HydroMag published a fantastic article in their May/June 2014 issue by Charles Chillington who posed the question "What are the best grow room extract fans in the hydroponic market?". Continue reading below to discover his findings to help you try and make sense of this often confusing area when setting up an indoor grow room.
So then… extractor fans. I’m going to assume you all know why you need one of these. As it happens, I could do with an upgrade soon as well myself.
Seeing as how there’s chuffing loads available now it would be good to know if there is any discernable difference between any of the various types before making my next purchase.
All I really want is to get a fan that’s going to actually work well enough to keep my room cool. Simple as that. I’ve been looking at all the fans and their different ratings and trying to figure out which one I’m actually going to buy. In this day and age, this should be a relatively simple task. As a modern day consumer I expect products to work as well as the marketing jive claims they do. For those that don’t know me, I’m a fairly sceptical fellow, and quite rightly so: I’m sure the veterans of the hydroponic industry reading this can testify how sometimes products aren’t always what they are cracked up to be.
There is now a lot of choice as to what fan you should be buying. Many companies are all after the coin in your purse, and will try to get it by any means necessary. You need to make them work for your cash; don’t just give it up straight away like a cheap slag. So before we go any further, I have put together a chart so you can quickly see the base statistics of the fans we are going to look at, and get an idea of what your initial options are. It’s not quite as intricate as the tent one last issue thank god, that one nearly gave me an embolism putting it together.
So that’s that then, yeah? I can see what fans blow the most and that, see how much they all cost and stuff. That’s all I need right? I’m gonna go get me that ACME Fan-tassT1C one that looks so good up in this here chart. Bob’s your Uncle and Fanny’s your Aunt, my work here is done, and all my life problems are now sorted.
For those of you that didn’t pick up on it (probably Americans), the above paragraph was steeped in sarcasm. Unfortunately that there chart doesn’t give you any indication as to how they actually perform. Seeing as how this is a critical product for my grow room; I want to know for sure the fan I get is the right choice for my situation. I don’t want to have to make several purchases in order to finally get the fan that works for me. My name’s not Moneybags McGee and I’m sure not many of yours are either. So let’s stop with all this hilarious rhetoric and get down to business then shall we?
Ok time for a sciencey bit, try not to zone out here...
This comparison is all based on how fans react when placed under pressure. Anything you attach to your fan will cause airflow resistance, increase the pressure loss in the ventilation system and therefore decrease the overall airflow the fan creates. Imagine you’re trying to blow out as hard as you can and someone sticks their hand over your mouth. It will make you strain to blow, and reduce the amount you can actually get out. Same thing with fans. In a nut shell, how much pressure loss your ventilation system will create depends on: How good a motor the fan has, the impellor/fan blade design (if any) and what you are attaching to it.
The main cause of pressure loss in an extraction run will usually be the carbon filter. So this makes it a good example to use to properly describe the effects of an increase in pressure loss. You should find that most reputable fan manufacturers will provide you with pressure curve graphs that actually show how their fans perform with increasing pressure. (See example A).
This is the starting point of how to actually gauge how the fan will work when put under pressure. You can’t really just use this alone though. What you now need to do is compare it against the pressure curve graph supplied from the carbon filter you intend to put on it. (See example B).
This filter graph shows two measurements on each axis: Airflow (measured in cubic metres per hour, or m3/h) and Pressure (Measured in Pascals or Pa). Find the value of air that your fan moves, in our case 7963/h. Look up the graph from this point to the part of the curve that this value cuts. Then follow along the pressure axis from this point to get the pressure that will be created, in this case roughly 155Pa. (See example C).
Now you simply perform the same step on the original fan pressure graph, but start from the pressure axis with the value you have just got. In our case you can see that a pressure of roughly 155Pa means that our fan will be blowing 550m3/h. (See example D).
This gives you a much more accurate idea of how much air you will be moving but still by no means what is actually coming out. As mentioned previously, most ventilation equipment will cause some degree of airflow resistance and increase the pressure loss, even something as innocent as a straight bit of ducting.
