Terrarium growing experiments

[Metallising]

I'm using a 20W 1meter heater cable buried in the substrate of my terrarium (pine bark) and it increases temperature by 3C, the terrarium is made of glass 5mm.
I also would like to have some insulating in my terrarium, however it won't be easy build something aesthetically pleasing for display in a living room.

Have you put some thought on cooling? Summer will be here soon.
I'm really tempted on ordering a peltier module. I have read a few trials with poor results but I still think there's some room for tweaking and make it work.

[Draikan]

In my climate cooling isn't really an issue. It rarely gets over 80 here, and then usually only for a few days at a time. My apartment is half underground so it tends to stay even cooler.

As for Peltiers, meh. There is nothing wrong with them, they do work, just aren't a great fit for terrarium cooling imo. They generally use a lot of power for the amount of cooling they provide, compared to anything compressor based. Most folks aren't using them right, they CAN work, but you can't just stick one to the glass and expect it to work some chilly magic.

If you want to use a peltier, make sure you do a really good job of getting the heat AWAY from the hot side. This is even more important to overall performance than how much power you give the module. If you aren't cooling the hot side well, more power can even be detrimental, and reduce the cooling output. When I built peltier chillers for work, I always used a water cooling loop on the hot side. Once you get the heat out of the hot side of the peltier it's not too hard to deal with. The hot side of the peltier usually ends up being the limiting factor for the rest of the system. Using a few extra modules in parallel, and running them all at slightly lower power is a great way to overcome this limitation (because you have more surface area to transfer the same amount of power through).

Cold fan -> cold heatsink -> peltier module -> water block -> radiator -> radiator fans

You can mostly use parts intended for PC water cooling loops to build the hot side loop.

I wouldn't bother attempting cooling until you've made a decent effort to reduce any sources of heat in the tank. Generally this means making sure the lights are LED, outside the tank, and well ventilated. And then insulating as much of the tank as possible, If it's a display tank you don't have great options. Use thicker glass (or double pane windows if you're building from scratch) on the viewing sides, stick styrofoam panels to the back and bottom, and do what you can for the top. Have a plan for ventilation, air exchange will bring in a lot of heat if you're trying to cool the tank.

[Metallising]

Any compressor based option for cooling is expensive, bulky and noisy, apart from being much more efficient and reliable. While a peltier module with two heatsinks and a fan for each side has a total cost of 20-30$ and takes very little space.
Is water cooling much more efficient than simply having a big heatsink with a fan on the hot side? I didn't want to go that direction due being more complex to set and for requiring a water pump. I would prefer to oversize the heatsink rather than having a water cooling system, if similarly efficient.

It's interesting when you say

If you aren't cooling the hot side well, more power can even be detrimental, and reduce the cooling output.

It would be interesting to apply different voltages to the peltier and see how it correlates with cooling power. Assuming the hot side couldn't dissipate the heat fast enough, it could be beneficial to run the peltier at a lower voltage, thus using less energy and producing more cooling power.

Yes I do have LED lights outside the terrarium. My terrarium has a few gaps but I can easily close most of them and keep air exchange to minimum. What I want from the peltier is to be able to have a significant drop in temperature at night. My house averages 25C in the Summer, I want to be able to drop temperature 3-4C below that in the terrarium during 5-6h at night. A power consumption up to 100W would be ok to achieve that purpose.

[Draikan]

What size tank are we talking about? 3-4C drop seems like a pretty modest goal, especially at night when the lights are off.

Any compressor based option for cooling is expensive, bulky and noisy, apart from being much more efficient and reliable. While a peltier module with two heatsinks and a fan for each side has a total cost of 20-30$ and takes very little space.

This is true, but only at very low cooling capacities. As you scale up compressors are clear winners. This is why all serious appliances (refrigerator) use compressor based coolers, and only the small/cheap devices (12V travel cooler) use peltiers. My gut reaction is that cooling a terrarium is edging into the range where smaller compressors will be competitive. This is because the heat load from most terrariums will probably be a bit much for most peltier systems, so you have to use a more powerful system, and compressors start to look better. If you did want to try a compressor, maybe pull one out of an old minifridge, or look for a used aquarium chiller.

If you are getting a 3C rise from a 20W cable, a 20W cooler should give you the same 3C drop. 20W of cooling is super reasonable from a peltier.

Is water cooling much more efficient than simply having a big heatsink with a fan on the hot side? I didn't want to go that direction due being more complex to set and for requiring a water pump. I would prefer to oversize the heatsink rather than having a water cooling system, if similarly efficient.

Yes, water cooling can be that much more effective, but again only as you scale up to higher cooling capacities. Let's use this cheap module as an example, just so we have some real numbers to talk about: Thermoelectric Cooler - COM-15082 - SparkFun Electronics

The problem is twofold:

1) It's hard to get heat into the air. This is why you need a heatsink at all. Aluminum fin heatsinks are adequate in many cases, but heat still has to travel from the base up through the fins before it can reach the air. This extra distance creates a temperature drop that reduces how much cooling power you'll have available for a given peltier module. The one I linked is roughly (we should use real datasheet values to be more specific, but napkin math is ok for now) 7A*15.4V = 107.8W of electrical power, PLUS 60W pumped through from the cold side. That's almost 170W total, even a very oversized heatsink is going to struggle with that. Every bit of temperature rise in the heatsink comes right out of the performance of the peltier. You don't just need to move 170W, you need to do it while keeping the heatsink as cool as possible.

