Transcritical CO2 Heat Pump Design #497
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MikeSennis
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UPDATE Hello again, Code: from tespy.networks import Network
from tespy.components import (
HeatExchanger, CycleCloser, Compressor, Turbine, Source, Sink
)
from tespy.connections import Connection, Bus
from CoolProp.CoolProp import PropsSI as PSI
working_fluid = "CO2" # cycle's refrigerant
nw = Network(T_unit="C", p_unit="bar", h_unit="kJ / kg")
# components
ev = HeatExchanger('evaporator')
gc = HeatExchanger('gas cooler')
cp = Compressor('centrifugal compressor')
tu = Turbine('turbo-expander')
cc = CycleCloser('cycle closer')
sw_so = Source('source water source')
sw_si = Sink('source water sink')
dw_so = Source('district water source')
dw_si = Sink('district water sink')
# connections
# source water loop
c11 = Connection(sw_so, "out1", ev, "in1", label="11") # in1 for heat exchanger's hot side inlet
c12 = Connection(ev, "out1", sw_si, "in1", label="12") # out1 for heat exchanger's hot side outlet
nw.add_conns(c11, c12)
# refrigerant (closed) loop
c0 = Connection(cc, "out1", gc, "in1", label="0")
c1 = Connection(gc, "out1", tu, "in1", label="1")
c2 = Connection(tu, "out1", ev, "in2", label="2")
c3 = Connection(ev, "out2", cp, "in1", label="3")
c4 = Connection(cp, "out1", cc, "in1", label="4")
nw.add_conns(c0, c1, c2, c3, c4)
# district water loop
c21 = Connection(dw_so, "out1", gc, "in2", label="21") # in2 for heat exchanger's cold side inlet
c22 = Connection(gc, "out2", dw_si, "in1", label="22") # out2 for heat exchanger's cold side outlet
nw.add_conns(c21, c22)
# power bus
motor = Bus("electric motor")
motor.add_comps(
{"comp": tu, "char": 1, "base": "component"},
{"comp": cp, "char": 1, "base": "bus"},
)
nw.add_busses(motor)
# parametrization
# making a good guess of pressure levels and enthalpy values
p_wf_GC_inlet = 181 # working fluid pressure in gas cooler inlet [bar], design (point) value,
# for CO2 it has to be > Pcrit = 73.773 bar (for supercritical state)
T_wf_GC_exit = 45 # working fluid temperature in gas cooler exit [oC], assuming its value,
# for CO2 it has to be > Tcrit = 30.978 °C (for supercritical state)
h_wf_GC_exit = PSI('H', 'P', (0.98*p_wf_GC_inlet)*1e5, 'T', T_wf_GC_exit + 273.15, working_fluid) # [J/kg]
T_wf_ev = -5 # working fluid temperature in evaporator [oC], evaporation temperature, assuming its value,
# for CO2 it has to be < Tcrit = 30.978 °C (for subcritical state)
h_wf_ev_exit = PSI('H', 'Q', 1, 'T', T_wf_ev + 273.15, working_fluid) # [J/kg], saturated gas (gas CO2)
p_wf_ev_exit = PSI('P', 'Q', 1, 'T', T_wf_ev + 273.15, working_fluid) # [Pa], saturated gas (gas CO2)
h_wf_ev_inlet = PSI('H', 'P', p_wf_ev_exit / 0.98, 'T', T_wf_ev + 273.15, working_fluid) # [J/kg], in case of two-phase region
# occurs in turbine exit (temperature and pressure combination isn't enough for this thermodynamic state)
gc.set_attr(pr1=0.98, pr2=0.98) # Q=48.4 MWth (Q=48.4e6), design (point) value (assuming pressure ratios)
ev.set_attr(pr1=0.98, pr2=0.98)
motor.set_attr(P=15.9e6) # P=15.9 MWe, design (point) value
c1.set_attr(h=h_wf_GC_exit / 1e3, fluid={working_fluid: 1}) # [kJ/kg]
c2.set_attr(h=h_wf_ev_inlet / 1e3) # [kJ/kg], using enthalpy and pressure combination in case of two-phase region occurs
c3.set_attr(p=p_wf_ev_exit / 1e5, h=h_wf_ev_exit/ 1e3) # [bar], [kJ/kg]
c4.set_attr(T=200, p=p_wf_GC_inlet) # design (point) values
c11.set_attr(T=10, p=10, fluid={'HEOS::Water': 1}) # design (point) values (assumption for pressure value and mass flow rate)
c12.set_attr(T=7) # design (point) value
c21.set_attr(T=40, p=10, fluid={'HEOS::Water': 1}) # design (point) values (assumption for pressure value)
c22.set_attr(T=110) # design (point) value
nw.solve("design")
nw.print_results()
COP = abs(gc.Q.val) / abs(motor.P.val)
print(f"Heating COP = {round(COP, 3)}")
print(f"Thermal output (heating capacity) = {round(abs(gc.Q.val)/1e6, 3)} MWth")
# unsetting stable starting values' specifications and setting target values instead
c1.set_attr(h=None, T=40) # assumption for the working fluid temperature in gas cooler exit (common range: 35°C - 55°C)
