Connecting 2 tanks that run at different temperatures

[pledosophy]

Dumb idea right?

Here is my plan. I currently have a 125g reef with a 65g refugium a 30g refugium, a 75g sump. I run the reef at 79F.

I am planning on getting a 120g tank which will be a macro algae seahorse tank and will be kept at 73F.

I am thinking of trying to connect them, and maybe using a small pump like a Maxijet 900 to feed the 120g tank for 5 minutes or so every hour. That time can be adjusted of course as needed. The tanks share a common wall so one little hole makes it all very easy.

The benefit is the macro/seahorse tank will be a great filter for the reef tank , plus the current system has very nice filtration, reactors, etc so the cooler tank will benefit from all of that.


I will be running a chiller on the macro tank.

So, dumb idea or do you think it can work. Anyone have experience with this.

I will be running a chiller on the macro tank.

 

[BeanAnimal]

If you move (exchange) enough water to benefit from the filtration you will be moving enough water to equallize the temperature.

The problem is going to be balancing the flow rate to allow the temperature gradiant to be stable between the two tanks and this will not be easy.

So, to use your words... dumb idea.

 

[BPro32]

John Copps (sorry I can't spell his full name off the top of my head) does this. Look for his tank of the month thread from a few months ago.

 

[BeanAnimal]

It certainly can be done... but as mentioned, maintaining the balance is going to be tough. In theory you would have a large chiller on the colder (smaller) tank.

Lets use a simple example:

The small tank (73F) is mixing water with the big tank (79F) at a rate of 100 GPH. The temperature differential is 6F. At 1 BTU per pound, that is 5,100 BTU/h of heat being ADDED to the colder tank from the warmer tank. So the chiller for the colder tank would need to be rated AT THE MINIMUM around 6,000 BTU/h and run almost a 100% duty cycle. However, running at the edge of the envelope means that there is no capacity to accomodate temperature fluctuations from the larger tank. So, in reality the chiller on the small tank will need to be roughly 2x the calculated size. This will allow a roughly 50% duty cycle and plenty of headroom to quickly react to temperature swings and keep the smaller tank at the colder target temperature.

At the same time the larger (warmer) tank is losing that 5,100 BTU/h of heat to the smaller tank. Depending on the heat load of the larger tank, this may or may not allow it to stay stable at the target temperature. It may need a heater or even additional chilling to stay stable. The ideal would be a situation where more chilling was needed, as things would be easier to keep in balance and you would have two chillers working toward a common goal, with one of them simple oversized for the lower flow in the smaller tank (thus allowing it to be a colder part of an overall larger system). The not so ideal situation would be the one that requires a heater to maintainthe larger tank temperature, as at that point they two tanks would be fighting each other.

Walk in coolers in large facilities (and your fridge/freezer at home) use the same basic method. One section has a compressor setup to create freezing temperatures and another area refrigeration temperatures. They share common air but the freezing side is overwhelmed by the size of the compressor and therefore is much colder.

So back to the original question: Sure it can be done, but is there really that much of a benefit for the trouble? = (IMHO) dumb idea

 

[Chris27]

I'm on the "dumb idea" bandwagon as well.

Unless you have a great deal of spare time and a tremendous amount of patience, it would be that much easier to run the tank separably from the other. Sure the ancillary equipment on the other tank looks good, however it's really not very expensive to buy for the new tank.

The two tanks will be radically different when it comes to things like the water change schedule, dosing, lighting and feeding....so with the two hooked together...it could be a hole'nuthr can o worms aside from just the temperature issue.

That said though, get building, a colorful macro tank is really nice to look at and very easy to maintain, we've got a few running at the shop and they are just plain cool. Most everyone that comes in has a hard time passing it without wanting to set one up themselves.

 

[copps]

As was mentioned above, I've done this on one of my systems and it's worked out wonderfully... I cannot understand why people would consider it to be a dumb idea... you could read about my system here...

http://reefkeeping.com/joomla/index.php/current-issue/article/76-tank-of-the-month

If you move (exchange) enough water to benefit from the filtration you will be moving enough water to equallize the temperature.