I don’t know about you, but all this sort of finger-in-the-air ambiguity tends to get on my tits. What I really want to know is how each brand of fan actually compares to the others when put under the same conditions. Something that actually tells me how each fan really works. So that’s exactly what I decided to show. Get everyone’s fans all together and measure the varying outputs of each one.
To get a good idea of their performance, there were three things that I wanted to measure with all the fans, so let’s just take a little bit of time to explain how each of these were measured:
Measuring this will show me exactly what fans are blowing what when put under various conditions. I used a Testo 417 anemometer to measure the airflow. A highly accurate hand held device kindly supplied to us by Alasdair from Solar & Palau. You simply set the parameters for the surface area of duct you are measuring (in our case the area of an 8” or 200mm circle), and the unit calculates the airflow. After taking the first few measurements, it became obvious that air doesn’t travel uniformly down the length of ducting. Imagine looking at a cross-section of the ducting, cut into four quarters. Air may well be travelling faster in the top left of the cross-section than it is the bottom right. However the variance I got over these areas was only ever up to +/- 50m3/h, and they always averaged out to the reading obtained from the centre of the ducting. I therefore held the meter as close and central to the vent hole as possible, and as perpendicular to the duct run as possible to achieve the most accurate results I could get for every type of fan.
2. Sound Levels
As any hen-pecked husband can testify, no-one likes a constant noise droning away in the background, so a comparison of the dB levels would indicate if any fans are relatively quieter than any others. We used a dB meter provided to us again from Solar & Palau and mounted it on a tripod at the same height as the fans. Then set to a distance of a metre away from the fan and at an angle of 45 degrees to the outlet. There was a fair amount of background noise (occasional angle grinding or baselines from the local chavs’ cars), so we measured the dB over the quietest periods we could, and took the lowest readings it gave us. The lowest reading being the one with the least background noise interference.
3. Power Consumption
By far the easiest to measure. We simply purchased a power meter from Maplins, plugged the bugger in, plugged the fans into it and BAM, we get a lovely accurate power consumption reading.
We used the same filter throughout the whole process, the Phresh 200/1000. I was initially a bit worried that it may not have been adequate for two of the fans that we had to test, but after being reassured that these filters are actually good for accepting more air than they are officially rated at anyway I calmed down a little. Then after seeing none of the fans get close to moving 1000m3/h in the first test, these worries completely evaporated.
All the equipment was hung up onto 1.2m3 tent frames using rope ratchets, to keep things as close to how the equipment is actually normally used as possible. A smaller 1.6m high tent frame was used to keep the double elbow, and idiot loop duct run in the same position for each fan. Basically everything was kept the same except for the fans themselves, to avoid anything affecting the results other than the fan itself.
Now at this point it’s worth mentioning (even though you’ve probably already deduced this) that this was by no means a laboratory grade clinical testing environment whereby the results we get are 100% accurate. I would hazard a guess that at a very maximum, there could be a 5-10% tolerance of error in the results we obtained, but even factoring that in, we still got a great set of comparative results for all the fans. Whilst these results may not be stating what is exactly being blown, what they do show is how all the fans compare against one another directly in the real-life situations I’m putting them under. To be completely honest, that’s all I’m after really. Call me selfish, but I just want to know what fan is going to work for me.
1 Metre Ducting - Free Flow
Now I don’t know about you, but I was pretty flabbergasted by these results. The order they are here is the order I tested them in. So I started with the RVK and thought “yep that’s as expected compared to what it’s rated at, everything going according to plan”. But as soon as I got to any others though I became somewhat boggled. None of them seemed to be moving the amount of air that they were stating or using the power they stated. Most shockingly the box fans were moving half the amount of air they are rated at. “Well fuck me” I thought, “I must have dropped a particularly large bollock here”. So I checked the machine, called and checked with Testo I’d set it right then came back another day to repeat it all. And well... I got the same results.
