Design Methods of Attachment Ventilation Systems

Abstract

This chapter expounds on a fundamental design principle, design methods, and case studies for attachment ventilation. The design flow charts are provided that describe the primary considerations required and detailed procedures when designing wall-attached air distribution for rooms (spaces) heating or cooling. A comparison of attachment, mixing, and displacement ventilation design methods are also presented. Lastly, the step-by-step design procedures of attachment ventilation systems for typical application scenarios are demonstrated, such as office buildings, exhibition halls, subway stations, and waiting halls of high-speed railway stations.

The primary goal of building ventilation is to provide occupants with clean air for breathing. Creating an appropriate indoor environment is vital for building designers, especially HVAC engineers. The essence of the attachment ventilation design is to clarify the airflow movement path for a given space and determine the air supply parameters (e.g., u₀, △t₀, etc.). Based on the established correlations of characteristic parameters of attachment ventilation in Chaps. 3 and 4, we are able to design attachment ventilation to remove “excessive” heat or pollutants efficiently to meet the demand of parameters in the control zone, which is the scientific connotation of ventilation.

This chapter expounds on fundamental design principles, design methods, and case studies for attachment ventilation. A comparison of attachment, mixing, and displacement ventilation design methods are also presented. Lastly, the step-by-step design procedures of attachment ventilation systems for typical application scenarios are demonstrated, such as office buildings, exhibition halls, subway stations, and waiting halls of high-speed railway stations.

6.1 Scope of Application of Attachment Ventilation Systems

6.1.1 Distinguishing Features of Attachment Ventilation Systems

As described in Sect. 4.4.2, the control zone is the volume of the room with a height of 2.0 m above the floor for human-oriented comfort air conditioning, while for industrial air conditioning, the control zone denotes the room-conditioned zone of the equipment or facilities. Distinguishing features of the attachment ventilation system are as follows.

• 1. Reduce primary investment and operating costs of ventilation and air conditioning systems. Attachment ventilation divides the indoor space into two significant parts: the control zone and the noncontrolled zone, aiming to ensure the control zone environment. In fact, the removed load for the control zone merely occupies part of the whole room load; hence it can remarkably reduce the indoor cooling/heating load and improves the ventilation efficiency. Correspondingly, it also reduces the energy consumption and costs of HVAC systems compared with mixing ventilation.

• 2. Solve the problem that displacement ventilation is not used to supply warm air to the occupied zone in the wintertime. For large spaces, like airport terminals, attachment ventilation can effectively supply a warm jet to the control zone in wintertime, overcoming the inherent defect that displacement ventilation is normally used for occasions where there is a cooling load.

• 3. Improve indoor air quality. The fresh air can reach the occupied zone first, so it delivers better air to the target control zone and benefits the building occupants’ health and well-being.

• 4. Save valuable workspace or occupied space. The attachment ventilation system is a kind of less-duct air supply system and is usually installed in the upper part of a room, avoiding occupying lower space or raising the floor (for the installation of displacement ventilation static pressure plenums and piping systems).

Therefore, to some extent, attachment ventilation has the merit of both traditional mixing and displacement ventilation by offering a lowering cooling or heating load on the demand side.

As every coin has two sides, if there are protruding obstacles on the wall surface or equipment nearby the jet-attached wall, attachment ventilation performance will be influenced by those existing obstacles.

6.1.2 Occupied Zone

As summarized above, attachment ventilation aims to eliminate the occupied zone’s cooling/heating load and provides an intended environment for the conditioned zone, the control zone, or the occupied zone. The occupied zone is between 0.1 and 2.0 m above the floor and more than 1.0 m from the attached wall, exterior walls/windows or fixed heating, ventilating, or air-conditioning equipment, and 0.5 m from the interior walls. The European Heating, Ventilation and Air Conditioning Association (REHVA) defines the scope of the occupied zone (REHVA 2002), see Table 6.1. The detailed boundaries of the occupied zone are defined as follows.

Table 6.1 Occupied zones

• 1. 1.0 m from the wall or column where air inlets or openings are contained.

• 2. 1.0 m from exterior walls, doors, and windows.

• 3. 0.5 m from the interior walls.

• 4. 0.1–2.0 m above the floor.

Figure 6.1 presents the occupied zone of the VWAV, RCAV, and CCAV, see the shaded area. It should be noted that the occupied zone can be changed according to the actual requirements.

Fig. 6.1

Occupied zone of attachment ventilation. a AWAV, b RCAV, c CCAV

6.1.3 Airflow Parameters and Diffusers in the Occupied Zone

According to related standards (GB/T 50155-2015, BS EN ISO 7730-2005, ANSI/ASHRAE Standard 55-2020, etc.), the following airflow parameters are derived for designing attachment ventilation.

• ① Occupied zone temperature difference t_0.1 − t_1.7 ≤ 4.0 °C for standing occupants, t_0.1 − t _1.1 ≤ 3.0 °C for sedentary occupants.

