Fan question for scrubbing

[mad librettist]

so now we have an empirical and theoretical basis for rejecting the notion that mm h20 is a function of cfm.

Jesus, we could have just looked at some fan specs, and noticed cfm and mm h2o are completely independent.


So again I join the chorus of those who actually know - If you can't make sense of the specs, go by the amps.

if you're looking at amps, you're simply looking at how fast the fan can spin (since higher rpm means more resistance hence requiring more current to maintain a higher momentum.) i checked out the delta fan specs and DAMN those are LOUD!!! 60dB!?!?! they do make a lot of pressure but yeah they're spinning at twice the RPM of most pc fans. up to 7000rpm

are you reading with your glasses on? I run the fans at 5 volts. I repeated that - repeatedly!

this brings us to important statement #2 - for stealth and power, undervolt a powerful fan.

 

[spezee]

did not expect to be back, but it all started with this ignorant statement.

I gotta mak this clear so I am not a dick for not telling you: CFM has nothing to do with anything you need to worry about when pulling through a scrubber.

the whole point ml, was that cfm is only a marker point. just as amps, or any other variable you care to mention. the function is inclusive of everything, but subjective to the users needs and application. understanding the function is flat out useful. so is trial and error, but understanding why is good for finding efficiency for your design. for me, trial and error is great and has been an aid more times than not. though i would prefer to understand why, as the trials are going on. or in hindsight as to avoid wasting time in the future.

want a quick way to pick a fan? go by the amps. Why would they bother supplying all that power if they aren't pushing the air?

because all things (fans) are created equal, riiighhht...wrong! I agree on the topic of the dc and axial fans (micro grow section afterall), that you are speaking with good experience and giving solid information about your trial and error. I do not agree with why your reasoning stands, that cfm is not useful. It is as useful as voltage or pressure! How many times can this be said? Product design and intended use (1+2=efficiency) are the factors. The function to gauge the fans capability has been illustrated, your intended use is subjective. Your experience with a few fan models does not make the function any less useful, only your ignorant reasoning is flat out comical.

The spec sheets you want to look for are the adjustable graphs. The ones that allow manipulation to each variable, or as ml said you will find the advertised cfm a load of shit more times than not. I just can not agree that voltage or other variables can be substituted to gauge the products design efficiency, because that has to do with all variables (the function as a whole) plus the subjective needs of the user, environment blah blah.

ml i agree with you about your findings from trial and error, but stress the importance of flow is as important as voltage( edit should be "current"). your initial statement was all i disagree with, and your logic following. but the findings and what works for you is legit and concrete. thank you for sharing. understanding these principals can help avoid future trial and errors, but finding the accurate spec sheets can be difficult. not all products are designed the same, efficiency varies.

so now we have an empirical and theoretical basis for rejecting the notion that mm h20 is a function of cfm.

Jesus, we could have just looked at some fan specs, and noticed cfm and mm h2o are completely independent.

who exactly is we? you are no bernoulli.
iused2dance

 

[spezee]

Adjustable spec sheet for one (of many) fan designs. I do not believe this company to produce axial fans (we are in the micro grow section), but many different fans can be "spec'd" out on their site. All with different intended uses and capabilities. The function plays true, the design and efficiency with intended use is what to be on the lookout for. Point is, these are the type of spec sheets to look for; OR understand the function fully to apply the general spec sheet usually given (as shown by ml).

Starting with max efficiency for this particular model (does not mean max efficiency for alternate uses). This helps me understand the importance of understanding the function and intended use. Mostly finding accurate spec charts. These were from manually setting different pressure points, but any variable in any graph changes with different marker points. Showing the function, on graph along the board. Determining the blah blah in between is up to the user. I feel like a parrot, and didn't want to spend the evening like this.

without continuing this "debate", i can only suggest research only gets you so far. experience takes you to the destination. avoiding all unneeded pit stops along the way can get you there sooner than later.

