BALANCING BASICS

1 Introduction

2 Background

3 Flow of water through systems

4 Valve types

5 Valve identification

6 Taking readings

7 Taking readings with electronic manometers

8 System balancing

Comdronic Ltd would like to extend gratitude to the following Companies for the
photographic images that support this document.

Crane Fluid Systems www.cranefs.com

Oventrop UK Ltd www.oventrop.co.uk
1. Introduction

A basic discussion of the processes involved to establish the flow of water through valves
which, in turn, will lead to the balancing of water flows in the various parts of a water based
system.

Balancing basics is intended to be used by engineers and technicians who are not
specifically trained as commissioning engineers. I can also be used as a reference for those
training to become commissioning engineers.

2. Background
The flow of water in a system with multiple branches and terminals might at first glance seem
mystifying, however, a basic knowledge of the physics involved will help to clarify the
process.

The type of system we are interested in for flow balancing is a closed loop system such as a
heating system or chilled water system.

Those of us with central heating systems at home have all endeavoured to get the balance
right in the system by simply adjusting each radiator until it feels ‘about right’ This process is
ok if we have enough time, however, if the system is large, such as a commercial heating
system then the process has to be formalised to ensure correct building comfort.

3. Flow of water through systems

If we are to ensure that the space is heated or cooled by the correct amount we have to
make sure that the flowrate of water to the space is in keeping with the requirements set out
by the design engineer. Each space will have been analysed for heat loss/gain and a
heating/cooling load in kW (kilowatts) determined.

In order to transport the kW to the space we use water either heated or cooled. The designer
will normally convert the kW value into flow rate using the formula:

Mass flow rate = Emitter output (kW) / Specific heat capacity for water X ∆t (Deg C)

For heating the temp change (∆t) in the emitter is usually 11 Degrees
For cooling the temp change (∆t) in the emitter is usually 6 Degrees

The specific heat capacity of water is 4.187 kj/kgC

Because the ∆t in cooling is less than that in heating we can see that for each kW delivered
to the space we will need more water if it is cooling.

Do not let any of the above cause you concern because the designer will have already
carried out the calculation for flow rates and it is this that we are interested in.

The basic building block for the commissioning engineer is the balancing valve. This is a
generic term for a variety of valves used for balancing systems. There are 4 main varieties of
traditional device as described below.
4 Valve types

Double regulating valves (DRV)

For flow regulation only.

Typically this valve is a Y pattern globe valve arranged in this way to

present the smallest pressure loss to the system when fully open. Adjustment of this valve
will add resistance to the system and hence reduce the flow. The description DOUBLE
regulating means that it has a feature whereby you can set the position that the valve is to
operate at in such a way that you can still close the valve for maintenance purposes.

When using computerised electronic manometers with a valve database you will not find any
data relating to these valves because they do not have a measuring facility.

Flow measurement devices and valves (FMD/FMV)

For flow measurement with or without isolation facility.

These devices are usually fixed orifice

devices. More recently there has been
more venturi devices appearing on the
market (Mostly from US). A fixed orifice
is the simplest device that we can use
for measurement. The fixed orifice can
be used on its own or with an isolating
valve fitted downstream to provide
isolation. Installed on their own these
devices can give the most accurate
results. When using electronic manometry to display the flow through this product the Maker,
model and size of the unit must be entered into the meter. (See section ‘Taking readings’)

Photographs courtesy of Crane Fluid Systems

Double regulating valves combined with flow measurement devices (FODRV)

For regulation and flow measurement combined in one valve unit based on the Fixed Orifice
principle.

This combined assembly traditionally was assembled from a double regulating valve and
fixed orifice device. More commonly nowadays the orifice is fitted directly into the body of the
valve.

When made up of a regulating valve and separate orifice the unit is often referred to as a
‘Commissioning set’

When using electronic manometry to display the flow through this product the Maker, model
and size of the unit must be entered into the meter. (See section ‘Taking readings’)

Double regulating valves with integral flow measurement facility. (VODRV)

For regulation and flow measurement combined in one valve unit based on the variable
orifice principle.

