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rygh
02-05-2010, 03:22 PM
Background:
I have been getting ready for Rev-2 of my ATS.
I have a lot power/height requirements, so I am a bit stumped on what to build.
So as an engineer, I try to separate out the issues, and write down the tradeoffs.
Might as well make it nice for the forum.
And, best to make sure various assumptions are not wrong.
Obviously a lot of this info is already in the FAQ.



## Single versus dual sided.

* In a horizontal, dual sided is basically impossible.

* Dual sided doubles surface area for same overall screen area.
Pretty obvious math. A 10x10 single sided = 100, dual sided = 200.
You can of course double the area of a single sided to equal that of a dual sided.
But that doubling will have impact on size, efficiency or pump requirements.

* Dual sided doubles the flow requirement for same width.
You really need a certain flow per inch, per side.
So a vertical double sided needs 35 GPH/inch, where a vertical single sided may be 17 GPH/inch.
Not to be confused with horizontal/vertical flow tradeoff.

* Dual sided might be more light-effficient.
Even with a thick growth of algae, light will pass though.
If a single sided screen is not reflective, you lose all light that passes through.
On a double sided, it can help on the other side.

* Dual sided may be better for regrowth after cleaning.
You can clean one side at a time.
Dual screens are generally thicker, with more algae left in the center after cleaning.

* Single sided can have a rigid screen.
Dual sided is generally 2 layers of screen, maybe 3. More, and it does not work.
Single sided can be solid underneath.
This can sometimes have advantages when cleaning, or in design.

* Dual sided systems will usually be smaller overall, but more cubic.
The screen area largely determines the size of the ATS box itself, so dual
sided will usually result in a system that takes less space. Lighting will cancel
out on area, but since it is on both sides, will be more square.


## Aspect ratio, tall versus wide.

* A wider screen, of the same area, will require a more flow.
Assuming 35 gph/inch, 200 sq in screen:
A 20W x 10H = 700 GPH
A 10W x 20H = 350 GP
So a tall/thin design will reduce flow (pump) requirements.

* A wider screen is more efficient.
As algae absorb nutrients, CO2, etc, the higher algae will have higher concentration
than the lower. At some point lower algae may be starved.
So a wider/shorter design can be more efficient, and smaller.
However, it has been argued that nutrient uptake is very slow, and it takes many passes
to make a difference, so this tradeoff might not be critical.

* Match aspect ratio to lighting.
If you plan to use T5 lighting, that means long thin fixtures, so the ATS should match.
If you plan to use a single CFL flood, which produces a circle, then square is best.
Not an issue with LED.

* Even flow can be a problem at extreme aspect ratios.
With a very wide design, getting equal flow out of a long pipe, especially after growth,
can be tricky. Similarly, with a very tall thin design, small horizontal inconsistancies can add up.


## Horizontal versus Vertical

* A vertical system produces much higher velocities at the boundary layer.
Clearly the highest velocity water reaches is in a waterfall.
This higher velocity aids in nuetrient absorbtion.

* A vertical system produces a more constant layer.
In a horizontal sytem, uneven growth can cause channeling, resulting in very uneven flow.

* A vertical system produces a thinner layer.
In a vertical system, as the water layer gets thicker, the outer layers
have far less friction, so travel faster, limiting the thickness.
This thickness can help significantly with light penetration.

* Eliminating splashing is slightly easier on horizontal
Either one can splash if done wrong. Neither will splash if done right.
The lower velocities of a horizontal likely mean a small amount less splashing.

* Horizontal is often easier to clean.
It is generally made with a solid tray, that simply lifts out for cleaning.
No pumps to turn off, no unions to disconnect.
It is somewhat more difficult to make a super-cleanable vertical. But possible.

* Horizontal requires more flow for given width.
To get the turbulence needed, it takes a somewhat higher flow/inch than vertical.
Not to be confused with the single/double sided tradeoff.


## Lighting choice

* Simple CFL floods are the easiest and cheapest up front cost.
Simple home-depot lights. Work well. Easy to replace.

* T5 seem the be the best of the fancier proven designs.
Very efficient. Reasonable cost. Widely used already in the aquarium.

* LEDs are theoretcially best, if they can ever be done correctly.
Should be the most efficient, especially is spectrum is tailored correctly.
Much safer, and many other plusses.
However, very tricky to get right, not a lot of success stories.

