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.
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"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.
