Issue with solver fails to converge with repetitive solver calls

[sorheimen]

I have a problem with a network of simple heat exchangers where I want to store the network and then load and perform new solves. Doing this using the export function the solver fails to converge on the re-imported network, it also fails if I immediately call the solver after the first solve. What is going on here? (I use version 0.9.4.post2)

###
# Copyright (c) 2012-2025, OpenGeoSys Community (http://www.opengeosys.org)
# Distributed under a Modified BSD License.
# See accompanying file LICENSE.txt or
# http://www.opengeosys.org/project/license
###

# Execute this file to generate TESPy network csv files
import numpy as np
from tespy.components import (
    SimpleHeatExchanger,
    Merge,
    Pump,
    Sink,
    Source,
    Splitter,
)
from tespy.connections import Connection, Ref, Bus
from tespy.networks import Network
from tespy.tools.characteristics import CharLine as char_line

# %% network
btes = Network(fluids=["water"], T_unit="K", p_unit="bar", h_unit="kJ / kg")

# %% components
fc_in = Source("from consumer inflow")
fc_out = Sink("from consumer outflow")

sp1 = Splitter("splitter1", num_out=4)
sp2 = Splitter("splitter2", num_out=8)

# bhe:
bhe_name = "BHE1"
assert "BHE1" in bhe_name, "BHE should be named with 'BHE1'"
bhe1 = SimpleHeatExchanger(bhe_name)
bhe_name = "BHE2"
assert "BHE2" in bhe_name, "BHE should be named with 'BHE2'"
bhe2 = SimpleHeatExchanger(bhe_name)
bhe_name = "BHE3"
assert "BHE3" in bhe_name, "BHE should be named with 'BHE3'"
bhe3 = SimpleHeatExchanger(bhe_name)
bhe_name = "BHE4"
assert "BHE4" in bhe_name, "BHE should be named with 'BHE4'"
bhe4 = SimpleHeatExchanger(bhe_name)
bhe_name = "BHE5"
assert "BHE5" in bhe_name, "BHE should be named with 'BHE5'"
bhe5 = SimpleHeatExchanger(bhe_name)
bhe_name = "BHE6"
assert "BHE6" in bhe_name, "BHE should be named with 'BHE6'"
bhe6 = SimpleHeatExchanger(bhe_name)
bhe_name = "BHE7"
assert "BHE7" in bhe_name, "BHE should be named with 'BHE7'"
bhe7 = SimpleHeatExchanger(bhe_name)
bhe_name = "BHE8"
assert "BHE8" in bhe_name, "BHE should be named with 'BHE8'"
bhe8 = SimpleHeatExchanger(bhe_name)
bhe_name = "BHE9"
assert "BHE9" in bhe_name, "BHE should be named with 'BHE9'"
bhe9 = SimpleHeatExchanger(bhe_name)
bhe_name = "BHE10"
assert "BHE10" in bhe_name, "BHE should be named with 'BHE10'"
bhe10 = SimpleHeatExchanger(bhe_name)
bhe_name = "BHE11"
assert "BHE11" in bhe_name, "BHE should be named with 'BHE11'"
bhe11 = SimpleHeatExchanger(bhe_name)
bhe_name = "BHE12"
assert "BHE12" in bhe_name, "BHE should be named with 'BHE12'"
bhe12 = SimpleHeatExchanger(bhe_name)
bhe_name = "BHE13"
assert "BHE13" in bhe_name, "BHE should be named with 'BHE13'"
bhe13= SimpleHeatExchanger(bhe_name)

mg1 = Merge("merge1", num_in=4)

mg2 = Merge("merge2", num_in=8)

#cons = SimpleHeatExchanger("consumer")

# %% connections
fc_bhe13 = Connection(fc_in, "out1", bhe13, "in1")

bhe13_sp1 = Connection(bhe13, "out1", sp1, "in1") 
sp1_bhe9 = Connection(sp1, "out1", bhe9, "in1")
sp1_bhe10 = Connection(sp1, "out2", bhe10, "in1")
sp1_bhe11 = Connection(sp1, "out3", bhe11, "in1")
sp1_bhe12 = Connection(sp1, "out4", bhe12, "in1")

bhe9_mg1 =  Connection(bhe9, "out1", mg1, "in1")
bhe10_mg1=  Connection(bhe10, "out1", mg1, "in2")
bhe11_mg1=  Connection(bhe11, "out1", mg1, "in3")
bhe12_mg1=  Connection(bhe12, "out1", mg1, "in4")
         
mg1_sp2  =  Connection(mg1, "out1", sp2, "in1")
         
sp2_bhe1 = Connection(sp2, "out1", bhe1, "in1")
sp2_bhe2 = Connection(sp2, "out2", bhe2, "in1")
sp2_bhe3 = Connection(sp2, "out3", bhe3, "in1")
sp2_bhe4 = Connection(sp2, "out4", bhe4, "in1")
sp2_bhe5 = Connection(sp2, "out5", bhe5, "in1")
sp2_bhe6 = Connection(sp2, "out6", bhe6, "in1")
sp2_bhe7 = Connection(sp2, "out7", bhe7, "in1")
sp2_bhe8 = Connection(sp2, "out8", bhe8, "in1")
         
