Belimo Damper Air Flow Linearizing Tutorial Rev 1
DAMPER AIR FLOW LINEARIZING TUTORIAL
Goal is a linear change in air flow quantity per volt of signal change. Actuator Response Damper and Characterized Actuator 100% 90% 80% 70% 60% 50% 40% % Air Flow % Air 30% 20% 10% Damper Response 0% ) n 0 0 0 0 0 0 1 2 3 40 50 60 7 8 (ope 0 Degrees Open 9
Resulting Flow with respect to control signal
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Contents
Introduction ...... 3 Problem Applications...... 4 System Self-Correction ...... 5 Control Loop Tuning...... 6 Authority Concept...... 6 Summary of Damper Characterization Methods...... 10 AMCA Figure Numbers – Geometric Set-ups...... 10 The Danger in Over-Generalizing from Ducted to Other Geometries...... 12 Linearizing Actuator and Damper Combination...... 13 Review ...... 14
Appendix 1 Testing Results from ASHRAE RP1157...... 17 AMCA 5.1 Entrances ...... 17 Louvered Entrances...... 18 AMCA Type 5.2 Exits...... 19 Louvered Exits...... 20 AMCA 5.3 Ducted Type Applications...... 20 AMCA 5.3 Ducted Type Applications...... 21 AMCA 5.4 Plenum Entrances ...... 23 AMCA 5.5 Plenum Exits ...... 24
Appendix 2 Estimating Authority...... 25
Appendix 3 Estimating full open damper losses ...... 26
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Damper Air Flow Response
Introduction
Figure 1 Problems and Design Goal Total quantity of air flow through a system.
Problems TOTAL
Q TOTAL Q EA or EA or OA OA A ) B) RA RA
ROTATION ROTATION
Design Goal TOTAL Q At any given fan speed modulation of economizer dampers should ) C allow flow quantity to remain near constant.
ROTATION
In modulating dampers for air flow control a number of non-linearities are possible and must be defeated to gain accuracy. The applications here concentrate on the economizer section of air handlers, but the ideas can be applied to less complex arrangements of dampers also. The goal is to present the concept of a programmable actuator and damper combination dependent on the geometry of the situation. Figure 1 shows the problems that sometimes exist and the design goal.
The exact shape of any damper curve depends on these main factors: 1. Action – opposed blade (OB) or parallel blade (PB). 2. Geometry – Entry, ducted, plenum, etc. 3. Authority – the amount of pressure loss within the damper itself compared to the subsystem in which it is installed.
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4. Presence of jackshafts and/or linkages which may or may not change the rotation of the blades with respect to the actuator rotation. The full open flow is not affected by linkages or jackshafts, nor by PB or OB use. 5. The entering flow profile – e.g., if near an elbow, most of the air can be moving thru the top area of the damper and flowing backwards in the bottom. 6. Free area ratio of the damper with respect to the duct or wall. This is an orifice effect where A1/A2 can have a significant effect. For small areas inside the damper, the application is similar to that of a wall.
Problem Applications
Figure 2 Parallel Blade Overflow
EA RP RA Total Flow
EAD Q OA & OAD RAD EA
OA MA SA RA
Damper Position
In Figures 2 and 3 the common problem applications are depicted. The dampers could be matched to the system by selecting PB or OB and by adjusting the authority. In Figure 2, all PB dampers cause an increase in air flow at modulating conditions, particularly at near 50% rotation of the dampers. A balancing damper, more duct restriction, or an orificed damper in the RA is needed to keep flows near constant during modulation. This can cause hunting of control systems, interaction with other control loops, and degradation of control and lifespan of components. In Figure 3 a different geometry is shown. All OB dampers lead to a decrease in flow at 50% rotation. Fans may ride up their curves to a degree sufficient to cause very high pressure and other problems. A choice of PB or OB needs to be made based on geometry. While an OB damper in the RA path causes underflow, a PB causes overflow. Engineering is necessary to control the system. Controls should fine tune a mechanically balanced system. They are not suited to establishing balance itself. The worst condition on problem projects occurs when OB dampers with certain linkage or jackshaft arrangements are used. Some geometric set-ups lower the response curves too far under the linear. This starves flow at the 50% positions.
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Figure 3 OB Damper Underflow
OA MA RP EA
OAD RAD EAD
SA RA
Total flow with OB dampers will be Q under the linear when half open in Total Flow the geometric configuration above.