 

[mad librettist]

without continuing this "debate", i can only suggest research only gets you so far. experience takes you to the destination. avoiding all unneeded pit stops along the way can get you there sooner than later.

:

 

[ScrubNinja]

 

[mad librettist]

ml i agree with you about your findings from trial and error, but stress the importance of flow is as important as voltage( edit should be "current")

no amps to generate work required to overcome forces impeding air or surface area to let you push enough molecules means your actual cfm takes a nose dive. Yet the fan retains its cfm rating. It spins and spins, and air on the other side of the scrubber fails to move.

The cfm we care about are in the cab, not in the lab.

A great way to approximate your real cfm is with a blown out candle or some incense. Or a sheets of progressively heavy material. In the lab they don't test it with a scrubber. Why don't you use those theories of yours to build a quiet cab exhausted only with a scrubber running 5 watts per gallon? I'm being generous, and letting you hit the easy marks.

And I said amps, not volts.

Sure, I only understand this heuristically. but better than some it seems.

 

[spezee]

You can not use these variables:cfm, amp, mmhg ect.. across the board for all fan models. Each fan model and design is case specific. And if you want to go by "amp" or what I refer to as current, then you also must accept cfm as an equal! They are in relation to each other for specific values given a specific product design. One is not superior to another. That is what I am trying to explain. Ex. Fan A @ B current yields C cfm. The point is case specific, but the function remains. The function explains trial and error for each specific fan. The values are not made up or based on hypothesis. They are based on individual product design. PERIOD which is why they differ fan to fan, model to model.

You keep eluding to cfm's and amps and all these terms that are used in place of the function properties. ie.) FLOW, CURRENT, PRESSURE ect. that directly affect one another. They all depend on the PRODUCTS DESIGN, and should be treated case specific. Which is why you notice different outcomes in your trial and error given different products.

You are correct cfm is not constant (because it depends on many other variables including "amps" aka current.) You must start to treat current "amps" and all the other variables the same. Product design, is how you can have one item require more energy than another more efficiently designed product that both give the same output at all variables across the function. Not all products are designed for the same reasons. Efficiency is highly subjective, and in turn the reason there are many different fan models.

You are again correct they don't test in the lab with a scrubber. I wonder? Maybe because not all scrubbers are the same. Just like fans. Imagine that. Using the function you can insert the exact given additional pressure from a scrubber, and in turn see the actual values for each variable change across the board for a given specific fan model! A scrubber is part of pressure in the function! It is illustrated on the previous page if you care to look at the progression of illustrations noticing with different marker values (for any variable) will change the rest of them within the function.

I dont know what heuristically means so you must win. I agree with all of your findings from trial and error, and when you say cfm drops with some models. How much of a drop depends on the product design. When you say cfm is bogus to go on, you are right. Going on cfm alone, just like amps alone is bogus. I think you are picking at different things, as am I. We are not on the same page. Your findings are correct, and most of your statements. But understanding of the function between all the variables, coupled with product design and personal needs is a personal thing. I'll stop talking to a brick wall. The info is there for anyone who wants.

 

[thujone]

Not true, amps have nothing to do with how fast the fan spins. That is totally an issue of how the fan is designed. Some are designed to spin higher rpms, others are designed to spin slower. Amps simply mean power (think horsepower) to resist the friction loss in the system, which is what creates static pressure.

Amps have everything to do with how fast the fan spins. Axial fans are not designed to function in a closed system like centrifugal ones are. Therefore, aside from the electromagnetic resistance and the resistance from the ambient, still air, there is generally no other resistance for the fan to overcome.

The sole purpose of the high amps in a Delta is to enable it spin faster and therefore with more force to suck more reluctant air through a computer than it's competitors with similar fan diameters but lower RPMs. The high amperage, intended to make the fan spin faster and maintain air flow, just HAPPENS to be convenient for growers because that extra current comes to good use when you put a carbon scrubber in front of it and create even more resistance.

