Function overview

Due to the dynamic switching between heating and cooling operation, the control function "Control valve for changeover" requires additional parameters: one set of parameters for heating operation and one set for cooling operation. The control function is configured via ABT Go.

The following functions are available for "Control valve for changeover":

 

Control mode

Intelligent Valve can be operated in 3 operating modes (CtlMod).

The operating mode determines the interpretation of the internal setpoint.

  • Position: The local PI control determines the control valve position
  • Volume flow: The local PI control determines the volume flow of the Intelligent Valve
  • Power: The local PI control determines the power of the Intelligent Valve

 

Maximum volume flow limit

Intelligent Valve is an ePICV (PICV = pressure independent control valve) – i.e. it is fundamental that the maximum volume flow is independent of the operating mode. The maximum volume flow limitation is always activated.

The setting is done via the objects VflMax (heating) and VflMaxC (cooling):

  • Default: Nominal volume flow of the specific valve type V100 = VflNomVlv
  • Setting range: 5…100 % of V100

In volume flow control mode, the set flow rates VflMax and VflMaxC are interpreted as 100% setpoints. In the other control modes, they are merely limitation values.

 

Minimum volume flow limit

The pre-setting of the minimum volume flow is optional and has to be enabled as needed.

  • Default: Inactive
  • Setpoint = 0 → PrVfl = 0

However, a minimum volume flow can be set so that:

  • Setpoint = 0 → PrVfl = X

As follows:

  • Enable volume flow minimum limitation with EnVflMin (heating) / EnVflMinC (cooling)
  • Define values VflMin (heating) and VflMinC (cooling)
  • Setting range: 2.5...20 % of V100 *) / max. VflMax
    (VflMin cannot be greater than VflMax!)

*)

V100: Nominal volume flow of the specific valve type (VflNomVlv)

 

Maximum power limit

In addition to functioning as an ePICV, Intelligent Valve allows the limitation of max. power to a heat exchanger or user. For this purpose, power control has to be selected.

The design power is defined via:

  • Max. volume flow (VflMax, VflMaxC)
  • Design temperatures for flow (TFlPrimDsgn, TFlPrimDsgnC) and return (TRtPrimDsgn, TRtPrimDsgnC)

Thus, the design power can be calculated as follows:

  • For heating: PwrDsgn = VflMax * (TFlPrimDsgn - TRtPrimDsgn) * c
  • For cooling: PwrDsgnC = VflMaxC* (TFlPrimDsgnC - TRtPrimDsgnC) * c

The power can be limited to the power limitation value (PwrMax,PwrMaxC ) in a range between 0 and the design power.

 

Return temperature limitation

This function controls the primary return temperature at B7 (TRtPrim) according to the set heating/cooling setpoint.

If the return temperature drops below/rises above the limitation value, the present valve control setpoint is lowered. The limitation is supplied by the PI controller; gain (GainTRtCtr) and reset time (TnTRtCtr) can be adjusted.

Defaults

Enable return temperature limitation

EnTRtLm

Inactive

Return temperature setpoint for heating

SpHTRt

40 °C

Return temperature setpoint for cooling

SpCTRt

12 °C

Gain for return temperature controller

GainTRtCtr

1% / K

Reset time for return temperature controller

TnTRtCtr

30 s

The starting conditions are based on whether the controller is operating in heating or cooling mode:

  • Heating mode (B7 < B26): TRtPrim > SpHTRt
  • Cooling mode (B7 > B26): TRtPrim < SpCTRt

The function reduces the calculated setpoint for the valve controller. An already nearly closed valve prevents the return temperature limitation from being enabled.

In order to ensure reliable temperature measurement, the function only closes to a minimum volume flow of 2.5 %.

 

Temperature difference limitation between flow and return (ΔT limitation)

ΔT limitation prevents the primary temperature difference (TFlPrim - TRtPrim) from dropping below a selected setpoint. This counteracts the "low ΔT syndrome", where an oversized valves opens as the load requirement increases. However, the heat exchanger can only transfer a limited amount of heat. This means that for little additional power (Q), the volume flow (V) has to be increased a large amount. The additional pump capacity required reduces the efficiency of the system.

Low ΔT syndrome

If the flow/return temperature difference drops too far, the present valve position is limited. The limitation is supplied by the PI controller, with gain (GainTDiffFlRtCtr) and reset time (TnTDiffFIRtCtr) being adjustable.

