Solar-powered NH3-H2O absorption refrigerator for off-grid cooling — thermodynamic model, CAD, P&ID
Python
1
20 commits
updated Oct 5, 2026
See what people are saying
README
Solar Absorption Fridge
Solar-powered NH₃-H₂O absorption refrigeration system for off-grid use. Designed for household deployment in Sudan and similar climates.
Overview
A research-stage design and simulation repository for a solar-powered absorption refrigerator. Its stated performance values are model targets, not independently demonstrated prototype results or a released build design.
Not approved for fabrication, pressure testing, ammonia charging, or operation. This project contains unresolved pressure, material, geometry, and safety issues. Do not build from the repository; see the build-release gate.
We welcome independent technical review from engineers and researchers worldwide. See the engineering validation call.
| Parameter | Value |
|---|---|
| Cooling capacity | 200 W |
| Cold box | 150 L (2 to 8 °C) |
| Working pair | NH₃ (refrigerant) + H₂O (absorbent) |
| COP | 0.424 |
| Solar collector | CPC, 1.59 m² aperture |
| Generator temperature | 135 °C |
| Operating pressures | 2.36 bar (low) / 15.55 bar (high) |
Full design in docs/DESIGN_SUMMARY.md.
Why this exists
CoolProp's HEOS backend requires departure-function parameters (βij, γij) for every binary pair. For ammonia-water (CAS 7664-41-7 + 7732-18-5), those parameters are not available.
This is a deliberate design choice, not an oversight. As clarified by the CoolProp maintainer in CoolProp Issue #341:
"I think this is a little bit out of scope to use non-reference-grade models in CoolProp for a system that wants a reference-grade implementation."
CoolProp's scope is limited to reference-grade formulations (Helmholtz free energy, IAPWS-2001). The Gibbs-excess class of models — including Ziegler-Trepp — is explicitly out of scope.
This project provides a validated engineering alternative for users who need ammonia-water mixture properties without a REFPROP license.
Three paths for NH₃-H₂O properties
| Path | Status | Accuracy | License |
|---|---|---|---|
| CoolProp (pure components) | Works today | NIST-traceable, < 0.1% | MIT |
teqp AmmoniaWaterTillnerRoth | Works on x86_64 | IAPWS-2001 reference | MIT |
| Ziegler-Trepp (this repo) | Validated | ±0.63 °C vs CoolProp | MIT |
Validation Results
The Ziegler-Trepp implementation was validated against CoolProp for pure components and published literature for the mixture.
| Test | Computed | Reference | Error |
|---|---|---|---|
| Pure NH₃ at 15.5 bar | 39.70 °C | 40.0 °C (CoolProp) | 0.30 °C |
| Pure NH₃ at 10 bar | 24.65 °C | 24.9 °C (CoolProp) | 0.25 °C |
| Pure H₂O at 1 bar | 98.98 °C | 99.6 °C (NIST) | 0.62 °C |
| y_NH₃ at 15.5 bar, x=0.25 | 0.9059 | 0.90–0.92 (Herold) | in band |
| Cycle COP (T_gen = 135 °C) | 0.424 | 0.4–0.6 (published) | within band |
| Energy balance closure | 0.00 W | 0.00 W (ideal) | exact |
Full numerical comparison against teqp (IAPWS-2001): 12 points, P = 1 to 25 bar, max error 0.63 °C, mean error 0.32 °C.
See src/thermo/comparison/teqp_vs_zt.py
and results/logs/ for details.
Testing Notes
Five independent approaches were tested. Full summary:
| Approach | Status | Notes |
|---|---|---|
| CoolProp (pure components) | ✅ Works | NIST-traceable, < 0.1% error |
| Ziegler-Trepp (this repo) | ✅ Validated | Max 0.63 °C error vs CoolProp |
teqp AmmoniaWaterTillnerRoth | ✅ Loads | API functional, get_Ar01() verified |
| teqp VLE solvers | ⚠️ Unstable | 56 grid attempts, 0 physical results |
| CoolProp HEOS mixture | ❌ No data | No binary pair for NH₃-H₂O |
Details
- CoolProp does not include binary interaction parameters for NH₃-H₂O. Documented at Issue #341.
- teqp 0.23.2 loads
AmmoniaWaterTillnerRothand exposes the full API. However, the mixture VLE solvers (mixture_VLE_px,mix_VLE_Tp) fail to converge for NH₃-H₂O with physically plausible initial guesses. Documented at teqp Issue #193. - Ziegler-Trepp (this repository) is the validated engineering alternative. It is a Gibbs-excess model, not a Helmholtz reference formulation, which is why it is not suitable for direct inclusion in CoolProp.
