Evaporative Coolers: How To Build Your Own Off-The-Grid Refrigerator
Feb 18th, 2013 | By NathanF | Category: Energy, Miscellaneous | Print This Article
The burning of fossil fuels for energy is primitive, cheap, and easy, which has given it the comparative advantage over other sources of energy for a very long time. But too much of a good thing inevitably creates dependency and addiction, and as the world continues to extract more and more oil, coal, and natural gas from the ground to feed its insatiable appetite for petroleum-based products, supplies that at one time seemed limitless are now dwindling rapidly and may be reaching dangerously low levels. In addition, according to most scientists, the carbon dioxide pollution that accompanies fossil fuel consumption has become so massive that it is now threatening the very survival of life on this planet.
While peak oil and man-made global warming are still considered controversial theories in some circles, the unhealthiness of becoming overly dependent on one source of energy to power everything is becoming crystal clear. And while our fossil fuel addiction is ultimately counterproductive, no one can argue that access to reliable supplies of cheap energy has led to numerous innovations that have improved the quality of our lives significantly in many ways. Modern refrigeration, for example, has expanded our food storage capacities and capabilities astronomically, allowing us to preserve perishable fruits, vegetables, meat, and dairy products for weeks at a time without having to worry about spoilage.
It is hard to imagine life these days without refrigeration, but like everything else, our refrigerators run on electricity, and all of them, including the newest energy-efficient models, consume fossil fuels at prodigious rates. Fridges can be run by alternative sources of energy such as solar or wind, but those who do so will be using up a lot of precious power supplies in the process, and for off-the-gridders who must look for ways to save energy at every turn, meeting energy demands for refrigeration can cause a noticeable strain on tight energy budgets.
There is another possibility, however, and it is an exciting one – evaporative coolers. By tapping in to some of the marvelous unseen and unrecognized energy that exists all around us, evaporative coolers will cool any food or other objects resting inside of them by slowly but surely draining away their heat until only a fraction of it remains. Refrigerators function in the same way, of course, but with evaporative coolers, absolutely no outside electrical input whatsoever is required.
Constructing Your Own Miracle Cooler At Home
As we all know, sweating is our body’s way of cooling itself down when it is overheated. This works because as sweat evaporates, it wicks away a portion of the skin’s heat as water molecules are converted from liquid to gas. Evaporation is always fueled by kinetic (heat) energy, and as more and more energy is expended, cooling will occur naturally and inevitably.
This principle of heat loss is the secret behind evaporative coolers. All you need to build a fully functioning evaporative cooler are two clay pots of varying sizes (like those used for flowers or plants), some sand, a reliable supply of fresh water, a damp cloth or towel, and possibly some caulking, duct tape, or silicone sealant to cover any holes in the bottom of your pots. In total, all of this should cost you no more than a few dollars at most, which means you could build several pot-in-pot coolers without having to spend much at all. You will need to choose two pots that have the same basic shape, but there should be at least a two-inch difference in diameter between the larger and the smaller.
To start the construction of your evaporative cooler, you will first cover the bottom of the bigger pot with a layer of sand; this layer should be as deep as it needs to be to ensure the top of the second pot will match the height of the first when it is inserted. If you have chosen to use flower pots or another type of clay pot that has holes in the bottom for drainage, however, you will need to plug these holes with caulking or silicone sealant or even good old duct tape before you actually begin.
After the smaller pot has been set inside the bigger on the bed of sand, you should fill circular space between the two pots with more sand, all the way to the top. Next, you will need to saturate the sand completely with water; there should not be so much that a free-standing pool begins to form on top, but enough so that the sand is thoroughly moist all the way through. Because clay pots are permeable, you could have an issue with water seeping in through the walls of the smaller pot, where the items in your “refrigerator” will be stored, so you have a couple of choices here: you can either glaze the inside of the small pot to make it watertight, or you if you don’t mind a little moisture, you can just leave it the way it is and use clean, potable water to saturate your sand. (In most cases glazing is probably the more sensible option.)
