terrarium cooling - ive got an idea, need some advices :)

[Guest someone927]

hi all 8)

besides of collecting cp's, im collecting terarriums

summer is comming up bringing massive heat with it, and my terrariums are getting hotter and hotter each day passes, not too good for my heli and my upcoming darli (waiting for seedlings ) even the drosera's show signs of overheating...

so, after a week of intence brainstorming, ive came up with the cheapest and most efficient way to cool a terarrium.

(tho this method is cheap only when used to cool down more then one object...)

its gonna work on 5 terarriums (one is on construction at the moment) and if itll have enough energy left after the cycle itll also be a cooling element for my computer ^_^ not just 2 birds... get the whole bunch !

so, those are the system's needed parts and way of working scheme :

1 - high flow rate pump

2 - mini bar refrigerator (15+/- liters is what im thinking about.)

3 - a few metres of copper pipe at a desired diameter

4 - also a few metres of plastic pipe at a desired diameter

5 - a plastic container to hold the water inside the fridge

6 - tools ! any kind and any color

for me it cost less then 100$ and i guess that anywhere else in the globe it would be much cheaper..

so, this is how it works :

now... theres only one thing im not sure about,

if everything will go as planned, the water in the terarriums would get to a temp as low as 10degrees (Cel), could it do any harm to the plants instead of helping them ? also.. will it cool the whole space of the terarrium or just the lowest 10 cm's ? because the other option is to put the copper pipes outside the water level and just twist them around the terarrium's space.

well, i will update as soon as i will have something to update about :)

also i will post some pics of the terarriums next time

p.s

why choosing a mini bar ? well, i was investigating the whole subject of mini cooling, mostly as computer cooling, ive found out that theres a device called peltier which works with the..ahm.. peltier effect, which works as a heat pump (in short :? ) but all of those devices are pretty complicated to apply and modify, so accidenlty ive seen a mini bar on some commercial website, and that mini bar and a whole lot more (appearantly) works on with the thermo-electric system ("peltier")

so... instead of putting the money on something that will take me alot of time to apply... ill just get a complete isolated chamber with that same device at the same or even lowered cost ! 8)

[dortyuz]

My advice would be to pass the cool water through a kind of air/water heat exchanger and blow air through that into the terrarium, this way you will have cool air, not cool water.

Cheers,

Burak.

[Guest someone927]

yeah that was the basic idea, but i had bad experiences with fans in the terrariums already : the droseras didnt liked the air movement, it dried out all the dew. all the other plants did well but the droseras looked pretty bad :?

thats why i wanted this passive heat exchanger, so itll only radiate the coolness without using fans..

but now that i think of it.. maybe even a tiny fan like those fans from the graphic cards (comp) so the air movement will be as minimal as possible just enough to spread the coolness...that worth to be tested 8)

making a heat exchanger for a fan wont be too difficult to make, so it wont be such a big change in the plans 8)

but my question still stands - can water with low temps (10-/+) do any harm ? and also, can it affect germination rates..?

because even if ill use a fan, theres still one terrarium (germination terrarium) which is just too small to contain a big cooling construction (even 5*5*5cm's is too big), and its one of my hottest terrariums :?

[Martin_mtl]

Why do you spec a high flow rate pump? Water circulating too fast will not have the time to be cooled down by the cooler again. Ther result will be that the water temp will rise gradually until the system attains stabilisation point.

In order to maximize the water heat exchange in the terrariums, you will probably want to have it make a serpentine inside.

Also, the basic concept of cooling the water, that will in turn cool the air above it is not the best because cool air does NOT rise up, it will stay low on the bottom.

Good luck with your project!

