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
Static静压 pressure 气流 Air flow
动压
Total全压 pressure
Dynamic pressure
Duct 风管
细孔 Pore
Ps
Pt
Pd
Pt 型管 U-pipe
2. Air volume Common unit for air volume CMM — m3/min CMH — m3/H CFM — ft3/min
m3/min
m3/H
ft3/min
1
60
35.32
0.0167
1
0.5881
0.0283
1.6989
1
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 2 poles 4 poles
6 poles
Frequency 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 Application (noise Main duct Branch duct reference) Air supply Air return Air supply Air return Residence Apartment, guest room of hotel, sick room in the hospital Theater, audio-visual hall Library, personal office General office, high-grade restaurant, high-grade shops, bank Common shop, coffee bar, common restaurant Workshop
3
5
4
3
3
5
7.5
6.5
6
5
4
6.5
5.5
5
4
10
7.5
8
6
15
9
11
7.5
6
7.5
9 12.5
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 Main duct, Sub-main duct, in Branch duct noise machine room the ceiling NC-15 NC-20 ≤8m/s ≤6m/s ≤4m/s NC-25 ≤8m/s ≤7m/s ≤5m/s NC-30 ≤10m/s ≤10m/s ≤10m/s
Allowable Blow-out Air Velocity at Blow-out Outlets Blow-out air Place Place velocity (m/s) Office (personal) Studio ≤3 Residence
≤4
Apartment Guest room in hotel Theater
≤4 ≤4 ≤5
Office (general) Workshop
End duct ≤3m/s ≤3m/s ≤10m/s
Blow-out air velocity (m/s) ≤4 ≤6 ≤10
Allowable Air Velocity at Intake Inlets Surface air velocity of effective opening ratio Intake location (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 1.0—2.0 door
•
Calculation on intake and fresh air/air outlet shutter: 3
Surface air velocity = Q(m /h)/[W(m) ╳H(m)
╳
effective opening ratio
3
Core air velocity = Q(m /h)/[W(m) ╳H(m) ╳3600], (m/s)
(External) (外部)
(Duct) (风管)
Surface air velocity 面风速
Core air 核心风速 velocity (Air velocity (风管内风速) in the duct)
<面风速与核心风速> <Surface air velocity and core air velocity>
3600], (m/s)
╳
Type
Nozzle outlet
Point Outlet
Ball outlet
Diffuser
Disk outlet
Surface outlet
Line outlet
Strip outlet Strip outlet of lighting appliance Air curtain Perforated board Fixed grille Grille with adjustable direction
Characteristics
⊙ 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; ⊙The blow-out air flow is similar to that of nozzle outlet. Due to its rotary head, air flow direction can be changed freely. ⊙ Good diffusion; ⊙Particularly suitable for rooms with low ceiling. ⊙ 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. ⊙ 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.
⊙Small effective opening ratio requires a large outlet area. ⊙As the grille is fixed, it is usually used as intake inlet. ⊙As the air direction and distance is adjustable, it is usually used as blow-out outlet.
Adjustment of blow-out air flow
Characteristics of Various Blow-out Outlets Performance Noise Allowable blow-out Noise at air the same velocity blow-out for noise air velocity NC30— 35
Blow-out air flow
Distance reached
Diffusion
Air flow form
No
Very low
Below 15m/s
Long
Small
Axial
Yes
Very low
15m/s
Long
Small
Axial
No
Medium
6m/s
Short
Largest
Radial
Yes
Medium
7m/s
Medium
Large
Radial
Yes
Low
5m/s
Short
Large
Axial
No
Low
5m/s
Short
Large
Axial
No
Low
Long
Smallest.
Axial
No
High
5m/s
Short
Large
Axial
No
Medium
6m/s
Medium
Medium
Axial
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.
