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 Post subject: Passive house ventilation with computer fans
PostPosted: Thu Dec 13, 2012 4:02 pm 
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It's been a while since I last asked a question on the SPCR forums, but I'm pretty sure this is the right place to ask for feedback and advice on a project I'm working on. Many thanks in advance for your comments.

Next summer we're planning to build a 85-90 square metre (900-950 square feet) passive house in Austria. One absolute prerequisite of passive houses is that they're built airtight. A ventilation system makes sure enough fresh air enters your home, while at the same time recovering the heat of the exiting air.

One can opt for two types of ventilation system, either central or decentral. A central ventilation system transports air to all rooms via ducts. I'm not a fan of central ventilation systems, because they're expensive and noisy. After installing them there are extra costs for maintenance (electronics) and the bi-yearly exchange of expensive filters. Installing ducts throughout the entire house is also a lot of extra work, and has to be done perfectly or you get problems with noise and/or bacteria.

And so I prefer a decentral solution, this one to be precise: Ökolüfter. The Ökolüfter (translates as 'Ecovent') is a German decentral heat recovery ventilation system, meaning there are no ducts. What I like about the Ökolüfter is its simplicity. It can deliver plenty of air (80-200 m3/hr), but uses very little energy (4-31 W), is relatively quiet (22-42 dBA), recovers moisture as well (very important in winter), has no filters or electronics, just two high-quality Papst fans. It's small, simple and 3-4 cheaper and easier to install than central ventilation systems. To me this is the picoPSU of ventilation systems (watch this video to see how it works, it's pretty nifty).

The downside of decentral ventilation systems is that there aren't any ducts to transport the air to other rooms. However, we need fresh air in our bedrooms at night, but can't open any windows. I want to compensate that by building a so-called Ringlüftung, which roughly translates to 'air circuit' or 'ventilation circuit'. Air is transported from room to room by using computer fans and short ducts. In our case it would look something like this:

Image

Here's a bigger version.

The air enters the house via the Ökolüfter in the lower right or southeast corner of the building (where the kitchen is). Passing three ducts and fans it gets transported all around the house in a clockwise direction. Three important aspects:

1) Ventilation

There are several numbers out there describing how much CFM or m3/hr there needs to be to prevent air in a home from going stale. For instance 22-36 m3/hr per person is recommended. We're a family of three, so 80-120 m3/h should be enough. Another way to look at it is by calculating air changes per hour, in other words: how many times per hour does the air in a home need to be changed? According to the German Passivhaus Institute 30-40% of the air needs to be changed every hour. Our house will be 85-90 square metres, with a 2.5 metre high ceiling, so the volume will be approximately 200-225 m3 -> 40% of 225 m3 every hour amounts to 90 m3/hr.

Put simply, the three computer fans that circulate the air through the house must be able to deliver around 100 m3/hr (or 59 CFM). Perhaps even less, as the two bedrooms have a total volume of 50 m3, and 40% of 50 m3 every hour is just 20 m3/hr (or 12 CFM). But I'm not sure about this.

2) Noise

Of course, the fans need to be quiet! According to experts noise in bedrooms must not exceed 23 dBA. Of course, the fans will be high up, in the corner of the room, at least 3-4 metres away, but I'm very sensitive to noises. The fans will also be hooked up to the Scythe Kaze Server fan controller, for power, rpm readings and fan control.

More on fans after 3).

3) Acoustics

There will be air ducts between rooms (two will be approximately 1.5 metres long, the last one twice that), and I'm not sure if sounds get carried from one room to the next. It's possible to install duct silencers/mufflers to dampen the sounds, if that would help (have no idea). I could build them myself, but they're not very expensive.

---

In the past week I've been reading up a lot on fans, and here are the candidates for the project:

Image

The Noctuas have a very good reputation and they are designed in Austria. The brown colours would also fit well in the house, although I'm not sure yet how visible the fans will be. Everyone agrees on the quality, but not on performance.

