Belimo Damper Air Flow Linearizing Tutorial Rev 1 - Alps

Belimo Damper Air Flow Linearizing Tutorial Rev 1

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DAMPER AIR FLOW LINEARIZING TUTORIAL

Damper and Characterized Actuator

0%

10%

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40%

50%

60%

70%

80%

90%

100%

0 10 20 30 40 50 60 70 80

90 (o

pen)

Degrees Open

% A

ir Fl

ow

Damper Response

Actuator Response

Goal is a linear change in air flowquantity per volt of signal change.

Resulting Flow with respectto 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

Q

ROTATION

RA

EA orOA

TOTAL Q

ROTATION

EA orOA

TOTAL

Q

ROTATION

A )

C )

B)

At any given fan speed modulationof economizer dampers shouldallow flow quantity to remain nearconstant.

Figure 1 Problems and Design Goal

RA

TOTAL

Problems

Design Goal

Total quantity of air flow through a system.

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

OA

EA

RADOAD

EAD

RA

SAMA

RP

RA

OA &EA

Total Flow

Q

DamperPosition

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

EA

EAD

RA

RP

RAD

OA

SA

MA

QTotal flow with OB dampers will beunder the linear when half open inthe geometric configuration above.

OAD

ROTATION

OARA

Total Flow

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

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.


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Control Loop Tuning

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.

Authority = damper loss / subsystem loss.Authority = damper C / sum of C in subsystem.

Authority = damper full open ?P / damper closed ?P

AIRFLOW

ΔP across subsystemmust remain constant

Figure 5 Authority

Damper Cs

A subsystem is defined as the duct elementsbetween two constant pressure points.

Cs stands for the total sum of C’s of the duct elements.

1 2005 ASHRAE Handbook - Fundamentals, Chapter 15, p.15.5 -15.7. Note the incorrect overgeneralization from the ducted to all applications.

Q

ROTATION

dQ/ds =2

dQ/ds = .25

Figure 4 Control Loop Tuning


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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.


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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

OA

EA

RAD

OAD

EAD

RA

SAMA

RP

OA Damper = Δ P’s Louver + Damper + ductelements + Flow Monitoring + Compressionand Expansion. (Given Minimum OA may betwo dampers and associated controls.

Authority =ΔP DamperΔP Subsystem

RA Damper = ΔP’s TRP +damper + any ductelements +

EA Damper = ΔP’s Louver +Damper + Any duct elements

The points EA to RP, RP to MA, and MA to OAare the pressure references for linearity of the

dampers. Disregarding wind, these are constantpressure points if the system is linearized.

The points RPand MA are

constantpressure points ifthe dampers are

linear.

Subsystems are indicated by dashed linesbetween the constant pressure points.

TMA


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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.

LOUVERS

OAD

RAD RADRAD

OAD OAD

RA RA

RELIEF FANS

AH

The RAD’s are open tothe equipment room

space.RA’s are open to

ceiling return.They are holesin the floor withprotective bars.

Figure 9 Authority Calculation Points - Equipment Room Subsystem Example

AHAH

Indicates constant pressure pointfor linearization of the OA Damper

Indicates constant pressure pointfor linearization of the RA Damper

RAD

OAD

AIR FLOW

RA damper isclosest to anAMCA 5.4

configuration.

OA damper isclosest to anAMCA 5.1

configuration.

AIRFLOW

Since the EA damper interacts with thefan curve, linearization is near

impossible to calculate.


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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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Ducted

5.25.15.3

Figure 10 Geometric Applications with AMCA Figure numbers

Walled

5.4 5.5Case

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Any individual damperin the AH figures here

could be any of theAMCA figures

depending on thesituation.

Other geometrical effects existwhich 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

AMCA 5.1

Wall, like a 5.3but with a

rough enteringflow profile

Relief

RA

OA

OA Half 5.4 &Half wall

RA fan

SA

Relief Chaseto

OutsideEAD

Half 5.4 & half5.2

RAAMCA

5.2

Indicates constant pressure pointfor linearization of the OA Damper

Indicates constant pressure pointfor 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

LOUVER

Louvered Exit OB 6" B-16

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ax F

low A

E

Elbow-Damper OB B-29

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Amount Open

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ax F

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ABEF

36W X 48HAIR FLOW

36"

AIR FLOW

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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PB Absolute Velocities at 1" Pressure Drop

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12000

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90 (o

pen)

Amount OpenAMCA 5.3 in Bold

Velo

city

A5.1 3V

A5.1 AF

A5.2 3V

A5.2 AF

A 5.3 3V

A5.3 AF

A5.3 AE 3V

A 5.4 3V

A5.4 AF

A5.5 3V

A5.5 AF

Figure 13

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.V = 4005 Pv½. Pv = Pt/C. V = 4005 x (1/170)1/2 = 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.

DUCTED ENTRANCEAMCA 5.1

AIRFLOW

Anti PB actionDAMPER

LOUVER ENTRY Anti PB

AIR FLOW

LOUVER

Close

AIR FLOW

OB after EL disturbance

ENTRANCE PLENUM AMCA 5.4

SAMA

RARP

OB DUCTED EXITWITH LOUVER

AIRFLOW

LOUVER

Any of the otherAMCA Figuresmay apply also.