Honeycombed Beams ( 蜂房状梁)
H
1
h1
l
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 Duct 风管
Static pressure chamber 静压箱
吹出口 Blow-out Machine at the end
末端机器
outlet
D. Ventilation patterns <1st ventilation method> Exhaust air fan 排风风机
Supply air fan 送风风机
过滤器 Filter
•
VD
•
VD
• 室内 Indoor
• • <2nd ventilation method >
•
送风风机 Supply air fan Filter 过滤器
VD Indoor positive 室内 pressure 正压
Air 排气口 outlet
•
or other rooms) ((outdoor 屋外或他室)
•
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. Usually used in large-scale kitchen, laundry, boiler room and parking yards. 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.
• <3rd ventilation method>
• Exhaust 排风风机air fan
VD 给气口 Air inlet
•
室内 Indoor <负压> <negative pressure>
• <Natural ventilation>
• •
• • •
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.
Usually used in toilets, tea room and garbage piling places in a building. 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 Conditions for Duct-Meter and Pressure Drop Graph:
Air Volume
Standard Status
Temperature=20℃DB Humidity=60%RH (γ=1.2kg/m3)
Duct-meter
Absolute Roughness=0.18mm
Duct Pressure Drop Graph
≒ Galvanized Steel Plate
Derating Under Different Conditions
Absolute Roughness k1
Temperature. k2 (usually not considered)
Galvanized steel plate Plastic pipe Glass wool duct Cement duct
Humidity k3 (usually not considered)
Air Pressure k4 (usually not considered)
Absolute roughness Derating factor k1 ε 0.15 1.0 0.005 0.83 0.8 1.27 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 Q m3/ h
d=cm
10000
0. 1
摩擦损失 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 K1 Galvanized steel plate 1.0 Plastic pipe 0.83 Glass wool duct 1.27 Cement duct 1.60
Air Volume
Q （m3/h）
Pressure Drop Graph for Ducts of Galvanized Steel Plates
Friction Loss (mmwg/m) Note: Condition: 20℃DB, 60%RH, 760mmHg Left – recommended for low-speed ducts Right – recommended for high-speed ducts
Air Volume Q （m3/h）
Pressure Drop Graph for Glass Wool Ducts
Frication Loss (mmwg/m)
Friction Loss (mmwg/m)
Pressure Drop Graph for Flexible Ducts
Air Volume Q
(m3/h)
Air Volume
Q （m3/h）
Pressure Drop graph for Spiral Ducts
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[(aâ&#x2022;łb)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 b
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
105
110
unit: cm 115
120
125
a 5
5.5
10
7.6
10.9
15
9.1
13.3
16.4
20
10.3
15.2
18.9
21.9
25
11.4
16.9
21.0
24.4
30
12.2
18.3
22.9
26.6
29.9
32.8
35
13.0
19.5
24.5
28.6
32.2
35.4
38.3
40
13.8
20.7
26.0
30.5
34.3
37.8
40.9
43.7
45
14.4
21.7
27.4
32.1
36.3
40.0
43.3
46.4
49.2
50
15.0
22.7
28.7
33.7
38.1
42.0
45.6
48.8
51.8
54.7
55
15.6
23.6
29.9
35.1
39.8
43.9
47.7
51.1
54.3
57.3
60.1
60
16.2
24.5
31.0
36.5
41.4
45.7
49.6
53.3
