Technical Guidelines

Shunt groups and

protection against
freeze damage
Application in air handling units

RC1 ROOM
* *
GT2 GT2 GT2
EF

SECONDARY SECONDARY
GT8 CIRCUIT, CIRCUIT,
ST1 HEAT COOLING
GT3 GT1
SF

H₂O H₂O
HRC

AIR HANDLING UNIT (AHU)

CP1 CP2

SF Supply air fan

EF Extract air fan
CP1 Circulation pump, heat SHUNT GROUP, SV1 SV2 SHUNT GROUP,
CP2 Circulation pump, cooling
HRC Rotary heat exchanger
HEAT, WITH COOLING, WITH
TWO-WAY TWO-WAY
GT1 Supply air sensor REGULATING REGULATING
GT2 Extract air sensor/room sensor
(*alternative location) VALVE VALVE
GT3 Outdoor air sensor
GT8 Freezing protection monitor

SV1 Regulating valve (shunt) and actuator, heat

SV2 Regulating valve (shunt) and actuator, cooling
ST1 Outdoor air damper actuator PRIMARY CIRCUIT, PRIMARY CIRCUIT,
RC1 Microprocessor unit (controller) DISTRICT HEATING SYSTEM DISTRICT COOLING SYSTEM
 Technical Guidelines Shunt groups & freeze protection

Shunt groups and freeze damage protection for air handling units
Shunt groups A shunt group usually consists of the following com-
ponents:
A shunt group is an assembled unit consisting of a
regulating valve, circulation pump, initial adjustment
valves, shut-off valves, etc. Regulating valve
Regulates the flow in the shunt group’s pri-
The purpose of the shunt group is to serve as a link mary and secondary circuit. The regulating
between primary and secondary systems in water- valve is operated by a valve actuator wired
borne heating and cooling systems, e.g. between a to a control unit.
boiler (primary circuit) and a heating coil inside an air
handling unit (secondary circuit). The regulating valve is used for obtaining
the correct water temperature in a heating
The pipework package is required for regulating the or cooling system. The regulating valve,
capacity to meet the heating or cooling load since also called shunt valve, mixes inlet water
the secondary system most often operates with other from the primary circuit with water from
temperatures and flows than the primary system. the return pipe (secondary circuit).
The capacity is regulated as follows: The shunt group The regulating valve can be of two-way or
mixes the media (primary/secondary) in a controlled three-way design depending on the nature
manner to achieve the correct temperature in the of the pipe system to which it will be con-
secondary system. nected.
Circulation pump
Keeps the liquid circulating in the circuit
on the secondary side.
Manual commissioning valve
For adjusting (balancing) the flow and
pressure drop to achieve an optimum
shunt group duty point.
Manual shut-off valve
Enables you to dismantle the shunt group
without having to empty the entire system.
Typical prefabricated shunt group (Siemens)
Bypass with non-return valve
Enables circulation of liquid in the shunt
group’s secondary circuit, as indicated by
the flow arrow, even if the regulating valve
is closed against the secondary circuit.

Prevents the medium from flowing in the

wrong direction in the event of a power
failure to the secondary circuit pump.
Thermometers
Provide an overview of the operating con-
ditions and to show how the system is
operating.
Basic circuit diagram showing the makeup of a prefabri-
cated shunt group (Siemens)

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 Technical Guidelines Shunt groups & freeze protection

Examples of shunt groups

Two-way regulating valve Pipework package (code STD-05)

Översikt
Primary Secondary Primary Pipework Secondary
package

H2O H2O

H2O

Top
Shunt group with two-way regulating valve fitted in Pipework package with three-way regulating valve
the return pipe from a heating or cooling coil. fitted in the supply pipe to the heating coil. The flow
can be commissioned with the rated KVS value of
• Variable flow in the primary circuit the regulating valve.

Compact
• Constant flow in the secondary circuit
• Variable flow in the primary circuit
• Suitable for use in e.g. district heating/district
• Constant flow in the secondary circuit
cooling systems in which low or high return tem-
peratures are desirable. • Suitable for use in e.g. district heating systems in
which low return temperatures are desirable and
• ”Bleeder valve”, if required, enables the circula-
in systems with low primary pressure.
tion of water to the secondary circuit. Used e.g. to
quickly supply heat/cooling energy to the coil (in • Adjustment valve, if required. Commissioning
long supply flow pipes) or for outdoor installation. is normally carried out with the rated Kvs value

Flex
in the pipework package. (IV Produkt regulating
Three-way regulating valve valve (code STD-05) has variable Kvs).

