I'm planning a terrarium/vivarium or however you want to call such a thing. It will be a closed case about 55x23x35 inches (a bit under 200 gallons). It's intended for highland nepenthes (and some highland miniature orchids). It will be placed outside protected from the sun. Temperature range will be (50/55 night and 70/75 day, might get down to 40 in winter).
- part of the year without doing anything, outside temperature range will do
- a couple months I'll need a bit of heating on cold days. It rarely freezes (not every year) so heating will be very mild, mostly some days to increase day temperature. Even without heating it won't freeze inside the case.
- a few months it will require some night cooling, days will be ok
- cooling in summer, night and day.
I'm trying to decide a cooling method.
1 - One option is to use an aquarium chiller. These would work but they are expensive
2 - Another idea is using a small freezer (or refrigerator) and pass a lot of tubbing with water through it.
3 - peltier. Not sure it will be powerful enough for such a big case. For smaller ones I believe it can work with enough insulation. To do it well I would need a powerful heat sink, water cooled with a good radiator. Such a system also gets expensive fast.
4 - evaporative cooling. Won't allow me to control temperature enough. Also, humidity around here is usually around 60-80% so not very useful (about 100 meters from the sea). I have a smaller tank outside in a drier place and humidity is usually between 85 - 95% inside, I just spray once a day.
5 - air conditioning. Units I've seen are just too big and throw too much air for such a small place. They would be ok for a room, but as this will be outside it's impossible to cool ambient.
6 - frozen water bottles. Not enough freedom, I'm tired of them in a smaller tank. Impossible to control temperature. For a tank this size I would need a freezer just to store the bottles.
7 - hire a professional to add "fridge machinery" to the chamber
Most options cool water which must then cool the air. Terrarium will have a couple inches of water at bottom. I was thinking about having a cooled water tank (insulated) right next to the plant tank where I would have a humifier. This should send a very cold fog inside the case. As I'll need some fans for air movement, I could make one send air through this water almost constantly. It could even have some moist materials around to get more humid and do some evaporative cooling (I don't expect much inside the case as humidity will be very high).
I could also cool the water below the plants, with air movement that would cool all the air. I think it will be difficult to replicate night/day temperature drop this way. Also, water below the tank ends up dirty which can cause problems to the pump so I don't like this part much.
I also thought about using an air pump through the cold water. I'm not sure about the noise. I would probably need a fairly powerful air pump to make a difference. Will air get cold just by going through a bit of water?
Would connecting a heat sink from the cold water to the tank help? Maybe if I use enough aluminum?
Please, no "grow something else" replies. This is something I WILL have soon. I know some people have similar things for growing orchids (masdevallia, dracula and the like)