Simple Duct Design Method A. Fundamental Knowledge 1. Pressure Classification Static pressure – pressure acting vertically upon the duct wall surface, PS mmwg; Dynamic pressure – pressure generated by air velocity, Pd mmwg; Total pressure – sum of static pressure and dynamic pressure, Pt mmwg; Pd = (γ/2g)• V2 = (V/4.05)2

Pt = PS + Pd

where, γ – specific gravity of air, kg/m3

V – air velocity, m/s

Pt

PsPt

Pd

型管

动压

细孔

静压 全压

气流风管

Static pressure Total pressure Dynamic pressure Air flow Duct

2. Air volume

m3/min m3/H ft3/min 1 60 35.32

0.0167 1 0.5881

0.0283 1.6989 1

Common unit for air volume CMM — m3/min CMH — m3/H CFM — ft3/min

U-pipe

Pore

Air velocity in the duct can be measured in the following two ways: • Measure dynamic pressure with pitot, and then calculate out the air velocity; • Measure air velocity directly with a hot-wire anemometer; 3. Relations between frequency and the rotation speed of motor: Theoretically, the rotation speed of motor and the frequency of power supply have following relations:

Rotation speed = frequency ╳ 2 ╳ 60/number of poles, (rpm)

(Synchronous speed) Rotation Speed of Electric Motor (rpm)

No. of poles

Frequency

2 poles 4 poles 6 poles

50HZ 3,000 1,500 1,000

60HZ 3,600 1,800 1,200

Actual motor rotation speed has a drop of 3-7% due to sliding ratio. 4. Relations between motor rotation speed, air volume, pressure and shaft power: • Relation between pressure (P) and air volume (Q): Air volume increases Static pressure decreases • Relation between rotation speed (N) and pressure (P): P2 = (N2/N1)2

╳ P1

• Relation between rotation speed (N) and air volume (Q): Q2 = (N2/N1) ╳ Q1

• Relation between rotation speed (N) and shaft power (L): L2 = (N2/N1)3

╳ L1

• Aerodynamic A(kw): A = Q ╳ Pt/6120, where: Q—air supply, m3/min

Pt—full pressure of the supply air fan, mmwg • Shaft power L (kw) L = A/η , η—full pressure efficiency of the fan The motor capacity needed by the fan will have an allowance of 10-20% when compared with shaft power. B. Classification Of Duct 1. Low-speed duct • Air velocity in the duct is below 15m/s (static pressure is below 50mmwg); • Most widely applied (for A/C and ventilation); • Smaller error for resistance calculation and less noise; • For the same air volume, the low-speed duct has larger sizes but simpler structure (seal

etc.), when compared with high-speed duct.

Recommended max. air velocity in various parts of the low-speed duct, m/s Resistance reference

Main duct Branch duct Application Main duct

(noise reference) Air supply Air return Air supply Air return

Residence 3 5 4 3 3 Apartment, guest

room of hotel, sick room in the hospital

5 7.5 6.5 6 5

Theater, audio-visual hall 4 6.5 5.5 5 4

Library, personal office 6

General office, high-grade restaurant,

high-grade shops, bank

7.5

Common shop, coffee bar,

common restaurant 9

10 7.5 8 6

Workshop 12.5 15 9 11 7.5

Note: Reference noise refers to the limited air velocity set for preventing hazardous noise.

Recommended Values for Allowable Noise and Max. Air Velocity, m/s

Allowable noise

Main duct, machine room

Sub-main duct, in the ceiling Branch duct End duct

NC-15 NC-20 ≤8m/s ≤6m/s ≤4m/s ≤3m/s NC-25 ≤8m/s ≤7m/s ≤5m/s ≤3m/s NC-30 ≤10m/s ≤10m/s ≤10m/s ≤10m/s

Allowable Blow-out Air Velocity at Blow-out Outlets

Place Blow-out air velocity (m/s) Place Blow-out air velocity

(m/s)

Studio ≤3 Office (personal) ≤4

Residence ≤4 Office (general) ≤6

Apartment ≤4 Workshop ≤10 Guest room in hotel ≤4

Theater ≤5

Allowable Air Velocity at Intake Inlets

Intake location Surface air velocity of effective opening ratio (m/s)

Above residential area 3—4 In the residential area, away from the seats 3—4

In the residential area, close to the seats 2.0—3.0 Opening below the door, shutter above the

door 1.0—2.0

• Calculation on intake and fresh air/air outlet shutter:

Surface air velocity = Q(m3/h)/[W(m) ╳H(m) ╳ effective opening ratio ╳3600], (m/s)

Core air velocity = Q(m3/h)/[W(m) ╳H(m) ╳3600], (m/s)

(外部)

核心风 速

面风速

<面风速与核心风速>

(风管内风速)

<Surface air velocity and core air velocity>

(风管)

Core airvelocity (Air velocityin the duct)

(Duct)

Surface air velocity

(External)

Characteristics of Various Blow-out Outlets

Performance

Noise Blow-out air flow

Type Characteristics

Adj

ustm

ent o

f blo

w-o

ut

air f

low

Noise at the same blow-out

air velocity

Allowable blow-out

air velocity for noise NC30—

35

Distance reached Diffusion

Air flow form

Nozzle outlet

⊙ Mostly installed at the back wall in a large space for long distance it reaches; ⊙ Mostly used in TV (radio) studio for its low noise;

No Very low

Below 15m/s Long Small Axial

Ball outlet

⊙The blow-out air flow is similar to that of nozzle outlet. Due to its rotary head, air flow direction can be changed freely.

Yes Very low 15m/s Long Small Axial

Diffuser ⊙ Good diffusion; ⊙Particularly suitable for rooms with low ceiling.

No Medium 6m/s Short Largest Radial

Poin

t Out

let

Disk outlet

⊙ Air flow blows out horizontally after passing through disk baffle; ⊙ Simple structure, low price. As air flow blows out evenly in all directions, it is difficult to adjust air volume in a particular direction.

Yes Medium 7m/s Medium Large Radial

Strip outlet Yes Low 5m/s Short Large Axial

Strip outlet of lighting

appliance

⊙ The outlet is like a seam with large L/W ratio; ⊙ Mostly installed in the ceiling along the wall or window. It is popular among designers for its non-obvious outlet.

No Low 5m/s Short Large Axial

Line

out

let

Air curtain No Low Long Smallest. Axial

Perforated board

⊙Small effective opening ratio requires a large outlet area. No High 5m/s Short Large Axial

Fixed grille

⊙As the grille is fixed, it is usually used as intake inlet. No Medium 6m/s Medium Medium Axial

Surf

ace

outle

t

Grille with

adjustable direction

⊙As the air direction and distance is adjustable, it is usually used as blow-out outlet.

Yes Medium 6m/s Variable Variable Axial

2. High-speed duct • Air velocity over 15m/s (static pressure over 50mmwg) • Mainly used as smoke exhaust duct • Also used where duct space in the ceiling and pipe shaft can not be ensured

(The main duct is often designed as high-speed duct, which turns into low-speed duct after passing through the sound-attenuating chamber)

• Pay attention to duct strength.

C. The Layout Of Duct 1. Main duct type • This is the most common method, in which one or more main ducts are connected to

the blow-out outlet. • Due to the large main duct, it is necessary to check if there is sufficient space under

the beam.

(a) (b)

2. Layout of header type duct • This type is adopted in ultra-high rise buildings or those with short floor-to-floor

distance when the main duct has to pass through iron beams (such as honeycombed beams).

• It is passed through by passing the branch duct (spiral duct) through the round section below 1/3 of the beam height.

l 1

(蜂房状梁)

h1 H

Honeycombed Beams (集管式风管)Header Type Duct

3. Single duct type • Air is supplied directly from the A/C to the blow-out outlets. • It is easier to balance air volume. But the cost is high due to many ducts.

Single Duct Type

风管

静压箱

吹出口

末端机器

D. Ventilation patterns

• Equipped with supply air fan and exhaust air fan;

• It is easy to control the air exhaust volume and air flow distribution;

• Balance between air supply volume and exhaust volume can be adjusted with the air volume regulating valve (VD);

• An coarse filter is usually needed at the fresh air inlet.

<1st ventilation method>

送风风机 排风风机

VD VD过滤器

室内

• Usually used in large-scale kitchen, laundry, boiler room and parking yards.

<2nd ventilation method >

• Equipped with only supply air fan. Air is exhausted through the outlet at proper locations on the wall;

• It is positive pressure indoor, suitable for rooms where it is unexpected to be polluted by air from other rooms, or for ventilation in rooms where air combustion is needed;

• An coarse filter is usually needed at the fresh air inlet.