• ② Minimum air temperature at 0.1 m above the floor in the occupied zone t_0.1,min ≥ 19 °C for winter, t_0.1,min ≥ 21 °C for summer.

• ③ Air velocity in the occupied zone

  • For ordinary office and residential buildings, u_n ≤ 0.2 m/s for winter, u_n ≤ 0.3 m/s for summer.

  • Regard to temporary staying zones, e.g., railway stations, subway stations and airport terminals, etc., u_n ≤ 0.3–0.8 m/s; for industrial buildings, e.g., underground power plants, etc., u_n ≤ 0.2–0.8 m/s.

  • Air velocity in the control zone can also be determined according to the needs of production processes.

• ④ Control zone boundary jet velocity u_m,1.0

  • For ordinary offices, residential buildings, etc., u_m,1.0 ≤ 0.5 m/s.

  • For temporary staying zones, u_m,1.0 ≤ 1.0 m/s.

  • For industrial workshops, according to the needs of the industrial manufacture process.

  In addition, the following principles should be abided by when installing inlets and outlets of attachment ventilation:

  • The inlets or openings should not be laid on the exterior wall or the wall with a window.

  • There should not be protruding obstacles on the jet-attached wall.

6.2 Attachment Ventilation Design Procedure

The design process of attachment ventilation is to provide appropriate air supply parameters, such as air velocity, temperature, and air opening size, etc., on the premise of meeting the thermal comfort in the occupied zone or industrial processing requirements. The related design parameters are given in Fig. 6.2.

Fig. 6.2

Design parameters related to attachment ventilation

Based on the correlations establised in Chaps. 3 and 4, a design method of attachment ventilation has been developed. The design procedure is as follows.

• 1. Design parameters

• ① Determine air temperature t_d,1.1

Since t_n in the occupied zone depends mainly on the temperature at the height of 1.1 m above the floor, t_d,1.1 and t_n can be regarded as identical (Hu 2010).

• ② Determine vertical temperature gradient Δt_g in the occupied zone

The experiments and analysis show that the vertical temperature difference in the horizontal air reservoir region of the attachment ventilation is slightly small, and its temperature gradient is generally lower than that of the displacement ventilation (2.0 °C/m). Δt_g is generally taken as 1.0–1.5 °C/m for attachment ventilation.

• ③ Calculate the excessive heat Q_n within the occupied zone

Q_n is the actual excessive heat in the occupied zone, which is obtained by multiplying the whole room’s excessive heat Q by the heat distribution coefficient $m = \frac{{t_{{\text{n}}} - t_{0} }}{{t_{{\text{e}}} - t_{0} }}$. Here, m is the ratio of heat in the control zone (or the occupied zone) to the total heat in the whole room, i.e., m can be determined according to the interface height of thermal stratification (Zhao 2010), or from field tests and calculations. For large spaces with interface heights ranging from 5 to 20 m, m is generally taken from 0.50 to 0.85. For ordinary office rooms, when there is a lack of measurement data, m can be approximately taken as 0.70 (Lu 2007; Huang and Li 1999; Zou et al. 1983).

• ④ Determine the height of the slot inlet and outlet h, h_e, referring to the attached wall/column size.

• 2. Calculate exhaust air temperature t _e

  Calculate t_e from Eq. (6.1)

  $$t_{{\text{e}}} = t_{{{\text{d,1}}{.1}}} + {\Delta }t_{{\text{g}}} \left( {h_{{\text{e}}} - 1.1} \right)$$

  (6.1)

  • 3. Determine air supply temperature t₀

    Calculate t₀ from Eq. (6.2)

    $$t_{{0}} = t_{{{\text{d}},1.1}} - \frac{{1 + \kappa \left( {h_{{\text{e}}} - 1.1} \right)}}{1 - \kappa }\Delta t_{{\text{g}}}$$

    (6.2)

Determine the air supply dimensionless temperature increment near the floor (0.1 m away from the floor) from $\kappa = \frac{{t_{0.1} - t_{0} }}{{t_{{\text{e}}} - t_{0} }}$, which is related to indoor heat source types and locations. In general, for rooms with multiple type of heat sources, κ = 0.50 is recommended; for distributed heat sources, κ can be assumed to be 0.65 (Lu 2007).

For VWAV, κ can be taken as 0.55, and Eq. (6.2) becomes $t_{{0}} = t_{{{\text{d}},1.1}} - \left( {0.88 + 1.22h_{{\text{e}}} } \right)\Delta t_{{\text{g}}}$.

