The location of the cleanroom air-conditioning plant room directly affects project cost, noise, and air-conditioning performance, so the layout of the plant room should be considered as a whole during the floor-plan design stage. The cleanroom air-conditioning plant room is best located close to cleanrooms requiring large supply air volumes, keeping duct runs as short as possible. However, for noise and vibration prevention, the plant room should be separated from the cleanroom. Both aspects must be considered. There are several ways of separation:

1. Structural Separation link

• 1.1 Separation by settlement joint: the settlement joint passes between the cleanroom and the plant room, acting as a divider.
• 1.2 Separation by cavity wall: if the plant room is directly adjacent to the cleanroom, rather than sharing one partition wall, each side has its own partition wall, with a cavity of a certain width between the two walls.
• 1.3 Separation by an auxiliary room: an auxiliary room is placed between the cleanroom and the plant room to serve as a buffer.

2. Distributed Arrangement link

• 2.1 Distributed on the roof or above suspended ceilings.
• 2.2 Distributed below ground level: the plant room is located in the basement.

It goes without saying that, because of the large air volumes and the additional air filtration equipment, the plant room of a cleanroom air-conditioning system is larger than an ordinary air-conditioning plant room; the clean area must be taken into account, the unit size calculated, and adequate plant room space reserved.

Section 2 Medical Laboratory Ventilation System

I. Basic Concepts of Ventilation link

• 1. Concepts of ventilation and fume hoods: ventilation means exhausting contaminated indoor air directly or after purification to the outside and supplying fresh air in, thereby maintaining indoor air conditions that meet hygiene standards and production process requirements; the former is called exhaust air, and the latter supply air. A fume hood can be simply understood as a box and a fan: gases generated in the box are exhausted by the fan and safely discharged into the atmosphere.
• 2. Classification of ventilation: by driving force, ventilation systems can be divided into natural ventilation and mechanical ventilation; mechanical ventilation can be further divided into general (dilution) ventilation and local ventilation. General ventilation is a method of ventilating the entire room; local ventilation limits the ventilation scope to places where harmful substances are concentrated or where staff frequently work, such as fume hoods, articulated extraction arms, and atomic absorption hoods.
• 3. Laboratory ventilation: laboratory ventilation is the technology of controlling the influence and damage of hazardous laboratory substances on indoor and outdoor air environments.

II. Purpose and Requirements of Ventilation

Laboratory ventilation differs from the ventilation design of comfort air-conditioning systems; its main purpose is to provide a safe and comfortable working environment and reduce the possibility of personnel exposure to hazardous environments. Ventilation mainly addresses the health and labor protection of laboratory personnel in the working environment.

III. Fresh Air Principle

A fresh air system works on the following principle: dedicated equipment supplies fresh air into a closed room on one side, while dedicated equipment exhausts air to the outside on the other side, creating a "fresh air flow field" indoors that satisfies the need for indoor fresh air exchange. The implementation is as follows: a high-pressure-head, high-flow, low-power DC high-speed brushless motor drives a centrifugal fan; air is forced into the room from one side by mechanical power, and a specially designed exhaust fresh-air fan discharges air outdoors from the other side, forcing a fresh air flow field to form in the system. While supplying air, the incoming air is filtered, sterilized, disinfected, oxygen-enriched, and preheated (in winter). As the exhaust air passes through the main unit, heat is recovered and exchanged with the fresh air, and most of the recovered energy is returned indoors with the fresh air. Borrowing the scheme for forming a clean space over a large area, the air entering the room is guaranteed to be clean, thereby achieving indoor air purification.

Fresh air systems can be divided into: unidirectional-flow fresh air systems, bidirectional-flow fresh air systems, and bidirectional-flow heat-exchange fresh air systems.

1. Unidirectional-Flow Fresh Air System link

Implemented with one fan and a window-type air inlet: when the fan starts, contaminated indoor air is exhausted outdoors, creating negative pressure indoors; under outside atmospheric pressure, outdoor air enters the room through the window-type inlet, achieving air replacement.

2. Bidirectional-Flow Fresh Air System link

Implemented with two main units: one fan forcibly exhausts contaminated indoor air outdoors while the other draws fresh air into the room. The characteristic of a bidirectional-flow system is forced intake and exhaust of air, with an air filtration system (optional) added upstream of the supply unit to ensure the air supplied indoors is clean—suitable for laboratories.