Defaults

Enable flow/return temperature difference limitation

EnTDiffFlRtLm

Inactive

Flow/return temperature difference limitation

SpTDiffFlRtLm

6 °C

Gain for flow/return temperature difference limitation

GainTDiffFlRtCtr

2% / K

Reset time for flow/return temp. difference limitation

TnTDiffFIRtCtr

30 s

The function lowers the present valve position. Due to the limited acting range, a nearly closed valve prevent the flow/return temperature difference limitation from being released. To ensure reliable temperature measurement, the functions only closes to a min. volume flow of 2.5 %.

 

Weighted return temperature limitation

This function controls the primary return temperature at B7 (TRtPrim) according to an appropriate "weighted" setpoint for heating and cooling.

Depending on the present volume flow (PrVfl), the function calculates the present return temperature setpoint (PrSpTRt), and if the temperature drops below/rises above the limitation value, the present valve control setpoint is raised/lowered. The limitation is supplied by the PI controller; gain (GainTRtCtr) and reset time (TnTRtCtr) can be adjusted.

Defaults

Enable weighted return temperature limitation

EnTRtLmWgd

Inactive

Design primary flow temperature

TFlPrimDsgn

55 °C

Design primary return temperature

TRtPrimDsgn

40 °C

Volume flow maximum

VflMax

100 %

Enable weighted return temperature limitation cooling

EnTRtLmWgdC

Inactive

Design primary flow temperature cooling

TFlPrimDsgnC

6 °C

Design primary return temperature cooling

TRtPrimDsgnC

12 °C

Volume flow maximum cooling

VflMaxC

100 %

Gain for return temperature controller

GainTRtCtr

1% / K

Reset time for return temperature controller

TnTRtCtr

30 s

The starting conditions are based on whether the controller is operating in heating or cooling mode:

  • Heating mode (B7 < B26): TRtPrim > PrSpTRt
  • Cooling mode (B7 > B26): TRtPrim < PrSpTRt

In heating mode, the function increases the calculated setpoint for the valve controller. In cooling mode, the function reduces the calculated setpoint.

An already nearly closed valve prevents the return temperature limitation from being enabled.

In order to ensure reliable temperature measurement, the function only closes to a minimum volume flow of 2.5 %.

 

Adapted maximum volume flow limitation

When this function is enabled (EnAdaVflMax, EnAdaVflMaxC), Intelligent Valve limits the adapted max. volume flow PrAdaVflMax.

PrAdaVflMax can take values within an upper and a lower limit:

  • Upper limit: configured value of the manual flow limitation (VflMax, VflMaxC)
  • Lower limit: smallest possible manually set limit value V5 = 5 % of V100)

Basically, two types of application are possible:

  1. Application with VflMax = V100 or VflMaxC = V100
    This type of application is suitable, when the design volume flow is unknown and/or changes frequently. The adapted volume flow max. limitation prevents excessive flow rates without the need to set a value for VflMax/VflMaxC.
  2. Application with VflMax < V100 or VflMaxC < V100
    This type of application is suitable, when the design volume flow is known and only rarely changes. Here, too, the adapted volume flow max. limitation prevents flow rates that are excessive as well as inefficient in terms of energy. Additionally, the manually set flow limitation prevents VflMax/VflMaxC from being exceeded at all times.

In operation, the adapted flow max. limitation acts as a sliding maximum filter, and calculates the adapted max. limitation value from the measured volume flow values (PrVfl) of the last 4 days. Short-term increases are limited to the value. Longer-term increases (lasting more than 3 hours) lead to a gradual upward adjustment of the adapted max. limitation value (in increments of 3 % of V100 every 3 hours).

During the first 4 days of the calculation, PrAdaVflMax = VflMax (heating) / PrAdaVflMax = VflMaxC (cooling) applies. The calculation restarts, if:

  • ...the adapted volume flow max. limitation is set from inactive to active.
  • ...the adapted volume flow max. limitation is already active, but the manual flow limitation VflMax/VflMaxC is set to a new value.

The following diagram illustrates the functionality of the adapted volume flow max. limitation for the application type VflMax < V100.

V =

Volume flow

t =

Days

 

Adapted maximum power limitation

When this function is enabled (EnAdaPwrMax, EnAdaPwrMaxC), Intelligent Valve limits the adapted max. power PrAdaPwrMax.

PrAdaPwrMax can take values between 1 % of PwrDsgn/PwrDsgnC and an upper limit, which corresponds to the configured value of the manual power limitation (PwrMax, PwrMaxC).

Basically, two types of application are possible:

  1. Application with PwrMax = PwrDsgn / PwrMaxC = PwrDsgnC
    This type of application is suitable, when the max. power is unknown and/or changes frequently. The adapted power max. limitation prevents excessive power outputs without the need to set a value for PwrMax/PwrMaxC.
  2. Application with PwrMax/PwrMaxC otherwise set
    This type of application is suitable, when the max. power is known and only rarely changes. Here, too, the adapted power max. limitation prevents power outputs that are excessive as well as inefficient in terms of energy. Additionally, the manually set power limitation prevents PwrMax/PwrMaxC from being exceeded at all times.