Shown in the photo is a cast iron VODRV which allows the measurement of the flow across
the entire valve. There is no fixed orifice fitted to this valve – the signal measured on an
electronic manometer relates to the loss across the whole valve

When using electronic manometry to display the

flow through this product the Maker, model and
size of the unit must be entered into the meter.
(See section ‘Taking readings’)

Because the signal being measured on this valve

relates to the loss across the entire valve the size
of the signal depends on the position of the
handwheel. This process will be dealt with in
some detail later and really only affects those
working on systems overseas. The use of this
type of valve is popular in Europe and Ex Russian
states.
Photographs courtesy of Crane Fluid Systems
5 Valve identification
Before any readings can be taken it is important to identify the type of valve or orifice device
being used. The section above describes each type of device but when approaching a job
on-site it might not be so obvious as to the type of valve in use.

The first job is to identify which valves are for measuring and which are simply installed for
regulating.

Rule 1 is to check for testpoints installed on the valve. If there are no testpoints then the
valve is a simple regulating valve which will have been installed to regulate flow. The
measurement of flow will have to take place elsewhere. Typically in these instances a fixed
orifice might be installed for measurement purposes. If the regulating valve is installed on the
return side of a circuit then the orifice might be installed on the flow side. (This is not always
the case but is usual)

Regulating valve Fixed orifice

If the valve is fitted with testpoints then a bit more care is required. The first valve shown
below has testpoints fitted which are a significant distance apart when measuring along the
axis of the valve.

This indicates that the differential pressure will be measured

across the entire valve. If this is the case then the size of the
orifice will change when the valve is operated. This valve is
therefore a Variable Orifice Double regulating valve
(VODRV)

If the valve is fitted with testpoints that are very close together
when measured along the axis of the pipe then the valve is likely
to be a Fixed Orifice Double Regulating Valve (FODRV)

Photographs courtesy of Crane Fluid Systems

Important note.

Some European manufacturers fit testpoints on the stem area of the valve body.

The Oventrop example here shows a combined testpoint and drain unit very
close to another testpoint. This valve is a variable valve. The testpoint
nearest to the centre of the valve is ported downstream of the valve seat.
If in doubt get the information from the manufacturer.

Photograph courtesy of Oventrop

6 Taking Readings

For all discussions relating to measurement using valves as described above we will only
consider the use of electronic manometers such as Comdronic AC6, Crane and Hattersley
ProComm, Cimdronic AC6, Frese AC6, MMA AC6 and LRI 8170

The principle behind the measurement of flow through a balancing valve is the way in which
we exploit the pressure loss created across the orifice or valve when water flows through it.
We know that every device inserted into the system will create a small amount of resistance
to flow. The resistance to flow will create a situation where the pressure on the inlet side of
the valve will be very slightly higher than the outlet side of the valve. This difference in
pressure is called the DIFFERENTIAL pressure or SIGNAL.

The design and manufacture of the balancing valves is carried out to strict limits of tolerance
so that the signal read across one valve of a type is the same as another. Small errors do
exist but these keep the overall measurement tolerance to a very small level.

Using an electronic commissioning meter the following calculations are carried out
automatically but the mathematics is included for those wishing to see how we arrive at the
flow rate.
The only reading we take with the electronic manometer is the differential pressure (dP) –
When we have taken the reading we have to equate this to the balancing valve design
figures so that we can establish the flow through the valve.

Each valve is given a value which links the dP with the flow rate. This value is the Kvs value.

The equation which we commonly use in the UK is:

Flow ‘Q’ = [Kvs X √dP] / 36

Flow is litres/second
dP is KiloPascals (kPa) Note: 100 kPa = 1 Bar = 10 metres head

This formula is very simple to use.