At this point, your evaporative cooler will be close to completion. As a cover you can use just about anything that will cover the opening of the second pot, which will act as the inside of your cooler; a clay or ceramic lid or some kind of a wet towel or cloth are common choices, and the latter will actually cool the contents of your pot-in-pot fridge a little more as its moisture evaporates. Finally, you will need to find a spot that is exposed to the breeze but protected from direct sunlight, and when you set your evaporative cooler up, it should be mounted on some kind of framework that elevates it off the ground so air currents can flow underneath the bottom of the cooler.
And believe it or not, that is all you need to do to get started. As the water in the sand begins to evaporate, it will draw away heat from the inside areas of the cooler, and any food or drink items or other types of products requiring refrigeration that have been put inside the covered bowl of the smaller pot will slowly but surely lose heat. In order to keep the process going in perpetuity, it will be necessary to add water to the sand in the evaporative cooler twice each day, and once equilibrium is reached, a steady temperature will then be maintained inside of the cooler.
But when we speak of equilibrium and a steady temperature, it raises an obvious question – just how low can we expect the temperatures to drop inside an evaporative cooler’s storage pot? Unfortunately, not as much as some boosters of this “technology,” if we can call it that, are claiming on various websites.
The refrigerating ability of an evaporative cooler is determined by the confluence of four factors: the air temperature, the relative humidity level, air flow (wind speed), and the surface-area-to-volume ratio of the smaller storage pot. To get your DIY refrigerator into the sub-fifty degrees Fahrenheit range, where refrigeration begins to occur in earnest, if the relative humidity is 30 to 40 percent the outdoor temperatures would need to be below 65˚F for effective cooling to take place. If atmospheric temperatures rise above 75˚F, breaking the fifty-degree barrier might be all but impossible, and if relative humidity levels are above 50 percent the temperature inside of an evaporative cooler is unlikely to drop much more than ten degrees lower than outdoor mercury readings. This is why evaporative coolers are not generally recommended for those who live in humid environments, like the American Deep South, and they may not be able to produce excellent results even in drier climates on extremely hot days. (High desert environments are probably the best locations for these coolers.) So while evaporative coolers can perform quite capably as a substitute for electrically powered refrigerators, if you decide to build one, you will have to be realistic about what you can expect. They will help prolong the shelf life of fruits and vegetables even at temperatures a little above fifty degrees, but if you expect them to keep your beer ice cold on days when the temperatures soar into triple digits, you are going to end up being disappointed.
Because evaporative coolers work better with relatively large amounts of surface area in comparison to their volume, building multiple smaller units will deliver better results than simply building one large unit. In this case, bigger is not better, and quantity is synonymous with quality rather than being its opposite.
As long as the basic design is preserved, do-it-yourself evaporative coolers can be built using a broad range of materials. For example, metal, plastic, and wooden pots or cylinders can be used in place of clay, although if you use one of these material, it will be necessary to cut holes in the sides of the outer container to make sure air can get in to facilitate efficient evaporation. (The natural permeability of clay pots is what makes them the preferred option.) If holes are needed for ventilation, a fine mesh will be needed to keep the sand from leaking out. And speaking of sand, alternative materials such as soil, charcoal, or sponge can be used as filler in an evaporative cooler, just as long as they are able to efficiently absorb and hold water. (The cheapness of sand is why it is normally used.)
Imagining Our Way To A Brighter Future
The clay pot-in-pot design described here is based on a version of the evaporative cooler called the zeer. The zeer was invented (or perhaps we should say re-invented, since evaporative coolers in one form or another have been around for more than 4000 years) in the 1990s by a Nigerian teacher named Mohammed Bah Abba, who wanted to help poor African villagers without access to electricity preserve perishable foods. This simple but ingenious cooling device has proven to be a fabulous success, and thousands of families who were formerly hovering on the edge of starvation have been able to dramatically improve the quality of their lives thanks to the inspired vision of one dedicated public servant. Evaporative coolers are literally changing the world, and they are certainly an attractive option for those who are making a concerted effort to increase their self-sufficiency while reducing their dependence on a power grid that may no longer be there in the years to come.
Potential sources of free natural energy are available all around us, and the only limits we face in learning how to use them are the barriers we have constructed in our own imaginations.
©2013 Off The Grid News