RA OA
ROTATION
The solution is not so simple as simply using OB or PB in the appropriate geometry although that is a big help. The authority is also important. One cannot generalize to all cases from the drawings above.
System Self-Correction
The amount of pressure drop in the economizer portion is usually much lower than the rest of the system and the fan will not move far off the design operating point. This self-corrects. In other cases when the dampers or economizer system is a significant amount of the total pressure drop – 20% or more - failure to select dampers and analyze the system can lead to the problems shown in these figures. When the economizer section at 50% damper positions is still a low (<20%) proportion of the fan total loss, then the effects of poorly characterized dampers are mitigated. But some severe problems can and have occurred. Trusting in system self- correction without analysis is wishful thinking
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Control Loop Tuning
Figure 4 Control Loop Tuning
Q dQ/ds = .25
dQ/ds =2
ROTATION
When dampers are not linear the control loops require a difficult if not impossible tuning process. The amount of air flow change per volt of signal change varies with non linear dampers. See Figure 4. Hunting, erratic control, energy waste, equipment wear, and comfort problems can occur.
Authority Concept
Within a certain range of parameters, the authority concept as defined in ASHRAE1 can be applied to linearize the relationship between a control signal (2-10V or 4-20mA) and the velocity through a damper.
Figure 5 Authority
A subsystem is defined as the duct elements between two constant pressure points.
ΔP across subsystem must remain constant
C Damper AIR s FLOW
Cs stands for the total sum of C’s of the duct elements. Authority = damper loss / subsystem loss. Authority = damper C / sum of C in subsystem. Authority = damper full open ?P / damper closed ?P
1 2005 ASHRAE Handbook - Fundamentals, Chapter 15, p.15.5 -15.7. Note the incorrect overgeneralization from the ducted to all applications.
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The basic authority concept is shown in Figure 5. In Figure 5, Cs symbolizes the sum of all the series loss. The authority is ΔPdamper / ΔPsub-system. This is Cdamper / Cdamper + Cs if the ducts are all the same area. Figure 5 is the geometric set-up used for the charts in Figures 6 and 7.
Figure 6 Installed Characteristics of PB dampers in AMCA 5.3 Geometry
Figure 7 Installed Characteristics of OB dampers in AMCA 5.3 Geometry
Figure 6 shows typical PB response curves in the AMCA2 5.3 type set-up. Figure 7 shows typical OB response curves in the AMCA 5.3 type set-up. The AMCA 5.3 set-ups use long duct runs to get good flow profiles with unrealistically low pressure
2 See www.amca.org for information. AMCA is the Air Movement and Control Association.
7 Belimo Damper Air Flow Linearizing Tutorial Rev 1 drops as a result. For laboratory repeatability, good flow profiles are necessary. The authority curves do not take bad duct flow profiles into account. Examination of Figures 6 and 7 shows that a typical PB damper is linear at about 25% to 35% authority and a typical OB damper is roughly linear between 10% and 15% authority. These charts are based on tests on old style dampers used in the 1950’s and are not highly accurate. In addition, they are ducted only and one cannot generalize to other geometries. This is a geometric application dependent issue. We cannot generalize from the ducted application to say, a plenum wall application. Figure 6 Installed Characteristics of PB damper in AMCA 5.3 Geometry Interaction of airflows is another complication – as dampers are placed closer together, the interactions affect the flows – for the most part, untested. The curves in Figures 6 and 7 are not as regular as shown and once thought, but they show the tendency in the damper responses in the geometry tested. If the damper is the only pressure loss in a subsystem between two constant pressure points, then it has an authority of 100%. If it has .25 in. w.c. in a system with 1 in. w.c., then it would have 25% authority. Examination of the curves shows that if the authority is 100%, that the PB has a shallow equal percentage curve similar to the ball or butterfly valve. If an OB damper has 100% authority, then it has a deeper equal percentage curve similar to the Belimo characterized control valve or globe valve.
Figure 8 Authority Calculation Points - Ducted Air Handling Unit Subsystems
Authority = ΔP Damper Subsystems are indicated by dashed lines ΔP Subsystem between the constant pressure points.
The points EA to RP, RP to MA, and MA to OA EA Damper = ΔP’s Louver + are the pressure references for linearity of the Damper + Any duct elements dampers. Disregarding wind, these are constant pressure points if the system is linearized.
EA RP RA
The points RP EAD and MA are RA Damper = ΔP’s TRP + constant RAD damper + any duct pressure points if elements + TMA the dampers are OAD linear.
