BALANCE.PPS

8/20/2019 BALANCE.PPS

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AN OVERVIEW ON HVAC

HYDRONIC BALANCING

By

Ahmed Abdel Ghani MetawieConsultant


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Why Balancing?


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Types of HVAC ys!e"s

Two Basic System arrangements:

Direct eturn

everse eturn


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Di#ec! Re!$#n


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Di#ec! Re!$#n


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!ost suitable for buildings utili"ing energy

saving variable volume.

equires a minimum of piping and usually hasless pipe friction than equivalent reveres return.

#ump head can be exerted across the

temperature control valves.

Di#ec! Re!$#n


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Re%e#se Re!$#n


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&lo' Types ( )#ess$#e G#a*ien!s

Constant fow

% Three way valves.


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&lo' Types ( )#ess$#e G#a*ien!s

Constant fow

% Three way valves.


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+a#,e! A%aila-le Balancing Techni.$es

!anual or Static Balancing

To ad*ust by hand p across coil and control valve circuits.

Tools used are balancing valves and commissioning sets.

+utomatic balancing To maintain constant( a water flow rate independently of the

changes of the differential pressure.

Types of flow controllers

% +utomatic variable orifice.

% Self%acting valve.


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A$!o"a!ic Va#ia-le O#ifice

,imitations and disadvantages:


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Limitations and disadvantages:

)o possibility to measure the flow rate.

!inimum differential pressure required is

relatively high.

emain loc-ed on position due to scaling.

These disturbances are not measurable.

Dirt in water reduces the section area of the orifice(

with a much higher deviation in the flow.


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Limitations and disadvantages:

)oisy

ave to be removed during flushing

Cartridge must be replaced when flow changes

&verpressure is ta-en away in the small flow

controllers in series with the terminal units.

/ery sensitive to the particles in the water.

0ssential to protect with an efficient filter.


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A elf/Ac!ing Val%e +ain!ainsCons!an! !he ∆p Ac#oss a &i0e* O#ifice

Description and operation:


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1f the flow rate has to be changed( the cartridgemust be replaced or read*usted.

2low rate can be chosen at any value between 3

and a maximum( without being obliged to remove

any part of the device. 2low can be measured with the balancing valve.

During flushing( it is *ust sufficient to open fully the

balancing valve.

The maximum possible pressure drop is 433 -#a.

2low range from 533 to 5633 17h 83.35 to 3.94 17s;.

!inimum operating pressure drop between


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Co"pa#ison Be!'een &lo' Con!#olle#san* Balancing Val%es

Constant fow distribution


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Constant fow distribution

% 'ith flow controllers

2low rate is maintained constant independently on the port characteristics

of the three%way valve.

)o balancing procedure is required and balancing of branches and risers

is obtained naturally. The balancing procedure( which

detects most of the hydronic

anomalies( is not carried out.

The flow is not measurable.

!ore costly than balancing valves. +s a constant flow distribution is

charachterised by an absence of

disturbances( a controller is in fact

not necessary.


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C i B ! &l C ! ll


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Variable fow distribution

C i B ! &l C ! ll


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% 'ith flow controllers

&ne flow limiter is in series

with each control valve.

+ balancing procedure is

not required. owever( the

actual flow cannot be

measured.

The control valve authority

can be destroyed by theincrease of differential

pressure leading to

unstable control loops.

C i B ! &l C ! ll


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% 'ith balancing valves

Balancing valve gives the

possibility to measure the

flow rate and to ad*ust it at

the correct value. The partner valve creates the

main pressure drop

corresponding for instance

with the overpressure created

on a riser close to the pump.

1t is only when all controlvalves shut simultaneously

that the increase of the

differential pressure is as

dramatic as for flow controllers.

+YTH ( &ACT


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+YTH ( &ACT

MYTH:

The coil%modulating valve will control better if some of

the drop can be ta-en across the balancing valve.

FACT:The coil%modulating valve will always control better if the

balancing valve is not used and the drop across the control

valve is increased by the drop that would be allocated to the

balancing valve. The control valve will then be smaller andthe rangeability and close%off rating will be greater.

+YTH ( &ACT


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+YTH ( &ACT

MYTH:

The control valve can close against higher pressure

drops if balancing valves ta-e some of the drop.

FACT:

The balancing valve has nothing to do with the close off

rating of the 4%way modulating valve. The balancing

valve only ta-es a drop when there is flow. 'hen the

modulating valve is seating or unseating( all the drop isacross this valve. )one of the drop is across the

balancing valve.

+YTH ( &ACT


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+YTH ( &ACT

MYTH:

The modulating control valves will be quieter if

balancing valves are used.

FACT:

The balancing valves have no bearing on control valvesnoise.

Control valves are the noisiest when they are seating or

unseating that is when the pressure drop across the

control valve is greatest( because there is no drop

across the balancing valve or any of the other

components in the branch circuit.

+YTH ( &ACT


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+YTH ( &ACT

MYTH:

The coils will not get their design flow if balancing valves

are not used.

FACT:

1f the control valves are si"ed properly and actuators

are large enough to position the valve plugs properly(

the system is self%balancing. 0ach coil will receive only

enough flow to satisfy the load.

+YTH ( &ACT


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+YTH ( &ACT

MYTH:

The coils nearest the pump will =rob= flow to the other coils

when the system is first started.

FACT:

&n start%up( there may be a brief flow unbalance but this lasts only untilthe thermostat ta-es over and repositions the coil valve. 'hen the flow

unbalance occurs( the excess flow through the coil should bring the valve

under thermostat control very quic-ly. +s an option( a high limit differentia

pressure sensor can be connected across each coil to limit the flow

through the control valve to the design >.#.!. This sensor could be field

ad*usted for the design differential( or it could be set at the factory to avoid

having to ma-e field ad*ustments.

+YTH ( &ACT


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+YTH ( &ACT

MYTH:The valves nearest the pump will not modulate because

much of the valve stro-e will be lost in balancing the flow.

FACT:

1f properly selected valves 8those with equal percentage ports

and with correct actuators; are used( 43? or less of the stro-e

will be used to balance the flow. The rest of the stro-e will still

be available to modulate the flow within the design limits.


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Dyna"ic Balancing 'i!h ∆) Con!#olle#s


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y g1eep Cons!an! !he ∆p ac#oss !he Con!#ol Val%e

Main Characteristics: )o need for other balancing devices in the branches and risers.

+s the differential pressure across the modulating control valve is practically

constant( its authority is close to one and the control valve is never oversi"ed.

The p control device does not wor- against the control valve( as flow controllers do(

but dynamically maintains the best conditions for the stability of the control loop.

The use of a balancing valve with a differential pressure controller can be consideredas a little bul-y( however( this combination has the following advantages:

The modulating control valve wor-s in the best conditions with an authority of one.

The flow rate remains measurable for diagnostic purposes.

The Control valve is never oversi"ed and the design flow is always obtained for the

control valve fully open.

There is no need of balancing the branches and risers if all control loops are equippedwith this device.


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1eep cons!an! !he ∆p ac#oss


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1eep cons!an! !he ∆p ac#oss-#anch 'i!h se%e#al ci#c$i!s

1eep cons!an! !he ∆p ac#oss


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1eep cons!an! !he ∆p ac#oss-#anch 'i!h se%e#al ci#c$i!s

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