[Guest someone927]

well first, you are right on one hand but wrong on the other, if the flow rate is low then the water will have more time to cool, but also more time to loose energy (temp,coolness) on heat exchanging points (inside the terrariums) so, when the flow rate is high the water loose much less energy and get to the end of the cycle a bit cooler which means - less time to cool back at the fridge and less energy used by the fridge itself

and besides, with all the tricks in the world.. any system needs to get to a certain stabilisation point, the point is to get the stability point as closer to the one you want 8)

also i didnt understood what you mean by serpentine please explain..

and yes, for now im convinced, fan itll be.

im gonna make a few tests just when ill get all the parts (pump,fridge,pipes) to see if a mini fan (1" i think) does the trick, and i will update about it with photos and everything :)

and last, thanks

[phissionkorps]

If you want to cool the water, just stick a couple Peltier units on the side of the terrarium:

http://www.philip.davis.dsl.pipex.com/imag..._coldfinger.jpg

These things are amazing heat exchangers. I saw a thing online where a guy used just 1 to keep a beer just above freezing on a 100°F day. Or, I just you could stick them to the sides of the terrarium that don't have water touching them, which would cool the glass, and technically since hot air rises, it would get pushed out?

Of course, you'd have to be pretty good a wiring to make all this work, but if you're good with circuits and stuff, its a great idea, since there are no moving parts to break...

[cp_produtos]

just a litle warning , in your schematic the copper pipe goes inside the water in the terrarium , if this water is the same that the pots are on this is not a god ideia because the copper will poison the plants.

[manders]

well first, you are right on one hand but wrong on the other, if the flow rate is low then the water will have more time to cool, but also more time to loose energy (temp,coolness) on heat exchanging points (inside the terrariums) so, when the flow rate is high the water loose much less energy and get to the end of the cycle a bit cooler which means - less time to cool back at the fridge and less energy used by the fridge itself Wink

You are right, the faster the water goes the higher the heat transfer coefficient, and you should have higher heat removal over all.

If you have a lot of water in contact with the air, you will probably find the air cools down quite easily, and definately would with some small air movement, like a small fan. I don't really know if the copper pipe would cause a problem with the plants, i suspect not enough would get in the water to cause a problem and of course youll get much better heat transfer with copper than with plastic.

[Guest someone927]

copper poisoning, hadnt thought of that option :?

as it shows on the scheme i was about to put the copper pipes inside the water (atleast in 1 terrarium) which are also the plant's water.

is the any other material (which conducts heat better then plastic..) i can use instead of copper ? atleast for that 1 terrarium which is too small for a heat exchanger and a fan..

[manders]

Maybe somebody can comment on the copper poisoning? All i know is i have used copper sulphate in my fish tank years ago, which had many plants in, including utricularia and it didnt harm the plants. The level of copper would have been much higher than youll get of the pipes.

[pulsar]

i sounds similar to a chargecooler used for turbocharged cars and they work vey well

[Martin_mtl]

You are right, the faster the water goes the higher the heat transfer coefficient, and you should have higher heat removal over all.

I dont agree on that. If what you say is true, if the flow rate would theoreticaly pushed to infinity, the temperature of the heat exchanger would reach absolute zero. That is not possible. I believe that the heat exchange would be optimal when you could find the peak system flow rate (i.e. when increasing the flow rate would lower the heat exchange performance).

also i didnt understood what you mean by serpentine please explain

I believe that the correct word in english would be coil (to maximize the heat exchanger surface area).

[manders]

I dont agree on that. If what you say is true, if the flow rate would theoreticaly pushed to infinity, the temperature of the heat exchanger would reach absolute zero. That is not possible. I believe that the heat exchange would be optimal when you could find the peak system flow rate (i.e. when increasing the flow rate would lower the heat exchange performance).

Heat transfer is a function of surface area, delta T and the heat transfer coeficient, usually expressed as U or UA.

e.g. Heat Transfered = UA * Delta T

The U part is dependant on the velocity of the liquid, as it shears away the lamina boundary layer next to the tube wall which provides resistance to heat transfer, unless the outer surface heat transfer coefficent is rate controlling by being much smaller than the inner surafce coeficient (for copper the metal heat transfer resistance can be assumed zero).