1- Take the reading from the balancing valve or orifice device and find the square
root of the value.
2- Establish the Kvs value for the balancing valve or orifice device (From
manufacturer chart.
3- Multiply 1 and 2 above and divide the answer by 36
4- The answer is now the flow rate.

As an example let us say that the dP reading is 5.2 kPa across an orifice device which has a
Kvs of 2.2 – the calculation is as follows:

Flow Q = [2.2 X √5.2] / 36

= [2.2 X 2.28] / 36 = 0.139 L/S

Now- if you know the flowrate that you are seeking and want to calculate the dP value that
you have to adjust the valve to achieve we need to re-arrange the formula.

dP = [36Q / Kvs]2

Simply multiply the desired flow rate by 36 then divide by the Kvs and finally square the
answer.
So- if we are looking to adjust the valve to achieve 0.139 L/S our calculation is as follows:

dP = [36 X 0.139 / 2.2] 2 = 5.2 kPa

In order to simplify the process of deriving the flow from the measured differential pressure
the manufacturers publish graphs for each of the valves as shown below.
 Kvs = 2.2
6000 60
5000 50
4000 40

3000 30

2000 20

1000 10

(kPa)

500 5
400 4

300 3
FLOWRATE

Q = K VS p
200 2

Where 36
Q = Flowrate l/s

100 1 p = Signal kPa

K VS = Signal Coefficient
70 0.7
0.05 0.1 0.2 0.3 0.4 0.5 1 2 3 4 5

Graph showing performance of valve with Kvs 2.2

To derive flowrate from graph simply take the differential pressure reading in kPa and find
this value on the vertical (Y) axis – Read across and from the point where the lines cross
read down to find the flow.

Note: the graphs are log/log graphs so care must be taken to derive the correct flow.

If you are using any of the electronic meters mentioned above all you have to do is enter the
correct measuring device or balancing valve into the meter using SELECT VALVE option.
The information entered is Maker, type, model and size.

When you return to the display screen the type of valve will be displayed on the scroll bar at
the bottom of the screen.

The dp can be taken from the valve and the flow is automatically calculated and displayed.
The calculations shown above are all taken care of by the meter.
7 Step by step guide to taking a reading with electronic
manometers

Fixed orifice devices

1 Identify the maker, type, model and size of the valve being measured.
(For our purposes we will assume it is a Crane fixed orifice type D931 size 15mm.)

2 Select the correct connection fittings provided with the electronic meter. For the
Crane valve we need the angle insertion probes. (These are often referred to as
‘Binder’ adaptors)

3 Remove white plastic protectors and snap the connectors onto the red and blue
tagged nylon connection tubes. It is possible to connect to either end of the tube – it
would be normal to connect it to the end opposite that with the ball valve fitted. (The
end you choose is personal preference)

4 Connect the other end of the two connection tubes to the electronic meter.
5 Ensure that the small bypass valve on the side of the meter is OPEN. And the two
ball valves on the connection tubes are closed.
6 The insertion probes can now be inserted into the fitting (testpoint) on the Crane
D931 valve. It is advisable to wet the probe first as this has to push its way through a
rubber seal in the testpoint. This can be difficult especially when the testpoint is new.

7 Open both ball valves on the connection tubes. If there is a flow through the Crane
balancing valve there will be a differential pressure across the valve which will force
 water through the red connection tube, through the meter and back to the balancing
valve via the blue connection tube. This process known as purging can only happen
when the small bypass valve is open.

When the flow through the balancing valve is high the dP will be large and will purge the
tubes quickly. When the flow is low then the process could take some time (1-2
minutes).The nylon tubes are supplied in clear nylon to allow you to see the air bubbles
being purged. Do not leave the unit purging for more than the necessary time as this can
make the internal temperature of the unit change dramatically, particularly on heating
systems. The unit has temperature compensation built-in but changes in temp take some
time to settle.

