Heat pump model with incomrepssible fluid on the heat source side #473

nschnait · 2024-01-12T09:56:35Z

nschnait
Jan 12, 2024

Good morning Tespy Comunity,

I need help please.
I would like to simulate the heat source temperature below 0°C in the heat pump model I have created.
For this I use the incompressible fluid ethylene glycol.
I always get the following error message:

I don't understand where this high temperature comes from according to the error message.

I provide my code here.

from tespy.components import(HeatExchanger,
                             Compressor,
                             Condenser,
                             Valve,
                             CycleCloser,
                             Sink,
                             Source,
                             Pump)
from tespy.connections import(Connection,
                              Bus)
from tespy.networks import Network
from tespy.tools.characteristics import CharLine
from fluprodia import FluidPropertyDiagram
import numpy as np
import pandas as pd
import math
import matplotlib.pyplot as plt
import CoolProp.CoolProp as CP
# %%
# Global Settings for plot
plt.rcParams["figure.dpi"] = 400
plt.rc("font", **{"size": 18})
# %% conditions
working_fluid = "R290"      # refrigerant
sink_fluid = "water"        # heating side
#source_fluid = "water"      # cold side
source_fluid = "INCOMP::MEG[0.25]"      # cold side
pamb = 1.013                # ambient pressure
Tamb = 2.8                  # ambient temperature
T_sink_VL =  35             # feed temperature sink system
T_sink_RL =  30             # return temperature sink system
T_source_VL = 10            # feed temperature source system
T_source_RL = 7             # return temperature source system
v_source_system = 1.6
v_sink_system = 1.3

V_dis = 17.2e-6             # dicplacement volumne
n = 120                     # rotational speed
# creat a network object
# Definie system of unitis:
nw = Network(h_unit="kJ / kg",
                 m_unit="kg / s",
                 p_unit="bar",
                 s_unit="kJ / kgK",
                 T_unit="C",
                 v_unit="m3 / h",
                 vol_unit="m3 / kg",
                 iterinfo=True)
# ==========
# components
# ==========
# heat pump system
ev = HeatExchanger("evaporator")
cp = Compressor("compressor")
co = Condenser("condenser")
va = Valve("valve")
cc = CycleCloser("cycle closer")
# heat source system
hso_in = Source("heat feed flow")
hso_out = Sink("heat return flow")
hso_pump = Pump("heat circulation pump")
# heat sink system
hs_feed = Sink("heating system fedd flow")
hs_ret = Source("heating system return flow")
hs_pump = Pump("heating system pump")
# ===========
# connections
# ===========
# heat pump system
c0 = Connection(cp, "out1", cc, "in1", label="0")
c1 = Connection(cc, "out1", co, "in1", label="1")
c2 = Connection(co, "out1", va, "in1", label="2")
c3 = Connection(va, "out1", ev, "in2", label="3")
c4 = Connection(ev, "out2", cp, "in1", label="4")
nw.add_conns(c1, c2, c3, c4, c0)
# heat source system
c11 = Connection(hso_in, "out1", hso_pump, "in1", label="11")
c12 = Connection(hso_pump, "out1", ev, "in1", label="12")
c13 = Connection(ev, "out1", hso_out, "in1", label="13")
nw.add_conns(c11, c12, c13)
# heat sink system
c21 = Connection(hs_ret, "out1", hs_pump, "in1", label="21")
c22 = Connection(hs_pump, "out1", co, "in2", label="22")
c23 = Connection(co, "out2", hs_feed, "in1", label="23")
nw.add_conns(c21, c22, c23)
# =========================
# component parametrization
# =========================
# heat pump system:
# condensation temperature:
T_co = T_sink_VL + 7
print("T_co", T_co, "°C")
# evaporating temperature:
T_ev = T_source_VL - 9
print("T_ev", T_ev, "°C")
# Superheating:
T_sh = 5
# Subcooling:
T_sc = 4.5
# condensation pressure:
p_co = CP.PropsSI("P", "Q", 0, "T", T_co + 273.15, working_fluid)/1e5
print("p_co", p_co)
# evaporating pressure:
p_ev = CP.PropsSI("P", "Q", 1, "T", T_ev + 273.15, working_fluid)/1e5
print("p_ev", p_ev)

# evaporator
ev.set_attr(pr1=1, pr2=1) # Set the pressure rations on the hot and cold side

# codenser
co.set_attr(pr1=1, pr2=1) # Set the pressure ratios on the hot and cold side
co.set_attr(subcooling=True)
# compressor
# Polynomial for quality grade:
eta_s=1.39582264e-10*n**5+-5.95908423e-08*n**4+1.01057591e-05*n**3+-8.51144668e-04*n**2+3.42271905e-02*n+2.37267492e-01
print("eta_s", eta_s)
cp.set_attr(eta_s=eta_s) # Set the isentropic efficiency of the compressor

