Transcript Module 3: Understanding Differential Pressure Control Valves

Introduction
Danfoss Training Module-3
******
Understanding Differential
Pressure Control Valves
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Introduction
Hello and welcome to the Danfoss training
module ‘Understanding Differential
Pressure Control valves
The purpose of this training module is to
give you the knowledge required to select,
specify, and understand Danfoss
products.
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Introduction
We will examine the types of valves used to
balance hydronic systems...
…and how we select the correct product
for the application they are to be used in.
This module takes around 20 minutes and
forms part of a ‘Continuous Professional
Development’ training course.
Once 3 modules are complete you can
apply to Danfoss for a certificate of your
achievement.
Now let us begin….
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The History of Danfoss Balancing Valve
1989
2003
2009
In 1989 Danfoss produced its first series of
MSV commissioning and ASV automatic
balancing valves.
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The History of
Danfoss Balancing Valve
1989
2003
2009
In 2003 Danfoss was the first major valve
manufacturer to introduce a combined
control and automatic balancing valve,
the AB-QM.
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The History of
Danfoss Balancing Valve
1989
2003
2009
The LENO MSV-O, unique commissioning
valve was launched by Danfoss in 2009.
By choosing Danfoss you have over 75
years of expertise behind you…
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Modernising Heating & Cooling Systems
As clients look to improve the efficiency of heating
and cooling systems, building services designers are
increasingly looking at ways to reduce energy.
Poor control and in-efficient system design are
contributing factors to high building energy usage.
By providing the correct temperature, using the least
amount of energy possible, we can make heating and
cooling systems comfortable for users, and run at a
lower cost.
A common way to improve a systems energy
efficiency is to use variable speed pumps.
Let us look at how variable speed pumped systems
operate…
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Modernising Heating & Cooling Systems
Variable speed pumps work by matching the pumps
flow
with the requirement of the system at any one time.
As parts of the system reach temperature,
and the control valves close, the pump senses a
change in pressure.
This pressure sensor is linked to a variable speed
drive which matches the pump speed with the system
requirement.
Variable Speed Drive
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Modernising Heating & Cooling Systems
Prior to variable speed, pumps ran at either 0% or 100%.
Controlling the pump speed means we can provide enough
flow
to achieve the comfortable temperatures, and at the same time
dramatically reduce the energy used to get it there.
However this modulation of the pump, makes the system
pressure
and flow variable. This variable pressure means traditional
static
balancing (commissioning) valves cannot operate effectively
in this type of system.
In variable flow systems we need dynamic balancing valves
which react to the changes in system pressure.
Danfoss ASV Differential Pressure Control Valves will provide
the dynamic balance required in variable flow systems.
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Variable Speed Drive
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ASV Differential Pressure Control Valves
The use of Differential Pressure Control Valves is
essential in modern hydronic systems.
They provide dynamic balancing to react to
pressure changes from the pump and to keep
constant pressure in the circuits.
This constant circuit pressure enables the system
to balance and be accurately controlled.
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ASV Differential Pressure Control Valves
The outcome of using DPCV’s is:
-Good control whether the system is running at
full or partial capacity
-High control valve authority
-Improved user comfort
-Maximised pump energy savings
To understand how we achieve these benefits,
we first need to examine how ASV Differential
Pressure Control Valves operate…
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Operation of Differential Pressure
Control Valves
Danfoss ASV-PV DPCV’s are installed on the
return pipe of the circuit. Danfoss ASV-I partner
valve are used on the flow pipe.
Partner Valve
An impulse tube is installed from the partner
valve to the DPCV and allows the flow pressure
to act upon the top of the valve diaphragm.
DPCV
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Operation of Differential Pressure
Control Valves
The return pressure acts upon the underside of
the diaphragm.
The spring within the valve is set by the installer,
using an allen key, to deliver a set circuit
pressure loss.
