ADSORPTION-DESORPTION SOLAR REFRIGERATOR

by Needful Provision, Inc. (NPI) (This article Copyright 2005 Needful Provision, Inc., USA. This page is a mirror of part of thier page at http://www.needfulprovision.org/main/solaroven.php to ensure that it is not lost. I will remove this mirror as requested.)

The solar refrigerator, developed by NPI, is a simplified and improved version of prior solar adsorption-desorption refrigerators ---refrigerators developed in recent years in Germany, France, and the U.S. All of these solar refrigerators have no moving parts. Water is used as the working fluid. The naturally occurring, highly porous silicon compounds (zeolites) are used as adsorbers. NPI’s unique solar powered refrigerator produces about 5 lbs. of ice daily per cu. ft. of storage space.

NPI’s seeks to help meet food storage needs for Third World families, with locally constructed solar refrigerators having the following parts:

1. An insulated, open-top solar collector box, about 7 ft. x 7 ft. (painted black), with

two-layers of glass (or other glazing) attached to the open-top. This box is used to collect solar heat via exposure to direct sunlight. A single 2 1/16-inch hole is drilled, on one side, to allow the exit of a 2-inch PVC pipe (see drawing).

2. A container, for zeolites, made of 6-inch PVC pipe generally forming a square

that fits inside the above collector box ---with four added cross-sections as shown on the drawing to follow. (Pipe should be black PVC, or paint the outside black.) Locate 2-inch PVC pipe in the center of the above 6-inch pipe, after drilling the 2-inch pipe to provide numerous, scattered 3/16-inch holes. Fill around this smaller pipe with ¼ to ½ -inch zeolite gravel (some 300 cubic inches per lineal foot).

This gravel is to hold smaller pipes in the center of the 6-inch pipes, and to help perform an adsorption-desorption function. All the holes in the 2-inch pipe must be drilled so they fit inside the 6-inch PVC pipe. Cap the opening of the 6-inch pipe joint using a 2 1/16-inch hole to allow the 2-inch pipe to pass through. Use PVC glue to seal the crack between the cap and the 2-inch PVC pipe. (The overall pipe system is of a size to fit within the above solar collector box.)

3. A vacuum hand-pump is used to help maintain a partial vacuum in the above

Described pipe container system sealed with PVC glue to prevent air leaks. (A good hand-operated vacuum pump, with gauge, is available from Triple Helix for US $39.95 --tel. 1-803-360-7872 or see website: http://www.triplehelixspores.com/hand_pump.htm.)

4. An attached heat exchanger, made from copper or brass tubing, also acts as a

condenser to convert hot water vapor into water, or water droplets.

5. An insulated cooler (refrigerator) box of at least 4 cu. ft. may be located in the ground or partly below ground to improve insulation (also use an insulated top door). This size is suggested to meet the food cooling needs of a family of four.

6. A one (1) cu. ft. sealed container to be located inside the above cooler box. At the

various stages of operation, this container holds a combination of water, water vapor, and ice. There is an airtight cap, over a 2-inch hole, that may be opened to add water as needed to keep this container at least 2/3rds full of water and/or ice. A sealed, attached float-gauge indicates the level of the water/ice without opening this container. (Loss of water vapor, and loss of the partial vacuum, may occur if any of the above components develop a leak.)

7. An adapter and appropriate glue or sealing materials are used to connect the 2-inch PVC pipe to the copper or brass tubing used for the condenser (item 4 above). Use solder, or similar means, to fix (and seal) the tube-end to the sealed container (item 6 above). Air leaks will greatly reduce the cooling efficiency of this refrigerator.

Concept of operation is based on the fact that when cool (at night) the zeolite acts somewhat like a sponge soaking up or adsorbing the water vapor ---then when heated during the solar day, this water vapor is desorbed or released. Operating under a partial vacuum, the water vapor moves with high efficiency under low pressures. At about 100F, water vapor begins to desorb from the zeolite. This water vapor is condensed into water droplets as heat is given off by the heat exchanger. The resulting water runs down, using gravity, into a sealed storage tank inside the cooler.

During the night, zeolite is cooled close to ambient temperature and starts adsorbing water vapor. Two sides of the solar collector box are opened to allow night air to help cool the zeolite inside the PVC pipes. Liquid water, in the storage tank (a tank also operating as an evaporator) adsorbs heat from the space to be cooled and is converted into water vapor. Since the system is sealed under very low pressure, any water remaining in the storage tank is then frozen into ice. This ice then melts slowly during the next day providing sustained cooling at reasonably constant temperatures.

The Zeopower Company, and EG Solar, both manufacture commercial versions of solar adsorption cooling (or refrigeration) systems. Other companies, like SunDanzer, manufacture solar coolers (or refrigerators) that use conventional compression-type refrigeration achieved by electrical systems based upon photovoltaics. NPI’s cooler (as above described) was developed to provide food storage for the poorest of the poor, and is not intended to be a commercial system. The NPI cooler has been designed to allow village users to easily obtain their own inexpensive means of local food preservation, with no power other than solar. Every effort has been made to avoid any possible patent infringement related to existing, somewhat similar, commercial solar powered refrigerators.