3. Bidirectional-Flow Heat-Recovery Fresh Air System link

A heat-recovery main unit: in northern regions, where the indoor–outdoor temperature difference in winter is large and the air supplied indoors is cold, the heat-recovery unit exchanges heat between the air exhausted outdoors and the incoming fresh air to achieve energy savings.

[Figure: Floor plan layout of laboratory air-conditioning fresh and exhaust air, including the biochemistry hall, cold storage, sample storage area, toilets, office area, meeting and training rooms, reception hall and various buffer zones, electrophoresis area, sequencing area, library testing area, amplification area, etc., with axis-grid dimensions and duct routing marked]

Fig. 6-25 Floor Plan Layout of Air-Conditioning Fresh and Exhaust Air

IV. Basic Composition of a Ventilation System

• Ventilation terminal equipment: mainly includes fume hoods, articulated extraction arms, atomic absorption hoods, push–pull exhaust hoods, etc., as shown in Figures 6-26 and 6-27.

[Figure: Photograph of a laboratory with multiple red articulated extraction arms mounted above laboratory benches]

Fig. 6-26 Articulated Extraction Arm

[Figure: Photograph of a laboratory with multiple stainless-steel atomic absorption hoods mounted above an instrument analysis bench]

Fig. 6-27 Atomic Absorption Hood

2. Ventilation ductwork system: mainly includes ducts, dampers, silencers (mufflers), waste gas treatment towers, etc.

3. Ventilation fan units: mainly fans.

V. Ventilation System Design Parameters

1. For clients who require ventilation design for laboratories, the ventilation air-exchange volume can be determined from the room air change rate; the laboratory air change rate is 10–12 air changes per hour, and may be increased accordingly in special cases. [For room ventilation, a 500 mm × 500 mm sheet-metal hood is generally selected as the terminal device; each hood can ventilate up to 600 m³/h. Room length × width × height × 10 (air changes) = the room's hourly ventilation volume; dividing the hourly ventilation volume by 600 gives the number of hoods; branch and main duct velocities are calculated at 6 m/s.]

2. The branch-duct velocity for fume hoods is 6–10 m/s (10 m/s is generally used for calculation); in special cases it may exceed 10 m/s but should not exceed 12 m/s; the main-duct velocity is 10–14 m/s (10 m/s is generally used; choose 12 m/s for long ducts and 14 m/s for large air volumes).

3. The fume hood face velocity is generally controlled between 0.375–0.75 m/s; the acceptance standard is generally 0.5 m/s, and the optimum face velocity is 0.508 m/s. (When measuring face velocity, the sash is generally raised to 5 cm; a velocity of 0.3–0.5 m/s is considered acceptable. If the sash opening is too large, the velocity measured 5 cm below the sash may also be accepted.) See Table 6-4.

Table 6-4 Fume Hood Face Velocity Parameters

Fume Hood Hazard Level	Average Face Velocity (m/s)	Minimum Face Velocity (m/s)
High	0.622–0.75	0.5
Medium	0.5	0.4
Low	0.375–0.4	0.25

4. Outdoor noise shall be controlled at 70 dB(A), and laboratory indoor noise at 55 dB(A) (the indoor noise GB limit of 60 dB is exceeded when the outdoor noise is about 75 dB). Fan noise can be divided into the fan's own mechanical noise (mainly caused by differences in fan quality) and airflow noise (the main noise). When the fan power is not large, airflow noise can be reduced by adding a rain hood above the fan; for high-power fans, silencers are generally added at the fan inlet and outlet. Mechanical noise is mainly addressed by building sound-insulating walls or small acoustic enclosures, or by adding flexible connectors at the fan inlet and outlet. The main vibration-damping method is to make the fan base a vibration-isolated base and install vibration isolators or damping pads.

5. Ventilation volume (Q) = face velocity (vs) × fume hood opening area. The function of an electronic air-volume control valve is to adjust each fume hood's ventilation volume by adjusting the duct radius of each hood, so that the face velocity remains constant when the hood opening area changes.

6. Exhaust volume (Q) = face velocity (vs) × fume hood opening area. The function of a variable-frequency (VFD) system is to change the fan speed and thus the fan's ventilation volume; when only a few fume hoods in a ventilation system are operating, the VFD system automatically adjusts the fan speed, changing the fan's ventilation volume and thereby keeping the fume hood face velocity constant. The VFD system functions similarly to an air-volume control valve, but if only control valves are used, the fan still runs at maximum speed when only a few hoods are operating; with a VFD system, adjusting the fan speed saves energy.