The diaphragm along with the spring act
together to react to system changes and to keep
this constant pressure loss.
So as the system pressure rises, the diaphragm
moves the valve cone down, to keep a
controlled circuit pressure.
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Operation of Differential Pressure
Control Valves
The commercial radiator heating circuit shown
below demonstrates this process in action.
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Operation of Differential Pressure
Control Valves
The pressure in the system (P1) is variable
as the pump modulates to match the
systems requirements.
As the Differential Pressure Control Valve
detects a change in the variable system
pressure it reacts to keep a constant circuit
pressure (P2).
P1
P2
This constant pressure in the circuit gives
the radiators a controlled flow.
The controlled flow to the radiators allows
the
Thermostatic Radiator Valve to achieve a
controlled temperature. This controlled
temperature improves comfort for the
users.
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Benefits of using Differential Pressure
Control Valves
Whilst the operation of Differential Pressure
Control Valves demonstrate the benefits of
improved temperature control, we should not end
there.
Comfort is not just about temperature.
A common problem for variable flow systems
without pressure control is noise.
Here is why…
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Benefits of using Differential Pressure
Control Valves
System Noise
As parts of our variable flow systems close down
(this state is called partial load), the open circuits
without pressure control see an increase in
pressure.
This increase in pressure results in a higher
differential pressure across the radiator
valves.
If the differential pressure across the radiator
valve becomes too high it will cause noise and
this noise will be uncomfortable for users,
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Benefits of using Differential Pressure
Control Valves
Differential pressure control ensures the pressure over the radiator valve will not increase
at partial loads. Thus excess noise emissions caused by the radiator valves will be
eradicated.
Without ASV’s
Dp
Dp
Pnom
With ASV’s
Dp supply
system
Pnom
Pressure Drop
5x
50%
0%
100% Flow
0%
50%
100% Flow
The system without Danfoss ASV DPCV’s allows the excess pressure to be lost across the
radiator valve (shown in red). By installing DPCV’s we remove the excess pressure in the
balancing valve (yellow) giving the TRV’s a constant pressure. This eliminates noise.
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Benefits of using Differential Pressure
Control Valves
When looking for improved efficiency we
should recognise the importance of the cost of
installing the system.
Danfoss Differential Pressure Controls Valves
give clear cost savings by reducing the time
taken to balance and commission.
The traditional proportional balancing method
requires each balancing valve to be visited at
least twice to complete commissioning.
This is because the setting of each
commissioning valve affects others in the
system.
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Benefits of using Differential Pressure
Control Valves
This is not the case when using
DPCV’s.
By installing ASV Differential Pressure
Control Valve Sets you can divide the
system into pressure independent
zones.
This means once the DPCV has been
set, the flow balance in this circuit is
unaffected by any other changes in the
rest of the system, e.g. Other circuits
opening or closing down, pump
speeding up or slowing down.
Each valve is only visited only once.
By reducing the number of visits to
each valve by more half, we more than
half the cost of water system
commissioning.
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Heat Interface Unit Application
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Benefits of using Differential Pressure
Control Valves
To achieve the perfect balance
Danfoss recommend the
installation of ASV’s on all
branches.
When used on every branch,
DPCV’s ensure accurate control
and noise protection throughout
the system.
Time savings during
commissioning are also best
realised with complete DPCV
coverage.
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Benefits of using Differential Pressure
Control Valves
Common applications for DPCV’s are to
balance:
-Under-floor heating manifolds (as
pictured)
-Radiator circuits
-Heat interface units
-Circuits with radiant panels
DPCV’s can also be used in cooling
systems to balance fan coils, chilled
beams and air handling units. However
Danfoss recommend utilising the
additional benefits of Pressure
Independent Control Valves in cooling
applications.
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Selecting ASV-PV Differential Pressure
Control Valves
Sizing and selecting an ASV-PV Differential
Pressure Control Valve is simple.