56.7
59.8
62.8
65.6
65
16.7
25.3
32.1
37.8
42.9
47.4
51.5
55.3
58.9
62.2
65.3
68.3
71.1
70
17.2
26.1
33.1
39.1
44.3
49.0
53.3
57.3
61.0
64.4
67.7
70.8
73.7
76.5
75
17.7
26.8
34.1
40.2
45.7
50.6
55.0
59.2
63.0
66.6
69.7
73.2
76.3
79.2
82.0
80
18.1
27.5
35.0
41.4
47.0
52.0
56.7
60.9
64.9
68.7
72.2
75.5
78.7
81.8
84.7
87.5
85
18.5
28.2
35.9
42.4
48.2
53.4
58.2
62.6
66.8
70.6
74.3
77.8
81.1
84.2
87.2
90.1
92.9
90
19.0
28.9
36.7
43.5
49.4
54.8
59.7
64.2
68.6
72.6
76.3
79.9
83.3
86.6
89.7
92.7
95.6
98.4
95
19.4
29.5
37.5
44.5
50.6
56.1
61.1
65.9
70.3
74.4
78.3
82.0
85.5
88.9
92.1
95.2
98.2
101.1
103.9
100
19.7
30.1
38.4
45.4
51.7
57.4
62.6
67.4
71.9
76.2
80.2
84.0
87.6
91.1
94.4
97.6
100.7
103.7
106.5
109.3
105
20.1
30.7
39.1
46.4
52.8
58.6
64.0
68.9
73.5
77.8
82.0
85.9
89.7
93.2
96.7
100.0
103.1
106.2
109.1
112.0
114.8
110
20.5
31.3
39.9
47.3
53.8
59.8
65.2
70.3
75.1
79.6
83.8
87.8
91.6
95.3
98.8
102.2
105.5
108.6
111.7
114.6
117.5
120.3
115
20.8
31.8
40.6
48.1
54.8
60.9
66.5
70.7
76.6
81.2
85.5
89.6
93.6
97.3
100.9
104.4
107.8
111.0
114.1
117.2
120.1
122.9
125.7
120
21.2
32.4
41.3
49.0
55.8
62.0
67.7
73.1
78.0
82.7
87.2
91.4
95.4
99.3
103.0
106.6
110.0
113.3
116.5
119.6
122.6
125.6
128.4
131.2
125
21.5
32.9
42.0
49.9
56.8
63.1
68.9
74.4
79.5
84.3
88.8
93.1
97.3
101.2
105.0
108.6
112.2
115.6
118.8
122.0
125.1
128.1
131.0
133.9
27.3
136.7
130
135
140
145
150
b
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
21.9
33.4
42.6
50.6
57.7
64.2
70.1
75.7
80.8
85.7
90.4
94.8
99.0
103.1
106.9
110.7
114.3
117.7
121.1
124.4
127.5
130.6
133.6
136.5
139.3
142.1
135
22.2
33.9
43.3
51.4
58.6
65.2
71.3
76.9
82.2
87.2
91.9
96.4
100.7
104.9
108.8
112.6
116.3
119.9
123.3
126.7
129.9
133.0
136.1
139.1
142.0
144.8
147.6
140
22.5
34.4
43.9
52.2
59.5
66.2
72.4
78.1
83.5
88.6
93.4
98.0
102.4
106.6
110.7
114.6
118.3
122.0
125.5
128.9
132.2
135.4
138.5
141.6
144.6
147.5
150.3
153.0
145
22.8
34.9
44.5
52.9
60.4
67.2
73.5
79.3
84.8
90.0
94.9
99.6
104.1
108.4
112.5
116.5
120.3
124.0
127.6
131.1
134.5
137.7
140.9
144.0
147.1
150.3
152.9
155.7
158.5
150
23.1
35.3
45.2
53.6
61.2
68.1
74.5
80.5
86.1
91.3
96.3
101.1
105.7
110.0
114.3
118.3
122.2
126.0
129.7
133.2
136.7
140.0
143.3
146.4
149.5
152.6
155.5
158.4
161.2
164.0
155
23.4
35.8
45.7
54.4
62.1
69.1
75.6
81.6
87.3
92.6
97.4
102.6
107.2
111.7
116.0
120.1
124.1
127.9
131.7
135.3
138.8
142.2
145.5
148.8
151.9
155.0
158.0
161.0
163.9
166.7
160
23.7
36.2
46.3
55.1
62.9
70.0
76.6
82.7
88.5
93.9
99.1
104.1
108.8
113.3
117.7
121.9
125.9
129.8
133.6
137.3
140.9
144.4
147.8
151.1
154.3
157.5
160.5
163.5
166.5
169.3
165
23.9
36.7
46.9
55.7
63.7
70.9
77.6
83.8
89.7
95.2
100.5
105.5
110.3
114.9
119.3
123.6
127.7
131.7
135.6
139.3
143.0
146.5
150.0
153.3
156.6
159.8
163.0
166.0
169.0
