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Comment by gavia1 | Hacker News Reader

I wonder how they control humidity inside the home and prevent mildew/mould? The air in the greenhouse would be very humid all year round I would have thought?

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I think heat exchange air ventilation systems are quite common in Northern Europe. Presumably you could just keep the windows of the inner house closed most of the time, and then have a ventilation coming from outside through the heat exchanger.

Why would it be humid? Heat doesn't cause humidity. Deserts can be hot and dry.

(Edited are to can be for the pedantic people.)

I think standard household activity would generate a lot of humidity. Usually dwellings vent outside, but here the outside is in a larger "inside".

I'm guessing the greenhouse has its own air regulation set up.

In my part of Northern Europe, in the winter the issue is keeping the inside humid enough. During winter when the air temperature is -10c or less there is basically no water in the air.

We have a MHRV system, but it doesn't account for humidity, so will happily replace all the air inside with dry air from outside (I'm trying to automate it with HASS). Our bathroom fan has a humidity sensor, so doesn't run so much in the winter, but even so the humidity often gets down to 25% rh inside.

Yeah, same here. When it's -10 C or less in the winter, relative humidity can drop to 15%. Because we have a standard heat-exchanger HRV. The rotating-filter ones do manage humidity, but they also tend to freeze up if indoor humidity goes too high.

So we end up using an aerosol humidifier in the winter, and AC plus a dehumidifier in the summer.

Soviet Moscow flats are notorious for constant ~15% humidity in winter. Somehow they manage this even when there is a thaw outside and humidity is quite high.

Yes, this is possibly true, depending on the details of their lifestyle.

On the other hand, the article talks about their use of composting toilets, recycling water, etc. So they may well not be engaging in the same high levels of water consumption as typical modern families in developed countries.

So I remain unconvinced that a warmer environment automatically and without exception translates to high humidity and mold. (I will confess to being born and raised in the state of Georgia. So my idea of hot and humid is perhaps more extreme than average.)

Edit: If you've never lived in dramatically different living arrangements, you may not realize how much lifestyle choices impact details like heat and humidity.

While getting divorced, my sons and I spent a year sharing a single bedroom at a relative's home. We eventually found that removing all cardboard from all food products not only dropped the temperature by 5 degrees Fahrenheit, it put a stop to roaches being attracted to our room.

Prior to that discovery, our room was frequently too hot and humid. Afterwards, it was vastly more comfortable.

We were shocked by the difference. We initially wondered if we were imagining things, but the room had a thermometer in the window. It consistently made a 5 degree difference.

I think you've been here long enough to know that a phrase like "automatically and without exception" is likely a poor interpretation of what the parent poster meant with "standard household activity".

I was born and raised in Florida. In Miami I lived in a 1950s house designed w/o A/C and with effectively no insulation. In Tallahassee I lived in a 1970s house designed for A/C. But we didn't have money, so we didn't run the A/C unless it was nasty hot.

The differences were remarkable. For the same temperature and humidity, the Miami house was much more comfortable. The vernacular architecture of high ceilings, open crawlspace, and massive amounts of windows meant there was still cooling with any sort of breeze.

With the Tallahassee home, the building was designed to insulate, to keep the A/C power bills low. The windows were small, there wasn't much cross-breeze even with all the windows open.

A/C systems include dehumidifiers, and the building has a vapor barrier to prevent the high outside humidity from coming in.

But w/o the A/C's dehumidifier, standard household activity like breathing, cooking, and showering raise the inside humidity more than the outside, with a slow rate of equilibriation.

We finally kicked on the A/C when, among other things, yes, mold started to form.

Of course 'lifestyle choices impact details like heat and humidity'. So does architecture, as I just pointed out. But btbuildem said 'standard' and 'usually'.

I'm damned if I do, damned if I don't. It doesn't matter how I phrase it, people will have a problem with my real point and will have a problem with me giving first-hand testimony from my life.

So I tried to avoid that. It didn't help.

I slept in a tent for nearly six years. I'm back in housing, but I still don't live conventionally. I'm in a hundred year old building with no AC. But I have no upholstered furniture, no mattress, a minimum of bedding.

When other residents are desperately trying to create a cross breeze to cool off their too hot room in summer, I'm usually fine. With no cardboard and no upholstered furniture, my room is not too hot.

So I tried to use specifics from the article itself, like the composting toilet. Toilets are one of the ways modern families go through a lot of water each and every day.

