Open loop vs Closed Loop

[ciaus]

I recently found out that what I want in a SW tank, effect wise anyways,  is something called a closed loop...Very discreet hardware, with little to nothing visible inside the display tank.  I asked the question of a few people and got very informative responses, but since I stumbled upon the distinction I thought it might be a worth while thread to have so that other would be SW addicts can consider if closed loop is for them, or not...

As I have already said, one advantage of Closed loop is much less hardware in the main tank.  I would like to invite people to discuss the pros and cons of Closed loop vs Open here along with what drove them to the type of system that they are currently using...Would you switch?

I know what closed loop is, but I cant quite define it just yet...someone want to take a stab at that too?

Ciaus.

[Contains Moose]

It's pretty simple, you take water from well below the waterline send it to the pump and return it back to the tank .

[10gnano]

so what is the differene between open and closed??

[JD]

My take...

Closed loop circulation is water circulation within one tank. Usually an external pump is used with fairly high flow rates. This allows you to take water from one part of your tank and discharge somewhere else of your choosing. SPS dominated tanks require very high water flows. Using a closed loop is one way of achieving it. Using a maxi jet or koralia powerhead is also an example of closed loop circulation. The main difference using an external pump is usually much high flow rate and no powerhead/s in sight. Drilling the tank and the use of bulkheads is the norm but can be achieved without.

Open loop circulation is water circulation between more than one tank, usually a sump tank and a display tank. This allows, typically, surface skimmed water to be returned to a sump for filtration, heating/cooling etc.

http://www.3reef.com/forums/new-hobby/closed-open-loop-34555.html

An example:
I have a frag tank, it has both open and closed loop circulation.
For the open loop portion I pump water from my sump tank into the frag tank. It fills up and then overflows into a pipe that returns to my sump tank for heating/cooling, skimming, carbon treatment, GFO treatment etc.
The closed loop portion takes water from one end of the tank and pumps it back to the other end through an external pump and plumbing. The only hardware seen for the closed loop is bulkheads with strainers(pump suction) and bulkheads with diffusers.(pump discharge)

Closed loop circulation can be used on any size tank but is usually used on larger tanks, say 90 gallon or more.

Here is a site that talks about lots of stuff including some closed loop stuff.

http://www.melevsreef.com/links.html

[Canoe]

I like the idea of having two pumps operating in open-loop for providing the increased circulation. One fails while you're at work, you've got surface skimming still taking place.

Although for maximizing the circulation, I believe the same pump working against the extra head to pump the water back up from the sump, will have lower flow rates than if plumbed in a closed loop. So if the name of your game is to maximize flow for the least pump cost...

[Contains Moose]

  Using open loop pumps flow for circulation reduces the effectiveness of the  skimmer,  use a return pump of close to equal the capacity of the skimmer, use a closed loop pump to get the desired flow that is recommended for the critters you want to keep, ensure the closed loop pump is moving the water in such a manner that the surface water of the tank is moving to the overflow box and getting rid of surfactants.

[Hookup]

I was not familiar with the term "open loop" before JD's description.  I can say that I am not a fan, though it has proven successful for some.

WRT closed loops, they should primarily be considered for their aesthetic purposes as they generally are more expensive to implement than throwing powerheads into a system.  Secondly, as you change your mind over time, or as corals grow in and mature (become large) a powerhead is very easy to move and reposition where CL's can possibly be more difficult to adapt.

That said, I have a CL because I believe that they are the "best way" to get things done in the tank.  The move water, lower maintenance, and above all, they let you look at the reef, not the equipment.  With some good planning they are easily the best system for the reef tank, they can accomplish everything some fugly powerheads can, and look... invisible.  What else could you want from your circulation system.

[Canoe]

  Using open loop pumps flow for circulation reduces the effectiveness of the  skimmer...

Why?
skimmer has its own pump, no?

[Hookup]

Hey Canoe,
  I've used this loose analogy when debating low-flow sumps and high-flow sumps.  I think of the sump as a car-wash.  The slow moving car gets cleaner than a higher speed car.  If you keep your car at a steady 60mph, no slowing down, it seems like a lot more effort to get the car clean than going slow.

  Most cleaning "tools" in the sump have performance increases that are directly proportional to the duration of contact with the water.  Phosphate Reactor, Carbon Reactor, Skimmers all have a performance curve that peaks in the lower-flow range.  If you can get the water moving in your sump at or lower than those peaks then you're cleaning the water more efficiently.

  I know the analogy is not bulletproof but at a basic level it supports the slow-flow sump concepts.

  Another supporting theory/development is the concept of recirculating skimmers.  If you compare two skimmers that are identical except for the recirculating feature/design, the recirc is almost always rated at a higher gallon/volume.  Keeping the same water in the skimmer longer gets the water cleaner.  Again, not a direct correlation to low-flow sumps, but a related concept.

  I know for me, 200gph is MORE than enough for my sump.  It's not about xTimes turnover, it's about sending dirty water to the "car wash" and having it come back in clean.

  Think of this.  If you had an unlimited supply of "clean salt water"  say from a 100000000 gallon barrel in your basement, and you pumped 100gal/hr into your 100gal display where your overflow was connected to the drain, you'd basically be doing a 100% water change every hour.  How much better can that get for your fish/corals?  It's about perfect!   NO sump can get water back to 100% clean/perfect, but the longer the water stays in the "car wash" the better, to a point of course.

Does that help?

[redbelly]

Nice analogy hookup!


Open loop techincally refers to your sump system. The flow that you receive from the "open loop" part of your system should not really be calculated in your total tank turn over rate as the flow rate should be low anyways.