c2.set_attr(h=None, T=-10) # assumption for the evaporation temperature
tu.set_attr(eta_s=0.85) # assumption
c3.set_attr(h=None, p=None)
cp.set_attr(eta_s=0.85) # assumption
# ev.set_attr(ttd_l=5) # assuming 5 K [oC] pinch point temperature difference (ttd_l=5)
nw.solve("design")
nw.print_results()
COP = abs(gc.Q.val) / abs(motor.P.val)
print(f"Heating COP = {round(COP, 3)}")
print(f"Thermal output (heating capacity) = {round(abs(gc.Q.val)/1e6, 3)} MWth") |
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2 replies
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Hi @MikeSennis, sorry for the late reply, I was out of office for a couple of days. Good to see you have found a solution. In general, temperature and pressure combination should be as stable as are enthalpy pressure specification combinations for generating starting values. I have not looked into the details yet, I'll do that and see, if there is something to improve in the back-end. Best |
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Hello @fwitte, Regarding the heat pump modeling/simulation in TESPy, I've tried to set up another transcritical CO2 heat pump unit, similar to the previous one (described in my above post), but now with a slightly higher level of complexity (addition of an expansion valve and an internal heat exchanger, as shown in the figure below). Everything seems to work as intended during the design point simulations (retrieving the desired results), but when switching to the off-design mode, the solver fails to converge on some occasions (for a given set of specs' values). For example, when setting the source water's supply temperature to 15 degrees Celcius (from 10 degrees), the district heating network's return temperature to 45 degrees (from 40 degrees), and the district heating network's supply temperature to 115 degrees (from 110 degrees) the following error message occurs (off-design case 3 in the code below): I've already verified that the off-design case with no changes to the design case gives identical results to the design case. So, I assume that my off-design point specifications are correct. But I can't understand what's the source of the above error message. Does it occur due to a physical/technical limit in my heat pump model/performance or does it have to do with something in the software's back-end? Sorry for the excessive writing, but I tried to be more explanatory. Any help or suggestion for these issues would be much appreciated! Heat Pump topology: Code: from tespy.networks import Network
from tespy.components import (
HeatExchanger, CycleCloser, Compressor, Turbine, Source, Sink, Valve
)
from tespy.connections import Connection, Bus
from CoolProp.CoolProp import PropsSI as PSI
working_fluid = "CO2" # cycle's refrigerant
nw = Network(T_unit="C", p_unit="bar", h_unit="kJ / kg")
T_sw_so = 10 # source water supply temperature
T_dw_so = 40 # district heating network's return temperature
T_dw_si = 110 # district heating network's supply temperature
# components
ev = HeatExchanger('evaporator')
re = HeatExchanger('recuperator')
gc = HeatExchanger('gas cooler')
cp = Compressor('centrifugal compressor')
tu = Turbine('turbo-expander')
va = Valve('expansion valve')
cc = CycleCloser('cycle closer')
sw_so = Source('source water source')
sw_si = Sink('source water sink')
dw_so = Source('district water source')
dw_si = Sink('district water sink')
# connections
# source water loop
c11 = Connection(sw_so, "out1", ev, "in1", label="11") # in1 for heat exchanger's hot side inlet
c12 = Connection(ev, "out1", sw_si, "in1", label="12") # out1 for heat exchanger's hot side outlet
nw.add_conns(c11, c12)
# refrigerant (closed) loop
c0 = Connection(cc, "out1", gc, "in1", label="0")
c1 = Connection(gc, "out1", re, "in1", label="1") # in1 for heat exchanger's hot side inlet
c2 = Connection(re, "out1", tu, "in1", label="2") # out1 for heat exchanger's hot side outlet
c3 = Connection(tu, "out1", va, "in1", label="3")
c4 = Connection(va, "out1", ev, "in2", label="4")
c5 = Connection(ev, "out2", re, "in2", label="5") # in2 for heat exchanger's cold side inlet