bhe1_mg2 =  Connection(bhe1, "out1", mg2, "in1")
bhe2_mg2 =  Connection(bhe2, "out1", mg2, "in2")
bhe3_mg2 =  Connection(bhe3, "out1", mg2, "in3")
bhe4_mg2 =  Connection(bhe4, "out1", mg2, "in4")
bhe5_mg2 =  Connection(bhe5, "out1", mg2, "in5")
bhe6_mg2 =  Connection(bhe6, "out1", mg2, "in6")
bhe7_mg2 =  Connection(bhe7, "out1", mg2, "in7")
bhe8_mg2 =  Connection(bhe8, "out1", mg2, "in8")


mg2_fc = Connection(mg2, "out1", fc_out, "in1")

btes.add_conns(
    fc_bhe13, bhe13_sp1,sp1_bhe9,sp1_bhe10,sp1_bhe11,sp1_bhe12,bhe9_mg1 ,bhe10_mg1,bhe11_mg1,bhe12_mg1,mg1_sp2,sp2_bhe1,sp2_bhe2 ,sp2_bhe3 ,sp2_bhe4 ,sp2_bhe5 ,sp2_bhe6 ,sp2_bhe7 ,sp2_bhe8 ,bhe1_mg2 ,bhe2_mg2 ,bhe3_mg2 ,bhe4_mg2 ,bhe5_mg2 ,bhe6_mg2 ,bhe7_mg2 ,bhe8_mg2 ,mg2_fc
)
# bhes
bhe1.set_attr(Tamb=283.13,D=0.0215, L=50, ks=0.00001,kA= 1000.0)
bhe2.set_attr(Tamb=283.13,D=0.0215, L=50, ks=0.00001,kA= 1000.0)
bhe3.set_attr(Tamb=283.13,D=0.0215, L=50, ks=0.00001,kA= 1000.0)
bhe4.set_attr(Tamb=283.13,D=0.0215, L=50, ks=0.00001,kA= 1000.0)
bhe5.set_attr(Tamb=283.13,D=0.0215, L=50, ks=0.00001,kA= 1000.0)
bhe6.set_attr(Tamb=283.13,D=0.0215, L=50, ks=0.00001,kA= 1000.0)
bhe7.set_attr(Tamb=283.13,D=0.0215, L=50, ks=0.00001,kA= 1000.0)
bhe8.set_attr(Tamb=283.13,D=0.0215, L=50, ks=0.00001,kA= 1000.0)
bhe9.set_attr(Tamb=283.13,D=0.0215, L=50, ks=0.00001,kA= 1000.0)
bhe10.set_attr(Tamb=283.13,D=0.0215, L=50, ks=0.00001,kA= 1000.0)
bhe11.set_attr(Tamb=283.13,D=0.0215, L=50, ks=0.00001,kA= 1000.0)
bhe12.set_attr(Tamb=283.13,D=0.0215, L=50, ks=0.00001,kA= 1000.0)
bhe13.set_attr(Tamb=283.13,D=0.0215, L=50, ks=0.00001,kA= 1000.0)

inflow_head = 4.0 # bar

fc_bhe13.set_attr(p=inflow_head, m=0.8, fluid={"water": 1},T=273.15 + 40.0,h0=200.0)
bhe13_sp1.set_attr(h0=200)

# %% solve
try:
    btes.solve("design")
    btes.print_results()
    btes.solve(mode="design")
    btes.print_results()
except Exception as e:
    print(f"An error occurred during solving: {e}")
    # These methods are helpful for debugging convergence issues:
    #btes.check_missing_properties()
    #btes.check_degrees_of_freedom()    

# %% save to csv:
btes.save_csv("tespy_nw")
btes.export("tespy_nw_orig.json")
nw = Network.from_json("tespy_nw_orig.json")
nw.solve(mode="design",init_previous=False,max_iter=1000,min_iter=100)
nw.print_results()

[sorheimen]

The output for running this is:

(py313) (base) einar@d1-cmp-phy-lin5:~/work/inaventa/bhes_network/pre$ uv run ina13_bhes_no_pump.py
FutureWarning: The API for specification of units in a Network changed. The old variant will be removed in the next major release. Please use the 'Network.units.set_defaults' method instead.

 iter  | residual   | progress   | massflow   | pressure   | enthalpy   | fluid      | component  
-------+------------+------------+------------+------------+------------+------------+------------
 1     | 3.02e+06   | 0 %        | 5.28e+00   | 8.91e+05   | 6.23e+06   | 0.00e+00   | 0.00e+00   
 2     | 1.03e+06   | 0 %        | 6.11e-01   | 6.20e+05   | 3.49e+05   | 0.00e+00   | 0.00e+00   
 3     | 4.05e+05   | 4 %        | 3.48e-01   | 1.46e+05   | 4.71e+06   | 0.00e+00   | 0.00e+00   
 4     | 3.07e+05   | 5 %        | 1.58e-01   | 1.38e+03   | 1.28e+06   | 0.00e+00   | 0.00e+00   
 5     | 9.29e+04   | 11 %       | 2.37e-02   | 5.60e+01   | 1.21e+05   | 0.00e+00   | 0.00e+00   
 6     | 9.96e+02   | 33 %       | 1.21e-03   | 1.19e+01   | 1.38e+03   | 0.00e+00   | 0.00e+00   
 7     | 1.08e+01   | 55 %       | 3.70e-06   | 3.44e-02   | 2.58e+01   | 0.00e+00   | 0.00e+00   
 8     | 1.93e-02   | 85 %       | 2.02e-09   | 1.56e-05   | 4.73e-02   | 0.00e+00   | 0.00e+00   
 9     | 9.81e-08   | 100 %      | 1.26e-14   | 5.70e-09   | 2.49e-07   | 0.00e+00   | 0.00e+00   
 10    | 8.17e-08   | 100 %      | 1.57e-14   | 7.91e-09   | 2.10e-07   | 0.00e+00   | 0.00e+00   
Total iterations: 10, Calculation time: 0.76 s, Iterations per second: 13.18