送风风机

VD

(屋外或他室)

过滤器

室内

正压排气口Air outlet

(outdoor or other rooms)

Filter

Supply air fan

Indoor positive

pressure

Indoor

Filter

Exhaust air fan Supply air fan

Blow-out

outlet Machine at the end

Static pressure

chamber Duct

• Usually used in small-scale substation, boiler room and warehouses.

• Equipped with only supply air fan. Air is exhausted through the outlet at proper locations on the wall;

• It is positive pressure indoor, suitable for ventilation in toilets and bath rooms, where odor or vapor should not flow into other rooms.

<3rd ventilation method>

VD

<负压>

排风风机Exhaust air fan

室内Indoor <negative pressure>

给气口Air inlet

• Usually used in toilets, tea room and garbage piling places in a building.

<Natural ventilation> • Ventilation is enabled through natural ventilation force such as wind power and buoyancy.

• Air inlet and exhaust funnel can be combined.

• Full area ventilation – ventilation for the whole room with large ventilation volume. • Local ventilation – ventilation for the vicinity of the contaminant source by using

exhaust hood and ventilation cupboard with limited ventilation volume. • Ventilation frequency = ventilation volume (m3H)/ room volume(m3), (time/H) Example: Volume of warehouse = 5m╳10m╳3mH = 150m3

Ventilation volume of warehouse = 5 times/H ╳150m3 = 750m3/H E. The Calculation Method For Duct’s Pressure Drop 1. Constant pressure methods (Constant Pressure Method) • This is the most common method, with the full name as constant friction loss

method with total pressure reference; • The pressure drop per meter duct is determined based on the air velocity and air

volume of the main duct. The size of ducts in each section can be calculated out based the obtained pressure drop;

Low-speed duct (for A/C ventilation) 0.08—0.15 mmwg/m (avg. 0.1mmWg/m) High-speed duct (for smoke exhaust) 0.3—0.6 mmwg/m (avg. 0.4mmWg/m) • Duct’s sizes can be determined by using a duct-meter or pressure drop graph. 2. Constant Speed Method • This is a method for calculating duct sizes, where the air velocity in the duct is

assumed to be constant, mainly intended for design of industrial exhaust ducts. 3. Total Pressure Method • The total pressure drop of the paths from the fan outlet to each blow-out outlet is all

the same. For its minimum error of air volume, it is the most reasonable design method. It is mainly intended for calculation of pressure balance of duct systems designed with constant pressure method.

F. The Decision Of Fan’s Static Pressure • For static pressure, the pathway with the largest pressure drop (the longest pathway

for instance) is selected; • Constant friction method is adopted for calculation (including air supply and air

return).The blow-out dynamic pressure need not be deducted at the fan outlet. 1. Straight Duct Part Air Volume Conditions for Duct-Meter and Pressure Drop Graph:

Standard Status Temperature=20℃DB Duct-meter Humidity=60%RH (γ=1.2kg/m3)

Duct Pressure Drop Graph Absolute Roughness=0.18mm

≒ Galvanized Steel Plate

Derating Under Different Conditions

Absolute Roughness k1 Temperature. k2 Humidity k3 Air Pressure k4

(usually not considered) (usually not considered) (usually not considered) Absolute roughness

ε Derating factor k1

Galvanized steel plate 0.15 1.0 Plastic pipe 0.005 0.83 Glass wool duct 0.8 1.27 Cement duct 2.0 1.60

Calculate duct sizes according to air volume and friction loss (mmwg/m) Size of straight duct Example: Q=10,000m3/H, △P=0.1mmwg/m (galvanized steel plate), L/W ratio 1:2.5: ① For duct-meter Size of the rectangular duct directly read: 1000mm╳400mm Size of the round duct: 650mm

For cement duct, unit friction loss in case of same air volume and size = 0.1mmwg/m╳1.6 = 0.16mmwg/m ② For duct pressure drop graph

10000

m3/hQ

0. 1 摩擦损失

d=cm

Friction Loss a) Find the crossing point of vertical axis 10,000m3/H and horizontal axis 0.1mmWg; b) Read the size of the round duct =650mm; c) The size of the rectangular duct can be found in the following conversion table ≈1000mm╳400mm. K1 is the derating factor for duct materials Duct materials K1Galvanized steel plate 1.0 Plastic pipe 0.83 Glass wool duct 1.27 Cement duct 1.60

