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Introduction

Danfoss Training Module-3

* * * * * *

Understanding Differential

Pressure Control Valves

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C O M F O R T C O N T R O L S - Page 3

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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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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C O M F O R T C O N T R O L S - Page 5

The History of Danfoss Balancing Valve

1989 2003

In 1989 Danfoss produced its first series of MSV commissioning and ASV automatic balancing valves.

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1989 2003

In 2003 Danfoss was the first major valve manufacturer to introduce a combined

control and automatic balancing valve,

the AB-QM.

The History of

Danfoss Balancing Valve

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C O M F O R T C O N T R O L S - Page 7

1989 2003

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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2009

The History of

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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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C O M F O R T C O N T R O L S - Page 9

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

Modernising Heating & Cooling Systems

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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.

Modernising Heating & Cooling Systems

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C O M F O R T C O N T R O L S - Page 11

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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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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C O M F O R T C O N T R O L S - Page 13

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.

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.

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Operation of Differential Pressure

Control Valves

DPCV Partner Valve

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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.

Operation of Differential Pressure

Control Valves

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C O M F O R T C O N T R O L S - Page 15

The commercial radiator heating circuit shown below demonstrates this process in action.

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Operation of Differential Pressure

Control Valves

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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).

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

Operation of Differential Pressure

Control Valves

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C O M F O R T C O N T R O L S - Page 17

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

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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,

Benefits of using Differential Pressure

Control Valves

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C O M F O R T C O N T R O L S - Page 19

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.

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Benefits of using Differential Pressure

Control Valves

100% Flow

D

p

0%

50% Pnom Pressure Drop

5x

Without ASV’s

D

p

Pnom

0%

50% 100% Flow Dp supply system With ASV’s

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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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.

Benefits of using Differential Pressure

Control Valves

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C O M F O R T C O N T R O L S - Page 21

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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Benefits of using Differential Pressure

Control Valves

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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.

Benefits of using Differential Pressure

Control Valves

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C O M F O R T C O N T R O L S - Page 23 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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Benefits of using Differential Pressure

Control Valves

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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. The total circuit pressure loss does not include the ASV-PV DPCV pressure loss. When sizing an ASV-PV we aim to have a

valve pressure loss of 10 kPa.

10 kPa is the most efficient operating

ASV-PV Pressure Loss F low Pipe R et urn Pipe ASV-I Pressure Loss Radiator Circuit Pressure Loss

Selecting ASV-PV Differential Pressure

Control Valves

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C O M F O R T C O N T R O L S - Page 25

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.

ASV Flow Chart

Thread Flange

Selecting ASV-PV Differential Pressure

Control Valves

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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 5-25 kPa.

This leads us to select the ASV-PV DN40 valve with a 5-25 kPa spring range.

This is Danfoss code number: 003L7605.

Selecting ASV-PV Differential Pressure

Control Valves

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C O M F O R T C O N T R O L S - Page 27

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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-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.

Danfoss ASV Range of Differential

Pressure Control Valves

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C O M F O R T C O N T R O L S - Page 29 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 Range of Differential

Pressure Control Valves

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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

Danfoss ASV Differential Pressure

Control Valve

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C O M F O R T C O N T R O L S - Page 31

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.

Danfoss ASV Differential Pressure

Control Valve

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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.

Danfoss ASV Differential Pressure

Control Valve

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C O M F O R T C O N T R O L S - Page 33

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

Danfoss ASV-I Partner Valves

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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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C O M F O R T C O N T R O L S - Page 35

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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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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C O M F O R T C O N T R O L S - Page 37

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.

A Final Review

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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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C O M F O R T C O N T R O L S - Page 39

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.

A Final Review

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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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C O M F O R T C O N T R O L S - Page 41

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.

A Final Review

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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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