##### RESULTS (SimpleHeatExchanger) #####
+-------+-----------+----------+----------+----------+----------+----------+----------+---------+------------+----------+
|       |         Q |       pr |       dp |     zeta |        D |        L |       ks |   ks_HW |         kA |     Tamb |
|-------+-----------+----------+----------+----------+----------+----------+----------+---------+------------+----------|
| BHE1  | -3.07e+03 | 9.88e-01 | 3.33e-02 | 4.12e+08 | 2.15e-02 | 5.00e+01 | 1.00e-05 |     nan | nan        | 2.83e+02 |
| BHE10 | -1.30e+04 | 9.65e-01 | 1.02e-01 | 3.13e+08 | 2.15e-02 | 5.00e+01 | 1.00e-05 |     nan |   1.00e+03 | 2.83e+02 |
| BHE11 | -1.30e+04 | 9.65e-01 | 1.02e-01 | 3.13e+08 | 2.15e-02 | 5.00e+01 | 1.00e-05 |     nan |   1.00e+03 | 2.83e+02 |
| BHE12 | -1.30e+04 | 9.65e-01 | 1.02e-01 | 3.13e+08 | 2.15e-02 | 5.00e+01 | 1.00e-05 |     nan |   1.00e+03 | 2.83e+02 |
| BHE13 | -2.60e+04 | 7.25e-01 | 1.10e+00 | 2.11e+08 | 2.15e-02 | 5.00e+01 | 1.00e-05 |     nan |   1.00e+03 | 2.83e+02 |
| BHE2  | -2.57e+03 | 9.88e-01 | 3.33e-02 | 4.10e+08 | 2.15e-02 | 5.00e+01 | 1.00e-05 |     nan |   1.00e+03 | 2.83e+02 |
| BHE3  | -3.07e+03 | 9.88e-01 | 3.33e-02 | 4.12e+08 | 2.15e-02 | 5.00e+01 | 1.00e-05 |     nan | nan        | 2.83e+02 |
| BHE4  | -2.57e+03 | 9.88e-01 | 3.33e-02 | 4.10e+08 | 2.15e-02 | 5.00e+01 | 1.00e-05 |     nan |   1.00e+03 | 2.83e+02 |
| BHE5  | -2.57e+03 | 9.88e-01 | 3.33e-02 | 4.10e+08 | 2.15e-02 | 5.00e+01 | 1.00e-05 |     nan |   1.00e+03 | 2.83e+02 |
| BHE6  | -2.57e+03 | 9.88e-01 | 3.33e-02 | 4.10e+08 | 2.15e-02 | 5.00e+01 | 1.00e-05 |     nan |   1.00e+03 | 2.83e+02 |
| BHE7  | -2.57e+03 | 9.88e-01 | 3.33e-02 | 4.10e+08 | 2.15e-02 | 5.00e+01 | 1.00e-05 |     nan |   1.00e+03 | 2.83e+02 |
| BHE8  | -2.57e+03 | 9.88e-01 | 3.33e-02 | 4.10e+08 | 2.15e-02 | 5.00e+01 | 1.00e-05 |     nan |   1.00e+03 | 2.83e+02 |
| BHE9  | -1.30e+04 | 9.65e-01 | 1.02e-01 | 3.13e+08 | 2.15e-02 | 5.00e+01 | 1.00e-05 |     nan |   1.00e+03 | 2.83e+02 |
+-------+-----------+----------+----------+----------+----------+----------+----------+---------+------------+----------+
##### RESULTS (Connection) #####
+---------------------------------------+-----------+-----------+-----------+-----------+-----------+---------+
|                                       |         m |         p |         h |         T |         x | phase   |
|---------------------------------------+-----------+-----------+-----------+-----------+-----------+---------|
| BHE10:out1_merge1:in2                 | 2.000e-01 | 2.798e+00 | 7.045e+01 | 2.899e+02 | 0.000e+00 | l       |
| BHE11:out1_merge1:in3                 | 2.000e-01 | 2.798e+00 | 7.045e+01 | 2.899e+02 | 0.000e+00 | l       |
| BHE12:out1_merge1:in4                 | 2.000e-01 | 2.798e+00 | 7.045e+01 | 2.899e+02 | 0.000e+00 | l       |