• 4. Derive the air supply velocity u₀

  Select the slot inlet width b (generally 0.03–0.15 m) and the length l. Hence, the inlet area F can be preliminarily obtained. Then, u₀ can be derived from the energy balance equation. It should be noted that the air supply velocity u₀ of warm air in wintertime should not be less than 2.0 m/s.

  $$u_{{0}} = \frac{{Q_{{\text{n}}} }}{{\rho \cdot c_{{\text{p}}} \left( {t_{{\text{n}}} - t_{{0}} } \right) \cdot F}}$$

  (6.3)

• 5. Check the air velocity at 1.0 m away from the vertical wall u_m,1.0

  Establish u_m,1.0 from Eqs. (6.4), (4.18), and (4.21)

  $$\frac{{u_{{\text{m}}} \left( {y_{\max }^{*} } \right)}}{{u_{0} }} = \frac{1}{{0.012\left( {\frac{{y_{\max }^{*} }}{b}} \right)^{1.11} + 0.90}}$$

  (6.4)
  $$y_{\max }^{*} = 0.92h - 0.43$$

  (4.18)
  $$\frac{{u_{{\text{m}}} \left( {y_{\max }^{*} } \right)}}{{u_{0} }} = k_{{\text{v}}} \frac{{u_{{{\text{m}},1.0}} }}{{u_{0} }} + C_{{\text{v}}}$$

  (4.21)

The coefficients k_v and C_v are related to types of attachment ventilation. k_v = 1.808, C_v = −0.106 for VWAV; k_v = 1.374, C_v = −0.060 for CAV.

If u_m,1.0 ≤ 0.5 m/s for office and residential buildings, or u_m,1.0 ≤ 1.0 m/s for temporary staying zones, such as waiting halls of high-speed railway stations, etc., the design requirements can be met. Otherwise, return to step (4) to reselect b and l.

• 6. Check the centerline air velocity u_m,x

  u_m,x at the end of the air reservoir x can be calculated from Eq. (3.44)

  $$\frac{{u_{{\text{m,x }}} }}{{u_{0} }} = \frac{0.575}{{C\left( {\frac{x}{b} + K_{{\text{h}}} } \right)^{1.11} + 1}}$$

  (3.44)

  where

  • C = shape factor, C = 0.0075 for vertical walls; C = 0.0180 for rectangular columns; C = 0.0350 for circular columns.

  • K_h = Correction factor, $K_{{\text{h}}} = \frac{1}{2}\frac{h - 2.5}{b}$ for vertical walls and rectangular columns; $K_{{\text{h}}} = \frac{1}{6}\frac{h - 2.5}{b}$ for circular columns.

When u_m,x ≤ 0.3 m/s (or u_n ≤ 0.3−0.8 m/s for the temporary staying zone), if the size of the wall or column can meet the demands of the total slot length, then the whole design procedure is completed. Otherwise, return to step (4) to reselect b and l.

The design procedure is summarized in the flow chart shown in Fig. 6.3.

Fig. 6.3

Design procedure flow chart for attachment ventilation

6.3 Adaptive Attachment Ventilation Design Procedure

Adaptive attachment ventilation with deflectors mode (AAV with deflectors) provides us with an “act according to actual circumstances” air distribution method for the scenarios with variable control zones. As described in Chap. 5, it is the deflector that leads the airflow directionally to the breathing zone or the control zone.

For comfort-oriented air conditioning, AAV with deflectors is generally applied to a medium space with a length of 3.0–5.0 m (horizontal jet throw direction). For a large space, the deflector height h₀ can be raised appropriately, see Fig. 6.4. The representative parameters of AAV are shown in Fig. 6.4.

Fig. 6.4

Design parameters of AAV

The design procedure of AAV is as follows.

• 1. Assume the value of b, h₀. For comfort-oriented air conditioning, h₀ = 1.1–1.7 m; for industrial process production, h₀ is determined according to the required control zone, and for b₀ = 0.2–0.6 m is recommended.

• 2. Determine the horizontal jet throw x′ = x − b₀ − 0.5, and the drop y = h₀ − 0.1.

• 3. Establish the Archimedes number Ar of air supply from Eqs. (6.5a, 6.5b) for given values of x′ and y.

  $$\frac{y}{b}{ = }Ar\left( {\frac{{x^{\prime}}}{b}} \right)^{2} \left( {0.51\frac{{ax^{\prime}}}{b} + 0.35} \right)$$

  (6.5a)

or

$$Ar = \frac{\frac{y}{b}}{{\left( {\frac{{x^{\prime}}}{b}} \right)^{2} \left( {0.51\frac{{ax^{\prime}}}{b} + 0.35} \right)}}$$

(6.5b)

where

x′:

 throw, the horizontal distance between the end of the deflector and the side-boundary of the control zone;

y:

 drop, the vertical distance between the deflector and the ground of the control zone, 0.1 m above the floor, see Fig. 6.4;

a:

turbulence coefficient of slot inlets, generally, 0.108 is taken for the flat inlet or derived by experiments.

