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OfflineBlackHaze
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Registered: 07/05/20
Posts: 11
Last seen: 3 days, 5 hours
extraction power reduction
    #846483 - 08/15/20 09:32 PM (1 month, 6 days ago)

hi everyone
i have been lurking around here for a while but this is my first post.

i have been building a room for my first proper grow (a plan to be completely self sustaining). i almost have all my materials and gear and most of the construction is complete already, so right now i am looking at a plan for efficiency as well as learning good practices etc.

the question i am focusing on in this thread is about reducing the power of an exhaust fan (via external power reduction) to save resources and potentially reduce unnecessary wear.

my room is: D=65cm(2.13ft) W=84cm(2.7ft) H=200cm(6.5ft).
so the volume is just over 1m³ (37.3815 ft³).

i already have an extractor and i am limited to using that exact extractor, so buying a different one is not an option. funds are low and a friend helped me out by gifting this one to me.
that extractor has a rate of 245m³/hr (144.2CFM) and my calculated needs are around 26.25m³/hr (15.45CFM).
as you can see i am extracting air at almost 10 times the rate that is necessary.

because i am on a tight budget i am trying to cut costs wherever possible and obviously this is standing out to me as a potential point to work on, both for electricity use and the lifespan of components.
i am not too worried about the extra strain on the motor that you might see with a room with little intake and large outtake because i custom built my intake to allow the same volume of air through as a 100mm (4") duct.
i chose 100mm because i knew this was the size of the duct on that extractor before i knew its CFM etc. this is also assuming the manufacturer made a good decision by opting for a 100mm intake.

my question is about the power reduction of these fans and how that affects the CFM capabilities of the fan.
in an ideal world i would drop the power supplied to the fan down to 11%, which would give me slightly more (ratio-wise) than my rooms needs, however i assume that the relationship is not linear and the topic is not that simple.

i assume an 89% power drop would equate to a much larger than 89% efficiency drop, particularly with such a large drop where physical characteristics play a large role, i feel confident that the motor will not even run.


can anybody offer any insight into this topic?
my current mindset is to try running it at 50% power and see how it goes, but i dont even have a way of measuring the resulting volume being extracted, so the only way i would know i pushed it too far is to kill the plants that i know i would have already fallen in love with by then.

there seems to be a lot of solid theory on the topic of extraction volumes and ideal power requirements etc, but i cant find anything about reducing the CFM by reducing the input voltage.

any tips and info would be a great help
thank you :heart:


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InvisibleDataM
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Re: extraction power reduction [Re: BlackHaze]
    #846484 - 08/16/20 01:20 AM (1 month, 6 days ago)

Is this an AC induction motor? How are you planning on controlling the voltage? Is your primary focus the reduction of energy consumption, or the reduction of wear?

The reason it's hard to find info on this topic is that you are asking an impossibly general question, and without specifics you won't find a general answer.

If you can provide more details about the fan motor, and possibly your plans for controlling the input voltage, then I might be able to help answer some of what you're looking for.


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OfflineBlackHaze
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Registered: 07/05/20
Posts: 11
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Re: extraction power reduction [Re: Data]
    #846493 - 08/17/20 08:12 AM (1 month, 5 days ago)

thank you very much for the help.
i thought that might be the case.
my fan is a turbo tube pro 100. it seems to have a "capacitor motor with thermal overload protection".

i was planning to use something external to control voltage, although i do not know exactly what yet. my fan has a wall plug wired so i was going to use something that you plug in to the power source and plug your fan into it. that was the idea, but i am not committed to that if there are better options and i am not even 100% sure yet if something like that will even work as intended.
e.g. something like this.

my primary focus is the saving of money. to be honest a noise reduction would be a great bonus too to help prevent theft, but i can explore other avenues to help with that. i think its possible that simply reducing voltage could cause more wear to the motor though, making it potentially counter productive? my knowledge in this area is minimal.

i have noticed in the info that there should be a 2 speed switch with a slower option at 23w that gives around 96CFM (using the same static pressure that the 144CFM must have used). my friend mentioned that there was 2 wiring options for speed. i do not have it with me yet, but i think i should be able to rewire it within its intended use to get it to pull 96CFM, closer, but still much more than necessary.

maybe with my room being so small i might even be better off waiting until i have the funds available for a smaller fan? im not sure of average prices though, i will shop around.

thank you very much for the help.

edit:
would something like this work?
although i do not ever remember seeing something like this in a grow room. i would assume they are not really designed to be running 24/7?
the example is just as loud though, so i would probably keep looking for something quieter, but it would at least run at around a quarter of the cost and still move 6 times the amount of air i require.

i am wondering how much i am over-thinking this. the cost of running 23w is not huge, but it does all add up.


