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Central heating - two-pipe system
System description
Two-pipe systems for distributing heat are most common in
Europe. The radiators are connected in parallel and supplied with the same flow temperature by means
of supply and return pipes. In modern buildings, heat distribution is horizontal: each apartment is
supplied by a dedicated section. In pre-existing systems, on the other hand, vertical distribution
is common, with supply and return lines running through multiple floors.
Hydronic balancing
For modern two-pipe systems with speed-regulated pumps,
hydronic balancing using automatic differential pressure controllers is recommended. These ensure
constant, pre-set pressures and, in combination with adjustable thermostatic valves, also ensure the
correct, consumer-specific flow and thus the correct distributionof heat. This maximises convenience
and energy savings.
Dynamic solutions:
Automatic differential pressure regulators Kombi-Auto and
Kombi-3-Plus with membrane regulator for applications from DN10 to DN100

Kombi-Auto
Kombi-S

Kombi-3-Plus Red

Kombi-Auto
Static solutions:
Static balancing valves for applications from DN10 to DN400

Kombi-3-Plus Blue

Kombi-2-Plus

Kombi-F

Kombi-Auto
Kombi-S

Kombi-3-Plus Red

Kombi-Auto

Kombi-3-Plus Blue

Kombi-2-Plus

Kombi-F
Central Heating – heat interface units
System description
Central heating systems equipped with local heat interface
units are in principal comparable to two-pipe systems. Radiators connected in parallel or heating
circuits in panel heating are supplied with the same flow temperature via supply and return pipes.
Heat interface units contain all the components for combined local water heating and hot water
distribution and for horizontal distribution of the heating water to individual apartments.
Hydronic balancing
As in modern two-pipe systems with speed-regulated pumps,
hydronic balancing using automatic differential pressure controllers is recommended. These ensure
constant, pre-set pressures and, in combination with adjustable thermostatic valves, also ensure the
correct, consumer-specific flow and thus the correct distribution of heat. In the case of
applications with heat exchange units, the differential pressure controller on the primary side
should be arranged upstream of these heat exchange units so that the generation of heat for hot
water is also balanced.
Dynamic solutions:
Automatic differential pressure regulator Kombi-Auto for
applications from DN10 to DN100. Alternatively: Kombi-QM

Kombi-Auto
Kombi-S

Kombi-3-Plus Red
Static solutions:
Static balancing valves for applications from DN10 to DN400

Kombi-3-Plus Blue

Kombi-Auto
Kombi-S

Kombi-3-Plus Red

Kombi-3-Plus Blue
Central heating - One pipe system
System description
One-pipe systems for heat distribution are still widespread
in existing building stock in Europe in some regions. The radiators are connected one after the
other in series and are each supplied with a proportion of the heating water. The majority of the
circulating heating water bypasses the respective radiator on a bypass circuit so that it can be
mixed with the cooled water from the radiator downstream of that radiator. The flow of mixed water
is then fed to the next radiator in the circuit. As a result, all the radiators in a one-pipe system
have different flow temperatures dictated by the system. One-pipe systems can have a horizontal or
vertical network architecture.
Hydronic balancing
For modernised one-pipe systems with a constant flow,
hydronic balancing by means of automatic flow controllers or return-temperature-flow-controlled,
pressure-independent control valves is recommended. Flow controllers ensure defined flow in radiator
groups arranged horizontally or vertically. Return-temperature flow-controlled, pressure-independent
control valves enable defined return flow temperatures when the heating system is operated in design
mode or under partial load. Thermostatic valves with distribution ensure correct flow at the
radiator and thus correct distribution of heat.
Dynamic solutions:
Volume flow regulator Kombi-VX and backflow-controlled
pressure-independent control valves Kombi-QM with thermostat Thera-2080-WL for applications from
DN15 to DN25

Kombi-VX

Kombi-QM mit
Thera-2080-WL
Static solutions:
Static balancing valves Kombi-3-Plus and Kombi-2-Plus for
applications from DN10 to DN25

