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Solar Ammonia Ice Maker - Open Knowledge — LiveJournal

Apr. 6th, 2004

01:59 am - Solar Ammonia Ice Maker

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http://homepower.com/files/solarice.pdf (PDF)



Everywhere in our world, refrigeration is a major energy user. In poor areas, “off-

grid� refrigeration is a critically important need. Both of these considerations

point the way toward refrigeration using renewable energy, as part of a

sustainable way of life. Solar-powered refrigeration is a real and exciting possibility.

20

Home Power #53 • June / July 1996

Working with the S.T.E.V.E.N. Foundation (Solar

Technology and Energy for Vital Economic Needs), we

developed a simple ice making system using ammonia

as a refrigerant. A prototype of this system is currently

operating at SIFAT (Servants in Faith and Technology),

a leadership and technology training center in Lineville,

Alabama. An icemaker like this could be used to

refrigerate vaccines, meat, dairy products, or

vegetables. We hope this refrigeration system will be a

cost-effective way to address the worldwide need for

refrigeration. This icemaker uses free solar energy, few

moving parts, and no batteries!

Types of Refrigeration

Refrigeration may seem complicated, but it can be

reduced to a simple strategy: By some means, coax a

refrigerant, a material that evaporates and boils at a low

temperature, into a pure liquid state. Then, let’s say you

need some cold (thermodynamics would say you need

to absorb some heat). Letting the refrigerant evaporate

absorbs heat, just as your evaporating sweat absorbs

body heat on a hot summer day. Since refrigerants boil

at a low temperature, they continue to evaporate

profusely — thus refrigerating — even when the milk or

vaccines or whatever is already cool. That’s all there is

to it. The rest is details.

One of these details is how the liquid refrigerant is

produced. Mechanically driven refrigerators, such as

typical electric kitchen fridges, use a compressor to

force the refrigerant freon into a liquid state.

Heat-driven refrigerators, like propane-fueled units and

our icemaker, boil the refrigerant out of an absorbent

material and condense the gaseous refrigerant to a

liquid. This is called generation, and it’s very similar to

Above: Steven Vanek with his machine which uses solar thermal energy to make ice.

Jaroslav Vanek,

Mark “Moth� Green

Steven Vanek

©1996 Jaroslav Vanek, Mark “Moth� Green, Steven Vanek


Page 2

21

Home Power #53 • June / July 1996

Refrigeration

the way grain alcohol is purified through distillation.

After the generation process, the liquefied refrigerant

evaporates as it is re-absorbed by an absorbent

material. Absorbent materials are materials which have

a strong chemical attraction for the refrigerant.

This process can be clarified using an analogy: it is like

squeezing out a sponge (the absorbent material)

soaked with the refrigerant. Instead of actually

squeezing the sponge, heat is used. Then, when the

sponge cools and becomes “thirsty� again, it reabsorbs

the refrigerant in gas form. As it is absorbed, the

refrigerant evaporates and absorbs

heat: refrigeration!

In an ammonia absorption

refrigerator, ammonia is the

refrigerant. Continuously cycling

ammonia refrigerators, such as

commercial propane-fueled

systems, generally use water as the

absorbent, and provide continuous

cooling action.

The S.T.E.V.E.N. Solar Icemaker

We call our current design an

icemaker. It’s not a true refrigerator

because the refrigeration happens

in intermittent cycles, which fit the

cycle of available solar energy from

day to night. Intermittent absorption

systems can use a salt instead of

water as the absorbent material.

This has distinct advantages in that

the salt doesn’t evaporate with the

water during heating, a problem

encountered with water as the

absorber.

Our intermittent absorption solar icemaker uses calcium

chloride salt as the absorber and pure ammonia as the

refrigerant. These materials are comparatively easy to

obtain. Ammonia is available on order from gas

suppliers and calcium chloride can be bought in the

winter as an ice melter.

The plumbing of the icemaker can be divided into three

parts: a generator for heating the salt-ammonia mixture,

a condenser coil, and an evaporator, where distilled

ammonia collects during generation. Ammonia flows

back and forth between the generator and evaporator.