| BHE13:out1_splitter1:in1              | 8.000e-01 | 2.900e+00 | 1.354e+02 | 3.054e+02 | 0.000e+00 | l       |
| BHE1:out1_merge2:in1                  | 9.980e-02 | 2.765e+00 | 3.969e+01 | 2.825e+02 | 0.000e+00 | l       |
| BHE2:out1_merge2:in2                  | 1.001e-01 | 2.765e+00 | 4.481e+01 | 2.838e+02 | 0.000e+00 | l       |
| BHE3:out1_merge2:in3                  | 9.980e-02 | 2.765e+00 | 3.969e+01 | 2.825e+02 | 0.000e+00 | l       |
| BHE4:out1_merge2:in4                  | 1.001e-01 | 2.765e+00 | 4.481e+01 | 2.838e+02 | 0.000e+00 | l       |
| BHE5:out1_merge2:in5                  | 1.001e-01 | 2.765e+00 | 4.481e+01 | 2.838e+02 | 0.000e+00 | l       |
| BHE6:out1_merge2:in6                  | 1.001e-01 | 2.765e+00 | 4.481e+01 | 2.838e+02 | 0.000e+00 | l       |
| BHE7:out1_merge2:in7                  | 1.001e-01 | 2.765e+00 | 4.481e+01 | 2.838e+02 | 0.000e+00 | l       |
| BHE8:out1_merge2:in8                  | 1.001e-01 | 2.765e+00 | 4.481e+01 | 2.838e+02 | 0.000e+00 | l       |
| BHE9:out1_merge1:in1                  | 2.000e-01 | 2.798e+00 | 7.045e+01 | 2.899e+02 | 0.000e+00 | l       |
| from consumer inflow:out1_BHE13:in1   | 8.000e-01 | 4.000e+00 | 1.679e+02 | 3.131e+02 | 0.000e+00 | l       |
| merge1:out1_splitter2:in1             | 8.000e-01 | 2.798e+00 | 7.045e+01 | 2.899e+02 | 0.000e+00 | l       |
| merge2:out1_from consumer outflow:in1 | 8.000e-01 | 2.765e+00 | 4.353e+01 | 2.834e+02 | 0.000e+00 | l       |
| splitter1:out1_BHE9:in1               | 2.000e-01 | 2.900e+00 | 1.354e+02 | 3.054e+02 | 0.000e+00 | l       |
| splitter1:out2_BHE10:in1              | 2.000e-01 | 2.900e+00 | 1.354e+02 | 3.054e+02 | 0.000e+00 | l       |
| splitter1:out3_BHE11:in1              | 2.000e-01 | 2.900e+00 | 1.354e+02 | 3.054e+02 | 0.000e+00 | l       |
| splitter1:out4_BHE12:in1              | 2.000e-01 | 2.900e+00 | 1.354e+02 | 3.054e+02 | 0.000e+00 | l       |
| splitter2:out1_BHE1:in1               | 9.980e-02 | 2.798e+00 | 7.045e+01 | 2.899e+02 | 0.000e+00 | l       |
| splitter2:out2_BHE2:in1               | 1.001e-01 | 2.798e+00 | 7.045e+01 | 2.899e+02 | 0.000e+00 | l       |
| splitter2:out3_BHE3:in1               | 9.980e-02 | 2.798e+00 | 7.045e+01 | 2.899e+02 | 0.000e+00 | l       |
| splitter2:out4_BHE4:in1               | 1.001e-01 | 2.798e+00 | 7.045e+01 | 2.899e+02 | 0.000e+00 | l       |
| splitter2:out5_BHE5:in1               | 1.001e-01 | 2.798e+00 | 7.045e+01 | 2.899e+02 | 0.000e+00 | l       |
| splitter2:out6_BHE6:in1               | 1.001e-01 | 2.798e+00 | 7.045e+01 | 2.899e+02 | 0.000e+00 | l       |
| splitter2:out7_BHE7:in1               | 1.001e-01 | 2.798e+00 | 7.045e+01 | 2.899e+02 | 0.000e+00 | l       |
| splitter2:out8_BHE8:in1               | 1.001e-01 | 2.798e+00 | 7.045e+01 | 2.899e+02 | 0.000e+00 | l       |
+---------------------------------------+-----------+-----------+-----------+-----------+-----------+---------+