This is not true. I turn over water in my subtropical tank about once every four hours, trickle feeding it in at about 20 gallons per hour. I have a closed loop on the subtropical tank with two chillers running in series... where I run one chiller I always run two, so that you have a back up as chillers will eventually go on the fritz. Also, on days like today and tomorrow (where it will be 101 and 103 respectively), the temp does not bat an eyelash. I successfully keep low nutrient sps in the subtropical tank so the turn over is enough.

It certainly can be done... but as mentioned, maintaining the balance is going to be tough. In theory you would have a large chiller on the colder (smaller) tank.

Maintaining the balance is effortless... finding it originally could be tricky but once it is found your system will do it effortlessly... One note though, is there any reason you have to run your reef at 79? Anything that thrives at 79 will thrive at 75... there is no reason to heat your reef. If you work your system out and your main reef runs at 76 what does it matter? Ideally I would run all of my warm water reefs at 75 if I did not have to pay the electric bill.

Some questions for you... does your reef right now naturally run at 79? What do you do for heating chilling? This will be telling to help with your system design...

I'm on the "dumb idea" bandwagon as well.

Unless you have a great deal of spare time and a tremendous amount of patience, it would be that much easier to run the tank separably from the other. Sure the ancillary equipment on the other tank looks good, however it's really not very expensive to buy for the new tank.

For me, the reason I did it is because it is much easier running them TOGETHER. We all know what we do for our systems... water testing, changes, the full accompaniment of life support... why would you need more patience? You would need more patience in order to deal with a completely separate system!

The two tanks will be radically different when it comes to things like the water change schedule, dosing, lighting and feeding....so with the two hooked together...it could be a hole'nuthr can o worms aside from just the temperature issue.

Why would different lighting or feeding matter if the tanks were connected or not? And why would you have a different water change schedule or dosing schedule? What other can of worms? Again I am doing this successfully and it's been all that I've wanted... and the benefits will go beyond your savings of time... how many of us run refugiums that grow like gangbusters helping export nutrients to keep our reefs low nutrient as in the wild? There is no reason this refugium could not be a beautiful display of macroalgae... or hold seahorses!:celeb1:

Copps

 

[BeanAnimal]

Copps,

I think if you read my second post, my initial remarks have been clarified. However (and with all due respect) there are a huge number of variables that makes this harder to do than what it appears to be. The volume of the two systems in question (total and as they relate to each other) and the flow rate between the two systems are only part of the variables. The heat load on each system also comes into play (as I tried to explain above).

Correct me if I am wrong:
You have (2) 1/2 HP chillers servicing 430 gallons at ~78F
You have (2) 1/3 HP chillers servicing 70 gallons at ~70F
You exchange 20 GPH (or between the two systems or ~1360 BTUs per hour

As mentioned in my post above, your system needs a chiller on BOTH sides, so things work out fairly well and, as mentioned above, your "small system" is equipped with a greatly oversized chiller to accomodate the slow, but continual heat input from the larger system. The colder water from the small system that gets mixed into the larger systems simply helps the chillers on that larger system....

FWIW, as flow between the two systems increases, so does heat transfer. The small system chiller has to work harder to maintain the small system temperature and the large system chiller has to work less to maintain the large system temperature.

So I suppose in a more general sense, this can be though of as "easy" if you maintain a low flow between the two systems and significantly oversize the chiller that would be required for the small system if it were "stand alone".

I suppose, that is where I conclude in reference to the OP's scenerios... dumb idea (his words). Then again, it is not my system to setup or maintain

BTW, your system is beautiful

 

[copps]

Thanks for the complement beananimal... You are right, there are a huge number of variables, and you are right that it is trickier to DESIGN up front, but it can absolutely be done. The decision is ultimately up to the owner of the system, but I would rather do extra planning up front that results in years of doing less of the crap in this hobby I do not like to do! And in all reality it is not extra planning because while you are spending more time thinking about heat exchange you are completely avoiding the time investment of design AN ENTIRELY NEW SYSTEM! Much of the variables you talk about come into play whether you are running one system or two, and as I said could be designed around.

