DIY Chiller

[whuntley]

What I am saying, is that if you reduce the length of hose in the chiller bag the freezer will be able to remove more heat creating a better heat sink.

How can it be, Tyrone? Common sense dictates that the longer it takes for the water from the fish tank to pass through the chiller bag, the colder my tank will become. You sure there's nothing wrong with your formula?

I have to say I'm sceptical that your suggestion will work. I want a second opinion If someone else says your idea is worth a try, I'll reduce the length of the hose by a quarter. And then if it works, I'll reduce it by another quarter.

Loh K L

Here's that second opinion (engineer style).

Any system for delivering energy (in this case "coolth" ) does best when all impedances are matched from source to load. A too-long (or too-small-diameter) hose passes the water too slowly for best efficiency, and a short fat one doesn't give enough contact time.

For a given set of circumstances of pump pressure, hose conductivity, diameter, etc., there will always be some length that extracts the maximum number of BTUs from the tank and moves them to the refrigerator. Calculating this often is too tough, so just experiment.

OK?

Wright

[FC]

KL,
You get more than 2nd opion .

Try this:
1) cut the tubing in the fridge into 2 halfs
2) run them in parrallel:
"in" -------============-------"out"
- the "====" are the tubings in the fridge running in parrellel
- the "----" are the tubings outside the fridge

Cutting short the tubing will reduce water surface contact like what you are skeptical of. But in this configuration, you get:
1) maintain maximum water surface contact with the fridge's cold.
2) reduce the resistance of water flow by almost half.

[aquafans]

In long run, the temperature in chiller should be only a bit lower than fish tank, 2 degrees celsius different is make sense, considering there are heat from light, filter and fish. Length of hose is only about time how fast that balance will get.

To lower one degree celsius of one litre water, you need one kilocalories energy (if I'm right).
In this case, if you fillfull the chiller tank with water (including a very long hose), thats will increase total volume of water to be coolth, in other words need more energy to lower the temperature.

So try this, get smaller and shorter hose, fill with water the chiller just above the hose level, it may lower the temp.

Sorry for my poor english, I hope you get what I meant.

Jan

[TyroneGenade]

Here is the essense of my argument again taken from a different angle.

You want to heat your room. The cold outside is drawing 100 W of heat from the house and has now equilibriated so that both the house and outside is 4°C. What do yu do? Build an igloo? No, you turn on the heater.

The heater is now putting out 100 W of heat. This will raise the internal temperature slowly. Because there is little temp difference initially between the outside and inside the cold is drawing now less than 100 W of heat.

Heat moves at a factor of (the heat differnece) squared. As the indoor temp raises more heat will leave. Eventually you will be at a point where you are putting 100 W into the house and 100 W is being drawn out. If the temp is now at 10°C and you can't up the heater output you are in touble. What can you do? Reduce the surface area at which heat is lost: put up curtains (glass is an excellent thermal conductor) and pad the walls with styrofoam (a shoddy thermal conductor). Now you are putting 100 W in and loosing only 50 W so the temp will raise to a new equilibrium level where again the temp diff is big enough for the available surface area to loose 100 W.

This is the inverse of your situtation. Your freezer can't remove the x W of heat yoru tank is putting in. You can't change the surface area of the freezer but you can change the surface area of the hose---that is the surface area where the tank is shedding heat.

If you reduce the amount of heat entering the freezer then it will lower the equilibrium temp. It will take some time for this equilibrium to establish so don't panic! You will probably see an increase in temp initially but it should decline as the temp difference between the freezer and hose increases to the point where it will draw off as much heat as before... in theory at least.

tt4n

[timebomb]

Okay, guys, you got me convinced. Not that I believe it will work, mind you but I'm convinced that it's worth a try. If you ask me, the length of the hose is an important factor but I would imagine I should lengthen instead of shortening it.

I'll work on it this weekend. I'll chop off a quarter first and see how things go.

Loh K L

[TyroneGenade]

It is a great pitty you can't stick a thermometer down the hose and find out where the water temp equals the chiller tank/bag temp. From that point on the hose would be useless... It may be that the chiller bag does 90% of its cooling along the 1st quater of hose. In that case lobbing off 1/4 won't make any difference at all..

Good luck

[timebomb]

In that case lobbing off 1/4 won't make any difference at all..

Well, that isn't necessarily the case. Even if it does nothing for the temperature, the flow rate will definitely improve with a shorter hose. Before I chop the hose though, I'm going to be more *scientific* about it. If your theory is correct, the difference between the temp in my fish tank and the DIY chiller will become closer. I'm going to monitor the temp difference closely by taking down the figures every hour or so. Only then, will we know for sure if a shorter hose helps.

Loh K L

[PohSan]

Hi Loh,

If you are to record the temperatures for every hour, you may want to plot a line chart or presents them in tabular format. It will be useful to determine the best time to power off/on the "chiller". And if you are going to experiment with different hose length, it might be useful also.

Regards.
Ong Poh San

[TyroneGenade]

Any change? Did shortening the hose have any effect?

I'm really curious...

[timebomb]

I was too busy to work on the chiller over the weekend, Tyrone. But seeing how curious you are, I decided to do it just now. I knew before I started that its going to be quite a hassle but it turned out to be much more work than I had expected. I have a CO2 system positioned between the 2 Eheim filters which I have to remove first before I can do anything else. Here's a pic:



I've been monitoring the temperatures in the fish tank and the freezer over several days. I won't bore you all with the figures so I'll just show you all a summary:

The lowest recorded temp for fish tank is 24.0 C. For freezer, it's 21.6 C. Highest is 24.9 for fish tank and 22.9 for freezer. The difference between the temps for the fish tank and freezer fluctuated between 1.2 degrees and 2.8 degrees.