c6 = Connection(re, "out2", cp, "in1", label="6") # out2 for heat exchanger's cold side outlet
c7 = Connection(cp, "out1", cc, "in1", label="7")
nw.add_conns(c0, c1, c2, c3, c4, c5, c6, c7)
# district water loop
c21 = Connection(dw_so, "out1", gc, "in2", label="21") # in2 for heat exchanger's cold side inlet
c22 = Connection(gc, "out2", dw_si, "in1", label="22") # out2 for heat exchanger's cold side outlet
nw.add_conns(c21, c22)
# power bus
motor = Bus("electric motor")
motor.add_comps(
{"comp": tu, "char": 1, "base": "component"},
{"comp": cp, "char": 1, "base": "bus"},
)
nw.add_busses(motor)
# parametrization
# for a good guess of pressure levels and enthalpy values
p_wf_GC_inlet = 181 # working fluid pressure in gas cooler inlet [bar], design (point) value,
# for CO2 it has to be P > Pcrit = 73.773 bar and T > Tcrit = 30.978 °C (for supercritical state)
T_wf_GC_outlet = 45 # working fluid temperature in gas cooler outlet [oC], assuming its value,
# for CO2 it has to be P > Pcrit = 73.773 bar and T > Tcrit = 30.978 °C (for supercritical state)
h_wf_GC_outlet = PSI('H', 'P', (0.98*p_wf_GC_inlet)*1e5, 'T', T_wf_GC_outlet + 273.15, working_fluid) # [J/kg]
#----------------------------------------------------------------------------------------------------------------------#
T_wf_GC_inlet = 200 # working fluid temperature in gas cooler inlet [oC], design (point) value,
# for CO2 it has to be P > Pcrit = 73.773 bar and T > Tcrit = 30.978 °C (for supercritical state)
h_wf_GC_inlet = PSI('H', 'P', p_wf_GC_inlet*1e5, 'T', T_wf_GC_inlet + 273.15, working_fluid) # [J/kg]
#----------------------------------------------------------------------------------------------------------------------#
T_wf_tu_outlet = -4 # working fluid temperature in turbo-expander outlet [oC], design (point) value (approximately),
# for CO2 it has to be < Tcrit = 30.978 °C (for subcritical state)
p_wf_tu_outlet = PSI('P', 'Q', 0, 'T', T_wf_tu_outlet + 273.15, working_fluid) # [Pa], saturated liquid (liquid CO2)
#----------------------------------------------------------------------------------------------------------------------#
T_wf_ev = -10 # working fluid temperature in evaporator [oC], evaporation temperature, assuming its value,
# for CO2 it has to be < Tcrit = 30.978 °C (for subcritical state)
h_wf_ev_outlet = PSI('H', 'Q', 1, 'T', T_wf_ev + 273.15, working_fluid) # [J/kg], saturated gas (gas CO2)
p_wf_ev_outlet = PSI('P', 'Q', 1, 'T', T_wf_ev + 273.15, working_fluid) # [Pa], saturated gas (gas CO2)
#----------------------------------------------------------------------------------------------------------------------#
h_wf_ev_inlet = PSI('H', 'P', p_wf_ev_outlet / 0.98, 'T', T_wf_ev + 273.15, working_fluid) # [J/kg], in case of two-phase region
# occurs in expansion valve outlet (temperature and pressure combination isn't enough for this thermodynamic state)
#----------------------------------------------------------------------------------------------------------------------#
T_wf_RE_hot_outlet = 35 # working fluid temperature at recuperator's hot outlet [oC], assuming its value,
# it has to be Tcrit = 30.978 °C < T_wf_RE_hot_outlet < T_wf_GC_outlet (for supercritical state in "c2")
# or
# it has to be T_wf_tu_outlet < T_wf_RE_hot_outlet < Tcrit = 30.978 °C (for subcritical state: gas CO2 in "c2")
h_wf_RE_hot_outlet = PSI('H', 'P', (0.98*0.98*p_wf_GC_inlet)*1e5, 'T', T_wf_RE_hot_outlet + 273.15, working_fluid) # [J/kg]
########################################################################################################################
gc.set_attr(pr1=0.98, pr2=0.98) # Q=48.4 MWth (Q=48.4e6), design (point) value (assuming pressure ratios)
re.set_attr(pr1=0.98, pr2=0.98, ttd_u=2) # assuming ... K [oC] pinch point (approach) temperature difference (ttd_u=...),
# the approach temperature difference can be as low as 2 oC in compact HEXs (like PCHEs)
ev.set_attr(pr1=0.98, pr2=0.98)
motor.set_attr(P=15.9e6) # P=15.9 MWe, design (point) value
c1.set_attr(h=h_wf_GC_outlet / 1e3, fluid={working_fluid: 1}) # [kJ/kg]
#c2.set_attr(h=h_wf_RE_hot_outlet / 1e3) # [kJ/kg], supercritical CO2 or gas CO2 in "c2"
c3.set_attr(p=p_wf_tu_outlet / 1e5) # [bar]