I like the Thermalright fan because it's bigger (150 mm) and will thus definitely be able to deliver the needed CFM at lower rpm. I'm not sure about the quality though and they don't come with anti-vibration rubber screws. This round-up had some positive figures.

The be quiet! Silent Wings 2 are rated as very quiet in the same round-up as the TY-150, but they might be lacking in CFM. MTBF looks great, if true.

People are pretty enthusiastic about the Corsair AF140 Quiet Edition (such as X-bit labs). I saw this Youtube video and you don't hear anything (I'm not sure about their methodology though, and whether it's consistent, a vid of the Noctua NF-P14 FLX is pretty loud). Mike C is also optimistic. This post on the Corsair blog inspires confidence when it comes to the CFM specification, seeing they bought a 40K machine to test it themselves.

The Nanoxia fan is ugly as hell, but the numbers look good. Also, it's designed in Germany, often a good sign. What I also like, is that the impeller can be removed, which makes it easy to clean.

If it's at all possible to make this idea work with computer fans, I think one of these would have to fit the bill. Suggestions are welcome. Maybe I'll order one or two fans to test in January.

---

What I'd like to know:
- Is it possible to make this work, a noiseless Ringlüftung that can transport enough air around the house?
- How about the ducts? Will their length impede airflow, or increase air noise? Would duct silencers help, also with noises/talking from other rooms? I was thinking about 150 mm ducts, slightly bigger than the fan diameter. Would that be enough?
- Which fan would be most suitable?

This idea is pretty central to my project of building a house that can run on 3500-4000 kWh a year (including heating, which should be practically zero), so I hope this has a chance of working.

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 Post subject: Re: Passive house ventilation with computer fans
PostPosted: Fri Dec 14, 2012 2:03 am 
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Your reasons for not wanting centralised ventilation apear to be:
-noise, this is usualy caused by: -airducts that are to small, if they are designed better that would be no problem.
-the centralised ventilation system is not in an unused room(the best place usualy is in an attic or something) or it transfers to much noise from that room to
the other which would mean the location of the ventilation system does not have enough sound insulation/isolation(not sure which is the correct english word
as we have the same word for both) or you could install a mufler if that sound comes trough the mufler.
- the filters are expensive or take to much work, there are many systems with washable filters, so you buy 2 or 3 and just wash them, the first half year the filter should be replaced every month but after 2 years replacing it twice a year should be enough. The filters do improve the air quality.
- as for maintainence, duct don't need maintainence, they should remain clean and as for the ventilation unit you have a valid point, but except for the filters it needs less maintaince then heating systems.

centralised air heat recovery is usualy more efiecient as in more localised ones

an important thing to consider is you probably want an outtake in the bathroom and toilet as you don't want nasty odors and moist air in the other rooms(in the netherlands that air is not alowed to be transfered to other rooms by ventilation, we have a min posible outtake of 14 and 7 dm³/s for those rooms respectively.) furthermore in the kitchen you probably would like an outtake aswell (in the netherlands that would be a minimum of 21 dm³/s) in the netherlands those 3 rooms often have enough air outtake for the whole house if it is a small one, therfor we often use either a centralised ventilation system or natural air intake (often intakes that reduce their intake with higher wind presures)

in the netherlands your solution would not be alowed, i don't know about your country, we have a specified distend between outtake and intake of air (on the outside of the house) so that the air that exits does not go back in. And we need to get at least 50% of a specified amount of fresh air from the outside which therefor can't come from other rooms.

edit:
as for the muflers in ducts to reduce nois trough those ducts, they do work, they absorb part of the noise that passes trough them with absorbtion material(often rockwool is used) so you could line your ducts with rockwool as a cheaper solution but you will have to line any exposed rockwool with linnen or something so you don't blow rockwool particles trough your home.

and the ducts do reduce the capacity of the fans, however as long as the duct is at least as big as the fans used (the inside diameter or width of the ducts compared to the diameter of the fans) and does not have corners that reduction should be so small you won't notice it


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 Post subject: Re: Passive house ventilation with computer fans
PostPosted: Sat Dec 15, 2012 10:36 am 
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Thanks a lot for your reply, mercyfull_fate.

