enerhabitat 0.4.0

Thermal simulation of opaque constructive systems (walls and roofs) from EPW data — 1D and 2D

EnerHabitat

EnerHabitat is a Python package for the thermal simulation of opaque constructive systems (walls and roofs) driven by EPW weather data. It solves the time-dependent heat conduction equation across the system and produces indoor temperatures and air-conditioning energy demands for an average day of a chosen month. Homogeneous layer stacks are solved in 1D (System); units that are heterogeneous across their width, such as concrete hollow-block walls and joist-and-block (vigueta y bovedilla) roofs, are solved in 2D over their cross-section (System2D).

📖 Documentation

Full documentation lives at https://ener-habitat.github.io/EnerHabitat/:

• Usage: setup (materials file and configuration), with the executable examples in 1D and 2D, free-running and air-conditioned.
• Theory: 1D model · 2D model · Numerical method (equations, boundary conditions, convergence, validation).
• API reference.

Overview

EnerHabitat models the heat transfer through opaque constructive systems; windows, ventilation, infiltration and internal heat gains are outside its scope. Each layer is described by a material name and three properties: thermal conductivity k (W/(m·K)), density rho (kg/m³) and specific heat c (J/(kg·K)). The properties come from a user-supplied materials.ini file; no defaults are bundled.

Given an EPW file and a constructive system, EnerHabitat computes the outdoor (Ta), sun–air (Tsa), indoor (Ti) and neutrality (Tn) temperatures, the solar irradiances (Ig GHI, Ib DNI, Id DHI and the plane-of-array Is) and the energy demands over the average day of the selected month.

Theoretical background (summary)

EnerHabitat solves the time-dependent heat conduction through the constructive system, in 1D across multilayer stacks and in 2D over the cross-section of non-homogeneous units, with flux continuity at the layer joints. The full derivations (equations, boundary conditions, cavity physics, assumptions and numerical method) are in the theory pages.

At the outdoor surface the boundary condition uses the sun–air temperature, which lumps convection, absorbed solar radiation and the long-wave sky exchange:

$$ T_{sa} = T_a + \frac{a, I_s}{h_o} - RF, $$

with a the solar absorptance, $I_s$ the irradiance on the tilted surface (computed with pvlib) and $RF$ decreasing linearly from 3.9 °C at tilt = 0 (roof) to 0 at tilt = 90 (wall).

At the indoor surface the system exchanges heat with the indoor air, and two solution modes exist. In the free-running mode (solve()) the indoor air is a lumped thermal mass whose temperature Ti evolves freely, and the daily energy delivered to it is reported as energy_transfer. In the air-conditioned mode (solveAC()) Ti is held at the neutrality temperature of the adaptive comfort model of Humphreys & Nicol, $T_n = 0.54,\overline{T_a} + 13.5$ °C, and the required cooling_energy and heating_energy are reported. The average-day data also includes the comfort-zone half-width DeltaTn, after Morillón, for comfort analyses.

For 2D systems, System2D solves the same problem on the unit's cross-section, adding the cavity physics: radiation between the cavity walls (solved as a radiosity enclosure) and temperature-dependent Nusselt convection with a lumped cavity-air node.

The equations are discretised with implicit finite control volumes and solved with the TDMA; the average day is iterated until the solution is periodic. Full derivations, boundary conditions, convergence criteria and the validation record are in the theory pages.

Installation

pip install enerhabitat

With uv:

uv add enerhabitat

EnerHabitat requires Python ≥ 3.10. The section inspector plots are an optional extra: pip install enerhabitat[viz].

Quickstart

EnerHabitat bundles no materials. Create a materials.ini in your working directory (or point eh.config.file to one) before running anything. A minimal file for this example:

[Adobe]
k   = 0.58    # W/(m·K)
rho = 1500    # kg/m³
c   = 1480    # J/(kg·K)

import enerhabitat as eh

# 1) Materials file (required — no defaults are bundled)
eh.config.file = "./materials.ini"

# 2) Location from an EPW file
loc = eh.Location("./epw/example.epw")

# 3) Define the constructive system
wall = eh.System(location=loc)
wall.azimuth = 90                    # east-facing
wall.absortance = 0.3
wall.layers = [("Adobe", 0.20)]      # outside → inside

# 4) Average day and solar inputs
loc.meanDay(month=5, year=2025)
wall.Tsa()

# 5) Solve (free-running); Tsa() and solve() share the same time grid,
#    so results concatenate directly.
ti = wall.solve()
print(wall.energy_transfer)          # J/(m²·day)

For a wall with air conditioning, call wall.solveAC() and read wall.cooling_energy / wall.heating_energy.