A radiator like this: Amazon.com
uses the water to bring the heat right to surface of the metal. The heat only has to flow through a few mm of metal to get to the air, and the total surface area can be higher than a heatsink of similar volume.

2) The 40mm x 40mm surface area of the peltier is a limitation. No matter how big the heatsink is you still have to squeeze all 170W through the base of the peltier, and when the heat first enters the heatsink it does so through this same 40mm x 40mm surface area. Again this causes a temperature rise that takes away from the performance of the peltier. A liquid loop improves this by reducing the total distance the heat must travel while subject to this 40mm x 40mm area limitation. The water block has a thin aluminum wall with water on the other side. The heat only has to move through a thin aluminum plate, and then it gets carried away by the water. The heat does not have to flow through the water, it literally gets carried from the water block to the radiator fins by the water flow. The result is more heat dissipated and less temperature drop, for more performance from the same peltier.

If you are using a single peltier module and being cost conscious, you probably can use a modestly oversized (80mm x 80mm base heatsink just as a rough ballpark ) heatsink with a fan, and run the peltier at reduced power and it will work ok.

Just turning up the peltier power without improving the cooling of the hot side won't get you much extra cooling. You can add more of these peltier+heatsink modules, but at some point you are better off improving your hotside cooling, and running the peltiers harder, than you would be buying more modules to run at reduced power.

If you really want to push a single module hard without a liquid cooler, you need a really good air cooler. Something like a CPU cooler, which is designed to pull a lot of heat from a small surface while staying as cool as possible: Amazon.com

I think you should try the simple cheap version. See what kind of performance you get. Measure the hot and cold side temperatures. Find the weak spots in your system. Improve them until you get the performance you want.

[Metallising]

What size tank are we talking about? 3-4C drop seems like a pretty modest goal, especially at night when the lights are off.

18x18x24 (45cmx45cmx60cm).
Considering I grow mostly intermediate species I'm aiming for 21C-23C night temperatures and 24-27C during the day in Summer. A 3-4C drop seems enough to keep everyone happy and flowering, also important to reduce stress during warmer days. To achieve a more significant temperature drop would require adding complexity, parts and costs, I believe the effort wouldn't worth the gains.

If I had a large indoors space like a grow tent or basement I would go for compressor, hands down, for a display terrarium it's overkill.

If you are getting a 3C rise from a 20W cable, a 20W cooler should give you the same 3C drop. 20W of cooling is super reasonable from a peltier.

It's much easier to heat than to cool efficiently when not using compressors, from what I have read so far, I don't think I will achieve anything close to 3C drop per 20W with peltiers. I would be happy with half of that.

Indeed, a 40mm x 40mm module producing 170W of heat won't be easy to dissipate through a conventional heatsink. I like the radiator you linked, note taken.
The peltier module you are using in this exemple is too powerful for the application we are talking about, the most commonly used in small applications and hobbies is the TEC1-12706 - 60W 12V * 6A. Same size 40mm x 40mm though.
Two of these would have a similar cooling power to the one you mentioned and the surface area would double.

If you really want to push a single module hard without a liquid cooler, you need a really good air cooler. Something like a CPU cooler, which is designed to pull a lot of heat from a small surface while staying as cool as possible: Amazon.com

I think with a heatsink like that my terrarium would lift-off.

I think you should try the simple cheap version. See what kind of performance you get. Measure the hot and cold side temperatures. Find the weak spots in your system. Improve them until you get the performance you want.

That's me.

Just ordered one of these.

Thank you for the tips.

[Draikan]

Looks like a great start! Be sure to let us know how it works.

It's much easier to heat than to cool efficiently when not using compressors, from what I have read so far, I don't think I will achieve anything close to 3C drop per 20W with peltiers. I would be happy with half of that.

When I said a 20W cooler, I meant 20W of cooling output. That might require 40W+ of electrical input, and any power spent on pumps or fans. Could easily be 70W or more on the hot side to get that 20W of cooling.

20W is 20W, doesn't matter if it's heating or cooling, should produce similar temp rise/drop for the same system. It's just much harder to get that 20W of cooling than it is to get 20W of heating.

[Draikan]

Side by side of root growth on one of the Stelis. These photos were taken about two weeks apart.

2/07/21:


2/25/21:

[Draikan]

Lepanthopsis astrophora is a keiki machine. I mounted up 3 of it's keikis today. I think ideally these would have a few more leaves, but the roots were almost an inch long and starting to grow into the mount, so I wanted to get them off before they stuck.

These are the first orchids I've mounted with live sphagnum, and also the first that have had so little moss on the mount. The moss is very airy and not compacted at all. We'll see how they do.

[Draikan]

Trisetella hoeijeri is slowly coming back from the brink. It had 2 leaves left after being shipped, but now it's up to 6. That's four new leaves in 7 months, so it has roughly tripled. The new leaves are small, but each one has been bigger than the last, so it looks like if I just keep doing what I'm doing this one is gonna make it!

I think this one appreciates the cooler temps, hopefully spring and summer don't slow it down too much.

[SADE2020]

What's the green base..is it life sphagnum moss?