FLOW RATE DYNAMIC BALANCINGPressure independent flow regulator - FLOWMATIC®

TECHNICAL FOCUS

In variable displacement systems, it is often necessary to have both an adjustment (ON/OFF or modulating zone valve) and a balancing for each output terminal. Air conditioning systems with fan-coils are an example. For this system situation, the automatic flow rate regulators have a limited scope of application as they must be combined with a zone valve and require a fixed flow rate setting (corresponding to the size of the selected cartridge).Using the pressure independent flow regulator (FLOWMATIC®) it is possible instead to pre-set the flow rate to the desired value and adjust the circuit through an ON/OFF or modulating actuator: two functions in one device.

The pressure independent control valves allow a very easy sizing (avoiding laborious calculations required by traditional balancing) and a possible re-balancing in case of variations during the operation. The valve high authority also avoids verification calculations.

The automatic flow rate regulators are able to keep a constant flow rate of the medium that passes through the circuit in which they are installed.

They are pressure independent flow regulators (they are indicated by the abbreviation PICV: Pressure Independent Control Valve). They keep the flow constant to the pre-set value when the operating conditions change. By means of a suitable actuator they can change the nominal flow rate.

FLOW RATE DYNAMIC BALANCING

Automatic flow rate regulator

Pressure independent adjustment

Balancing part 5

OPERATING PRINCIPLE AND SELECTIONThe Pressure Independent Control Valve (PICV) is a device consisting of an automatic ΔP regulator (A) and a control valve (B) that can be driven by an actuator.The ΔP regulator maintains constant the pressure difference acting on the control valve (P2 - P3 ). Therefore, this valve can adjust the flow rates regardless of the pressure differential acting on the circuit in which it is inserted and therefore on the valve itself. Where:

If (P1-P3) increases, the internal ΔP regulator reacts to close the bore and maintains (P2 - P3 ) = constant; in these conditions the flow rate will remain constant.

The flow rate is then regulated at a constant value in a differential pressure range as for the flow rate regulators mentioned in the previous technical focus:

Unlike a flow rate regulator, the valve is fitted with an adjustment device (B) that controls the flow modifying its bore cross section (essentially by modifying the valve Kv) can be adjusted to different values in two different modes:• maximum flow rate pre-setting. It can be achieved by mechanically changing the obturator adjustment

window position:

P1

A B

P1= upstream pressureP2= intermediate pressureP3= downstream pressure

P1- P3=DValve P

P2- P3= cost

P2 P3

regulator ofDP

regulating valve

P1

A B

P1= upstream pressureP2= intermediate pressureP3= downstream pressure

P1- P3=DValve P

P2- P3= cost

P2 P3

regulator ofDP

regulating valve

P1

A B

P1= upstream pressureP2= intermediate pressureP3= downstream pressure

P1- P3=DValve P

P2- P3= cost

P2 P3

regulator ofDP

regulating valve

p1

p2

p3

A

B

Flow

rate

GNOM100%

25 kPa 400 kPa ∆P Valve∆PMIN ∆PMAX

400∆P (kPa)

G10= Maximum nominal flow rate

G8= 80% G10

G6= 60% G10

G2= 20% G10

The secondary circuits connected to a primary circuit through the distribution lines are subject to different heads depending on the configuration of the distribution circuit.Two identical circuits calculated to have a nominal flow rate GNOM connected to a primary circuit are in this way subject to different heads (H1 and H2) that generate in their circuits flow rates (G1 and G2) different from the design flow rates and therefore load losses (ΔP1 and ΔP2) different from the nominal design load loss.

The flow rate dynamic balancing of a secondary circuit consists in introducing within each circuit a pressure independent control valve to neutralize the influence of the primary distribution circuit, especially in the case of very variable loads; in addition, this type of valve allows to achieve the partial flow rate on the secondary circuit always in balanced circuit conditions. In essence, in the previous diagram it is necessary to insert a FLOWMATIC® in every secondary circuit selected according to the nominal flow rate GNOM.

• flow rate adjustment through the use of a modulating actuator that operates on the obturator. Once the maximum flow rate has been fixed, it is possible to change it starting from the maximum per-adjusted

value GMAX up to zero.