Not sure what "contains moose" was saying about openloop pumps there but they do also mention the importance of your flow directing the waste up to your overflows for removal which is not required, but a VERY benificial feature!

[salvini55]

For the sump I like Low flow through the sump and high flow in the sump. Return is throttled back with a modded MJ to keep it from going stagnate

Oh and so I dont thread jack, Im all for closed loops! clean, powerfull and controlable flow rates ++

[Hookup]

Neat ideas Salvini55.... The thing I've learned is that there are a huge amount of ways of doing things that will work.  Some better than others for specific applications, but there are just loads of ways of doing things. 

[Canoe]

Interesting, but I thought one could address the "dwell" time for a recirculating effect for skimmers (or other devices) through having multiple chambers in the sump. I can see where if your sump was one big tub you'd have less than optimum circulation speeds and you'd want to dial it back. To myself, I see skimmer efficiency, skimming efficiency and sump circulation as inter-related yet separately addressable considerations.

In that end, in place of a traditional skimmer, I'm considering making an air scrubber Air Stripper down one length of my sump (design phase only: still planning, just got a 280G tank, setup in the fall).

• I can manage the water flow rate through the air scrubber Air Stripper (separate from the open loop flow rate) such that I can maximize the bubble dwell time in each stage.
• Each stage is cleaning water already cleaned by the previous stages - with each stage, there should be less competition for the moderately polarized DOS from the largely already removed heavily polarized DOS.
• The available height in the sump and the bubble rise time makes for an absolute limit on bubble dwell time in an in-sump air scrubber Air Stripper - as it does for in-sump skimmers - so it means that the hard-to-foam DOS never get a long enough dwell time to get foamed.
• I'd have a reservoir at the end of the air scrubber Air Stripper, with it's overflow returning to the main sump area.
• Out of this reservoir I'd run (and return, for some recirc effect) a relatively narrow but very high (height from the floor to the top of the display tank) skimmer to have the already skimmed water subjected to a very long dwell time foam fractionation for those hardest to foam DOS.  

Should be the same, similar or better than running several skimmers in series, with the benefit of a final high dwell time skim.

However, with vodka dosing, it appears that such a rigorous skimming requirement may be redundant due to vodka binding with the difficult-to-skim DOS for their easy skimming removal. Yes, no?

[Contains Moose]

ALL skimmer manufacturers I speak with test skimmers in a container, they add foul stuff and see how much they remove, they do not pour the said crap into a tank and have it returned to the container with a 10 times turnover rate, if you ask them they will tell you that the best way to utilize there skimmers properly is to give them approximately a 1 times turnover rate, however if the surfactants from the tank are not getting to the overflow box because of improper flow direction then this will not happen, the direction of the correct flow and combined with the correct amount of turnover rate will be the most effective, most beneficial and the most inexpensive form of skimming.

increasing the turnover rate only serves to dilute the surfactants and make the skimmer inefficient.

[Hookup]

Hey Canoe,
   - what is an air scrubber?

   - I agree that multi-chamber sump can recreate the recirc concept.  In fact I would argue that is what I have running now.  My skimmer is running with a 5600gph pump driving it that draws from the first chamber, which is a 40gallon tank with ~35+ gallons.  There is about 400gph flowing thru the sump.  The sump turns over 12x per hour but the skimmer turns over the water almost 160x hour.   I really like this setup and believe that it is super-cleaning the water.

[Canoe]

Hey Canoe,
   - what is an air scrubber?

My bad. It's not Air Scrubber, but "Air Stripper".
The type I'd emulate is a horizontal chamber-to-chamber flow design, only with closed baffles (like bubble removers in sumps) to direct the water flow downwards to create more dwell time for the bubbles.

A skimmer as we know it is essentially a single chamber air stripper (for foam fractionation) with directed water flow for maximizing bubble dwell time.

If you can DIY baffles into a sump to remove bubbles you can build a multi-chamber horizontial air stripper. It's essentially the same, only you put a bubble source at the bottom of the downflow side and you add a higher overflow to the side for the foam to overflow into a collection channel. You run the series-chambers in parallel with an open flow channel, using the entering and exiting baffle heights to control the flow rate through the Air Stripper, with the bulk of the water flow going through the open channel. 

I have some designs, but they're on paper, not computer yet. And there's the issue as to the bubble source, and a pump capable of supplying that much air... and at what cost to run and the noise...

[mikerobart]

Air strippers normally remove volatile light components to the gas phase. Doc's have much lower volatility than components normally removed in an air stripping column. I don't think a stripper would work well.

Even if the compounds to be removed were volatile enough, where is the doc enriched air going to go ? You certainly wouldn't want to vent it inside your house. Good packing material to increase surface area is another issue. Unless you've got low weight alkanes in your water I think another technology might be best.

[Hookup]

wooosh.... most of that went right over my head... and FWIW, Air stripper/Air Scrubber... I didn't know the difference... 

Looking forward to seeing your test & mockups!

[Canoe]

horizontial style for foam fractionation, not vertical style for VOCs

[mikerobart]

It's still foam fractionation then no ? In air stripping the stuff you want to remove has to actually enter the gas phase. You pass water over beads or other packing material and blow air the other way. The more volatile stuff says " I like air better, I'll leave the water for you . " The air exits the top ( lighter) and eater falls to bottom of system. In all my chem eng courses this is what air stripping was. Foam fractionation relies specifically on the interface between air and water as a preferred location for polar molecules. Stripping relies on the preference of a molecule for the particular gas or liquid phase.

Just the semantics maybe but I think you talking about a horizontal as opposed to vertical foam fractionator. I'm interested to see the design though, contact time seems to be a limiting factor is many skimmers.