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.
The hoop house itself leaves much to be desired. I bought it used on Craigslist for $100, and it’s full of holes that no tape will hold shut over time. Rather than replacing the plastic, I hope to add another layer of protection next winter by purchasing a solar pool cover, folding it over itself and cinching it down over the greenhouse to add some insulating value and stop the air leaks in winter.
Probably the most important layer of thermal protection lies in the controller software. I built my own controller from an Arduino with relays and temperature sensors, and programmed it myself. It gathers all the data, publishes it online, sends me text messages when problems occur, and makes decisions about what to do depending on conditions. In winter, the controller varies the frequency of flooding and draining the beds based on temperature. At lower temperatures, the beds flood less often. When the greenhouse temperature drops below 10°F, the beds each flood every 5 hours. This balance avoids freezing in pipes and the pump, prevents the bacteria from going dormant, and keeps the water in the highly insulated and sealed tanks most of the time. The controller also manages the water heater, which I built by modifying a bucket heater with gobs of epoxy.
While it drove me nuts while it dragged on, the polar vortex we experienced up here in Wisconsin gave my system a great test run. I raised 45 trout and 40 catfish this winter in 50°F water and never lost a fish. The catfish didn’t eat much but didn’t lose weight either, while the trout grew like weeds; tripling in size over the winter months. The bacteria kept up with ammonia conversion throughout the winter. While nitrate levels went through the roof, the fish showed no adverse effects. I did a 1/3 water change every month, and with more water changes could raise more fish. In warmer weather or with better thermal protection, the plants would have kept growing and taken up more nitrates, allowing for fewer water changes.
The aquaponics energy bills over the winter surprised me with how low they stayed. In the coldest January of my life I only spent $30 for the whole month. The plants themselves didn’t fare quite as well: while the temperature in the greenhouse never dropped below zero, it did stay right close to zero for weeks on end. All my various types of lettuce and Asian greens gave up the ghost in January, although some of the spinach hung on into early February. By the end, only one Giant Winter Spinach plant, which I now call “Frosty” and intend to save seed from, still lives.
Despite this, I’m grateful for the worst winter in memory because it gives me a worst case scenario that I can design for. I still have a few improvements up my sleeve to improve my plant survival rates for the next polar vortex. These include:
- Improving the low tunnels through the use of a layer of plastic over the Agribon, and better air sealing.
- Adding a double-layer of pool cover to the outside of the hoop house for insulation.
- Rebuilding the north half to add an insulated thermal mass wall, like Penn & Cord use.
- Making an insulated blanket to pull over the hoop house for cold nights like Chinese growers use.
Next year, I hope to replicate my success with winter fish growth and focus on plant growth, for a bounty of 2015 winter greens.
A Word of Caution
I read a blog post late last year which said that a majority of people who begin building aquaponics systems give up before finishing. I believe it. I would add that attempting to build energy efficient system for use in a cold climate probably results in even higher quit rates. The cold adds significantly to the number of things you have to worry about and the number of things that can go wrong. Once it works, it works. But up till that point, you can drive yourself stark raving mad with endless troubleshooting.
I had the unfortunate privilege to be the first person to build a backyard aquaponics system in my area and the first I know of to systematically wrestle with cold-proofing at the component level (like a factory). Without any experienced aquapons to guide me through the process, I spent three times as many hours, 40% more money, and a great deal more of my sanity than I could have, had I known better. There’s only so much you can learn online and from books.
If you do decide to build a cold weather system care about energy efficiency, I highly recommend that you offer to pay some more experienced folks to help with your design and guide you through the process. Had someone offered me this option, I’d have jumped on it. It’ll cost you some money but save you a lot too. And you’ll have your sanity.
If you’re in my area, I’d be happy to give you a tour, share some winter spinach, and chat about what we can do together. I live in the low income south side of Madison, near a lot of out-of-work neighbors who I’d love to hire. I hope to begin building systems for others and gather up a crew once business gets going, as well as start producing custom-designed controllers.
I walked into the scrap metal dealer. Torches, snips, welding masks, and all sorts of half-disassembled machinery littered the former auto shop they used. Grungy men worked, or chatted and smoked. Most sported extensive tattoos. I approached one. “Hey I’m the one who called asked about the freezers. You said you had a couple for me?” As I spoke, I saw the people in the shop dart awkward and intrigued glances around at each other. Why would they be interested in me? “Sure that’ll be $24. You want the Freon taken out?” “Yes, please.” “Need help loading them?” “Sure – thanks.” As I watched them remove the refrigerant, I saw that none of the workers left the room. They all seemed to want to see what I was going to do. As one walked over to help me load the first freezer onto my trailer, he asked casually, “so, on the phone you said you’re gonna bury these in the ground?” “Yeah, that’s the plan anyway.” He kind-of stared at me and seemed to be working up the nerve for something. What, I couldn’t guess.
Finally he came up close and whispered in my ear, “So we all kinda been wondering… who you gonna bury in them things?”
Jeremiah Robinson is an energy efficiency engineer with DNV GL, and is passionate about aquaponics systems. He and his family live on a permaculture homestead in Madison, WI, and he enjoys helping others find solutions for their own aquaponic endeavors.
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