Pressure Drop Graph for Ducts of Galvanized Steel Plates

Air

Volu

me

Q （

m3 /h

）

Friction Loss (mmwg/m) Note: Condition: 20℃DB, 60%RH, 760mmHg Left – recommended for low-speed ducts Right – recommended for high-speed ducts

Pressure Drop Graph for Glass Wool Ducts

Air

Volu

me

Q （

m3 /h

）

Frication Loss (mmwg/m)

Pressure Drop Graph for Flexible Ducts

Fric

tion

Loss

(mm

wg/

m)

Air Volume Q (m3/h)

Pressure Drop graph for Spiral Ducts

Air

Volu

me

Q （

m3 /h

）

Friction Loss (mmwg/m)

Note: The joint of the spiral duct in the above table is connected by inserting.

Conversion Between Rectangular Ducts and Round Ducts de=1.3[(a╳b)5/(a+b)2]1/8

Where: de: equivalent diameter, m (diameter of the round duct with the same resistance as the rectangular duct) a: Long edge of the rectangular duct, m b: Short edge of the rectangular duct, m unit: cm b

a

5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 120 125 130 135 140 145 150

5

10

15

20

25

5.5

7.6

9.1

10.3

11.4

10.9

13.3

15.2

16.9

16.4

18.9

21.0

21.9

24.4

27.3

30

35

40

45

50

12.2

13.0

13.8

14.4

15.0

18.3

19.5

20.7

21.7

22.7

22.9

24.5

26.0

27.4

28.7

26.6

28.6

30.5

32.1

33.7

29.9

32.2

34.3

36.3

38.1

32.8

35.4

37.8

40.0

42.0

38.3

40.9

43.3

45.6

43.7

46.4

48.8

49.2

51.8

54.7

55

60

65

70

75

15.6

16.2

16.7

17.2

17.7

23.6

24.5

25.3

26.1

26.8

29.9

31.0

32.1

33.1

34.1

35.1

36.5

37.8

39.1

40.2

39.8

41.4

42.9

44.3

45.7

43.9

45.7

47.4

49.0

50.6

47.7

49.6

51.5

53.3

55.0

51.1

53.3

55.3

57.3

59.2

54.3

56.7

58.9

61.0

63.0

57.3

59.8

62.2

64.4

66.6

60.1

62.8

65.3

67.7

69.7

65.6

68.3

70.8

73.2

71.1

73.7

76.3

76.5

79.2

82.0

80

85

90

95

100

18.1

18.5

19.0

19.4

19.7

27.5

28.2

28.9

29.5

30.1

35.0

35.9

36.7

37.5

38.4

41.4

42.4

43.5

44.5

45.4

47.0

48.2

49.4

50.6

51.7

52.0

53.4

54.8

56.1

57.4

56.7

58.2

59.7

61.1

62.6

60.9

62.6

64.2

65.9

67.4

64.9

66.8

68.6

70.3

71.9

68.7

70.6

72.6

74.4

76.2

72.2

74.3

76.3

78.3

80.2

75.5

77.8

79.9

82.0

84.0

78.7

81.1

83.3

85.5

87.6

81.8

84.2

86.6

88.9

91.1

84.7

87.2

89.7

92.1

94.4

87.5

90.1

92.7

95.2

97.6

92.9

95.6

98.2

100.7

98.4

101.1

103.7

103.9

106.5

109.3

105

110

115

120

125

20.1

20.5

20.8

21.2

21.5

30.7

31.3

31.8

32.4

32.9

39.1

39.9

40.6

41.3

42.0

46.4

47.3

48.1

49.0

49.9

52.8

53.8

54.8

55.8

56.8

58.6

59.8

60.9

62.0

63.1

64.0

65.2

66.5

67.7

68.9

68.9

70.3

70.7

73.1

74.4

73.5

75.1

76.6

78.0

79.5

77.8

79.6

81.2

82.7

84.3

82.0

83.8

85.5

87.2

88.8

85.9

87.8

89.6

91.4

93.1

89.7

91.6

93.6

95.4

97.3

93.2

95.3

97.3

99.3

101.2

96.7

98.8

100.9

103.0

105.0

100.0

102.2

104.4

106.6

108.6

103.1

105.5

107.8

110.0

112.2

106.2

108.6

111.0

113.3

115.6

109.1

111.7

114.1

116.5

118.8

112.0

114.6

117.2

119.6

122.0

114.8

117.5

120.1

122.6

125.1

120.3

122.9

125.6

128.1

125.7

128.4

131.0

131.2

133.9

136.7

b

a

5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 120 125 130 135 140 145 150