Primary Secondary * The Kvs value expresses the amount of 20-degree

water flow (m³/h) allowed to pass through a fully open
regulating valve at 100 kPa motive pressure.

Styr
Example: A regulating valve with a Kvs value of 16
H2O allows 16 m³/h (4.44 l/s) to pass through at 100 kPa
(1 bar) motive pressure.

H2O
Filteröversikt
Shunt group with three-way regulating valve fitted in
the return pipe from a heating or cooling coil.

• Constant flow in both the primary and secondary

circuits.
• Suitable for use in systems with their own source
Kodnycklar

of energy, e.g. boiler systems, in which constant

flow in the primary circuit and a slight drop in
temperature are desirable.
The pump in the shunt group forces a constant flow
of water through the coil and the three-way valve
mixes a portion of the primary water with a portion
of the return water from the coil, to provide the cor-
rect ultimate capacity.

TGS120524.01.EN 3

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 Technical Guidelines Shunt groups & freeze protection

Basic circuit diagrams, shunt groups in ventilation installations

District heating and district cooling

RC1 ROOM
* *
GT2 GT2 GT2
EF

SECONDARY SECONDARY
GT8 CIRCUIT, CIRCUIT,
ST1 HEAT COOLING
GT3 GT1
SF

H₂O H₂O
HRC

AIR HANDLING UNIT (AHU)

CP1 CP2

SF Supply air fan

EF Extract air fan
CP1 Circulation pump, heat SHUNT GROUP, SV1 SV2 SHUNT GROUP,
CP2 Circulation pump, cooling
HRC Rotary heat exchanger
HEAT, WITH COOLING, WITH
TWO-WAY TWO-WAY
GT1 Supply air sensor REGULATING REGULATING
GT2 Extract air sensor/room sensor
(*alternative location) VALVE VALVE
GT3 Outdoor air sensor
GT8 Freezing protection monitor

SV1 Regulating valve (shunt) and actuator, heat

SV2 Regulating valve (shunt) and actuator, cooling
ST1 Outdoor air damper actuator PRIMARY CIRCUIT, PRIMARY CIRCUIT,
RC1 Microprocessor unit (controller) DISTRICT HEATING SYSTEM DISTRICT COOLING SYSTEM

Example: Two-way shunt groups in a ventilation installation with district heating and district cooling

The illustration shows pipework packages with two-way regulating valves fitted in the return pipes from heat-
ing and cooling coils. The pipework connections that are suitable for district heating and district cooling involve
the following:

• The primary circuit operates with variable flow

• The secondary circuit operates with constant flow
• A low return temperature (substantial Δt) is obtained in the heating case
• A high return temperature (substantial Δt) is obtained in the cooling case
• A ”bleeder valve” , if required, enables the circulation of water forward to the secondary circuit to
quickly supply heat/cooling energy to the coil (e.g. in the case of long supply flow pipes).

Since a district heating plant’s distribution pipes often are long, the greatest portion of the costs for water
produced for district heating is for distribution. It is therefore important to extract necessary heating capacity
out of as little water flow as possible, which means that in the case of district heating a substantial decrease
in water temperature is required.
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 Technical Guidelines Shunt groups & freeze protection

Private heat source and private cooling plant

Översikt
RC1 ROOM
* *
GT2 GT2 GT2
EF

SECONDARY SECONDARY

Top
GT8 CIRCUIT, CIRCUIT,
ST1 HEAT COOLING
GT3 GT1
SF

Compact
H₂O H₂O
HRC

AIR HANDLING UNIT (AHU)

CP1 CP2

SF Supply air fan

EF Extract air fan
CP1 Circulation pump, heat SHUNT GROUP, SHUNT GROUP,

Flex
SV1 SV2
CP2 Circulation pump, cooling
HRC Rotary heat exchanger
HEAT, WITH COOLING, WITH
THREE-WAY THREE-WAY
GT1 Supply air sensor REGULATING REGULATING
GT2 Extract air sensor/room sensor
(*alternative location) VALVE VALVE
GT3 Outdoor air sensor
GT8 Freeze protection monitor

SV1 Regulating valve (shunt) and actuator, heat

Styr
SV2 Regulating valve (shunt) and actuator, cooling
ST1 Outdoor air damper actuator PRIMARY CIRCUIT, PRIMARY CIRCUIT,
RC1 Microprocessor unit (controller) HEAT COOLING

Example: 3-way shunt groups in a ventilation installation with boiler and private cooling plant

The illustration shows shunt groups with three-way regulating valves fitted in the return pipes from heating and Filteröversikt
cooling coils. The pipework connections that are suitable for e.g. a boiler and your own cooling plant involve
the following:

• Both the primary and secondary circuits operate with constant flows
• The regulating valves mix the supply flow and return water (mixing valve)
Kodnycklar

• Relatively little drop in temperature (little Δt) is obtained.