Fan Filter and 4M Ducting
As you can see, the variance between how much air each brand of fan drops from just plonking the same filter on them all, is quite a significant one. The fan with the least amount of airflow drop from our initial readings is the Isomax from Can, which would imply that under this initial amount of pressure exerted, this fan performs best. The fan with the largest amount of airflow drop, is the Tornado box fan. Over a 60% drop in output from it’s initial rating. It would appear that all the bad mouthing of box fans I’ve been hearing is becoming justified.
However, one thing they do at least have in their favour is that they are a clear 5-6 dB quieter than the others (more detailed tables available online). Seeing as how the decibel scale is a logarithmic one, this is actually a very significant benefit they have over competing fans.
Fan, Filter, 2x Elbows and 4M Ducting
Probably the most notable point for the two elbows is just how much more this massively effects the airflow. In general it almost doubles the pressure loss you see from the previous straight duct run. I was expecting there to be a fairly large airflow drop after attaching these, but not quite this much. As you can see, in some cases it more than doubles the amount of drop in airflow that you get from just the straight run of ducting. Also you can see at this point that the overall difference between the amounts of air being blown across all fans is reduced significantly. Excluding the box fans there is only a difference of just over 100m3/h between them. I say ‘only’, this amount can actually be make or break for a grow room so it is still fairly significant, but you get what I mean.
Fan, Filter and 360 Degree Spiral in 4M Ducting (Idiot Loop)
I was actually quite surprised by the idiot loop results, on two counts. I thought that the airflow drop from an idiot loop would be roughly double that of the elbows (twice the curve). It is more (again varying over brand), but not as much as I initially thought. Also, whether it was quieter than with elbows varied a lot from fan to fan. Strange, but thems the results.
This has all been a bit word heavy so time for some easier on the eye visuals. The following bar graphs show all the fans lined up next to each other and how they performed in each duct run. The first is in terms of airflow and the second is in terms of sound level. This way you can quickly see how they all compare:
The initial airflow of the fans was by far the biggest surprise to me. Even if you ignore the exact figure and just look at the bars in the graph as comparative airflows, many fans rated higher than the RVK simply aren’t blowing out as much. Which by the wonders of logical progression, means that they are blowing less than they are rated at. It’s worth pointing out that these are just the results for the 8” versions also. Each different size of fan within each brand has its own unique pressure curves and will therefore operate differently. This is a good indication of how fans vary between brands but is by no means a ‘be all and end all’ set of results.
Disregarding the whole ‘initial airflow’ quandary for a minute, of all the bars of data there are shown here, the one I think I’m most interested in knowing about is the idiot loop. My duct runs often have stupid bends and unnecessary kinks in (I’m an idiot), so I really want to know how the fans cope in these harshest of environments. This completely rules out box fans for me. Despite them being very quiet, they simply crumble under pressure: 60% less than rated is not what I need. They generally all use the same style Torin motors so are all highly likely to perform in a similar way. Also simply getting one with a higher rated motor in is just going to give more pressure loss, and a greater reduction of airflow from the rated amount. They are quiet, which is a good thing, but not at the expense of airflow.
There are two, almost three fans (answers on a postcard) that catch my eye after looking through the above charts, but even still, before I can narrow it down further I need to consider all the other ins and outs that affect my grow room and analyse all this data further (plus any more that’s out there). Then when I’m confident enough in my decision, I’ll go and shower a lucky shopkeeper with the entire contents of my man purse. That’s also exactly what I recommend you do. Think about what the fundamental requirements are specifically for you, whether it’s: noise level, airflow or simply price. Apply these requirements as you deduce from all the data in this article (and elsewhere) which one is most likely to fit your needs, then go buy it (or wait till the next trade show you go to and see how lucky you can get on the blag!).
Check out the full article including results and comparison charts in the HydroMag May/June 2014 issue.