Cooling Systems

I use an air conditioner mounted in a basement window, with cold air ducted into the 8x2x2 growing space. Drops night temps down to low 60s-upper 50s in the summer. In winter, I use outside air.

 

I use an aquarium chiller connected to a computer radiator/fan setup in the tank. In line, I also have a cooler as a reservoir with an aquarium pump. I found that it's really important to vent the aquarium chiller exhaust out of them room and do a good job insulating the tank/tubing. If you don't, you'll get temperature gradients within your tank and water will condense on your radiator since the system has to work really hard. I recommend using water proof fans for the radiator.

Temps I get are 70-72 in the day, 52-54 at night. I use an Inkbird ITC-310T to control the temperature with a schedule.

 

What are the advantages to using a cooled water/radiator setup, as opposed to just ducting cool air from an air conditioner (possibly with a modified thermostat) into the tank?

 

I have never done either, but I would think that a window a/c unit moves a large volume of somewhat dried air, while the aquarium chiller setup, with the heat exchanger inside the tank, would not require the air flow volume to achieve the same effect, while allowing the RH to stay higher.

 

That's a great question and even after building the chiller/radiator setup, I'm still not sure it was the right decision. I've only built the heat exchanger system and I'm interested to hear what people using air conditioners or other systems think.

Budget
Chillers and air conditioners are both pretty expensive. Luckily, I was able to find an aquarium chiller secondhand for very cheap. I struggled to find an air conditioner in my price range that met my temperature requirements. The costs of the radiator, waterproof fans, and chiller exhaust fan aren't negligible either. I'm not sure which system runs more efficiently power-wise. Buying a used air conditioner or chiller makes this category a toss up.

Temperature
The air conditioner needs to pump out air at a few degrees lower than your target nighttime temperature (i.e. 45-50°F). I could not find an air conditioner that does so in my budget and I wasn't willing to experiment with cheaper ones that have unpublished numbers. If the air conditioner has a programmable temperature setting, it needs to remember that setting after a power reset if you use a relay to control the temperature.

Aquarium chillers go down to these temperatures really easily and the JBJ Arctica chillers remember the temperature on power reset. My heat exchanger gives me extremely consistent tank temperatures. I get about 1°F variance both during the day and night, which is near the accuracy limit of my temperature sensors. My nighttime temps are ~53°F year round. I'm sure there are air conditioners out there that will do the same. I know OrchidKarma used one and obviously had great success.

One downside of my particular chiller is that there's a few minute delay between when the power turns on and when the compressor turns on. Something to watch for.

Humidity
Radiators condense water and will drip - watch out for rust and make sure your fans are waterproof. The heat exchanger system lets me use a really tiny fogger as a humidifier. If I leave it on, it can fog the entire tank in a couple minutes.

I live in Colorado, which is very dry. Like Ray mentioned, I didn't want an air conditioner to blow low-humidity air into the tank whenever I needed to cool it. I assumed that this could be a problem at night when the air conditioner would be running more often. A more powerful humidifier would probably be more suitable for an air conditioner setup. I'm not sure if condensation in the pipe is an issue or a vent flap is necessary on the tank's cool air inlet.

Setup/Maintenance
The radiator/chiller system has a lot more components and it's a pain to keep clean. The radiator is bulky, so you have to be careful about its positioning in the tank. That said, I've never had my heat exchanger system leak or fail. Air conditioners seem simpler. In either case, if you have electrical cables running in your tank, don't forget to waterproof any connectors.

If I were to build the system again and I could find an affordable/reliable air conditioner, I would use that. While I've had great results with my system and I'm very happy with it, it is tempting to trade less complexity and components within the tank for a (possibly) less consistent or higher nighttime temperature. The grass is always greener and I won't be swapping to an air conditioner anytime soon. I'd rather just build a greenhouse.

 

I bought my air conditioner from Walmart, the cheapest one they had, around $100. It's mounted in a basement window, and I made a hood out of pink styrofoam insulation sheets to allow me to use clothes drier duct to move air into the plant enclosure. The outlet air is around 40-45F. The thermostat senses ambient basement conditions, not the area cooled, and I run it at max cool and max airflow.

I have since modified my setup to use sheet metal ductwork (4" diam), wrapped with insulation (don't remember the R-value, it was left-over from another project). The only uninsulated segments is the flexible metallic dryer duct connecting the a/c hood to the insulated ductwork.

 

I remember seeing a couple of other alternatives - One was to use a wine chiller and convert it by adding lights and humidity (I saw this done with a small refrigerator once, as well), and another is to build an enclosure on top of a small dormitory refrigerator, circulating air through the floor of the tank into the fridge. All I can say is that it had better be self-defrosting.

Another variant on that dorm fridge is circulating water through metal tubing coiled in the fridge, to avoid condensation issues.

 

That's awesome Carl! Did you insulate the tank as well? Does the humidity change at all when the a/c is on or you're using the winter air?

In an AOS video talk on terrariums (mostly small and intermediate), the presenter had bought a large, horizontal, food display fridge. I'm not sure if they finished the project though.

 

I'm currently following this (DIY Air Conditioner - Cooling Systems for Highland Nepenthes) tutorial. Which has a cheap alternative for an aquarium chiller. I bought the parts for the water cooler itself, the cooler box and the window AC, for less than $40 canadian.

