The idea of using an open flame or concentrated solar heat to make ice or to cool an insulated box is not new, but little information is available on how to actually accomplish this feat. Prior to the availability of cheap electricity, many of these small ammonia based "Icy Ball" refrigeration units could be found in homes in the United States. Over the last 30 years several experimental units have been constructed for the purpose of laboratory testing. These units were custom made by the experimenters and could not be easily replicated. Now for the first time simple plans are available which will allow a moderately skilled handyman to construct a practical, low cost, portable absorption refrigeration unit.

HOW IT WORKS


These units use liquid anhydrous ammonia as a refrigerant. The pure anhydrous ammonia is mixed with water. Heat is then applied to the ammonia solution that has been contained in a pressure vessel. The heat drives off the ammonia which then condenses in another pressure vessel. The entire apparatus is then allowed to cool down. Since pure liquid ammonia boils at -28 F, the ammonia starts to boil absorbing heat out of the condenser vessel. The condenser vessel then freezes at temperatures below 0 F. This causes a ball of ice to form around the vessel if it is submerged in water. If the condenser vessel is placed in an insulated box, the temperature in the box will drop drastically depending on the amount of insulation. This may seem hard to understand, but it is the same principle as a compressed-gas keyboard duster can becoming cold during heavy use. It needs to be emphasized that ammonia gas is extremely toxic and fammable. One deep breath of pure ammonia gas will KILL a human being. If you are not a mechanically inclined person who pays close attention to details, do not attempt to build one of these units. If built with quality materials and used with the proper precautions this unit can be safely operated since it is designed to contain the gas within the unit.

The system which can be constructed from these plans will produce 5 to 7 lb. of ice after being heated on a small propane or gas stove for about 90 min. Any heat source which will result in a final generator temperature of 255 F may be used The condenser vessel is submerged in room temperature water during the generation process. After the generation process is complete, the generator vessel is cooled off in the same water. This produces about 2 gal. of boiling hot water suitable for other uses. A small valve is then closed which causes the liquid ammonia in the condenser vessel to start to boil off and be absorbed back into the water in the generator vessel as the refrigeration process begins. A "ball" of ice can be harvested in about 4 hr. if the condenser vessel is submerged in cool water. Additional hot water can also be obtained by further cooling of the generator vessel.

 

HOW IT IS BUILT


The refrigerant solution is a mixture of distilled water and liquid anhydrous ammonia. Although anhydrous ammonia is not illegal to possess in a closed refrigeration system, it is sometimes difficult to obtain. In some states (especially in the Midwest) laws have recently been passed restricting the transfer of anhydrous ammonia due to its use in the manufacture of crystal meth. Be sure to check the situation in your state before you attempt to build one of these units! Companies that service commercial air conditioners and refrigeration systems usually have stockpiles of ammonia. Also municipal maintenance facilities have access to liquid anhydrous ammonia. Anhydrous ammonia must be stored in large metal cylinders under pressure. So to receive it, you must have a pressure vessel such as an 11 lb. propane tank ready to go. Showing these folks who service these commercial cooling units the plans or the absorption refrigerator unit that you have constructed usually gets them to give or sell you the 7 lb. of ammonia that you need. As a last resort, you might try someone who repairs camper refrigerators. These people rarely give anything away.

The generator vessel for this system is an 11lb. propane tank in new or excellent condition. The condenser vessel is a 5 lb. CO2 fire extinguisher bottle. A stainless steel (SS) charging valve, a SS shut-off valve, and a SS pressure relief valve also need to be obtained. The same people that have the ammonia usually have the valves also. Some commercial machine shops also might be able to order these valves.

One word of caution here. Don't scrimp on the vessels and the valves. You cannot use the brass valves available in building supply stores. Pressures of up to 250 lb. will be produced within the system. FREON CONTAINERS MUST NOT BE USED UNDER ANY CIRCUMSTANCES. Since even small quantities of ammonia gas can be lethal, the entire system must be absolutely gas tight. All testing, charging and bleeding must be done outside in the open air. Defective or corroded components must not be used. When completed, the fully charged system weighs about 47 lb. Smaller and lighter systems can be built by scaling down the sizes of the various components.

The total cost of the system will depend on your scrounging abilities and the local availability of the various components. The unit shown in the photograph cost the author about $ 100.00 to build. If you end up buying all the components new, you could spend about $ 250.00. Liquid ammonia costs about $ 2.00/lb. The 26% ammonia available in janitorial supply stores can be used to test the unit but it is not concentrated enough to produce ice. Once the system has been completed and charged, the only additional expense to produce ice will be the cost of fuel used to heat the unit and the plastic bags for the ice. Detailed plans and operating instructions may be purchased for $15.00 US.

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Detailed plans and operating instructions may be purchased for $15.00 US.

Download the plans HERE

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