GNOMGNOM

ΔH1 ΔH2

SECONDARY CIRCUIT

G (m3/h)

Gmax8

50% Gmax8

75% Gmax8

G1G2

H1

ΔP2ΔP1

H2

• The selection of the cartridge must be made according to the design nominal flow rate. As each cartridge has its own flow rate range, first those that include the design flow rate are identified. Among these, as a general rule, the one with the smallest range is preferred.

• Depending on the nominal flow rate value, the pre-setting position of the maximum flow rate for the selected cartridge is evaluated.

• The choice of the connection size is made according to the needs, depending on those available for the selected cartridge.

ADJUSTMENT AND FLOW RATE RANGE SELECTION

BALANCED CIRCUIT: initial condition

2

6

225

30

40

20

10

0

0 300 400 Q [l/h]

ΔP [kPa]

200100

0 300 400 Q [l/h]

ΔP [kPa]

200100

1

3

130

1

3

135

30

40

20

10

0

0 300 400 G [l/h]

ΔP [kPa]

200100

30

40

20

10

0

10

5

5

[kPa]

[kPa]

[kPa]

PICV DYNAMIC BALANCING

35 kPa 320 l/h

ΔPVBΔPT

Case 1: initial conditions

HC=3

5 kP

a

ΔPVBΔPT

Case 2 : �ow rate adjustment

HC=3

5 kP

a

35 kPa 230 l/h

40 kPa 230 l/h

25

25

Case 3: Head increase

30

ΔPVBΔPT

HC=4

0 kP

a

30 35

ΔP N

OM

= 10

kPa

Condition: initial

Flow rate adjustment

Flow rate adjustment

Head increase

Condition: initial

ΔPC+D ΔPC+D

ΔPC+D ΔPC+D

ΔPC+D ΔPC+D

The elements that make up a limiting circuit that controls the flow rate are essentially: distribution lines characterized by distributed and concentrated losses, a zone (or adjustment) valve, and the output terminal. In case a FLOWMATIC® control valve is used it is no longer necessary to use a zone valve (or adjustment valve) as this type of valve performs two functions, balancing and adjustment at the same time.To illustrate the situation, a numerical example is introduced. The circuit in consideration has a GNOM of 320 l/h.

The head to be absorbed by the FLOWMATIC® is 35-10= 25 kPa equal to the minimum value (25 kPa) and therefore it works correctly within the adjustment range.To ensure the nominal flow, the valve self-regulates itself in order to have a Kv value equal to:

If at the circuits ends there is a head of 35 kPa H, it is necessary to insert a pressure independent control valve, that absorbs the excess differential pressure, to maintain a constant flow rate in the circuit.For a nominal flow rate of 320 l/h, the circuit components have load losses of:distributed and concentrated ΔP of two sections= 4 kPaemission system Δp = 6 kPa.

As shown in the diagram, the design load loss of the circuit without control valve is 10 kPa, the head persisting on the circuit is 35 kPa and therefore the excess of head must be absorbed by the balancing valve for 25 kPa.

Kv = 0,01 ⋅

= 0,01 ⋅

= 0,64 m3/h

G √ ΔPVB

320 √ 25

2

6

225

30

40

20

10

0

0 300 400 Q [l/h]

ΔP [kPa]

200100

0 300 400 Q [l/h]

ΔP [kPa]

200100

1

3

130

1

3

135

30

40

20

10

0

0 300 400 G [l/h]

ΔP [kPa]

200100

30

40

20

10

0

10

5

5

[kPa]

[kPa]

[kPa]

PICV DYNAMIC BALANCING

35 kPa 320 l/h

ΔPVBΔPT

Case 1: initial conditions

HC=3

5 kP

a

ΔPVBΔPT

Case 2 : �ow rate adjustment

HC=3

5 kP

a

35 kPa 230 l/h

40 kPa 230 l/h

25

25

Case 3: Head increase

30

ΔPVBΔPT

HC=4

0 kP

a

30 35

ΔP N

OM

= 10

kPa

Condition: initial

Flow rate adjustment

Flow rate adjustment

Head increase

Condition: initial

ΔPC+D ΔPC+D

ΔPC+D ΔPC+D

ΔPC+D ΔPC+D

Flow

rate

230

A

25 kPa 400 kPa

B

Flow

rate

320A

25 kPa 30 kPa 400 kPa

230B

Flow

rate

320A

25 kPa 30 35 kPa 400 kPa

C

320

∆P∆PMIN ∆PMAX

∆P∆PMIN ∆PMAX

∆P∆PMIN ∆PMAX

Graph for load loss Circuit operating curves

BALANCED CIRCUIT: flow rate adjustment

2

6

225

30

40

20

10

0

0 300 400 Q [l/h]