Parabolic Trough Collectors:

7 X 20 feet total collecting area

West – East

Generator Pipe:

filled with calcium-chloride-ammonia mixture

Condenser Coil:

in water bath

Evaporator / Collecting Tank:

in insulated ice-making Box

Condenser Coil: 1/4" pipe

shaped by wrapping around form

Valves: stainless steel

1/4" or 1/8" pipe thread

3" Black Iron Cap

1/4" nipple & coupling

tapped & welded in

Collector Suspended by U-bolt

into 1-1/2" angle iron bracket

Condenser Tank:

half of a 55 gallon drum

Icemaker Box:

scrap chest freezer

or wood/metal box

Storage Tank:

welded from 1/4" steel plate

& 3" pipe

Union: 1/4" stainless steel or black iron

(optional union at base of condenser coil)

Plumbing Detail

All plumbing is ungalvanized steel (black iron) unless indicated

Layout of the Solar Thermal Icemaker


Page 3

22

Home Power #53 • June / July 1996

Refrigeration

The generator is a three-inch non-galvanized steel pipe

positioned at the focus of a parabolic trough collector.

The generator is oriented east-west, so that only

seasonal and not daily tracking of the collector is

required. During construction, calcium chloride is

placed in the generator, which is then capped closed.

Pure (anhydrous) ammonia obtained in a pressurized

tank is allowed to evaporate through a valve into the

generator and is absorbed by the salt molecules,

forming a calcium chloride-ammonia solution (CaCl

2

-

8NH

3

).

The generator is connected to a condenser made from

a coiled 21 foot length of non-galvanized, quarter-inch

pipe (rated at 2000 psi). The coil is immersed in a water

bath for cooling. The condenser pipe descends to the

evaporator/collecting tank, situated in an insulated box

where ice is produced.

Operation

The icemaker operates in a day/night cycle, generating

distilled ammonia during the daytime and reabsorbing it

at night. Ammonia boils out of the generator as a hot

gas at about 200 psi pressure. The gas condenses in

the condenser coil and drips down into the storage tank

where, ideally, 3/4 of the absorbed ammonia collects by

the end of the day (at 250 degrees Fahrenheit, six of

the eight ammonia molecules bound to each salt

molecule are available).

As the generator cools, the night cycle begins. The

calcium chloride reabsorbs ammonia gas, pulling it

back through the condenser coil as it evaporates out of

the tank in the insulated box. The evaporation of the

ammonia removes large quantities of heat from the

collector tank and the water surrounding it. How much

heat a given refrigerant will absorb depends on its “heat

of vaporization,� — the amount of energy required to

evaporate a certain amount of that refrigerant. Few

Above: Detail of the condenser bath, containing the

condenser coil, and the icemaker box below.

Above: About ten pounds of ice are created in one cycle

of ammonia evaporation / condensation.

materials come close to the heat of vaporization of

water. We lucky humans get to use water as our

evaporative refrigerant in sweat. Ammonia comes close

with a heat of vaporization 3/5 that of water.

During the night cycle, all of the liquefied ammonia

evaporates from the tank. Water in bags around the

tank turns to ice. In the morning the ice is removed and

replaced with new water for the next cycle. The ice

harvesting and water replacement are the only tasks of

the operator. The ice can either be sold as a

commercial product, or used in a cooler or old-style ice-

box refrigerator.

Under good sun, the collector gathers enough energy to

complete a generating cycle in far less than a day,

about three hours. This allows the icemaker to work

well on hazy or partly cloudy days. Once generating

has finished, the collector can be covered from the sun.

The generator will cool enough to induce the night cycle

and start the ice making process during the day.


Page 4

23

Home Power #53 • June / July 1996

Refrigeration

Future Design

A refrigerator, which is able to absorb heat at any time

from its contents, is more convenient than our current

intermittent icemaker. To enable constant operation, a

future design will include several generator pipes in

staggered operation as well as a reservoir for distilled

ammonia. Staggered operation will allow the

refrigerator to always have one or more of the

generators “thirsty� and ready to absorb ammonia, even

during the day when generation is simultaneously

happening. Generation will constantly replenish the

supply of ammonia in the storage reservoir. We are

currently in the first stages of making these

modifications to the icemaker.

Caution: Safety First!

Working with pure ammonia can be dangerous if safety

precautions are not taken. Pure ammonia is poisonous

if inhaled in high enough concentrations, causing

burning eyes, nose, and throat, blindness, and worse.

Since water combines readily with ammonia, a supply

of water (garden hose or other) should always be on

hand in the event of a large leak. Our current unit is a

prototype. We will not place it inside a dwelling until

certain of its safety. Unlike some poisonous gases,

ammonia has the advantage that the tiniest amount is

readily detectable by its strong odor. It doesn’t sneak up

on you!

For the longevity of the system, materials in contact

with ammonia in the icemaker must resist corrosion.

Our unit is built with non-galvanized steel plumbing and

stainless steel valves, since these two metals are