raw · articles · ingested 2026-09-19
Absorption Chiller for the Chena Hot Springs Aurora Ice Museum (Geo-Heat Center Bulletin, Sept 2006)
Source: http://digitallib.oit.edu/digital/api/collection/geoheat/id/11412/download
Provenance: Geo-Heat Center Bulletin (OIT, DOE-funded), co-authored by the resort owner (Holdmann) and the chiller manufacturer (Erickson, Energy Concepts). Two seasons of operating data. Companion engineering paper: Erickson, Kyung, Makar, Holdmann, “Year Round Ice Hotel Chilled by Hot Spring Water,” IEA Heat Pump Centre Newsletter 2006 — https://www.energy-concepts.com/_pdfs/iea_heat_pump_centre_ice_hotel_2006_text.pdf. Retrieved via research agent; PDF text extracted locally.
Why it matters
The article states there were no absorption chillers on US geothermal sites between 1989 (OIT shutdown) and 2004: “the 230ºF minimum temperature classically considered necessary to make an air-cooled system cost effective encroached on temperature ranges which could similarly be used for power generation. For this reason, and because of increased maintenance issues when working with unique systems, no absorption chillers were in operation on geothermal sites between 1989 and 2004.” Chena broke that pattern by using a very cold heat sink instead of a hot source.
The installation
| Parameter | Value |
|---|---|
| Driving heat | Hot-spring water 165 °F (74 °C), 85 gpm (5.4 L/s) [IEA paper: 73–75.5 °C, 322 L/min] |
| Drive outlet | 63 °C → cascaded to greenhouse and outdoor pool heating |
| Heat rejection | River water 40 °F (4 °C), 80 gpm (5.0 L/s) to absorber and condenser |
| Cycle | Custom ammonia-water, three-pressure double-lift (“ThermoChiller”), designed for high lift from low-temperature heat |
| Output | 4.26 kW chilling; CaCl₂ brine delivered at −20 °F (−29 °C), 55 gpm (3.5 L/s) |
| Space held | Ice Museum at 24 °F (−4 °C), even at 32 °C outdoors; ~1,000 t of ice |
| Materials | Stainless steel on all hot-spring, river and brine surfaces; carbon steel internally |
| Storage | 2,000 gal (7.56 m³) brine tank ≈ 1 h of cooling ride-through |
| Electrical | 2 × 0.37 kW solution pumps; whole system ~33 kW (15 kW supply pumps, 2 kW brine pump, 15 kW air handler) vs 110 kW for the backup vapor-compression plant |
| Savings | ~$400/day diesel (>$12,000/month at $0.65/L; site power ~30 ¢/kWh) |
| Availability | ~95% |
Ordered January 2005, installed end of February/March 2005, air-shipped without shop test; initially run as two-pressure, reconfigured to three-pressure after two months for summer load.
Problems and lessons
- Cold sink is the enabler. Diurnal creek warming to ~7.2 °C mid-afternoon (coincident with peak load) cut efficiency; owners planned a 3.9 °C shallow cold-water well instead. The 4 °C sink is what made 74 °C drive heat workable for −29 °C brine.
- Defrost: the automatic CaCl₂ drip on the air handler never worked; manual defrost several times a day. Brine below −34.4 °C crashed the chiller; fixed with bypass ducts and a low-brine-temperature auto shutdown.
- Precedent: a similar Energy Concepts unit had run ~10 years in Kotzebue, AK making fishing-fleet ice from 74 °C diesel jacket water.
Key quotes
- “With 165ºF (74ºC) hot spring water (85 gpm (5.4 l/s)), and 40ºF (4ºC) (80 gpm (5.0 l/s)) river water, the brine is delivered at -20ºF (-29ºC) (55 gpm (3.5 l/s)) and the temperature in the ice hotel is maintained at a constant 24ºF (-4ºC).”
- “It demonstrates that absorption refrigeration is possible with very low driving temperatures, and in very compact packages.”
- (IEA paper) “The hot spring water is cooled to 63 C in the absorption unit, and is subsequently used to heat a large greenhouse and an outdoor pool.”
Context from NREL (Davalos Elizondo, Kolker, Warren, Stanford GW 2023)
https://pangea.stanford.edu/ERE/pdf/IGAstandard/SGW/2023/Davalos.pdf — “Chena Hot Springs remains the only geothermal power plant in Alaska. It exploits a low-temperature geothermal resource of 73°C to produce 730 kW … as well as several cascaded direct uses including greenhouse heating, absorption chilling, district heating, and others … It should be noted that Chena Hot Springs has 4°C cooling water from a stream, enabling a temperature differential across the power system that yields an acceptable cycle efficiency.” (Chena’s 730 kW ORC is the lowest-temperature geothermal power plant in the world; the same cold sink makes both the ORC and the chiller work.)
Relevance to the cooling wiki
The single best-documented geothermal → ammonia absorption → sub-zero refrigeration installation. Its lesson inverts the usual framing: at low drive temperature, a cold rejection sink is worth more than a few extra degrees of source heat — which is exactly the argument the wiki’s ground-source article makes for pairing sorption chillers with earth-coupled rejection.