ISAAC Solar Icemaker

Energy Concepts Co., LLC
627 Ridgely Ave.
Annapolis, MD 21401
Tel: 410-266-6521
Fax: 410-266-6539

ISAAC Solar Ice Maker

The ISAAC Solar Icemaker is an Intermittent Solar Ammonia-water Absorption Cycle. The ISAAC uses a parabolic trough solar collector and a compact and efficient design to produce ice with no fuel or electric input, and with no moving parts.

The ISAAC Solar Icemaker operates in two modes. During the day, solar energy is used to generate liquid ammonia refrigerant. During the night, the generator is cooled by a thermosyphon and ice is formed in the evaporator compartment as ammonia is reabsorbed to the generator.

The daily ice production of the ISAAC is about 5 kg per square meter of collector, per sunny day. The construction of the ISAAC Solar Icemaker involves only welding, piping and sheet metal work, and there are no expensive materials. It is estimated that, when produced in-country where wages are low and transportation costs can be minimized, the 11 square meter
ISAAC can be produced for less than $7,000. When produced in-country, the creation of urban employment is an additional advantage of ISAAC technology.

The characteristics of the ISAAC which make it particularly well suited to provide refrigeration to unelectrified rural communities are:

1. It is solar thermally powered, avoiding expensive diesel fuel or photovoltaics.
2. Low cost construction requires only welding, piping and sheet metal work.
3. Very low maintenance.
4. The quantity of ice is sufficient to support small scale businesses while maintaining sustainability in fragile environments, or provide low cost household refrigeration.

The ISAAC design was developed by Energy Concepts Company. Over forty systems have been built and twenty installed in seven countries. The ISAAC is on display in Annapolis, Maryland and at Sandia National Lab, Albuquerque, New Mexico. ISAAC is now being distributed and commercialized by Solar Ice Co.

Providing Jobs to Remote Communities - By Providing Ice

The ISAAC Solar Icemaker makes enough ice at low cost to support many small scale businesses in rural unelectrified areas. Enterprises using ISAAC will be environmentally sustainable because no fuel is required. They will be economically sustainable because the cost of producing the ice by the ISAAC is sufficiently less than the value of the ice that it can easily be recovered by a micro-enterprise.

Ice is of major economic importance. In rural communities of developing countries, there is frequently a shortage of ice to support business activities. The result is loss of revenue, jobs, and substantial food spoilage.

Three important community needs for electricity are:

* lights
* communications and entertainment
* refrigeration.

Lights, communication and entertainment require modest amounts of electricity and are affordable even at the high cost of electricity from emergency generators, diesel mini-grids or photovoltaics.

When refrigeration is needed also, the amount of electricity required from the power system increases drastically. Thus it is usually omitted to keep costs down. An ISAAC Solar Icemaker supplies refrigeration without the intermediary step of electricity and at a much lower cost. Thus ISAAC Solar Icemakers, in combination with mini-grids and/or photovoltaics, are a good method of supplying remote community needs.

For example, ISAAC can provide domestic refrigeration. An ISAAC produces six blocks of ice each day, weighing ten kilograms each. If an icebox requires five kilograms of ice per day to stay cool, then one ISAAC will be able to supply domestic refrigeration to twelve households. The cost of a standard electric refrigerator, plus the constant requirement of expensive electricity, would be much higher.

The Absorption Process

The Absorption Cycle was invented in 1846 by Ferdinand Carré for the purpose of producing ice with heat input. It is based on the principle that absorbing ammonia in water causes the vapor pressure to decrease. Absorption cycles produce cooling and/or heating with thermal input and minimal electric input, by using heat and mass exchangers, pumps and valves.

An absorption cycle can be viewed as a mechanical vapor-compression cycle, with the compressor replaced by a generator, absorber and liquid pump. The absorption cycle enjoys the benefits of requiring a fraction of the electrical input, plus uses the natural substances ammonia and water, instead of ozone depleting halocarbons. The absorption cycle enjoyed widespread use from the 1920’s as gas powered refrigerators/ice-makers.

The basic operation of an ammonia-water absorption cycle is as follows. Heat is applied to the generator, which contains a solution of ammonia water, rich in ammonia. The heat causes high pressure ammonia vapor to desorb the solution. Heat can either be from combustion of a fuel such as clean-burning natural gas, or waste heat from engine exhaust, other industrial processes, solar heat, or any other heat source. The high pressure ammonia vapor flows to a condenser, typically cooled by outdoor air. The ammonia vapor condenses into a high pressure liquid, releasing heat which can be used for product heat, such as space heating.

The high pressure ammonia liquid goes through a restriction, to the low pressure side of the cycle. This liquid, at low pressures, boils or evaporates in the evaporator. This provides the cooling or refrigeration product. The low pressure vapor flows to the absorber, which contains a water-rich solution obtained from the generator. This solution absorbs the ammonia while releasing the heat of absorption. This heat can be used as product heat, or for internal heat recovery in other parts of the cycle, thus unloading the burner and increasing cycle efficiency. The solution in the absorber, now once again rich in ammonia, is pumped to the generator, where it is ready to repeat the cycle.

