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 control input is the setpoint of the evaporator leaving temperature, which is met exactly at steady state if the chiller has sufficient capacity.
The model allows to either specify the Carnot effectivness ηCarnot,0, or a COP0 at the nominal conditions, together with the evaporator temperature Teva,0 and the condenser temperature Tcon,0, in which case the model computes the Carnot effectivness as
ηCarnot,0 = COP0 ⁄ (Teva,0 ⁄ (Tcon,0-Teva,0)).
On the Advanced
tab, a user can specify the
temperatures that will be used as the evaporator and condenser
temperature.
During the simulation, the chiller COP is computed as the product
COP = ηCarnot,0 COPCarnot ηPL,
where COPCarnot is the Carnot efficiency and ηPL is a polynomial in the cooling part load ratio yPL that can be used to take into account a change in COP at part load conditions. This polynomial has the form
ηPL = a1 + a2 yPL + a3 yPL2 + ...
where 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 condenser has sufficient mass flow rate. Based on the evaporator mass flow rate, temperature difference and the efficiencies, the model computes how much heat will be added to the condenser. If the mass flow rate is too small, very high outlet temperatures 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 Buildings.Fluid.HeatPumps.Examples.Carnot_TCon.
effInpEva
and
effInpCon
and updated documentation. This is for
issue
497.