c4.set_attr(h=h_wf_ev_inlet / 1e3) # [kJ/kg], using enthalpy and pressure combination in case of two-phase region occurs
c5.set_attr(p=p_wf_ev_outlet / 1e5, h=h_wf_ev_outlet/ 1e3) # [bar], [kJ/kg]
c7.set_attr(h=h_wf_GC_inlet / 1e3, p=p_wf_GC_inlet) # design (point) values, [kJ/kg]
c11.set_attr(T=T_sw_so, p=10, fluid={'HEOS::Water': 1}) # design (point) values (assumption for pressure value and mass flow rate)
c12.set_attr(T=7) # design (point) value
c21.set_attr(T=T_dw_so, p=10, fluid={'HEOS::Water': 1}) # design (point) values (assumption for pressure value)
c22.set_attr(T=T_dw_si) # design (point) value
nw.solve("design")
nw.print_results()
COP = abs(gc.Q.val) / abs(motor.P.val)
print(f"Heating COP = {round(COP, 3)} | Target value: 3.04")
print(f"Thermal output (heating capacity) = {round(abs(gc.Q.val)/1e6, 3)} MWth | Target value: 48.4 MWth", "\n")
# check
print(f"check result = {nw.lin_dep} | Target value: False", "\n") # if True the simulation run into a parametrisation's linear dependency
# unsetting stable starting values' specifications and setting target values instead - design point
c1.set_attr(h=None)
gc.set_attr(ttd_l=2) # assuming ... K [oC] pinch point (approach) temperature difference (ttd_l=...),
# assumption for the working fluid temperature in gas cooler outlet (common range: 35°C - 55°C),
# 45 oC for a 5 K [oC] pinch point (approach) temperature difference (ttd_l=5),
# the approach temperature difference can be as low as 2 oC in compact HEXs (like PCHEs)
#c2.set_attr(h=None)
#re.set_attr(ttd_u=2) # assuming ... K [oC] pinch point (approach) temperature difference (ttd_u=...),
# the approach temperature difference can be as low as 2 oC in compact HEXs (like PCHEs)
c3.set_attr(p=None, T=-4) # T=-4 °C and p=30 bar (design point values, approximately) for the working fluid
# in turbo-expander outlet [oC]
c4.set_attr(h=None, T=-10) # assumption for the evaporation temperature (common range for CO2: -20°C - 20°C)
tu.set_attr(eta_s=0.9) # assumption, isentropic efficiencies as high as 90 % are readily achieved with a turbo-expander,
# typical % eta_s range: mid-80s to low-90s
c5.set_attr(h=None, p=None, Td_bp=10) # assuming ... K [oC] of evaporator superheat (superheated gas at evaporator outlet),
# (TESPy uses it as evaporator superheat),
# it depends on pressure corresponding to this connection
nw.solve("design")
nw.print_results()
print(f"compressor's eta_s = {cp.eta_s.val},", f"compressor's pr = {cp.pr.val},",
f"closed cycle's volumetric flow rate = {c1.v.val} (m^3)/s")
COP = abs(gc.Q.val) / abs(motor.P.val)
print(f"Heating COP = {round(COP, 3)} | Target value: 3.04")
print(f"Thermal output (heating capacity) = {round(abs(gc.Q.val)/1e6, 3)} MWth | Target value: 48.4 MWth", "\n")
# check
print(f"check result = {nw.lin_dep} | Target value: False", "\n") # if True the simulation run into a parametrisation's linear dependency
# sensitivity analysis/"optimization", checking different parameters' values for achieving the desired outcome:
# desired heating capacity and COP - design point
gc.set_attr(ttd_l=2) # assuming ... K [oC] pinch point (approach) temperature difference (ttd_l=...),
# assumption for the working fluid temperature in gas cooler outlet (common range: 35°C - 55°C),
# 45 oC for a 5 K [oC] pinch point (approach) temperature difference (ttd_l=5),
# the approach temperature difference can be as low as 2 oC in compact HEXs (like PCHEs)
# cycle's optimum value: ttd_l=2 (for centrifugal compressor's eta_s < 0.94)
re.set_attr(ttd_u=19) # assuming ... K [oC] pinch point (approach) temperature difference (ttd_u=...),
# the approach temperature difference can be as low as 2 oC in compact HEXs (like PCHEs),
# the centrifugal compressor's isentropic efficiency has to be < 1,
# typical % eta_s range for the centrifugal compressor of a turbo-expander's assembly: mid-70s to low-80s
# cycle's optimum value: ttd_u=19 (for centrifugal compressor's eta_s < 0.94)
c3.set_attr(T=-4) # T=-4 °C and p=30 bar (design point values, approximately) for the working fluid
# in turbo-expander outlet [oC]
# cycle's optimum value: T=-4 (design value)
c4.set_attr(T=-10) # assumption for the evaporation temperature (common range for CO2: -20°C - 20°C)
