[Greenbuilding] Annual Cycle humidity control by increasing desiccant capacity of building

Mon Jul 6 10:09:24 CDT 2015

Setting aside the issue of what kind of desiccant we use, I would like well reasoned feedback on the concept of an annual cycle desiccant capacity in a building to offset the peak and valley of wet and dry in a house to achieve a desirable range through out the year.  Except for that video describing the many uses of charcoal in Japan, I do not know of other examples using this concept.  A few years ago, I experimented with bentonite clay in an attempt to absorb humidity on a daily cycle.  I found the rate of adsorption was way to slow to be affective.  The material was so dusty, I did not have a vision of how to actively circulate air through it with out mixing with the air.  

The relevant part of 28 minute video for this aspect comes at 21:28
https://www.youtube.com/watch?v=jiVmKC8xXJ8 

From: John Salmen 
Sent: Friday, July 03, 2015 1:10 PM
To: 'Green Building' 
Subject: Re: [Greenbuilding] Fw: Biochar as Annual CycleBuilding Dehumidifier

Sorry I didn’t see the video but wouldn’t zeolites (volcanic rock dessicant) be more effective than any source of carbon. It is a pretty common dessicant and pretty cheap – works by storing water to a saturation or equilibrium – so when the humidity level drops the zeolite will cycle and release moisture to about 80% of its dry weight – so a 100 lbs will hold about 12 gallons of water.

Not sure what kind of moisture you need to pull out but if its about 12 gallons a day you would need about 10,000 lbs or about 7 cubic yards – would definitely fill a crawlspace – but then you have to draw your air through the crawlspace.

I could imagine making an air filter using a buried concrete or poly tank. 

From: Greenbuilding [mailto:greenbuilding-bounces at lists.bioenergylists.org] On Behalf Of conservation architect
Sent: July-03-15 7:15 AM
To: Green Building
Subject: Re: [Greenbuilding] Fw: Biochar as Annual Cycle Building Dehumidifier

Many of us living on the East side of the Mississippi River, have high humidity in summer and low humidity in winter inside our homes when heated.  The relative humidity can be high in the winter outside.  However, by heating the cold air, it becomes very dry inside.  In the summer, the common practice is to cool with refrigerant driven air conditioner.  Never mind that all the refrigerant will leak when the seals break.  We do not have air conditioning.  In mountains of Virginia, we are able to keep the house in 70sF all summer with night flushing and closing up during the day with HRV running.  

Setting aside the issue of biochar, let me speak of increasing the desiccant capacity of the house similar to the what was described in video referenced below.  I have observed that our house has an annual cycle of humidity.  After heating through the winter, the house is very dry.  In the spring as the humidity begins to rise, past the heating season, the house will act as a desiccant and dehumidify  the air coming in by aDsorbing the humidity.  As summer and early fall, continually adds moisture, the capacity to aDsorb humidity out of the air becomes saturated.  By late summer and early fall, without active dehumidification, the house will have it’s highest humidity.  Then when heating season starts again, the heat will begin to dry out the aDsorbed humidity.  In the gradation from being too high, to too low RH, there will be a time where humidity released by drying will be a beneficial humidifying of the air, just as late spring, early summer the house’s dehumidifying affect is a benefit.  

For the past 3 years, I have been reducing the humidity in my house in the summer by temporarily heating to 100F+ temperature for a few hours.  Living near a creek may be raising my ambient humidity above normal.  However, when I have done that with a wood stove, I am able to cool house again by the following morning with RH reduced by 15%.  Because initially, my wife did not want me to do this, I waited until it was 90%RH in late August.  This brought it down to a still too high, 75%RH.  On a slightly cool day, I got permission to do a smaller fire to get RH to 65%.  The second year, I pointed to the mold forming to convince here it was a problem, also in August.  Similar results to first year.  This year, I convinced my wife to proactively dehumidify by drying the house when I first saw it get to 80%RH temporarily.  I did this last week to get down to 64%RH.  Also, on select days where RH is in 50s%, I ventilate the house with fans.  I was able to reduce by 5% the last time this way.  

Now if you could increase the desiccant capacity such that describe in video, we can lower the peaks of dry and wet to achieve desirable levels of humidity without the use of refrigerants.  This assumes you can maintain a suitable temperature by other means.  Now if people use biochar as the desiccant, they can prevent the readmission of half the carbon contained in the wood it was created from for millennias.  In addition to sequestering the carbon from wood, it also reduces the carbon from manufacturing and running refrigerant equipment to dehumidify.  

This video about charcoal in Japan shows its use as an annual cycle dehumidifier in a home.  The relevant part of 28 minute video for this aspect comes at 21:28.  Any thoughts? 4,500 kilograms of charcoal were laid in what looked like a crawl space to absorb humidity during the summer and give off humidity in the winter.  Much information was not included, like climate, size of house, thermal envelope construction, ventilation, et.  However, this application of a desiccant is relevant to our core subject of  greenbuilding.  Does anybody on list have experience using enough desiccant to absorb humidity in summer and release back in the winter inside a thermal envelope? 

https://www.youtube.com/watch?v=jiVmKC8xXJ8

Eli 

From: Reuben Deumling 

Sent: Sunday, June 28, 2015 8:59 PM

To: Green Building 

Subject: Re: [Greenbuilding] Fw: Biochar as Annual Cycle BuildingDehumidifier

  Does anybody on list have experience using enough desiccant to absorb humidity in summer and release back in the winter inside a thermal envelope? 

Some of us live in climates with low humidity in the summer and very high humidity in the winter. I'm thinking this would not work for us, eh?

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