This generic grey-box heat pump model uses empirical data to model
the refrigerant cycle. The modelling of system inertias and heat
losses allow the simulation of transient states.
Resulting in the choosen model structure, several configurations are
possible:
- Compressor type: on/off or inverter controlled
- Reversible heat pump / only heating
- Source/Sink: Any combination of mediums is possible
- Generik: Losses and inertias can be switched on or off.
Concept
Using a signal bus as a connector, this heat pump model can be easily
combined with the new HeatPumpSystem
or several control or safety blocks from AixLib.Controls.HeatPump.
The relevant data is aggregated. In order to control both chillers
and heat pumps, both flow and return temperature are aggregated. The
mode signal chooses the type of the heat pump operation. As a result,
this model can also be used as a chiller:
- mode = true: Heating
- mode = false: Chilling
To model both on/off and inverter controlled heat pumps, the
compressor speed is normalizd to a relative value between 0 and 1.
Possible icing of the evaporator is modelled with an input value
between 0 and 1.
The model structure is as follows. To understand each submodel,
please have a look at the corresponding model information:
-
InnerCycle
(Black Box): Here, the user can use between several input models or
just easily create his own, modular black box model. Please look at
the model description for more info.
- Inertia: A n-order element is used to model system inertias (mass
and thermal) of components inside the refrigerant cycle (compressor,
pipes, expansion valve)
-
HeatExchanger: This new model also enable modelling of thermal
interias and heat losses in a heat exchanger. Please look at the
model description for more info.
Parametrization
To simplify the parametrization of the evaporator and condenser
volumes and nominal mass flows there exists an option of automatic
estimation based on the nominal usable heating power of the HeatPump.
This function uses a linear correlation of these parameters, which
was established from the linear regression of more than 20 data sets
of water-to-water heat pumps from different manufacturers (e.g.
Carrier, Trane, Lennox) ranging from about 25kW to 1MW nominal power.
The linear regressions with coefficients of determination above 91%
give a good approximation of these parameters. Nevertheless,
estimates for machines outside the given range should be checked for
plausibility during simulation.
Assumptions
Several assumptions where made in order to model the heat pump. For a
detailed description see the corresponding model.
-
Performance data 2D: In order to model inverter controlled heat
pumps, the compressor speed is scaled linearly
-
Performance data 2D: Reduced evaporator power as a result of
icing. The icing factor is multiplied with the evaporator power.
-
Inertia: The default value of the n-th order element is set
to 3. This follows comparisons with experimental data. Previous
heat pump models are using n = 1 as a default. However, it was
pointed out that a higher order element fits a real heat pump
better in.
-
Scaling factor: A scaling facor is implemented for scaling
of the heat pump power and capacity. The factor scales the
parameters V, m_flow_nominal, C, GIns, GOut and dp_nominal. As a
result, the heat pump can supply more heat with the COP staying
nearly constant. However, one has to make sure that the supplied
pressure difference or mass flow is also scaled with this factor,
as the nominal values do not increase said mass flow.
Known Limitations
- The n-th order element has a big influence on computational time.
Reducing the order or disabling it completly will decrease
computational time.
- Reversing the mode: A normal 4-way-exchange valve suffers from
heat losses and irreversibilities due to switching from one mode to
another. Theses losses are not taken into account.
Contents
Name | Description |
---|
PerDataMainHP | Performance data of a heat pump in main operation mode |
PerDataRevHP | Performance data of a heat pump in reversible operation mode |
-
May 22, 2019 by Julian Matthes:
Rebuild due to the introducion of the thermal machine partial model
(see issue #715)
-
November 26, 2018 by Fabian Wüllhorst:
First implementation (see issue #577)
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