In the past two years I've given a lot of thought to the central vs decentral issue. In fact, for a long time, I thought we would use the Hoval HomeVent RS-180 because it's very well-rated and it also recovers moisture (which is very important in a passive house, if you don't want relative humidity to drop below 30% during winter).

But then I ran into the Ökolüfter in an online discussion and after reading everything there is to know about this machine (there are some very good discussions on several German home building forums) I concluded this was the way to go for me, as I'm a bit of a minimalist. Six years ago I asked for help here to design a low power computer. That ended up as a PC in a wooden casing using 17-18 Watts at idle. That's where looking for the limits got me.

What goes for a low-power, eco-friendly computer, goes for a low-power, eco-friendly house as well. In a way a passive house's ventilation system can be viewed as as PSU for a computer. Like I said, the Ökolüfter is like the picoPSU of ventilation systems. In comparison central ventilation systems are like 80+ certified PSUs. They're good and everything, but the Ökolüfter is on the edge of minimalism.

Take for instance the Hoval HomeVent RS-180. If you look at the image in the link you'll see that it's much bigger and complicated than the Ökolüfter, meaning it has cost much more resources and energy to build. It weighs 50 kg, the ÖL only 8. It provides 40-180 m3/h, the ÖL 80-200 m3/hr. It uses 40 W at 126 m3/hr, the ÖL won't be using more than 15 W. The HomeVent is rated at 40 dBA at 100 m3/hr, the ÖL probably still below 30 dBA. And thus the HomeVent needs an insulated space taking up about half a square meter (adding to the costs), not to mention all those ducts running through the ceiling. They both recover around 90% of the heat, and quite a bit of the moisture as well.

So, I'm really tending to the Ökolüfter (forgot to mention it's 5 times cheaper than the HomeVent), but of course only if I can make the whole set-up work.

Quote:
an important thing to consider is you probably want an outtake in the bathroom and toilet as you don't want nasty odors and moist air in the other rooms


Absolutely. As you see on the drawing I made the third duct runs through the toilet+bathroom but it's closed, because I don't want the computer fans to come into contact with too much moisture. So ventilation of toilet and bathroom is a separate issue. This is one thing I haven't figured out yet.

Quote:
furthermore in the kitchen you probably would like an outtake aswell


That's where the Ökolüfter will be.

Quote:
in the netherlands your solution would not be alowed, i don't know about your country


One of the reasons I have left Netherlands (hoi, ik ben Nederlands :-)) is that it's really difficult to build a passive house there. First of all because a plot of land would be really expensive there. Second because the Netherlands doesn't have a tradition of people building their own house and so there's a lack of expertise, as well as difficulties with getting building approval. I'm not saying that Austria is perfect, but there are a lot of companies that know how to build a wooden passive house, which makes it relatively cheap.

Quote:
we have a specified distend between outtake and intake of air (on the outside of the house) so that the air that exits does not go back in.


This is not an issue with the Ökolüfter. I thought it would be at first, but reading several online discussions and a test by the Europäischen Testzentrums für Wohnungslüftungsgeräte (TZWL), I'm convinced this is not an issue.

Quote:
as for the muflers in ducts to reduce nois trough those ducts, they do work, they absorb part of the noise that passes trough them with absorbtion material(often rockwool is used) so you could line your ducts with rockwool as a cheaper solution but you will have to line any exposed rockwool with linnen or something so you don't blow rockwool particles trough your home.


Yes, the inside of a muffler looks something like this:

Image

And like this on the outside:

Image

I'm still not sure if they're needed, but this is probably something I will have to test myself.

Quote:
and the ducts do reduce the capacity of the fans, however as long as the duct is at least as big as the fans used (the inside diameter or width of the ducts compared to the diameter of the fans) and does not have corners that reduction should be so small you won't notice it


That's good to know! I want to use 140 mm fans, and I'm thinking about a duct with a 160 mm diameter. If the reduction of airflow is as small as you say it is, computer fans should be able to deliver enough air to the bedrooms.