The small system chiller is not as greatly oversized as you may think... during most of the year one of the teco handles the load fine, it just runs longer. If you are trickling in the water you will not have to greatly oversize your chiller, as the closed chill loop turns over water in the many hundreds of gallons per hour range as opposed to the inflow of just 20 gallons per hour. And on my system the ratio of subtropical water to "tropical" water is much lower than this system would be, so the upsizing would be even less. The design would be more complex if pledosophy absolutely wanted to run the reef at 79, but as I said is there a reason? Anything between 75 and 79 is fine... I target a temp on my subtropical tank and let my reef run in a range, as pledosophy could do. Regardless of whether the tanks are connected or not, running 120 gallons of water at 73 degrees will be expensive... but the delta between what you'll save in time and money on a complete new system is much greater than the small extra investment in upsizing your chillers... so again it's ultimately up to the owner...

And, perhaps most importantly, it's easier to justify to the wife adding a "refugium" onto an existing system rather than setup a whole new one!

But again, however you design it running 120 gallons at 73 is not a cheap thing to do!

Copps

 

[BeanAnimal]

I also prefer to spend my time with upfront design (and expense) as opposed to ending up with something that is cumbersome (or just sucks) to maintain.

I suppose one day I could end up with my 80F reef (no chiller) attached to a tiny 70F seahorse tank, using the excuse that I needed a place to plumb in a chiller

Interesting thread to say the least.

 

[fishysteve]

Like copps said, why do you need to run them at different temps if you could run them both at 75 or so? I've kept seahorses at around 78 with no problems. I don't see why you are going to make it more difficult than it needs to be. Maybe I'm missing something.

 

[Opcn]

I think running them at different tamps make sense. There is a compromise temp in there but looking at macros it seems that most of them do prefer cooler waters than corals do.

As for the benefits I think the way to look at it is something more akin to a water change than a filtration system. To the small tank you are adding dirty warm water that has had reactors fill it with important elements, to the large tank you are adding cool clean water that is a little element poor.

I think the most difficult problem would be balancing water flow. You already have an overflow/sump balance to maintain in each tank, it would be easy to just draw water from one tank and send it to the other but sending it back at the same volume is a little more difficult. I do think that just 5 times a day is perhaps a good idea. Maybe if you could get two sets of really beefy peristaltic pumps and have one facing each way... but that would require quite a high rate of speed, the fastest peristaltic pumps in the hobby are only about 50 mL/min, which might be enough if run continuously.

 

[BeanAnimal]

Opcn,

You would led gravity do the work. Pump from large tank to small and let small gravity drain back to large...

I don't see any benefit running a few degrees cooler just to grow macro.

 

[Opcn]

Bean, he already has a sump on each tank, which means that each tank already has an overflow. I think it would be difficult to add a second overflow with out working to balance the flows. If he just pumped more into the small tank then it would just overflow into the small sump and he would be in trouble.

The benefit I think comes from looking at and enjoying the macro. There is a tremendous variety of slightly cooler water macro that just doesn't make it in the tropical reefs that our corals come from.

 

[BeanAnimal]

Sure, it all depends on the physical location of each system

As for the benefit, I suppose if the simple desire is to grow and look at species that will not survice in the warmer water, then it makes sense and may be worth the trouble. I speaking in reference to the benefit as it relates to filtration or overall system health.

 

[pledosophy]

Thanks for all of the replies.

In answer to the questions.

The Benefits

1. The cost for the added equipment on the second tank (protein skimmer, reactors, top offs, eventually a reefkeeper) would be well into the thousands. So figuring out how to do this right could save me a couple grand.

2. IME with seahorses, which is more then most they do better at lower temperatures, as do many of the algae I wish to keep.

Copps,

Thanks for everything.

Right now my reef maintains 79F without a chiller. The heater does come on at night. This is true for about 10.5 months a year. We have about 6 weeks of hot weather a year here in which my display can jump to 81-82F. During the winter I will be having to heat the tank up to 73, 79F respectively.

In the past my seahorse systems have run in the mid to high 60's to the low 70's without a chiller as the pumps and lighting I was using was so much less then the reef.