* Metal Halide are generally a bad idea.
Hot, wrong spectrum, point source. But would work.


## Various intermittent flow designs.
There are various dump bucket, wheel, and other designs that have been tried.
In theory, the only way to grow true "turf" algae is with those methods.
Done right, they may out-perform the simpler standard methods.
However, the success stories seem few and far between.
These are best left for other specific forum threads.



#### Common Treadeoffs

* Vertical height restrictions:
Clearance between tank and sump is a very common problem.
Horizontal is one solution, although lighting may in fact cause this to be taller than a vertical.
Short/wide vertical is a great solution, although this signficantly increases flow requirements.
Note that the way screen is removed from ATS also has a large impact. Never forget cleaning.
So no obvious winner.

* Width/lenght restrictions.
Other than height, volume is a big restriction as well.
Higher efficiency design can help a lot.
Double sided can help a lot. But that eliminates a horizontal design.

* Power cost.
The cost of lights and pumps can be significant.
A taller/thinner design helps, because it lowers flow requirements, thus less pump power.
But it makes it less efficient, adding to lighting cost.
Using the tank-sump return is a huge win, since it eliminates the pump completely.
But that gives hard (and usually small) limits on the width of the screen.
A higher efficiency dual sided design helps.
Higher efficiency lighting helps.

SantaMonica
02-05-2010, 05:49 PM
Pretty much all accurate, with just these clarifications for others who may not understand completely yet...



Dual sided doubles the flow requirement for same width.

Actually you want all 35 gph on the top side of a horizontal too. This is to make up for slower horizontal flow, and also to "jump" over algae growth which block flow to downstream areas.


Single sided can be solid underneath. This can sometimes have advantages when cleaning, or in design.

Double sided can be solid too. No problem.


With a very wide design, getting equal flow out of a long pipe, especially after growth, can be tricky. Similarly, with a very tall thin design, small horizontal inconsistancies can add up.

But the advantage of wide is that a typical algae clump is about an inch across, and this would only slow down 1/20 of a 20" wide screen, whereas it would slow down 1/3 of a 3" wide screen.


The lower velocities of a horizontal likely mean a small amount less splashing.

One would think. But what some people find is that a vertical screen inserted into an enclosed pipe has the water "handed" to it via the slot, right there on the surface. A horizontal screen, however, is not inserted into a pipe; instead the water outlet "drops" the water onto the screen. This dropping is what actually causes the spraying, especially since most of the algae grows right there around the drop-area because of high turbulence.

whites
02-06-2010, 03:11 AM
thats a great summary Rygh!!

rygh
02-06-2010, 01:55 PM
Dual sided doubles the flow requirement for same width.
Actually you want all 35 gph on the top side of a horizontal too. This is to make up for slower horizontal flow, and also to "jump" over algae growth which block flow to downstream areas.
To clarify, you are combining two tradeoffs at once. horizontal/vertical with single/double sided.

Single sided should be half the flow requirement of double sided, for same width, both vertical.
After all, half should flow down each side for double sided.

Yes, the increased flow requirement for horizontal is covered in that section. But really should be "double" I guess, instead of "more".

inkidu
02-06-2010, 06:48 PM
Great right up. Nothing like weighing your options to make an informed decision.

Any thoughts on the pros and cons of different types of screens (mesh size, material, backing etc...)

I notice there is an ultra stiff mesh good idea???


Conclusions?

Thanks for any help.

rygh
02-15-2010, 09:55 AM
I ended up deciding on a semi-horizontal design.
A long 6.5" wide x 30" long single sided, sluce-box type design. With about a 6" drop over that 30".
I really have 2 key constraints: I want it to fit in a certain spot, and I don't want to add another pump.
A big 800 GPH pump can be $200/year in electricity. Plus not cheap up front.
My current sump gives me 256 GPH. (Way below the 400 GPH rating, due to head, losses, etc)
I only have about 7" of drop. GPH limits me to 7" wide.
So I could do a 7x7 vertical max, which is just too small.
The horizontal planned is basically double the surface area. Sure, not as good at growing, but I hope that doubling
the size will make up for it.
Plus, it makes it a lot easier to clean every week. I had height restrictions for simply removing the screen as well.
Lighting will eventually be all LED, but first be LED+CFL, and maybe PC.

Design is in progress. When completed, expect some posts in the other forum. Even if it fails, still worth learning from.