2D systems

System2D is used like System (see the API page for the differences). Its layers list contains exactly one 2D element: a HollowBlock (walls, tilt = 90) or a Slab (joist-and-block roofs, tilt = 0). The materials named below (Concreto, Mortero, Yeso) must also be defined in your materials.ini (see the full example set):

block = eh.HollowBlock(
    material   = "Concreto",
    emissivity = 0.9,
    geometry   = {"web": 0.02, "block_width": 0.16,
                  "cover_top": 0.02, "cavity": 0.08, "cover_bottom": 0.02},
)

wall = eh.System2D(eh.Location("./epw/example.epw"))
wall.tilt = 90
wall.azimuth = 90
wall.absortance = 0.6
wall.layers = [("Mortero", 0.02), block, ("Yeso", 0.01)]
wall.location.meanDay(month=5, year=2025)
wall.Tsa()
ti = wall.solve()

⏱ A 2D solve at the default mesh (80×160) takes ~10–20 minutes; the 1D ones take seconds. For a quick smoke test, reduce the mesh first (e.g. eh.config2d.nx, eh.config2d.ny = 24, 60) and check wall.converged.

All the examples (the full 1D/2D × free-running/AC matrix, the joist-and-block roof, and the to-scale section inspector) are in the Usage — 1D and Usage — 2D pages.

API at a glance

Object	Purpose	Key methods / attributes
Location	Reads an EPW file, builds the average day	meanDay(month, year)
System	1D multilayer wall/roof	layers, Tsa(), solve(), solveAC(), Tso, Tsi, energy_transfer, cooling_energy, heating_energy, days, converged
System2D	2D heterogeneous wall/roof	mirror of System (see the API page for the differences), plus preview(), section_report(), Thueco, Tfield
HollowBlock / Slab	The 2D element inside System2D.layers	material(s), fill_type (Fill.AIR/Fill.SOLID), geometry
config	Global parameters	file, La, Nx, ho, hi, hi_up, hi_down, hi_flow, dt (fixed)
config2d	2D mesh & convergence	nx, ny, tol_inner, tol_day, max_days, max_inner

The film coefficients are the NOM-008/020-ENER values: ho = 13 and, for walls, hi = 8.1 W/(m²·K); roofs switch every time step between hi_up = 9.4 (upward heat flow) and hi_down = 6.6 (downward). Set hi_flow = False to force the fixed hi everywhere. dt is fixed at 10 s (see why). Full reference: API page.

Dependencies

Direct dependencies: numba and pvlib (numpy, pandas and pytz come with them). Optional: matplotlib via enerhabitat[viz].

How to cite

If you use EnerHabitat in academic work, please cite the reference paper:

Barrios, G., Casas, J.M., Huelsz, G., Rojas, J. (2016). Ener-Habitat: An online numerical tool to evaluate the thermal performance of homogeneous and non-homogeneous envelope walls/roofs. Solar Energy 131, 296–304. https://doi.org/10.1016/j.solener.2015.12.017

@article{Barrios2016,
  author  = {Barrios, G. and Casas, J.M. and Huelsz, G. and Rojas, J.},
  title   = {Ener-Habitat: An online numerical tool to evaluate the thermal
             performance of homogeneous and non-homogeneous envelope walls/roofs},
  journal = {Solar Energy},
  volume  = {131},
  pages   = {296--304},
  year    = {2016},
  doi     = {10.1016/j.solener.2015.12.017}
}

The repository also ships a CITATION.cff (GitHub's Cite this repository button) covering the software itself.

Authors of the package

Developed at the Instituto de Energías Renovables, UNAM.

• Guillermo Barrios del Valle, [e-mail]
• Fernando Rodríguez Calderón, [e-mail]

Source code: https://github.com/Ener-Habitat/EnerHabitat · Issues: https://github.com/Ener-Habitat/EnerHabitat/issues

License

Released under the MIT License.