OA MA SA
OA Damper = Δ P’s Louver + Damper + duct elements + Flow Monitoring + Compression and Expansion. (Given Minimum OA may be two dampers and associated controls.
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Figure 8 shows an air handling unit and the points for calculating the three dampers’ authorities. The ASHRAE RP1157 testing makes the damper curves in Figures 6 and 7 obsolete. The general concept of Authority is correct, but the detailed shapes of the curves are quite different in most cases. If all the dampers are near linear, then the points RP and MA become nearly constant pressure points at any given fan speed. Fan speed changes and the consequent changes in velocities do not affect the authority calculations. The values of C of each duct element are nearly constant and a change in velocity pressure is proportional across each.. Each duct element retains its ratio of losses when the total value changes. If a damper is 10% of the subsystem drop at any given velocity, it will be nearly the same 10% at any other. With this in mind, Figure 2 should have OB OA and EA dampers and a PB RA damper to be roughly linear. Search Figures 6 and 7 for the nearest linear curves.
Figure 9 Authority Calculation Points - Equipment Room Subsystem Example
LOUVERS
Indicates constant pressure point for linearization of the OA Damper
OAD OAD OAD Indicates constant pressure point for linearization of the RA Damper
Since the EA damper interacts with the RAD RAD fan curve, linearization is near RAD impossible to calculate. AH AH AH The RAD’s are open to the equipment room space. RA’s are open to ceiling return. They are holes RA RA in the floor with protective bars.
RELIEF FANS RA damper is closest to an AIR FLOW AMCA 5.4 configuration.
OA damper is RAD closest to an AIR FLOW AMCA 5.1 configuration. OAD
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Figure 3 shows a more complex system. The full open damper with a 70-80% free area ratio has Copen = about 1. The recirculation damper and each of the T’s then has C =1. The authority of the damper is 33%. A PB is indicated. The EA and OA can use OB dampers since each approaches 10% authority given the louver drop. We must be careful not to over-generalize here. The recirculation path is often convoluted due to space constraints and as its duct element pressure losses increase, an OB becomes the better choice. Knowledge of the loss coefficients of the dampers and a hydraulic analysis of the duct system must be performed to arrive at the correct sizing and selection. One should also be aware of the variation in loss coefficients in the RP and MA tees. C varies with the percent of flow from 1 to 5 in some configurations.
Summary of Damper Characterization Methods
There are a number of methods of maintaining constant flow. Refer to the Dampers and Air Flow Control book at www.belimo.us (or www.belimo.ca) “AF Linearizing Actuator” for a free copy. Material in the book details the methods that are merely listed here. The other methods are: 1. MIDPOINT LINEARIZATION 2. VAV FAN ADJUSTMENT 3. COMBINATION PARALLEL AND OPPOSED BLADE DAMPERS 4. AUTHORITY TOTALIZATION 5. MULTI-POINT COMMISSIONING AND SIGNAL CONDITIONING 6. SOFTWARE RANGE CONTROL 7. HARDWARE RANGE CONTROL 8. BLANKOFF LINEARIZATION 9. LINKAGE LINEARIZATION 10. FULLY CHARACTERIZED DAMPERS 11. MULTI STAGE DAMPER CONTROL 12. LINEARIZING ACTUATOR (Covered in this document.)
AMCA Figure Numbers – Geometric Set-ups
The AMCA figures listed in Figure 10 are well recognized. If all other factors were the same, the geometry would cause the same damper to respond differently. For that reason, we must be able to identify the application.
1. AMCA 5.1, entrance, ducted downstream only. 2. AMCA 5.2, exit, ducted upstream only. 3. AMCA 5.3, fully ducted as shown already. 4. AMCA 5.4, wall entrance, ducted downstream only. 5. AMCA 5.5, exit, wall mounted with upstream duct. 6. Wall mounted
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Figure 10 Geometric Applications with AMCA Figure numbers
5.1 5.2 Any individual damper 5.3 in the AH figures here could be any of the AMCA figures Ducted depending on the situation. Walled
5.4 5.5 Case 6
Other geometrical effects exist which are still untested.
Many applications are part one and part another AMCA Figure. Given that approximate linearization is much more accurate than none, one can average two or pick the closest. See Figure 11. Sometimes, simple logic must be applied. For example, with a face and bypass damper, one must assume that if sized correctly, the up and down stream pressures are nearly constant. If linearizing the damper, use those pressures.