8 Close the two ball valves on the unit. Switch the unit on by pressing any button. When
the unit starts it will ‘boot-up’ to a display screen which is defaulted to show FLOW
and PRESSURE. Look at the pressure reading to establish if the unit has settled
following the purge process. Press the zero button. The display should now display
zero and be stable on this reading. Re-zero the unit if necessary. The unit is now
ready to read from the balancing valve.
9 Open the two ball valves on the connecting tubes and then close the small bypass
valve on the unit. The pressure reading should now be showing.
10 To display the flow reading it is necessary to enter the valve into the unit. Press the
menu button and use the right arrow button to change menus until MAIN menu is
displayed. The first item in this menu is SELECT VALVE press the tick (  ) button.
11 Use right arrow button to select maker (Crane in this case) – when Crane is visible
use down arrow to move in the menu to the valve type – this is FIXED in our
example. Use down arrow to move to menu item valve type – this is D931 in our
example so you will have to use the right arrow button to find the valve. When found
use the down arrow to move to the size option. The first size is 15mm. At this point
you can look at the complete selection. It should be Crane-Fixed-D931-15mm. At this
point press the tick button to select.
12 The screen display will now return to the PRESSURE and FLOW screen. The flow
will now be displayed.

Note: because a period of time has elapsed it may be necessary to re-zero the unit. To do
this make sure that you open the small bypass valve first followed by closing the ball valves.
Re-zero at this point then open the ball valves followed by closure of the bypass valve. You
should now be reading flow and pressure.

Please remember to open the small bypass valve each time you zero the unit or move the
unit from one balancing valve to another. The bypass valve in the open position provides
additional protection to the sensor from harmful overpressures which can be present when
the unit is disconnected and re-connected.

Variable orifice devices (VODRV)

Why use this procedure?

This procedure is for setting the handwheel on a VODRV such that the desired flowrate is
achieved without having to refer to manufacturer’s multi line graphs.
 (kPa)
HANDWHEEL SETTING (Number of turns)
3 4 5 10 16
10000 100

5000 50

1000 10

500 5

100 1

70 0.7
0.5 1 5 10 50 100 500

It is important to note that the KVs value of the valve changes as the handwheel is operated.
Therefore the flow reading cannot be taken from the AC6 until the handwheel position has
been entered into the meter.

How do I know if the valve is VODRV or a fixed device?

If there is any doubt about whether a variable orifice valve is being measured then simply
take a differential pressure (dp) reading when the valve is fully open and then close the
handwheel by a couple of turns. Without changing anything on the meter if the differential
reading appears to go up and the flow appears to go up then the valve is a variable orifice
valve (VODRV)

If the same procedure is used and the dp and flow go DOWN then the valve is a FIXED
orifice device.

Information that you will need to have available.

1. The MAKE, MODEL, TYPE AND SIZE of the valve being measured
2. The desired flowrate through the valve.

Procedure for setting the valve.

1. Select the correct valve and size from the database using MAIN MENU- SELECT
VALVE-MAKER- MODEL- SIZE
Return to the display screen using the X button or return button (bottom left) – The correct
valve should now be scrolling across the bottom of the screen.
2. Enter the desired flowrate for the valve using MAIN MENU- DESIGN FLOW
Return to the display screen.
 3. Change the display menu to MULTIDISPLAY in the DISPLAY menu

You should now see a display with a lot of information. On the right hand side there is the DP
and the FLOW readings. On the left side in a small box there is the PERCENTAGE OF
DESIGN FLOW.

With the balancing valve connected and set in the fully open position the flow reading on the
meter will be correct because the meter is automatically set to the fully open position when it
was selected. The handwheel position is shown at the top of the small valve schematic
image on the left of the screen.

Assuming that when the valve is fully open there is a surplus of flow then the PERCENTAGE
OF DESIGN FLOW box will show a figure greater that 100%

If the figure is less that 100% then the balancing valve will have to be left fully open.

Because the adjustment of a balancing valve can have a varied effect on the flowrate due to
the unknown authority the valve has over the circuit, the process of adjustment involves an
iterative process and some careful judgement.

