[TX2_DMD] tx2 demand
Function block TX2_DMD calculates the weighted demand signals for the processes heating, cooling, humidification, and dehumidification, used by the function block TX2_ACTN for cost-optimized use of ERC (energy recovery).
TX2_DMD calculates the weighted demand signals for the processes heating, cooling, humidification, and dehumidification, used by the function block TX2_ACTN for cost-optimized control of ERC (energy recovery). The current demand is determined from the positioning signals of the individual air handling aggregates and the design values for the aggregates. The demand is weighted with regard to energy consumption or costs.
Control strategy Economizer TX2
The Economizer TX2 control strategy comprises two focal points:
- ERC control with regard to energy-optimized air handling processes.
- Control of air handling processing with regard to weighting (e.g. costs).
The function blocks TX2_DMD and TX2_ACTN are part of the Economizer TX2 control strategy and have the following functions:
- The function block TX2_DMD calculates energy-optimized air handling processes (based on enthalpy and aggregates used) and then calculates an energy-optimized demand for ERC. The energy-optimized demand signals additionally are multiplied by a weighting factor (e.g. with regard to costs), so that several weighted (e.g. costly) air handling processes have a superordinate demand for ERC. ERC then focuses on weighted (i.e. costly) air handling processes. Cheaper air handling processes thus are carried out mostly by other air handling processes.
- The function block TX2_ACTN controls ERC based on the demand signals weighted by function block TX2_DMD. Here, the function block TX2_ACTN determines the optimal operating point for ERC.
Process procedure in the function block
Step | Process procedure in the function block |
|---|---|
1 | The function block calculates the currently active energy use:
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2 | The function block calculates the weighted demand signals for ERC ([WgHDmd], [WgCDmd], [WgHuDmd], [WgDhuDmd]) so that the sum of the costs for the air handling processes (e.g. cooling) is optimized to a minimum:
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The weighted demand signals are calculated from the following inputs:
[WgHDmd]: | [YReHcl], [DsReHcl], [YPreHcl], [DsPreHcl], [YErcH], [DsErcH], [WgH], [TOa], [HuAbsOa], [TEx], [HuAbsEx], [TEfcy], [HuEfcy] |
[WgCDmd]: | [YCclC], [DsCclC], [YAwC], [DsAwC], [YErcC], [DsErcC], [WgC], ([WgHu] if [AwCActv] = On), [TOa], [HuAbsOa], [TEx], [HuAbsEx], [TEfcy], [HuEfcy] |
[WgHuDmd]: | [YAwHu], [DsAwHu], [YErcHu], [DsErcHu], [WgHu], [TOa], [HuAbsOa], [TEx], [HuAbsEx], [TEfcy], [HuEfcy] |
[WgDhuDmd]: | [YCclDhu], [DsCclDhu], [YErcDhu], [DsErcDhu], [WgDhu], [TOa], [HuAbsOa], [TEx], [HuAbsEx], [TEfcy], [HuEfcy] |
Input | Description | Data type | Default value |
|---|---|---|---|
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AwCActv | Air washer cooling active | Boolean | 0 |
On: Air washer cooling is active. | |||
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YReHcl | Positioning signal reheating coil | Real | 0.0 [%] 0.0…100.0 [%] |
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YPreHcl | Positioning signal preheating coil | Real | 0.0 [%] 0.0…100.0 [%] |
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YErcH | Positioning signal energy recovery for heating | Real | 0.0 [%] 0.0…100.0 [%] |
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YErcC | Positioning signal energy recovery for cooling | Real | 0.0 [%] 0.0…100.0 [%] |
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YAwC | Positioning signal air washer for cooling This input is interconnected only if the humidifier is needed for cooling (e.g. air washer). [AwCActv]=On. | Real | 0.0 [%] 0.0…100.0 [%] |
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YCclC | Positioning signal cooling coil for cooling | Real | 0.0 [%] 0.0…100.0 [%] |
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YAwHu | Positioning signal air washer for humidification | Real | 0.0 [%] 0.0…100.0 [%] |
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YErcHu | Positioning signal energy recovery for humidification | Real | 0.0 [%] 0.0…100.0 [%] |
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YErcDhu | Positioning signal energy recovery for dehumidification | Real | 0.0 [%] 0.0…100.0 [%] |
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YCclDhu | Positioning signal cooling coil for dehumidification | Real | 0.0 [%] 0.0…100.0 [%] |
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TOa | Outside temperature | Real | 20.0 [°C] -70.0...70.0 [°C] |
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HuAbsOa | Outside air absolute humidty
| Real | 7.8 [g/kg] 0.0...20.0 [g/kg] |
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TEx | Extract air temperature Room extract air temperature (see Engineering). | Real | 0.0 [°C] 0.0…50.0 [°C] |
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HuAbsEx | Extract air absolute humidity Room extract air humidity (see Engineering) | Real | 7.8 [g/kg] 0.0...20.0 [g/kg] |
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DsReHcl | Reheating coil design Nominal air temperature increase by reheater. | Real | 5.0 [K] 0.0...50.0 [K] |
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DsPreHcl | Preheating coil design Nominal air temperature increase by reheater. | Real | 5.0 [K] 0.0...50.0 [K] |