 

• 4. Calculate the air supply temperature t₀ by Eq. (6.6).

$$t_{0} = t_{{\text{e}}} - \Delta t_{{{\text{oz}}}}$$

(6.6)

where △t_oz is the temperature difference between supply air and exhaust air, which is ascertained from the related design codes (△t_oz should be less than 10 ℃ for ordinary rooms with a height of 3.0–5.0 m). For AAV, t_e = t_n + (2–3 ℃).

• 5. Determine the air velocity u_s at the deflector by Eq. (6.7).

$$u_{{\text{s}}} = \sqrt {\frac{{gb\Delta t_{{\text{o}}} }}{{Ar\left( {t_{n} + 273} \right)}}}$$

(6.7)

The temperature difference between air supply and occupied zone Δt_o = t₀ − t_n, ℃;

• 6. Establish the jet centerline velocity u_m,x, and jet averaged velocity u_p by Eqs. (6.8a, 6.8b).

$$u_{{{\text{m}},{\text{x}}}} = u_{{\text{s}}} \frac{0.48}{{\frac{{ax^{\prime}}}{b} + 0.145}}$$

(6.8a)

$$u_{{\text{p}}} = 0.5u_{{{\text{m}},{\text{x}}}}$$

(6.8b)

u_p should meet the following requirements. In the control zone, u_p ≤ 0.2 m/s for winter, u_p ≤ 0.3 m/s for summer. Particularly, for the temporary staying zone as mentioned before, or industrial air-conditioning, u_p is determined according to the specific demands. Otherwise, b needs to be reassumed.

• 7. Calculate the air supply velocity u₀ by Eq. (6.9).

$$\frac{{u_{{\text{s}}} }}{{u_{0} }} = \frac{1}{{0.012\left( {\frac{{h - h_{0} }}{b}} \right)^{1.11} + 0.90}}$$

(6.9)

• 8. Derive l from the energy balance Eq. (6.10) for a given value of Q, and check whether the room wall size is satisfied or not. Additionally, the number of inlets can be adjusted according to the room size.

$$l = \frac{mQ}{{c_{{\text{p}}} \rho u_{0} b\Delta t_{{{\text{oz}}}} }}$$

(6.10)

The above design procedure is summarized in the flow chart shown in Fig. 6.5.

Fig. 6.5

Design procedure flow chart for AAV with deflectors

6.4 Comparison of Design Methods of Attachment, Mixing and Displacement Ventilation

Traditional mixing ventilation, displacement ventilation, as well as novel attachment ventilation are discussed and compared in this section.

• 1. Mixing ventilation

Mixing air distribution aims to dilute room pollutants with cleaner and cooler/warmer fresh air, to promote well mixing and uniform temperature and pollution distribution in the control zone. As shown in Fig. 6.6a, point P₁, where the flow passes the imaginary horizontal surface that defines the occupied zone (Nielsen 2007), represents the intersection between the jet centerline and the upper boundary line/surface of the occupied zone. To ensure thermal comfort in the occupied zone, the centerline velocity at the boundary should equal 2u_n, and the air supply temperature difference should be in the range of 5.0–10 °C for h ≤ 5.0 m for comfort-oriented air conditioning (Zhao 2008; GB50736). The mixing air distribution bears the cooling/heating load of whole rooms.

Fig. 6.6

Comparison of air distribution design scheme of a mixing ventilation, b displacement ventilation, c attachment ventilation

• 2. Displacement ventilation

Displacement ventilation has been used in industrial premises for many years, and it has also been used more extensively in non-industrial premises. To reach the same air quality in the occupied zone, displacement ventilation typically requires a lower airflow rate than mixing ventilation. As shown in Fig. 6.6b, point P₂ demonstrates the intersection point between the piston flow centerline and the lateral boundary line/surface of the occupied zone. The thermal comfort can be achieved by controlling the centerline velocity of about 0.25 m/s at P₂, the air supply temperature to be no less than 18 ℃, and the vertical temperature difference to be lower than 3.0 ℃ (GB50736; Nielsen 2007). Displacement ventilation is used in buildings with large occupancy and internal heat gains where mainly cooling is required (Awbi 2008). The air supply inlets/openings are usually mounted in the occupied zone, occupying the workspace. Unlike mixing ventilation, it only bears part of the cooling load of rooms.

• 3. Attachment ventilation

To overcome the inadequacy of mixing and displacement ventilation mentioned above, attachment ventilation has been developed. As shown in Fig. 6.6c, similar to points P₁ and P₂, point P₃ illustrates the intersection point between the wall-attached jet centerline and the boundary line/surface of the occupied zone. The ventilation and air conditioning design requirements can be met by controlling the centerline velocity at the lateral boundary of the occupied zone u_m,1.0 (1.0 m away from the jet-attached wall surface), and vertical temperature difference to be less than 3.0 ℃ in the occupied zone. It is recommended that u_m,1.0 ≤ 0.5 m/s for office and residential buildings, u_m,1.0 ≤ 1.0 m/s for temporary staying zones, or u_m,1.0 be determined according to design requirements. Similar to displacement ventilation, attachment ventilation only bears part of the room cooling/heating loads, so it is a high energy-efficiency ventilation mode.