# cycle's optimum value: T=-10 (for centrifugal compressor's eta_s < 0.94)
tu.set_attr(eta_s=0.92) # assumption, isentropic efficiencies as high as 90 % are readily achieved with a turbo-expander,
# typical % eta_s range: mid-80s to low-90s
# cycle's optimum value: eta_s=0.92 (it has to be <= 0.92)
c5.set_attr(Td_bp=None)
ev.set_attr(ttd_u=2) # assuming ... K [oC] pinch point (approach) temperature difference (ttd_u=...),
# the approach temperature difference can be as low as 2°C in compact HEXs (like PCHEs),
# cycle's optimum value: ttd_u=2 (it corresponds to 18.71°C of evaporator superheat)
nw.solve("design")
nw.print_results()
print(f"compressor's eta_s = {cp.eta_s.val},", f"compressor's pr = {cp.pr.val},",
f"closed cycle's volumetric flow rate = {c1.v.val} (m^3)/s")
COP = abs(gc.Q.val) / abs(motor.P.val)
print(f"Heating COP = {round(COP, 3)} | Target value: 3.04")
print(f"Thermal output (heating capacity) = {round(abs(gc.Q.val)/1e6, 3)} MWth | Target value: 48.4 MWth", "\n")
# check
print(f"check result = {nw.lin_dep} | Target value: False", "\n") # if True the simulation run into a parametrisation's linear dependency
# preparation for the off-design simulation
c7.set_attr(h=None, p=None)
cp.set_attr(eta_s=0.9341007965731289, pr=7.115369816303609) # design point values
motor.set_attr(P=None)
c1.set_attr(v=0.1832149979137217) # design point value, (assuming) constant volumetric flow for cycle's refrigerant
nw.solve("design")
nw.save("TCC HP_CO2_v5_design point")
COP = abs(gc.Q.val) / abs(motor.P.val)
print(f"Heating COP = {round(COP, 3)} | Target value: 3.04")
print(f"Thermal output (heating capacity) = {round(abs(gc.Q.val)/1e6, 3)} MWth | Target value: 48.4 MWth", "\n")
# check
print(f"check result = {nw.lin_dep} | Target value: False", "\n") # if True the simulation run into a parametrisation's linear dependency
# off-design performance
# gas cooler
gc.set_attr(design=["pr1", "pr2", "ttd_l"], offdesign=["zeta1", "zeta2", "kA_char"])
# recuperator (internal heat exchanger)
re.set_attr(design=["pr1", "pr2", "ttd_u"], offdesign=["zeta1", "zeta2", "kA_char"])
# turbo-expander
c3.set_attr(design=["T"])
tu.set_attr(design=["eta_s"], offdesign=["eta_s_char", "cone"]) # Stodola's cone law
# expansion valve
c4.set_attr(design=["T"])
va.set_attr(offdesign=["zeta"])
# evaporator
from tespy.tools.characteristics import CharLine
from tespy.tools.characteristics import load_default_char as ldc
kA_char1 = ldc("heat exchanger", "kA_char1", "DEFAULT", CharLine) # for the evaporator's hot side
kA_char2 = ldc("heat exchanger", "kA_char2", "EVAPORATING FLUID", CharLine) # for the evaporator's cold side
ev.set_attr(
kA_char1=kA_char1, kA_char2=kA_char2,
design=["pr1", "pr2", "ttd_u"], offdesign=["zeta1", "zeta2", "kA_char"]
)
# centrifugal compressor
cp.set_attr(design=["eta_s"], offdesign=["eta_s_char"]) # in the ideal case compressor's pressure ratio
# should be variable, design=["pr"], offdesign=["char_map_pr"]
#cp.set_attr(design=["pr", "eta_s"], offdesign=["char_map_pr", "char_map_eta_s"])
#cp.set_attr(igva='var')
# source water loop
c11.set_attr(offdesign=["v"]) # (assuming) constant volumetric flow for water
c12.set_attr(design=["T"]) # source water return temperature should be an output of the off-design simulations
# district water loop
#c21.set_attr(offdesign=["v"]) # (assuming) constant volumetric flow for water
#c22.set_attr(design=["T"]) #
print("Off-design performance")
nw.solve("offdesign", design_path="TCC HP_CO2_v5_design point")
nw.print_results()
COP = abs(gc.Q.val) / abs(motor.P.val)
print(f"Heating COP = {round(COP, 3)} | Target value: 3.04")
print(f"Thermal output (heating capacity) = {round(abs(gc.Q.val)/1e6, 3)} MWth | Target value: 48.4 MWth", "\n")
# check
print(f"check result = {nw.lin_dep} | Target value: False", "\n") # if True the simulation run into a parametrisation's linear dependency
# configuring/calibrating the model/simulation (its parameters) according to my Case Study specs
# case 1
T_sw_so = 10 # source water supply temperature
T_dw_so = 35 # district heating network's return temperature