Let us assume that the flow percentage in the lower box is 120% then we know we must
close the valve slightly to reduce the flow. If we have a valve that has 8 full turns to the
handwheel then we can attempt to set the valve to say, position 7. We must now adjust the
handwheel position in the meter also the position 7 ( Using the UP arrow) At this point the
flowrate reading will now reflect the flow through the valve at handwheel position 7. Again,
because we are unaware of the authority of the valve over the circuit the flow might either be
higher than design or perhaps lower than design.

If the flow is higher than design then the balancing valve must be closed a little more and the
new handwheel position entered into the meter. Keep using this method until the percentage
of flow through the valve is at 100% of design.

In order to achieve a quick adjustment it might be better in practice to ‘over-adjust’ the valve
so that the user can assess the effect of the valve authority over the circuit. With practice the
user should be able to set the valve correctly with perhaps only 3 or 4 adjustments.

This process may seem involved but it is a lot simpler than trying to use the graphs provided
by the manufacturers.

Please note: the handwheel setting shown in the percentage box adjacent to the left arrow
symbol is the setting that would be correct if the differential pressure was constant when the
valve is adjusted. This setting should not be used unless differential pressure controllers are
present in the circuit.

What do I do if I need to restart this procedure?

If the process of setting the valve has not gone according to plan then we can reset the
meter and balancing valve to the start position.

1. Use the UP arrow key which will prompt for a handwheel setting. At the top of the
screen the max and min handwheel positions are shown. Set to the Max POSITION.
2. Adjust the balancing valve to the fully open position.
 Check on the MULTIDISPLAY screen that the handwheel position shown above the
schematic is the correct fully open value.

Now start the setting procedure again.

Remember that each time you move from one balancing valve to another the meter and the
valve have to be set for the fully open position before starting the procedure.

8 System balancing.
Now that we are able to establish the flow rate through a balancing valve the next step is to
understand the process of balancing.

In the UK we use a system of balancing called ‘Proportional Balancing’. The reason for this
name will become apparent later!
The balancing process described here is simply a guide to the principle of proportional
balancing. It is important to point out that the pre-commissioning checks need to be made,
these however are not the subject of this paper. The pre-commissioning checks would
include but would not be limited to:

1 Installation check to manufacturer’s requirement.

2 Inclusion of correct venting and draining
3 Inclusion of correct strainers
4 Correct installation of measuring/balancing valves with respect to pipe size/type
and the clear lengths of upstream/downstream pipe
5 Checks on the correct chemical cleaning
6 Checks on the correct water treatment
7 Checks on glycol content if used.
8 Checks on pump motor conditions

Terminal 3 Terminal 2 Terminal 1

Branch
valve 1

Terminal 6 Terminal 5 Terminal 4

Branch
valve 2

Riser valve
1
Referring to the idealised system above we will assume that the pump is located at the base
of the riser and each of the terminals is designed to have the same flow rate. We will
assume that the pump has been sized to give a small percentage extra flow (This is quite
common although nowadays variable speed pumps allow for this)

Assume that each terminal is to have 0.1 l/s flow and the valves have a Kvs value of 2.2

We have 6 terminals therefore we have a requirement for 0.6 l/s flow

If we are using an electronic commissioning meter the process will be as follows:

1 Ensure that all balancing valves and control valves are fully open.
2 We have to establish which terminal is getting the least flow. Generally the
terminal furthest from the pump is likely to have the greatest resistance to flow
because of the length of pipe connecting it to the pump. This is not always the
case so it is wise to carry out a quick check by measuring the flow at each of the
likely terminals. In our example we would perhaps check terminal 1, 2 and 4.
3 The terminal with the lowest flow is the INDEX circuit. Note: if all the terminal
balancing valves are the same then it is a simple process to check which is the
index circuit – the circuit with the lowest dP showing when connected to the
meter.
4 We will assume that terminal 1 is the index.
5 Take a flow reading at terminal 1 – this is likely to be something other than 0.1 l/s
–for this example we will say the flow is 0.096 l/s which is 96% of our requirement.
The important point here is that we are in ‘underflow’ and adjusting the balancing
valve will only reduce the flow. Do not be concerned with this, simply record the
percentage of flow (i.e. 96%)
6 Take a reading at terminal 2 – this is nearer the pump so the flow will be slightly
higher than terminal 1 – say 0.098 l/s. We must now make a small adjustment to
the balancing valve so that the percentages are the same i.e. 96%. We can now
say that the terminals 1 and 2 are balanced even though they are still in
underflow.
7 Take a reading at terminal 3 – again, this is nearer the pump and perhaps the
percentage of flow is 102%. We must again adjust the balancing valve until we
achieve the same percentage through terminals 1, 2 and 3.

Note: We must remember that because we are making adjustments to balancing valves we
are forcing water to go elsewhere – some of this water will go through the previously set
terminals so a quick check on terminal 2 will establish if there has been any increase in the
percentage. If the flow has increased then make the necessary adjustment to terminal 3 so
that the percentages are all the same. Remember that a quick check on the previous valve
will reveal the flow percentage through all of the previously balanced terminals because they
are balanced.

8 We now have a branch where all three terminals are balanced and the
percentage of flow is 96% (assuming it has not changed when making the
adjustments)
9 Take a reading at terminal 4 which is much nearer the pump and will therefore
have a higher percentage of flow – say 114% Record this figure.
10 Continue with the balancing process on this branch in exactly the same way as
the previous branch.
11 When you have completed this the terminals will be balanced at ‘say’ 114%
12 We must remember the effect of making adjustments to balancing valves will
affect the flow elsewhere in the system, as such, the first branch may have
increased.
 13 Take reading on branch valve 1 which might have increased to 98%. We now
have a situation where the flow in the top branch is 98% and the lower branch
114%
14 With the meter set on branch valve 2 adjust the valve until this branch is the same
percentage as the first branch. We have already discussed the fact that by
adjusting a valve the water will flow elsewhere and it is for this reason that checks
of the flow in branch 1 need to be made. As the flow reduces in branch 2 when
adjusting the valve the flow will increase in branch 1. A second meter or perhaps
a manometer set on branch 1 would be useful in this situation.
15 The adjustment is made to equalise the percentage flow and in our example this
might be 106%
16 All terminals and branches are now balanced at 106%. The final measurement
and adjustment being made to riser valve 1 which should show that the flow is
106%. Make the adjustment to 100%

By adjusting just the one riser valve all terminals are affected by the same PROPORTION!

The process described above is very simplistic but it gives details of the basic requirements
of proportional balancing. Commercial systems are normally far more extensive than the
system described but the process of creating balanced groups of valves such as branches
before balancing the branches with each other can be extended to balancing multiples of
branches or even multiples of risers.

We have discussed the principle of ‘percentage’ of design flow where the actual flow is
related to the design flow. This process is made very easy with any of the above electronic
commissioning meters. Simply select the correct menu to enter the design flow for the valve
being measured and then display this using the MULTI display. The percentage of design
flow will be displayed alongside the actual flow and differential pressure. As the balancing
valves are adjusted the percentage of design flow figure will change.

Using the AC6 meter will reduce the laborious task of continued reference to the flow charts
or tedious calculations.

The AC6 electronic manometer is designed to facilitate measurement of systems using

traditional balancing valves as shown above. Standard software within the unit also allows
the display of flow associated with automatic balancing valves. The AC6 is unique in this
area and coupled with its ability to store data (using optional PcomPRO software add-on)
makes the unit the preferred meter for commissioning engineers.

Further reading.
CIBSE Knowledge guides Commissioning code W (2010)
BSRIA guides. Commissioning water systems BG2/2010
Commissioning Specialists Association

Acknowledgements
Crane Fluid Systems
Oventrop Ltd

E&OE Copyright Comdronic Ltd 2008 and amended May 2017