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== Project Requirements == | == Project Requirements == | ||
Construct a working solar powered food dehydrator for the | Construct a working solar powered food dehydrator for the Arcata Educational Farm to use this season. This project will be used as a educational tool for community members and farmers alike. This solar dehydrator will be an example of how to build your own food dehydrator, encouraging people to be more self sufficient and energy conscious. | ||
== Criteria == | == Criteria == |
Revision as of 03:42, 12 May 2009
ABSTRACT
The Plan:
The idea for building a solar dehydrator is to provide the Arcata Educational Farm with a reliable hybrid dehydrator. Its purpose is to help preserve surplus crops. In addition to using this dehydrator as an alternative method in preserving vegetable, fruits, and meat, it will promote sustainable practices.
This solar dehydrator will not only serve as a tool for preserving and storing foods but will be a demonstration. This display is for the farmers, share holders and communities members to how to witness and apply sustainable and alternative methods of technology to their everyday lives.
Unlike the electric dehydrator, this solar dehydrator will draw its energy from harnessing the sun's energy, allowing electricity to not be needed. Solar designed dehydrators allow the ability to dehydrate and preserve food available to anyone, with little material, cost or solar design knowledge.
Introduction
Overview:
Solar dehydration is another great example of appropriate technology. This alternative method allows the use of solar design and food preservation, which is key to the livelihoods of people all over the world. This technology has multiple designs often which use less material and are more energy efficient and cost efficient.
Dehydrating food has been a long standing practice of cultures all over the world. With many cultures dehydrating food by placing it on roof tops or ground to dry. This unfortunately has the high risk of contamination from dirt, pest, and unfavorable weather. By creating a dehydrator which has covering it is less liking that the food content will be exposed to contaminants.
The principle behind dehydrating is taking out the excess water in the fruit, vegetable, or meat, as a means of preserving and storing. By taking out the water content it limits the medium that harbors bacteria or fungi. Dehydrating food allows it to have a storage life of multiple years.
Solar dehydrators work by creating a consistent warm air flow through a cabinet containing the agricultural products on various shelves. Solar energy is absorbed in a chamber with a black corrugated steel backing. The energy is transformed into heat that warms the heating chamber. This induces a convection of hot air that rises through the cabinet. The warm air passes through the shelves and evaporates the moisture from the food. It is simple in principle but profound in action.
Project Requirements
Construct a working solar powered food dehydrator for the Arcata Educational Farm to use this season. This project will be used as a educational tool for community members and farmers alike. This solar dehydrator will be an example of how to build your own food dehydrator, encouraging people to be more self sufficient and energy conscious.
Criteria
- Durability
- Able to withstand weathering and continual use
- Educational Aspect
- Informative for users and visitors of the farm
- Expediency of Drying
- Quick and complete removal of moisture from products with time constraints of rotting
- Dehydrating Capacity
- Accommodates loads of agricultural products from the farm not gathered by CSA members
- Appropriateness of Material
- Construction Materials come from sustainable sources (reused, reconditioned)
- Functionality
- Performs to the liking of the farmers
- Mobility
- Lightweight and portable in case of moving needs or for tracing the sun.
Design
We will be adapting a simple upright design used by CCAT several years ago and proven to work in the area. The Energy receiving component will be slightly larger than the one CCAT had. The structure will be 6 feet tall, and have about 30 square feet of shelving space for produce. We have adapted the design of the Solar Food Dryer Cookbook to accommodate for a larger window, so the duct and window collector dimensions in the adjacent schematics do not exactly equate to the dimensions of our final product. The principles of how the components work remain unchanged.
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Side View
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Window Collector
Our window has just under 3 square feet more surface area for absorption than the window box of the prototype. This should allow for additional conveyance of heat through the cabinent. Also, rather than a horizontal cutout on the bottom of the window box frame, we chose to use six 1.5 inch diameter holes drilled with a spade bit. This allows for less air flow that is instead warmer overall. We adapted the duct system to allow play and pivot for the window box so that seasonal angles of incidence could be accommodated for. However, The looser-fitting union between the two major components needs some sort of rubber flap sealing to ensure warm air enters into the cabinet rather than escaping around the sides of the duct.
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Cost Table
Table 1. Solar Food Dehydrator (Materials) Cost
Testing ResultsIt is far to early to draw conclusions. | |||||||||||||||||||||||||||||||||||||||||||||||||||||
Table 3. Solar Food Dehydrator Efficacy Data
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Table 4. Electric Food Dehydrator Drying Times
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Design Consideration
- Solar energy
Solar Positioning: It is extremely important to know your solar position when you do any building that harbors the energy of the sun. Learning the suns path in the sky helps to understand where it will rise and fall throughout the season. The actual position of the sun is dependent on the observer’s actual latitude. To find suns position their are two angles in which you need to obtain, the solar altitude and solar azimuth. This is done by measuring from true south. Pointing at due south with one arm with the other point at the sun the length from the sun to the horizon is the solar altitude. The angle between your arms is the solar azimuth.
Isolation: Solar insulation effect the amount of the suns radiation you receive from a given spot. This is also determinate on length of day, humidity, cloudiness, elevation and any object obtrusion. In Arcata it will be important to understand summer time climate and weather patterns. Having high cloud coverage will dramatically change the solar isolation
- Heat Transmission
Heat Flow: Heat flow is heat’s energy in motion. The heat flow is determinate of the temperature difference between where is flowing towards. Heat will always equalize temperature differences by flowing to appropriate place .This path at which hot air rises and moves is dependent on resistance, this can be a mechanism of inside and outside temperature. This will need to be utilized by having our solar collection bring warm heated air to our dehydrating box, good heat flow from the solar collection will be key in our design.
Conduction and Convection Heat Loss: The ability for a material to allow the transfer the flow of heat is very important in designing a structure designed for drying food. Different materials have an array of resistance to the transfer of heat. This need to be taken to account when determined the thermal effects of each building material. Calculating the heat loss due to outside temperatures by estimating the lowest expected temperature. The convection heat loss happens within walls of the building. Having a gap between outside and inside temperatures allow their to be less temperature severity. In one of the books (Anderson and Riordan,1976) it states that “for insolating value to be significant the width of the air gap must be greater then ¾ inch”. To wide of an air gap can allow to such circulation between the air gap which can off set the insolating ability.
Literary Review
Sources
- MacDonald college of McGill University, Brace Research Institute. a survey of agriculture dryers. Quebec: Macdonald college of McGill University, 1975.
- Riordan, Bruce, and Michael Anderson. The Solar Home Book, heating, cooling and designing with the sun. unknown: Brick House Pub. Co., Inc., 1976.
- Valdez, Annie, and Maria Valdez. A Cookbook for Building a Solar Food Dehydrator. Alamosa Colorado: O&V Printing Inc, 1977.
- Macdonald college of McGill University, Brace Research institute. How to make a solar Cabinet Dryer For Agricultural Produce. Quebec: Brice Research Institute, Macdonald college of McGill University, 1975.
- Riordan, Bruce, and Michael Anderson. The Solar Home Book, heating, cooling and designing with the sun. unknown: Brick House Pub. Co., Inc., 1976.
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