T_dw_si = 105 # district heating network's supply temperature
c11.set_attr(T=T_sw_so)
c21.set_attr(T=T_dw_so)
c22.set_attr(T=T_dw_si)
nw.solve("offdesign", design_path="TCC HP_CO2_v5_design point")
nw.print_results()
COP = abs(gc.Q.val) / abs(motor.P.val)
print(f"Heating COP = {round(COP, 3)} | Nominal (design) value: 2.958")
print(f"Electric Power input (motor's power) = {round(abs(motor.P.val)/1e6, 3)} MWe | Nominal (design) value: 15.9 MWe")
print(f"Thermal output (heating capacity) = {round(abs(gc.Q.val)/1e6, 3)} MWth | Nominal (design) value: 47.028 MWth", "\n")
# reset to base source water supply temperature
T_sw_so = 10 # source water supply temperature
c11.set_attr(T=T_sw_so)
# case 2
T_sw_so = 15 # source water supply temperature
T_dw_so = 30 # district heating network's return temperature
T_dw_si = 100 # district heating network's supply temperature
c11.set_attr(T=T_sw_so)
c21.set_attr(T=T_dw_so)
c22.set_attr(T=T_dw_si)
nw.solve("offdesign", design_path="TCC HP_CO2_v5_design point")
nw.print_results()
COP = abs(gc.Q.val) / abs(motor.P.val)
print(f"Heating COP = {round(COP, 3)} | Nominal (design) value: 2.958")
print(f"Electric Power input (motor's power) = {round(abs(motor.P.val)/1e6, 3)} MWe | Nominal (design) value: 15.9 MWe")
print(f"Thermal output (heating capacity) = {round(abs(gc.Q.val)/1e6, 3)} MWth | Nominal (design) value: 47.028 MWth", "\n")
# reset to base source water supply temperature
T_sw_so = 10 # source water supply temperature
c11.set_attr(T=T_sw_so)
# case 3
T_sw_so = 15 # source water supply temperature
T_dw_so = 45 # district heating network's return temperature
T_dw_si = 115 # district heating network's supply temperature
c11.set_attr(T=T_sw_so)
c21.set_attr(T=T_dw_so)
c22.set_attr(T=T_dw_si)
nw.solve("offdesign", design_path="TCC HP_CO2_v5_design point")
nw.print_results()
COP = abs(gc.Q.val) / abs(motor.P.val)
print(f"Heating COP = {round(COP, 3)} | Nominal (design) value: 2.958")
print(f"Electric Power input (motor's power) = {round(abs(motor.P.val)/1e6, 3)} MWe | Nominal (design) value: 15.9 MWe")
print(f"Thermal output (heating capacity) = {round(abs(gc.Q.val)/1e6, 3)} MWth | Nominal (design) value: 47.028 MWth", "\n")
# reset to base source water supply temperature
T_sw_so = 10 # source water supply temperature
c11.set_attr(T=T_sw_so) |
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Sorry, this is my first time leaving a comment on github, so I made such a mistake.Recently, I was working on a trans-critical carbon dioxide energy storage system, and I separated the energy storage system from the energy release system. In the energy storage system, I used source to replace the gas storage tank and sink to replace the liquid carbon dioxide storage tank, and adopted a double compression mode. However, similar problems always occurred when I set the operating value of carbon dioxide. Do you know how to solve this problem |
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1 reply
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Could you provide a minimal code example to replicate the exact error? |
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from tespy.networks import Network
working_fluid = "CO2"
nw = Network(
T_unit="C", p_unit="bar", h_unit="kJ / kg", m_unit="kg / s", s_unit="kJ / kgK"
)
from tespy.components import Condenser
from tespy.components import SimpleHeatExchanger
from tespy.components import Sink
from tespy.components import Source
from tespy.components import Compressor
c_in = Source("refrigerant in")
amb_out = Sink("sink ambient")
c_in1 = Source("refrigerant in1")
amb_out1 = Sink("sink ambient1")
cp_o = Compressor(" Compressor1")
cp_t = Compressor(" Compressor2")
cd = Condenser("condenser")
cons = SimpleHeatExchanger("SimpleHeatExchanger")
from tespy.connections import Connection
c0 = Connection(c_in, "out1", cp_o, "in1", label="0")
c1 = Connection(cp_o, "out1", cons, "in1", label="1")
c2 = Connection(cons, "out1", cp_t, "in1", label="2")
c3 = Connection(cp_t, "out1", cd, "in2", label="3")
c4 = Connection(cd, "out2", amb_out, "in1", label="4")
c10 = Connection(c_in1, "out1", cd, "in1", label="10")
c20 = Connection(cd, "out1",amb_out1, "in1", label="20")
