Adaptive Attachment Ventilation with Deflectors

Abstract

This chapter mainly expounds on the principle of adaptive attachment ventilation (AAV), which is beneficial for directionally delivering fresh air or cold/warm air to the breathing zone or occupied zone with a deflector. The appropriate setting of deflectors can effectively improve ventilation efficiency. The deflector forms and installation height are analyzed, which directly influences ventilation effectiveness. In contemporary architectural engineering, especially in some symbolic modern architectural styles, the wall structure often adopts circular arc, elliptical and inclined wall forms. Hence, curved surface attachment ventilation is proposed, and its airflow patterns are discussed. Moreover, the attachment ventilation modes applied to some particular spaces, such as the concave corner attachment ventilation, are briefly introduced.

The point of departure for designing attachment ventilation airflow distribution is to ensure that the air temperature and velocity, etc., in the occupied zone or control zone with excessive heat meet the requirements of hygiene and human comfort. In most cases, the control zone occupies only a tiny portion of the room volume and height. The percentage of zones of control in residential and office buildings is 40–60%, while the percentage of zones of control in industrial workshops is only 10–30%. The appropriate air distribution created by attachment ventilation can allow the entire room space to divide into the control zone and the noncontrolled adjacent zone. By removal of the excessive heat in the occupied zone, the total energy consumption of the built environment control system is reduced accordingly.

This chapter mainly expounds on the principle of adaptive attachment ventilation (AAV). AAV denotes the ventilation mode in which the discharge jet moves downwards to the deflector and is then directionally distributed or injected into the target control zone by a deflector or a guide plate. By AAV, cooling air can be directly delivered to the human breathing zone or the conditioned zone. The deflector forms and installation height are analyzed, which directly influences ventilation effectiveness.

In contemporary architectural engineering, especially in some symbolic modern architectural styles, the wall structure often adopts circular arc, elliptical and inclined wall forms. Hence, curved surface attachment ventilation is proposed, and its airflow patterns are discussed. Moreover, the attachment ventilation modes applied to some particular spaces, such as the concave corner attachment ventilation, are briefly introduced.

5.1 Adaptive Attachment Ventilation for Breathing Zone

As mentioned earlier, the indoor occupied zone (control zone) is only a part of the whole internal space, which are usually the zone people live in or industrial manufacture. In some instances, those control zones need to be adjusted frequently according to different scenarios. Variable control zone refers to the zone where the control zone can be adjusted when industrial and agricultural production activities changes. AAV for the breathing zone or target zone is an effective air supply mode applicable to the control zone (Li et al. 2019), see Fig. 5.1.

Fig. 5.1

Schematic diagram for AAV with deflectors. a Air supply for human’s occupied zone (breathing zone), b air supply for facility agriculture plant growth zone, c air supply for animal’s breathing zone

5.1.1 Deflector Forms

Generally, deflectors’ shape, width, installation height, etc., will directly impact the airflow movement in the occupied zone. Taking an operation room in a hospital as a case study, we analyze the influence of deflector forms on AAV (Li et al. 2016). As indicated in REHVA Guidebook—Displacement Ventilation, the breathing zone refers to the zone within 1.1 m (sedentary occupant) or 1.7 m (standing occupant) away from the floor. As shown in Fig. 5.2, the room size is 3.6 m × 4.2 m × 2.7 m, and the slotted tuyere size is 1.2 m × 0.05 m, with a desk and staff inside. As a case study, two deflectors, i.e., horizontal deflector and circular arc deflector, are applied, see Fig. 5.2. See Table 5.1 for detailed parameters.

Fig. 5.2

Forms and layouts of two types of deflectors. a Horizontal deflector, b circular arc deflector, c front view of the horizontal deflector, d front view of the circular arc deflector

Table 5.1 Structural forms and air supply parameters of deflectors

The deflector structure, such as the deflector width b₀, will have a direct impact on air jet motion. The airflow movement velocity and temperature distribution in the room’s central cross-section (z = 2.1 m) are shown in Figs. 5.3 and 5.4.

