pygfunction 2.2.3

A g-function calculator for Python

pygfunction: A g-function calculator for Python

What is pygfunction?

pygfunction is a Python module for the calculation of thermal response factors, or g-functions, for fields of geothermal boreholes. g-functions form the basis of many simulation and sizing programs for geothermal heat pump systems. g-Functions are superimposed in time to predict fluid and ground temperatures in these systems.

At its core, pygfunction relies on the analytical finite line source solution to evaluate the thermal interference between boreholes in the same bore field. This allows for the very fast calculation of g-functions, even for very large bore fields with hundreds of boreholes.

Using pygfunction, g-functions can be calculated for any bore field configuration (i.e. arbitrarily positionned in space), including fields of boreholes with individually different lengths and radiuses. For regular fields of boreholes of equal size, setting-up the calculation of the g-function is as simple as a few lines of code. For example, the code for the calculation of the g-function of a 10 x 10 square array of boreholes (100 boreholes total):

import pygfunction as gt
import numpy as np
time = np.array([(i+1)*3600. for i in range(24)]) # Calculate hourly for one day
boreField = gt.boreholes.rectangle_field(N_1=10, N_2=10, B_1=7.5, B_2=7.5, H=150., D=4., r_b=0.075)
gFunc = gt.gfunction.gFunction(boreField, alpha=1.0e-6, time=time)
gFunc.visualize_g_function()

Once the g-function is evaluated, pygfunction provides tools to predict borehole temperature variations (using load aggregation methods) and to evaluate fluid temperatures in the boreholes for several U-tube pipe configurations.

Requirements

pygfunction was developed and tested using Python 3.7. In addition, the following packages are needed to run pygfunction and its examples:

• matplotlib (>= 3.5.1),
• numpy (>= 1.21.5)
• scipy (>= 1.7.3)
• SecondaryCoolantProps (>= 1.1)

The documentation is generated using Sphinx. The following packages are needed to build the documentation:

• sphinx (>= 4.4.0)
• numpydoc (>= 1.2.0)

Quick start

Users - Download pip and install the latest release:

pip install pygfunction

Alternatively, download the latest release and run the installation script:

pip install .

Developers - To get the latest version of the code, you can download the repository from github or clone the project in a local directory using git:

git clone https://github.com/MassimoCimmino/pygfunction.git

Install pygfunction in development mode (this requires pip >= 21.1):

pip install --editable .

Once pygfunction is copied to a local directory, you can verify that it is working properly by running the examples in pygfunction/examples/.

Documentation

pygfunction's documentation is hosted on ReadTheDocs.

License

pygfunction is licensed under the terms of the 3-clause BSD-license. See pygfunction license.

Contributing to pygfunction

You can report bugs and propose enhancements on the issue tracker.

To contribute code to pygfunction, follow the contribution workflow.

Contributors

Massimo Cimmino 💻 📖 💡 :rocket: 🤔 🚧 👀

Jack Cook 💻 💡 🤔 📖

Matt Mitchell 💻 🤔

This project follows the all-contributors specification. Contributions of any kind welcome!

History of changes

Version 2.2.3 (2024-07-01)

New features

• Issue 276 - Added functions to the boreholes module for the generation of rectangular fields in a staggered configuration.

Enhancements

• Issue 291 - Simplified the expressions in heat_transfer._finite_line_source_steady_state`. The function is now approximately 25% faster.

Bug fixes

• Issue 255 - Default to an orientation of 0. when tilt is 0. in boreholes.Borehole class.
• Issue 266 - Fixed an issue were SingleUTube.get_temperature returned incorrect results when the fluid-to-pipe wall resistance was small in coaxial configurations. New coefficients are introduced in SingleUTube.coefficients_temperature and SingleUTube.coefficients_outlet_fluid_temperature. This also solves issues encountered when the fluid mass flow rate is small.
• Issue 274 - Fixed scalar assignment from ndim-1 array. It is deprecated as of numpy version 1.25. Only ndim-0 arrays can be treated as scalars.
• Issue 285 - Use numpy.complex128 instead of numpy.cfloat. This is to comply with backward-incompatible changes introduced in numpy version 2.0.
• Issue 286 - Fixed incorrect coefficients in pipes.SingleUTube._continuity_condition_base which caused errors in all dependent class methods when segment_ratios were not symmetric around the borehole mid-length.
• Issue 298 - Fixed incorrect coefficients in pipes._basePipe, pipes.MultipleUTube and pipes.IndependentMultipleUTube which caused errors in fluid temperature profiles and outlet fluid temperatures.