The design principles and methods of mixing, displacement, and attachment ventilation are listed in Table 6.2.

Table 6.2 Comparison of air distribution design procedure of mixing ventilation, displacement ventilation and attachment ventilation

6.5 Case Study and Design of Attachment Ventilation Systems

In previous chapters, the semi-empirical correlations have been established by the author to predict the centerline velocity and temperature distribution, etc., characterizing attachment ventilation, which also helps to explain in a basic way room air movement. The essence of air distribution design is to guarantee the critical parameters in the occupied zone (control zone), such as air velocity, temperature, gradient, etc., to meet the design requirements. If the air distribution is designed inappropriately, there may be a draft sensation, and the air conditioning system’s energy consumption will be increased remarkably.

This section presents some typical engineering applications of attachment ventilation, including office buildings, exhibition halls, subways, and high-speed railway stations, and describes the air distribution design procedure.

6.5.1 Office Room

Typically, the air distribution design of office rooms is considered as a kind of comfort-oriented air conditioning design.

Take an air-conditioned office with dimensions of 4.0 m × 5.0 m × 3.5 m (length × width × height) as an example, the excessive heat Q of this room is 1.56 kW in summer. The schematic diagram of attachment air distribution is shown in Fig. 6.7.

Fig. 6.7

Schematic diagram of VWAV

The VWAV design procedure of the office is as follows.

• 1. Design parameters

  • ① Select t_d,1.1 = t_n = 26 ℃ (t_d,1.1 depends mainly on t_n);

  • ② Assume vertical temperature gradient Δt_g = 1.3 ℃/m (1.0–1.5 ℃/m is recommended, where 1.0 ℃/m for low heat dissipation, 1.5 ℃/m for high heat dissipation);

  • ③ Calculate excessive heat in the occupied zone by Q_n = mQ = 0.80 × 1.56 = 1.25 kW (Yuan et al. 1999);

  • ④ Assume heights of inlet and outlet, h = h_e = 3.5 m.

• 2. Calculate the exhaust air temperature t_e

  $$t_{{\text{e}}} = t_{{{\text{d,1}}{.1}}} + {\Delta }t_{{\text{g}}} \left( {h_{{\text{e}}} - 1.1} \right) = 26 + 1.3 \times \left( {3.5 - 1.1} \right) = 29.1\;^\circ {\text{C}}$$

• 3. Calculate the air supply temperature t₀

Determine the air supply dimensionless temperature rise near the floor (0.1 m above the floor) from $\kappa = \frac{{t_{0.1} - t_{0} }}{{t_{{\text{e}}} - t_{0} }} = 0.55$, then calculate t₀ from $t_{{0}} = t_{{{\text{d}},1.1}} - \left( {0.88 + 1.22h_{{\text{e}}} } \right)\Delta t_{{\text{g}}} = 26 - \left( {0.88 + 1.22 \times 3.5} \right) \times 1.3 = 19.3\;^\circ {\text{C}}$.

• 4. Calculate the air supply velocity u₀

Assume b = 0.05 m, l = 2.0 m, and F = b × l. Then calculate u₀ from $u_{{0}} = \frac{{Q_{{\text{n}}} }}{{\rho \cdot c_{{\text{p}}} \left( {t_{{\text{n}}} - t_{{0}} } \right) \cdot F}} = 1.55\,{\text{m/s}}$.

• 5. Check the air velocity at 1.0 m from the vertical wall u_m,1.0

  $$y_{\max }^{*} = 0.92h - 0.43 = 0.92 \times 3.5 - 0.43 = {2}{\text{.79}}\,{\text{m}}$$
  $$\frac{{u_{{\text{m}}} \left( {y_{\max }^{*} } \right)}}{{u_{0} }} = \frac{1}{{0.012\left( {\frac{{y_{\max }^{*} }}{b}} \right)^{1.11} + 0.90}} = 0.5$$
  $$0.5 = {1}.808\frac{{u_{{{\text{m}},1.0}} }}{{u_{0} }} - 0.106$$

u_m,1.0 = 0.55 m/s > 0.50 m/s, return to step (4) to reselect b and l, and the calculation process is as follows:

Firstly, assume b = 0.05 m, l = 3.0 m, so F = 0.15 m². Then, it can be calculated that u₀ = 1.03 m/s, u_m,1.0 = 0.34 m/s ≤ 0.5 m/s. In addition, u_m,x = 0.3 m/s, which meets the required of air velocity in the occupied zone. In this case, it is finally obtained design parameters including u₀ = 1.03 m/s, t₀ = 19.3 ℃, b = 0.05 m, l = 3.0 m, as shown in Fig. 6.8. Two slot inlets (1.5 m × 0.05 m) are evenly arranged along the length of the room.