Fig. 5.3

Velocity and streamline distribution created by AAV with different deflector forms. a Horizontal deflector, b circular arc deflector, c velocity field with streamline of circular arc deflector

Fig. 5.4

Indoor temperature field affected by deflectors (air supply temperature is 16 ℃). a Horizontal deflector, b circular arc deflector

Horizontal deflector

As shown in Fig. 5.3, the horizontal deflector is located in the middle of the left-side wall, 1.1 m away from the floor. The discharged jet moves downward along the vertical wall surface, impinges on the deflector, and turns its direction. So, the air jet dominated by the horizontal deflector can remain inertial motion in the horizontal direction. The desk, as an obstacle, affects the airflow movement, causing some airflow to flow obliquely downward; the other part of the horizontal flow is induced by the thermal plume generated by the human body, showing upward movement with a velocity of approximately 0.2 m/s.

Circular arc deflector (radius 0.2 m, 1/4 circular arc)

Similarly, the circular arc deflector can directionally deliver the airflow to the occupied zone or control zone. As we can see from the velocity field and airflow pattern of Fig. 5.3b, c, the airflow approaches the human body’s vicinity through inertial motion, resulting in large vortex recirculation in the upper space of the room. The airflow velocity around the human body and ankle (y = 0.1 m) is about 0.3 m/s.

Figure 5.4 shows the room temperature field distribution of two deflector forms. Comparing horizontal and circular arc deflectors, the former’s airflow temperature in the human breathing zone is 1.0–2.0 ℃ lower than that of the latter, which is attributed to different deflectors’ inertia effects. For a horizontal deflector, the breathing zone of a human is located within the air supply jet zone. Under the same air supply conditions, the horizontal deflector can achieve a longer horizontal jet throw.

Deflector width

The deflector width b₀ will directly affect the flow field. As noted in Sect. 5.1.1, while the deflector width increases, the inertial momentum retention is enhanced for the airflow moving along the horizontal direction after impinging the deflector. The velocity and temperature fields in the room’s central cross-section (z = 2.1 m) with different deflectors’ widths (0.2, 0.4, and 0.6 m) are presented in Figs. 5.5 and 5.6.

Fig. 5.5

Air age and indoor flow field under different deflector-width b₀. a b₀ = 0.2 m, b b₀ = 0.4 m, c b₀ = 0.6 m, d air age (b₀ = 0.4 m)

Fig. 5.6

Indoor airflow temperature field with different deflector-width. a b₀ = 0.2 m, b b₀ = 0.4 m, c b₀ = 0.6 m

When the deflector width becomes narrower (such as 0.2 m), the airflow can drop down at the edge of the deflector earlier, as shown in Fig. 5.5a. With the increase of the deflector width from 0.4 to 0.6 m, the inertial motion retention of the airflow along the horizontal direction is further enhanced. The air age reflects the freshness of indoor air to some extent, see Fig. 5.5d.

More details can be derived in Fig. 5.6. Comparing the temperature field with different deflector widths from 0.2 to 0.6 m, it is found that the air temperature in the breathing zone decreases by about 1.0–2.0 ℃ successively. The wider the deflectors, the more inclined the airflow stratification to a certain extent (Zou et al. 1983).

In engineering applications, it is recommended to utilize a horizontal deflector with width b₀ = 0.4–0.6 m to achieve better supply airflow distribution in the breathing zone. When the deflector width exceeds 0.6 m, it may occupy a larger room space. In this case, the deflector can be made folding to occupy less space.

5.1.2 Installation Height of Deflectors

First of all, the orientation of the deflector relative to the direction of incoming jet flow has a significant influence on the control zone’s flow field. Figure 5.7 shows the indoor velocity field distribution corresponding to the heights of three different deflectors (1.1, 1.3, and 1.5 m). Similar to the air reservoir flow field created by the VWAV, Fig. 5.8 demonstrates the indoor temperature stratification phenomena. For the breathing zone, it is recommended that the installation height of deflectors be in the range of 1.1–1.7 m from the floor. It should be pointed out that a deflector can also be installed or fixed at any location as required. In this scenario, the airflow pattern may be different from the above-mentioned.