 iter  | residual   | progress   | massflow   | pressure   | enthalpy   | fluid      | component  
-------+------------+------------+------------+------------+------------+------------+------------
 1     | 2.17e+12   | 0 %        | 1.70e-03   | 2.01e+01   | 3.70e+04   | 0.00e+00   | 0.00e+00   
 2     | 3.14e+09   | 0 %        | 1.79e-04   | 2.15e+00   | 8.64e+01   | 0.00e+00   | 0.00e+00   
 3     | 7.94e+03   | 23 %       | 4.50e-08   | 8.21e-04   | 1.37e-02   | 0.00e+00   | 0.00e+00   
 4     | 1.27e+01   | 54 %       | 6.99e-15   | 8.03e-09   | 2.85e-07   | 0.00e+00   | 0.00e+00   
 5     | 4.64e+00   | 59 %       | 1.43e-14   | 3.33e-09   | 2.32e-07   | 0.00e+00   | 0.00e+00   
 6     | 1.00e+01   | 55 %       | 1.82e-14   | 9.38e-09   | 3.07e-07   | 0.00e+00   | 0.00e+00   
 7     | 4.65e+00   | 59 %       | 8.03e-15   | 2.87e-09   | 2.29e-07   | 0.00e+00   | 0.00e+00   
 8     | 7.45e+00   | 56 %       | 1.54e-14   | 4.19e-09   | 2.04e-07   | 0.00e+00   | 0.00e+00   
 9     | 1.60e+01   | 53 %       | 1.53e-14   | 9.66e-09   | 3.30e-07   | 0.00e+00   | 0.00e+00   
 10    | 7.71e+00   | 56 %       | 1.16e-14   | 1.28e-08   | 2.02e-07   | 0.00e+00   | 0.00e+00   
 11    | 1.36e+01   | 54 %       | 1.03e-14   | 1.25e-08   | 2.65e-07   | 0.00e+00   | 0.00e+00   
 12    | 1.12e+01   | 55 %       | 7.33e-15   | 6.15e-10   | 2.53e-07   | 0.00e+00   | 0.00e+00   
 13    | 4.94e+00   | 58 %       | 7.79e-15   | 1.13e-09   | 1.94e-07   | 0.00e+00   | 0.00e+00   
 14    | 1.49e+01   | 53 %       | 1.09e-14   | 3.78e-09   | 2.72e-07   | 0.00e+00   | 0.00e+00   
 15    | 3.21e+00   | 61 %       | 1.13e-14   | 3.49e-09   | 1.58e-07   | 0.00e+00   | 0.00e+00   
 16    | 1.22e+01   | 54 %       | 9.57e-15   | 4.78e-10   | 2.41e-07   | 0.00e+00   | 0.00e+00   
 17    | 2.30e+00   | 62 %       | 6.90e-15   | 5.63e-09   | 1.61e-07   | 0.00e+00   | 0.00e+00   
 18    | 5.96e+00   | 58 %       | 7.20e-15   | 4.00e-10   | 2.08e-07   | 0.00e+00   | 0.00e+00   
 19    | 7.05e+00   | 57 %       | 1.36e-14   | 4.81e-10   | 2.29e-07   | 0.00e+00   | 0.00e+00   
 20    | 4.92e+00   | 58 %       | 1.00e-14   | 2.19e-09   | 2.14e-07   | 0.00e+00   | 0.00e+00   
 21    | 5.67e+00   | 58 %       | 9.13e-15   | 4.90e-09   | 1.45e-07   | 0.00e+00   | 0.00e+00   
 22    | 9.65e+00   | 55 %       | 1.40e-14   | 5.74e-10   | 2.56e-07   | 0.00e+00   | 0.00e+00   
 23    | 8.36e+00   | 56 %       | 8.47e-15   | 1.54e-09   | 2.13e-07   | 0.00e+00   | 0.00e+00   
 24    | 3.97e-01   | 71 %       | 1.00e-14   | 1.16e-09   | 1.34e-07   | 0.00e+00   | 0.00e+00   
 25    | 8.76e+00   | 56 %       | 1.22e-14   | 4.02e-09   | 1.91e-07   | 0.00e+00   | 0.00e+00   
 26    | 5.94e+00   | 58 %       | 8.91e-15   | 1.24e-09   | 1.41e-07   | 0.00e+00   | 0.00e+00   
 27    | 9.53e+00   | 55 %       | 9.72e-15   | 4.66e-09   | 1.86e-07   | 0.00e+00   | 0.00e+00   
 28    | 7.13e+00   | 57 %       | 5.07e-15   | 4.80e-10   | 1.59e-07   | 0.00e+00   | 0.00e+00   
 29    | 1.13e+01   | 54 %       | 6.65e-15   | 1.43e-09   | 2.47e-07   | 0.00e+00   | 0.00e+00   
 30    | 3.82e+00   | 60 %       | 1.34e-14   | 1.26e-09   | 1.58e-07   | 0.00e+00   | 0.00e+00   
 31    | 1.08e+01   | 55 %       | 1.06e-14   | 4.06e-09   | 2.33e-07   | 0.00e+00   | 0.00e+00   
 32    | 9.98e+00   | 55 %       | 1.27e-14   | 1.70e-09   | 2.29e-07   | 0.00e+00   | 0.00e+00   
 33    | 4.78e+00   | 59 %       | 9.49e-15   | 4.32e-09   | 2.08e-07   | 0.00e+00   | 0.00e+00   
 34    | 1.09e+01   | 55 %       | 1.22e-14   | 5.75e-10   | 2.63e-07   | 0.00e+00   | 0.00e+00   
 35    | 1.67e+01   | 53 %       | 1.61e-14   | 1.75e-09   | 3.59e-07   | 0.00e+00   | 0.00e+00   
 36    | 1.76e+01   | 52 %       | 1.02e-14   | 1.29e-09   | 3.73e-07   | 0.00e+00   | 0.00e+00   
 37    | 6.76e+00   | 57 %       | 5.15e-15   | 3.87e-09   | 2.65e-07   | 0.00e+00   | 0.00e+00   
 38    | 5.92e+00   | 58 %       | 1.08e-14   | 1.60e-09   | 1.65e-07   | 0.00e+00   | 0.00e+00   
 39    | 1.02e+01   | 55 %       | 1.71e-14   | 4.82e-09   | 2.46e-07   | 0.00e+00   | 0.00e+00   
 40    | 1.10e+01   | 55 %       | 1.71e-14   | 4.86e-10   | 2.67e-07   | 0.00e+00   | 0.00e+00   
 41    | 1.34e+01   | 54 %       | 1.38e-14   | 1.74e-09   | 2.97e-07   | 0.00e+00   | 0.00e+00   
 42    | 1.12e+01   | 54 %       | 7.38e-15   | 1.36e-09   | 2.29e-07   | 0.00e+00   | 0.00e+00   
 43    | 4.65e+00   | 59 %       | 1.16e-14   | 3.85e-09   | 2.09e-07   | 0.00e+00   | 0.00e+00   
 44    | 9.67e+00   | 55 %       | 6.83e-15   | 1.65e-09   | 1.63e-07   | 0.00e+00   | 0.00e+00   
 45    | 1.02e+01   | 55 %       | 1.25e-14   | 4.99e-09   | 2.20e-07   | 0.00e+00   | 0.00e+00   
Total iterations: 45, Calculation time: 2.60 s, Iterations per second: 17.33
The solver does not seem to make any progress, aborting calculation. Residual value is 1.02e+01. This frequently happens, if the solver pushes the fluid properties out of their feasible range.