Fig. 6.8

Design plan of VWAV of an office room (unit: m)

The air distribution of this office is simulated by CFD, and the results are shown in Fig. 6.9.

Fig. 6.9

Air distribution for VWAV of the office room. a Indoor air velocity contour, b indoor air temperature contour

6.5.2 Exhibition Hall

In this section, the VWAV air distribution design of an exhibition hall is conducted.

Take an exhibition hall with dimensions of 24.0 m × 16.0 m × 4.5 m (length × width × height) as an example, the ceiling height of the exhibition hall is 3.5 m. The excessive heat Q of this exhibition hall is 19.2 kW.

In this built space of the exhibition hall, vertical wall attachment air distribution is utilized. The following is the VWAV design procedure for the exhibition hall.

• 1. Design parameters

  • ① Select t_d,1.1 = t_n = 26 ℃ (t_d,1.1 depends mainly on t_n);

  • ② Assume vertical temperature gradient Δt_g = 1.2 ℃/m (take account of the disturbance of human activities on airflow, Δt_g takes a lower value);

  • ③ Calculate excessive heat in the occupied zone by Q_n = mQ = 0.8 × 19.2 = 15.36 kW;

  • ④ Assume the height of inlet and outlet, h = h_e = 3.5 m, which are the same as the ceiling height.

• 2. Calculate the exhaust air temperature t_e

  $$t_{{\text{e}}} = t_{{{\text{d}},1.1}} + \Delta t_{g} \left( {h_{{\text{e}}} - 1.1} \right) = 26 + 1.2 \times \left( {3.5 - 1.1} \right) = 28.9\,^\circ {\text{C}}$$

• 3. Calculate the air supply temperature t₀

Determine the air supply dimensionless temperature rise near the floor (0.1 m above the floor) from $\kappa = \frac{{t_{0.1} - t_{0} }}{{t_{{\text{e}}} - t_{0} }} = 0.55$, then calculate t₀ from $t_{{0}} = t_{{{\text{d}},1.1}} - \left( {0.88 + 1.22h_{{\text{e}}} } \right)\Delta t_{{\text{g}}} = 26 - \left( {0.88 + 1.22 \times 3.5} \right) \times 1.2 = 19.8\;^\circ {\text{C}}$.

• 4. Calculate the air supply velocity u₀

Assume b = 0.12 m, l = 18 m, and F = b × l. According to the building structure, slot inlets are mounted on the north and south walls, respectively, as shown in Fig. 6.10. Then calculate u₀ from $u_{0} = \frac{Q}{{\rho \cdot c_{{\text{p}}} \Delta t \cdot F}} = \frac{15.36}{{1.2 \times 1.004 \times 6.2 \times 2.16}} = 0.95\,{\text{m}}/{\text{s}}$.

Fig. 6.10

Design plan of VWAV of exhibition hall (unit: m)

• 5. Check the air velocity at 1.0 m from the vertical wall u_m,1.0

  $$y_{\max }^{*} = 0.92h - 0.43 = 0.92 \times 3.5 - 0.43 = 2.8$$
  $$\frac{{u_{{\text{m}}} \left( {y_{\max }^{*} } \right)}}{{u_{0} }} = \frac{1}{{0.012\left( {\frac{{y_{\max }^{*} }}{b}} \right)^{1.11} + 0.90}} = 0.77$$
  $$\frac{{u_{{\text{m}}} \left( {y_{\max }^{*} } \right)}}{{u_{0} }} = 1.808\frac{{u_{{{\text{m}},1.0}} }}{{u_{0} }} - 0.106$$

u_m,1.0 = 0.46 m/s < 0.50 m/s, which satisfied the reqirements.

• 6. Check the centerline velocity u_m,x at the end of the air reservoir x = 12 m

  $$\begin{aligned}{{u_{{\text{m,x }}} }} & = \frac{0.575u_0}{{0.0075\left( {\frac{x}{b} + \frac{1}{2}\frac{h - 2.5}{b}} \right)^{1.11} + 1}} \\ & = 0.24\,{\text{m/s}} < 0.3\,{\text{m/s}} \\ \end{aligned}$$

Considering that a number of doors and windows are set on the east and west walls of this exhibition hall, so the inlets are arranged on the north and south walls. However, there are fire safety doors on the top of north and south walls; consequently, the length of the slot inlets is not exactly equal. Finally, the outcome is as follows: four slot inlets of 3.5 m × 0.12 m, and two slot inlets of 2.0 m × 0.12 m, u₀ = 0.95 m/s, t₀ = 19.8 ℃, as shown in Fig. 6.10.

Both the velocity and temperature contours of the exhibition hall are simulated, and the results are shown in Fig. 6.11.

