​​air intake 14 f4. Opening area of ​​air exhaust port 15

[0021] <Design method for chimney structure 3 inside a building> As shown in the flowchart of Figure 2, the in-building chimney structure 3 is designed as follows. The design is based on the assumption that heat is steadily transferred from the inside to the outside at a predetermined height hs of the in-building chimney structure 3. The predetermined height hs is preferably set above the middle height of the shaft 10, and more preferably near the top end of the shaft 10 (slightly below the air outlet 15). The heat transfer at the predetermined height hs is analyzed. The analysis is preferably performed by a computer equipped with an analysis program incorporating calculation formulas that apply basic formulas for heat conduction such as Fourier's law and basic formulas for thermal convection such as Newton's law of cold.

[0022] <Setting design heat transfer conditions> In the analysis, design heat transfer conditions are set regarding the degree of steady heat transfer in the inward and outward directions at a predetermined height hs of the in-building chimney structure 3. That is, at least some of the factors a to i described above are set as design heat transfer conditions (step 101). The heat transfer coefficient on the inner surface of the chimney 20 is determined by the material of the inner surface material 22. Therefore, by selecting the material of the inner surface material 22, the heat transfer coefficient on the inner surface of the chimney 20 is set. b. The thermal conductivity of the chimney 20 is mainly determined by the insulating material of the main wall material 21 of the chimney 20. Therefore, the thermal conductivity of the chimney 20 is set by selecting the material of the main wall material 21. c. In step 101, the thickness of the chimney 20 is arbitrarily set to a provisional value within a range that provides the required chimney function or within an empirical range. d. The heat transfer coefficient on the outer surface of the chimney 20 is determined by the material of the outer surface material 23. Therefore, by selecting the material of the outer surface material 23, the heat transfer coefficient on the surface of the chimney 20 is set. e. The cross-sectional shape and dimensions of the chimney 20 and shaft 10 are set in accordance with the design information of the building 1.

[0023] f. Regarding the ventilation flow rate, in step 101, the cross-sectional shape and dimensions of the shaft 10 and the chimney 20, the height difference h between the air intake 14 and the air exhaust 15, 13 Taking into consideration the opening area of ​​the air intake 14, the opening area of ​​the air exhaust 15, etc., the "required ventilation flow rate Q" required to cool the shaft 10 is determined. 13 Set "s". f1. Height difference h 13 is set according to the design information of building 1. f2. The cross-sectional area of ​​the flow path of the ventilation layer 13 is determined by the cross-sectional shape and dimensions of the shaft 10 and the chimney 20. f3. In step 101, a provisional value is set for the opening area of ​​the air intake 14. f4. A provisional value is also set for the opening area of ​​the air outlet 15 in step 101. This simplifies the calculation process.

[0024] g. The heat transfer coefficient on the inner surface of the shaft 10 is determined by the material of the shaft 10, that is, the type of concrete that makes up the shaft 10 (regular concrete, ALC, etc.). h. The thermal conductivity of the shaft 10 is also determined by the type of concrete that makes up the shaft 10. Therefore, by selecting the type of concrete that makes up the shaft 10, the heat transfer coefficient on the inner surface of the shaft 10 and the thermal conductivity of the shaft 10 are set. i. The thickness of the shaft 10 is set according to the design information of the building 1. A database linking the materials of each element 21 to 23 of the chimney 20 and the type (material) of concrete that makes up the shaft 10 with their thermal conductivity may be stored in a computer, so that the thermal conductivity can be read out when the material is entered.

[0025] <Setting the expected temperature of flue gas> Furthermore, an assumed temperature tgs of the flue gas g passing through the flue 29 is set (step 102). The assumed temperature tgs is set, for example, in a temperature range of tgs = 35°C to 650°C, taking into consideration the type of flue gas discharge equipment 2, etc. A plurality of assumed temperatures tgs may be set at intervals of several degrees Celsius to several tens of degrees Celsius within the temperature range. The higher temperature within the temperature range may be set as the assumed temperature tgs.

[0026] <Calculating the expected shaft temperature> Based on the assumed temperature tgs of the flue gas g and the design heat transfer conditions a to i, the predicted temperatures of the inner and outer surfaces of the stack 20 and the shaft 10 at a predetermined height hs are calculated (step 103). Once the temperature of the flue gas g and the values ​​of the design heat transfer conditions a to i are determined, the internal temperature t of the chimney 20 can be calculated by applying the basic formula of heat conduction such as Fourier's law and the basic formula of heat convection such as Newton's law of cold. 22 , the outer surface temperature of the chimney 20 t 23 , the inner surface temperature t of the shaft 10 12 , the outer surface temperature t of the shaft 10 13 is obtained.