Quick Start
git clone https://github.com/claythe3ed/solar-absorption-fridge.git
cd solar-absorption-fridge
python3 -m venv venv
source venv/bin/activate
pip install -r requirements.txt
# Thermodynamic validation
python src/thermo/ziegler_trepp_props.py
# Full cycle model
python src/thermo/cycle_model.py
# teqp vs Ziegler-Trepp comparison
python src/thermo/comparison/teqp_vs_zt.py
# Solar collector sizing
python src/geometry/solar_collector.py
# Mechanical components sizing
python src/geometry/components_sizing.py
# Bill of Materials
python src/geometry/bom_quantities.py
Requirements
· Python 3.12 or newer · CoolProp 8.0 · numpy, scipy, matplotlib · teqp 0.23.2 (optional, for validation)
Design Summary
Component Specification Cooling capacity 200 W Cold box 150 L, target 2–8 °C COP 0.424 Working pair NH₃ (refrigerant) + H₂O (absorbent) Generator / receiver 200 mm × 4 m carbon steel, 2.5 mm wall, 48.5 kg Solar collector CPC, 400 mm aperture, 3.98 m length, 1.59 m² Condenser 7.5 m × 15 mm finned steel, air-cooled Evaporator 6.37 m × 10 mm finned steel, in cold box Solution heat exchanger 70% effectiveness, 277 W duty Solution tanks 3.0 L rich + 2.3 L poor Operating pressures 2.36 bar (low) / 15.55 bar (high)
Full design in docs/DESIGN_SUMMARY.md.
Thermodynamic Model
· Pure components (NH₃, H₂O): CoolProp 8.0 (NIST-accurate) · Mixture (NH₃-H₂O): Ziegler-Trepp (1984) Gibbs-excess model · Coefficients E1–E16 cross-validated between two independent sources (Kherris 2013, Sadhukhan et al.) · Bubble and dew points: Patek & Klomfar (1995) · Reference validation: teqp 0.23.2 (AmmoniaWaterTillnerRoth) · 12 pure-component points, max error 0.63 °C · Full mixture VLE comparison: convergence issues documented
CAD Models
All models generated by Python scripts in FreeCAD 1.0 (headless).
Component Dimensions Script Generator 200 mm OD × 4 m, 2.5 mm wall cad/scripts/generator.py CPC Mirror 400 mm × 3980 mm parabolic cad/scripts/all_components.py Condenser 15 mm × 7.5 m, 5 rings cad/scripts/all_components.py Evaporator 10 mm × 6.37 m, 7 rings cad/scripts/all_components.py Cold Box 700 × 700 × 800 mm hollow cad/scripts/all_components.py
Assembly renders in results/plots/.
Bill of Materials
35 items across 8 categories. Quantities only — no prices, since the SDG/USD rate is not stable.
Full list in results/bom.csv. Generator script: src/geometry/bom_quantities.py.
Project Structure
solar-absorption-fridge/
├── src/
│ ├── thermo/ # Thermodynamic models
│ │ ├── ziegler_trepp_props.py
│ │ ├── cycle_model.py
│ │ ├── ammonia_properties.py
│ │ └── comparison/ # teqp vs ZT validation
│ ├── geometry/ # Solar, components, BOM, P&ID
│ └── main.py
├── cad/
│ ├── scripts/ # FreeCAD generator scripts
│ ├── step/ # STEP files
│ └── stl/ # STL files
├── docs/
│ ├── DESIGN_SUMMARY.md
│ ├── SESSION_SUMMARY.md
│ ├── images/ # Engineering diagrams
│ ├── datasheets/ # Coefficient tables
│ ├── patents/ # Reference patents
│ └── report/ # PDF report + HTML source
├── results/
│ ├── plots/ # P&ID, assembly renders
│ ├── logs/ # Simulation logs
│ └── bom.csv # Bill of Materials
└── notes/
└── log.md # Development journal
Documentation
· Design Report (PDF) — 6-page Swiss-design report · Wiki — Detailed design notes · CoolProp Issue #341 — NH₃-H₂O binary pair gap · teqp Issue #193 — ARM64 build + VLE findings · Design Summary — Components and cycle data · Session Summary — Development log
References
· Ziegler & Trepp (1984), Int. J. Refrigeration 7(2):101–106 · Patek & Klomfar (1995), Int. J. Refrigeration 18(4):228–234 · Tillner-Roth & Friend (1998), J. Phys. Chem. Ref. Data 27(1):63–96 · Kherris et al. (2013), Thermal Science 17(3):891–902 · Herold, Radermacher, Klein — Absorption Chillers and Heat Pumps, CRC Press
Related Work
· teqp — Same author as CoolProp. Provides AmmoniaWaterTillnerRoth() as a direct implementation of Tillner-Roth & Friend (1998). Recommended by the CoolProp maintainer. · CoolProp Issue #341 — The long-standing gap this project documents and works around.
License
MIT — see LICENSE.