Fig. 5.7

Heights of deflectors influencing indoor airflow movement (deflector width 0.4 m). a h₀ = 1.1 m, b h₀ = 1.3 m, c h₀ = 1.5 m

Fig. 5.8

Temperature field with different deflector heights (deflector width 0.4 m). a h₀ = 1.1 m, b h₀ = 1.3 m, c h₀ = 1.5 m

5.1.3 Deflector Application

Adaptive attachment ventilation (AAV) with deflectors is used in office buildings, industrial fields, facility agriculture, animal husbandry, and other occasions. Taking the ordinary train compartment as an example (3.1 m × 3.0 m × 2.5 m), the attachment air distribution can be utilized, and air slots are located at both sides of the compartment ceiling, with the slot size of 3.0 m × 0.1 m. The deflectors are installed 2.0 m away from the floor, at an angle of 30° with the sidewalls. The exhaust outlets are located on the lower parts of two sidewalls, with a size of 0.4 m × 0.2 m, as shown in Fig. 5.9.

Fig. 5.9

AAV compartment deflectors. a Compartment physical model, b schematic diagram of AAV in the compartment

For AAV with deflectors, the air supply at a temperature of 20 ℃, a velocity of 1.0 m/s, the floor and wall loads are 120 W/m² and 80 W/m², respectively. The air velocity and temperature contours are shown in Fig. 5.10. In compartments with air distribution, the concern about thermal comfort mainly focuses on draught at the neck and discomfort due to the directly blowing airflow. The ceiling corner-mounted slots could be regarded as two wall-attached air supply modes with regard to the length of the control zone. The deflectors make the discharge flow deflected from the sidewalls to avoid draught risk at the neck of the human body, see Fig. 5.10.

Fig. 5.10

Airflow velocity and temperature distribution in the compartment (t₀ = 20 ℃, u₀ = 1.0 m/s). a Velocity distribution, b temperature distribution

5.2 Curved Surface Attachment Ventilation

Normally, a building has two duties to fulfill: protecting man from adverse elements and providing a comfortable environment for him to work and live in. John Ruskin once asked the question: “Can anything be beautiful as well as functional?”. It is suggested a building performing its duties should also enhance its aesthetic quality (Croome and Roberts 1981). In modern architecture, there are a number of curved and inclined-wall structures. These special-shaped structural forms combine architects’ inspiration, aesthetics, environment, function, structure, and other factors. However, regarding the built environments with these special-shaped structural forms, creating a comfortable environment is a challenging task for HVAC engineers. This section deals with the problems of curved or inclined surface attachment ventilation airflow movement.

The functionally curved surfaces of various buildings could be described by mathematical functions such as spherical, ellipsoidal, cylindrical, conical, and other regular surfaces. For instance, among the curved surfaces, the fastest descent curve surface is the brachistochrone surface, i.e., the curved cycloid surface proposed by Galileo, as shown in Fig. 5.11. Newton and Leibniz first presented their analytical Eq. (5.1)

$$x = r \times \left( {\varphi - {\text{sin}}\varphi } \right);\quad y = r \times \left( {{1} - {\text{cos}}\varphi } \right)$$

(5.1)

Fig. 5.11

Coordinates representation of brachistochrone

where r indicates the radius of a circle, m; φ indicates the radian (rolling angle) of the radius of a circle, rad.

In this section, we take the curved surface of brachistochrone as a case study (Yang 2017; Li et al. 2019). As shown in Fig. 5.12, the room area is 5.4 m × 7.0 m, and the height is 2.5 m. The slot size is 2.0 m × 0.05 m, and an air inlet of 0.3 m × 0.3 m is used. The centerline velocity and temperature distribution of curved surface attachment ventilation are illustrated below under isothermal or nonisothermal air supply conditions with different curvatures (0.236–0.436 m⁻¹).