[0027] <Optimization process> Furthermore, the expected temperature t of the outer surface of the shaft 10 13 is the predetermined temperature t 13 s or less (t 13 ≦t 13 s), the optimum value of "b. Thermal conductivity of the chimney" or "c. thickness" among the design heat transfer conditions is found (step 104). That is, by selecting the material (or grade) of the heat insulating material that constitutes the main wall material 21 of the chimney 20 or changing the setting of the thickness of the main wall material 21, t 13 ≦t 13 There is no need to change the design of the building frame, such as the shaft 10.

[0028] <Judgment process> After the optimization process, i.e., when the thermal conductivity or thickness of the chimney 20 is set to the optimum value, the predicted air temperature t at the air outlet 15 15 (Step 105). 15 is the assumed temperature of the flue gas tgs, the cross-sectional shape and size of the chimney 20, the thermal conductivity of the chimney 20, the heat transfer coefficient between the chimney 20 and the ventilation layer 13, the heat transfer coefficient between the ventilation layer 13 and the shaft 10, the cross-sectional shape and size of the shaft 10, the thermal conductivity of the shaft 10, the outside air temperature (normal temperature), the height difference h from the air intake 14 to the air exhaust 15 13 It can be calculated using the thermal conduction and thermal convection equations that include the factor Preferably, in step 105, the expected air temperature t at the air outlet 15 when the expected temperature tgs of the flue gas g is set to the highest temperature within the temperature range is calculated. 15 It is preferable to calculate

[0029] Furthermore, the expected temperature difference (Δt 13 =t 15 -t 14 ) is calculated (step 106). 14 can be considered to be approximately equal to the external temperature, for example, t 14 Set the temperature within the range of 25℃ to 35℃.

[0030] Next, the height difference hs between the air intake 14 and the air exhaust 15 and the expected temperature difference Δt 13 , and the ventilation flow rate Q of the ventilation layer 13 based on the opening areas of the air intake 14 and the air exhaust 15. 13 is recalculated (step 107). And the calculated ventilation flow rate Q 13 The required ventilation flow rate Q 13 It is determined whether Q is equal to or greater than s (step 108). 13 ≧Q 13 If s, the set heat transfer conditions a to i are within the allowable range, and the chimney structure design can be deemed good. In other words, when the in-building chimney structure 3 is actually operated, the outer surface temperature of the shaft 10 can be kept within the allowable temperature range. This prevents the building 1 from becoming too hot due to the heat of the flue gas g.

[0031] <Re-optimization process> Q 13 13 When s, the chimney structure design is poor, so the thermal conductivity or thickness of the chimney 20 is set to "t 13 ≦t 13 By adjusting it again within the range where "s" is maintained, 13 ≧Q 13 s (steps 104 to 108).

[0032] <Opening area setting process> Only by adjusting the thermal conductivity or thickness of the chimney 20, 13 ≧Q 13 ​If it is difficult to set the opening area of ​​the air intake port 14 to s, the opening area of ​​the air exhaust port 15 may be changed. By changing at least one of the opening areas of the air intake 14 and the air exhaust 15, the ventilation flow rate of the ventilation layer 13 can be changed, and Q 13 ≧Q 13 s. There is no need to change the design of the building frame, such as the shaft 10.

[0033] <Realistic model of chimney structure inside a building> As shown in FIG. 3, the chimney 20A in an actual in-building chimney structure 3A is composed of multiple chimney units 25. These chimney units 25 are stacked one on top of the other. A chimney unit 25 is provided on each floor of the building 1. Each floor slab 5 of the building 1 is provided with a protruding portion 5b that protrudes into the shaft 10. Each chimney unit 25 is supported by the protruding portion 5b of the corresponding floor slab 5 via a support arm 26. The protruding portion 5b may also be used as an inspection passage for the chimney 20. The protruding portion 5b narrows the cross-sectional area of ​​the ventilation layer 13, forming an intermediate narrow portion 13c in the ventilation layer 13.