Version 2.2.2 (2023-01-09)

Enhancements

• Issue 204 - Added support for Python 3.9 and 3.10. CoolProp is removed from the dependencies and replace with SecondaryCoolantProps.

Bug fixes

• Issue 231 - Fixed an issue where the evaluation of g-functions at very low times raises an error due a singular matrix. g-Functions below a threshold time value t=max(r_b)**2/(25*alpha) are now linearized.

Other changes

• Issue 229, Issue 247 - Added citation to IGSHPA conference paper on pygfunction v2.2 in the documention. Added a CITATION.cff file to suggest a correct citation on github.
• Issue 230 - Configured github actions to publish pygfunction on Pypi on creation of a release on github.

Version 2.2.1 (2022-08-12)

Bug fixes

• Issue 220 - Fixed the expected line length in boreholes.field_from_file() to correctly import fields of inclined boreholes.
• Issue 224 - Fixed an issue where tests were not run on maintenance branches.

Version 2.2.0 (2022-07-10)

New features

• Issue 50 - Implemented inclined boreholes for the evaluation of g-functions. The implementation includes an approximation of the FLS solution for inclined boreholes based on the method of Cimmino (2021) (see Issue 138). The 'equivalent' solver is not yet supported.
• Issue 138 - Implemented the approximation of the finite line source solution of Cimmino (2021). The approximation avoids the numerical evaluation of integrals. This speeds up the calculation of g-functions when enabled.
• Issue 148 - Implemented effective_borehole_thermal_resistance() and local_borehole_thermal_resistance() methods for all pipe classes. Deprecated pipes.borehole_thermal_resistance(), which computed the effective borehole thermal resistance. It will be removed in v3.0.0. Implemented a new update_thermal_resistances() method to all pipe classes. This method allows to update the delta-circuit of thermal resistance of the boreholes based on provided values for the fluid thermal resistances. This allows simulations with time-variable fluid thermal resistances.

Enhancements

• Issue 152 - Vectorized coefficients_temperature and _general_solution in pipe objects to accept depths z as an array. This speeds up calculations for get_temperature and get_borehole_heat_extraction_rate class methods.
• Issue 183 - Vectorized pipes.multipole() and pipes._Fmk() to decrease the calculation time of pipes.thermal_resistances(). A memoization technique is implemented to reduce computation time for repeated function calls to further speed-up the initialization of Pipe and Network objects.
• Issue 198 - Refactored the 'detailed' solver to evaluate same-borehole thermal response factors in a single call to finite_line_source_vectorized(). This speeds up calculations of g-functions using the 'detailed' solver.
• Issue 199 - Changed the integral bounds to avoid repeated evaluation of integrals over semi-infinite intervals. This speeds up calculations of g-functions using all solvers and the evaluation of the finite line source solution with time as an array.
• Issue 206 - Refactored boreholes.find_duplicates() to use scipy.spatial.distance.pdist() for the calculation of distances between boreholes. This leads to faster initialization of the gFunction class for large borefields.

Other changes

• Issue 80 - Added references to the pipes module for the evaluation of borehole thermal resistances.
• Issue 171 - Refactored modules and examples to use the built-in enumerate(x) instead of range(len(x)).
• Issue 172 - Refactored reports of calculation time to use time.perf_counter() instead of time.time().
• Issue 173 - Refactored strings into f-strings instead of using str.format().
• Issue 177 - Converted setup.py script to setup.cfg and pyproject.toml files. This is motivated by PEP518 and PEP621.
• Issue 179 - Refactored tests to use the pytest package instead of unittests.
• Issue 180 - Configured tox and github actions for continuous integration.

Bug fixes

• Issue 192 - Fixed comparison of time with numpy.inf in heat_transfer.finite_line_source that caused the function to fail when time is an array.
• Issue 193 - Fixed heat_transfer._finite_line_source_integrand, heat_transfer._finite_line_source_equivalent_boreholes_integrand, and heat_transfer._finite_line_source_steady_state to return an array of zeros of the expected shape when reaSource==False and imgSource==False.
• Issue 196 - Fixed "invalid escape sequence" warnings when running tests on github actions.
• Issue 202 - Added missing package recommonmark to requirements for documentation and development.
• Issue 208 - Fixed an issue where boreholes.field_from_file() failed when the text file only contained 1 borehole.