171.9
170
24.2
37.1
47.5
56.4
64.4
71.8
78.5
84.9
90.8
96.4
101.8
106.9
111.8
116.4
120.9
125.3
129.5
133.5
137.5
141.3
145.0
148.6
152.1
155.6
158.9
162.2
165.3
168.5
171.5
174.5
175
24.5
37.5
48.0
57.1
65.2
72.6
79.5
85.9
91.9
97.6
103.1
108.2
113.2
118.0
122.5
127.0
131.2
135.3
139.3
143.2
147.0
150.7
154.2
157.7
161.1
164.4
167.7
170.8
173.9
177.0
180
24.7
37.9
48.5
57.7
66.0
73.5
80.4
86.9
93.0
98.8
104.3
109.6
114.6
119.5
124.1
128.6
132.9
137.1
141.2
145.1
148.9
152.7
156.3
159.8
163.3
166.7
170.0
173.2
176.4
179.4
185
25.0
38.3
49.1
58.4
66.7
74.3
81.4
87.9
94.1
100.0
105.6
110.9
116.0
120.9
125.6
130.2
134.6
138.8
143.0
147.0
150.9
154.7
158.3
161.9
165.4
168.9
172.2
175.5
178.7
181.9
190
25.3
38.7
49.6
59.0
67.4
75.1
82.2
88.9
95.2
101.2
106.8
112.2
117.4
122.4
127.2
131.8
136.2
140.5
144.7
148.8
152.7
156.6
160.3
164.0
167.6
171.0
174.4
177.8
181.0
184.2
195
25.5
39.1
50.1
59.6
68.1
75.9
83.1
89.9
96.3
102.3
108.0
113.5
118.7
123.8
128.5
133.3
137.9
142.2
146.5
150.6
154.6
158.5
162.3
166.0
169.6
173.2
176.6
180.0
183.3
186.6
200
25.8
39.5
50.6
60.2
68.8
76.7
84.0
90.8
97.3
103.4
109.2
114.7
120.0
125.2
130.1
134.8
139.4
143.8
148.1
152.3
156.4
160.4
164.2
168.0
171.7
175.3
178.8
182.2
185.6
188.9
210
26.3
40.3
51.6
61.4
70.2
78.3
85.7
92.7
99.3
105.6
111.5
117.2
122.6
127.9
132.9
137.8
142.5
147.0
151.5
155.0
160.0
164.0
168.0
171.9
175.7
179.3
183.0
186.5
189.9
193.3
220
26.7
41.0
52.5
62.5
71.5
79.7
87.4
94.5
101.3
107.6
113.7
119.5
125.1
130.5
135.7
140.6
145.5
150.2
154.7
159.1
163.4
167.6
171.6
175.6
179.5
183.3
187.0
190.6
194.2
197.7
230
27.2
41.7
53.4
63.6
72.8
81.2
89.0
96.3
103.1
109.7
115.9
121.8
127.5
133.0
138.3
143.4
148.4
153.2
157.8
162.3
166.7
171.0
175.2
179.3
183.2
187.1
190.9
194.7
198.3
201.9
240
27.6
42.4
54.3
64.7
74.0
82.6
90.5
98.0
105.0
111.6
118.0
124.1
129.9
135.5
140.9
146.1
151.2
156.1
160.8
165.5
170.0
174.4
178.6
182.8
186.9
190.9
194.8
198.6
202.3
206.0
250
28.1
43.0
55.2
65.8
75.3
84.0
92.0
99.6
106.8
113.6
120.0
126.2
132.2
137.9
143.4
148.8
153.9
158.9
163.8
168.5
173.1
177.6
182.0
186.3
190.4
194.5
198.5
202.4
206.2
210.0
260
28.5
43.7
56.0
66.8
76.4
85.3
93.5
101.2
108.5
115.4
122.0
128.3
134.4
140.2
145.9
151.3
156.6
161.7
166.7
171.5
176.2
180.8
185.2
189.6
193.9
198.0
202.1
206.1
210.0
213.9
270
28.9
44.3
56.9
67.8
77.6
86.6
95.0
102.8
110.2
117.3
124.0
130.4
136.6
142.5
148.3
153.8
159.2
164.4
169.5
174.4
179.2
183.9
188.4
192.9
197.2
201.5
205.7
209.7
213.7
217.7
280
29.3
45.0
57.7
68.8
78.7
87.9
96.4
104.3
111.9
119.0
125.9
132.4
138.7
144.7
150.6
156.2
161.7
167.0
172.2
177.2
182.1
186.9
191.5
196.1
200.5
204.9
209.1
213.3
217.4
221.4
290
29.7
45.6
58.5
69.7
79.8
89.1
97.7
105.8
113.5
120.8
127.8
134.4
140.8
146.9
152.9
158.6
164.2
