DIY Chiller

[FC]

It seems there's a psychological barrier or something. The thermometer simply refused to go below 24.

Not the thermometer, it's you! Start believing and you'll see it comes... I guess it would bottoms out at 23 degree celcius at best.

[whuntley]

For those next couple of degrees, here's something you can try for no great cost.

Right now, you are getting a lot of insulation from the air around your glass sump. [Measure the difference between freezer wall temp. and the water temp.] Try stuffing paper or rags down between the freezer walls and the glass, then wetting them to get better thermal contact between the freezer and the glass. If that works, you may want to consider buying pads of open-cell foam to perform the same function, and rig a sump to keep it wet/frozen.

I was not clear on why the freezer cannot be made to hold water. Even if only up to the thermostat, water would be a lot better heat conductor than air, I suspect.

You might also see if efficiency improves by blowing some air over the warmest parts of the outside of the freezer case. Finned aluminum heat-sink material is often available at electronics surplus houses. Some fins attached to the outside of the hot case could make a big difference, if the fins are oriented so air flows up through them by convection (slots vertical).

Planning a heat-pump system is a bit like a flowing water system. You need to look for any thing that is slowing or obstructing flow, anything that is diverting energy where it isn't wanted, and take appropriate measures to fix each of them. [You guys are taking me way back to my undergraduate courses in thermodynamics and fluids. ]

Wright

[TyroneGenade]

My physics lecture (Prof Koen, there is a constant named after him so his opinon must we worth something...) was of the opinon that still air is the best insulator. Filling that void between the tank and freezer is in my humble opinon very important. I don't know about using wet anything as it may freeze and crack the glass... maybe steal wool?

Ciao

[whuntley]

You need the wet for thermal conductivity. Steel wool or dry newsprint, etc. will just keep air from circulating and make things worse (assure the air is more still).

If a rag or wet paper freezes, it's not likely to crack the glass, as it will freeze near the freezer wall, first. Monitor, of course. You'll have to reduce the freezer setting before freezing is a really serious problem, if the thermal conductivity is really high (air is all displaced). The tank will be too cold before then.

I heard stainless steel mentioned here, a while back. If you want thermal conductivity, it is terrible. Barely better than clear vinyl. Copper and aluminum are far, far better for heat transfer. Ever notice how warm stainless feels compared to other metals? It is because it has rather poor thermal conductivity.

Here's another thought. Get rid of the glass tank and that surrounding air insulation. Put a large plastic garbage bag in the freezer and fill it with water. Then immerse your tubing in the bag of water. Bet you will have to turn the freezer way down to keep from overcooling your tank! Particularly true if you insulate the lines and cannister between freezer and tank.

May need to add that power head to minimize local freezing.

Wright

[FC]

Wright,
Brilliant idea!
Below are the scenarios that ran through my mind on what would happen to the Wet Paper Pulp (Pulp), the chill tank's Glass Wall (Glass) and the Freezer Wall (Wall):
1) Pulp begins to freeze at/near the Wall, slowly propagating towards the Glass;
2) heat from the Glass (easily more than 10 degree Celsius) travels to the Pulp, melting any froze from on the Pulp near the Glass;
3) repeat
In a nutshell, the Pulp will only freeze at the Wall and never at the Glass. Thus, improving the cooling efficiency without the danger of breaking the glass.

[FC]

For those who may be puzzled why I said:
"heat from the Glass (easily more than 10 degree Celsius) travels to the Pulp, melting any froze from on the Pulp near the Glass"
And not the "cold" from the Pulp travel to the Glass (thereby cooling the chill tank).
This is because scientifically, hot always travels towards the cold and not/never the other way round.

[whuntley]

Freddy,

It depends on your source. What you say is true if the heat source is warmth, but what direction is the propagation when you start with coolth?

Wright

[FC]

Wright,
You caught me. :P
However, as we are trying to remove heat from the tank, naturally, I would assume these:
- the Chill Tank is warmer than the Wet Paper Pulp;
- the Wet Paper Pulp is warmer than the Fridge Wall and
- the Fridge Wall is warmer than the Fridge’s Evaporator

[timebomb]

The temperature went up today. It hovered between 24.5 and 25.5 for most of the day.

Thanks for all the suggestions. I have to mull over them for a while before I decide what to do. I checked the tank inside the chiller and the space between the glass and the walls of the freezer is mostly caked with ice. In some places, the ice is already touching the glass but in others, there's still a small gap. It would be difficult to fill this gap with paper pulp and I don't know how I can keep them wet.