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 Post subject: Re: Passive house ventilation with computer fans
PostPosted: Sat Dec 15, 2012 12:39 pm 
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Interesting project, and outlining all the details makes it easy to understand!

If 60cfm is all you need, that seems quite feasible to do quietly with a big fan -- I'd actually look for something bigger than 14cm diameter. The biggest issue could be the air resonance of those tubes.

I've mentioned this many times in SPCR -- any enclosed or semi-enclosed space has air resonances which can amplify & exacerbate any noise in or near that space. The sound absorption sleeves you describe are probably necessary, but this could depend on how quiet the fans are too.

More later, after I've re-read and thought more about your project.

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 Post subject: Re: Passive house ventilation with computer fans
PostPosted: Sat Dec 15, 2012 12:44 pm 
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Palindroman wrote:
Thanks a lot for your reply, mercyfull_fate.

no problem, fun to have a thread more in the direction of my "expertise"

Palindroman wrote:
One of the reasons I have left Netherlands (hoi, ik ben Nederlands :-)) is that it's really difficult to build a passive house there. First of all because a plot of land would be really expensive there. Second because the Netherlands doesn't have a tradition of people building their own house and so there's a lack of expertise, as well as difficulties with getting building approval. I'm not saying that Austria is perfect, but there are a lot of companies that know how to build a wooden passive house, which makes it relatively cheap.


well i guess the buildingregulation is a lot better now in any case faster:P (it won't take longer as 14 weeks now and should take only 8 ) also there are more options for passive buildings now in the netherlands but yes it still is an upstart thing.....


I just thought about another option you might want to consider that is relatively simple (but needs even more ducting so you probably don't like it that much :P) but would be efficient:

if the intake ducts pass through the ground and or beneath the building before entering the house, it extract warmth from the ground in the winter and cold during summer. the intakes would go to all the rooms that need ventilation (but not bathroom, toilet and hallway) you would need only 2 outtakes, 1 for the toilet and bathroom and 1 in the kitchen. if you leave enough space beneath the doors for the ventilation, all rooms between intake and outtake get ventilation.

on the outtake(s) (you could link both outtakes by 1 duct) you could place a heat pump (not sure if thats the right word but it's warmtepomp in dutch), that heatpump would then provide heating for the rooms and warm water

the biggest problem in this solution is that you need to make sure the intake duct in the ground is watertight so that it doesn't collect ground water


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 Post subject: Re: Passive house ventilation with computer fans
PostPosted: Sun Dec 16, 2012 7:05 am 
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MikeC wrote:
Interesting project, and outlining all the details makes it easy to understand!

More later, after I've re-read and thought more about your project.

Thanks for the feedback, Mike. We had some contact years ago concerning the low-power computers I built. I had to give that up because it took up too much time, and also because we left the Netherlands to make this home building project possible.

Quote:
If 60cfm is all you need, that seems quite feasible to do quietly with a big fan -- I'd actually look for something bigger than 14cm diameter. The biggest issue could be the air resonance of those tubes.

I tried to find bigger computer fans, but only found the Antec Tricool thing (200mm). The reason I resort to computer fans, is that I know they are often made to be ultra-quiet, easy to buy (relatively cheap too), and easy to find info about. I've looked around the Papst website as well, but they have like 10 million different fans!

And then there's the TY-150 (150mm) fan that you reviewed not too long ago. At 7V it's really quiet and still delivers 87 m3/hr according to this 2011 PC-experience 140mm round-up. But again, I'm not too sure about MTBF and quality. Like the colour though.

Quote:
I've mentioned this many times in SPCR -- any enclosed or semi-enclosed space has air resonances which can amplify & exacerbate any noise in or near that space. The sound absorption sleeves you describe are probably necessary, but this could depend on how quiet the fans are too.