I know my lifestyle generates less heat and humidity in my home compared to other people in the same building as me. I also know most people act like my first-hand experience doesn't count.

I'm routinely downvoted for making such observations, no matter how I try to phrase it. I'm routinely told I'm making stuff up, that's anecdotal, it doesn't count, I need a study or something.

I've seen men here on the leader board give similar personal anecdotes and get treated like they're brilliant. Tokenadult used to tell stories of opening the shades on his windows when he was a young man living in China to use solar power to heat his room and giggling about management accusing him hiding a forbidden heater.

But my first-hand observations are not similarly respected and oohed and aahed over for their insight. Instead, I'm routinely attacked and dismissed.

After a decade, I'm pretty damn sure it isn't my phrasing. It's my gender and general lack of credibility for reasons wholly unrelated to my intelligence, veracity, etc.

It's open contempt for me as a person. And I'm quite fed up with it and even more fed up with being told it's somehow my fault that I'm subjected to this double standard.

Had no idea who you were, hadn't even considered what gender you may be, and I can say that it is your writing style and phrasing that rubs the wrong way. (IMHO) reading your posts came across as if I was being lectured to/talked down to by someone with feelings of superiority.

I'm a male with a literally randomly-selected username and have stopped posting here because of just the kind of thing you cite. It feels too much like school...it's this project to figure out what to say that people will like; fail to please the mob and out come the vultures. Life's too short and full of more wonderful adventures than that. And the payoff from getting it right just isn't there to justify the downside.

I observed that the statement "I remain unconvinced that a warmer environment automatically and without exception translates to high humidity and mold" - while absolutely a personal observation - was a non-sequitur as no one was making that claim.

Was it a non-sequitur?

I then made a personal observation that architecture was also important, using a similar anecdotal construction that you did. So clearly I don't have a problem with anecdotal evidence. I present a similar anecdotal observation at https://news.ycombinator.com/item?id=14876398#14878461 .

I then ended up with the comment that I don't disagree with your comment, because it's clearly true, just like how other factors are also involved.

If you look through my history you'll see I have a long history of making similar observations for other posters. I see four such on the first page of my comments history.

The greenhouse isn't 100% sealed and the top would regularly open during the warm months to regulate the heat inside. On top of that the regular vents could easily be extended slightly to just reach the outside of the greenhouse.

Plants/watering cause humidity and the glass traps it.

And although I guess they probably could, people aren't generally maintaining desert ecosystems in their greenhouses.

This is not a problem in the winter -- outside air (if brought up to room temperature) is extremely dry. So just a bit of air exchange would dry out any jungle if humidity is not supplemented.

Deserts aren’t necessarily hot, they just have very little water.

They have little precipitation. There's plenty of ice in the Antarctic.

Are you sure about that? A river delta could be completely lush without any precipitation, but I don’t think that’d be a desert.

From the link someone else already provided:

Most polar deserts are covered in ice sheets, ice fields, or ice caps.

(I'm getting a chuckle out of the multiple layers of pedantry here.)

Nile delta is in a desert (4-8" rain/yr), so yes.

https://en.wikipedia.org/wiki/Polar_desert

But greenhouses are humid. Deserts aren't covered in a dome and the dome blocks water from evaporating like in the deserts.

Not much grows in a dry desert though, to grow stuff you need water. Even if you weren't growing stuff then you'd still have the soil as an access point for moisture and get excess evaporation because of the greenhouse heat.

Depends on the desert. Here are pics of Saguaro National Park:

https://www.bing.com/images/search?q=saguaro+national+park&q...

Desert plants are adapted to low rainfall. That doesn't mean all deserts are just barren rock and sand.

Yes, and when the rain comes they burst forth with vibrant life .. hence the specifiers "dry" & "not much".

I guess if they plan to eat agave and saguaro they'll have less humidity issues?

saguaro national park has really grown on me. It’s a surprisingly and eerily beautiful place.

>Why would it be humid?

The hotter air is, the higher its capacity to hold water vapor.

https://en.wikipedia.org/wiki/Psychrometrics

https://en.wikipedia.org/wiki/File:PsychrometricChart.SeaLev...

Which actually drop relative humidity, because water does not magically appear.

Dry cold air gets in during the winter, it expands and the RH goes down, warm humid air escapes, more dry cold air gets in, creating an extremely dry environment. Still you can get mold because of condensation when warm air meets cold rooftop.

