At he risk of sounding like an infomercial (I have nothing to sell related to this, so I'll continue), I've always disliked off-the-shelf dehydrators. They are good for drying fruits in small quantities, but herbs are always an issue because is hard to fit very much inside. Alternatively, drying herb bundles slowly by hanging around the house is not ideal either, as there is oxidization during the slow drying process leading to flavor loss. Across the board with off-the-shelf dehydrators, I am unhappy by the flavor loss created by the heated drying process. One major part of dehydrating is airflow to pick up and whisk away the moisture. Low humidity airflow can speed that process up a lot.
I wanted something that would allow for drying whatever quantity, big or small, of food I need to dry. I didn't want to waste harvested food by having a bottleneck at the humidifier.
I mitigate these issues by making a large dehumidifier through a process that I have been using since 2009. What are we trying to do when dehydrating? Remove moisture. There is a higher absolute humidity with higher temps, so the air can pick up more moisture which is one reason most of the shelf dehydrators use heat. Also, size-wise they can more compactly add a heater than give sufficient air flow. Due to those using heat, people assume that the heat is necessary. Using a dehumidifier, you go straight for the goal, with less added heat. The process by which a dehumidifier removes moisture creates a small amount of heat, but its still lower than a purchased dehydrator. My current dehydrator is in my basement so the temps during harvest time remain low with the coolness of the basement.
I built a large wooden box (3 feet tall x 4 ft wide x 2 ft deep) and put the dehumidifier inside with the humidity set to zero. In previous homes, I have used a closet, which was great for drying very large amounts of things. I added a box fan to the equation for extra airflow, since the closet was so sizeable. I also had a speed rack inside with baking sheets and woven mats for drying shelves in addition to herbs hanging overhead. With the current box and dehumidifier, if I put the fan setting on high, there is sufficient airflow. You could add small fans that produce little heat by salvaging computer fans wired to an old cell phone charger for power. Inside the box, I have two lips that run the length of the box on opposing sides. I cut dowels to length to span this gap. From there, I can hang whole basil bushes or bundles of parsley before the frost. This last year, we clear cut all the parsley before the frost and then hung and dried all of the bundles.
What is required to make one yourself... a contained space that can be a closet or a dedicated box, a dehumidifier, an outlet nearby, a way to tie up the herbs and other things that need to hang, and perhaps a fan if the airflow isn't sufficient. It is also nice to have sheet trays as well as silicone baking sheets on top (silicone is especially nice for drying fruit because as the fruit dries, it gets sticky and you can easily obtain both the stickiness and the fruit from the sheet this way).
I'll update with pics at a later date, when the dehydrator is more active. Its not seeing much action currently with a northern winter. I wanted to post a how-to now, so that if you find it interesting, you will be able to get going on it before harvest times begin.