ΔP [kPa]

200100

0 300 400 Q [l/h]

ΔP [kPa]

200100

1

3

130

1

3

135

30

40

20

10

0

0 300 400 G [l/h]

ΔP [kPa]

200100

30

40

20

10

0

10

5

5

[kPa]

[kPa]

[kPa]

PICV DYNAMIC BALANCING

35 kPa 320 l/h

ΔPVBΔPT

Case 1: initial conditions

HC=3

5 kP

a

ΔPVBΔPT

Case 2 : �ow rate adjustment

HC=3

5 kP

a

35 kPa 230 l/h

40 kPa 230 l/h

25

25

Case 3: Head increase

30

ΔPVBΔPT

HC=4

0 kP

a30 35

ΔP N

OM

= 10

kPa

Condition: initial

Flow rate adjustment

Flow rate adjustment

Head increase

Condition: initial

ΔPC+D ΔPC+D

ΔPC+D ΔPC+D

ΔPC+D ΔPC+D

As mentioned, through an actuator it is possible to directly adjust on the FLOWMATIC® valve the flow rate passing through the secondary circuit. In this way it is hypothesized that there are the same head (H) conditions upstream of the secondary circuit equal to 35 kPa and that it is necessary to reduce the flow rate to 230 l/h. Reducing the flow rate, the load losses of the other components constituting the secondary circuit are reduced to the following values:distributed and concentrated ΔP of two sections= 2 kPaemission system Δp = 3 kPa.The nominal load loss under these conditions would therefore change from 10 to 5 kPa.

The FLOWMATIC® Kv value will therefore change from 0,64 to 0,42 m3/h. This change of Kv, due to the flow rate adjustment, occurs by means of the valve component B obturator movement as shown in the figure.

As the head value (H) remains constant at 35 kPa at the circuit ends, the FLOWMATIC® valve must adapt its Kv value automatically to absorb the excess head for 35-5 = 30 kPa.

Kv = 0,01 ⋅

= 0,01 ⋅

= 0,42 m3/h

G √ ΔPVB

230 √ 30

2

6

225

30

40

20

10

0

0 300 400 Q [l/h]

ΔP [kPa]

200100

0 300 400 Q [l/h]

ΔP [kPa]

200100

1

3

130

1

3

135

30

40

20

10

0

0 300 400 G [l/h]

ΔP [kPa]

200100

30

40

20

10

0

10

5

5

[kPa]

[kPa]

[kPa]

PICV DYNAMIC BALANCING

35 kPa 320 l/h

ΔPVBΔPT

Case 1: initial conditions

HC=3

5 kP

a

ΔPVBΔPT

Case 2 : �ow rate adjustment

HC=3

5 kP

a

35 kPa 230 l/h

40 kPa 230 l/h

25

25

Case 3: Head increase

30

ΔPVBΔPT

HC=4

0 kP

a

30 35

ΔP N

OM

= 10

kPa

Condition: initial

Flow rate adjustment

Flow rate adjustment

Head increase

Condition: initial

ΔPC+D ΔPC+D

ΔPC+D ΔPC+D

ΔPC+D ΔPC+D

Flow

rate

230

A

25 kPa 400 kPa

B

Flow

rate

320A

25 kPa 30 kPa 400 kPa

230B

Flow

rate

320A

25 kPa 30 35 kPa 400 kPa

C

320

∆P∆PMIN ∆PMAX

∆P∆PMIN ∆PMAX

∆P∆PMIN ∆PMAX

Graph for load loss Circuit operating curves

REFERENCE DOCUMENT: TECH. BROCHURE 01262

BALANCED CIRCUIT: head increase

2

6

225

30

40

20

10

0

0 300 400 Q [l/h]