Yes, but the absolute humidity is the amount of water in air, and particularly n cold climates, this water load can cause considerable trouble in structures. The correct way to design airflows and location of dew point inside the walls etc can be considerable trouble; ad hoc design tends to lead to mildew problems.

I am a little confused about this fear people have of mold and mildew in their houses. Up until very recently people's houses weren't far off from the outside environment. Generally in the summer the best they did was keep the rain out and provide some shade. Houses weren't uninhabitable mold pits back then, why would they be now?

There is some additional risk with modern homes being much better sealed than old homes which always had some air moving through it. If you don't have a proper HVAC system and use like electric heaters instead of forced air, humidity levels can build up and slowly absorb into materials if you don't have enough airflow, and you likely won't notice, unless maybe the dew point gets high enough that all of a sudden every surface in your house is damp. It is less of a concern in places without high humidity but some swampy areas can be 90% humidity for weeks or months at a time and then all of a sudden you got mold behind your walls because some idiot decided to seal up every seam with plastic or glue or whatever other impermeable material.

Part of this is a misunderstanding of building techniques that block airflow, ive seen numerous houses with all the roof vents plugged up to "save heat", walls with plastic sheeting on the inside wall creating air/moisture traps, or people replacing air-permeable house wrap with solid sheet plastic, foam and glue on every board and seam with a sealed up and moist crawl space underneath, ect. It is fairly easy to get mold in a humid place with a sealed home and no forced air, and nearly impossible to kill it all without tearing out all the drywall in the house. If everything was done right, shouldn't be a problem, but people are far more likely to pay for size and speed over quality materials or careful quality labor.

Here’s an accessible and illustrated page with some additional details around your point https://www.popularmechanics.com/home/interior-projects/how-...

I’ve seen this turn into a problem with big renovation of old residential structures twice. My personal takeaway was make sure your envelope and HVAC are of roughly equivalent quality and era.

Well exactly because of that. If your house has plenty of air circulation (that's what "people's houses weren't far off from the outside environment" means) then things might get damp, but they will also dry out naturally too. Now you get a huge plastic bag and wrap it around a building. It will keep out rain yes, but also trap in moisture internally and the damp parts will get mouldy. Obviously nobody will do something as silly as that, but with modern materials it become much easier to accidentaly approximate the plastic-bag-wrap experience.

There's lots of things we don't understand about the health interactions, but even if you don't suffer ill effects at least you'll risk stigma if you and your clothes smell of mildew.

It's sometimes hard to imagine how hard and unprecitable lives of past generations were. For most of history people's indoor firepits didn't have chimneys, for example, and the health effects were less of a concern than wars, infectious diseases, getting hurt in physical labour, or famine.

Also, most old houses were well ventilated and built of mildew resistant materials (= poor insulation and wood).

Well just as an example, around here concrete cellars were usually not insulated before. They were storage areas.

In the 80s people started insulating them in the wrong way (on the inside), creating a condensation point between the insulation and concrete => mold.

These days we have learned that cellars must be insulated on the outside (by digging up the garden) or somehow make sure humid indoor air dont make contact with concrete behind insulation.

If you basically don't have plastic and insulation then mold is less of a problem, but you also need to spend a ton of energy keeping the house warm...

It is actually easy to ruin a home by trapping moisture using modern materials carelessly. It happened to many centuries old buildings in the twentieth century after being renovated and modernized to save on heating. Traditional techniques allowed more circulation of air that avoided mold.

The walls of a normal modern insulated house are already completely air tight, first layer behind the walls seen from the inside is a plastic sheet to prevent humidity from indoor human activities to get into the insulation. After building a new house they literally try to inflate it like a balloon and measure the pressure to ensure there is no leakage.

Controlling humidity and air freshness is done through vents, usually combined with a heat exchange to not let out all the warm air you just heated up.

Condensation accumulating larger drops might be a bigger issue with glass though, but only if it's already humid on the inside.

I could be wrong but I think mould appears when humidity condenses to water drops. So you need both humidity and a temperature contrast (e.g., hot inside air meets a cold wall).

So as long as the inside and outside of the house has the same temperature, condensation in random spots should not happen?..

Condensation will be on the glass panels, where mould cannot grow.

I suspect noise level might be quite high too, especially with children.

Still a cool house though, I like their water treatment

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