Exergy Analysis in a GSHP #408

Barandier · 2023-04-18T16:06:22Z

Barandier
Apr 18, 2023

Hello everyone,

I'm quite new in TESPy and I'm trying to perform an exergy analysis in model that comprises a closed loop ground source heat pump. At the moment, I'm working with it in Heating Mode. When I execute the algorithm, both "E_F" and "Epsilon" values in the Network exergy analysis, and the "E_P" value in the generated dataframe are all "nan".
I would like to know, please, if anyone has a solution for this problem.

Thank you very much.

Answered by fwitte

Apr 27, 2023

Thank you.

You added the CycleCloser to the fuel exergy busses, that does not really make sense, since it does not serve any purpose other than modeling. Its balance is not defined and it therfore crashes the analysis. I will make some changes to the source code to prevent people from adding cycle closers to busses.

Also, it is a little bit strange to me, how you are patching the busses to the GHSP function. I have never seen something like this in Python, and it does not really look correct in my eyes. I propose the following solution:

from tespy.components import CycleCloser, HeatExchangerSimple, Pump, HeatExchanger, Compressor, Source, Sink, Valve, Condenser
from tespy.networks import N…

View full answer

fwitte · 2023-04-18T16:18:09Z

fwitte
Apr 18, 2023
Maintainer

Hi @Barandier,

could you share your code here to reproduce the issue?

best

3 replies

Barandier Apr 18, 2023
Author

For sure.

pamb = 1.013  # ambient pressure
Tamb = 2  # ambient temperature

# GSHP Model
def GSHP_Heating(working_fluid, T_ev_in, T_cond_out):
    sec_fluid = 'water'
    T_ev_out = T_ev_in - 15
    T_cond_in = T_cond_out - 15

    # Network
    gshp = Network(fluids=[sec_fluid, working_fluid],
                   T_unit='C',
                   p_unit='bar',
                   h_unit='kJ / kg',
                   m_unit='kg / s',
                   iterinfo=False)

    # Components
    cycle_closer = CycleCloser('Refrigerant Cycle Closer')

    # Heat Source
    heatsource = HeatExchangerSimple('Ground U Tube')
    ground_pump = Pump('Heat Source Pump')
    evaporator = HeatExchanger('Evaporator')
    cc_heatsource = CycleCloser("Cycle Closer Heat Source")

    # Compression
    compressor = Compressor('Compressor')

    # Heat Sink
    in_heatsink = Source("Heat Sink In")
    sink_pump = Pump('Heat Sink Pump')
    condenser = Condenser('Condenser')
    out_heatsink = Sink("Heat Sink Out")

    # Expansion Valve
    exp_valve = Valve('Expansion Valve')

    # Connections
    ## Main Cycle
    c0 = Connection(cycle_closer, 'out1', evaporator, 'in2', label='0')
    c1 = Connection(evaporator, 'out2', compressor, 'in1', label='1')
    c2 = Connection(compressor, 'out1', condenser, 'in1', label='2')
    c3 = Connection(condenser, 'out1', exp_valve, 'in1', label='3')
    c4 = Connection(exp_valve, 'out1', cycle_closer, 'in1', label='4')

    gshp.add_conns(c0, c1, c2, c3, c4)

    ## Heat Source Cycle
    c5 = Connection(cc_heatsource, 'out1', heatsource, 'in1', label='5')
    c6 = Connection(heatsource, 'out1', ground_pump, 'in1', label='6')
    c7 = Connection(ground_pump, 'out1', evaporator, 'in1', label='7')
    c8 = Connection(evaporator, 'out1', cc_heatsource, 'in1', label='8')

    # Heat Sink Cycle
    c9 = Connection(in_heatsink, 'out1', sink_pump, 'in1', label='9')
    c10 = Connection(sink_pump, 'out1', condenser, 'in2', label='10')
    c11 = Connection(condenser, 'out2', out_heatsink, 'in1', label='11')

    gshp.add_conns(c5, c6, c7, c8, c9, c10, c11)

   ## Heat Source Cycle
    c6.set_attr(T=T_ev_in, p=3, fluid={sec_fluid: 1, working_fluid: 0})
    c8.set_attr(T=T_ev_out)

    # Heat Sink Cycle
    c9.set_attr(T=T_cond_in, p=2, fluid={sec_fluid: 1, working_fluid: 0})
    c11.set_attr(T=T_cond_out, p=2)