Fig. 5.12

Curved surface attachment ventilation. a Schematic diagram of curved surface attachment airflow distribution, b airflow patterns, c room structure and slot layout

5.2.1 Isothermal Curved Surface Attachment Ventilation

With regarding to the brachistochrone curved surface, the indoor air flow fields with different curvatures and air supply velocities are investigated. See Table 5.2 for different cases, the velocity field distribution is shown in Fig. 5.13.

Table 5.2 Parameters of isothermal curved surface attachment ventilation

Fig. 5.13

Curved surface attachment ventilation velocity field with different curvatures (u₀ = 2.0 m/s). a Curvature 0.236, b curvature 0.336, c curvature 0.436

Although the curvatures of the three cases are quite different, the airflow patterns in the curved surface attachment region behave similarly. All three cases can form air reservoir distribution in the occupied zone, as shown in Fig. 5.13. It is found that the air reservoir thickness is about 0.4 m, which can effectively deliver fresh air or cool/warm air to the occupied zone without causing drafts to people. It is worth noting that, compared to a vertical wall attached jet, the airflow attached to the curved surface may move forward more smoothly along the floor than that attached to a vertical wall, without resulting in the large vortex from the jet impinging on the floor. Hence, the curved surface attachment ventilation can achieve a minor momentum loss, a greater centerline velocity, and a larger energy efficiency, as shown in Fig. 5.14b.

Fig. 5.14

Centerline velocity of curved surface attachment ventilation with different curvatures (curved surface 1: curvature 0.236; curved surface 2: curvature 0.336; curved surface 3: curvature 0.436). a Centerline velocity in the wall attachment region, b centerline velocity in the air reservoir region

The influence of curvatures on the air supply centerline velocity is shown in Fig. 5.14. The centerline velocity distributions demonstrate a consistent attenuation tendency along the curved surface attachment region. With curvature further increasing, the centerline velocity attenuation of both vertical and horizontal attachment regions increases slightly, and the amplitude of variation is less than 10% in the range of 0.236–0.436 m⁻¹ of curvature.

5.2.2 Nonisothermal Curved Surface Attachment Ventilation

The work carried out in a curved surface attachment ventilation room has been compared the patterns of air movement and temperature distribution resulting from different surface curvatures. Detailed parameters can be found in Table 5.3. Taking the curve surface of brachistochrone with curvature of 0.336 m⁻¹ as an example, the indoor temperature distribution of nonisothermal curved surface attachment ventilation is shown in Fig. 5.15.

Table 5.3 Nonisothermal curved surface attachment ventilation parameters

Fig. 5.15

Indoor temperature distribution, nonisothermal curved surface attachment air supply (curvature 0.336 m⁻¹). a t₀ = 17 ℃, u₀ = 2.0 m/s, b t₀ = 21 ℃, u₀ = 2.0 m/s, c t₀ = 21 ℃, u₀ = 1.0 m/s

• 1. Indoor temperature field

When the indoor cooling load remains constant, the room temperature fields formed by different air supply temperatures and velocities are shown in Fig. 5.15. There is a significant vertical temperature stratification in the ventilation room, whereas the temperature remains almost uniform over the entire occupied zone. In addition, the maximum temperature gradient does not exceed 3.0 °C, which meets the comfort requirements of the temperature gradient between the head and ankle levels.

When the air supply temperature further rises (Fig. 5.15a, b), the indoor air temperature increases correspondingly; in other words, both temperature rises are almost identical.

The jet discharge velocity will significantly affect the indoor vertical temperature stratification. Compared with Fig. 5.15b, c, the smaller the air supply velocity, the more significant the vertical temperature stratification, quite similar to displacement ventilation.

• 2. Centerline excess temperature distribution

The curvature of a wall has little effect on the centerline temperature distribution, as shown in Fig. 5.16. For the curved surface attachment region, there are no much differences in excess temperature during the initial section, 0 ≤ y^*/b ≤ 10. When y^*/b > 10, the centerline excess temperature of the curved surface attachment region at a lower air supply velocity is less than that at a higher air supply velocity (such as u₀ = 1.5 and 2.0 m/s). It indicates that more attention should be paid to selecting the appropriate air supply velocity in designing curved surface attachment ventilation.