Figure 11 Mixed applications
RA AMCA 5.1
Relief Wall, like a 5.3 but with a rough entering OA flow profile
Relief Chase EAD to Outside AMCA RA fan RA 5.2
OA Half 5.4 & SA Half wall Half 5.4 & half 5.2
Indicates constant pressure point for linearization of the OA Damper Indicates constant pressure point for linearization of the RA and Relief Dampers
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The Danger in Over-Generalizing from Ducted to Other Geometries
The Figure 12 graph shows the ASHRAE testing results for two applications with the same OB damper. The curves deviate significantly from each other. The point of Figure 12 is that over-generalization leads to erroneous assumptions. By comparing the different responses of the same dampers in different geometric set-ups, one sees that they respond with different characteristic curves.
Figure 12 Various Response Curves in Different Geometric Set-ups
DAMPER Louvered Exit OB 6" B-16
100%
AIR FLOW 90%
80% LOUVER 70% 60% A 50% E 40%
30% % MaxFlow
20%
10%
0% 12345678910Amount Open
Elbow-Damper OB B-29 100% A 90% B
80% E
70% F 36W X 48H 60% AIR FLOW
50% 36"
40% % Max Flow 30%
20%
10%
0% 12345678910 Amount Open
Figure 13 shows two dampers in a number of different AMCA configurations and the response curves that occur. The available pressure in each case is 1”. The ASHRAE testing included louvers which had never before been tested with dampers. Note that for the most part the curves are the same until the damper is 60º to 70º open. The plenum wall has significant orifice effects which affects the flow curves.3
3 C1 is a function of F = A2/A1 (orifice area / wall area). At .1 free area C1 will typically equal 2/F2 = 2/.01 = 200 with respect to the duct velocity. C2 would be the coefficient with respect to the velocity pressure inside the damper; C2 = 2 in this case. The velocity pressure inside the orifice is all lost to atmosphere.
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Figure 13
PB Absolute Velocities at 1" Pressure Drop
A5.1 3V A5.1 AF 12000 A5.2 3V A5.2 AF 10000 A 5.3 3V A5.3 AF 8000 A5.3 AE 3V A 5.4 3V 6000 A5.4 AF Velocity A5.5 3V 4000 A5.5 AF
2000
0
0 0 0 0 ) 1 20 30 4 5 60 70 80 n pe Amount Open o AMCA 5.3 in Bold 90 ( The combined response curves and the absolute velocity are shown here. The AMCA 5.3 test set-up has C =apx. .15 for an air foil. V = 4005 Pv½. Pv = Pt/C. V = 4005 x (1/.15)1/2 = 10,300
The AMCA 5.5 test set-up has C =apx. 170. ½ 1/2 V = 4005 Pv . Pv = Pt/C. V = 4005 x (1/170) = 300.
Linearizing Actuator and Damper Combination
In Figure 14 the damper response is shown as an under the linear curve. The actuator is programmed to compliment the damper so that the actual flow with respect to input signal is linear. The dashed line indicates the desired linear flow. With a standard actuator, the movement would follow this line resulting in a non- linear response between damper and flow quantity. Standard actuators are linear with respect to the control signal. The LIN actuator rotation is pre-programmed to compliment the damper. For example, a 3V signal with a 0-10V actuator would normally result in 3/10 = 30% rotation. Given 90 degrees of damper-actuator rotation this would be 27 degrees of damper rotation. However this would result in about 10% flow in this geometry. Follow up the 27 degree open to the damper response line and read 10% on the left y-axis % air flow. A programmed Belimo linearizing actuator sees 3V and moves to about 60 degrees open. At 60 degrees actuator rotation the damper is about 60 degrees open also. This results in about 30% flow.
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To see this: Go to the x-axis “Open” category, go over to 27 degrees (Or just approximate to 30.) Go up to the actuator curve. Go over to the left y-axis to 60%. Go back down to the x-axis. Look at 60 degree damper rotation. Read over to the y-axis to % Air Flow. It is about 30%. Instead of getting 10% flow for 3V signal, one gets 30%. The goal was 30%. There is significant improvement. The numbers here are approximate. While damper manufacturers may test the geometry in the lab, there are always variations in the field. However the main point is that the improvement by using linearizing actuators is significant. When some significant variation occurs due to unknowns, the actuators are field programmable to correct as necessary.
