Ep. 8: Absorption Refrigerator- Cooling with Fire, Water, & Salt | Greenhill Forge Podcast

This week we’re talking about Eric’s recent video on his absorption refrigerator design that uses water as the refrigerant and calcium chloride (road salt) to absorb the vapor, powered by heat instead of a compressor. We’re going through how the cycle works, the main components, the practical limits, and what it takes to keep the system running. Full video:    • Fire Powered Refrigeration — A/C & Fridge ...   We’ll answer a listener question each week, so send yours to https://forms.gle/zNzKTtjDnBEupLBQA. In this episode: How an absorption refrigerator cycles water as the refrigerant with calcium chloride as the absorbent Why calcium chloride is used instead of regular salt or other common absorbents like lithium bromide The roles of the generator, absorber, condenser, expansion valve, and evaporator How vacuum lowers the boiling point to produce cooling and why the system stays below ambient pressure Temperature limits of water as a refrigerant and why making ice is difficult How the U-bend and pressure differences create directional flow without a compressor Practical considerations for off-grid use, including supplementing a root cellar and managing heat input Power needs for pumps and fans, and options for using solar heat on the generator Challenges with scaling evaporators, absorber capacity, and monitoring pressures and temperatures Structural and vacuum-related details that affect building and operating the system --- Welcome to the Greenhill Forge Podcast, with Eric from the Greenhill Forge YouTube channel, and my buddy Amal, a fellow builder of many trades. In this podcast we’ll talk about where the real world meets experiments in alternative energy, wood heating, metal fabrication, off-grid engineering and self sufficiency, so expect discussions about workshops, tools, fabrication, building, homesteading, and what it actually takes to make those dreams real. *LISTEN* to this podcast on all your favorite podcast platforms. See you next Friday! --- CHAPTERS 00:00:04 Absorption refrigerator design overview 00:01:05 Importance of cooling and off-grid power sources 00:02:36 Choosing water and calcium chloride over other options 00:03:05 How calcium chloride absorbs water vapor in a closed system 00:05:26 Exothermic reaction when calcium chloride hydrates 00:06:30 Calcium chloride as road salt and a concrete accelerator 00:07:47 Water as the refrigerant and the absorber’s role 00:08:08 Cooling the absorber to maintain absorption capacity 00:09:26 Multiple heat cycles compared with vapor compression 00:10:23 Expansion valve, pressure drop, and one-time coolers 00:11:48 Generator and absorber replacing the compressor 00:13:09 Lifting refrigerant with heat and gravity feed 00:13:41 Water’s heat capacity advantages and drawbacks as a refrigerant 00:14:08 Latent heat and phase change explained 00:15:46 Boiling point changes with pressure and elevation 00:16:54 Using vacuum to lower the boiling point for cooling 00:17:58 Freezing limitations of water as a refrigerant 00:19:03 Using the system to supplement a root cellar 00:19:43 Achievable evaporator temperatures and ice-making challenges 00:20:24 Issues with antifreeze additives in the system 00:21:47 Flow through the condenser, needle valve, and evaporator 00:22:05 U-bend as a check valve and pressure separation 00:22:57 Running the generator leg with the valve closed 00:24:18 Split of flow between the evaporator and recirculation 00:27:34 Design process and differences from industrial systems 00:28:00 Sizing the U-bend for the pressure differential 00:29:07 Ambient temperature effects on evaporator performance 00:30:35 Enclosing the evaporator and accounting for fan heat 00:31:45 Adding evaporators in parallel and absorber capacity 00:33:29 Limited published data on calcium chloride as an absorbent 00:36:22 Off-grid challenges with compressors and mechanical energy 00:37:13 Power draw and solar options for heat and pumps 00:39:00 Solar heating the generator and thermal storage ideas 00:41:11 Solar irradiance and concentrating sunlight 00:42:45 Solar panel efficiency versus direct heat collection 00:43:30 Using solar-heated fluid to drive the generator 00:44:37 Potential cooling capacity for small units 00:45:57 Sensors, Arduino modules, and voltage readings 00:48:26 Pressure sensors, absolute versus gauge pressure 00:50:07 System pressures remaining below ambient 00:51:15 Structural deflection and reinforcement under vacuum 00:52:58 Vacuum distillation and related applications 00:56:35 Water level shifts between generator and absorber 01:00:06 Water column acting as a barometer