Indeed. In my design I've tried to create spaces between the rooms that should be acoustically independent. For instance, my home office is between the living room and the master bedroom. A walk-in wardrobe separates the two bedrooms. And the bathroom is between the second bedroom and the living room. All this to impede noise transfer.

Another type of muffler/silencer looks a bit like this:

Image

If I think it can be pulled off, I will probably build the house as envisaged and then tinker around with those ducts. Provided I have the right fans, of course.

mercyfull_fate wrote:
if the intake ducts pass through the ground and or beneath the building before entering the house, it extract warmth from the ground in the winter and cold during summer. the intakes would go to all the rooms that need ventilation (but not bathroom, toilet and hallway) you would need only 2 outtakes, 1 for the toilet and bathroom and 1 in the kitchen. if you leave enough space beneath the doors for the ventilation, all rooms between intake and outtake get ventilation.

on the outtake(s) (you could link both outtakes by 1 duct) you could place a heat pump (not sure if thats the right word but it's warmtepomp in dutch), that heatpump would then provide heating for the rooms and warm water

It does sound a bit complicated, what with the ducts and the heat pump and the space beneath doors (which usually isn't sufficient, you need special doors or muffled slits), but using 150-200mm PE ducts with a length of 30-40 metres, 1.5-2 metres below the ground, is a very interesting way of pre-heating fresh air. I'm actually thinking about incorporating that in the design as well.

On the other side of the wall that holds the Ökolüfter we are planning to build a greenhouse. Ideally, it would work as a buffer zone for the air that goes into the house, but conversely would keep the greenhouse a tad warmer during winter, preventing freezing temperatures (and the CO2 we breathe out would be beneficial to plants). But there are of course some problems, as this is a simplification (I'm aware of that, so don't laugh at me :-) ).

Here's a sketch of the idea:

Image

One problem is that the greenhouse contains about 50 m3, so there has to be some air intake to make sure there's enough fresh air for the home. This can be either done by another HRV (cheaper than the Ökolüfter), or perhaps two of those underground ducts that bring in air at ground temperature. Or both. A small wood oven in the greenhouse also enables some extra heat on very cold days (-10 °C (14 °F) isn't a rarity here in Austria, though I do live in the warmer south, not in the Alps).

Though still part of the whole ventilation concept, it is a bit off-topic, as I'm mostly interested in the Ringlüftung-idea right now. But I thought I'd share it, as it's pretty crazy.

I'm going to ask the manufacturer of the Ökolüfter for some advice. I'll report back here.

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 Post subject: Re: Passive house ventilation with computer fans
PostPosted: Sun Dec 16, 2012 9:41 am 
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Palindroman wrote:
I tried to find bigger computer fans, but only found the Antec Tricool thing (200mm). The reason I resort to computer fans, is that I know they are often made to be ultra-quiet, easy to buy (relatively cheap too), and easy to find info about. I've looked around the Papst website as well, but they have like 10 million different fans!

And then there's the TY-150 (150mm) fan that you reviewed not too long ago. At 7V it's really quiet and still delivers 87 m3/hr according to this 2011 PC-experience 140mm round-up. But again, I'm not too sure about MTBF and quality. Like the colour though.

Another type of muffler/silencer looks a bit like this:

Image

Given the prices you cite, the TY150 would be my first choice to try. You could get double the # of fans (for replacement in future if/when bearing get noisy, etc) compared to some of the others. And I would not hold out too much hope for the Corsairs (tho admittedly I haven't spent much time in the lab with them yet).

That second style of muffler -- don't do it. I used such designs in DIY computer systems in the past -- their airflow impedance is too high. There are ways to ameliorate the resonance effect of the round tubes. For example, mount the fan in such a way that acoustically, it is not in the tube at all -- ie, use soft mounting, and make the first few inches tube wall (from the fan) somewhat porous -- ie, perhaps made entirely of open cell foam. You will lose a bit of airflow, but acoustically, the fan may be far enough away from the more reflective portion of the tube to make the resonance effect inaudible. Again, this depends on how quiet the fan is in the first place.