Average difference over 36 readings taken at one hour interval is 2.06 degrees C. That's the magic figure, right? If shortening the hose works, this figure should become lower. In other words, the difference in temp between the freezer and fish tank becomes narrower.

I took off 12 metres from the 50 metre hose. It sounds like a simple matter to shorten the hose but the way the whole thing is rigged up, I have to ensure there's no water in the hose before I can start the filter running. If, at anywhere along the hose or in one of the Eheims, there's water, the thing won't run. An Eheim is a wonderful piece of equipment but it can't push water through that long a hose if there's already water inside. Imagine trying to get rid of the water in a 38 metre long hose. I thought about using a balloon pump but I couldn't find it anywhere in the house. So I had no choice but to uncoil the hose, lift it up so that the water flows out from one end and coiled the whole thing back again. Here's what I chopped off:



I'll let it run for a day before monitoring the temperature again. I'll let you all know if there's an improvement.

Loh K L

[TyroneGenade]

Hi Loh

If I new it was that much trouble I would of told you leave it... way too much work for 2°C...

Actually I'm hoping to see 2 things:
1) lobbing off a small section of hose makes no difference. This would confirm the hypothesis that your hose is too long and is shedding all the heat it can over the first few meters and that your freezer doesn't have the capacity to remove the heat being put into it.

2) that the temp difference between the freezer and tank increases but that there is a downward shift for both (i.e. your freezer sits at 18°C and your tank at 22°C)...

The 2nd point is the BIG experiment. Can we but reducing the length of the hose reduce the heat being put into the chiller tank so allowing it to cool further and draw more heat out. It sounds odd but that is why physicists who study thermodynamics get Nobel prizes.

I just tried to go and do the math to demonstrate but found myself reliving my undergrad years... I'm satisfied with the thoeries and leave the math to someone else... As someone pointed out the heat exchange depends on the flow rate of the water. On one site, using Newton's Law of Cooling, the heat capacity of water varies from 500 to 10 000 depending on the pace at which it moves!

tt4n

[timebomb]

Can we but reducing the length of the hose reduce the heat being put into the chiller tank so allowing it to cool further and draw more heat out. It sounds odd but that is why physicists who study thermodynamics get Nobel prizes.

I don't think I'll win any prizes but I'll give it a shot. What you wrote makes perfect sense. By making the freezer colder, the tank should get colder too. And one sure way to make the freezer colder is to shorten the hose. I'll let the system run a few days before making the change. I'll take out the 38 metre hose from the freezer and replace it with the 12 metre that I chopped off. Even if the temperature does not get lower, it would be a big help if the flow rate becomes faster.

It may interest you to know, Tyrone, that I came home from work today to see my thermometer in the fish tank reading 23.2 C. It isn't the lowest I've seen but the temp in the freezer was 20.7, one of the lowest I've seen so far. We can't be sure this is because of the shortened hose though as it's been a very cold day today. The ambient temp is 27.0 C, far lower than the usual 30 to 31 C.

Loh K L

[TyroneGenade]

hmmm... very interesting... I will reserve further commentary till after the experiment. In the mean time I will play with the math and build a model... see what I can find without causing you too much labour.

I need to know several things:
the volume of your fishtank
the volume of your chiller tank/bag
the diameter of your hose (inside and ourside)
average day temp
average day humidity

Keep well

[keehoe]

Today is a very cold day in fact.

[RonWill]

It may interest you to know, Tyrone, that I came home from work today to see my thermometer in the fish tank reading 23.2 C...

We can't be sure this is because of the shortened hose though as it's been a very cold day today. The ambient temp is 27.0 C, far lower than the usual 30 to 31 C

Kwek Leong, your thermo reading looks good but I suspect the weather plays a big part.

The past week has been hazy and drizzly, getting pretty darn cold at night. The temp in my sump registers between 24.5 to 25.2 ºC and a good cool breeze makes those Henri filters even more efficient.

I'll be interested in the results with a shorter hose as I may have to rig one up for my pending 4tier x 3ft rack in the study. These will house my breeders and more maybe my shot at cool water killies. I'd rather keep all my tanks outside but... guess who came aknocking on my door.

[PeterGwee]

I'd rather keep all my tanks outside but... guess who came aknocking on my door.

Who eh? The people from the town council or even worst..the police?

Regards
Peter Gwee :wink:

[stormhawk]

With the current cool weather chillers are really having a field day. My thermometers registered a cool 24.1 degC earlier this morning without using Henri filters .

[TyroneGenade]

Loh...

Actually I need the dimensions of your tank and hose and an approximation of the volume of your chiller bag/tank. Then I should be able to figure everything out. I will share the math and model when I have sorted everything out.:-)

The results may be surprising...

[timebomb]

Tyrone,

Here are the figures you want:

Volume of fish tank - 380 litres
Volume of Chiller bag - about 60 litres
Diameter of hose (internal) - 12 mm
Diameter of hose (external) - 16 mm
Length of current hose - 38 metres
Average day temp - 30 degrees C
Average day humidity - 84.4 %

Let me know when you come up with a good length for the hose and I'll get to work right away. By the way, wouldn't the flow rate be a factor? I don't know what it is though. All I can tell you is that it's powered by an Eheim 2215.

Loh K L

[RonWill]

Who eh? The people from the town council or even worst..the police?

Peter, I transgressed no civil laws here so there's no need to fear the police. OTOH, my unexpected 'guests' are rightfully doing their jobs.

I'll have to 'tidy up' my act albeit taking a little longer than expected, especially with all the hanky panky activities in the tanks!

That said, a chiller sure looks tempting. Let's see if Tyrone's 'mathematical modules' will hold water... in this case, chill the tank!