##### RESULTS (SimpleHeatExchanger) #####
+-------+-----------+----------+----------+----------+----------+----------+----------+---------+----------+----------+
|       |         Q |       pr |       dp |     zeta |        D |        L |       ks |   ks_HW |       kA |     Tamb |
|-------+-----------+----------+----------+----------+----------+----------+----------+---------+----------+----------|
| BHE1  | -3.07e+03 | 9.88e-01 | 3.33e-02 | 4.12e+08 | 2.15e-02 | 5.00e+01 | 1.00e-05 |     nan | 5.00e+11 | 2.83e+02 |
| BHE10 | -1.30e+04 | 9.65e-01 | 1.02e-01 | 3.13e+08 | 2.15e-02 | 5.00e+01 | 1.00e-05 |     nan | 1.00e+03 | 2.83e+02 |
| BHE11 | -1.30e+04 | 9.65e-01 | 1.02e-01 | 3.13e+08 | 2.15e-02 | 5.00e+01 | 1.00e-05 |     nan | 1.00e+03 | 2.83e+02 |
| BHE12 | -1.30e+04 | 9.65e-01 | 1.02e-01 | 3.13e+08 | 2.15e-02 | 5.00e+01 | 1.00e-05 |     nan | 1.00e+03 | 2.83e+02 |
| BHE13 | -2.60e+04 | 7.25e-01 | 1.10e+00 | 2.11e+08 | 2.15e-02 | 5.00e+01 | 1.00e-05 |     nan | 1.00e+03 | 2.83e+02 |
| BHE2  | -2.57e+03 | 9.88e-01 | 3.33e-02 | 4.10e+08 | 2.15e-02 | 5.00e+01 | 1.00e-05 |     nan | 1.00e+03 | 2.83e+02 |
| BHE3  | -3.07e+03 | 9.88e-01 | 3.33e-02 | 4.12e+08 | 2.15e-02 | 5.00e+01 | 1.00e-05 |     nan | 5.00e+11 | 2.83e+02 |
| BHE4  | -2.57e+03 | 9.88e-01 | 3.33e-02 | 4.10e+08 | 2.15e-02 | 5.00e+01 | 1.00e-05 |     nan | 1.00e+03 | 2.83e+02 |
| BHE5  | -2.57e+03 | 9.88e-01 | 3.33e-02 | 4.10e+08 | 2.15e-02 | 5.00e+01 | 1.00e-05 |     nan | 1.00e+03 | 2.83e+02 |
| BHE6  | -2.57e+03 | 9.88e-01 | 3.33e-02 | 4.10e+08 | 2.15e-02 | 5.00e+01 | 1.00e-05 |     nan | 1.00e+03 | 2.83e+02 |
| BHE7  | -2.57e+03 | 9.88e-01 | 3.33e-02 | 4.10e+08 | 2.15e-02 | 5.00e+01 | 1.00e-05 |     nan | 1.00e+03 | 2.83e+02 |
| BHE8  | -2.57e+03 | 9.88e-01 | 3.33e-02 | 4.10e+08 | 2.15e-02 | 5.00e+01 | 1.00e-05 |     nan | 1.00e+03 | 2.83e+02 |
| BHE9  | -1.30e+04 | 9.65e-01 | 1.02e-01 | 3.13e+08 | 2.15e-02 | 5.00e+01 | 1.00e-05 |     nan | 1.00e+03 | 2.83e+02 |
+-------+-----------+----------+----------+----------+----------+----------+----------+---------+----------+----------+