Huh?

I really don't know how to make that point ANY clearer. It's simple: fan creates VACUUM on one side in order to feed PRESSURE on the other side. To make that formula complete, the fan MUST move a prerequisite amount of air (i.e. CFM.) No offense, but if you knew anything about this topic you'd know that in simplest terms, air makes pressure. This is something a high-school graduate should know. What do you inflate tires with? AIR! What is the capacity measured in? PSI! Pressure doesn't magically manifest itself out of the void! you put a fan out in space and it can spin as fast as it fucking wants and it won't make a single unit of pressure because it will have nothing with mass to move.

Do you know what the formula for pressure is? It's pressure = force / area. Do you know where the force comes from? it comes from the air being moved. Air has mass, and the more air a fan moves the more inertia the air carries. the more inertia it carries, the more pressure it creates. Imagine an SUV hitting a brick wall travelling at 1mph. The wall (resistance) will stop the SUV. Imagine that same SUV hitting a brick wall at 50mph. It'll go right the fuck through it. Now let's apply that image to fans. Imagine a 92mm, 100CFM fan pushing air (the SUV/mass with inertia) into standing air (the wall/resistance.) You can feel the pressure with your hand if you put it up close to the fan, but the further away you move it the less you feel it. Now compare that to a 92mm, 200CFM fan. It's able to push more air through the same area (remember pressure = force/area) therefore, it must impart the mass of air with more force in order to push double the amount through the fan's frame in the same time as the 100CFM fan can. As a result, fan must create more vacuum to gulp up the additional air and as a result it creates more pressure as it forces more air to collide with the resistance of the standing air on the other side of the fan.

So let's tie this back to the relationship with amps. Current enables a fan to overcome the resistance in the fan's motor and also the resistance of the standing air. The higher it goes in RPMs, the more current it must draw to maintain momentum in the face of increasing parasitic loss generated by the motor. Funny thing is, the air actually becomes less and less resistant as the fan establishes a good flow in the confines of it's environment because it no longer has to move standing air but just move air that's already queued up to move in the direction the fan wants to send it in.

Now, mad librettist was saying that his Delta at half power still functions better than another fan at high power, but since he cannot provide accurate details about how much pressure the Delta fan makes, or current it draws, or air it flows at half power, I'm inclided to side with the laws of physics than with mad librettist's perception of the situation.

Could it be that fan design is so good it picks up all the slack? Possibly, but what is NOT possible is for the fan to create something from nothing as some of you think it does. It will NOT magically draw more current to overcome any resistance unless the fan was designed with a mechanism that tells it to max out on power if it detects more resistance. Rather, most PC fans will simply stop if you tried, say, sticking your finger into the moving blades. If you tried stopping a Delta fan with your fingers then felt immediately that the blade started exerting more force on your finger than it was when you stopped it, then you know the fan is equipped with such a mechanism, although for such a simple device it's a rather unlikely feature.

No, you haven't. You had a couple people try to offer you knowlege. It's not good form to come back and pull sh*t out of thin air trying to defend yourself when you what you really don't know what you're talking about. There's a lot of helpful people here with good information. If you want to learn you must first recognize you don't know.

Listen, I'm not here to argue or stir shit, I'm simply trying to explain the concrete physics behind the phenomenae discussed. ScrubNinja and mad librettist's experiences with their fans are great for knowledge of what is good to use and what is bad to use, but that still does not change the physics behind WHY certain fans are better or worse. As for pulling shit out of thin air, well, I have years of experience with car engines and turbochargers, and fluid dynamics is an intrinsic part of getting to know how they work. Hell, moving gases is the means by which an engine makes power. You cannot make gasoline combust without an adequate mixture of AIR in the chamber. Now, it is NOT in my best interests to just make wild conjecture about how pressure and vacuum work because too much of either makes parts break and when thousand dollar parts in an engine break, it's quite a significant loss.

