Bayside Park Farm solar dehydrator
Bayside Park Farm (formerly known as the Arcata Educational Farm) has been in operation since 1993, and was Arcata's first CSA (community supported agriculture) farm. In order to allow for the preservation of the farm's excess crops, a solar dehydrator was implemented in 2009 by a previous ENGR305 class. Dehydrating food is an especially important process for farms because it allows them to maintain their livelihood (food) for the long term. However, after problems with adequately drying produce, the dehydrator fell into disuse and was ultimately removed from the property. We were asked to build an effective, educational follow-up to the initial dehydrator.
The objective of this project is twofold:
- To produce a durable and effective solar dehydrator to aid in the preservation of Bayside Park Farm's excess produce.
- To design the solar dehydrator simply and accessibly enough to foster adoption and replication of the solar dehydration process.
In summary, it is our ultimate goal to provide the Bayside Park Farm with a solar powered food dehydrator that will meet their produce needs, is easy to maintain, and will last much longer than the one before it.
This criteria list, while not final, represents what we feel are the most important considerations concerning the scope and objective of this project. The scale is weighted from "1" being of the least significance to "10" being of the most significance.
|Functionality||Device working as intended|
|Maintainability||Has to be maintenance friendly to the user, little knowledge required for maintenance and repairs|
|Safety||Device must pose no outstanding operational dangers to user|
|Usability||Ease of regular operation is key, intuitive handling|
|Budget||Must not exceed budget|
|Reproducibility||Design can be easily reproduced by others|
|Aesthetics||Must look like a natural extension of the farm|
This is a review of the available literature pertinent to the proposed solar dehydrator at Bayside Park Farm.
The dehydration of food is the oldest method of preservation, dating back as far as 12,000 B.C., with proponents and users including the Roman empire, ancient Middle Eastern and Asian cultures, and the Europeans of the Middle Ages.  Solar dehydration was likely the first (and least resource intensive) method of food drying, and is very simple to do in a sunny, warm environment. Food is placed in a container designed to trap heat, and the air is then heated to a temperature high enough to prevent microbial growth, but not high enough to actively cook the food (roughly 130 degrees Fahrenheit for produce and 150F for meat).  One of the most important aspects of a dehydrator is the airflow: the air should be able to flow in one side, heat up and absorb water from the food, and escape from the other side.
One of the biggest issues with solar dehydration, particularly in Humboldt County, is its reliance on the ambient climate. Arcata falls and winters are typically characterized by cool temperatures with intermittent sun. Alongside the cool, cloudy days, an average relative daytime humidity of roughly 60% (with nighttime humidities commonly reaching 90%) will pose a challenge to achieving satisfactory food dehydration. 
Components of solar dehydrators
There are a multitude of designs, shapes, and plans for solar dehydrators; none of which are standardized. However, all of them share a few similar components: a heat chamber, a method of keeping it off the ground, and a removable tray that contains the food.
The heat chamber is most often a solid-sided box with a clear polycarbonate top; this acts as a greenhouse and traps incoming solar heat in order to facilitate the drying process. It is almost always backed by a dark material in order to promote heat absorption. The heat chamber can either be used as a simple heat collector (which acts as a way to foster convective air currents in a system) or as the drying chamber itself. 
In order to prevent the intrusion of insects and foreign contaminants, the dehydrator is commonly placed on legs or elevated in some way. 
The trays must be permeable in order to allow for either good airflow or to allow any excess moisture to easily escape from the materials being dried. Some sources advocate the use of readymade plastic trays , others suggest custom-building the trays in order to allow for optimal circulation and permeability.