Fig. 5.16

Excess temperature, nonisothermal curved surface attachment air supply (curvature 0.336 m⁻¹). a Curved surface attachment region, b horizontal air reservoir region

Similar to VWAV, for the horizontal air reservoir region, the centerline excess temperature attenuates exponentially with the jet throw, which is the distance from the centerline of an air opening perpendicular to a point in the airstream where the velocity has been reduced to a specified terminal velocity (e.g., 0.25 m/s).

The curvature variation has little effect on the air movement in the occupied zone. It should be noted that the conclusion derived from the brachistochrone curved surface attachment ventilation with the curvatures of 0.236–0.436 m⁻¹ might also be applicable to other types of curved surface attachment ventilation. Special-shaped structural forms or curved surfaces are often encountered for commercial or industrial buildings, including circular arc, elliptical arcs, brachistochrone surfaces, etc. For ordinary rooms, at the same height, there is virtually no remarkable curvature difference; see Fig. 5.17.

Fig. 5.17

Three kinds of curved surfaces with equal height (curvature 0.336 m⁻¹)

• 3. Inclined wall attachment ventilation

An inclined wall can be regarded as a particular case of curved surface. See Fig. 5.18 for indoor airflow distribution of inclined wall attachment ventilation. The discharge air moves along the inclined wall and downwards to the floor, then gently turns to a horizontal direction, and spreads forward over the floor, forming an air reservoir in the occupied zone with a vertical temperature stratification.

Fig. 5.18

Diagram for inclined wall attachment ventilation. a Slope wall, b schematic diagram of inclined wall attachment airflow distribution

In the wintertime, it is worth noting that for a thermal wall-attached jet, the smaller the slope angle β, the more unfavorable for the thermal jet to reach the occupied zone, which means more air supply momentum (or jet discharge velocity) could be needed for small β, as shown in Fig. 5.19. For ordinary residential or office rooms, the velocity of warm air supply should not be less than 2.0–3.0 m/s so as to ensure that the warm air is supplied to the occupied zone in wintertime.

Fig. 5.19

Effect of inclination angle on the indoor velocity field. a β = 45°, u₀ = 2.0 m/s, b β = 45°, u₀ = 3.0 m/s, c β = 75°, u₀ = 2.0 m/s, d β = 75°, u₀ = 3.0 m/s

5.3 Some Applications of Attachment Ventilation

5.3.1 Tiny Interior Spaces

In addition to being used in large spaces, attachment ventilation has also been used more and more in some tiny spaces. Often the cooling systems are installed in particular rooms, such as crane control rooms and subway carriages, to remove excessive heat from the room. The interior spaces are pretty compact and occupied by facilities. An appropriate air distribution design is required to ensure its internal air environment and thermal comfort.

This section briefly discusses several air supply modes suitable for tiny spaces, such as impinging side-wall attachment ventilation (Fig. 5.20a), concave corner attachment ventilation (Fig. 5.20b), and impinging-ceiling attachment ventilation (Fig. 5.20c).

Fig. 5.20

Airflow distribution modes for particular spaces. a Impinging side-wall attachment ventilation, b concave corner attachment ventilation, c impinging-ceiling attachment ventilation

For the air distribution of those particular spaces mentioned above, air supply modes, such as impinging side-wall attachment, concave corner attachment, and impinging-ceiling attachment ventilation, etc., can be used. For impinging side-wall attachment ventilation (Fig. 5.20a), two air openings are mounted at the both sides of the ceiling. The discharge air jet is attached to the ceiling and reaches both sidewalls, then downwards further to the bottom and spreads at a low velocity, creating a uniform thermal environment.

For concave corner attachment ventilation (Fig. 5.20b), its features lie that two air jets are supplied separately from the plenum opening fixed at the ceiling, and move downwards along the intersection line of adjacent sidewalls, impinging on the floor. This mode almost behaves the same air distribution as the impinging side-wall attachment ventilation with a smaller air discharge velocity.