130

135

140

145

150

21.9

22.2

22.5

22.8

23.1

33.4

33.9

34.4

34.9

35.3

42.6

43.3

43.9

44.5

45.2

50.6

51.4

52.2

52.9

53.6

57.7

58.6

59.5

60.4

61.2

64.2

65.2

66.2

67.2

68.1

70.1

71.3

72.4

73.5

74.5

75.7

76.9

78.1

79.3

80.5

80.8

82.2

83.5

84.8

86.1

85.7

87.2

88.6

90.0

91.3

90.4

91.9

93.4

94.9

96.3

94.8

96.4

98.0

99.6

101.1

99.0

100.7

102.4

104.1

105.7

103.1

104.9

106.6

108.4

110.0

106.9

108.8

110.7

112.5

114.3

110.7

112.6

114.6

116.5

118.3

114.3

116.3

118.3

120.3

122.2

117.7

119.9

122.0

124.0

126.0

121.1

123.3

125.5

127.6

129.7

124.4

126.7

128.9

131.1

133.2

127.5

129.9

132.2

134.5

136.7

130.6

133.0

135.4

137.7

140.0

133.6

136.1

138.5

140.9

143.3

136.5

139.1

141.6

144.0

146.4

139.3

142.0

144.6

147.1

149.5

142.1

144.8

147.5

150.3

152.6

147.6

150.3

152.9

155.5

153.0

155.7

158.4

158.5

161.2

164.0

155

160

165

170

175

23.4

23.7

23.9

24.2

24.5

35.8

36.2

36.7

37.1

37.5

45.7

46.3

46.9

47.5

48.0

54.4

55.1

55.7

56.4

57.1

62.1

62.9

63.7

64.4

65.2

69.1

70.0

70.9

71.8

72.6

75.6

76.6

77.6

78.5

79.5

81.6

82.7

83.8

84.9

85.9

87.3

88.5

89.7

90.8

91.9

92.6

93.9

95.2

96.4

97.6

97.4

99.1

100.5

101.8

103.1

102.6

104.1

105.5

106.9

108.2

107.2

108.8

110.3

111.8

113.2

111.7

113.3

114.9

116.4

118.0

116.0

117.7

119.3

120.9

122.5

120.1

121.9

123.6

125.3

127.0

124.1

125.9

127.7

129.5

131.2

127.9

129.8

131.7

133.5

135.3

131.7

133.6

135.6

137.5

139.3

135.3

137.3

139.3

141.3

143.2

138.8

140.9

143.0

145.0

147.0

142.2

144.4

146.5

148.6

150.7

145.5

147.8

150.0

152.1

154.2

148.8

151.1

153.3

155.6

157.7

151.9

154.3

156.6

158.9

161.1

155.0

157.5

159.8

162.2

164.4

158.0

160.5

163.0

165.3

167.7

161.0

163.5

166.0

168.5

170.8

163.9

166.5

169.0

171.5

173.9

166.7

169.3

171.9

174.5

177.0

180

185

190

195

200

24.7

25.0

25.3

25.5

25.8

37.9

38.3

38.7

39.1

39.5

48.5

49.1

49.6

50.1

50.6

57.7

58.4

59.0

59.6

60.2

66.0

66.7

67.4

68.1

68.8

73.5

74.3

75.1

75.9

76.7

80.4

81.4

82.2

83.1

84.0

86.9

87.9

88.9

89.9

90.8

93.0

94.1

95.2

96.3

97.3

98.8

100.0

101.2

102.3

103.4

104.3

105.6

106.8

108.0

109.2

109.6

110.9

112.2

113.5

114.7

114.6

116.0

117.4

118.7

120.0

119.5

120.9

122.4

123.8

125.2

124.1

125.6

127.2

128.5

130.1

128.6

130.2

131.8

133.3

134.8

132.9

134.6

136.2

137.9

139.4

137.1

138.8

140.5

142.2

143.8

141.2

143.0

144.7

146.5

148.1

145.1

147.0

148.8

150.6

152.3

148.9

150.9

152.7

154.6

156.4

152.7

154.7

156.6

158.5

160.4

156.3

158.3

160.3

162.3

164.2

159.8

161.9

164.0

166.0

168.0

163.3

165.4

167.6

169.6

171.7

166.7

168.9

171.0

173.2

175.3

170.0

172.2

174.4

176.6

178.8

173.2

175.5