    # evaporation to fully saturated gas
    c1.set_attr(x=1, fluid={sec_fluid: 0, working_fluid: 1})

    # parametrization components
    # isentropic efficiency
    ground_pump.set_attr(eta_s=0.7, design=['eta_s'], offdesign=['eta_s_char'])
    compressor.set_attr(eta_s=0.85, design=['eta_s'], offdesign=['eta_s_char'])
    sink_pump.set_attr(eta_s=0.8, design=['eta_s'], offdesign=['eta_s_char'])

    # pressure ratios
    condenser.set_attr(pr1=1, pr2=0.995)
    evaporator.set_attr(pr1=0.995, pr2=0.98)
    heatsource.set_attr(pr=0.995)

    # Evaporation Point - STARTING PARAMETERS
    p_eva = PropsSI('P', 'Q', 1, 'T', T_ev_out - 5 + 273.15, working_fluid) * 1e-5
    c1.set_attr(p=p_eva)

    # Condensation Point - STARTING PARAMETERS
    p_cond = PropsSI('P', 'Q', 0, 'T', T_cond_out + 5 + 273.15, working_fluid) * 1e-5
    c3.set_attr(p=p_cond)

    # Consumer Heat Demand
    condenser.set_attr(Q=-1e3)

    # Creating Busses for exergy Analysis
        # characteristic function for motor efficiency
    x = array([0, 0.2, 0.4, 0.6, 0.8, 1, 1.2])
    y = array([0, 0.86, 0.9, 0.93, 0.95, 0.96, 0.95])

    char = CharLine(x=x, y=y)
    GSHP_Heating.power = Bus('Total Power Consumption')
    GSHP_Heating.power.add_comps({'comp': compressor, 'char': char, 'base': 'bus'},
                                 {'comp': ground_pump, 'char': char, 'base': 'bus'},
                                 {'comp': sink_pump, 'char': char, 'base': 'bus'})

    GSHP_Heating.heat_rej_bus = Bus('Heat Rejected')
    GSHP_Heating.heat_rej_bus.add_comps({'comp': in_heatsink, 'base': 'bus'}, {'comp': out_heatsink})

    GSHP_Heating.heat_abs_bus = Bus('Heat Absorbed')
    GSHP_Heating.heat_abs_bus.add_comps({'comp': heatsource, 'base': 'bus'}, {'comp': cc_heatsource})

    gshp.add_busses(GSHP_Heating.power, GSHP_Heating.heat_rej_bus, GSHP_Heating.heat_abs_bus)

    gshp.solve('design')

    # Evaporation Point
    c1.set_attr(p=None)
    evaporator.set_attr(ttd_l=5)

    # Condensation Point
    c3.set_attr(p=None)
    condenser.set_attr(ttd_u=5)

    # Solving it

    gshp.solve('design')
    cop = f'{abs(condenser.Q.val / (compressor.P.val + ground_pump.P.val + sink_pump.P.val)):.2f}'
    print(f'\033[34mCOP with a ground temperature of {T_ev_in}°C with {working_fluid}: {cop}\033[m')

    return gshp

# EXERGY ANALYSIS


def exergyanalysis():

    exergy = ExergyAnalysis(network=GSHP_Heating('R134a', 16, 45),
                            E_F=[GSHP_Heating.power, GSHP_Heating.heat_abs_bus],
                            E_P=[GSHP_Heating.heat_rej_bus])
    exergy.analyse(pamb, Tamb)
    print("\n##### EXERGY ANALYSIS #####\n")
    exergy.print_results()
    comps = ['E_F']
    E_F = exergy.network_data.E_F
    E_D = [0]
    E_P = [E_F]
    for comp in exergy.component_data.index:
        if exergy.component_data.E_D[comp] > 1:
            comps.append(comp)
            E_D.append(exergy.component_data.E_D[comp])
            E_F = E_F - exergy.component_data.E_D[comp]
            E_P.append(E_F)

    comps.append("E_P")
    E_D.append(0)
    E_P.append(E_F)

    df_comps = DataFrame(columns=comps)
    df_comps.loc["E_D"] = E_D
    df_comps.loc["E_P"] = E_P
    df_comps.to_csv('GSHP_Heating_R134a_E_D.csv')
    print(df_comps)


exergyanalysis()

fwitte Apr 27, 2023
Maintainer

Thank you.