To demonstrate how to size a DPCV we shall
use an example of a radiator circuit requiring
a flow of 0.7 l/s and a total circuit pressure
loss of 18 kPa. The pipe-work is DN40.
The 18 kPa total circuit pressure loss is the
radiator circuit pressure loss added to the
ASV-I partner valve pressure loss.
Radiator Circuit
Pressure Loss
ASV-I
Pressure
Loss
ASV-PV
Pressure Loss
10 kPa is the most efficient operating
pressure for a system with ASV-PV valves.
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Return Pipe
When sizing an ASV-PV we aim to have a
valve pressure loss of 10 kPa.
Flow Pipe
The total circuit pressure loss does not
include the ASV-PV DPCV pressure loss.
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Selecting ASV-PV Differential Pressure
Control Valves
Thread
Flange
Now we have all the information required to
select our valve, the next stage is to consult
the ASV-PV datasheet.
In this datasheet you will find a flow chart
showing the achievable flow through the
different valve sizes, when we have a 10 kPa
valve pressure loss.
Firstly we turn our 0.7 litre per second (l/s)
flow rate in to litres per hour (l/h):
0.7 l/s *3600= 2520 l/h
We then take a line (red) horizontally
through
2520 l/h on the chart.
The smallest valve which can achieve the
flow is then selected. This is a DN40 valve.
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ASV Flow Chart
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Selecting ASV-PV Differential Pressure
Control Valves
Once we have our valve size we then consult
the datasheet for the available spring
ranges for DN40 valves.
The spring range is the differential pressure
loss, we require in the circuit, and that we set
in the DPCV.
As you can see below we have 3 spring
ranges for DN40 ASV-PV valves.
In our example we require a circuit pressure
loss of 18 kPa.
The ideal spring range would therefore be 525 kPa.
This leads us to select the ASV-PV DN40
valve with a 5-25 kPa spring range.
This is Danfoss code number: 003L7605.
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Danfoss ASV Range of Differential
Pressure Control Valves
Now we have looked at the theory behind
Differential Pressure Control Valves, it will be
useful to look at the products in more detail.
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Danfoss ASV Range of Differential
Pressure Control Valves
Danfoss ASV-PV’s are compact, high
performance valves, available in sizes ranging
from 15-100mm.
The valves have pressure spring ranges from as
low as 5 kPa, up to a maximum of 100 kPa.
The 15-40mm valves combine three services in
one.
They are a differential pressure control valve,
an isolation valve, and a drain point.
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Danfoss ASV Range of Differential
Pressure Control Valves
ASV-PV valves come complete with a 1.5m
impulse tube with connectors, moulded valve
insulation, and valve tags.
In addition to this they feature:
- Internal or external threaded pipe connections
- Pressure range spring options of 5-25 kPa and
20-40 kPa in sizes 15-25mm
- Spring options in sizes 32-40mm of 5-25 kPa,
20-40 kPa, and 35-75 kPa.
- A very compact design
- An operating temperature down as low as -20℃
and up to +120℃
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Danfoss ASV Differential Pressure
Control Valve
Danfoss ASV-PV valves in sizes 50-100mm are
PN16 cast iron, DPCV’s with additional spring
pressure ranges for higher pressures.
They also incorporate three services in one.
Acting as a differential pressure control valve, an
isolation valve, and a drain point.
The DN50 valve has four spring ranges. They are
5-25 kPa, 20-40 kPa, 35-75 kPa, 60-100 kPa.
The DN65-100 valve sizes have three spring
ranges, 20-40 kPa, 35-75 kPa, 60-100 kPa.
The ASV-PV valves in 65-100mm are capable of
handling valve pressure losses as high as 250
kPa.
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Danfoss ASV Differential Pressure
Control Valve
Setting the ASV-PV is very
simple.
Once installed an allen key is
used to set the circuit pressure
loss.
Each turn of the allen key relates
to
a pressure in kPa.