Kombi-3-Plus Red

Kombi-2-Plus

Kombi-VX

Kombi-QM mit
Thera-2080-WL

Kombi-3-Plus Blue

Kombi-2-Plus
Fan coil -two-conductor system
System description
Two-conductor systems with local fan coils as heat
exchangers are in principle realised as a two-pipe system. All fan coils connected in parallel are
supplied with heating or cooling at the same flow temperature via supply and return pipes. The
switch from heating to cooling operation and vice versa is carried out centrally. Fan coils are
usually used to supply heating or cooling room by room. The cooling or heating is fed to the room
using temperature-controlled air by means of heat exchangers and fans. Engineered control is on a
room-byroom or group-by-group basis using room thermostats or by incorporation in the building
automation system.
Hydronic balancing
As in modern two-pipe systems with speed-regulated pumps,
hydronic balancing using automatic differential pressure controllers in the pipes/circuits is
recommended. These ensure constant, pre-set pressures and, in combination with adjustable control
valves with actuation at the fan coil, also ensure the correct, consumer specific flow and thus the
correct distribution of heat. Alternatively, hydronic balancing in modern systems is carried out on
a consumer-specific basis with pressure-independent control valves and actuators at the fan coil. It
is also recommended that pre-control be carried out in this case using automatic differential
pressure controllers.
Dynamic solutions:
Automatic differential pressure regulator Kombi-Auto for
applications from DN10 to DN100. Alternatively: Kombi-QM

Kombi-Auto
Kombi-S

Kombi-Auto

Kombi-QM
Static solutions:
Static balancing valves for applications from DN10 to DN400

Kombi-3-Plus Blue

Kombi-2-Plus

Kombi-F

Kombi-Auto
Kombi-S

Kombi-Auto

Kombi-QM

Kombi-3-Plus Blue

Kombi-2-Plus

Kombi-F
Fan coil - four-conductor system
System description
Four-conductor systems are in principal realised as a
“double” two-pipe system. All fan coils connected in parallel are simultaneously supplied with
heating or cooling at the same flow temperature via supply and return pipes. The switch from heating
to cooling operation is carried out for each room as needed. This “switchover” prevents simultaneous
cooling or heating operation. A choice of cooling/heating is fed to the room using
temperature-controlled air by means of heat exchangers and fans. Engineered control is on a
room-by-room or group-by-group basis using room thermostats with “switchover” or by incorporation in
the building automation system.
Hydronic balancing
As in modern two-pipe systems with speed-regulated pumps,
hydronic balancing using automatic differential pressure controllers in the pipes/circuits is
recommended. These ensure constant, pre-set pressures and, in combination with adjustable control
valves with actuation at the fan coil, also ensure the correct, consumer specific flow and thus the
correct distribution of heat. Alternatively, hydronic balancing in modern systems is carried out on
a consumer-specific basis with pressure-independent control valves and actuators at the fan coil. It
is also recommended that pre-control be carried out in this case using automatic differential
pressure controllers.
Dynamic solutions:
Automatic differential pressure regulator Kombi-Auto for
applications from DN10 to DN100. Alternatively: Kombi-QM

Kombi-Auto
Kombi-S

Kombi-Auto

Kombi-QM
Static solutions:
Static line balancing valves Kombi-3-Plus for applications
from DN10 to DN400

Kombi-3-Plus Blue

Kombi-2-Plus

Kombi-F

Kombi-Auto
Kombi-S

Kombi-Auto

Kombi-QM

Kombi-3-Plus Blue

Kombi-2-Plus

Kombi-F
Surface temperature control - underfloor heating
System description
Central heating systems with surface heating underfloor,
panel or overhead heating) are generally realised as a two-pipe system. One or more heating circuit
distributors (manifolds) are supplied with heat at the same flow temperature via supply and return
pipes. Heat is supplied to the room-specific heating circuits from the heating circuit distributor
as required. The heat is supplied to the rooms to be heated via the floor structure by means of
pipelines laid across the surface, through which hot water flows. The control is done on a
room-by-room or group-by-group basis using room thermostats, if required together with individual
timing control.
Hydronic balancing
As in modern two-pipe systems with speed-regulated pumps,
hydronic balancing using automatic differential pressure controllers in the pipes/circuits is
recommended. These ensure constant, pre-set pressures and, in combination with adjustable control
valves for each heating circuit at the heating circuit distributor, also ensure the correct,
consumer-specific flow and thus the correct distribution of heat. The heating-circuit specific
control valves are controlled by means of room thermostats. This maximises convenience and energy
savings.
Dynamic solutions:
Automatic differential pressure regulator Kombi-Auto and
Kombi-3-Plus with membrane regulator for applications from DN10 to DN50

