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Passive homes and dealing with atmospheric humidity?

andré-johnmas

I am  currently looking into passive home designs and technologies, but the one thing I am not sure how to deal with is ambient (atmospheric) humidity, coming from outside the building.  

Currently the only real solution I have is using a heat pump based air-conditioner, so I am curious if there are any passive or lower energy solutions to deal with this?

 
Aug 24, 20 5:26 pm
Almosthip

Vapour Barrier

Aug 24, 20 5:58 pm  · 
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chris-chitect

I'm quite interested in the "Passive House" standard as well. I've taken two courses, a single day intro, and a more in-depth 4 day course covering the principles. 

Sounds like you need an ERV in your climate and not an HRV.

I'm going to assume you might be just starting as well like me. It's really something you should know inside and out before going down the path of construction. I think you need to be recognised by the passive house institute in Germany, or use a builder that is, if you want the certification. 

I don't know where you're located, but you should sign up for courses run by your regional Passive House Chapter. Even an intro day course will really open your eyes.

Aug 24, 20 6:30 pm  · 
1  · 
randomised

pop open a window ;-)

Aug 25, 20 6:27 am  · 
1  · 
Koww

in Arizona we just press desiccant packs into the stucco. keeps the humidity down, but it's a pretty dry climate anyway. you need like 8-12 packs per square foot.

Aug 25, 20 6:51 am  · 
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tduds

That's a lotta beef jerky.

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andré-johnmas

What I meant is how do I reduce the internal air humidity, relative to outside, such as in a tropical environment, in a passive home design?
Ideally low to zero power, using natural physics, such as with cooling in dryer environments (ceiling height, wind catchers, wall thickness,  increase air circulation, etc).

@chri-tect I’ll take a look at ERVs and the course is an interesting idea.

 

Aug 25, 20 8:54 am  · 
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In a passive design you won't really be able to reduce the humidity inside a structure without some type of mechanical system. At most you'll be able to provide air movement to make the space more comfortable.

2  · 
Jay1122

LOL, if you provide too much natural ventilation, then your insulation goes down because outside hot air comes in or vice versa. The best is pretty much super insulation then ERV(or HRV) for ventilation. If humidity is really really bad there is the full house dehumidifier but i doubt you will need it.

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chris-chitect

I guess I should have asked, are you looking to actually build to the passive house (PassivHaus) standard and have the building certified, or are you just looking at ideas and principles for a passive solar design? The PassiveHaus courses and certification are somewhat expensive. I've taken the courses not to become a passive house designer myself, but encourage my organisation to pursue passive house designs in future design/build contracts.

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Jay - I wonder if a ERV system would even work in a passive house as they have no mechanical air movement.

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andré-johnmas

Currently I am more in the research phase, exploring the concepts. In doing this I am exploring multiple geographies around the world, seeing how each has approached the problem and how well each work, rather than keeping to what the accepted local approaches are. 

Certification would be useful in a final build, but at the same time I would need to see how far it pushes the requirements and how narrow they are, based on available options.

Aug 25, 20 3:08 pm  · 
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x-jla

build it out of salt blocks



Aug 25, 20 3:22 pm  · 
1  · 
IAQ Pro

The most efficient system is indeed an air source heat pump (ASHP) based system to remove all the excessive moisture (a dehumidifier). Not an ERV! ERVs are good to keep indoor moisture when needed (like in winter when indoor is getting too dry) but are INCAPABLE of getting ride of real excessive moisture in the summer because of the limitations of their technology. This is why many are using now ERVs along a dedicated dehumidifier plus an ASHP for cooling and heating.

Actually the most interesting solution for passive house and apartments  is an all-in-one HVAC machine which combines those 3 machines into one (plus it provides medical-grade HEPA MERV15 air filtration). It’s called the PentaCare V12 (name comes from taking care of 5 things: fresh air, heating, cooling, moisture and air filtration). Company making those is called Minotair and they’re based in Canada selling across North America. There’s a Philadelphia architect using them regularly, Tim McDonald from Onion Flats firm. You really should look them up.

Aug 26, 20 8:59 am  · 
3  · 
Wood Guy

As others have said, the only way to decrease the indoor relative humidity is with mechanical equipment. There are other ways to slow moisture transport and improve comfort, but if you specifically need to reduce the indoor RH, you need a mechanical dehumidifier. It's not that hard to reach Passive House standards in cold climates that typically require a lot of heating, so I'm sure it won't be too difficult in a tropical setting. The Passive House airtightness standard by default will slow moist air from getting into the house so the equipment will not have to work very hard.  