Zeolite deposits may be found worldwide, and the abundance of zeolite is part of the successful application of solar refrigeration. In many areas, zeolite is sold commercially for use in odor control. An example commercial source is USA Zeolite (with zeolite products shown on the company website: http://www.ZeoliteDepot.com).

See also:

• http://www.sjtuirc.sjtu.edu.cn/news/ISHPC%20-%20101%20K.pdf ADSORPTION REFRIGERATION - An efficient way to make good use of heat and solar energy.
   
• http://www1.eere.energy.gov/solar/pdfs/sda_not_in_kind.pdf Water-Zeolite Adsorption: size and cost are both factors working against zeolite adsorption heat pumps. A three ton heat pump would require 240 kg of zeolite and large amounts of copper. ADL estimated that materials and components alone for a three ton system would cost $2500 exclusive of labor, overheads, dealer markups, and installation costs (DOE 1993).
  
• http://www.solarabsorptioncooling.com/ Installs min 10 ton solar adsorption coolers in qualified geographical areas for little or no money down and are paid by the savings in your heating and cooling bill. wow. Heck of a claim, I'd be interested to hear from any actual customers.
   
• http://www.zeo-tech.de/e_index.htm Ice-Quick is available from Zeo-Tech
   
• http://www.ecosustainablevillage.com/solar_ice.htm "The Ice-Quick is a small device to demonstrate the adsorption technology with the sorption pair water/zeolite. It consists of a zeolite filled cartridge, connected via an adaptor to a plastic cup, which contains some water, and which is evacuated by means of a hand-vacuum pump."
   
• http://www.eduvinet.de/servitec/cooleep71.htm Air-conditioning and Cooling technology : Cooling with solar actuation
   
• http://www.solarserver.de/solarmagazin/artikeljuni2002-e.html Closed absorption refrigeration machines with liquid sorbent (water-lithium bromide) can be assisted by vacuum tube solar collectors.
   
• http://www.limsi.fr/Individu/mpons/solaradsor.htm Adsorption units built for solar refrigeration.
   
• http://www.sunfrost.com/vaccine_refrigerators.html Small but very high efficiency DC power refrigerator / freezer. Can run off a couple of solar panels and battery. On a 90'F day, it consumes only .28 kWh/day.
   
  http://www.sunfrost.com/vaccine_on_car_battery.html Details on development.
   
• US Patent No 4556049 "Integrated Solar Panel" a zeolite adsorbtion solar cooling and heating panel.

Questions:

• hoornbp@whitman.edu asks:

  Does anyone have any idea what the text around the diagram says? I want to build one of these, but I'd like to know more before I begin. Has anyone tried this?

• Ouch. I can't make any of it out. Have you tried to make one of these? James Newton replies: Not yet!

• hoornbp@whitman.edu asks:

  I sure wish I could read the script around the illustration, but no matter how much I enlarge it, it remains illegible. Any chance of getting a translation, or a switch to a legible font?

  James Newton replies: I'm only duplicating the illustration found on thier web page. Sadly, no better copy exists.

Comments:

• Perhaps I may be able to assist in clarifying the text surround the diagram. This is only my interpretation and cited as a disclaimer. That said the following is presented. The 7’X 7’ insulated collecting box should have depth to accommodate the glass “windowâ€� and the “6â€� PVC pipe. The six inch PVC is the solar energy collector and must be black. Any reduction of surface gloss to reduce radiation being reflected would improve effciency. The glazing should be insulating. The text fails to elaborate on assembling the collector. However, a “dryâ€� run assembly should allow any bugs to be corrected. NOTE PVC when assembled “wetâ€� will result in shorter overall assembled size. Make some allowance for this fact. The internal 2â€� PVC pipe is a fluid conduit for the refrigerant (water). Making this pipe configuration could be challenging as the 6â€� section must be vacuum tight. A consideration is to the infinity out gassing from the PVC material will continually degrade the vacuum. One may be bettered served to use a metal tube. The interior conduit will also present the same set of issues. The heat exchanger / condenser made of copper or brass would be next in the system. Though not indicated this should be constructed with a generous area for heat radiation. The greater heat transfer ability the greater the operating efficiency. Finally, the ice/cold water chest is located inside a well insulated cool box.
  The middle left figure indicates the collector orientation relating to the sun.
  When constructing this system the greater care and thought to efficiency will be handsomely rewarded. To check the system for vacuum integrity low pressurization with a bicycle pump and soapy water will reveal faults. Plan ahead to method to correct any revealed leaks when selecting the components. The vacuum value will vary through the day / night cycle. Restoration of vacuum should be undertaking at the highest collector temperature.
  
  If anyone builds this design please be kind enough to post outcome.