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DsErcH | Energy recovery design for heating Typical value: Width of room temperature setpoint band (e.g. 3 - 5 °K). | Real | 5.0 [K] 0.0...50.0 [K] |
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DsErcC | Energy recovery design for cooling Typical value: Width of room temperature setpoint band (e.g. 3 - 5 °K). | Real | 5.0 [K] 0.0...50.0 [K] |
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DsAwC | Air washer design for cooling Nominal air temperature decrease by air washer. | Real | 5.0 [K] 0.0...50.0 [K] |
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DsCclC | Cooling coil design for cooling Nominal air temperature decrease by cooling coil. | Real | 5.0 [K] 0.0...50.0 [K] |
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DsAwHu | Air washer design for humidification Nominal air temperature increase by air washer. | Real | 2.0 [g/kg] 0.0...20.0 [g/kg] |
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DsErcHu | Energy recovery design for humidification Typical value: Width of room humidity setpoint band (e.g. 3 - 5 g/kg). | Real | 2.0 [g/kg] 0.0...20.0 [g/kg] |
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DsErcDhu | Energy recovery design for dehumidification Typical value: Width of room humidity setpoint band (e.g. 3 - 5 g/kg). | Real | 2.0 [g/kg] 0.0...20.0 [g/kg] |
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DsCclDhu | Cooling coil design for dehumidification Nominal air humidity decrease by cooling coil. | Real | 2.0 [g/kg] 0.0...20.0 [g/kg] |
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TEfcy | Temperature efficiency Temperature efficiency degree of used ERC. Typical values: | Real | 1.0 0.0...1.0 |
1: Recirculated air | |||
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HuEfcy | Humidity efficiency Humidity efficiency degree of used ERC. Typical values: | Real | 1.0 0.0...1.0 |
1: Recirculated air | |||
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WgH | Weighting for heating Relates to 1 K. | Real | 1.0 1.0...10.0 |
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WgC | Weighting for cooling Relates to 1 K. | Real | 1.0 1.0...10.0 |
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WgHu | Weighting for humidification Relates to 1 g/kg. | Real | 1.0 1.0...10.0 |
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WgDhu | Weighting for dehumidification Relates to 1 g/kg. | Real | 1.0 1.0...10.0 |
Output | Description | Data type | Default value |
|---|---|---|---|
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WgHDmd | Weighted demand for heating Energy or cost-optimized demand signal for heating. Interconnected to function block TX2_ACTN. | Real | 0.0 [K] 0.0...100.0 [K] |
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WgCDmd | Weighted demand for cooling Energy or cost-optimized demand signal for cooling. Interconnected to function block TX2_ACTN. | Real | 0.0 [K] 0.0...100.0 [K] |
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WgHuDmd | Weighted demand for humidification Energy or cost-optimized demand signal for humidification. Interconnected to function block TX2_ACTN. | Real | 0.0 [g/kg] 0.0...50.0 [g/kg] |
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WgDhuDmd | Weighted demand for dehumidification Energy or cost-optimized demand signal for dehumidification. Interconnected to function block TX2_ACTN. | Real | 0.0 [g/kg] 0.0...50.0 [g/kg] |
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SysUnits | System of units Indicates the system of units used by the block. | Integer | 1: International system of units (SI) (fallback) 1...5 |
1: International system of units (SI) (fallback) | |||
ErrCode | Error code indication | Integer | 0: No error |
= 0 - No error | |||
Plant configuration
The Economizer tx2 control strategy is used for the following plant configurations:
- ERC, preheater, cooler, reheater, humidifier
- ERC, cooler, reheater, humidifier
(ERG = Mixing air dampers, rotational heat exchanger, plate heat exchanger, etc.)
The benefits of the Economizer tx2 strategy are used only if at least three air handling processes are present and ERC allows for humidity recovery. Recirculated air is best suited for humidity recovery.
Adiabatic cooling
If the humidifier is used as air washer for adiabatic cooling, the air washer must be placed after the cooling coil to prevent dehumidification by the cooling coil.
Temperature sensor [TEx], [HuAbsEx]
If the temperature difference between extract air before ERC and the room air is big, an additional temperature sensor must be placed in the extract air before ERC.
Weighting [WgH], [WgC], [WgHu], [WgDhu]
The following cost factors can be considered to weigh individual air handling processes:
- Primary energy costs.
- Operations and amortization costs for corresponding air handling.
- Efficiency across entire process.
The function blocks TX2_DMD and TX2_ACTN together form ERC control. These function blocks are linked with room and supply air control of an air conditioning system (min. 3 air handling processes) to form one control strategy (Economizer tx2).
Energy efficiency
The Economizer tx2 control strategy can be used as a supplement for other energy and cost optimization procedures:
- Peak demand optimization
- Ventilation time optimization: Scheduler program, Optimum Start Stop OSSC.
- Setpoint field control (tolerance band for temperature and humidity)
- Night ventilation
- Return limitation for district heating
The function block processes the value at the inputs. The values are either default values of the function block or output values or output values of the pre-configured function blocks.