177.8

180.0

182.2

176.4

178.7

181.0

183.3

185.6

179.4

181.9

184.2

186.6

188.9

210

220

230

240

250

26.3

26.7

27.2

27.6

28.1

40.3

41.0

41.7

42.4

43.0

51.6

52.5

53.4

54.3

55.2

61.4

62.5

63.6

64.7

65.8

70.2

71.5

72.8

74.0

75.3

78.3

79.7

81.2

82.6

84.0

85.7

87.4

89.0

90.5

92.0

92.7

94.5

96.3

98.0

99.6

99.3

101.3

103.1

105.0

106.8

105.6

107.6

109.7

111.6

113.6

111.5

113.7

115.9

118.0

120.0

117.2

119.5

121.8

124.1

126.2

122.6

125.1

127.5

129.9

132.2

127.9

130.5

133.0

135.5

137.9

132.9

135.7

138.3

140.9

143.4

137.8

140.6

143.4

146.1

148.8

142.5

145.5

148.4

151.2

153.9

147.0

150.2

153.2

156.1

158.9

151.5

154.7

157.8

160.8

163.8

155.0

159.1

162.3

165.5

168.5

160.0

163.4

166.7

170.0

173.1

164.0

167.6

171.0

174.4

177.6

168.0

171.6

175.2

178.6

182.0

171.9

175.6

179.3

182.8

186.3

175.7

179.5

183.2

186.9

190.4

179.3

183.3

187.1

190.9

194.5

183.0

187.0

190.9

194.8

198.5

186.5

190.6

194.7

198.6

202.4

189.9

194.2

198.3

202.3

206.2

193.3

197.7

201.9

206.0

210.0

260

270

280

290

300

28.5

28.9

29.3

29.7

30.1

43.7

44.3

45.0

45.6

46.2

56.0

56.9

57.7

58.5

59.2

66.8

67.8

68.8

69.7

70.6

76.4

77.6

78.7

79.8

80.9

85.3

86.6

87.9

89.1

90.3

93.5

95.0

96.4

97.7

99.0

101.2

102.8

104.3

105.8

107.3

108.5

110.2

111.9

113.5

115.1

115.4

117.3

119.0

120.8

122.5

122.0

124.0

125.9

127.8

129.5

128.3

130.4

132.4

134.4

136.3

134.4

136.6

138.7

140.8

142.8

140.2

142.5

144.7

146.9

149.0

145.9

148.3

150.6

152.9

155.5

151.3

153.8

156.2

158.6

160.9

156.6

159.2

161.7

164.2

166.6

161.7

164.4

167.0

169.6

172.1

166.7

169.5

172.2

174.8

177.5

171.5

174.4

177.2

180.0

182.7

176.2

179.2

182.1

185.0

187.7

180.8

183.9

186.9

189.8

192.7

185.2

188.4

191.5

194.5

197.5

189.6

192.9

196.1

199.2

202.2

193.9

197.2

200.5

203.7

206.8

198.0

201.5

204.9

208.1

211.3

202.1

205.7

209.1

212.5

215.8

206.1

209.7

213.3

216.7

220.1

210.0

213.7

217.4

220.9

224.3

213.9

217.7

221.4

225.0

228.5

b

a 150 155 160 165 170 175 180 185 190 195 200 205 210 215 220 225 230 235 240 245 250 255 260 265 270 275 280 285 290 295 300

150 164

155 166.7 169.4

160 169.3 172.1 174.9

165 171.9 174.8 177.6 180.4

170 174.5 177.4 180.3 183.1 185.8

175 177.0 180.0 182.9 185.7 188.6 191.3

180 179.4 182.5 185.4 188.4 191.2 194.0 196.8

185 181.9 184.9 188.0 190.9 193.8 196.7 199.5 202.2

190 184.2 187.4 190.4 193.4 196.4 199.3 202.1 204.9 207.7

195 186.6 189.7 192.9 195.9 198.9 201.9 204.8 207.6 210.4 213.2

200 188.9 192.1 195.3 198.4 201.4 204.4 207.3 210.2 213.1 215.9 218.6

205 191.1 194.4 197.6 200.8 203.9 206.9 209.9 212.8 215.7 218.6 221.3 224.1

210 193.3 196.7 199.9 203.1 206.3 209.3 212.4 215.4 218.3 221.2 224.0 226.8 229.6