[0034] <Process for setting the flow path cross-sectional area of ​​the intermediate narrow section> Only by adjusting the thermal conductivity or thickness of the chimney 20, 13 ≧Q 13 s, or when adjusting the opening area of ​​the air intake 14 or the air exhaust 15 does not result in Q 13 ≧Q 13 If it is difficult to achieve Q s, the cross-sectional area of ​​the flow passage in the middle narrow section can be changed. 13 ≧Q 13 It may be set to s. For example, by adjusting the protrusion amount of the protrusion portion 5b, the ventilation flow rate of the ventilation layer 13 can be changed, and Q 13 ≧Q 13 It can be made to be s.

[0035] The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the invention. For example, the thermal conductivity or thickness of the chimney may be adjusted so that the temperature of the inner surface of the shaft 10 is equal to or lower than a predetermined temperature. The order of steps 101 and 102 can be changed as appropriate. By adjusting the thermal conductivity or thickness of the chimney 20, the opening area of ​​the air intake 14, the opening area of ​​the air exhaust 15, etc., the required ventilation flow rate Q 13 If it is difficult to obtain a ventilation flow rate of s or more, forced ventilation means such as a fan or blower for forcibly ventilating the ventilation layer 13 may be provided. [Industrial Applicability]

[0036] The present invention can be applied to chimney structures provided in buildings such as commercial buildings and factories. [Explanation of symbols]

[0037] g Flue gas 1. Building 2 Smoke exhaust equipment 3,3A In-building chimney structure 4 Gas inlet pipe 5 Floor slab 5b Protruding part 10 shaft 13 Ventilation layer 13c Middle narrow area 14 Air intake 15 Air exhaust port 20,20A Chimney 21 Main wall material 22 Inner surface material 23 Exterior material 25 Chimney unit 26 Support arm 29 Flue

Claims

1. A design method for a chimney structure in a building, comprising: a cylindrical shaft provided so as to extend vertically in a building; a chimney provided inside the shaft to form an air layer between the shaft and the chimney; an air intake port connected to a lower end of the air layer; and an air exhaust port connected to an upper end of the air layer, a setting step of setting design heat transfer conditions relating to the degree of steady heat transfer in the inward and outward directions at a predetermined height of the chimney structure inside the building; Calculating a predicted temperature of the outer or inner surface of the shaft at the predetermined height based on an assumed temperature of the flue gas passing through the chimney flue and the design heat transfer conditions; A design method for a chimney structure inside a building, characterized by comprising a step of determining the optimal value of the thermal conductivity or thickness of the chimney among the design heat transfer conditions so that the predicted temperature is below a predetermined temperature.

2. 2. The design method for a chimney structure inside a building according to claim 1, wherein in the setting step, the design heat transfer conditions are set to at least some of the following: the heat transfer coefficient between the exhaust gas passing through the flue inside the chimney and the inner surface of the chimney, the thermal conductivity of the chimney, the thickness of the chimney, the heat transfer coefficient between the outer surface of the chimney and the air in the ventilation layer, the required ventilation flow rate of the ventilation layer, the heat transfer coefficient between the air in the ventilation layer and the inner surface of the shaft, the cross-sectional shape and dimensions of the chimney and the shaft, the thermal conductivity of the shaft, and the thickness of the shaft.

3. In the setting step, a required ventilation flow rate of the ventilation layer is set as one of the design heat transfer conditions, Calculating an expected temperature difference between the air intake and the air outlet when the thermal conductivity or thickness of the chimney is set to the optimum value; calculating a ventilation flow rate of the ventilation layer based on the elevation difference between the air intake and the air exhaust port, the predicted temperature difference, and the opening areas of the air intake and the air exhaust port to obtain a ventilation flow rate calculation value of the ventilation layer; 3. The design method for a chimney structure in a building according to claim 1, further comprising determining whether the calculated ventilation flow rate is equal to or greater than the required ventilation flow rate.

4. A design method for a chimney structure inside a building as described in claim 3, characterized in that the opening area of ​​at least one of the air intake and air exhaust is set so that the calculated ventilation flow rate value is greater than or equal to the required ventilation flow rate.

5. A design method for a chimney structure inside a building as described in claim 3 or 4, characterized in that the flow path cross-sectional area of ​​the intermediate narrow section of the ventilation layer is set so that the calculated ventilation flow rate value is greater than or equal to the required ventilation flow rate.

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