Version 2.1.0 (2021-11-12)

New features

• Issue 36 - Added a Coaxial class to the pipes module to model boreholes with coaxial pipes.
• Issue 135 - Added functionality for non-uniform discretization of the segments along the boreholes. This increases the accuracy of g-function calculations for the same number of segments when compared to a uniform discretization. Segment lengths are defined using the segment_ratios option in the gFunction class. A discretize function is added to the utilities module to generate borehole discretizations using an expanding mesh.
• Issue 146 - Added new solver 'equivalent' to the gFunction class. This solver uses hierarchical agglomerative clustering to identify groups of boreholes that are expected to have similar borehole wall temperatures and heat extraction rates. Each group of boreholes is represented by a single equivalent borehole. The FLS solution is adapted to evaluate thermal interactions between groups of boreholes. This greatly reduces the number of evaluations of the FLS solution and the size of the system of equations to evaluate the g-function.

Enhancements

• Issue 118 - Refactored checks for stored _BasePipe and Network coefficicients to use numpy.all(). This decreases calculation time.
• Issue 119 - Refactored Network class to change how coefficient matrices are calculated. This decreases calculation time.
• Issue 132 - Refactored SingleUtube and MultipleUTube classes to eliminate for loops in the calculation of matrix coefficients. This decreases calculation time when nSegments>>1.
• Issue 133 - The nSegments argument is now able to take in the number of segments for each borehole as a list. Each borehole must be split into at least 1 segment, and the length of the segment list must be equal to the number of boreholes.
• Issue 141 - Changed the calculation of the convective heat transfer coefficient in the transition region (2300. < Re < 4000.) by convective_heat_transfer_coefficient_circular_pipe(). The Nusselt number is now interpolated between the laminar value (at Re = 2300.) and the turbulent value (at Re = 4000.). This avoids any discontinuities in the values of the convective heat transfer coefficient near Re = 2300..

Other changes

• Issue 93 - Reformatted pipes and networks modules to use the @ matrix product operator introduced in PEP465. This improves readability of the code.
• Issue 100 - Replaced calls to numpy.asscalar() with calls to array.item(). numpy.asscalar() is deprecated as of numpy version 1.16.
• Issue 124 - Reformatted pipesand networks modules to clarify the expected values for m_flow parameters. These are replaced by any of m_flow_pipe, m_flow_borehole or m_flow_network depending on the function or class method. Added a nomenclature of commonly used variables to the documentation.
• Issue 125 - Refactored class methods and docstrings in Pipe and Network objects to better represent the expected shapes of array inputs and outputs.
• Issue 139 - Updated requirements for numpy from version 1.19.2 to 1.20.1. Clarified the Python version 3.7 requirement in the README.md file.
• Issue 154 - Replaced numpy.int and numpy.bool dtypes in array initializations with built-in types int and bool. numpy.int and numpy.bool are deprecated as of numpy version 1.20.
• Issue 158 - Changed default parameter values for g-function calculations. The gFunction class now uses the 'equivalent' solver by default and a non-uniform discretization of nSegments=8 given by utilities.segment_ratios().
• Issue 160 - Deprecated functions gfunction.uniform_heat_extraction, gfunction.uniform_temperature, gfunction.equal_inlet_temperature and gfunction.mixed_inlet_temperature. They will be removed in v3.0.0.

Bug fixes

• Issue 99 - Fixed an issue where MultipleUTube._continuity_condition() and MultipleUTube._general_solution() returned complex valued coefficient matrices.
• Issue 130 - Fix incorrect initialization of variables _mix_out and _mixing_m_flow in Network.
• Issue 155 - Fix incorrect initialization of variables in Network and _BasePipe. Stored variables are now initialized as numpy.nan instead of numpy.empty.
• Issue 159 - Fix segment_ratios function in the utilities module to always expect 0 < end_length_ratio < 0.5, and allows for nSegments=1 or nSegments=2. If 1<=nSegments<3 then the user is warned that the end_length_ratio parameter is being over-ridden.

Version 2.0.0 (2021-05-22)

New features

• Issue 33, Issue 54, Issue 85 - New class gFunction for the calculation of g-functions. The new class is a common interface to all boundary conditions and calculation methods. The new implementation of the solver reduces the memory requirements of pygfunction. The new class implements visualization features for the g-function and for heat extraction rates and borehole wall temperatures (both as a function of time and for the profiles along the borehole lengths).
• Issue 75 - New module media with properties of brine mixtures.
• Issue 81 - Added functions to find a remove duplicate boreholes.

