This is a model of a chiller whose coefficient of performance COP changes with temperatures in the same way as the Carnot efficiency changes. The input signal y is the control signal for the compressor.
Set use_eta_Carnot_nominal=true
to specify directly
the Carnot effectiveness ηCarnot,0,
in which case the value of the parameter COP_nominal
will not affect the simulation.
If use_eta_Carnot_nominal=false
, the model will use
the value of the parameter COP_nominal
together with the specified nominal temperatures
to compute the Carnot effectiveness as
ηCarnot,0 = COP0 ⁄ (Teva,0 ⁄ (Tcon,0 + Tapp,con,0 - (Teva,0-Tapp,eva,0))),
where Teva,0 is the evaporator temperature, Tcon,0 is the condenser temperature, Tapp,eva,0 is the evaporator approach temperature and Tapp,con,0 is the condenser approach temperature.
The COP is computed as the product
COP = ηCarnot,0 COPCarnot ηPL,
where COPCarnot is the Carnot efficiency and ηPL is the part load efficiency, expressed using a polynomial. This polynomial has the form
ηPL = a1 + a2 y + a3 y2 + ...,
where y ∈ [0, 1] is
the part load for cooling and the coefficients ai
are declared by the parameter a
.
On the Dynamics
tag, the model can be parametrized to compute a transient
or steady-state response.
The transient response of the model is computed using a first
order differential equation for the evaporator and condenser fluid volumes.
The chiller outlet temperatures are equal to the temperatures of these lumped volumes.
When using this component, make sure that the evaporator and the condenser have sufficient mass flow rate. Based on the mass flow rates, the compressor power, temperature difference and the efficiencies, the model computes how much heat will be added to the condenser and removed at the evaporator. If the mass flow rates are too small, very high temperature differences can result.
The evaporator heat flow rate QEva_flow_nominal
is used to assign
the default value for the mass flow rates, which are used for the pressure drop
calculations.
It is also used to compute the part load efficiency.
Hence, make sure that QEva_flow_nominal
is set to a reasonable value.
The maximum cooling capacity is set by the parameter QEva_flow_min
,
which is by default set to negative infinity.
The coefficient of performance depends on the evaporator and condenser leaving temperature since otherwise the second law of thermodynamics may be violated.
For a similar model that can be used as a heat pump, see BuildingSystems.Fluid.HeatPumps.Carnot_y.
etaCarnot_nominal(unit="1") = COP_nominal/(TUseAct_nominal/(TCon_nominal+TAppCon_nominal - (TEva_nominal-TAppEva_nominal)))
to
etaCarnot_nominal(unit="1") = 0.3
to avoid a circular assignment.effInpEva
and effInpCon
and updated documentation.
This is for
issue 497.
dTEva_nominal
to be negative rather than positive.
For positive values, the simulation will stop with an assertion.
staB1
and staB2
which mistakenly used the inStream
operator
for the configuration without flow reversal.
This is for
issue 476.
dTEva_nominal
to be consistent with
other models.
The model will still work with the old values for dTEva_nominal
,
but it will write a warning so that users can transition their models.
assert
statement for the efficiency curve.
This is for
issue 468.
prescribedHeatFlowRate=true
for vol2
.
sta_a1
,
sta_a2
, sta_b1
and sta_b2
.
P
as an output signal.