(I'm a Passive House Consultant and used to manage a panelized Passive House company.)

Aug 26, 20 9:08 am  · 
2  · 
MarissaT

I think you will need to tackle the problem from the ground up. IMO the first step would be to understand the climatic conditions and usual weather patterns of the area. i would recommend using a accurate system like Climacell or Weatherbit instead of ordinary weather information. And I think using an HVAC system with a dry mode should reduce the atmospheric humidity. 

Nov 4, 20 12:38 am  · 
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Wood Guy

When designing a Passive House, there is proprietary software and weather data that eliminates guesswork.

1  · 
Volunteer

Large trees outside the home will significantly lower the temperature in the house and make it more comfortable. Using passive airflow devices such as transom windows above the doors connecting the rooms helps. Opening up the chimney flue even helps. A lot of southern homes with second storys had doors in each room that opened up to a long porch to increase airflow throughout the house as well. Study the homes in Charleston, SC, Savannah, GA, New Orleans, LA, and Key West, FL. 

Nov 4, 20 9:14 am  · 
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andré-johnmas

Thanks for all the good information. I also came across the following article, from the perspective of an HVAC teaching organisation:

https://www.hvacrschool.com/ho...

In general, from reading here and other sources, humidity seems one of the more challenging passive home issues. My take is that the more appropriate solution will probably be a hybrid of some form.

Nov 11, 20 10:52 am  · 
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randomised

Use mud plaster...it absorbs moisture when it is humid and releases it when it is dry. It is also natural, non-toxic and “dirt” cheap...

2  · 
justavisual

also great for making thermal mass - we're using mud bricks to make a wall with wall heating/cooling embedded

1  · 
andré-johnmas

Just reading up on this, it sometimes needs to be mixed cement stabilizers or asphalt emulsion in order to conform to local building codes. Does this impact the benefits you mentioned?

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andré-johnmas

Deleted comment: posted in wrong place

Nov 13, 20 11:42 am  · 
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Volunteer

Here is the Pitot House, a Creole house in New Orleans, built in 1799, that uses bricks plastered over between the posts construction. Might be worth a detailed lock. 


Nov 13, 20 12:17 pm  · 
2  · 
andré-johnmas

That's interesting. Decided to read up on it: 

https://www.egernsund-tegl.com/why-use-bricks

This states:

"However, clay bricks when used as internal wall facades can help in creating a healthier indoor climate as the bricks breathe and absorb levels of humidity, helping in keeping the atmosphere dryer."

Just need to compare the benefits of bricks and the mud plaster mentioned above.

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Volunteer

Many of the homes in Louisiana were also built on brick piers, which not only was useful in keeping the first floor dry during the inevitable flooding but allowed air to circulate underneath the house. This helped to dry out the structure during normal times and help prevent structural rot. These raised structures were called Creole cottages.

1  · 
justavisual

Here's the mud brick "fat wall" we're doing now in a CLT house. It'll get finish layers of mud plaster after the heating/cooling pipes are added.

Acts to absorb humidity, but also as a thermal mass in the otherwise wood house.

Nov 15, 20 6:12 am  · 
3  · 
Volunteer

Many of the Creole homes in New Orleans were built without hallways to reduce dead air space and to improve air circulation. Also, high ceilings were employed to allow the hot ambient air to collect there before being evacuated through the transom windows above the interior doors. 

Nov 17, 20 6:05 am  · 
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kimchiandkraut

In most climate regions you'll likely require a stand alone dehumidifier; ideally a ducted whole house unit. This is based on personal experience as well as CPHC training.

This issue with Passive House and 'high performance' homes comes up semi-regularly on www.greenbuildingadvisor.com as well.

While an ERV can remove some humidity, it typically can't keep up with latent loads. And because cooling loads are small in a Passive House, and a heat pump doesn't have to work very hard to deal with sensible loads in order to maintain comfortable temperatures, you're left with elevated levels of indoor humidity above 60%. 

Using the heat pump in 'dry' mode didn't work for us --- it excessively cooled the rooms (down to 61º F) with little dehumidification.

A Minotair or CERV could work (or other future 'magic box' options), but they are newer companies, so not risk free. Currently they don't offer much Btu output, so, depending on your climate zone, you'll likely require some kind of supplemental heat to meet demand. If the company goes out of business, or they don't have a competent service person in your area, what will you do if issues come up? You'll have all your HVAC needs in one unit --- good or bad depending on actual performance and customer service. If things should go really bad, can you afford to replace it?

You can read about our experience here: https://kimchiandkraut.net/201...

Jan 20, 21 11:46 am  · 
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