Author
Muhammad Ali (@claythe3ed)
Similar repos
Solar-powered NH3-H2O absorption refrigerator for off-grid cooling — thermodynamic model, CAD, P&ID
Python
1
20 commits
updated Oct 5, 2026
See what people are saying
README
Solar Absorption Fridge
Solar-powered NH₃-H₂O absorption refrigeration system for off-grid use. Designed for household deployment in Sudan and similar climates.
Overview
A research-stage design and simulation repository for a solar-powered absorption refrigerator. Its stated performance values are model targets, not independently demonstrated prototype results or a released build design.
Not approved for fabrication, pressure testing, ammonia charging, or operation. This project contains unresolved pressure, material, geometry, and safety issues. Do not build from the repository; see the build-release gate.
We welcome independent technical review from engineers and researchers worldwide. See the engineering validation call.
| Parameter | Value |
|---|---|
| Cooling capacity | 200 W |
| Cold box | 150 L (2 to 8 °C) |
| Working pair | NH₃ (refrigerant) + H₂O (absorbent) |
| COP | 0.424 |
| Solar collector | CPC, 1.59 m² aperture |
| Generator temperature | 135 °C |
| Operating pressures | 2.36 bar (low) / 15.55 bar (high) |
Full design in docs/DESIGN_SUMMARY.md.
Why this exists
CoolProp's HEOS backend requires departure-function parameters (βij, γij) for every binary pair. For ammonia-water (CAS 7664-41-7 + 7732-18-5), those parameters are not available.
This is a deliberate design choice, not an oversight. As clarified by the CoolProp maintainer in CoolProp Issue #341:
"I think this is a little bit out of scope to use non-reference-grade models in CoolProp for a system that wants a reference-grade implementation."
CoolProp's scope is limited to reference-grade formulations (Helmholtz free energy, IAPWS-2001). The Gibbs-excess class of models — including Ziegler-Trepp — is explicitly out of scope.
This project provides a validated engineering alternative for users who need ammonia-water mixture properties without a REFPROP license.
Three paths for NH₃-H₂O properties
| Path | Status | Accuracy | License |
|---|---|---|---|
| CoolProp (pure components) | Works today | NIST-traceable, < 0.1% | MIT |
teqp AmmoniaWaterTillnerRoth | Works on x86_64 | IAPWS-2001 reference | MIT |
| Ziegler-Trepp (this repo) | Validated | ±0.63 °C vs CoolProp | MIT |
Validation Results
The Ziegler-Trepp implementation was validated against CoolProp for pure components and published literature for the mixture.
| Test | Computed | Reference | Error |
|---|---|---|---|
| Pure NH₃ at 15.5 bar | 39.70 °C | 40.0 °C (CoolProp) | 0.30 °C |
| Pure NH₃ at 10 bar | 24.65 °C | 24.9 °C (CoolProp) | 0.25 °C |
| Pure H₂O at 1 bar | 98.98 °C | 99.6 °C (NIST) | 0.62 °C |
| y_NH₃ at 15.5 bar, x=0.25 | 0.9059 | 0.90–0.92 (Herold) | in band |
| Cycle COP (T_gen = 135 °C) | 0.424 | 0.4–0.6 (published) | within band |
| Energy balance closure | 0.00 W | 0.00 W (ideal) | exact |
Full numerical comparison against teqp (IAPWS-2001): 12 points, P = 1 to 25 bar, max error 0.63 °C, mean error 0.32 °C.
See src/thermo/comparison/teqp_vs_zt.py
and results/logs/ for details.
Testing Notes
Five independent approaches were tested. Full summary:
| Approach | Status | Notes |
|---|---|---|
| CoolProp (pure components) | ✅ Works | NIST-traceable, < 0.1% error |
| Ziegler-Trepp (this repo) | ✅ Validated | Max 0.63 °C error vs CoolProp |
teqp AmmoniaWaterTillnerRoth | ✅ Loads | API functional, get_Ar01() verified |
| teqp VLE solvers | ⚠️ Unstable | 56 grid attempts, 0 physical results |
| CoolProp HEOS mixture | ❌ No data | No binary pair for NH₃-H₂O |
Details
- CoolProp does not include binary interaction parameters for NH₃-H₂O. Documented at Issue #341.
- teqp 0.23.2 loads
AmmoniaWaterTillnerRothand exposes the full API. However, the mixture VLE solvers (mixture_VLE_px,mix_VLE_Tp) fail to converge for NH₃-H₂O with physically plausible initial guesses. Documented at teqp Issue #193. - Ziegler-Trepp (this repository) is the validated engineering alternative. It is a Gibbs-excess model, not a Helmholtz reference formulation, which is why it is not suitable for direct inclusion in CoolProp.