Anyway, last night I was about to delve into why centrifugal fans often show a low CFM/high pressure relationship but after having to explain the facts yet again I'm too damn tired to keep typing. Now I have an engine to go work on, and put some of these principles to work in the process.

 

[mad librettist]

And if you want to go by "amp" or what I refer to as current, then you also must accept cfm as an equal!

not really... you are switching subjects there. going by amps falls under the "quick and dirty shopping strategy that succeeds more often than not" category, not the "understanding cooling" category.

herefore, aside from the electromagnetic resistance and the resistance from the ambient, still air, there is generally no other resistance for the fan to overcome.

I believe you left out turbulence... and negative pressure. woops! what do you think is going on between the fan blades and scrubber exhaust? I'm no genius, I just have senses and some sense. CFM ratings will not help you pick a fan.

Here are some other things I would look at for tip offs when shopping

weight
thickness
can be undervolted
bearings vs brushless
mm h2o as stated
amps as stated

look guys, argue all you want, but let's see you build the cabs. 5w per gallon minimum, no heat shields, unsealed lights, scrubber is only ventilation. Max fan size 120mm pc fan. I say your fans meet the specs suggested by scrub or fail to keep temps less than 5F above ambient 15 cm from the lights. Period.

 

[spezee]

It has been a while since a micro grow was done, but I will be on the lookout for some neat spaces. Nobody is arguing anything but the fan can only do what it can do, nothing more or less. Which variable you choose to reference for your marker point is up to you, it will either work or not work for your desired application. The function and spec's are a way to illustrate these findings if one wants to gain a more precise measure on their gardens required inputs.

going by amps falls under the "quick and dirty shopping strategy that succeeds more often than not" category, not the "understanding cooling" category.

That is correct, I fully agree with you about that statement. I was only trying to get across my opinion about: understand what you need, what the fan is capable of, and you are good to grow. I only had a quibble with that ignorant statement about cfm not being relative. IMO cfm is just as accurate a measure within the function as amps (or any of the other variables you have just listed). So long as the actual value is being used. Trial and error tests are great, and are how specs are made. The spec sheet is just language to illustrate the trial. One spec is useless as to the products performance under a host of variable conditions. There is no error because that is dependent on the intended use. Except I would rather have the fan spec'd out at many different variables within the function to see if it would work for my desired application BEFORE purchase with accurate units of measurement.

Making an aloof purchase based on insufficient data on the product is sometimes unavoidable, in that case more often than not will due me just fine. But your reasoning is denying the very evidence that supports your trials and outcomes, and for that I can not understand.

If it is easier for you to be naive to these facts, that is fine. Just don't spew out ignorant statements about flow and current. I never disagreed with your trials or outcomes. Just don't omit an actual cfm value's worth because of your ignorance, just the same I do not omit the actual amp value's worth. The amp's (current) imo have to do with the efficiency of said cfm's (flow). Either way you can not have one accurate value without the other, remember they are not constant within the function full of variables. I don't expect you to understand my opinions we obviously do not seem to share similar ideas on this subject. Your garden, your time, your purchases, do as you wish.


Aren't you using fans to cool? Or are you removing heat? lol @ my semantics. See how easy it is to continue nonsense? Continue with your logic, and stay naive to the reasoning of why. If it works it works. Why is just a way for us to reference, and a way to dial in, but they are just words. And in the end it either works or doesn't. How i want things to work differ than you. Everyone is correct, as long as we are having fun and enjoying it along the way. Thanks for sharing your point of view.

 

[mad librettist]

Making an aloof purchase based on insufficient data on the product is sometimes unavoidable, in that case more often than not will due me just fine. But your reasoning is denying the very evidence that supports your trials and outcomes, and for that I can not understand.

and yet, "aloof purchases" seem to work out so well for me and others, while "gregarious acquisitions" based on cfm ratings fail to do the job so often.

why is that? luck?