With regard to impinging-ceiling attachment ventilation (Fig. 5.20c), it is characterized by:

Air jet upward impinges on the ceiling → move along the ceiling → impinge on both sidewalls → turn direction and flow downwards to the floor. The indoor velocity and temperature fields of those three kinds of air supply modes are shown in Figs. 5.21 and 5.22.

Fig. 5.21

Indoor velocity field of three air supply modes (u₀ = 1.0 m/s, t₀ = 23 °C). a Impinging side-wall attachment, b concave corner (internal corner) attachment, c impinging-ceiling attachment

Fig. 5.22

Indoor temperature fields of three air supply modes (u₀ = 1.0 m/s, t₀ = 23 °C). a Impinging side-wall attachment, b concave corner (internal corner) attachment, c impinging-ceiling attachment

Comparing the three air supply modes mentioned above, at the same air supply velocity, the averaged velocity in the occupied zone is 0.20 m/s, 0.25 m/s, and 0.10 m/s, respectively, see Fig. 5.22. This indicates that the air opening’s installation position significantly affects the air distribution for those particular spaces and others.

5.3.2 Some Applications to Particular Spaces

More specialized attachment ventilation modes have been developed, as also shown in Fig. 5.23 (Li and Li 2016; Reese 2005; Li et al. 2011, 2012; Yin et al. 2018). For instance, the floor-based air distribution with a novel mushroom diffuser is presented in Fig. 5.23a. The horizontal airflow with the air velocity of 0.2–0.5 m/s is supplied from the bottom of seats, moves forward along the floor, and alters its direction after impinging on adjacent steps, which is suitable for theaters and conference rooms, etc.

Fig. 5.23

Schematic diagrams for some special attachment ventilation applications. a Floor-based air distribution with a novel mushroom diffuser, b horizontal-impinging attachment, c inclined-impinging attachment, d floor-impinging attachment created by circular opening arrays, e ventilation columns are set up in a large space to achieve zone control by attachment ventilation for the near zone and longitudinal jet ventilation for the far zone, f attachment ventilation for industrial muti-span buildings, g adaptive attachment ventilation with a deflector for isolation wards of hospitals, h attachment ventilation for ducted-type air conditioner

The horizontal-impinging attachment and inclined-impinging attachment modes are shown in Fig. 5.23b, c. They are applicable to indoor air environment control for certain confined spaces. Its typical feature is that the jet from the air ducts at any angle direction “sticks” on the surface and spreads along the wall. At an angle of $\theta = 90^\circ$, the spread of the air jet takes place uniformly in all directions; at an angle of $\theta = 45^\circ$, the majority of the air travels in the direction involving the smallest deviation (i.e., forwards), whereas $\theta = 22.5^\circ$, practically the whole of the jet flows in one direction. The floor-impinging attachment mode created by circular opening arrays is presented in Fig. 5.23d, which is similar to the impinging ventilation studied by Awbi (2008) to some extent.

As shown in Fig. 5.23e, the attachment ventilation columns have been installed for large spaces like Xi’an airport terminal T5 and the waiting halls of Xiong’an high-speed railway station in China. Rotary outlets/globe-type outlets and slot openings are installed in the same ventilation column. The former is used to create mixed air distribution for the far zones, and the latter is used to create attached air distribution for the near zone. Compared to mixing ventilation, this mode can meet the needs of indoor thermal environment and achieve higher energy efficiency. Figure 5.23f shows the schematic diagram of attachment ventilation application in industrial muti-span buildings.

As mentioned before, the ventilation effectiveness of the air distribution mode can be evaluated by ventilation efficiency or temperature efficiency, which reflects the system’s ability to remove excessive heat in a room. Take the ducted-type air conditioner as an example, as shown in Fig. 5.23h, its ventilation performance is jointed tested by the manufacturer and author in a standardized laboratory. Compared to the mixing ventilation mode, the temperature efficiency of the attachment ventilation mode increased by 26.9% at the medium air supply speed of the ducted-type air conditioner (Han et al. 2021).