215 195.5 198.9 202.2 205.5 208.6 211.8 214.8 217.9 220.9 223.8 226.7 229.5 232.3 235.0

220 197.7 201.1 204.5 207.7 211.0 214.1 217.3 220.3 223.4 226.3 229.2 232.1 235.0 237.7 240.5

225 199.8 203.3 206.7 210.0 213.3 216.5 219.7 222.8 225.0 228.8 231.8 234.7 237.6 240.4 243.2 246.0

230 201.9 205.4 208.9 212.2 215.5 218.8 222.0 225.2 228.3 231.3 234.3 237.3 240.2 243.1 245.9 248.7 251.4

235 204.0 207.3 211.0 214.4 217.8 221.1 224.3 227.5 230.7 233.8 236.8 239.8 242.8 245.7 248.5 251.4 254.1 256.9

240 206.0 209.6 213.1 216.6 220.0 223.3 226.6 229.9 233.0 236.2 239.3 242.3 245.3 248.2 251.1 254.0 256.8 259.6 262.4

245 208.0 211.7 215.2 218.7 222.2 225.6 228.8 232.2 234.4 238.6 241.7 244.7 247.8 250.8 253.7 256.6 259.5 262.3 265.1 267.8

250 210.0 213.7 217.3 220.8 224.3 227.8 231.1 234.4 237.7 240.9 244.1 247.2 250.2 253.3 256.2 259.2 262.1 264.9 267.8 270.5 273.3

255 211.9 215.7 219.3 222.9 226.4 229.9 233.3 236.7 240.0 243.2 246.4 249.6 252.7 255.7 258.7 261.7 264.7 267.5 270.4 273.2 276 278.8

260 213.9 217.6 221.3 225.0 228.5 232.1 235.5 238.9 242.2 245.5 248.7 251.9 255.1 258.2 261.2 264.2 267.2 270.1 273.0 275.9 278.7 281.5 284.2

265 215.8 219.6 223.3 227.0 230.6 234.1 237.6 241.1 244.5 247.8 251.0 254.3 257.4 260.6 263.7 266.7 269.7 272.7 275.6 278.5 281.3 284.2 286.9 289.7

270 217.7 221.5 225.3 229.0 232.7 236.2 239.8 243.2 246.7 250.0 253.3 256.6 259.8 263.0 266.1 269.2 272.2 275.2 278.2 281.1 284.0 286.8 289.6 292.4 295.2

275 219.5 223.4 227.2 231.0 234.7 238.3 241.9 245.4 248.8 252.2 255.6 258.9 262.1 265.3 268.5 271.6 274.7 277.7 280.7 283.6 286.6 289.4 292.3 295.1 297.9 300.6

280 221.4 225.3 229.2 232.9 236.7 240.3 243.9 247.5 251 254.4 257.8 261.1 264.4 267.6 270.8 274.0 277.1 280.1 283.2 286.2 289.1 292.0 294.9 297.8 300.6 303.3 306.1

285 223.2 227.2 231.1 234.9 238.6 242.3 246.0 249.6 253.1 256.6 260.0 263.3 266.7 269.9 273.2 276.3 279.5 282.6 285.6 288.7 291.6 294.6 297.5 300.4 303.2 306.0 308.8 311.6

290 225.0 229.0 232.9 236.8 240.6 244.3 248 251.6 255.2 258.7 262.1 265.5 268.9 272.2 275.5 278.7 281.9 285.0 288.1 291.1 294.1 297.1 300.1 303.0 305.8 308.7 311.5 314.3 317.0

295 226.8 230.8 234.8 238.7 242.5 246.3 250.0 253.7 257.3 260.8 264.3 267.7 271.1 274.5 277.7 281.0 284.2 287.4 290.5 293.6 296.6 299.6 302.6 305.5 308.4 311.3 314.2 317.0 319.7 322.5

300 228.5 232.6 236.6 240.6 244.4 248.2 252.0 255.7 259.3 262.9 266.4 269.9 273.3 276.7 280.0 283.3 286.5 289.7 292.9 296.0 299.1 302.1 305.1 308.1 311.0 313.9 316.8 319.6 322.4 325.2 328.0

2. Very Rough Estimation Method PS = PD+PA PD = R• L(1+K) where: PS: Necessary static pressure of the fan (mmWg);

PA: Sum of pressure drop of filter, coil and automatic air damper (mmWg); PD: Pressure drop of the duct (mmWg); R: Friction loss of straight duct (mmWg/m), usually R is 0.1mmWg/m;

L: Total length of supply air duct and return air duct of the longest path, m; K: Proportion of local resistance loss.

