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:
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:
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.
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).
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:
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.