# valve
# no parameterization

# heat circulation pump
hso_pump.set_attr(eta_s=0.50) # Set the isentropic efficiency of the circulation pump
# heating system pump
hs_pump.set_attr(eta_s=0.50) # Set the isentropic efficiency of the circulation pump
# ===========================
# connection parametriziation
# ===========================
# condenser
c1.set_attr(p=p_co, fluid={str(working_fluid): 1})
c2.set_attr(Td_bp=-T_sc)

# evaporator
d_4 = CP.PropsSI("D", "P", float(p_ev)*1e5, "T", T_ev + 273.15 +T_sh, working_fluid)
print("d_v", d_4)
# Polynomial fpr degree of delivery:
lambda_km=5.77469068e-16*n**8+-2.36384800e-13*n**7+3.14000090e-11*n**6+-3.64077967e-10*n**5+-3.03875097e-07*n**4+3.27295609e-05*n**3+-1.56988025e-03*n**2+3.92109697e-02*n+4.81753398e-01
print("lambda", lambda_km)
c4.set_attr(m=n*V_dis*d_4*lambda_km, p=p_ev, T=T_ev + T_sh)

# heat source system
c13.set_attr(fluid={str(sink_fluid): 1}, fluid_engines={}, T=T_source_RL)   # return temperature removed
c11.set_attr(T=T_source_VL, p=1)

# heat sink system
c23.set_attr(fluid={str(source_fluid): 1}, T=T_sink_VL) # temperature removed
c21.set_attr(T=T_sink_RL, p=1.5)

# ==================
# design calculation
# ==================
nw.solve(mode="design", design_path="tmp")
nw.save("tmp")
nw.print_results()

What am I doing wrong? Or which parameters do I have to change? Does anyone have any experience with this?

Many thanks for your help.

Answered by fwitte

Jan 15, 2024

Here is a full working model, you had been missing out on the pressure behind the evaporator/condenser on the secondary sides:

from tespy.components import(HeatExchanger,
                             Compressor,
                             Condenser,
                             Valve,
                             CycleCloser,
                             Sink,
                             Source,
                             Pump)
from tespy.connections import(Connection,
                              Bus)
from tespy.networks import Network
from tespy.tools.characteristics import CharLine
from fluprodia import FluidPropertyDiagram
import numpy as np
import pandas as pd
import math
import …

View full answer

fwitte · 2024-01-12T11:54:47Z

fwitte
Jan 12, 2024
Maintainer

Hi @nschait,

that issue is not on you, but on the software somehow. The starting value routine is not working well with the incompressible back-end. You could just add enthalpy starting value for all respective connections like so just before calling the solve() method. Once you have a good set of starting values (converged solution), you do not need to do this anymore.

[c.set_attr(h0=100) for c in nw.conns.loc[["21", "22", "23"], "object"]]

On top of that, your model seems to be overdetermined, I do not have the time to look into details at this moment, but I'd advise to build the system step by step and run your model to better understand, what specifications to make.

Best

1 reply

fwitte Jan 15, 2024
Maintainer

Here is a full working model, you had been missing out on the pressure behind the evaporator/condenser on the secondary sides:

from tespy.components import(HeatExchanger,
                             Compressor,
                             Condenser,
                             Valve,
                             CycleCloser,
                             Sink,
                             Source,
                             Pump)
from tespy.connections import(Connection,
                              Bus)
from tespy.networks import Network
from tespy.tools.characteristics import CharLine
from fluprodia import FluidPropertyDiagram
import numpy as np
import pandas as pd
import math
import matplotlib.pyplot as plt
import CoolProp.CoolProp as CP
# %%
# Global Settings for plot
plt.rcParams["figure.dpi"] = 400
plt.rc("font", **{"size": 18})
# %% conditions
working_fluid = "R290"      # refrigerant
sink_fluid = "water"        # heating side
#source_fluid = "water"      # cold side
source_fluid = "INCOMP::MEG[0.25]"      # cold side
pamb = 1.013                # ambient pressure
Tamb = 2.8                  # ambient temperature
T_sink_VL =  35             # feed temperature sink system
T_sink_RL =  30             # return temperature sink system
T_source_VL = 10            # feed temperature source system
T_source_RL = 7             # return temperature source system
v_source_system = 1.6
v_sink_system = 1.3