If the water is heated by means of a boiler/centralized boiler, the requirement for temperature reduction in the
water is normally not as much as for district heating. Too low return temperature may cause condensation to
form inside the boiler.

TGS120524.01.EN 5

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 Technical Guidelines Shunt groups & freeze protection

Shunt data from IV Produkt Designer

The IV Produkt Designer product selection program computes the shunt data for both two-way and three-way
regulating valves according to the examples below. The shunt data consists of Liquid temp in, Liquid temp out
and Liquid flow.

Envistar Flex Technical data

Project Project1
AHU AHU1
Size 300 1.80/1.80 m³/s

AIR HEATER WATER

Input Air temperature in 13.3 °C
Requested air temp out 20.0 °C
Liquid temp in 82.0 °C
Liquid temp out requested 71.0 °C
Output Air temperature out 20.0 °C
Air speed 1.9 m/s
Liquid flow 0.10 l/s
Pressure drop liquid 0.3 kPa
Power variant 00
Heating power 14.5 kW
Fin pitch 6.0 mm
Tube connection 25
Alt. 1
Primary side with 2-wayvalve
Liquid temp in 82.0 °C
Liquid temp out 45.9 °C
Liquid flow 0.10 l/s
Alt. 2
Primary side with 3-wayvalve
Liquid temp in 82.0 °C
Liquid temp out 71.0 °C
Liquid flow 0.32 l/s

Example: Technical data from IV Produkt Designer

Temperatures and flows at design drop in temperature according to data above:

SEK. 0,10 l/s 0,10 l/s SEK. 0,10 l/s 0,10 l/s

CP1 CP1

45,9 °C 82,0 °C 45,9 °C 82,0 °C

SV1 SV1 0,22 l/s

45,9 °C 82,0 °C 71,0 °C 82,0 °C

PRIM. 0,10 l/s 0,10 l/s PRIM. 0,32 l/s 0,32 l/s

Alt. 1 – Two-way regulating valve Alt. 2 – Three-way regulating valve

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 Technical Guidelines Shunt groups & freeze protection

Sizing of coils Things to consider...

• The water temperature specified in technical • ���������������������������������������������
Liquid pressure drop. Acceptable liquid pres-
data (examples on the previous pages) is ob- sure drops for coils vary depending on how
tained only when the design ”Air temperature, they are used. As approx. values for sizing, we

Översikt
out” has been reached. recommend the following (which refer to coils
installed in air handling units):
• The liquid flow through a coil should be kept
constant to achieve the best heat transfer - Heating coil, clean water < 15 kPa
characteristics. The Capacity is regulated - Cooling coil, clean water < 30 kPa
by changes in water temperature which take
place preferably in a pipework package. • Cooling coil – for air velocities more than ~2.8
m³/s we recommend the use of droplet sepa-
• If the flow of liquid in a coil is too low, the coil will rators (applies to standard aluminium fins. If
never operate optimally and there is high risk of

Top
the fins have been painted with Corropaint, the
freeze damage, laminar flow* and difficulty in corresponding limit value is ~1.5 m³/s.
regulating the temperature.

* There are two types of flows: laminar and tur-

bulent. At low airflow velocities the flow can

Compact
occur in parallel stratifications and this is called
laminar.
Laminar flow is difficult to regulate/stabilize and
has proportionately poor heating and cooling
transfer.
Flows normally consist of vortex movements of
varying size and frequency. Flows of this type
are called turbulent. When the flow is turbu-
lent, friction and heat/cooling energy transfer is

Flex
considerable greater than in the case of lami-
nar flow.

Styr
Filteröversikt
Kodnycklar

TGS120524.01.EN 7

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 Technical Guidelines Shunt groups & freeze protection

Freeze protection function for

heating coils
IN OUT
H₂O H₂O

Air Air
General
The purpose of freeze protection is to prevent ice OUT
H₂O
IN
H₂O

from forming in the rows of tubes in the heating coil.