169.6
174.8
180.0
185.0
189.8
194.5
199.2
203.7
208.1
212.5
216.7
220.9
225.0
300
30.1
46.2
59.2
70.6
80.9
90.3
99.0
107.3
115.1
122.5
129.5
136.3
142.8
149.0
155.5
160.9
166.6
172.1
177.5
182.7
187.7
192.7
197.5
202.2
206.8
211.3
215.8
220.1
224.3
228.5
a
b a
150
150
164
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
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
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
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
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
248
251
276
278.8
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
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
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 Pressure Drop Machine name (mmWg) 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 Diffuser Air volume 550 730 #25 H 0.6 1.0 V 1.2 2.2 Air volume 790 1055 H 0.6 1.0 #30 V 1.2 2.2 Air volume 150 240 Single H 4.7 12.5 column V 2.1 5.2 Air volume 240 420 Double Strip H 3.0 9.5 column outlet V 1.4 4.0 Air volume 360 540 3 H 3.0 7.0 column V 1.4 2.9 W H Air Air (m/m) (m/m) volume volume
Air volume unit: m3/H Remarks (reference value: Xin Huang) H: horizontal blow-out (cooling); V: vertical blow-out (heating); ⊙ With air volume regulating valve, add pressure drop by 2.5mmwg.
⊙Including pressure drop of the static pressure chamber at the blow-out outlet.
Remarks
VHS
Nozzle outlet
Ball outlet
300
300
500
300
(Pressure (Pressure drop ) drop) 650 975 0.8 1.9 1080 1620 0.8 1.9 260 520 0.4 1.4 450 900 0.4 1.4 85 171 0.6 2.5 222 445 0.6 2.5 Air supply 1.4, Air exhaust 0.9
152ø 200ø #8 #12
Shutter
⊙ With regulating pressure 1.0mmwg.
air volume valve, add drop by
Surface air v=2.5m/s.
Local pressure drop for sound-suppressing elbow (reference value: Linggong) 50
Guide Vane 导流叶片
25
L
w Ln=w+50
25
L
Inner Surface: Glass Cloth Lining 内表面：玻璃布内衬 Glass Wool 玻璃棉 Outside: galvanized steel plate 外面：镀锌钢板
50
25
w w+50
H
H+50
25
25
25
•
⊙Air valve fully open; ⊙Blow-out angle =45º.
m Glass玻璃棉25m Wool
m+导流叶片 Glass玻璃棉50m Wool Guide Vane
velocity
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 0.3-0.4 1.2-1.5 2.6-3.3 4.6-5.8 0.8-1.0 350—500 1.5 0.3 1.0-1.3 2.3-2.9 4.0-5.2 0.7-0.9 550—750 1.5 0.2-0.3 0.9-1.2 2.1-2.8 3.7-4.9 0.6-0.8 800—1200 1.5 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: L/R
Damper (split vane) L/R=W╳叶片枚数/2(H +W) L/R=W× Vane number/2(H+W)
0.6 H
θ
v W
1.0 1.5
0 20 0 20 0
v ζ 0.52 2.3 0.52 2.7 0.52
20
3.2
θ
4m/s
6m/s
8m/s
10m/s
15m/s
0.5 2.3 0.5 2.7 0.5
1.2 5.1 1.2 6.0 1.2
2.1 9.0 2.1 10.6 2.1
3.2 14.1 3.2 16.5 3.2
7.2 31.6 7.2 37.1 7.2
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
Exhaust air
Same area ratio
—
0.5
2.0
4.0
7.1
11.0
Shutter Air velocity: surface air velocity