In our quest for a better aquaponics, we each face our challenges. Here in Wisconsin, we average five feet of snow in wintertime along with temperatures below -20°F, and often go two solid months without a single day above freezing. When we try to grow plants in winter, our main battle is with the cold. Growing Power and Nelson & Pade, both here in Wisconsin, offer one solution which basically involves heating your greenhouses all winter long. A large commercial operation with high sales prices or a cheap source of heat may justify this, but as an urban homeowner with a backyard system the numbers don’t add up.
In my day job, I work with energy efficiency in buildings and factories; two building types that operate under two completely different philosophies in terms of temperature and humidity control. In occupied commercial or residential buildings, the exterior walls (called the shell), provide the only layer of thermal and humidity protection from outdoor conditions. You control heat and humidity in the same way for the entire interior of the building (called the envelope). In factories, however, temperature and humidity controls vary dramatically depending on whether you’re smelting aluminum, processing potatoes, or creating liquid nitrogen. Within the building shells are many additional layers of thermal and humidity protection that provide the right conditions for people, materials, and processes.
When you get down to it, an aquaponics room or greenhouse acts more like a small factory than an occupied building. It doesn’t need to be maintained at temperature and humidity levels designed for humans, and different parts of the system require different temperature and humidity conditions. Separating the different system components with thermal and humidity barriers allows you to maximize energy efficiency by providing only the needed energy inputs required by that component.
- The fish tanks require a certain minimum and maximum temperature, and can tolerate a limited range of daily swings, depending on the fish species.
- Pumps, filters, and piping require a different temperature profile, primarily to prevent freezing.
- The root zone of plants and the media on which the bacteria live require a third temperature profile, which allows for nutrient cycling and root growth, depending on the type of plant.
- The aboveground portion of the plant requires a final temperature profile and swing limits, again depending on the type of plant, its sensitivity to frost, and your expected growth rate.
All of these subsystems interact, but hold different requirements and need different levels of protection. Sure, heating the greenhouse to 74°F solves all these problems, but when nighttime temperatures hit -20°F, this will break the bank and burn a lot of coal, gas, or wood to make all that electricity. Treating these zones differently offers us the opportunity to save a lot of energy.
Maple Bottom Aquaponics
In the backyard system at my home, which we call Maple Bottom, the fish live in repurposed freezers that have been water-sealed and fitted with windows for light. Already air-sealed, well-insulated, and designed to contain humidity, they offer the perfect environment for aquatic climate control. On a cold winter night without any additional heating, with the aerators going but the water pumps off, the temperatures inside my tanks drop about a degree. Compared to an open-top, uninsulated fish tank, the energy loss from my tanks is almost negligible. For my four retrofitted freezers, I paid a total of less than $400.
For some additional temperature-moderating effects and to avoid the need for the increased surface area created by a sump tank, I buried my freezers in the ground up to their rims. In order to avoid dramatic water level fluctuations as I flood my beds, I purchased a high-durability exterior pump run on a timer with an indexing valve. This idea came courtesy of Aleece at Aquaponic Lynx; one of the most helpful and generous people I’ve met in the aquaponics community.
Because aquaponics systems require such large-diameter pipes, I insulated all my plumbing with specialty large-diameter foam insulation from a local plumbing supply warehouse. This required me to research exactly what I wanted ahead of time in order to pretend to be a contractor as they don’t serve homeowners.
My grow beds took a fair amount of trial and error, and I filled a lot of round files with crumpled graph paper. I tried halved barrels like Travis Hughey, but their round sides, small size, and irregular shape made pipe inlet and drain penetrations awkward as well as difficult to insulate with waterproof insulation (all flexible insulation like fiberglass loses its insulating properties when damp). After six months of wrestling with wet insulation, over-flooding beds, and failing drain pipes, I decided to start over.
Demolishing my barrel-based beds, I rebuilt new beds entirely out of 2” extruded polystyrene (EPS) insulation board with a wood structure and pond liner for water sealing. This provides an R-value of 10 on the bottom and sides of my grow beds, preventing cold spots at the edges or corners. Using a 4” pipe with slits as a protective chamber for the supply and drain piping prevents roots and rocks from getting into and clogging the pipes as happened on all my other designs. It also allows access to the piping without digging through gravel. Adding a homemade charcoal bucket filter upstream of the pump helped with clogging as well.
For the bed tops, I made the wood structure as level and flat as I could. This created a flat surface for the top layer of insulation to press against, creating a somewhat-effective air seal. In the top layer of insulation, I cut 3” holes for net pots in which to plant my seedlings. Above the net pots I added plastic covers that keep as much of the humidity and heat from escaping through the plant openings as possible. The primary way that heat escapes my system is through the drain action sucking cold air into the beds, and flood action expelling the warmed heated air out. To help with this, I built low tunnels over each grow bed with #4 steel wire and Agribon draped over it. Next year I plan to drape plastic over the Agribon.