[fwitte]

Hi @sorheimen,

thank you for reaching out. This seems to be a half parameter specification issue and half numerical issues, and then followed by a bug in tespy. It is a very similar situation as described here: #706 (comment)

• First the postprocessing for some of the BHEs (no 1, 3, 4 and 8 for me) results in kA being np.nan. This is because the outflow temperature results in a temperature below the ambient temperature. This should be impossible in your setup, but for numerical stability of the equations, the calculation is internally modifying the respective equation to make it always work in the iterations. What that means: After one iteration the outflow temperature of the fluid is below ambient temperature, then it is impossible to apply the calculation of the kA equation, because the logarithmic temperature difference cannot be calculated with such situations. However, one iteration later, this issue might already be resolved (you never know before fully obtaining the solution). Therefore, what is done is this:

  tespy/src/tespy/components/heat_exchangers/simple.py

  Lines 515 to 532 in ec1df92

  	i = self.inl[0]
  	o = self.outl[0]
  	ttd_1 = i.calc_T() - self.Tamb.val_SI
  	ttd_2 = o.calc_T() - self.Tamb.val_SI
  	# For numerical stability: If temperature differences have
  	# different sign use mean difference to avoid negative logarithm.
  	if (ttd_1 / ttd_2) < 0:
  	td_log = (ttd_2 + ttd_1) / 2
  	elif round(ttd_1, 6) == round(ttd_2, 6):
  	td_log = ttd_2
  	elif ttd_1 > ttd_2:
  	td_log = (ttd_1 - ttd_2) / math.log(ttd_1 / ttd_2)
  	else:
  	td_log = (ttd_2 - ttd_1) / math.log(ttd_2 / ttd_1)
  	return td_log

  . The model just makes both temperature differences positive. I guess it can be done more intelligently, I will give it a try and let you know.
• What happens after that when resolving the model or reloading it is an actual bug: With those results being np.nan for kA the original specification of kA done by you is overwritten. This is the reason, why the follow-up simulations cannot converge. I will implement something to prevent this from happening and instead issuing a warning/error, that the converged solution does not produce the same result as the inputted specification.

Best

Francesco

[fwitte]

What happens after that when resolving the model or reloading it is an actual bug: With those results being np.nan for kA the original specification of kA done by you is overwritten. This is the reason, why the follow-up simulations cannot converge. I will implement something to prevent this from happening and instead issuing a warning/error, that the converged solution does not produce the same result as the inputted specification.

Issue #608 will deal with this

For the first issue it might be a bit more tricky, because it is a numerical issue of the solver. I have drafted a first idea over here: #761

[fwitte]

And two more sidenotes:

• You can use "INCOMP::Water" as fluid, which has much faster calculation routines compared to the "normal" water. Since you do not need any kind of evaporation etc. it will be fully working. Also if you need temperatures below 0 °C, there are water glycol mixtures etc. in the "INCOMP" back-end of CoolProp.
• I do not know, what API is implemented in OGS for tespy. So not sure, if it is compatible with the lastest version. Ideally it should, because tespy has changed significantly since older versions (and improved!)

The version below works with the fix implemented in #761

import numpy as np
from tespy.components import (
    SimpleHeatExchanger,
    Merge,
    Pump,
    Sink,
    Source,
    Splitter,
)
from tespy.connections import Connection, Ref, Bus
from tespy.networks import Network
from tespy.tools.characteristics import CharLine as char_line

# %% network
btes = Network(T_unit="K", p_unit="bar", h_unit="kJ / kg")

# %% components
fc_in = Source("from consumer inflow")
fc_out = Sink("from consumer outflow")

sp1 = Splitter("splitter1", num_out=4)
sp2 = Splitter("splitter2", num_out=8)

# bhe:
bhe_name = "BHE1"
assert "BHE1" in bhe_name, "BHE should be named with 'BHE1'"
bhe1 = SimpleHeatExchanger(bhe_name)
bhe_name = "BHE2"
assert "BHE2" in bhe_name, "BHE should be named with 'BHE2'"
bhe2 = SimpleHeatExchanger(bhe_name)
bhe_name = "BHE3"
assert "BHE3" in bhe_name, "BHE should be named with 'BHE3'"
bhe3 = SimpleHeatExchanger(bhe_name)
bhe_name = "BHE4"
assert "BHE4" in bhe_name, "BHE should be named with 'BHE4'"
bhe4 = SimpleHeatExchanger(bhe_name)
bhe_name = "BHE5"
assert "BHE5" in bhe_name, "BHE should be named with 'BHE5'"
bhe5 = SimpleHeatExchanger(bhe_name)
bhe_name = "BHE6"
assert "BHE6" in bhe_name, "BHE should be named with 'BHE6'"
bhe6 = SimpleHeatExchanger(bhe_name)
bhe_name = "BHE7"
assert "BHE7" in bhe_name, "BHE should be named with 'BHE7'"
bhe7 = SimpleHeatExchanger(bhe_name)
bhe_name = "BHE8"
assert "BHE8" in bhe_name, "BHE should be named with 'BHE8'"
bhe8 = SimpleHeatExchanger(bhe_name)
bhe_name = "BHE9"
assert "BHE9" in bhe_name, "BHE should be named with 'BHE9'"
bhe9 = SimpleHeatExchanger(bhe_name)
bhe_name = "BHE10"
assert "BHE10" in bhe_name, "BHE should be named with 'BHE10'"
bhe10 = SimpleHeatExchanger(bhe_name)
bhe_name = "BHE11"
assert "BHE11" in bhe_name, "BHE should be named with 'BHE11'"
bhe11 = SimpleHeatExchanger(bhe_name)
bhe_name = "BHE12"
assert "BHE12" in bhe_name, "BHE should be named with 'BHE12'"
bhe12 = SimpleHeatExchanger(bhe_name)
bhe_name = "BHE13"
assert "BHE13" in bhe_name, "BHE should be named with 'BHE13'"
bhe13= SimpleHeatExchanger(bhe_name)

mg1 = Merge("merge1", num_in=4)

mg2 = Merge("merge2", num_in=8)

#cons = SimpleHeatExchanger("consumer")

