ELECTRIC HEATER
ELECTRIC HEATER - title
Electric Heater Component Model
ELECTRIC HEATER - model over view
Model Overview
Author / organization: Benedikt Leitner / AIT
Domain: Energy conversion device
Intended application: Return-supply connections in district heating networks or in combination with thermal storage tanks
Modelling of spatial aspects: Lumped (single device)
Model dynamics: Dynamic
Model of computation:
- Time-continuous
- The model avoids the use of events if possible
Functional representation: Explicit
ELECTRIC HEATER - input and output
Input and Output
Input variables :
- Real m_flow_set: mass flow setpoint for pump [kg/s]
- Modelica.Fluid.Interfaces.FluidPort port_a (acausal): fluid port at return side
Output variables:
- Real P: current electric load [W]
- Modelica.Fluid.Interfaces.FluidPort port_b (acausal): fluid port at supply side
ELECTRIC HEATER - related document
ELECTRIC HEATER - description
Short Description
A model of an electric heater including a pump. The pump controls the mass flow through the heater which heats the fluid to a set temperature. The electric heater has a constant power-to-heat efficiency and a nominal heat flow rate.
The electric heater takes water from the cold source (corresponding to the nominal return temperature value of the electric heater TemRet_nominal). The mass flow is set by the pump which is controlled through a ramping function. The heater increases the temperature of the fluid. In case the mass flow is below the nominal mass flow, the fluid temperature equals the nominal temperature TemSup_nominal. In case the mass flow is higher the heater is operating with full capacity Q_flow_nominal but is not able to reach the nominal temperature TemSup_nominal.
Present use / development status
A ramping function is used to control the mass flow of the pump m_flow_set of the electric heater. The function starts at zero. After one hour the ramp starts and increases to 0.1 within two hours. It stays at 0.1 till the end of the simulation.
The model is part of AIT’s internal Modelica library for district heating and is usable for co-simulation with electric network models. The Modelica library uses the Modelica standard library and the IBPSA library as a core.
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ELECTRIC HEATER
Model Details
Domain |
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Intended application (including scale and resolution) | Intended to be used for return-supply connections in district heating networks or in combination with thermal storage tanks, with a temporal resolution of seconds to minutes
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Modelling of spatial aspects |
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Model dynamics |
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Model of computation |
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Functional representation |
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Input variables (name, type, unit, description) |
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Output variables (name, type, unit, description) |
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Parameters (name, type, unit, description) |
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Internal variables (name, type, unit, description) |
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Model equations | Governing equations | ||
m_flow_nominal = Q_flow_nominal / (c_p*(TemSup_nominal - TemRet_nominal)) See Modelica models:
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Constitutive equations | |||
See Modelica models:
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Initial conditions | Medium is initialized with default values (see Modelica model)
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Boundary conditions | Connections to fluid ports at return and supply.
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Optional: graphical representation (schematic diagram, state transition diagram, etc.) |
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Model Validation | |||
Narrative | The electric heater is connected to a cold source (30°C) and receives mass flow setpoints. These setpoints start at zero and rise above the nominal mass flow of the component to show its behaviour at both design and off-design situations. | ||
Test system configuration |
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Inputs and parameters |
Inputs:
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Control function (optional) | A ramping function is used to control the mass flow of the pump m_flow_set of the electric heater. The function starts at zero. After one hour the ramp starts and increases to 0.1 within two hours. It stays at 0.1 till the end of the simulation.
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Initial system state | The system starts without any mass flow
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Temporal resolution | CVode is used as an integrator. It uses a variable integrator step size based on tolerance settings. Here a relative tolerance of 0.0001 is used. Simulation result outputs are generated every 60 seconds or on events (if any).
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Evolution of system state |
The electric heater takes water from the cold source (corresponding to the nominal return temperature value of the electric heater TemRet_nominal). The mass flow is set by the pump which is controlled through a ramping function. The heater increases the temperature of the fluid. In case the mass flow is below the nominal mass flow, the fluid temperature equals the nominal temperature TemSup_nominal. In case the mass flow is higher the heater is operating with full capacity Q_flow_nominal but is not able to reach the nominal temperature TemSup_nominal. | ||
Results | The results show that the pump generates a mass flow according to the control function described above. The temperature at the supply side of the electric heater rises to its nominal value as soon as the mass flow becomes positive. It stays at this value until the mass flow exceeds the nominal value m_flow_nominal. From there on the electric heater is operating at full capacity Q_flow_nominal and is not able to reach the nominal temperature anymore. This can be seen from the electric power consumption. It rises to the nominal power capacity (10 kW) until the nominal mass flow is reached and stays constant from there on. | ||
Model harmonization | |||
Narrative | Same as in model validation. | ||
Test system configuration | Same as in model validation. | ||
Inputs and parameters | Same as in model validation. | ||
Initial system state | Same as in model validation. | ||
Temporal resolution | Same as in model validation. | ||
Evolution of system state | Same as in model validation. | ||
Results | Mean weighted temperature:
Where ? is the electric power consumed. |