Review Installed damper response curves are dependent on five main factors: 1. The type of damper – opposed blade (OB) or parallel blade (PB).
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2. The geometric application – ducted, entrance or exit, plenum, wall mount. 3. Authority 4. Presence of jackshafts and/or linkages which may or may not change the rotation of the blades with respect to the actuator rotation. If each individual damper is linearized, then the pairs are near linear and the total flow is near linear. 5. Flow profile of the entering air 6. Free area ratio of the damper with respect to the duct or wall.
The authority concept is dependent on the duct configuration. It is limited to fully ducted applications where the full open damper subsystem loss is less than 20% of the total fan loss.
AF24-LIN Belimo programmable linearizing actuator
To most accurately preprogram the actuator these must be defined: 1. OB or PB. 2. Application geometry. Define the most similar AMCA Figure or case number. 3. Approximate Authority Statement of subsystem ΔP and damper ΔP for each damper is sufficient. Verbal description is not acceptable since verbal pictures are too fuzzy. A drawing is preferable. Do not apply wishful thinking. 4. Presence of Jackshafting or linkages.
Standard selection criteria must still be considered – static pressure, velocity at full open, size of duct, temperature limits, vertical or horizontal blades. These determine the damper model and the torque required.
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Figure 15 shows how any of the exact damper geometries may be used within a system.
Figure 15 Overview
LOUVER
AIR FLOW OB DUCTED EXIT WITH LOUVER RP RA EA AIR FLOW
OB DUCTED EXIT AMCA 5.2
EAD
OB after EL disturbance
AIR Any of the other FLOW AMCA Figures AIR FLOW may apply also.
RAD
OAD OA
Anti PB action DAMPER
AIR FLOW Close LOUVER
LOUVER ENTRY Anti PB MA SA AIR FLOW
DUCTED ENTRANCE AMCA 5.1
ENTRANCE PLENUM AMCA 5.4
AIR FLOW
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Appendix 1 Testing Results from ASHRAE RP1157
These are damper response curves – flow vs. amount open
The 100% authority curves are all from the ASHRAE RP1157 research project. The other curves are calculated and were randomly checked for validity. Calculations were based on multiple tests whose results were averaged. Variations of about ±10% were commonly observed.
AMCA 5.1 Entrances 5.1 PB at Varying Authorities
10 0 % 90%
AIR 80% FLOW 70% 60% 100%
DUCTED ENTRANCE 50% 50% AMCA 5.1 40% 25% 30% % Maximum Flow 10% 20% 10 % 5%
0% 0 102030405060708090 (open) Amount Open
5.1 OB at Varying Authorities 100% 100% 90% 50% 80%
w 70% 25% AIR FLOW 60% DUCTED ENTRANCE AMCA 5.1 50% 40%
% Maximum Flo 30% 20% 10% 0%
0 0 0 n) 1 20 30 40 50 60 70 8 e
0 (op Amount Open 9
If authority were redefined for the specific application geometry, then a PB is linear enough above 15% and an OB is not linear under any circumstances.
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Louvered Entrances Louvered OB Entry 100%
90%
80% LOUVER 70%
60% AIR FLOW 50% 40% OB Damper 10% % Maximum Flow 30% DUCTED ENTRANCE w/ Louver 5% 20% 10% 0%
0 0 0 0 0 0 0 0 0 1 2 3 4 5 6 7 8 pen) Amount Open 90 (o
Anti PB Louvered Entry 100% Anti PB action 90% DAMPER 80%
70% w 60%
AIR FLOW 50% Close 40% 10%
LOUVER Maximum% Flo 5% 30% 2.5% LOUVER ENTRY Anti PB 20%
10%
0%
0 10 20 30 40 50 60 70 80 en)
90 (op Amount Open
Entry Louver with PB
LOUVER PB Damper 100% 90%
80% AIR FLOW 70% w Close 60%
50% DUCTED ENTRY W/ LOUVER 10% 40%
% Maximum Flo 5% 30% 2.5%
20%
10%
0%
0 0 10 20 30 4 50 60 70 80
Amount Open 90 (open)
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AMCA Type 5.2 Exits 5.2 PB Exits at Varying Authorities
100% 90% 80%
w 70% 60% AIR FLOW 100% 50% 50% 40% PB DUCTED EXIT 25%
AMCA 5.2 % Maximum Flo 30% 10% 20% 5% 10% 0%
0 10 20 30 40 50 60 70 80 Amount Open 90 (open)
5.2 OB EXITS at Varying Authorities 100% 90% 80% 70% AIR FLOW 60% 100% 50% 50% 40% 25% 10%
OB DUCTED EXIT AMCA 5.2 % Maximum Flow 30% 5% 20%
10% 0% 0 0 0 10 2 30 40 50 60 7 80 (open) Amount Open 90
A PB is roughly linear at 5% to 50% authority. An OB is roughly linear at 10% to 25% authority.