An absorption cycle can use a variety of working pairs. The working pair is made up of a refrigerant, typically ammonia or water; and a solution which absorbs the refrigerant. Other working pairs include lithium-bromide-water; TriDroxide-water; and Alkitrate-water. Tridroxide and Alkitrate are Energy Concepts patented working pairs with specialty applications in industry.

Absorption cycles can operate at high efficiency by utilizing advanced cycles, using generator-absorber heat exchange, multiple pressures, and multiple effects. These cycles use extensive internal heat recovery to require less prime fuel input to produce the same thermal output. High efficiency operation, plus benefits of environmentally friendly refrigerants, clean-burning fuels, and few moving parts requiring maintenance make absorption a very good choice for consumers.

Absorption cycles can produce a variety of thermal outputs. In common commercial use today are gas-fired absorption chillers, which produce chilled water for space cooling applications. The absorption cycle can produce low temperature cooling for ice production or cold storage. Turbine inlet cooling is a very efficient use of absorption cooling, boosting turbine efficiency by up to 15%. Many other applications exist in industry, where waste heat is available and cooling is required. Advanced cycles can also produce electrical or shaft power by producing steam or high pressure vapor to power a turbine/generator pair.


Pierpont, J. P. "Energy Concepts Rises From Ashes To International Market." Baltimore Business Journal. February 1989.

"What’s New: News in Brief." Maryland Business Weekly: The Baltimore Sun. December 18, 1989.

"Hot Refrigeration" Environmental Protection Week. June 1990.

"Solar Refrigeration Brings Ice to Developing Countries." Solar Industry Journal. Second Quarter. 1990.

Maier, Timothy A. "Solar-Powered Refrigerator Heats Up Energy Concepts." Baltimore Business Journal. November 1990.

Erickson, Donald C. "Isaac Solar Absorption Icemaker." Soltech 91

Erickson, Donald C. "Isaac Solar Refrigerator." Environment-Friendly Technologies for the 21st Century. Proceedings of the Japanese Assocition of Refrigeration Absorption Heat Pump Conference. Tokyo. September 1991.

Erickson, Donald C. and Jorgensen, Paul. "Solar Absorption Ice-Making in a Mexican Fishing Village." Hawaii 1992.

Erickson, Donald C. "Solar Icemakers in Maruata, Mexico." Solar Today. July/August 1994.


The ThermoSorber™ is a gas-fired heat pump which supplies air conditioning or refrigeration at the cold end, and which uses all the reject heat (gas heat plus cooling duty ) to heat hot water. The high temperature glide achieved with the GAX absorption cycle makes it possible to heat hot water to 160°F, thus meeting the needs of commercial users. The hot water is normally the primary product, with the cooling in a supplementary role. This ensures high year round utilization and short paybacks. This appliance reduces the utility bill for hot water and cooling by more than half, compared to the most economic commercially available equipment.



Absorption Cycle with Integrated Heating System

Abstract -- An absorption system powered by low temperature heat for producing at least one of refrigeration and power is disclosed, wherein a low-pressure drop heat reclaimer 1 reclaims heat from the source into a heating agent, which in turn supplies heat to the absorption cycle desorber 5 via internal coils 7. The extra temperature differential normally present in closed cycle heating systems is avoided by using the absorption working fluid as the heating agent, in an integrated system.


Absorption Power Cycle with Two Pumped Absorbers

Abstract -- An absorption power cycle is disclosed which achieves a closer match to heat source temperature glide, and also lower heat source exit temperatures, and hence higher conversion efficiencies, in practical equipment. Referring to FIG. 7, two separate absorbers (725 and 706) are provided, each with a pumping path for a different concentration absorbent liquid to a different temperature location within counter-current high-pressure desorber 721. Heat source 710 heats the high-pressure desorber 721 and superheater 724 in parallel, and subsequently heats intermediate-pressure desorber 761. Dotted lines in the figures signify vapor.


Stationary Continuous Multimodular Trisorption Heat Pump

Abstract -- Apparatus and process are disclosed for sorption heat pumping at high efficiency in a smooth and continuous manner using a multiplicity of stationary triplex sorption modules. The hermetically sealed trisorption modules, each of which contains at least two solid sorbents, are free of pumps, valves, restrictors, or any similar devices for flow control of refrigerant or sorbent. The apparatus contains no moving parts beyond a small number of control and motive devices for the heat transfer fluids. The preferred refrigerant is ammonia and the preferred sorbents are the solid type with monovariant equilibrium, e.g., BaCl2, SrCl2, CaCl2, MnCl2, FeCl2 and SrBr2. The apparatus is preferably adapted for residential or small-scale commercial space-conditioning applications, and operates at double-effect efficiency in both the heating and cooling modes without inter-module heat transfer.

