Model for a reversable heat pump using the equation fit method and that takes as an input the set point for the leaving fluid temperature.
This reversable heat pump can be operated either in heating mode or in cooling mode.
It typically is used for a water to water heat pump, but if the performance data
per
are set up for other media, such as glycol, it can also be used for
such applications.
Note that if used with air, the results will only be valid if there is no
humidity condensation or frost build up.
The heat exchanger at medium 1 is to be connected to the building load,
and the other heat exchanger to the heat source or sink, such as
a geothermal loop.
If in heating mode, the heat exchanger at medium 1 operates as a condenser,
and in cooling mode it operates as an evaporator.
The model is based on the model described in the EnergyPlus 9.1.0 Engineering Reference, Section 16.6.1: Water to water heat pump model and the model based on C.Tang (2005).
The model takes the following control signals:
uMod
which controls the heat pump operational mode.
If per.reverseCycle = true
the signal can take on the values
-1 for cooling mode,
0 for off and
+1 for heating mode.per.reverseCycle = false
and uMod = -1
, the model stops with an error message.
TSet
is the set point for the leaving fluid temperature at port port_b1
.
The heating and cooling performance coefficients are stored in the data record per
and are available from
Buildings.Fluid.HeatPumps.Data.EquationFitReversible.
The electric power only includes the power for the compressor, but not any power for pumps, as the pumps must be modeled outside of this component.
The performance of the heat pump is computed as follows:
Let α be the set of heat load performance coefficients determined by the data
record per.hea.coeQ
and let
β be the set of electrical power performance coefficients determined by the data
record hea.coeP
.
Then, the performance is computed as
uMod = 1
, the heat pump is in heating mode and the load side available heat is
Q̇_{ava} = ( α_{1} + α_{2} T_{loa,ent}/T_{RefHeaLoa} + α_{3} T_{sou,ent}/T_{RefHeaSou} + α_{4} ṁ_{loa,ent}/(ṁ_{loa,0} s) + α_{5} ṁ_{sou,ent}/(ṁ_{sou,0} s) ) Q̇_{0} s,
where Q̇_{0} is the design capacity as specified by the parameter
per.hea.Q_flow
and s is the scaling factor specified by the parameter scaling_factor
.
The corresponding power consumption is
P= ( β_{1} + β_{2} T_{loa,ent}/T_{RefHeaLoa} + β_{3} T_{sou,ent}/T_{RefHeaSou} + β_{4} ṁ_{loa,ent}/(ṁ_{loa,0} s) + β_{5} ṁ_{sou,ent}/(ṁ_{sou,0} s) ) P_{0} s,
where P_{0} is the design power consumption as specified by the parameter
per.hea.P
.
The actual heat provided at the load side is
Q̇ = min(Q̇_{ava} , Q̇_{set}),
where Q̇_{set} is the heat required to meet the temperature setpoint for the leaving fluid on the load side.
uMod = -1
, the heat pump is in cooling mode, and the governing equations are as above, but
with per.coo
rather than per.hea
used for the performance data, and the min(· ·) function
replaced with max(· ·).
uMod = 0
, the model sets Q̇ = 0 and P = 0.
The coefficient of performance COP is computed as
COP = Q̇ ⁄ P.
C. Tang Equation fit based models of water source heat pumps. Master Thesis. Oklahoma State University, Oklahoma, USA. 2005.