You added the CycleCloser to the fuel exergy busses, that does not really make sense, since it does not serve any purpose other than modeling. Its balance is not defined and it therfore crashes the analysis. I will make some changes to the source code to prevent people from adding cycle closers to busses.

Also, it is a little bit strange to me, how you are patching the busses to the GHSP function. I have never seen something like this in Python, and it does not really look correct in my eyes. I propose the following solution:

from tespy.components import CycleCloser, HeatExchangerSimple, Pump, HeatExchanger, Compressor, Source, Sink, Valve, Condenser
from tespy.networks import Network
from tespy.connections import Bus, Connection
from tespy.tools import ExergyAnalysis
from tespy.tools import CharLine

from CoolProp.CoolProp import PropsSI
from numpy import array
from pandas import DataFrame


pamb = 1.013  # ambient pressure
Tamb = 2  # ambient temperature

# GSHP Model
def GSHP_Heating(working_fluid, T_ev_in, T_cond_out):
    sec_fluid = 'water'
    T_ev_out = T_ev_in - 15
    T_cond_in = T_cond_out - 15

    # Network
    gshp = Network(fluids=[sec_fluid, working_fluid],
                   T_unit='C',
                   p_unit='bar',
                   h_unit='kJ / kg',
                   m_unit='kg / s',
                   iterinfo=False)

    # Components
    cycle_closer = CycleCloser('Refrigerant Cycle Closer')

    # Heat Source
    heatsource = HeatExchangerSimple('Ground U Tube')
    ground_pump = Pump('Heat Source Pump')
    evaporator = HeatExchanger('Evaporator')
    cc_heatsource = CycleCloser("Cycle Closer Heat Source")

    # Compression
    compressor = Compressor('Compressor')

    # Heat Sink
    in_heatsink = Source("Heat Sink In")
    sink_pump = Pump('Heat Sink Pump')
    condenser = Condenser('Condenser')
    out_heatsink = Sink("Heat Sink Out")

    # Expansion Valve
    exp_valve = Valve('Expansion Valve')

    # Connections
    ## Main Cycle
    c0 = Connection(cycle_closer, 'out1', evaporator, 'in2', label='0')
    c1 = Connection(evaporator, 'out2', compressor, 'in1', label='1')
    c2 = Connection(compressor, 'out1', condenser, 'in1', label='2')
    c3 = Connection(condenser, 'out1', exp_valve, 'in1', label='3')
    c4 = Connection(exp_valve, 'out1', cycle_closer, 'in1', label='4')

    gshp.add_conns(c0, c1, c2, c3, c4)

    ## Heat Source Cycle
    c5 = Connection(cc_heatsource, 'out1', heatsource, 'in1', label='5')
    c6 = Connection(heatsource, 'out1', ground_pump, 'in1', label='6')
    c7 = Connection(ground_pump, 'out1', evaporator, 'in1', label='7')
    c8 = Connection(evaporator, 'out1', cc_heatsource, 'in1', label='8')

    # Heat Sink Cycle
    c9 = Connection(in_heatsink, 'out1', sink_pump, 'in1', label='9')
    c10 = Connection(sink_pump, 'out1', condenser, 'in2', label='10')
    c11 = Connection(condenser, 'out2', out_heatsink, 'in1', label='11')

    gshp.add_conns(c5, c6, c7, c8, c9, c10, c11)

   ## Heat Source Cycle
    c6.set_attr(T=T_ev_in, p=3, fluid={sec_fluid: 1, working_fluid: 0})
    c8.set_attr(T=T_ev_out)

    # Heat Sink Cycle
    c9.set_attr(T=T_cond_in, p=2, fluid={sec_fluid: 1, working_fluid: 0})
    c11.set_attr(T=T_cond_out, p=2)