ΔP [kPa]

200100

0 300 400 Q [l/h]

ΔP [kPa]

200100

1

3

130

1

3

135

30

40

20

10

0

0 300 400 G [l/h]

ΔP [kPa]

200100

30

40

20

10

0

10

5

5

[kPa]

[kPa]

[kPa]

PICV DYNAMIC BALANCING

35 kPa 320 l/h

ΔPVBΔPT

Case 1: initial conditions

HC=3

5 kP

a

ΔPVBΔPT

Case 2 : �ow rate adjustment

HC=3

5 kP

a

35 kPa 230 l/h

40 kPa 230 l/h

25

25

Case 3: Head increase

30

ΔPVBΔPT

HC=4

0 kP

a

30 35

ΔP N

OM

= 10

kPa

Condition: initial

Flow rate adjustment

Flow rate adjustment

Head increase

Condition: initial

ΔPC+D ΔPC+D

ΔPC+D ΔPC+D

ΔPC+D ΔPC+DIf in the new flow rate conditions adjusted at 230 l/h there is a head increase in the primary circuit from 35 a 40 kPa the FLOWMATIC® should absorb this increase to keep the flow rate constant to the new adjusted value.In this case the residual loss of the residual part of the circuit would always be 5 kPa (constant flow rate).The valve will have to adapt dynamically to absorb the new head, in particular 40-5 = 35 kPa.The valve therefore reduces its bore cross section, due to the component A, to keep the P2-P3 value constant at the ends of the control valve.The new valve Kv value will be:

Kv = 0,01 ⋅

= 0,01 ⋅

= 0,39 m3/h

G √ ΔPVB

230 √ 35

2 2

6

28

A

A

B

B

1 6,5

2,5

19

30

20

10

0

30

20

10

0

30

20

25

10

0

30

20

25

10

0

]h/l[ G0040030

H [kPa]

200100

]h/l[ Q0040030

H [kPa]

200100

]h/l[ Q0040030

H [kPa]

200100

]h/l[ Q0040030

H [kPa]

200100

A

B

2 2

6

213

A

B

1

114

2,5

6,5

HC

HC

[kPa]

[kPa]

[kPa]

BILANCIAMENTO CON REGOLATORE DI PRESSIONE DIFFERENZIALE

20 kPa

20 kPa

300 l/h

200 l/h

ΔPVB

HC

ΔPVR ΔPT

Caso 1: condizioni iniziale

Caso 2: varia la portata - prevalenza costante

Caso 3: portata costante - aumenta la prevalenza

Caso 4: portata varia- aumenta la prevalenza

ΔPVB

HC=2

5 kP

aH

C=25

ΔPVR ΔPT

ΔPVBΔPVR ΔPT

ΔPVBΔPVR ΔPT

10

10

25 kPa 300 l/h10

25 200 l/h10

HC=2

0 kP

aH

C=20

kPa

10

1010

10

10 10

Kv = 1,06

Kv = 0,67

Kv = 0,53

ΔPC+D ΔPC+D

ΔPC+D ΔPC+D

ΔPC+D ΔPC+D

ΔPC+D ΔPC+D

Regolazione portata

Aumento prevalenza

Flow

rate

230

A

25 kPa 400 kPa

B

Flow

rate

320A

25 kPa 30 kPa 400 kPa

230B

Flow

rate

320A

25 kPa 30 35 kPa 400 kPa

C

320

∆P∆PMIN ∆PMAX

∆P∆PMIN ∆PMAX

∆P∆PMIN ∆PMAX

Graph for load loss Circuit operating curves

Therefore the FLOWMATIC® valves are ideal for serving terminal units or zones in cases where a simple ON/OFF control logic has to be implemented, or when the flow rate modulation is required according to the thermal load thanks to the use of a proportional actuator.

WE RESERVE THE RIGHT TO MAKE CHANGES AND IMPROVEMENTS TO THE PRODUCTS AND RELATED DATA IN THIS PUBLICATION, AT ANY TIME AND

WITHOUT PRIOR NOTICE.

0852

018G

B

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