In 5-25 kPa and 20-40 kPa spring
ranges, one turn of the allen key
changes the pressure by 1 kPa.
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Danfoss ASV Differential Pressure
Control Valve
In 35-75 kPa and 60-100 kPa
valves,
one turn of the allen key
changes the pressure by 2 kPa.
Setting is commonly done by the
commissioning engineer who
monitors the pressure whilst
adjusting the valve.
When the required pressure loss
is achieved the valve is set.
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Danfoss ASV-I Partner Valves
Danfoss ASV-I partner valves are the ideal
accompaniment to ASV-PV Differential Pressure
Control Valves.
They are four services in one:
- A double regulating valve
- A measuring point for commissioning
- An isolation valve which is independent of the
valve setting
- A handy place to connect the impulse tube
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Danfoss ASV-I Partner Valves
By using a partner valve along with a DPCV, the
partner valve becomes a flow limiting double
regulating valve.
ASV-I valves are available in sizes 15-50mm.
Where a partner valve is required for sizes 65mm
and above, a Danfoss MSV-F2 flanged
commissioning valve can be used to partner the
ASV-PV.
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Pressure Independent Control Valves
Before we conclude our look at Differential
Pressure Control Valves, I’d like to look at just one
more.
This is the Danfoss type: AB-QM Pressure
Independent Control Valve (PICV’s).
AB-QM’s are used in fan coil, air handling, and
chiller applications as a combined differential
pressure and motorised control valve.
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Pressure Independent Control Valves
By using an AB-QM at each terminal, we create a
self balancing system with every coil receiving
only its desired flow.
By combining the control and balancing valve we
more than half the number of valves installed,
and reduce commissioning time by up to 2/3’s
AB-QM’s will be covered in detail in a future
Danfoss Training Module 4-’Pressure
Independent Control Valves’
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A Final Review
You now have all the information required to
specify,
select, and understand the Danfoss range of
Differential Pressure Control Valves
Before we finish, let us review the information you
have learned.
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A Final Review
Differential Pressure Control Valves (DPCV’s) are
used for dynamic balancing of hydronic heating
and cooling systems.
They react to changes in the system to keep a
constant pressure in the circuit they control.
This constant circuit pressure enables the system
to balance and be accurately controlled.
Differential pressure control valves are commonly
used in variable flow pumping systems.
Variable flow systems are used to improve the
energy
efficiency of heating and cooling systems.
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A Final Review
DPCV’s are installed on the return pipe of the
circuit.
Partner valve are used on the flow pipe.
An impulse tube is installed from the partner valve
to the DPCV and allows the flow pressure to act
upon the top of the valve diaphragm.
The spring within the valve is set by the installer,
using an allen key, to deliver a set circuit pressure
loss.
The diaphragm along with the spring act together
to react to system changes and to keep this
constant pressure loss.
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A Final Review
Common applications for DPCV’s are:
-Under-floor heating manifolds (as pictured)
-Radiator circuits
-Heat interface unit
-Circuits with radiant panels
Danfoss recommend the installation of DPCV’s on all
branches of the system.
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A Final Review
Danfoss ASV-PV valves are a compact, high
performance valve, available in sizes ranging from
15-100mm, and pressure spring ranges from as low as
5 kPa and up to 100 kPa.
They incorporate three services in one. Acting as a
differential pressure control valve, an isolation valve,
and a drain point.
Danfoss ASV-I partner valves are the ideal
accompaniment to our Differential Pressure Control
Valves.
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Final Review
Congratulations for completing
your third training module!
You now understand all that is required to select,
and specify Danfoss balancing valves.
Once you have completed three modules you
can apply to Danfoss Randall for your
‘Continuous Professional Development’
Certificate.
For more information on Danfoss products or
for Danfoss-Randall’s contact details please visit
our
website at:
www.danfoss-randall.co.uk
Thank you for your time.
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