    # evaporation to fully saturated gas
    c1.set_attr(x=1, fluid={sec_fluid: 0, working_fluid: 1})

    # parametrization components
    # isentropic efficiency
    ground_pump.set_attr(eta_s=0.7, design=['eta_s'], offdesign=['eta_s_char'])
    compressor.set_attr(eta_s=0.85, design=['eta_s'], offdesign=['eta_s_char'])
    sink_pump.set_attr(eta_s=0.8, design=['eta_s'], offdesign=['eta_s_char'])

    # pressure ratios
    condenser.set_attr(pr1=1, pr2=0.995)
    evaporator.set_attr(pr1=0.995, pr2=0.98)
    heatsource.set_attr(pr=0.995)

    # Evaporation Point - STARTING PARAMETERS
    p_eva = PropsSI('P', 'Q', 1, 'T', T_ev_out - 5 + 273.15, working_fluid) * 1e-5
    c1.set_attr(p=p_eva)

    # Condensation Point - STARTING PARAMETERS
    p_cond = PropsSI('P', 'Q', 0, 'T', T_cond_out + 5 + 273.15, working_fluid) * 1e-5
    c3.set_attr(p=p_cond)

    # Consumer Heat Demand
    condenser.set_attr(Q=-1e3)

    # Creating Busses for exergy Analysis
        # characteristic function for motor efficiency
    x = array([0, 0.2, 0.4, 0.6, 0.8, 1, 1.2])
    y = array([0, 0.86, 0.9, 0.93, 0.95, 0.96, 0.95])

    char = CharLine(x=x, y=y)
    power = Bus('Total Power Consumption')
    power.add_comps({'comp': compressor, 'base': 'bus'},
                                 {'comp': ground_pump, 'base': 'bus'},
                                 {'comp': sink_pump, 'base': 'bus'})

    heat_rej_bus = Bus('Heat Rejected')
    heat_rej_bus.add_comps({'comp': in_heatsink, 'base': 'bus'}, {'comp': out_heatsink})

    heat_abs_bus = Bus('Heat Absorbed')
    heat_abs_bus.add_comps({'comp': heatsource, 'base': 'bus'})

    gshp.add_busses(power, heat_rej_bus, heat_abs_bus)

    gshp.solve('design')

    # Evaporation Point
    c1.set_attr(p=None)
    evaporator.set_attr(ttd_l=5)

    # Condensation Point
    c3.set_attr(p=None)
    condenser.set_attr(ttd_u=5)

    # Solving it

    gshp.solve('design')
    cop = f'{abs(condenser.Q.val / (compressor.P.val + ground_pump.P.val + sink_pump.P.val)):.2f}'
    print(f'\033[34mCOP with a ground temperature of {T_ev_in}°C with {working_fluid}: {cop}\033[m')

    return gshp

# EXERGY ANALYSIS


def exergyanalysis():

    ghsp = GSHP_Heating('R134a', 16, 45)
    exergy = ExergyAnalysis(network=ghsp,
                            E_F=[ghsp.busses["Total Power Consumption"], ghsp.busses["Heat Absorbed"]],
                            E_P=[ghsp.busses["Heat Rejected"]])
    exergy.analyse(pamb, Tamb)
    print("\n##### EXERGY ANALYSIS #####\n")
    exergy.print_results()
    comps = ['E_F']
    E_F = exergy.network_data.E_F
    E_D = [0]
    E_P = [E_F]
    for comp in exergy.component_data.index:
        if exergy.component_data.E_D[comp] > 1:
            comps.append(comp)
            E_D.append(exergy.component_data.E_D[comp])
            E_F = E_F - exergy.component_data.E_D[comp]
            E_P.append(E_F)

    comps.append("E_P")
    E_D.append(0)
    E_P.append(E_F)

    df_comps = DataFrame(columns=comps)
    df_comps.loc["E_D"] = E_D
    df_comps.loc["E_P"] = E_P
    df_comps.to_csv('GSHP_Heating_R134a_E_D.csv')
    print(df_comps)
    print(exergy.network_data)


exergyanalysis()

Note, that the exergy balances do not resolve correctly, there might be some issue in the specifications still. I cannot find the issue for this quickly, so I'll have a look this or next weekend.

Answer selected by fwitte

Barandier Apr 27, 2023
Author

Hello @fwitte, thank you very much for your reply. I will test the code above right away.

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Exergy Analysis in a GSHP #408

Barandier Apr 18, 2023

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