Wright, the reason I didn't simply fill the freezer with water is because the guys who are selling them told me that freezers are not meant for holding water. It will leak and damage the compressor under the freezer. I wonder if it's a good idea to use a plastic bag instead of a glass tank to hold the water. The plastic bag is likely to leak over time unless I can find one which is pretty thick.

I bought another digital thermometer for the chiller tank and I noticed the temperature there is always about 2 degrees lower than the fish tank.

By the way, I noticed that the plants in my fish tank are pearling a lot more since the day I rigged up the chiller. I doubt its the lower temperature that's causing this. More likely, it's because the fans are switched off. I can't explain it but it seems like when there's less water movement ( no fans and weaker water circulation from the filters), the plants absorb light better.

Loh K L

[FC]

I checked the tank inside the chiller and the space between the glass and the walls of the freezer is mostly caked with ice.

KL,
This is not a good thing. Ice forming there will reduce the cooling efficiency of the freezer. The ice's water source is obviously from the chill tank (sign of warm travels toward cold).
My suggestions:
1) Do not be dismay, the chill tank idea can still be improve further;
2) Switch off the fridge. Let the filter continue to run;
3) The ice should melt within a day;
4) Do as what Wright suggest - pack the gap with wet paper pulp.
5) Monitor for 3~5 days.

[PeterGwee]

By the way, I noticed that the plants in my fish tank are pearling a lot more since the day I rigged up the chiller. I doubt its the lower temperature that's causing this. More likely, it's because the fans are switched off. I can't explain it but it seems like when there's less water movement ( no fans and weaker water circulation from the filters), the plants absorb light better.

Loh, its the availability of more CO2 to the plants that is causing the increase in pearling. Colder water holds more O2 and CO2....The lack of surface movement through the removal of the fans help to keep the CO2 in better but is generally not a good practice. Its fine if the plants are doing well and producing loads of O2 for the critters but if things go south due to the user not keeping up on the CO2 or nutrients, you are going to have possible O2 issues and gasping fishes. Better to lose some CO2 then a fish.

Regards
Peter Gwee :wink:

[elmike]

Sigh…

There’s only so much a low-maintenance guy needs to know.

But this sure looks like a big thing. I wonder if an innovation of such a scale and nature comes under any HDB regulations? I don’t know if anyone has raised the question before, but delving into electrical circuits to rig up an equipment such a coolant, which is no simple contraption, is no small matter to me.

In a closely-knit HDB context, what we do has a direct impact on our neighbours. If your floor is flooded, water seeps through to the neighbour’s unit downstairs. And if a fire breaks out, it could spread quickly to the neighbouring units. In the wake of the 26 fire breakouts from the use of poor-quality overhead filters not too long ago, the HDB may be training their eye on the aquarium hobby.

It pays to be circumspect and ask ourselves if everyone could duplicate the design successfully through knowledge gleaned from online discussions, although the originator’s design had proved to be workable and reliable. Someone must be accorded due credit, or otherwise... It's now in public domain.

Just a thought.

[timebomb]

I wonder if an innovation of such a scale and nature comes under any HDB regulations?

Mike, you worry too much.

Hey, it's just a freezer. Other than having 2 holes drilled on its cover, it's not much different from the fridge you have in your house. As for having an impact on the neighbours, a freezer/chiller definitely has less impact that a karaoke hi-fi system. It can be hell when your neighbour is a karaoke fan.

Loh K L

[TyroneGenade]

Hello

Been giving the "stuffing" topic some thought and think you may be able to get away with a mix of (a slurry) of ice, ethanol and potassium chloride. This mix can take temps down to -18°C without freezing. That way you can prevent the stuff between the freezer anc chiller tank freezing and cracking the latter. There are many other anti-freezes on the market that may also work. Ethanol will probably be the cheapest (and most enjoyable).

Cheerio

[timebomb]

Hi, everyone,

I've been mulling over your suggestions and I think I got it all cleared up in my mind now. Eureka!!

I thought about stuffing the gaps between my freezer walls and the glass of the chiller tank with pulp. I thought about using a plastic bag instead of a glass tank to hold the water. I thought about replacing the PVC hose with something that conducts heat better, something like the thermal plates which Poh San suggested.

I thought about many things but finally without even having to try them, I came to the conclusion that most of your suggestions won't work. Why, you ask? Well, the answer is rather simple but I may not be able to explain it well. But I'll try.

First, let's name the items clearly so we won't get confused. There's my fish tank which is about 380 litres of water. There's a freezer which has a certain cooling capacity. There's a chiller tank inside the freezer holding water, about 57 litres. There's a PVC hose, 50 metres long submerged in the chiller tank. There's an external cannister filter, used for pumping water from the freezer back into the fish tank. There are 2 filter hoses which connect the fish tank to the chiller tank.