Fig. 6.11

Air distribution of exhibition hall from CFD simulation. a Velocity contour of I-I section, b temperature contour of I-I section

6.5.3 Subway Station

Different from airflow patterns in office rooms or exhibition halls mentioned in Sects. 6.5.1 and 6.5.2, for the platform and concourse of a subway station, there is a distinguishing feature that passengers usually stay temporarily in the platform and concourse for no more than 10 min. The acceptable air velocity for a temporary staying zone is no more than 0.5 m/s.

Take a subway station with dimensions of 105.0 m × 12.0 m × 6.35 m (length × width × height) as an example, as shown in Fig. 6.11, there are 10 rectangular structural columns uniformly spaced, and the distance between two adjacent columns l = 9.0 m. The RCAV is used, and the height of the slot inlets is 4.0 m. The excessive heat Q is 112 kW. As the station is symmetrical along the length direction, the half-width of the station hall is taken into account for the ventilation design, as shown in Fig. 6.12.

Fig. 6.12

Plan of the subway station (unit: m)

The RCAV design procedure of the subway station is as follows.

• 1. Design parameters

  • ① Select t_d,1.1 = t_n = 26 ℃ (t_d,1.1 depends mainly on t_n);

  • ② Assume vertical temperature gradient Δt_g = 1.3 ℃/m;

  • ③ Calculate excessive heat in the occupied zone by Q_n = mQ = 0.75 × 56 = 42 kW;

  • ④ Assume heights of inlet and outlet, h = h_e = 4.0 m;

  • ⑤ The size of rectangular columns is 1.5 m × 1.1 m (length × width), 5 in total.

• 2. Calculate the exhaust air temperature t_e

  $$t_{{\text{e}}} = t_{{{\text{d}},1.1}} + \Delta t_{g} \left( {h_{{\text{e}}} - 1.1} \right) = 26 + 1.3 \times \left( {4.0 - 1.1} \right) = 29.8\,^\circ {\text{C}}$$

• 3. Calculate the air supply temperature t₀

Determine the air supply dimensionless temperature rise near the floor (0.1 m above the floor) from $\kappa = \frac{{t_{0.1} - t_{0} }}{{t_{{\text{e}}} - t_{0} }} = 0.55$, then calculate t₀ from $t_{{0}} = t_{{{\text{d}},1.1}} - \left( {0.88 + 1.22h_{{\text{e}}} } \right)\Delta t_{{\text{g}}} = 26 - \left( {0.88 + 1.22 \times 4.0} \right) \times 1.3 = 18.5\,^\circ {\text{C}}$.

• 4. Calculate the air supply velocity u₀

Assume b = 0.03 m, the number of columns is 5, and the total area of inlet F = 0.80 m². Then calculate u₀ from $u_{0} = \frac{Q}{{\rho \cdot c_{{\text{p}}} \left( {t_{{\text{n}}} - t_{0} } \right) \cdot F}} = \frac{42}{{1.2 \times 1.004 \times 7.5 \times 0.8}} = 5.81\;{\text{m/s}}$.

• 5. Check the air velocity at 1.0 m from the vertical wall u_m,1.0

  $$y_{\max }^{*} = 0.92h - 0.43 = 0.92 \times 4 - 0.43 = 3.25\;{\text{m}}$$
  $$\begin{aligned} \frac{{u_{{\text{m}}} \left( {y_{\max }^{*} } \right)}}{{u_{0} }} & = \frac{1}{{0.012\left( {\frac{{y_{\max }^{*} }}{b}} \right)^{1.11} + 0.90}} \\ & = \frac{1}{{0.012 \times \left( {\frac{3.25}{{0.03}}} \right)^{1.11} + 0.90}} = 0.33 \\ \end{aligned}$$
  $$\frac{{u_{{\text{m}}} \left( {y_{\max }^{*} } \right)}}{{u_{0} }} = 1.374\frac{{u_{{{\text{m}},1.0}} }}{{u_{0} }} - 0.060$$

u_m,1.0 = 1.63 m/s > 1.00 m/s, return to step (4) to reselect b, and the calculation process is as follows:

Assume b = 0.1 m, l = 3.0 m, so F = 2.8 m², u₀ = 1.67 m/s. We obtain u_m,1.0 = 0.89 m/s < 1.00 m/s, which meets the air velocity requirements in the occupied zone.

• 6. Check the centerline velocity u_m,x at the end of the air reservoir x = 7.5 m

  $$u_{{\text{m,x }}} = \frac{{0.575u_{0} }}{{0.018\left( {\frac{x}{b} + \frac{1}{2}\frac{h - 2.5}{b}} \right)^{1.11} + 1}} = 0.28\;{\text{m/s}}$$

u_m,x < 0.8 m/s, the air velocity at the end of the temporary staying zone of the subway station is satisfied, and the procedure is completed.

In this case, it is finally derived that u₀ = 1.67 m/s, t₀ = 18.5 ℃, b = 0.10 m, F = 2.8 m², as shown in Figs. 6.13 and 6.14.

