Staircase Pressurization Fan အရြယ္အစားတြက္နည္း

Precaution in Building hand book အရ ထြက္ေပါက္အျဖစ္သံုးမည့္ေလွခါး(fire escape staircase) မ်ားအားလံုးသည္ သဘာ၀အတိုင္း ေလ၀င္ေလထြက္ေကာင္းေအာင္ ျပဳလုပ္ထားျခင္း မရွိလွ်င္ (naturally ventilated မဟုတ္ခဲ့လွ်င္) mechanical ventilation လုပ္ထား႐ံုသာမက ဖိအားျမင့္ေအာင္ လုပ္ထား ေပးရန္(pressurization) လုပ္ထားေပးရန္ မျဖစ္မေန လိုအပ္သည္။
အေဆာက္အဦး အျမင့္ကိုလိုက္၍ တြက္နည္း (၂)မ်ဳိး ကြဲျပားသည္။ (၂၄)မီတာထက္ နိမ့္လွ်င္ “10 ACH နည္း”ကို အသံုးျပဳ၍ (၂၄)မီတာထက္ ပိုျမင့္လွ်င္ “full pressurization နည္း”ကို အသံုးျပဳရမည္။
(၁) 10 ACH နည္း
10 ACH (10 Air Change per Hour) ဆုိသည္မွာ တစ္နာရီလ်ွင္ ေလွခါး၏ ထုထည္ (၁၀)ဆႏွင့္ ပမာဏတူညီသည့္ ေလ၏ ထုထည္ထည့္ေပးရန္လုိအပ္သည့္ ဟုဆုိလုိသည္။
Normal mode တြင္ ေလွခါး(staircase)အတြင္း၌ ေလ၀င္ေလထြက္ေကာင္းရန္အတြက္ 4 ACH ႏႈန္းျဖင့္ ထည့္ေပးရန္ လိုအပ္သည္။ Fire mode တြင္ ေလွခါး(staircase) အတြင္း၌ ဖိအားျမင့္တက္ေနေစရန္ 10 ACH ႏႈန္းျဖင့္ ထည့္ေပးရမည္။
10 ACH နည္း - တြက္နည္းအဆင့္ဆင့္
(၁) ပထမဆင့္
အေဆာက္အဦ၏ အျမင့္သည္ (၂၄) မီတာထက္ ပိုျမင့္၊ မျမင့္စစ္ေဆးရန္
(၂) ဒုတိယအဆင့္
ေလွခါးထုထည္ကို တြက္ရန္
(၃) တတိယအဆင့္
Normal mode အတြက္ 4ACH ႏႈန္းျဖင့္ volume flow rate ကို တြက္ပါ။
(၄) စတုတၳအဆင့္
Fire mode အတြက္ 10 ACH ႏႈန္းျဖင့္ volume flow rate ကို တြက္ပါ။
ဥပမာ(၁) 10 ACH နည္း
(၁) ပထမဆင့္ - အေဆာက္အဦ အျမင့္သည္ (၂၄) မီတာထက္ ပိုျမင့္၊ မျမင့္ စစ္ေဆးရန္။
အေဆာက္အဦသည္ ၇ထပ္ျမင့္ေသာ္လည္း ထုထည္ရွာရန္ အျမင့္ကုိ တြက္သည့္အခါ (၁)ထပ္ႏုတ္ရသည္။ အဘယ္ေၾကာင့္ဆုိေသာ္ ေျမညီထပ္ကို ပထမထပ္ဟု သတ္မွတ္ထားေသာေၾကာင့္ျဖစ္သည္။
ေလွခါးအျမင့္(staircase high) = (7-1) ထပ္ x 3.4 m
= 20.4m<24m
အေဆာက္အဦသည္ (၂၄) မီတာထက္ ပိုနိမ့္ေသာေၾကာင့္ 10ACH နည္းကို အသံုးျပဳရမည္။
(၂) ဒုတိယအဆင့္ - ေလွခါး ထုထည္(staircase volume)ကို တြက္ရန္
ေလွခါး(staircase)၏ အလ်ားသည္ 4.5m ျဖစ္သည္။
ေလွခါး(staircase)၏ အနံသည္ 3m ျဖစ္သည္။
အေဆာက္အဦသည္ (၇)ထပ္ ျမင့္သည္။ တစ္ထပ္လွ်င္ ၾကမ္းျပင္(floor)မွ soffit အထိ 3.4 မီတာ ျမင့္သည္။
ေလွခါးထုသည္(staircase volume) = အလ်ား x အနံ x အျမင့္
= 4.5m x 3m x ((7-1)ထပ္ x 3.4m)
= 275.4 m3
(၃) တတိယအဆင့္ - Normal mode အတြက္ 4 ACH ႏႈန္းျဖင့္ volume flow rate ကို တြက္ပါ။
Normal Mode(4ACH)ကို တြက္ရန္
Air Volume Flow Rate = Staircase Volume x 4 ACH
= 275.4 x 4 ACH
= 1,101.6 CMH ဟု သတ္မွတ္ရန္
(၃) စတုတၳအဆင့္ -Fire mode အတြက္ 10 ACH ႏႈန္းျဖင့္ volume flow rate ကို တြက္ပါ။
Air V. F. R = Staircase Volume x 10ACH
= 275.4 x 10
= 2,754 CMH
= 2800 CMH ဟု သတ္မွတ္ရန္
ထု႔ိေၾကာင့္ ထုိေလွခါးတြင္အသံုးျပဳမည့္ fan ၏ volume flow rate သည္ normal mode အတြက္ 1,101.6 CMH ျဖစ္ၿပီး Fire mode အတြက္ 2800 CMH ျဖစ္သည္။ 2800 CMH (High speed) ႏွင့္ 1400 CMH(Low speed) ေပးႏုိင္သည့္ 2 speed fan ကို အသံုးျပဳႏုိင္သည္။
Duct size ႏွင့္ fan ၏ static pressure ကို တစ္ၿပိဳင္နက္ အတူတကြက တြဲ၍ တြက္ယူႏုိင္ပါသည္။ သတိျပဳရန္အခ်က္မွာ static pressure တြက္သည့္အခါ အျမင့္ဆံုးစီးႏႈန္း(fire mode)၏ volume flow rate ကို အေျခခံ၍ တြက္ယူရပါမည္။
ဤနည္းသည္ (၂၄) မီတာထက္ ပိုနိမ့္သည့္ အေဆာက္အဦမ်ားတြင္ တပ္ဆင္ထားသည့္ ေလွခါးအတြက္ တပ္ဆင္ရမည့္ fan အရြယ္အစားတြက္နည္း ျဖစ္ပါသည္။ (၂၄) မီတာထက္ ပိုျမင့္သည့္ အေဆာက္အဦမ်ားတြင္ တပ္ဆင္ထားသည့္ ေလွခါး၏ fan size တြက္နည္းကို ဆက္လက္ေဖာ္ျပပါမည္။
PDF File Download
http://www.acmv.org/…/Staircase_Pressurization-Calculation-…
ေကာင္းထက္ညြန္႔