OB DUCTED EXITAMCA 5.2

AIR FLOWEA

EAD

AIRFLOW

OAOAD

AIRFLOW

RAD

Figure 15 Overview


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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

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.

5.1 OB at Varying Authorities

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90 (o

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Amount Open

% M

axim

um F

low

100%

50%

25%

DUCTED ENTRANCE AMCA 5.1

AIR FLOW

5.1 PB at Varying Authorities

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100%50%25%10%5%

DUCTED ENTRANCEAMCA 5.1

AIRFLOW


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Louvered Entrances

Louvered OB Entry

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Flo

w

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5%

Anti PB Louvered Entry

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10%5%2.5%

Entry Louver with PB

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axim

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low

10%5%2.5%

DUCTED ENTRANCE w/ Louver

AIR FLOW

LOUVER

OB Damper

Anti PB actionDAMPER

LOUVER ENTRY Anti PB

AIR FLOW

LOUVER

Close

DUCTED ENTRY W/ LOUVER

AIR FLOW

LOUVER

Close

PB Damper


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AMCA Type 5.2 Exits

PB DUCTED EXITAMCA 5.2

AIR FLOW

OB DUCTED EXIT AMCA 5.2

AIR FLOW

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.

5.2 PB Exits at Varying Authorities

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10%

5%

5.2 OB EXITS at Varying Authorities

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50%

25%

10%

5%


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Louvered Exits

Louver Exit OB at Varying Authorities

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% M

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10%5%2.5%

PB Louver Exit at Varying Authorities

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2.5%

Louver Anti PB at Varying Authorities

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% M

axim

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low

10%

5%

2.5%

OB DUCTED EXIT WITH LOUVER

AIR FLOW

LOUVER

PB DUCTED EXIT W/ LOUVER

AIR FLOW

LOUVER

Open

Anti PB DUCTED EXIT W/ LOUVER

AIR FLOW

LOUVER

Close

No authority is linear.


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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.

AIR FLOW

PB 5.3 with Duct Restriction

AIR FLOW

OB 5.3 with Duct Restriction

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.

5.3 Type Damper-Elbow PB

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% M

ax F

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A 3VBC AF

5.3 Type Damper-Elbow OB

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ax F

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A 3VBC AF


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Damper A is a 3V, Damper B is flanged

AIR FLOW

PB after EL disturbance

AIR FLOW

OB after EL disturbance

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.

Elbow-Damper OB

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B

Elbow-Damper PB

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A 3V

B


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AMCA 5.4 Plenum Entrances

PB OB

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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3V A = 100%

AF A = 100%

3V A = 50%

3V A = 25%

3V A = 10%

3V A = 5%

0%

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AF at 100% 3V at 100% A = 50% 3V A = 25% 3V A = 10% 3V A = 5% 3V


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AMCA 5.5 Plenum Exits

EXIT PLENUM AMCA 5.5

AIR FLOW

PLENUM WALL

PB OB

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A =100%

A =50%

A =10%

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A =100%

A =50%

A =10%


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Appendix 2 Estimating Authority

C = 2

C = 1

C = 3(avj)

A = 1/6 = 16%

C = 1

A = 1/3 = 33%

C = 1 C = 1

C = 1

A = 1/6 = 16%

C = 2 C = 3

C = 1 C = 1

Clouver = 10 Clouver = 10

A = 7% A = 7%

C = 1A = 1/5 = 20%

C = 2

C = 2

C = 1Clouver = 10

A = 1/11 =7%

Duct sized dampers withstandard elbows and louvers.

A = Authority =

Cdamper / Csubsystemif areas of all ducts are equal.

A = Δpdamper / ΔPsubsystem

RP RP

RPRP

MA

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 = in w.g.abbreviated to “

A = .06 / 51 =12%

RP

MA

dP = .25"

dP = .06"

dP = .2"

MAMA

MA


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If all dampers are linearized, thenthe points RP and MA areconstant pressure points for anygiven fan speed.

The authorities will always be thesame since ALL the duct andelement losses are proportionalto 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 0.624" 0.6 0.65 0.7 0.736" 0.65 0.7 0.7 0.7548" 0.65 0.7 0.75 0.8FAR 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.]

W A LLE D

D U C TE D

5.4 5.5C ase6

A M C A F igures

5 .1 5 .25 .3

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.


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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, C0 = Fg x [ (1/F 2 ) - 1] F = √ ( Fg / (C0 + Fg) ) 2. For duct wall mounted dampers, .2 < F < .5 C0 = Fg x (1/F 2 ) F = √ [ Fg / C0 ] 3. For duct wall mounted dampers, F < .2 C0 = Fg x (1.5/F 2 ) F = √ [ 1.5 * Fg / C0 ] 4. For ducted entrances from large spaces, AMCA 5.1 C0 = Fg x (1.4/F 2 -1 ) F = √ ( 1.4 Fg / C0 + Fg) 5. For ducted exits into atmosphere or large spaces, AMCA 5.2 C0 = Fg x (1.1/F 2 ) F = √ [ 1.1 * Fg / C0 ] 6. For plenum exits and entrances, AMCA 5.4 and 5.5 C0 = Fg x (1.8/F 2 ) 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 .

Documents

Belimo Damper Air Flow Linearizing Tutorial Rev 1 - Alps