VI. Classification and Requirements of Ventilation Duct Materials

1. Classification by duct material: galvanized steel duct, stainless-steel duct, inorganic fiberglass (FRP) duct, silicate board duct, composite insulated-panel duct, flexible duct, etc.

Galvanized steel ducts are commonly used for air-conditioning supply and return ducts (advantages: long service life, low frictional resistance, quick and easy fabrication; disadvantage: limited by processing equipment, thickness should not exceed 1.2 mm).

Stainless-steel ducts are commonly used for supply ducts downstream of HEPA filters in ultra-clean systems, and for ducts conveying corrosive gases (advantages: attractive appearance, smooth inner wall, low resistance, good airtightness, high pressure strength, corrosion resistance, high-temperature resistance; disadvantage: high cost).

Inorganic fiberglass (FRP) ducts are commonly used in air-conditioning systems and fire smoke-control and exhaust systems (advantages: corrosion resistance, long service life, relatively high strength, cost essentially the same as steel ducts; disadvantages: unstable quality, rough inner surface, high resistance, high density, heavy weight, and difficult on-site repair).

Silicate board ducts are commonly used for smoke exhaust ducts (advantages similar to inorganic fiberglass board; the notable feature is better fire performance; disadvantage: relatively high overall cost).

Common composite insulated-panel ducts include aluminum-foil polyurethane, aluminum-foil phenolic, BBS polyurethane, and aluminum-foil glass-wool insulated ducts.

Flexible ducts are used to connect ventilation and air-conditioning ducts to terminal devices.

Other ducts mainly include brick-built ducts, cement ducts, and fabric ducts.

[Figure: Stainless-steel ducts (elbows, tees, and other fittings)]

Fig. 6-28 Stainless-Steel Ducts

[Figure: Inorganic fiberglass duct (white rectangular duct)]

Fig. 6-29 Inorganic Fiberglass Duct

[Figure: Photograph of aluminum-foil ducts; several rectangular duct sections and elbows laid on the floor]

Fig. 6-30 Aluminum-Foil Duct

[Figure: Product image of galvanized steel ducts; rectangular ducts with elbows, tees, and other fittings]

Fig. 6-31 Galvanized Steel Duct

• By duct function: supply air, return air, exhaust air, fresh air ducts, etc.
• By working pressure of the duct system: low-pressure, medium-pressure, and high-pressure systems.
• By duct shape: circular and rectangular ducts.

Circular ducts have high strength and low steel consumption but occupy more effective space, and their bends and tees require longer runs; high-velocity ducts should use circular spiral ducts.

Rectangular ducts occupy less effective space and are easier to arrange; the ratio of long to short sides of a rectangular section shall not exceed 4, and shall in no case exceed 10.

VII. Ventilation Duct Sizes and Calculation Methods

• Common circular duct sizes: ① a single atomic absorption hood mainly uses Φ160 (DN150) pipe; ② articulated extraction arms mainly use Φ110 (DN100) pipe; ③ branch and main ducts for one or two fume hoods mainly use Φ315 (DN300) pipe.
• Common rectangular duct sizes: if the system is more complex, or three or more fume hoods are installed in parallel in the same room, or the laboratory height is limited so that circular ducts cannot be installed, rectangular ducts may be considered. Standard side lengths of rectangular ducts (in mm) are: 120, 160, 200, 320, 400, 500, 630, 800, 1000, 1250. Since the fume hood width is 800 mm, the long side of a rectangular duct should not exceed 630 mm; square ducts are preferred—if conditions do not permit, rectangular ducts may be used, but each project should be uniform.
• Duct sizing methods: ① circular duct calculation: Q = (3600 × πd²v)/4 (Q — exhaust volume, (truncated at bottom of page)

(continued from previous page) m³/h; d — duct diameter, mm; v — air velocity in duct, m/s); ② rectangular duct calculation: Q = 3600 × a·b·v (Q — exhaust volume, m³/h; a, b — duct side lengths, mm; v — air velocity in duct, m/s).

4. Duct thickness standards: according to national standards, ventilation systems selected here are medium- and low-pressure systems. Thickness standards for PVC circular ducts in medium- and low-pressure systems are shown in Table 6-5.

Table 6-5 Thickness Standards for PVC Circular Ducts in Medium- and Low-Pressure Systems

Duct diameter d (mm)	Sheet thickness (mm)
d ≤ 320	3.0
320 < d ≤ 630	4.0
630 < d ≤ 1000	5.0
1000 < d ≤ 2000	6.0

Thickness standards for PVC rectangular ducts in medium- and low-pressure systems are shown in Table 6-6.