Simple Equal Friction For Duct Sizing

The equal friction method of sizing ducts is often preferred because it is quite easy to use. The method can be summarized to

1. Compute the necessary air flow volume (m³/h, cfm) in every room and branch of the system
2. Use ¹⁾ to compute the total air volume (m³/h, cfm) in the main system
3. Determine the maximum acceptable airflow velocity in the main duct
4. Determine the major pressure drop in the main duct
5. Use the major pressure drop for the main duct as a constant to determine the duct sizes throughout the distribution system
6. Determine the total resistance in the duct system by multiplying the static resistance with the equivalent length of the longest run
7. Compute balancing dampers

1. Compute the air volume in every room and branch

Use the actual heat, cooling or air quality requirements for the rooms and calculate the required air volume - q.

2. Compute the total volume in the system

Make a simplified diagram of the system like the one above.
Use ¹⁾ to summarize and accumulate the total volume - q_total - in the system.
Note! Be aware that maximum load conditions almost never occurs in all of the rooms at the same time. Avoid over-sizing the main system by multiplying the accumulated volume with a factor less than one (This is probably the hard part - and for larger systems sophisticated computer-assisted indoor climate calculations are often required).

3. Determine the maximum acceptable airflow velocity in the main ducts

Select the maximum velocity in the main duct on basis of the application environment. To avoid disturbing noise levels - keep maximum velocities within experienced limits:

• comfort systems - air velocity 4 to 7 m/s (13 to 23 ft/s)
• industrial systems - air velocity 8 to 12 m/s (26 to 40 ft/s)
• high speed systems - air velocity 10 to 18 m/s (33 to 60 ft/s)

Use the maximum velocity limits when selecting the size of the main duct.

4. Determine the static pressure drop in main duct

Use a pressure drop table or similar to determine the static pressure drop in the main duct.

5. Determine the duct sizes throughout the system

Use the static pressure drop determined in ⁴⁾ as a constant to determine the ducts sizes throughout the system. Use the air volumes calculated in ¹⁾ for the calculation. Select the duct sizes with the pressure drop for the actual ducts as close to the main duct pressure drop as possible.  

6. Determine the total resistance in the system

Use the static pressure from ⁴⁾ to calculate the pressure drop through the longest part of the duct system. Use the equivalent length which is

• the actual length + additional lengths for bends, T's, inlets and outlets

7. Calculate balancing dampers

Use the total resistance in ⁶⁾ and the volume flow throughout the system to calculate necessary dampers and the theoretical pressure loss through the dampers.

Note about the Equal Friction Method

The equal friction method is straightforward and easy to use and gives an automatic reduction of the air flow velocities throughout the system. The reduced velocities are in general within the noise limits of the application environment.
The method can increase the numbers of reductions compared to other methods, and often a poorer pressure balance in the system require more adjusting dampers. This may increase the system cost compared to other methods.

Example - Equal Friction Method

The equal friction method can be done manual or more or less semi automatic with a spreadsheet as shown in the table below.

The table is based on the diagram above. Air flow and friction loss from a diagram is added. Minor pressure loss coefficients must be summarized for for the actual applications.
The pressure loss in each path is summarized on the right and pressure loss is added manually in the dampers to balance the system.