Kombi-Auto
Kombi-S

Kombi-3-Plus
Static solutions:
Static line balancing valves Kombi-3-Plus for applications
from DN10 to DN50

Kombi-3-Plus

Kombi-2-Plus

Kombi-Auto
Kombi-S

Kombi-3-Plus Blue

Kombi-3-Plus Red

Kombi-2-Plus
Surface temperature control - chilled ceilings
System description
Central systems with chilled ceilings are generally realised
as a two-pipe system. chilled ceilings are supplied with cooling at the same fl ow temperature via
supply and return pipes. Chilled ceilings are usually used to cool non-residential buildings, such
as offices, retail and exhibition spaces, on a room-by-room basis. The cooling is supplied to the
room via the floor structure or extensive heat-exchange surfaces by means of pipelines laid across
the surface, through which cold water flows. The control is done on a room-by-room or group by-group
basis using room thermostats, if required together with individual timing control.
Hydronic balancing
As with modern two-pipe systems with speed-controlled pumps,
hydronic balancing via automatic differential pressure regulators in the lines/circuits is
recommended. These ensure constant, pre-set pressures and, in combination with pre-adjustable
regulating valves per cooling circuit on the cooling circuit distributor or per cooling surface
element, they ensure the correct, user-specific volume flow and thus the correct heat or cold
distribution. The cooling circuit-specific control valves are controlled using room thermostats.
Moisture sensors avoid condensation failure. Alternatively, hydronic adjustment can be carried out
in a user-specific manner by means of pressure-independent control valves with an actuator on the
cooling surface element.
Dynamic solutions:
Automatic differential pressure regulator Kombi-Auto and
Kombi-3-Plus with membrane regulator for applications from DN10 to DN50. Alternatively: Kombi-QM

Kombi-Auto
Kombi-S

Kombi-3-Plus Red

Kombi-QM
Static solutions:
Static line balancing valves Kombi-3-Plus and Kombi-2-Plus for
applications from DN10 to DN50

Kombi-3-Plus Red

Kombi-2-Plus

Kombi-Auto
Kombi-S

Kombi-3-Plus Blue

Kombi-QM

Kombi-3-Plus Blue

Kombi-2-Plus
Air handling units – air heaters
System description
Central heating systems with air handling units are in
principle realised as a two-pipe system. All air heaters connected in parallel are supplied with
heat at the same flow temperature via supply and return pipes. Air heaters are usually used to heat
non-residential buildings such as sports facilities and assembly halls on a room-by room basis or as
air-curtain systems in entrance areas. Heat is fed to the room in the form of heated air by means of
heat exchangers and electric fans. The control is done on a room-by-room or group-by-group basis
using room thermostats or by incorporation into a building management system.
Hydronic balancing
As in modern two-pipe systems with speed-regulated pumps,
hydronic balancing using automatic differential pressure controllers in the pipes/circuits is
recommended. These ensure constant, pre-set pressures and, in combination with adjustable control
valves with actuation at the fan heater, also ensure the correct, consumer specific flow and thus
the correct distribution of heat. Alternatively, hydronic balancing can be carried out on a
consumer-specific basis with pressure-independent control valves having actuators at the air heater.
Dynamic solutions:
Automatic differential pressure regulator Kombi-Auto for
applications from DN10 to DN100. Alternatively: Kombi-QM to DN150

Kombi-Auto
Kombi-S

Kombi-Auto

Kombi-QM
Static solutions:
Static balancing valves for applications from DN10 to DN400

Kombi-3-Plus Blue

Kombi-2-Plus

Kombi-F

Kombi-Auto
Kombi-S

Kombi-Auto

Kombi-QM

Kombi-3-Plus Blue

Kombi-2-Plus

Kombi-F