Table 6-6 Thickness Standards for PVC Rectangular Ducts in Medium- and Low-Pressure Systems

Duct long-side dimension b (mm)	Sheet thickness (mm)
b ≤ 320	3.0
320 < b ≤ 500	4.0
500 < b ≤ 800	5.0
800 < b ≤ 1250	6.0

Thickness standards for fiberglass (FRP) circular ducts in medium- and low-pressure systems are shown in Table 6-7.

Table 6-7 Thickness Standards for Fiberglass Circular Ducts in Medium- and Low-Pressure Systems

Duct diameter d (mm) or rectangular duct long side b (mm)	Sheet thickness (mm)
d (b) ≤ 200	2.5
200 < d (b) ≤ 400	3.2
400 < d (b) ≤ 630	4.0
630 < d (b) ≤ 1000	4.8

VIII. Ventilation Duct Design

1. First determine from the floor plan how many fume hoods each system includes, then determine the system's approximate ventilation volume from the number of fume hoods in each system (the design air volume of each 1200 mm fume hood is 1300 m³/h, (truncated at bottom of page)

(continued from previous page) each 1500 mm fume hood 1700 m³/h, each 1800 mm fume hood 2100 m³/h, each atomic absorption hood 600 m³/h, and each articulated extraction arm 250 or 300 m³/h), and then select a fan with a ventilation volume slightly greater than the system ventilation volume.

• Calculate the pressure loss in the ventilation process: the resistance of a single fume hood system is about 80–100 Pa; each meter of duct loses 5–6 Pa; each elbow loses 40–50 Pa; the fan outlet and the extraction inlet each lose 60 Pa; a silencer loses 50 Pa. Then select a suitable fan from the characteristic curve charts based on the calculated ventilation volume and pressure (in the calculation, only the pressure differential of the fume hood farthest away is calculated, and a margin of 200–300 Pa is reserved).

• Then calculate the duct radius from ventilation volume = duct cross-section × air velocity in duct (branch ducts are selected as 315 mm according to the fume hood size).

IX. Fan Classification and Selection

• Fan classification: by airflow pattern, fans are divided into centrifugal (usually placed outdoors), axial-flow (usually placed indoors), and mixed-flow (diagonal-flow) types; by material, fans mainly include ordinary steel fans, stainless-steel fans, PVC fans, and fiberglass (FRP) fans. The fan outlet should be larger than the main duct size when selecting a fan.

• ① Characteristics of axial-flow fans: low power consumption and operating cost, but high noise and low fan suction (low air pressure); suitable for simple systems, generally installed on walls or ducts. ② Characteristics of centrifugal fans: high power consumption and operating cost, relatively high noise, and strong fan suction (high air pressure); suitable for complex systems, mainly installed outdoors or on rooftops. ③ Characteristics of diagonal-flow fans: power consumption, operating cost, and fan suction fall between the two former types; lower noise; suitable for simple systems, generally installed indoors.

• Main fan parameters: ① Flow rate (Q): the volume of fluid flowing through a given duct cross-section per unit time. ② Fan speed (n): the speed of the fan rotor, in r/min. ③ Efficiency (η): the fan's work efficiency η = (W_useful/W_total) × 100%. ④ Pressure (P): the fan's total pressure (Pt) is divided into dynamic pressure (Pd) and static pressure (Ps). Static pressure is the pressure the fan must have to overcome the frictional resistance of the entire ventilation system, determined by the characteristics of the entire system—fume hoods, louvers, control valves, ducts, and fan. Dynamic pressure is the part of the pressure possessed by gas discharged at a certain velocity; under standard conditions the formula is: Pd = 0.5ρV² (ρ — air density, usually 1.2; V — air velocity, m/s).

• Fan selection: below 3.5F, below 4000 m³/h, and for up to 2 fume hoods, a diagonal-flow fan may be selected; above these values, select a centrifugal fan. ① For a single articulated extraction arm or atomic absorption hood, if the duct run is relatively simple—directly through the wall or window to the outside—a fiberglass diagonal-flow fan may be selected. The designer may select model FSJG-2.5F (motor power N = 0.09 kW) or FSJG-3.0F (N = 0.18 kW) diagonal-flow fans according to the system conditions; if the duct run is more complex with many elbows, model F4-72-3.0A (N = 0.55 kW or 0.75 kW) or F4-72-3.2A (N = 0.55 kW or 0.75 kW) centrifugal fans may be selected. ② For a single fume hood, if the duct system is relatively simple (truncated at bottom of page)