My MH's pretty much light my reef now.

I'll keep looking into things. Issue might become mute as my wife really wants the seahorses in the living room now.

 

[elegance coral]

1. The cost for the added equipment on the second tank (protein skimmer, reactors, top offs, eventually a reefkeeper) would be well into the thousands. So figuring out how to do this right could save me a couple grand.

IMHO, the price of cooling one tank while heating the other, would be much more than simply setting up the seahorse/macro independently. You don't need a great deal of filtration on a macro/seahorse tank. You want it to run a little nutrient rich. Trying to run two tanks, with different nutrient levels, and different temps would be challenging and expensive to say the least.

 

[copps]

Thanks for all of the replies.

In answer to the questions.

The Benefits

1. The cost for the added equipment on the second tank (protein skimmer, reactors, top offs, eventually a reefkeeper) would be well into the thousands. So figuring out how to do this right could save me a couple grand.

2. IME with seahorses, which is more then most they do better at lower temperatures, as do many of the algae I wish to keep.

Copps,

Thanks for everything.

Right now my reef maintains 79F without a chiller. The heater does come on at night. This is true for about 10.5 months a year. We have about 6 weeks of hot weather a year here in which my display can jump to 81-82F. During the winter I will be having to heat the tank up to 73, 79F respectively.

In the past my seahorse systems have run in the mid to high 60's to the low 70's without a chiller as the pumps and lighting I was using was so much less then the reef.

My MH's pretty much light my reef now.

I'll keep looking into things. Issue might become mute as my wife really wants the seahorses in the living room now.

No sweat... again why are you heating your reef to 79 with a heater? I bring up temperature in my talks and show photos with me and Julian Sprung in front of some of his beautiful systems (shown in the Reef Aquarium series books he coauthored) ... he too prefers cooler water as I do... if it naturally warms in the summer that's fine, but running a heater to warm to 79 is wasted electricity. So again the only negative to connecting the system would be if you HAD to run your reef at 79... which you don't have to. One other benefit that hasn't been mentioned if you connect them would be that it would give you more stability on the system in the summer. You mention you system could naturally jump to 81 to 82 without a chiller in the summer... that means that you are not far from a potential disaster if your AC were to go out in the summer or any of the other myriad of possibilities that could put the system temp a few degrees higher... at around 84 you'll start to see bleaching on certain corals... running the chiller on the intereconnected systems would give you a backup...

Just something to chew on... if your wife wants the system in the living room it doesn't matter, but did you tell her how much more expensive that would be and how much more maintenance it would take? Or perhaps she'd be willing to help with the extra maintenance?:celeb1:

 

[Opcn]

If you have a constant flow between the two tanks then the cost is going to more than outweigh the money saved on equipment.

 

[fppf]

Building a small heat exchanger and placing it between the supply and return between the two systems will cut your delta in half.

Then you would have 76 degree water entering both systems at the temperatures stated. Depending on the flow rates you could even try a peltier in the heat exchanger. It moves heat from one place to the other. You would have a net gain in heat due to the energy used but it would be one of the most efficient ways.

If that is not enough you could setup a chiller/heat pump combo. This would have the evaporator on water moving from the warm tank to the cool tank and then a condenser on water moving from the cool tank to the warm tank. You would have a net gain in heat from the energy used by the compressor. Would be difficult to design and balance but I have seen things like this done before in industry.

 

[MagicReefer]

I agree with fppf's theory.

If it were me, I would run an extended drain from the cooler tank via a spiraled tower of pvc with a way to use the heat exchange from the chiller to warm the water a few degrees in the pvc spiral before it hits the sump. This would allow one to run a chiller on a tank to a set degree and since the flow rate is minimal you should easily be able to get the drian water from the cooler tank to match up with the sump temp.

You could even go as far as installing an inline heater to the drain pipe to warm the water first before it hits sump but if you can just build a vent or chamber that houses the pvs pipe spiral and use the heat from the chiller you would be more efficient.

Seems like a simple enough thing to do to me. I would definitly go for it.