If the velocity is low, then two things happen, firstly the heat transfer coefficient is lower, and secondly the Delta T is potentially lower, both of which lower the rate of heat transfer.

When the velocity is higher the heat transfer coefficient is higher, the limit to heat transfer is reached as the Delta T approaches 0, hence you would never get below the below the temperature of the cooler.

Consider if the flowrate is zero, then you have no heat transferred, as the Delta T approaches zero.

Therefore, maximising the velocity maximises the amount of heat transfeered. Of course if you provide enough surface area, the Delta T and the Heat transfer coeficient are less important

[Guest someone927]

ok, updates.. first step made today, ive got a pump :)

(winston pack for proportions 8) )

its much less noisy then it looks, and makes good flow and pressure,

it supposed to make 2500 liters per hour thru 1/2" pipe.

a few days from now im gonna buy the pipes and connectors, fans, and maybe also the fridge if ill get the time (damn job gets me away from my plants and stuff )

also on sunday next week im supposed to get an RO unit and a TDS meter (none related to the topic, i just had to say it )

updates, soon.

p.s.

anyone who says drugs can take all of your money, they should try growing cp's ^_^

[JStrider]

If you want to make the heat exchanging a lot more efficient, instead of using just copperpipes buy a couple heater cores for a car and put one inside the fridge, and submerge the other in the terrarium,

a heater core is like a little radiator, so it will dramatically increase the surface area for the heat transfer and will make the whole system much more efficient.

[yoss]

Hi someone,

What RO unit are you getting? which one do you recommend here in Israel?

[Greg Allan]

Maybe somebody can comment on the copper poisoning?

Slack writes that copper based fundacides are deadly to all Heliamphora, so perhaps copper pipes may not be such a good idea.

Cheers,

[Guest someone927]

well, the plan has changed according to that possible copper poisoning, so now the plant's water will not touch the copper, only air is gonna get circulated thru the copper pipes ... i dont think that much copper will get thru air, not enough to hurt the plants anyways. 8)

and for your question yoss, (yossi ? 8) )

the RO unit im about to get (havent got it yet :? ) is a 2 filters + membrane unit, and its the cheapest ive found out there, 450 shkalim, its origin is somewhere in asia, but the membrane is made in the USA.

it also supposed to come with all the fittings and pipes needed in order to connect the unit to the water line, also,

the guy ive talked with on the phone (from the shop ive bought the unit..) claimed that the unit produces water with 70 PPM or less, so basicly, its supposed to be good enough.

for the next question, i dont have much to say nor recommend since i dont have a bit of experience with RO's and this one is my first ,

but as much as i know (not much.. 8) ) it doesnt matter which unit you get, its only the membrane that counts.

if your interested, i could post the water test results.., since im living in hevron mounts (harei hevron ) and my water comes from local underground water-pumping stations and not from the kineret, the water ive got have got very high calcium rates, so anywhere else in israel will get atleast 1/2 ppm resaults, i guess

[ilex]

Couple comments:

- It's critical that you insulate those terrariums very well. If they are very well insulated you can cool them without using much energy and the cold will stay there (cold air goes down). Poor insulated ones can be extremelly difficult to cool as you'll basically need to cool the whole room.

- the cooler idea has been tried and you need to run many meters of tube through it for the water to cool fast enough. Not very efficient but can cool somewhat. Move the water very slowly so it has time to cool.

- insulate

- I also agree on using a water to air exchanger. A car/motorcicle or computer water rediator with one computer fan will do. Just don't blow the air directly to the plants as some might not like it.

- insulate more

- The best is to use an aquarium chiller but these are terribly expensive, specially in Europe. I'm using a beer chiller as it was free. I can get the terrarium down to 5ºC or less easily.

- and finnally and most important, insulate.

[Guest PhantomPlants]

I agree completely to insulate it well if you are going to use radiant cooling through water.

Have you thought about using a chest freezer to put cold air into the terrarium instead?