[Greenbuilding] Dessicants - was Central vs window AC

Eli Talking elitalking at rockbridge.net
Sat Jun 16 09:07:49 CDT 2012


John, thanks for info on desiccant dehumidification equipment.  This product 
certainly is intriguing.  With average air temp in July at 75F here in 
mountains of Virginia, tempering the extreme heat of the day by night cooled 
thermal mass flywheel deals with the cooling needs.  However, humidity still 
needs to be controlled.  Perhaps this product can deal with dehumidification 
without additional cooling energy loads.

I have the following questions.

When a desiccant absorbs water vapor from humid air, does it condense into 
liquid?

If it is liquid, then drying out the desiccant involves evaporation. 
Therefore, does increasing the temperature of the desiccant mass heat the 
adjacent air, like a clothes dryer to reduce the relative humidity to allow 
drying?

Is the efficiency affected by the ambient humidity?

This apparatus uses hot water to deliver heat to desiccant.  This heats the 
mass of the material directly.  Is this more efficient than blowing hot dry 
air over such as a clothes or hair dryer?

If the water is re-circulated  the energy required for specs would be 
determined by temp of water after it has given off what heat it can.  How 
much does the water cool?  Can we figure the latent heat removed to 
determine this?  Using electricity to reheat gives an accurate energy cost 
since electricity converted to heat is 100%.  If weight of water to be 
evaporated can be determined, the latent heat required can be determined.

Since the dehumidification would be in greatest demand during the hot 
summer, particularly for aggressively night flushed buildings, I would think 
heat pump water heater COP could be quite high when there is so much ambient 
heat available.

Also, houses that use solar thermal water collectors for space heating, 
could use the extra heat available from their system out of the heating 
season for dehumidification.  I am still an advocate for annual cycle 
thermal storage for collecting heat in spring and summer for use in fall and 
winter.  However, this requires a huge basement size thermal tank.  Those 
that are storing winter collected heat for winter consumption may consider 
only 5 cloudy day storage tank size.  Therefore, this tank could get quite 
hot during the high light and humid time of the year.

Eli
http://www.conservationarchitect.net



-----Original Message----- 
From: John Straube
Sent: Monday, June 11, 2012 8:06 AM
To: Green Building
Subject: Re: [Greenbuilding] Dessicants - was Central vs window AC

Attached is a cut sheet for the only wheel based system we could find when 
we looked 2 years ago.
it uses hotwater to regen the dessicant.  Takes about 1 gallon per hour at 
120F to remove 60 pints per day (a tight house with ERV will generally need 
less than half this amount of dehumid.
This would require a pretty decent solar hotwater system to drive it.

The amount of tray area and rotation would seem like a crazy quantity given 
how much commercial systems (eg those actually built tested and used in the 
world) need to move from wet streams to cold streams.


On 12-06-11 5:55 AM, Ron Cascio wrote:
> No experience with this myself, but I've always thought this an
> interesting way to deal with human comfort in hot/humid climates.
> I've seen commercial dessicant wheels, but not ones made for
> residential purposes. The key (enviro wise) is how you dewater the
> wheel. Waste heat would seem a likely source. Ron
>
> ----- Original Message ----- *From:* Gennaro Brooks-Church - Eco
> Brooklyn <mailto:info at ecobrooklyn.com> *To:* Green Building
> <mailto:greenbuilding at lists.bioenergylists.org> *Sent:* Sunday, June
> 10, 2012 6:46 PM *Subject:* [Greenbuilding] Dessicants - was Central
> vs window AC
>
> Has anyone experimented with the powder desiccants on rotation? Say
> have two trays and when one is in the house getting wet the other is
> outside on a south wall protected from the rain drying out. Would you
> need too much of it to make it effective, and thus render it
> impractical?
>
>
> Gennaro Brooks-Church Director, Eco Brooklyn Inc. Cell: 1 347 244
> 3016 USA www.EcoBrooklyn.com <http://www.EcoBrooklyn.com> 22 2nd St;
> Brooklyn, NY 11231
>
>
> ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
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--
>
Prof. John Straube, Ph.D., P.Eng.
Faculty of Engineering
Dept of Civil Engineering / School of Architecture

www.buildingscience.com






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