Enhancements

• Issue 78, Issue 109 - Optimization of solvers for the calculation of g-functions. The finite line source (FLS) solution is now calculated using scipy.integrate.quad_vec which significantly improves calculation time over scipy.integrate.quad. The identification of similarities in the 'similarities' solver has also been refactored to identify similarities between boreholes as an intermediate step before identifying similarities between segments. The calculation time for the identification of similarities is significantly decreased.
• Issue 94 - Refactor visualization functions and methods to uniformize figure styles across modules.
• Issue 108 - Optimize the load aggregation algorithm of Claesson and Javed using numpy.einsum().
• Issue 112 - Optimization of _BaseSolver.temporal_superposition(). The computationally expensive for loop is replaced by a call to numpy.einsum(). This decreases the calculation time of large bore fields.
• Issue 114 - Optimization of _finite_line_source_integrand(). The call to _erfint() is now vectorized. This decreases the number of calls by a factor 8 during integration. The calculation time of g-functions is decreased, especially for smaller bore fields.

Bug fixes

• Issue 86 - Documentation is now built using Python 3 to support Python 3 features in the code.
• Issue 103 - Fixed gFunction class to allow both builtin float and numpy.floating inputs.
• Issue 104 - Raise an error if g-function is calculated with inclined boreholes. This will be supported in a later version of pygfunction.

Other changes

• Issue 72 - Added a list of contributors to the front page. The list is managed using all-contributors.
• Issue 87 - Drop support for Python 2. All package requirements are updated to the latest conda version.
• Issue 96 - Added a reference to the conference paper introducing pygfunction in the documentation.

Version 1.1.2 (2021-01-21)

New features

• Issue 47 - Added verification of the validity of pipe geometry to pipe classes. Extended visualization of the borehole cross-section.
• Issue 66 - Added a class method to the Claesson & Javed load aggregation method to retrieve the thermal response factor increment.

Enhancements

• Issue 59 - Use a relative tolerance instead of an absolute tolerance in the identification of borehole pair similarities. This provides faster execution times and similar accuracy.

Bug fixes

• Issue 58 - Store matrix coefficients in Network class methods for re-use when inlet conditions are constant.
• Issue 64 - Fixed an issue where the g-function was returned as an array of integers if time values were integers.

Version 1.1.1 (2020-06-20)

New features

• Issue 40 - Added Network class for simulations involving networks of boreholes.

Bug fixes

• Commit a4f6591 - Fixed import of Axes3D necessary in borehole.visualize_field().

Version 1.1.0 (2018-03-09)

New features

• Commit 2bd12bd - Implemented UTube.visualize_pipes() class method.
• Issue 30 - Laminar regime is now considered for calculation of convection heat transfer coefficient.
• Issue 32 - g-Functions for bore fields with mixed series and parallel connections between boreholes.

Bug fixes

• Commit 2523f67 - boreholes.visualize_field() now returns the figure object.
• Issue 25 - Fixed documentation of ./examples/uniform_temperature.py.
• Issue 27 - thermal_response_factors() is now part of the heat_transfer module (moved from gfunction).
• Commit 1f59872 - Fixed incorrect summation limit in pipes._F_mk.

Version 1.0.0 (2017-12-01)

New features

• Issue 4 - Unit testing and integration with Travis CI.
• Issue 16 - Added capability to import bore field from external text files.
• Issue 18 - Added capability to visualize bore fields.
• Issue 20 - Added utilities module.
• Issue 5 - Added setup.py installation script using setuptools. pygfunction will now be available on pypi.

Bug fixes

• Commit 0b2d364 - boreholes.U_shaped_field() and boreholes.U_shaped_field() did not construct the field properly when called with low form factors
• Commit 62acd42 - Criteria for smooth pipe correlation in calculation of Darcy friction factor was too large. Colebrooke-White equation is now always used for turbulent flow.
• Issue 14 - Evaluate g-functions at a single time value.
• Commit 7b408e9 - Fix interpolation of thermal response factors in cases where the minimum timestep does not correspond to the first timestep. This also fixes errors caused by rounding errors in the interpolation.
• Issue 22 - Allow 1d arrays for g-function values in the initilization of load aggregation algorithms.

Version 0.3.0 (2017-10-17)

New features

• Issue 6 - Store coefficients in pipe models for faster computation
• Issue 7 - Multipole method to evaluate borehole internal resistances

Copyright (c) 2017-2024, Massimo Cimmino All rights reserved.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

• Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.

• Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

• Neither the name of pygfunction nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.

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