Rotary Trisorption Heat Pump

Abstract -- Apparatus and process are disclosed for sorption heat pumping at high efficiency in a smooth and continuous manner using a multiplicity of intermittent cycle triplex sorption modules. The hermetically sealed trisorption modules, each of which contains at least two solid sorbents, are free of pumps, valves, restrictors, or any similar devices for flow control of refrigerant or sorbent. The preferred refrigerant is ammonia and the preferred sorbents are the solid type with monovariant equilibrium, e.g., BaCl2, SrCl2, CaCl2, MnCl2, FeCl2 and SrBr2. The apparatus is preferably adapted for residential or small-scale commercial space-conditioning applications, and operates at double-effect efficiency in both the heating and cooling modes without inter-module heat transfer.

Intermittent Sorption Cycle with Integral Thermosyphon

Abstract -- Intermittent sorption cycles with fixed heat supply and removal and comprised of a generator/absorber (4), a condenser (2), and a receiver/evaporator (10) are adapted and simplified so as to require at most only two control valves (8) and (15) for their operation. With an integral thermosyphon (6) for absorption heat removal, only a single refrigerant charge is necessary. The two valves are advantageously combined into a single three-way ball valve, and key gravity drains (14) and (17) are provided. Applications include hot water heating, solar refrigeration, and steam generation.


Triple-Effect Absorption Cycle with Condensate-to-Solution Sensible Heat Exchanger

Abstract -- A triple-effect cycle is disclosed which avoids the two primary limitations of currently known triple-effect cycles: super-atmospheric pressures and/or low pressure absorbers that operate without mass transfer enhancers. The cycle is comprised of two hermetic loops-one a conventional LiBr double-effect loop, and the other a single-effect loop which overlaps the high pressure portion of the double-effect loop, and exchanges heat with it at three locations. Referring to FIG. 3, the latent heat exchanges are with absorber 302, condenser 304, and evaporator 305 of the single-effect loop. Sensible heat losses are reduced by incorporating inter-loop condensate-to-solution sensible heat exchanger 314. The inter-loop CSSHX also applies to other triple-effect cycles.

Thermosyphon Cooled Absorber for Air Cooled Absorption Cycles

Abstract -- The absorption step of a continuous absorption cycle apparatus (refrigerator or heat pump) is externally cooled by an air-cooled thermosyphon having hot end 107 (FIG. 1), air-cooled end 115, and reservoir 123. The absorption step is further recuperatively cooled by internal fluids, in absorber heat exchanger 108 and/or GAX 109. Thus the absorber is highly compact and the cycle is highly efficient. A hotter hermetic thermosyphon can advantageously supply additional cooling.

Sorber with Multiple Cocurrent Pressure Equalized Upflows

Abstract -- A sorber for sorbing a vapor into (absorber) or out of (desorber) a liquid sorbent comprised of a sequential plurality of highly effective and intensified locally cocurrent sorptions, but with non-cocurrent flow of vapor and liquid between the individual sorptions. The structure containing the locally cocurrent upflow is preferably comprised of enhanced heat transfer surface, making the sorption diabatic, further enhancing the intensification, and improving the sorption efficiency. Referring to FIG. 12 , vertical cylinders (70) and (71) form an annular space within which desorption occurs, powered by external heat source (72) and internal heat recuperation (77). The liquid portion of the annulus is divided into multiple compartments by folded rectangular fin (73). The space above fin (73) allows pressure equalization of all compartments. Each compartment is divided by insert (80) into separate vapor-liquid riser channels and a liquid downcomer channel. The sorbent liquid flow sequentially through the compartments via flow ports (74). The same high effectiveness sequential liquid recirculating cocurrent upflow desorption can also be accomplished in a horizontal cylindrical annulus, in plate fin exchangers, and in other geometries.

Coiled Tubular Diabatic Vapor-Liquid Contactor

Abstract -- A non-diabatic vapor-liquid contact device is disclosed which achieves high heat transfer effectiveness without sacrificing mass transfer effectiveness. Referring to FIG. 2, a helical coil of crested tubing 84 is contained within the annualr space between shrouds 82 and 83. Liquid flows downward through the annulus, and vapor flows countercurrently upward. The mass exchanging fluids pass through the space between tube crests and the shroud, achieving very effective mixing. Heat transfer fluid is flowed through the tubing via connections 87 and 88. The heat and mass transfer is preferably additionally enhanced by interspersing contact media with the coiled tubing, either longitudinally or radially.

Intensified Locally Cocurrent Tray Contactors
Abstract -- An intensified means of multicomponent fluid multistage vapor-liquid contact is disclosed. The contactor achieves the thermodynamic advantages of global countercurrency, the tray efficiency advantages of tray crosscurrency, and the point efficiency advantages of local cocurrency with liquid recirculation. Referring to FIG. 6, each tray has multiple compartments formed by compartment dividers 62, 63, and 64, and each compartment has a channel divider 69, 66, 67 which forms separate locally cocurrent riser channels and liquid downcomer channels.

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