raw · papers · ingested 2026-09-19
Space Cooling Using Geothermal Single-Effect Water/Lithium Bromide Absorption Chiller (El Haj Assad et al. 2021) + Zhao et al. 2024 LiBr vs LiCl
Source: https://doi.org/10.1002/ese3.946
Provenance: Peer-reviewed modelling study (EES), 39 citations; open-access full text read from the Aalborg VBN copy. Companion Zhao et al. 2024 is open access at Oxford. Retrieved via research agent.
Concept
Reject geofluid from a single-flash geothermal power plant (production well 250 °C, separator 0.24 MPa, condenser 7.5 kPa; plant thermal efficiency 12.9–13%) is routed to the desorber of a single-effect LiBr/H₂O chiller before reinjection — cooling “bottomed” on a power plant. Case load: 39 kW residence in Sharjah, UAE (design 40 °C DB / 28 °C WB, max 43 °C).
Design point (generator inlet 100 °C, 1 kg/s geofluid)
| Component | kW |
|---|---|
| Generator (desorber) | 14.7 |
| Evaporator (cooling) | 10.7 |
| Condenser | 11.3 |
| Absorber | 14.1 |
| Solution HX | 3.1 |
| Pump | 0.02 |
| COP | 0.73 |
Cycle pressures 7.406 kPa / 0.676 kPa; LiBr concentrations 62.16% / 56.48%.
Parametric findings
- Minimum drive temperature: “To operate a single-effect water/lithium bromide absorption chiller, the supplied heat needs to be at least at 90 °C.” Studied desorber inlet 70–120 °C.
- COP reaches ~0.87 at 120 °C geofluid with solution-HX effectiveness 0.9. COP falls as geofluid temperature rises further (heat input grows faster than cooling) while capacity rises.
- Geofluid mass flow (1, 10, 50 kg/s) has essentially no effect on COP or capacity once heat-exchanger size is fixed — HX UA and drive temperature are the design levers.
- Crystallization: not recommended to operate at 90 °C and 110 °C with absorber UA above 1.9 and 2.5 kW/K respectively “due to the possible crystallization of LiBr.”
Literature nugget relayed: UWA deep-well campus cascade
2.5–3 km wells, 90–100 °C water, 1–3 MW campus base cooling; two single-effect LiBr chillers in series (90–100 °C then 80–85 °C) gave COP 0.74 and 0.60, cascade COP 0.67, payback 11–13 years.
Key quotes
- “The results show that the coefficient of performance (COP) reaches about 0.87 at solution heat exchanger effectiveness of 0.9, when the geofluid temperature is 120℃.”
- “To operate a single-effect water/lithium bromide absorption chiller, the supplied heat needs to be at least at 90℃.”
Companion: Zhao, Xu, Jin, An 2024 — LiBr/H₂O vs LiCl/H₂O geothermal single-effect (Int. J. Low-Carbon Technologies 19)
Source: https://academic.oup.com/ijlct/article/doi/10.1093/ijlct/ctae100/7718999 (open access, peer-reviewed)
- Compares 55% LiBr/H₂O vs 35% LiCl/H₂O single-effect driven by “medium-temperature geothermal resources (90–120 °C).” Nominal 14 kW.
- Envelope: heat-source inlet 80–105 °C; cooling water 27–36 °C; chilled water inlet 10–19 °C; cooling-water flow 0.3–1.2 kg/s.
- COP: LiBr 0.761–0.795 (max 0.795); LiCl 0.749–0.785. Exergy COP: LiBr 0.501–0.694; LiCl 0.495–0.684. LiCl within ~1–2% of LiBr.
- ECOP rises with chilled-water inlet temperature: higher-temperature comfort cooling is exergetically favoured over low-temperature chilled water.
- Quote: “The single-effect absorption refrigeration system is suitable for recycling medium-temperature geothermal resources (90°C-120°C).”
Relevance to the cooling wiki
Sets the geothermal-specific numbers for the wiki’s absorption article: 90 °C floor, COP 0.73–0.87 across 90–120 °C, flow-insensitive once the HX is sized, crystallization limits, and the flash-plant-bottoming configuration. Note the model bottoms on flash reject brine at 100 °C; a binary/ORC plant’s reject is typically colder, so the same configuration may not transfer to EGS binary plants without taking brine upstream of the turbine.