If any ice should form, this could cause the heating
coil to freeze and burst resulting in water damage.
Counter-flow coupling versus parallel-flow coupling
To prevent ice from forming on surfaces, the heating
coil should be fitted with a freeze protection sensor/ In the following information, we refer to counter-flow
freeze protection monitor wired to a microprocessor coupling only, since it offers the best capacity and
unit/controller. is most common.
The microprocessor unit protects the heating coil by
performing the following sequence: Clamp-on sensors
Clamp-on temp. sensors are mounted to be in direct
When the air handling unit is operating contact with the outlet pipe of the heating coil.
• Opens the regulating valve if the water tem-
perature drops below 12 °C (preset value)
• Switches off the fans and closes the outdoor
air damper if the water temperature drops be-
low 5 °C (preset value) IN
H₂O

When the air handling unit has stopped

• Starts the function for keeping the coil warm
by regulating the regulating valve to achieve
Air
the preset stay-warm temperature of 20 °C
(preset value) and in this way prevent frost
OUT
from forming and making the air handling unit Clamp-on H₂O
easy to start up. temperature
sensor
The location of the temperature sensor is very impor-
tant because the sensor must be able to sense if the
temperature drops too low. The sensor must there- Clamp-on temp. sensor location: supply air, from left to
fore always be located on the coldest point of the right
heating coil by the return/outlet pipe.

The temperature sensors are available in two versions:

Clamp-on
• Clamp-on sensors temperature
sensor
• Immersion sensors. OUT
H₂O
Counter-flow or parallel-flow coupling?
The tube rows of a heating coil can be connected/
coupled either for counter flow or parallel flow. Air
Counter-flow coupling means that the warm supply
flow water meets the airflow. The warmest section of
IN
the coil will be where the air leaves the coil. Counter-
H₂O
flow coupling offers the highest heating capacity.

Parallel-flow coupling means that the warm supply

flow water follows the direction of airflow. This results
in poorer heating capacity.
Clamp-on temp. sensor location: supply air, from right to left

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 Technical Guidelines Shunt groups & freeze protection

Immersion temperature sensor

Insert an immersion temp. sensor into the coil through the

coil’s built-in connection nipple. Depending on the direc-

Översikt
tion of airflow through the coil (supply air flowing from left
to right or vice versa) install the immersion sensor at the
bottom or top to sense the cold spot. See the follow-
ing illustrations.

Top
Compact
Flex
IN
H₂O

Styr
Air

OUT

Filteröversikt
H₂O

Immersion temp sensor

Immersion temp. sensor location, supply air, from left to right

Kodnycklar

Immersion temp. sensor location, supply air, from left to right

TGS120524.01.EN 9

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 Technical Guidelines Shunt groups & freeze protection

Immersion temp sensor

OUT
H₂O

Air

IN
H₂O

Immersion temp. sensor location, supply air from right to left

Immersion temp. sensor location, supply air from right to left

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 Technical Guidelines Shunt groups & freeze protection

ThermoGuard Things to consider...

Coils protected from freezing with • I��������������������������������������������
nstall the clamp-on and immersion temp. sen-
ThermoGuard have been developed sors according to the instructions.
as a result of the discovery that ice
• Insulate around the sensor where it is mounted

Översikt
itself is not what causes the tube
bends to burst. Freezing occurs first to ensure that it will operate correctly.
inside the tubes in the finned-tube
package. The pressure of the water
closed in by the ice is what eventually
causes the bursting.

The ThermoGuard function relieves the high water

pressure inside the tube bends and prevents the

Top
bends from bursting. The pressure is led away to the
pipe system or through a safety valve (SÄV).

ThermoGuard offers increased safety against freeze

damage. ThermoGuard coils are connected in the
same way as other coils.

Compact
ThermoGuard function

Pressure relief hole

Hot water return

Flex
Safety valve

Hot water inlet

Styr
Filteröversikt
Kodnycklar

Safety valve on ThermoGuard heating coils protected

against freezing

TGS120524.01.EN 11

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 TGS120524.01.EN

IV Produkt AB, Box 3103, 350 43 Växjö, Sweden

Phone: +46 470-75 88 00 • Fax: +46 470-75 88 76
info@ivprodukt.se • www.ivprodukt.se