In the louvered application, the damper is about 10% authority initially, since the louver pressure loss is about nine times higher.
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Louvered Exits
Louver Exit OB at Varying Authorities LOUVER 120%
100% AIR FLOW
w 80%
OB DUCTED EXIT WITH LOUVER 60% 10% 40% % MaximumFlo 5% 2.5% 20%
0%
0 0 0 0 0 ) 1 2 3 40 50 60 7 80 en op ( Amount Open 90
PB Louver Exit at Varying Authorities LOUVER 120%
AIR FLOW 100%
Open w 80%
60% PB DUCTED EXIT W/ LOUVER 10%
40% 5% % Maximum Flo
2.5% 20%
0%
0 0 0 10 20 3 40 50 60 70 8
90 (open) Amount Open
LOUVER Louver Anti PB at Varying Authorities
120% AIR FLOW
Close 100%
w 80% Anti PB DUCTED EXIT W/ LOUVER
60% 10% 40% 5% % Maximum Flo 2.5% 20%
0%
0 ) 10 20 30 40 50 60 70 80 open Amount Open 90 (
No authority is linear. 20 Belimo Damper Air Flow Linearizing Tutorial Rev 1
AMCA 5.3 Ducted Type Applications
Inherent characteristic (100% authority) only. Damper A is a 3V, Damper B is flanged, and Damper C is an airfoil.
PB 5.3 with Duct Restriction 5.3 Type Damper-Elbow PB 100%
90%
AIR FLOW 80% A 3V B 70% C AF 60%
50%
% Max Flow 40%
30%
20% 10%
0% 12345678910 Amount Open OB 5.3 with Duct Restriction 5.3 Type Damper-Elbow OB 100%
90% AIR FLOW 80%
70%
60%
50% A 3V B
% Max Flow 40% C AF
30%
20% 10%
0% 12345678910 Amount Open
This and the next application are the closest to the actual AMCA Figure 5.3 in this set. There is a small amount of series loss. PB is roughly linear at 25% authority. OB is most non linear at 5% authority.
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Damper A is a 3V, Damper B is flanged
PB after EL disturbance Elbow-Damper PB
100%
AIR FLOW 90% A 3V
80% B
70%
w 60% 50%
% Max Fl o 40%
30%
20% 10% 0% OB after EL disturbance 12345678910 Amount Open
Elbow-Damper OB AIR FLOW 100%
90% A 3V 80% B 70%
w 60%
50%
% Max Fl o 40%
30%
20% 10%
0% 12345678910 Amount Open
This is an AMCA 5.3 type application, but with a disturbed entering flow profile. The authority curves are not shown so that the differences in damper type stand out.
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AMCA 5.4 Plenum Entrances
100%
90%
80%
70%
60%
50% AF at 100% 3V at 100% 40% A = 50% 3V 30% A = 25% 3V PB A = 10% 3V 20% A = 5% 3V 10%
0% 0 10 20 30 40 50 60 70 80 90 (open)
100% 3V A = 100% AF A = 100% 90% 3V A = 50% 3V A = 25% 80% 3V A = 10% 70% 3V A = 5%
60%
50%
40%
30%
20%
OB 10%
0% 0 102030405060708090 (open)
An authority of 100% is roughly linear for a PB and the OB will be very roughly linear at 50% authority.
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AMCA 5.5 Plenum Exits
EXIT PLENUM AMCA 5.5 100%
90%
80%
70%
AIR FLOW 60%
PLENUM WALL 50% A =100%
40% A =50% 30% A =10% PB 20%
10 % 0% 0 10 20 30 40 50 60 70 80 90 (open)
10 0 % 90% 80% 70%
60%
50%
40%
30% A =100% A =50% OB 20% A =10% 10%
0% 0 10 20 30 40 50 60 70 80 90 (open)
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Appendix 2 Estimating Authority
C = 2 MA C = 1 RP C = 1RP C = 1 C = 1 A = 1/6 = 16% A = 1/3 = 33% MA C = 3 (avj) If all the ducts are the same size, the loss coefficients can be used as above.
