> most of the heat/humidity would stay in during the winter
Getting rid of humidity in winter is the main reason why you want to bring fresh air in a house though!
Getting rid of humidity in winter is the main reason why you want to bring fresh air in a house though!
A sponge drying up in your kitchen sink is enough to raise your kitchen's air humidity by 10%. Shut down your ventilation and you'll see, you won't suffocate but instead you'll get mold starting to pop-up. Moisture is the reason why houses have ventilation system in the first place.
As I said elsewhere in this thread, though, there's a problem with “dumb” ventilation systems though: they can't really adapt to big variations in outdoor conditions, and as such they tend to suck way too much air out of your house than needed during the cold days.
That's simply not correct.
I go through liters of water a day with my two humidifiers just to try to raise humidity by around 20 percentage points. In a small urban apartment that isn't much bigger than some people's whole suburban kitchens.
A damp sponge isn't going to do a thing, and I can't imagine where you would ever have gotten the idea that it would.
Moisture is not the primary reason for ventilation, except above showers -- it's to prevent CO2 buildup along with other toxic gases like CO and VOC's.
No surprise, that's because your water gets vented away…
My brother had a broken ventilation for a whole northern England winter in a flat he rented (and the landlord was too busy fixing this shit up), he had massive humidity issues with fungi spores making him sick before he understood what the problem was, and he'd tell you how much discipline it takes in manually venting your house by opening the windows to keep things from molding!
> A damp sponge isn't going to do a thing, and I can't imagine where you would ever have gotten the idea that it would.
Hey you know what, just do the math by yourself, it's just one pV = nRT away ! But of course, this is assuming you're not removing all that water directly as it evaporates.
> Moisture is not the primary reason for ventilation, except above showers -- it's to prevent CO2 buildup along with other toxic gases like CO and VOC's.
Maybe have a look at your local building code and see how the ventilation requirements are made. I've refurbished a house by myself and I did just that, it turns out the regulations are built on water extraction, as CO2 won't realistically kill or harm you, CO only matters in kitchens if/where you have gas stove (and in my country, this is subject to additional ventilation requirements in the kitchen itself independent of the house's ventilation), and VOC are only a recent concern. That's also why there have been hygrometer to pilot ventilation for a while.
Bringing in cold air at 50% humidity, then warming it up to room temp makes the humidity fall, leading to dryer air indoors than comfortable.
There's a problem with “dumb” ventilation systems though: they can't really adapt to big variations in outdoor conditions, and as such they tend to such way too much air out of your house than needed during the cold days (and it also tend to be designed to suck cold air into dry room first, and get out from wet rooms, when you want it the other way round when it's very cold).
In the hot and humid summer you're definitely trying to reduce indoor humidity.
But in the winter when it's bone-dry? A hot shower barely makes a difference.
I keep two humidifiers running all winter long just to bring indoor humidity up to 35% or 40% where it's healthy.
Otherwise it often goes down to 15% or even 10% on cold winter days, which is terribly unhealthy.
> In the hot and humid summer you're definitely trying to reduce indoor humidity.
No, you can't do that with ventilation when it's hotter outside than inside actually, that's not how thermodynamics works! But we don't care about that, because in the summer you don't have cold walls or window where water vapor can condense and let mold grow.
> But in the winter when it's bone-dry? A hot shower barely makes a difference.
The reason why it doesn't make a difference is because all the moisture is vented away by your ventilation system! And that's because that's what it's designed to do! Stop it and see how it goes! For the record a single wet sponge drying up in your kitchen is enough to raise humidity by 10%! You barely need 2cL of water per cubic meter to have 50% humidity at 20°C.
As I said the problem is that in winter, ventilation system often ventilate way too much.
Also, they are often designed so the cold and dry air enters in the bedrooms/living room and the warm/moist air is extracted in the kitchen and the bathroom, and because of that the rest of the house doesn't get any of the excess moisture of these places. This is done because the designers wanted to make sure that the humidity level never raise too much in the room, because again humidity will ruin your house and health pretty quick (having air that's too dry isn't very good for your lungs, but having fungi spores in the air is much worse!)
They say they let cold air in during the winter because they want to lower the humidity.
Then you say that, if you let cold air in (and then let it heat back up again) then you end up with lower humidity.
The only thing you might disagree on is exactly what humidity you would like inside your house. But that's subjective. (As it happens, I agree with them: I often find it too humid inside during the winter, because I've restricted airflow to keep the heat in.)
Aren't you missing a zero of something? Because 900ppm isn't “very poorly ventilated”.
I notice I'm not as mentally focused once it gets to 800 or so.
I have a CO2 monitor to keep it below 600 for productivity and concentration.
Remember, fresh air is around 420.
Possibly just different terms used in different countries where the humidity is a bigger problem (very hot and/or very cold outside air).
This current OpenERV product appears to use dessicants for this purpose but might be an optional add-on?
This is to avoid energy loss that would occur when moisture condenses (i.e. the latent heat) by using an adsorbant material to capture moisture before it escapes, or a membrane that allows moisture in the outbound flow to pass to the inbound flow.
Really a lot of our older homes shoud be retrofitted with a MVHR unit to help things as ventelation is awful in most houses. I'm actually quite surprised a lot of landlords in the UK don't do it as theres always a fight between them and their tenants who don't necesserily want to leave a window open all day in the winter to stop mold.
I think it basically trickles in cold (and therefore drier) air into a central space to reduce humidity, like an (slower, quieter) extractor fan in reverse.
Seems a bit of a conflict of interest still, especially if the tenant is paying for heating.