Fig. 6.13

Layout of the air supply system (unit: m)

Fig. 6.14

Section of air duct system of RCAV

6.5.4 Waiting Hall of High-Speed Railway Station

High-speed railway is an important urban infrastructure and transportation hub. Take the waiting hall of a high-speed railway station with dimensions of 200.0 m × 90.0 m × 13.8 m (length × width × height) as an example, the excessive heat Q is 1476 kW. The RCAV is applied to the waiting hall with 24 ventilation-columns, whose size is 3.0 m × 3.0 m × 4.0 m (length × width × height), and the installation height of slot inlets is 4.0 m from the ground, as shown in Fig. 6.15.

Fig. 6.15

Design for attachment ventilation, high-speed railway station waiting hall. a Plan of the waiting hall, b schematic diagram of the ventilation column, c plenum chamber and slot inlet, d ventilation column with top circular openings for the far zone, slots for the near zone, e application of RCAV in Xiong’an high-speed railway station

The RCAV design procedure for the high-speed railway station waiting hall is as follows.

• 1. Design parameters

  • ① Select t_d,1.1 = t_n = 26 ℃ (t_d,1.1 depends mainly on t_n);

  • ② Assume vertical temperature gradient Δt_g = 1.3 ℃/m;

  • ③ Calculate excessive heat in the occupied zone by Q_n = mQ = 1476 × 0.5 = 738 kW;

  • ④ Assume heights of inlet and outlet, h =h_e = 4.0 m;

  • ⑤ The size of rectangular columns is 3.0 m × 3.0 m × 4.0 m (length × width × height), 24 in total.

• 2. Calculate the exhaust air temperature t_e

  $$t_{{\text{e}}} = t_{{{\text{d}},1.1}} + \Delta t_{{\text{g}}} \left( {h_{{\text{e}}} - 1.1} \right) = 26 + 1.3 \times \left( {4.0 - 1.1} \right) = 29.8\,^\circ {\text{C}}$$

• 3. Calculate the air supply temperature t₀

Determine the air supply dimensionless temperature rise near the floor (0.1 m above the floor) from, $\kappa = \frac{{t_{0.1} - t_{0} }}{{t_{{\text{e}}} - t_{0} }} = 0.55$, then calculate t₀ by $t_{{0}} = t_{{{\text{d}},1.1}} - \left( {0.88 + 1.22h_{{\text{e}}} } \right)\Delta t_{{\text{g}}} = 26 - \left( {0.88 + 1.22 \times 4.0} \right) \times 1.3 = 18.5\;^\circ {\text{C}}$.

• 4. Calculate the air supply velocity u₀

Assume b = 0.18 m, the number of columns is 24, and the total area of inlet F = 54.95 m². Then calculate u₀ from $u_{0} = \frac{Q}{{\rho \cdot c_{{\text{p}}} \left( {t_{{\text{n}}} - t_{0} } \right) \cdot F}}{ = }\frac{738}{{1.2 \times 1.004 \times 7.5 \times 54.95}} = 1.49\;{\text{m/s}}$.

• 5. Check the air velocity at 1.0 m from the vertical wall u_m,1.0

  $$y_{\max }^{*} = 0.92h - 0.43 = 0.92 \times 4.0 - 0.43 = 3.25\;{\text{m}}$$
  $$\begin{aligned} \frac{{u_{{\text{m}}} \left( {y_{\max }^{*} } \right)}}{{u_{0} }} & = \frac{1}{{0.012\left( {\frac{{y_{\max }^{*} }}{b}} \right)^{1.11} + 0.90}} \\ & = \frac{1}{{0.012 \times \left( {\frac{3.25}{{0.10}}} \right)^{1.11} + 0.90}} = 0.83 \\ \end{aligned}$$
  $$\frac{{u_{{\text{m}}} \left( {y_{\max }^{*} } \right)}}{{u_{0} }} = 1.374\frac{{u_{{{\text{m}},1.0}} }}{{u_{0} }} - 0.060$$

u_m,1.0 = 0.97 m/s < 1.00 m/s, which satisfies the requirement.

• 6. Check the centerline velocity u_m,x at the end of the air reservoir x = 25 m

  $$u_{{\text{m,x }}} = \frac{{0.575u_{0} }}{{0.018\left( {\frac{x}{b} + \frac{1}{2}\frac{h - 2.5}{b}} \right)^{1.11} + 1}} = 0.16\;{\text{m/s}}$$

u_m,x < 0.8 m/s, the air velocity at the end of the temporary staying zone of the high-speed railway station waiting hall is satisfied, and the procedure is completed.

In this case, it is finally determined that u₀ = 1.49 m/s, t₀ = 18.5 ℃, b = 0.18 m, F = 54.95 m².

The air distribution of this waiting hall of high-speed railway station is simulated by CFD, and the results are shown in Fig. 6.16.

Fig. 6.16

Air distribution of high-speed railway station waiting hall. a Air velocity distribution, b temperature distribution