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Comment by 0wis | Hacker News Reader

Interesting subject tackling two important home issues at the same time : ventilation and heat exchange. It seems like a way to get the best of both worlds. However, I do not know why this forum is relevant or interesting. DIY solutions are easily doable but is it really surprising ? I am sure people have done this with old fridge parts, as someone suggest in the last post. Yes, DIY can be cheaper but reliability is key for such systems. Size can also be key.

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Yes, DIY can be cheaper but reliability is key for such systems.

If you know what you're doing (not hard to these days with so much information online), and depending on where you live, DIY HVAC can be far more reliable than getting a "licensed professional" who will attempt to overcharge for mediocre work or even scam you.

Reacting to your first point: As far as I know (western europe), heatpumps mostly are used to heat water to then heat your house, and renovating generally means reducing breathability of the house itself, which, combined with the temp difference, means condensation/mold problems. You then have to correct that by opening windows intelligently or installing air ventilation, and then a heat exchanger to not lose too much heat. Like you say, it seems to be a no-brainer then to instead combine heat pump _and_ ventilation, so that the ventilation itself works with a heat pump.

The only counter-argument I have is that if all the heating were done using ventilation, you might have to live in a very windy house, but I feel like entirely decoupling the two is not the best solution to that problem…

It makes a lot of sense to feed your ventilation output to a heatpump input for energy recovery with an air-source heatpump.

But otherwise I think there is a lot of value in other forms of heating. Specifically in radiative heating. Floor heating is great for that, but other water-based systems are also possible.

> if all the heating were done using ventilation, you might have to live in a very windy house

Not an issue at all. A properly installed ceiling vent will blow air along the ceiling, where Bernoulli's principle makes the fast moving air stick to the ceiling until the speed drops enough for the higher density to make it sink gently.

https://blog.swegon.com/hs-fs/hubfs/Bild4-1.png?width=1100&n...

There's also significant engineering calculations and guidelines/rules about the expected volume of air that is expected to enter/exit vents vs their size and grille restrictions. This is more to prevent loud airflow, but there's also charts for air distribution for room sizes.

Now, most HVAC contractors go by gut feel/rules of thumb, but if you want to pay for it, a well designed system would never be 'windy' or noisy.

> renovating generally means reducing breathability of the house itself, which, combined with the temp difference, means condensation/mold problems

Look up Passivehouse standard, modern construction can make extremely effocient buildings, but it relies on the building being nesrly airtight, so it must have ventillation.

'Natural' ventillation naturally steals your heat, it's incompatiable with efficiency

There was a period where I considered DIY for such machines impractical. I now think that to diy all the way through is impractical, the design process is too laborious even for those suitably skilled. However once the design is worked out it is actually pretty practical, with a 3d printer. You definitely have to own the printer, they charge way too much to have things printed at cloud services for some reason.

I have pubished my STL files for an earlier version of the TW4 energy recovery ventilator. It's totally practical to make your own with a printer, but it would take you a few days of labor time for sure to get everything working nicely.

Reliability is very much on offer even with diy. In reality I have looked at many commercial units and they have serious reliability problems for long term like 5 years or more, and we should be planning for 50 years wherever building tech is concerned, imo.

DIY is practice at learning new things and implementing what you've learned. It's a very good thing in that sense. Also, a healthy DIY (or maker, if you prefer) community is good as a check on commercial offerings. If businesses try to overcharge for something or don't offer it on acceptable terms, and you have a great need, having a 2nd way is important.

Making your own HRV may or may not be worthwhile for everyone who does so, but more people learning how to make one is doubtless a good thing.

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