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Comment by eliaspro | Hacker News Reader

Also looking at the German standards for low or even positive energy homes I see a huge potential for energy efficient homes in the US (but also other markets).

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The German Passivhaus standard just begs for factory prefab construction. I suspect a major factor is how one can reduce the cost of making the structure airtight.

Don't fully airtight structures need a lot of redundant safety systems to protect against just leaving a candle on killing everyone from carbon dioxide poisoning?

Airtight homes doesnt mean no ventilation but no cracks in walls and doors and window framing

In the context of avar's question the active ventilation is a safety system.

A little bit of research indicates that candles are not all that different in oxygen consumption and CO2 production than a human and that a single candle (or person) wouldn't use up the oxygen quickly if the ventilation ceased.

As long as a failure of the ventilation system is obvious (so a window can be opened or whatever), it doesn't seem like it would be a major concern.

Well, a candle isn't enough to be a concern. But state of the art air tight passive houses include ventilator units that exchange air while retaining (or rejecting) as much heat as possible.

There are several companies in the US producing prefab Passivhaus homes. Typically, a building membrane is used as the airtight layer. Joints get taped, both in the factory and on site. E.g. http://www.phoenixhaus.com E.g. https://www.ecocor.us/prefab

Im waiting for the day that a "positive energy" trumps energy efficiency in germany. With solar prices dropping we may get to the point that it is cheaper to not insulate or otherwise reduce energy use and instead achieve positive energy entirely by slapping on more solar panels. Zero-carbon is a net measurement. You dont actually need to be efficient in terms of total energy use.

But you need to build more solar panels. So the question is whether it'll be cheaper to insulate better, or to manufacture more solar panels.

I think the idea that energy would be cheap forever is what got us into the current mess of high utility bills for poorly insulated homes.

This has already started to a degree, as people trying to build net-zero homes find that at a certain point the cost (in money/effort/carbon/energy) to add further insulation exceeds the cost of adding heat to the home via adding solar PV. I believe retro-fits of older homes hit this point earlier, since it can be harder to insulate them beyond the low hanging fruit.

Obviously as PV price continues to drop, this point will be met earlier and earlier.

Ive observed this already in off-grid situation where the priorities are different (no net metering, power not used/stored is power abandoned) but when it hits the mainstream it could make a real dent in home construction/insulation biz.

I doubt that will ever happen. 1) Insulation is essentially passive for the lifespan of a building, PVs and other solar tech + associated heating & cooling systems need regular maintenance, cleaning, replacing etc. 2)highly energy efficient buildings provide better comfort and indoor environmental conditions than a poorly performing building with lots of active heating / cooling etc. 3) insulation works day and night, all year round, PV only produced electricity when the sun shines. There is a big gap between what PV can supply and day/night demand and summer/winter demand. Storage might get to the point where it can bridge the day/night supply/demand gap, but seems unlikely to bridge the summer/winter supply/demand gap.

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