Edited by BlackHaze (08/17/20 08:30 AM)


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OfflineBlackHaze
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Registered: 07/05/20
Posts: 11
Last seen: 3 days, 5 hours
Re: extraction power reduction [Re: BlackHaze]
    #846530 - 08/20/20 10:28 PM (1 month, 1 day ago)

i finally got to try the fan out in my space and it was insanely loud!
it is too much for my room so my new priority is the noise. i am going to wait to get a new, quieter fan (i have one in mind). the noise is a threat to my crops so i am just going to have to suck it up (no pun intended :grin: ) and wait for the cash to be available.

i am thinking about ways to get started now but i will save that for another thread. the questions in this thread are still valid so i will leave it open.

thanks for the help


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InvisibleDataM
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Re: extraction power reduction [Re: BlackHaze]
    #846532 - 08/21/20 12:23 AM (1 month, 1 day ago)

Yea sorry for the late reply.

It sounds like the model you have has a high and low speed setting by default.

That being said, driving the motor lower than its lowest default setting will probably result in reduced bearing life, and depending on the type of motor (I couldn't find a reference to the type of motor, but I'm assuming it's an induction motor) will result in a decent amount of buzzing noise.

A lot of fan noise comes from the ductwork, especially if you're running a large volumetric flow rate through small diameter duct, like the 4" flex duct. It forces the air to flow at higher velocity through the duct, and the correlations induce turbulence.

Using a carbon filter or snubber will help reduce noise, as will insulated flex ducting. When selecting a fan, try to select one with the largest inlet/outlet diameter you can within you desire range of flow rate. If you are limited to small fan inlet/outlets, buy a converter and step up to 6 or even 8 inch flex duct for the majority of the run.

But chances are just buying a smaller fan will solve your problems. :shrug:


--------------------
“The Universe is under no obligation to make sense to you” -NDT


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OfflineBlackHaze
Stranger
Registered: 07/05/20
Posts: 11
Last seen: 3 days, 5 hours
Re: extraction power reduction [Re: Data]
    #846536 - 08/21/20 08:23 AM (1 month, 1 day ago)

Quote:

Data said:
Yea sorry for the late reply.

It sounds like the model you have has a high and low speed setting by default.

That being said, driving the motor lower than its lowest default setting will probably result in reduced bearing life, and depending on the type of motor (I couldn't find a reference to the type of motor, but I'm assuming it's an induction motor) will result in a decent amount of buzzing noise.

A lot of fan noise comes from the ductwork, especially if you're running a large volumetric flow rate through small diameter duct, like the 4" flex duct. It forces the air to flow at higher velocity through the duct, and the correlations induce turbulence.

Using a carbon filter or snubber will help reduce noise, as will insulated flex ducting. When selecting a fan, try to select one with the largest inlet/outlet diameter you can within you desire range of flow rate. If you are limited to small fan inlet/outlets, buy a converter and step up to 6 or even 8 inch flex duct for the majority of the run.

But chances are just buying a smaller fan will solve your problems. :shrug:




thanks for the help.
yes the model has two speeds. the specs i wrote is for the higher speed because i had them written down, but i have actually wired up to the lower speed. the noise is still crazy :smile:

i have a carbon filter already attached. i havent tried acoustic ducting yet but it seems like the majority of the noise is coming from the motor itself, which i was surprised about. maybe it was sound bouncing off the walls in the right way to confuse direction though, im not convinced even with my own ears :stoned:

the replacement i am planning to buy is the same as the one my friend bought to replace the one he gave me, so i have heard it in action and i know it is quiet. the CFM is much lower too, but still plenty for the room, so should help with air movement noise too.
i think i will end up spending more money if i keep trying to remedy this one than i would if i just buy a new fan.

thanks for the help


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