nw.add_conns(c0, c1, c2, c3, c4, c10,c20 )
cd.set_attr(pr1=0.99, pr2=0.99)
cp_o.set_attr(eta_s=0.85)
cp_t.set_attr(eta_s=0.85)
cons.set_attr(pr=0.99)
c0.set_attr(p=30,fluid={working_fluid: 1})
c1.set_attr(p=80,h=500)
c2.set_attr(T=35)
c3.set_attr(T=90,p=150)
c4.set_attr(T=50)
c20.set_attr(T=25, fluid={"water": 1},m=1)
nw.solve(mode='design')
nw.print_results() |
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6 replies
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The problem I had was that the code would always get the wrong initial value, and I didn't know how to fix it, and I tried pressure and enthalpy, and I tried pressure and temperature, and they all failed. I'd appreciate it if you could help me ou |
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Two things:
I would start with this model, and then adjust to the requirements: from tespy.networks import Network
working_fluid = "CO2"
nw = Network(
T_unit="C", p_unit="bar", h_unit="kJ / kg", m_unit="kg / s", s_unit="kJ / kgK"
)
from tespy.components import HeatExchanger, Condenser
from tespy.components import SimpleHeatExchanger
from tespy.components import Sink
from tespy.components import Source
from tespy.components import Compressor
c_in = Source("refrigerant in")
amb_out = Sink("sink ambient")
c_in1 = Source("refrigerant in1")
amb_out1 = Sink("sink ambient1")
cp_o = Compressor(" Compressor1")
cp_t = Compressor(" Compressor2")
cd = HeatExchanger("condenser")
cons = SimpleHeatExchanger("SimpleHeatExchanger")
from tespy.connections import Connection
c0 = Connection(c_in, "out1", cp_o, "in1", label="0")
c1 = Connection(cp_o, "out1", cons, "in1", label="1")
c2 = Connection(cons, "out1", cp_t, "in1", label="2")
c3 = Connection(cp_t, "out1", cd, "in2", label="3")
c4 = Connection(cd, "out2", amb_out, "in1", label="4")
c10 = Connection(c_in1, "out1", cd, "in1", label="10")
c20 = Connection(cd, "out1",amb_out1, "in1", label="20")
nw.add_conns(c0, c1, c2, c3, c4, c10,c20 )
cd.set_attr(pr1=0.99, pr2=0.99)
cp_o.set_attr(eta_s=0.85)
cp_t.set_attr(eta_s=0.85)
cons.set_attr(pr=0.99)
c0.set_attr(p=30,fluid={working_fluid: 1})
c1.set_attr(p=80,h=500)
c2.set_attr(T=35, p0=80)
c3.set_attr(p=150)
c4.set_attr(T=50, p0=150)
c10.set_attr(T=25, fluid={"water": 1},m=1, p=1)
c20.set_attr(T=30)
nw.solve(mode='design')
nw.print_results() |
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I'm sorry, I may have encountered a problem again. When making the energy release system, I still had the problem of unstable starting values. I tried to use pressure and enthalpy as starting values, but failed. Do you know how to solve it？ |
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from tespy.networks import Network
working_fluid = "CO2"
from CoolProp.CoolProp import PropsSI as PSI
nw = Network(
T_unit="C", p_unit="bar", h_unit="kJ / kg", m_unit="kg / s", s_unit="kJ / kgK"
)
from tespy.components import HeatExchanger
from tespy.components import SimpleHeatExchanger
from tespy.components import Sink
from tespy.components import Source
from tespy.components import Turbine
c_in = Source("refrigerant in")
amb_out = Sink("sink ambient")
c_in1 = Source("refrigerant in1")
amb_out1 = Sink("sink ambient1")
tu_o = Turbine("Turbine1")
tu_t = Turbine("Turbine2")
cd = HeatExchanger("condenser")
cd_1 = HeatExchanger("condenser1")
cons = SimpleHeatExchanger("SimpleHeatExchanger")
c_in2 = Source("refrigerant in2")
amb_out2 = Sink("sink ambient2")
from tespy.connections import Connection
c0 = Connection(c_in, "out1", cd, "in1", label="0")
c1 = Connection(cd, "out1", tu_o, "in1", label="1")
c2 = Connection(tu_o, "out1", cd_1, "in1", label="2")
c3 = Connection(cd_1, "out1", tu_t , "in1", label="3")
c4 = Connection(tu_t , "out1", cons, "in1", label="4")
c5 = Connection(cons , "out1", amb_out, "in1", label="5")
c10 = Connection(c_in1, "out1", cd, "in2", label="10")
c20 = Connection(cd, "out2",amb_out1, "in1", label="20")
c01 = Connection(c_in2, "out1", cd_1, "in2", label="01")
c02 = Connection(cd_1, "out2",amb_out2, "in1", label="02")
nw.add_conns(c0, c1, c2, c3, c4,c5, c10, c20, c01, c02)
ev_in_H = PSI('H', 'P', 210*1e5, 'T', 30 + 273.15, working_fluid)
