This is a model of a heat pump 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 condenser leaving temperature, which is met exactly at steady state if the heat pump has sufficient capacity.
Set use_eta_Carnot_nominal=true
to specify directly
the Carnot effectiveness η_{Carnot,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
η_{Carnot,0} = COP_{0} ⁄ (T_{con,0} ⁄ (T_{con,0} + T_{app,con,0} - (T_{eva,0}-T_{app,eva,0}))),
where T_{eva,0} is the evaporator temperature, T_{con,0} is the condenser temperature, T_{app,eva,0} is the evaporator approach temperature and T_{app,con,0} is the condenser approach temperature.
The COP is computed as the product
COP = η_{Carnot,0} COP_{Carnot} η_{PL},
where COP_{Carnot} is the Carnot efficiency and η_{PL} is the part load efficiency, expressed using a polynomial. This polynomial has the form
η_{PL} = a_{1} + a_{2} y + a_{3} y^{2} + ...,
where y ∈ [0, 1] is
the part load for heating and the coefficients a_{i}
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 heat pump 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 removed by to the evaporator. If the mass flow rate is too small, very low outlet temperatures can result, possibly below freezing.
The condenser heat flow rate QCon_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 QCon_flow_nominal
is set to a reasonable value.
The maximum heating capacity is set by the parameter QCon_flow_max
,
which is by default set to 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 chiller, see Buildings.Fluid.Chillers.Examples.Carnot_TEva.
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.