Quick Start
git clone https://github.com/claythe3ed/solar-absorption-fridge.git
cd solar-absorption-fridge
python3 -m venv venv
source venv/bin/activate
pip install -r requirements.txt
# Thermodynamic validation
python src/thermo/ziegler_trepp_props.py
# Full cycle model
python src/thermo/cycle_model.py
# teqp vs Ziegler-Trepp comparison
python src/thermo/comparison/teqp_vs_zt.py
# Solar collector sizing
python src/geometry/solar_collector.py
# Mechanical components sizing
python src/geometry/components_sizing.py
# Bill of Materials
python src/geometry/bom_quantities.py
Requirements
· Python 3.12 or newer · CoolProp 8.0 · numpy, scipy, matplotlib · teqp 0.23.2 (optional, for validation)
Design Summary
Component Specification Cooling capacity 200 W Cold box 150 L, target 2–8 °C COP 0.424 Working pair NH₃ (refrigerant) + H₂O (absorbent) Generator / receiver 200 mm × 4 m carbon steel, 2.5 mm wall, 48.5 kg Solar collector CPC, 400 mm aperture, 3.98 m length, 1.59 m² Condenser 7.5 m × 15 mm finned steel, air-cooled Evaporator 6.37 m × 10 mm finned steel, in cold box Solution heat exchanger 70% effectiveness, 277 W duty Solution tanks 3.0 L rich + 2.3 L poor Operating pressures 2.36 bar (low) / 15.55 bar (high)
Full design in docs/DESIGN_SUMMARY.md.
Thermodynamic Model
· Pure components (NH₃, H₂O): CoolProp 8.0 (NIST-accurate) · Mixture (NH₃-H₂O): Ziegler-Trepp (1984) Gibbs-excess model · Coefficients E1–E16 cross-validated between two independent sources (Kherris 2013, Sadhukhan et al.) · Bubble and dew points: Patek & Klomfar (1995) · Reference validation: teqp 0.23.2 (AmmoniaWaterTillnerRoth) · 12 pure-component points, max error 0.63 °C · Full mixture VLE comparison: convergence issues documented
CAD Models
All models generated by Python scripts in FreeCAD 1.0 (headless).
Component Dimensions Script Generator 200 mm OD × 4 m, 2.5 mm wall cad/scripts/generator.py CPC Mirror 400 mm × 3980 mm parabolic cad/scripts/all_components.py Condenser 15 mm × 7.5 m, 5 rings cad/scripts/all_components.py Evaporator 10 mm × 6.37 m, 7 rings cad/scripts/all_components.py Cold Box 700 × 700 × 800 mm hollow cad/scripts/all_components.py
Assembly renders in results/plots/.
Bill of Materials
35 items across 8 categories. Quantities only — no prices, since the SDG/USD rate is not stable.
Full list in results/bom.csv. Generator script: src/geometry/bom_quantities.py.
Project Structure
solar-absorption-fridge/
├── src/
│ ├── thermo/ # Thermodynamic models
│ │ ├── ziegler_trepp_props.py
│ │ ├── cycle_model.py
│ │ ├── ammonia_properties.py
│ │ └── comparison/ # teqp vs ZT validation
│ ├── geometry/ # Solar, components, BOM, P&ID
│ └── main.py
├── cad/
│ ├── scripts/ # FreeCAD generator scripts
│ ├── step/ # STEP files
│ └── stl/ # STL files
├── docs/
│ ├── DESIGN_SUMMARY.md
│ ├── SESSION_SUMMARY.md
│ ├── images/ # Engineering diagrams
│ ├── datasheets/ # Coefficient tables
│ ├── patents/ # Reference patents
│ └── report/ # PDF report + HTML source
├── results/
│ ├── plots/ # P&ID, assembly renders
│ ├── logs/ # Simulation logs
│ └── bom.csv # Bill of Materials
└── notes/
└── log.md # Development journal
Documentation
· Design Report (PDF) — 6-page Swiss-design report · Wiki — Detailed design notes · CoolProp Issue #341 — NH₃-H₂O binary pair gap · teqp Issue #193 — ARM64 build + VLE findings · Design Summary — Components and cycle data · Session Summary — Development log
References
· Ziegler & Trepp (1984), Int. J. Refrigeration 7(2):101–106 · Patek & Klomfar (1995), Int. J. Refrigeration 18(4):228–234 · Tillner-Roth & Friend (1998), J. Phys. Chem. Ref. Data 27(1):63–96 · Kherris et al. (2013), Thermal Science 17(3):891–902 · Herold, Radermacher, Klein — Absorption Chillers and Heat Pumps, CRC Press
Related Work
· teqp — Same author as CoolProp. Provides AmmoniaWaterTillnerRoth() as a direct implementation of Tillner-Roth & Friend (1998). Recommended by the CoolProp maintainer. · CoolProp Issue #341 — The long-standing gap this project documents and works around.
License
MIT — see LICENSE.
Author
Muhammad Ali (@claythe3ed)