cd.set_attr(pr1=1, pr2=1)
cd_1.set_attr(pr1=1, pr2=1)
tu_o.set_attr(eta_s=0.85)
tu_t.set_attr(eta_s=0.85)
c0.set_attr(p=210,h=ev_in_H/3,fluid={working_fluid: 1},m=1.543)
c1.set_attr(T=75)
c2.set_attr(p=80)
c3.set_attr(p=80,T=70)
c4.set_attr(p=30)
c5.set_attr(T=15)
c10.set_attr(T=80, fluid={"water": 1},m=1, p=1)
c01.set_attr(T=80, fluid={"water": 1},m=1, p=1)
from tespy.connections import Bus
powergen = Bus("electrical power output")
powergen.add_comps(
{"comp": tu_o, "char": 0.97, "base": "bus"},
{"comp": tu_t, "char": 0.97, "base": "bus"}
)
nw.add_busses(powergen)
nw.solve(mode='design')
nw.print_results() |
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Hi, there are two issues here:
On top of that, you can also directly specify the temperature on the incoming from tespy.networks import Network
working_fluid = "CO2"
from CoolProp.CoolProp import PropsSI as PSI
nw = Network(
T_unit="C", p_unit="bar", h_unit="kJ / kg", m_unit="kg / s", s_unit="kJ / kgK"
)
from tespy.components import HeatExchanger
from tespy.components import SimpleHeatExchanger
from tespy.components import Sink
from tespy.components import Source
from tespy.components import Turbine
c_in = Source("refrigerant in")
amb_out = Sink("sink ambient")
c_in1 = Source("refrigerant in1")
amb_out1 = Sink("sink ambient1")
tu_o = Turbine("Turbine1")
tu_t = Turbine("Turbine2")
cd = HeatExchanger("condenser")
cd_1 = HeatExchanger("condenser1")
cons = SimpleHeatExchanger("SimpleHeatExchanger")
c_in2 = Source("refrigerant in2")
amb_out2 = Sink("sink ambient2")
from tespy.connections import Connection
c0 = Connection(c_in, "out1", cd, "in2", label="0")
c1 = Connection(cd, "out2", tu_o, "in1", label="1")
c2 = Connection(tu_o, "out1", cd_1, "in2", label="2")
c3 = Connection(cd_1, "out2", tu_t , "in1", label="3")
c4 = Connection(tu_t , "out1", cons, "in1", label="4")
c5 = Connection(cons , "out1", amb_out, "in1", label="5")
c10 = Connection(c_in1, "out1", cd, "in1", label="10")
c20 = Connection(cd, "out1",amb_out1, "in1", label="20")
c01 = Connection(c_in2, "out1", cd_1, "in1", label="01")
c02 = Connection(cd_1, "out1",amb_out2, "in1", label="02")
nw.add_conns(c0, c1, c2, c3, c4,c5, c10, c20, c01, c02)
ev_in_H = PSI('H', 'P', 210*1e5, 'T', 30 + 273.15, working_fluid)
cd.set_attr(pr1=1, pr2=1)
cd_1.set_attr(pr1=1, pr2=1)
tu_o.set_attr(eta_s=0.85)
tu_t.set_attr(eta_s=0.85)
cons.set_attr(pr=1)
c0.set_attr(p=210,T=30,fluid={working_fluid: 1},m=1.543)
c1.set_attr(T=75)
c2.set_attr(p=80)
c3.set_attr(T=70)
c4.set_attr(p=30)
c5.set_attr(T=15)
c10.set_attr(T=80, fluid={"water": 1},m=1, p=1)
c01.set_attr(T=80, fluid={"water": 1},m=1, p=1)
from tespy.connections import Bus
powergen = Bus("electrical power output")
powergen.add_comps(
{"comp": tu_o, "char": 0.97, "base": "bus"},
{"comp": tu_t, "char": 0.97, "base": "bus"}
)
nw.add_busses(powergen)
nw.solve(mode='design')
nw.print_results()Best Francesco |
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Hello,
I'm trying to model a transcritical (compression cycle) heat pump unit in TESPy, with CO2 as the working fluid (closed cycle's refrigerant). A turboexpander (turbine) is used in the cycle, instead of an expansion valve, with the aim of work recovery. The recovered work from the turbine moves the compressor (through a shaft between the turbine and compressor), and any additional power requirement for the compression process is satisfied by an electric motor.
During model setup, I've tried to follow the recommended practices for stable starting values so that the solving process converges. But, for some reason, it doesn't, and the following error occurs:
I assume that a possible reason for the solving process failure is that, after the turbine, a two-phase region occurs, or it may be because of a "bad" value for any of the used parameters. However, I checked for possible solutions for the above issues (e.g. forcing the CO2 state as liquid after the turbine with PropsSI function), but nothing worked.
Any help or suggestion for these issues would be much appreciated!
Thank you very much in advance.
Heat Pump topology:
Code:
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