Okay, suppose I replace the chiller tank with a plastic bag or do away with any sort of container altogether and simply use the compartment inside the freezer itself to hold the water. What would happen? Would a colder chiller tank translate into a colder fish tank? I think the answer is "no". Why, you ask?

Because no matter how cold the chiller tank gets, the temperature in the chiller tank and the fish tank will eventually balance out. My fish tank can only get as cold as the chiller tank. They will balance each other out because no matter how cold I can get the chiller tank to be, the fish tank will warm it up. I can get the water in my chiller tank to freeze in a short time by simply turning off the filter but what will happen when I start the filter running again? The fish tank will get cold for a while but over time, it will eventually melt the ice and warm up the chiller tank. And we'll be back to square one. The temperature of my fish tank is subjected to ambient temperature which is about 30 C on most days. With lights running 10 hours a day, the water will heat up to 33 C in the absence of cooling equipment.

The key lies in the cooling capacity (abilities) of the freezer and the conductivity of the hose. I turned the settings of the freezer up to maximum (coldest) 2 days ago and the temperature of my fish tank has been hovering around 24 to 26 C. I've been monitoring the temperature of my chiller tank too and it's always about 2 to 3 degrees lower. It should be the same but why the discrepancy? I think it's because of several factors. First is the poor conductivity of the PVC hose. If I use something that conducts heat better, it should help in a big way. Second are the filter hoses which connect the freezer to the fish tank and the filter itself. They cause heat loss. 2 to 3 degrees is what I'm losing due to poor conductivity of PVC hose and heat loss from filter hoses and filter. If I can find a way to prevent this heat loss, I believe I can bring the temp of my fish tank down to 22 C.

Just as an experiment, I'm going to switch on my 3 cooling fans right after I send this post. I took a look just now and the temperature of my fish tank is 25.5 C and my chiller tank is 22.7 C. Room temperature is 30.0 C. It's 7.52 pm now. Let's see how things go tomorrow.

Loh K L

[timebomb]

I forgot to add this:

If my theory is correct, I should wake up tomorrow morning to see a temperature of about 23 C in my fish tank. The chiller tank would be about 20 to 21 C then. The freezer can only do so much. It can cool my fish tank to a certain limit and that limit is about 24 C, I think. The cooling fans should help to bring the temp down further as it's another source of cooling power.

That's just my theory, of course. It's all fuzzy logic; I flunked Physics when I was in school. It was one subject I hate the most.

Loh K L

[TyroneGenade]

My next step would be to dispence with the chiller tank all together. Direct contact between the hose and freezer may be able to get you another degree or two.

Then think about wrapping those return hoses in styrofoam wrap or something so they are not in contact with the 30°C air. I think you could get another 1 or 2° that way.

Remember! Simple solutions stand the most chance of success!

[turaco]

KL, what if, you were to disconnect the hose for perhaps a day to let the chiller run without external heat from your tank(that is, trying to freeze the water in the chiller!), link up the system again & run your filter again. It should have an upper hand to cool your tank to a lower temperature. But whether it will be able to sustain that way I'm not too sure. Beware though, a sudden drop in temperature in your tank will do a lot of harm to the inhabitants ! By the way, what do you have in there? Guinea pigs?

[timebomb]

By the way, what do you have in there? Guinea pigs?

I'm the Guinea Pig, not the fish

Gan, I've already tried what you suggested. I turned off the filter the other day and within a few hours, the temp in the chiller tank dropped to about 12 C. After I turned on the filter, it went up to 22 C the next day. It's, as you have suspected, unsustainable. The chiller tank and the fish tank are linked to each other by the PVC hose and the temperature in these 2 tanks will eventually balance out, no matter what we do. To get lower temperatures in my fish tank, I either have to use a more powerful chiller or use another source. That's the reason I switched on the cooling fans just now.

Loh K L

[timebomb]

My next step would be to dispence with the chiller tank all together. Direct contact between the hose and freezer may be able to get you another degree or two.

Tyrone, I don't think it would make a difference. As I've said, I can get the chiller to become very cold in a short time by switching off the filter but it won't help because the fish tank will warm it up as soon as the filter starts running. The point I've been stressing is that the chiller tank and the fish tank are not 2 entities, as I've initially thought. They are one.

Then think about wrapping those return hoses in styrofoam wrap or something so they are not in contact with the 30°C air. I think you could get another 1 or 2° that way.

It will help but I seriously doubt we can get even one degree lower. The hoses are not very long and heat loss wouldn't be much.

Loh K L