V_dis = 17.2e-6             # dicplacement volumne
n = 120                     # rotational speed
# creat a network object
# Definie system of unitis:
nw = Network(h_unit="kJ / kg",
                 m_unit="kg / s",
                 p_unit="bar",
                 s_unit="kJ / kgK",
                 T_unit="C",
                 v_unit="m3 / h",
                 vol_unit="m3 / kg",
                 iterinfo=True)
# ==========
# components
# ==========
# heat pump system
ev = HeatExchanger("evaporator")
cp = Compressor("compressor")
co = Condenser("condenser")
va = Valve("valve")
cc = CycleCloser("cycle closer")
# heat source system
hso_in = Source("heat feed flow")
hso_out = Sink("heat return flow")
hso_pump = Pump("heat circulation pump")
# heat sink system
hs_feed = Sink("heating system fedd flow")
hs_ret = Source("heating system return flow")
hs_pump = Pump("heating system pump")
# ===========
# connections
# ===========
# heat pump system
c0 = Connection(cp, "out1", cc, "in1", label="0")
c1 = Connection(cc, "out1", co, "in1", label="1")
c2 = Connection(co, "out1", va, "in1", label="2")
c3 = Connection(va, "out1", ev, "in2", label="3")
c4 = Connection(ev, "out2", cp, "in1", label="4")
nw.add_conns(c1, c2, c3, c4, c0)
# heat source system
c11 = Connection(hso_in, "out1", hso_pump, "in1", label="11")
c12 = Connection(hso_pump, "out1", ev, "in1", label="12")
c13 = Connection(ev, "out1", hso_out, "in1", label="13")
nw.add_conns(c11, c12, c13)
# heat sink system
c21 = Connection(hs_ret, "out1", hs_pump, "in1", label="21")
c22 = Connection(hs_pump, "out1", co, "in2", label="22")
c23 = Connection(co, "out2", hs_feed, "in1", label="23")
nw.add_conns(c21, c22, c23)
# =========================
# component parametrization
# =========================
# heat pump system:
# condensation temperature:
T_co = T_sink_VL + 7
print("T_co", T_co, "°C")
# evaporating temperature:
T_ev = T_source_VL - 9
print("T_ev", T_ev, "°C")
# Superheating:
T_sh = 5
# Subcooling:
T_sc = 4.5
# condensation pressure:
p_co = CP.PropsSI("P", "Q", 0, "T", T_co + 273.15, working_fluid)/1e5
print("p_co", p_co)
# evaporating pressure:
p_ev = CP.PropsSI("P", "Q", 1, "T", T_ev + 273.15, working_fluid)/1e5
print("p_ev", p_ev)

# evaporator
ev.set_attr(pr1=0.98, pr2=1) # Set the pressure rations on the hot and cold side

# codenser
co.set_attr(pr1=1, pr2=0.98) # Set the pressure ratios on the hot and cold side
co.set_attr(subcooling=True)
# compressor
# Polynomial for quality grade:
eta_s=1.39582264e-10*n**5+-5.95908423e-08*n**4+1.01057591e-05*n**3+-8.51144668e-04*n**2+3.42271905e-02*n+2.37267492e-01
print("eta_s", eta_s)
cp.set_attr(eta_s=eta_s) # Set the isentropic efficiency of the compressor

# valve
# no parameterization

# heat circulation pump
hso_pump.set_attr(eta_s=0.50) # Set the isentropic efficiency of the circulation pump
# heating system pump
hs_pump.set_attr(eta_s=0.50) # Set the isentropic efficiency of the circulation pump
# ===========================
# connection parametriziation
# ===========================
# condenser
c1.set_attr(p=p_co, fluid={str(working_fluid): 1})
c2.set_attr(Td_bp=-T_sc)

# evaporator
d_4 = CP.PropsSI("D", "P", float(p_ev)*1e5, "T", T_ev + 273.15 +T_sh, working_fluid)
print("d_v", d_4)
# Polynomial fpr degree of delivery:
lambda_km=5.77469068e-16*n**8+-2.36384800e-13*n**7+3.14000090e-11*n**6+-3.64077967e-10*n**5+-3.03875097e-07*n**4+3.27295609e-05*n**3+-1.56988025e-03*n**2+3.92109697e-02*n+4.81753398e-01
print("lambda", lambda_km)
c4.set_attr(m=n*V_dis*d_4*lambda_km, p=p_ev, T=T_ev + T_sh)

# heat source system
c13.set_attr(fluid={str(sink_fluid): 1}, fluid_engines={}, T=T_source_RL, p=1)   # return temperature removed
c11.set_attr(T=T_source_VL, p=1)

# heat sink system
c23.set_attr(fluid={str(source_fluid): 1}, T=T_sink_VL, p=1.5) # temperature removed
c21.set_attr(T=T_sink_RL, p=1.5)

[c.set_attr(h0=100) for c in [c21, c22, c23]]

# ==================
# design calculation
# ==================
nw.solve(mode="design", design_path="tmp")
nw.save("tmp")
nw.print_results()

Answer selected by fwitte

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Heat pump model with incomrepssible fluid on the heat source side #473

nschnait Jan 12, 2024

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fwitte Jan 12, 2024 Maintainer

fwitte Jan 15, 2024 Maintainer

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Jan 12, 2024

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fwitte
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fwitte Jan 15, 2024
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