In operation, the adapted power max. limitation acts as a sliding maximum filter, and calculates the adapted max. limitation value from the measured power values (PrPwr) of the last 4 days. Short-term increases are limited to the value. Longer-term increases (lasting more than 3 hours) lead to a gradual upward adjustment of the adapted max. limitation value (in increments of 3 % of PwrDsgn every 3 hours).

During the first 4 days of the calculation, PrAdaPwrMax = PwrMax (heating) / PrAdaPwrMax = PwrMaxC (cooling) applies. The calculation restarts, if:

  • ...the adapted power max. limitation is set from inactive to active.
  • ...the adapted power max. limitation is already active, but the manual power limitation PwrMax/PwrMaxC is set to a new value.

The following diagram illustrates the functionality of the adapted power max. limitation for the application type PwrMax < PwrDsgn.

Pwr =

Power

t =

Days

 

Compensation mode

In volume flow and power control, the flow characteristic can be adapted to the behavior of the heat exchanger transfer. Three characteristics are available: linear, equal percentage, and heat exchanger optimized.

Linear

Recommended for plate heat exchangers water/water or injection circuits in precontrol circuits.

Caps the characteristic at min. volume flow min. limitation

Equal percentage, optimized in the opening range

Recommended for heating and cooling registers where the transfer characteristic is unknown

Modified characteristic with volume flow max. limitation at 60 %

Heat exchanger optimized

Recommended for heating and cooling registers where the transfer characteristic (a-value) is known.

Q = f(V) Heat exchanger characteristic

V = f(Y) Flow characteristic for Intelligent Valve

V̇ =

Volume flow V / V100

Y =

Setpoint

Q =

Heating power

With volume flow max. limitation, the characteristic adapts to the configured limitation setpoint (ex. for an equal percentage characteristic).

With volume flow min. limitation, the characteristic curve is capped below the minimum flow (ex. for a linear characteristic).

Defaults

Characteristic

CmpMod

Linear

Equal percentage (exponential)

Heat exchanger compensation

Linear

Compensation volume flow coefficient

CmpVflCoef

1…4

3

Compensation heat exchanger coefficient

CmpHxCoef

0.1…1

0.3

 

Self-test

A self-test is performed during the hydronic balancing. The self-test can be initiated and stopped via ABT Go or by pressing the SVC button.

  • During this time, the SVC LED flashes blue.

The following criteria are tested, and a corresponding report can be generated:

  • Flow sensor
  • Max. volume flow
  • Differential pressure at max. volume flow
  • Valve position at max. volume flow
  • Leakage rate

 

Forced max. volume flow

This function temporarily overrides the present setpoint. The valve supplies 10 minutes of maximum volume flow (VflMax) when the function is enabled.

  • During this time, the SVC LED flashes yellow.
  • Limitations (return temperature, flow/return temperature difference) are inactive while this function is active.
  • Self-tests are not possible while this function is active.

The function can be started as well as stopped via ABT Go or the SVC button.

 

Valve override mode

In override mode, the setpoint measured at X1 is overridden. Override mode is initiated via ABT Go with the object VovrMod.

  • During this time, the SVC LED flashes yellow.

The following options are available:

  • None
  • Fully open
  • Fully close
  • Minimum volume flow cooling
  • Minimum volume flow
  • Nominal volume flow
  • Maximum volume flow cooling
  • Maximum volume flow
  • Design power
  • Maximum power
  • Keep position

Override mode is automatically stopped after 2 hours.

 

Backup mode

If no relative setpoint (SpRel) is available, the backup mode determines the device behavior. Depending on the selected setpoint source, the function reacts to an invalid value at terminal X1, or disrupted Modbus or BACnet communication. It can be configured as follows:

  • None: In case of a setpoint loss, the valve remains closed until power returns.
  • Last setpoint: After the activation delay (BckpModDly), the device re-follows the last available setpoint. For this purpose, the last available setpoint is periodically written to the persistent memory. In case of a setpoint loss, the valve remains at the last available setpoint until power re-turns.
  • Predefined setpoint: After the activation delay (BckpModDly), the device goes to the pre-defined setpoint. In case of a setpoint loss, the valve follows this pre-defined setpoint until power returns.
    A backup setpoint is available for each of the 3 control modes:
    • Position: BckpModValPos
    • Volume flow: BckpModValTFl
    • Power: BckpModValPwr

The backup mode stops as soon as a valid setpoint is available again.