• For small systems (total length below 50m) or large systems where there is much

bending, K=1.0-1.5; • For a large system, K=0.7-1.0; • When there are many sound suppressing devices, K=1.5-2.5. Pressure drop at blow-out outlet, inlet and shutter Air volume unit: m3/H

Machine name Pressure Drop (mmWg)

Remarks (reference value: Xin Huang)

Air volume 195 260 H 0.7 1.2 #15 V 1.6 2.8

Air volume 350 465 H 0.7 1.2 #20 V 1.2 2.2

Air volume 550 730 H 0.6 1.0 #25 V 1.2 2.2

Air volume 790 1055 H 0.6 1.0

Diffuser

#30 V 1.2 2.2

H: horizontal blow-out (cooling); V: vertical blow-out (heating); ⊙ With air volume regulating valve, add pressure drop by 2.5mmwg.

Air volume 150 240 H 4.7 12.5 Single

column V 2.1 5.2

Air volume 240 420 H 3.0 9.5 Double

column V 1.4 4.0

Air volume 360 540 H 3.0 7.0

Strip outlet

3 column

V 1.4 2.9

⊙Including pressure drop of the static pressure chamber at the blow-out outlet.

W (m/m)

H (m/m)

Air volume

Air volume Remarks

(Pressure drop )

(Pressure drop)

650 975 300 300 0.8 1.9 1080 1620

VHS

500 300 0.8 1.9

⊙Air valve fully open; ⊙Blow-out angle =45º.

260 520 152ø 0.4 1.4

450 900 Nozzle outlet

200ø 0.4 1.4

⊙ With air volume regulating valve, add pressure drop by 1.0mmwg.

85 171 #8 0.6 2.5 222 445

Ball outlet

#12 0.6 2.5

Shutter Air supply 1.4, Air exhaust 0.9

Surface air velocity v=2.5m/s.

• Local pressure drop for sound-suppressing elbow (reference value: Linggong)

内表面：玻璃布内衬

外面：镀锌钢板

50

25 25

玻璃棉

L

2525

L 50

Inner Surface: Glass Cloth Lining Glass Wool

Outside: galvanized steel plate导流叶片Guide Vane

Ln=w+50

w

w+50w

玻璃棉25mm

2525

玻璃棉50mm+导流叶片

H+50H

Glass Wool Glass Wool Guide Vane

Pressure Drop of Sound Suppressing Elbow, mmwg

Average Air Velocity at Inlet Elbow size W L/L0 2.5m/s 5.0m/s 7.5m/s 10.0m/s

Damping system Ζ

Below 300 1.5 0.3-0.4 1.4-1.8 3.1-4.0 5.5-7.1 0.9-1.2 350—500 1.5 0.3-0.4 1.2-1.5 2.6-3.3 4.6-5.8 0.8-1.0 550—750 1.5 0.3 1.0-1.3 2.3-2.9 4.0-5.2 0.7-0.9 800—1200 1.5 0.2-0.3 0.9-1.2 2.1-2.8 3.7-4.9 0.6-0.8 Above 1250 1.5 0.2-0.3 0.9-1.2 2.1-2.6 3.7-4.6 0.6-0.8

Note: The pressure drop values in the table correspond to flatness (H/W)=1.0-0.5. If the flatness (H/W)>1.0, use the lower limit value:

Damper (split vane) L/R θ v ζ 4m/s 6m/s 8m/s 10m/s 15m/s

0 0.52 0.5 1.2 2.1 3.2 7.2 0.6 20 2.3 2.3 5.1 9.0 14.1 31.6 0 0.52 0.5 1.2 2.1 3.2 7.2 1.0 20 2.7 2.7 6.0 10.6 16.5 37.1 0 0.52 0.5 1.2 2.1 3.2 7.2

L/R=W╳叶片枚数/2(H+W)

θ

L/R=W× Vane number/2(H+W)

v

W

H

1.5 20 3.2 3.2 7.1 12.5 19.6 43.9

Fresh air Same area ratio

— 0.8 2.8 6.0 10.4 16.9

Shutter Exhaust air Same area

ratio — 0.5 2.0 4.0 7.1 11.0

Air velocity: surface air velocity