The problem I'm currently having is that the spray foam doesn't seal so the box leaks lol.

 

I did put styrofoam insulation sheets around three of the four sides of the enclosure - either 3/4 or 1 inch thick, I forget which. I do also have a mist system using a misting pump (150 psi) and r/o water for humidification. The misting system runs several times a day.

A plan is to automate all this, using an Arduino microcontroller, some sensors, and SSRs. I need to get off the stick and finish that project, though. Not particularly difficult if you know software and basic circuit design.

 

If anyone is reading this later, I did get DIY Air Conditioner - Cooling Systems for Highland Nepenthes working. It cools my 3ft x 3ft exo-terra to 12c below ambient.

However, it's much easier to skip the foam bit. Make the smallest possible cut in the wall of the cooler to get the condenser tubes through. It's a huge pain to seal it up otherwise. I also didn't use a cold air duct like he did, and just bolted some 120mm fans (https://www.amazon.ca/AC-Infinity-C...ds=muffin+fan&qid=1555211351&s=gateway&sr=8-2) to a heat exchanger for cooling CPUs, and put them in the tank. The fans are on 24/7 and serve as air circulation, and the pumps circulate cold water/propylene glycol mixture through them when the tank gets too warm.

 

I built an enclosure using a bar fridge (not a peltier wine cooler). It has a glass door so I can view things inside. I cut a square hole cleanly in the top of the fridge, siliconed in a sheet of clear acrylic that was maybe 1/8” or so thick and mounted two dimmable LED floodlights (one cool white and one warm white) in the recessed area.

I wanted to keep lighting and this heat generated for the most part external. A little less heat in the enclosure and less work for the fridge.

It’s climate controlled via a zoo med hydrotherm, not the best but easy to use. Although keep your receipt as the sensor is known to fail. Mine did after about s year but they sent new ones for free. Have a backup humidistat from amazon handy in case yours dies. The hydrotherm controls humidity via an ultrasonic fogged placed in a reservoir I made in the bottom of the fridge. An IP 67 rated 120mm noctua fan circulates the air at all times and moves the fog or mist through the enclosure. Fan sits just above the water reservoir. This also circulated the cool air up to the top of the fridge and helps keep a more consistent temperature throughout the enclosure.

Initially with just one plant (a dendrobium Nagomi yellow/red the fogger was on quite a bit. I played around with humidity levels and so on. Finding a sweet spot at about 75%. Any more and sensor issues begin to happen quickly. Now as I’ve put about 20 plants in the fridge, I find the humidifier rarely comes on and I generally leave the door open a crack to encourage a bit more air exchange.

The hygrotherm controller also does night and day temperature differentials easily. It’s got a photovoltaic sensor on it so when the light goes off it drops temps to set points. In my case around 12 Celsius. Daytime I’m around 23 Celsius.

It’s worked well so far. A few bumps in the road here and there. I used it for a whole year while figuring it all out and how it worked, igniting it for a week or so at a time to see how the plants did. I am pleased to report that the longest resident has been in there for about 1 year 4 months now... doubling in size and there are 6 flowers on it (the Nagomi yellow/red) it could be in a little better shape but I ran it through the ringer

I’ve since moved cuthrburtsonii’s in there, lepanthes, Dracula’s, trysetella hojerii, and a bunch of other cool growers. All seem to be doing well, Im still getting used to working with LEDs.

Cost to build this was around $500-600 Canadian. I went to a scratch and dent appliance place for the bar fridge ($100-150 I think). Ordered the zoo-med hygrotherm noctua ip67 120mm fan and fan speed controller as well as fan extension wires from amazon, and the lights from eBay (led security flood lights)

It’s been fun and it’s now basically full. It has no issue with temp control. I clean it out every now and then by taking all plants out, washing down, spraying with physan and washing again, then put egg crate back in and hang plants.

I water mounted stuff daily generally and potted stuff when required all with reverse osmosis water, sometimes as of more recently a weak solution of sea kelp and a dash of superthrive. Use a hand held pump sprayer. Takes about 1 -2 minutes to water everything and maybe 20 seconds to spray the mounted plants.

Water overflow from watering spills down through the egg crate and into the bottom reservoir. I empty it when I clean it maybe once a month.

Egg crate for hanging pots and mounts are on the side walls, and a shelf between the two. I don’t have egg crate mounted near the cooling plate on the back of the unit. Didn’t want to accidentally freeze roots of plants close to it.

Egg crate over the reservoir to allow water and minimal debris to drain from watered plants. And also allow me to store potted plants on the bottom of the fridge.

That’s all I can think about for now. In future I’ll be thinking about improved air exchange design. Something better than keeping the door barely cracked open with bamboo skewers.

Hope this helps

 

I've always felt like a cut flower cooler would be perfect for this sort of thing and lights are already in it.

 

I agree that it would be a great start, but I suspect you'd have to upgrade the lighting a fair amount.

 

I use an aquarium air pump attached to tubing,you may have to cut a tiny notch in the door seal,and run fresh air in that way.You can also attach an airstone,stick it in a jar of water and increase humidity.Anyways,works for hibernating lol.