# %% connections
fc_bhe13 = Connection(fc_in, "out1", bhe13, "in1")

bhe13_sp1 = Connection(bhe13, "out1", sp1, "in1")
sp1_bhe9 = Connection(sp1, "out1", bhe9, "in1")
sp1_bhe10 = Connection(sp1, "out2", bhe10, "in1")
sp1_bhe11 = Connection(sp1, "out3", bhe11, "in1")
sp1_bhe12 = Connection(sp1, "out4", bhe12, "in1")

bhe9_mg1 =  Connection(bhe9, "out1", mg1, "in1")
bhe10_mg1=  Connection(bhe10, "out1", mg1, "in2")
bhe11_mg1=  Connection(bhe11, "out1", mg1, "in3")
bhe12_mg1=  Connection(bhe12, "out1", mg1, "in4")

mg1_sp2  =  Connection(mg1, "out1", sp2, "in1")

sp2_bhe1 = Connection(sp2, "out1", bhe1, "in1")
sp2_bhe2 = Connection(sp2, "out2", bhe2, "in1")
sp2_bhe3 = Connection(sp2, "out3", bhe3, "in1")
sp2_bhe4 = Connection(sp2, "out4", bhe4, "in1")
sp2_bhe5 = Connection(sp2, "out5", bhe5, "in1")
sp2_bhe6 = Connection(sp2, "out6", bhe6, "in1")
sp2_bhe7 = Connection(sp2, "out7", bhe7, "in1")
sp2_bhe8 = Connection(sp2, "out8", bhe8, "in1")

bhe1_mg2 =  Connection(bhe1, "out1", mg2, "in1")
bhe2_mg2 =  Connection(bhe2, "out1", mg2, "in2")
bhe3_mg2 =  Connection(bhe3, "out1", mg2, "in3")
bhe4_mg2 =  Connection(bhe4, "out1", mg2, "in4")
bhe5_mg2 =  Connection(bhe5, "out1", mg2, "in5")
bhe6_mg2 =  Connection(bhe6, "out1", mg2, "in6")
bhe7_mg2 =  Connection(bhe7, "out1", mg2, "in7")
bhe8_mg2 =  Connection(bhe8, "out1", mg2, "in8")


mg2_fc = Connection(mg2, "out1", fc_out, "in1")

btes.add_conns(
    fc_bhe13, bhe13_sp1,sp1_bhe9,sp1_bhe10,sp1_bhe11,sp1_bhe12,bhe9_mg1 ,bhe10_mg1,bhe11_mg1,bhe12_mg1,mg1_sp2,sp2_bhe1,sp2_bhe2 ,sp2_bhe3 ,sp2_bhe4 ,sp2_bhe5 ,sp2_bhe6 ,sp2_bhe7 ,sp2_bhe8 ,bhe1_mg2 ,bhe2_mg2 ,bhe3_mg2 ,bhe4_mg2 ,bhe5_mg2 ,bhe6_mg2 ,bhe7_mg2 ,bhe8_mg2 ,mg2_fc
)
# bhes
bhe1.set_attr(Tamb=283.13,D=0.0215, L=50, ks=0.00001,kA= 1000.0)
bhe3.set_attr(Tamb=283.13,D=0.0215, L=50, ks=0.00001,kA= 1000.0)
bhe4.set_attr(Tamb=283.13,D=0.0215, L=50, ks=0.00001,kA= 1000.0)
bhe8.set_attr(Tamb=283.13,D=0.0215, L=50, ks=0.00001,kA= 1000.0)

bhe2.set_attr(Tamb=283.13,D=0.0215, L=50, ks=0.00001,kA= 1000.0)
bhe5.set_attr(Tamb=283.13,D=0.0215, L=50, ks=0.00001,kA= 1000.0)
bhe6.set_attr(Tamb=283.13,D=0.0215, L=50, ks=0.00001,kA= 1000.0)
bhe7.set_attr(Tamb=283.13,D=0.0215, L=50, ks=0.00001,kA= 1000.0)
bhe9.set_attr(Tamb=283.13,D=0.0215, L=50, ks=0.00001,kA= 1000.0)
bhe10.set_attr(Tamb=283.13,D=0.0215, L=50, ks=0.00001,kA= 1000.0)
bhe11.set_attr(Tamb=283.13,D=0.0215, L=50, ks=0.00001,kA= 1000.0)
bhe12.set_attr(Tamb=283.13,D=0.0215, L=50, ks=0.00001,kA= 1000.0)
bhe13.set_attr(Tamb=283.13,D=0.0215, L=50, ks=0.00001,kA= 1000.0)

inflow_head = 4.0 # bar

fc_bhe13.set_attr(p=inflow_head, m=0.8, fluid={"INCOMP::Water": 1},T=273.15 + 40.0)
bhe13_sp1.set_attr()

# %% solve
btes.solve("design")

# %% save to csv:
btes.save_csv("tespy_nw")
btes.export("tespy_nw_orig.json")
nw = Network.from_json("tespy_nw_orig.json")
nw.solve(mode="design")
nw.print_results()

[fwitte]

One more update to this: I have now implemented the fix for the convergence of that specification and a fix for not overwriting specifications by the user, if the convergence was not actually achieved (#767). I will make a release soon of version 0.9.5, then your model should work again.

Best