You could easily experiment with fans and lengths of cardboard tube or the actual tubes you will use -- before actually mounting them I'd err on the side of caution and use the widest diameter that's practical, with the acoustic damping... in case you find later that the airflow needs to be increased. CFM specs, measurements and theories are all good and fine, but until you actually do it, you cannot be 100% sure.

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 Post subject: Re: Passive house ventilation with computer fans
PostPosted: Mon Dec 17, 2012 9:34 am 
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I know nothing about passive houses, but this looks interesting. My first thought is what lengths are the ducts going to be? I'm a bit sceptical that a 120x25mm deep fan is going to do what you need, extract fans are a lot deeper e.g. 100x150mm (longer than the diameter.) I fitted one approximately this size recently, the specification says that 3m is the max. length for a dead straight duct, a single 90° bend reduces the maximum permitted duct to 2m.

Would something like this trickle extract fan be more suitable? specified as dB(A) @ 3m.


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 Post subject: Re: Passive house ventilation with computer fans
PostPosted: Mon Dec 17, 2012 9:52 am 
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Hi Ian,

Quote:
My first thought is what lengths are the ducts going to be?

The first duct about 1.8 metres, the second 1.3 metres, the third, 3 metres, depending on the size of the bathroom.

Quote:
Would something like this trickle extract fan be more suitable?

I looked at fans like these for a while, but usually they don't have enough capacity. For instance this trickle fan at high performance (15.5 dBA) delivers 9 l/s, which amounts to 32.4 m3/hr, which isn't enough.

I've asked the manufacturer a couple of questions concerning the Ringlüftung. I've read that keeping your doors open ensures enough airflow for fresh air to enter bedrooms (due to temperature differences, which was an eye-opener). But I'm not sure if this goes for a 85 square metre house as well.

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 Post subject: Re: Passive house ventilation with computer fans
PostPosted: Mon Dec 17, 2012 11:06 am 
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IanM wrote:
Would something like this trickle extract fan be more suitable? specified as dB(A) @ 3m.

Those fans look like they are even smaller diameter. The depth looks like it comes from a tube extension, not the fan blades.

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 Post subject: Re: Passive house ventilation with computer fans
PostPosted: Mon Dec 17, 2012 12:49 pm 
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MikeC wrote:
Those fans look like they are even smaller diameter
I don't know about the dimensions for the trickle fan I linked before, but yes the diameter of the domestic extractor fans tends to be surprisingly small, 100mm-150mm, but I don't think that's the important thing for driving air through ducts.

N.B. Vent Axia say somewhere in their recommendations and requirements that there should only ever be one fan on any duct run to avoid resonance and balance problems.

MikeC wrote:
The depth looks like it comes from a tube extension, not the fan blades.
I think that diagram for the 'Centra' trickle fan might just be for the grille, the vent axia shower fan I fitted has a similar diagram but the fan housing is separate. Anyway, your comment prompted me to have a another look at the shower fan - the blade depth is a lot shorter than I realised and the set of fins in the front area of the housing are fixed. So even though the fan unit is very long, the rotating blades are toward the rear and do look to be only around 25mm-30mm deep, but very different than a typical computer fan. The hub is actually huge, and the blades are oriented more acutely than the typical 'propeller' blades on 120x25mm fans.

This make me wonder how important the blade configuration is and how important the fixed fins are, particularly as this configuration seems quite typical for these types of domestic extractor fans...

Palindroman wrote:
The first duct about 1.8 metres, the second 1.3 metres, the third, 3 metres, depending on the size of the bathroom.
...so, given these duct lengths it would be very interesting to test the airflow with a 120x25mm fan and see what it can do vs an extractor fan on the same duct.

I actually wondered in the past about using an extractor fan with duct to cool a PC, but the reality is they're far too loud vs the conventional 120x25mm fans. This is one of the reasons I doubt the 120x25mm fans on the duct - if they're suitable for long ducts then why aren't they the normal configuration?


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