More commonly, the actual pressure losses are used as below.
dP = .2" RP A = .06 / 51 = dP = in w.g. dP = .06" 12% abbreviated to “ MA dP = .25" A = 1/5 = 20% C = 1 A = 1/6 = 16% MA C = 2 MA RP RP C = 2 C = 3 C = 2 C = 1 A = 7% A = 7% C = 1 C = 1 A = 1/11 = C = 1 7% C = 10 Clouver = 10 Clouver = 10 louver
C / C Duct sized dampers with damper subsystem if areas of all ducts are equal. standard elbows and louvers. A = Authority = A = Δpdamper / ΔPsubsystem
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If all dampers are linearized, then the points RP and MA are constant pressure points for any given fan speed.
The authorities will always be the same since ALL the duct and element losses are proportional to the velocity pressure.
The ratio is constant.
The duct loss is rarely significant. If a high amount of the loss in a subsystem, then add to the total.
Note that older ASHRAE Handbooks used the term “alpha.” This is not the same as authority and should not be used. Valves and all damper manufactures now use authority.
Appendix 3 Estimating full open damper losses
DAMPER LOSS COEFFICIENTS
Full open losses are most affected by profiles. Modulated losses are less affected since the damper closes and pressure backs up.
Height Width 12" 24" 36" 48" 12" 0.45 0.5 0.55 0.6 24" 0.6 0.65 0.7 0.7 36" 0.65 0.7 0.7 0.75 48" 0.65 0.7 0.75 0.8 FAR is free area ratio, that is the open area inside the damper / area of the frame.
Typical free area ratios are given above. Deduct .1 for insulated blades and industrial dampers.
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The most common damper installation cases: 1. AMCA 5.1, entrance, ducted downstream only. 2. AMCA 5.2, exit, ducted upstream only. 3. AMCA 5.3, fully ducted as shown already. 4. AMCA 5.4, wall entrance, ducted downstream only. 5. AMCA 5.5, exit, wall mounted with upstream duct. 6. Wall mounted 7. Ducted but with realistic short runs of duct before and after the damper. 8. The damper can be placed at right angles to the air flow. This is complex and no data exists. It may be best to add the losses of a right elbow and the damper.
Use ΔPt = C x Pv to find the loss of an individual element. Pv = (V/4000) 2 in. w.g. with V in f/s [Pv = .6V2 in Pa with V in m/s.]
AMCA Figures
WALLED
5.4 Case 5.5 6
5.1 5.2 5.3
DUCTED
For multi-section dampers: Use the entire wall as the area, A1. Use the free area of the damper as A2. Then F = A2/A1.
The method shown below is not absolutely precise, however it serves as a set of rules of thumb for more accurate estimation than no calculation at all.
27 Belimo Damper Air Flow Linearizing Tutorial Rev 1
For quick, rough calculation of open damper pressure loss, use these charts:
Geometric Application, C To calculate needed F:
1. For full duct mounted applications, 2 C0 = Fg x [ (1/F ) - 1] F = √ ( Fg / (C0 + Fg) )
2. For duct wall mounted dampers, .2 < F < .5 2 C0 = Fg x (1/F ) F = √ [ Fg / C0 ]
3. For duct wall mounted dampers, F < .2 2 C0 = Fg x (1.5/F ) F = √ [ 1.5 * Fg / C0 ]
4. For ducted entrances from large spaces, AMCA 5.1 2 C0 = Fg x (1.4/F -1 ) F = √ ( 1.4 Fg / C0 + Fg)
5. For ducted exits into atmosphere or large spaces, AMCA 5.2 2 C0 = Fg x (1.1/F ) F = √ [ 1.1 * Fg / C0 ]
6. For plenum exits and entrances, AMCA 5.4 and 5.5 2 C0 = Fg x (1.8/F ) F = √ [ 1.8 * Fg / C0 ]
Fg: a. Bad Flow Profile Less than one duct diameter before damper. Fg = 1.5 b. Poor Flow Profile This is most common factor; use as default. Fg = 1 c. Good Flow Profile 5 diameters before and after the damper. Fg = .6 Note that the modulated positions are not as affected by the geometry as those near full open due to pressure build-up. The method here is complicated enough, and the 80° and 70° positions are not included. By 60° the effects are mostly diminished .
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