Tag Archives for " dehumidifier "

It’s a dehumidifier that doesn’t use electricity AND has no moving parts!

It’s a dehumidifier that doesn’t use electricity AND has no moving parts!

Our clients know that here at HypoAir, we’re all about managing humidity for a healthier home.  If your house is above 60% humidity, you can start to have mold problems (the higher the humidity, the more quickly mold can grow).  We’ve written on dehumidifiers of all sizes for any room in your home, but none of them tops what this invention does.  It’s a passive dehumidifier that “sucks” the moisture out of air and evaporates it outside with help from the sun, even when the outside humidity was higher than inside!

Some of the best inventions have been developed by observing nature, called biomimicry.  In this case, researchers observed how trees “transpire” moisture, which includes lifting water from the roots to the leaves, where it evaporates through the pores, or stomata, of the leaves.  Thus, there are two parts of the tree that function in transpiration: the trunk of the tree contains xylem, which are very small capillaries or “straws”, and the pores in the leaves.  The sun’s energy starts the evaporation process and actually creates a negative pressure in the xylem, essentially sucking water up from the ground to the leaves.  (How do large trees, such as redwoods, get water from their roots to the leaves?)  

Researchers searched for similar behavior when they developed materials to mimic this water movement.  Two different materials were needed: one to absorb the water from the air (super-hygroscopic) and one to readily enable it to evaporate using the sun’s heat.  Metal-organic frameworks (MOFs) have been the subject of enormous research in the last decade.  They are like activated charcoal on steroids; because of their structured pores, internal surface area is huge.  When comparing the surface area per unit weight, the activated carbons are 400–2000 m2/g, zeolites up to 1500 m2/g, and MOFs are in the 1500–7000 m2/g range. MOFs are the porous materials with the highest surface area, with an ultra-high porosity of up to 90% of free volume.  (MOFs vs. other porous materials for carbon capture)  On top of this, MOFs can be custom-built to “adsorb” many different gasses or liquids, such as water, VOCs, metals, etc.  Thus, it made sense to make a very thirsty (hygroscopic) MOF to suck up water vapor, also known as a desiccant.  The researchers decided to try impregnating Lithium Chloride (LiCl, a salt) into an MOF. MOFs are typically granular, like sand, but the researchers wanted this component to be self-supporting, so they decided to nanospin the MOFs into a nanofibrous membrane (NFM) using polyacrylonitrile (PAN), a synthetic polymer resin.  The NFM would also enable the component to have a fast moisture absorption–desorption rate.  Thus, the “straw” component of the dehumidifier is abbreviated (PAN/MIL@LiCl) NFM, with MIL describing the “multilayer”. 

Passing the water vapor through to the outside of the space, the other component had to allow heat from the sun to evaporate this water, creating the “wicking” action.  This is the photothermal component.  Carbon black is a fine black powder produced by partial burning and pyrolysis of oil residues or natural gas at high temperatures.  (Carbon Black 101)  The black color works well to absorb solar heat, and adding it to a PAN NFM (PAN/CB) allows for great surface area, and thus evaporation rates.  The two layers put together are abbreviated PAN/MIL@LiCl-PAN/CB or for short, PML-PC NFM.

How did this layered dehumidifier configuration work out?  Impressively!  Being semi-flexible, it could be laid flat as a dehumidifier “panel” in a roof, or deformed to allow for water harvesting from the air (see diagram below). The scaled-down model of a house was constructed with dimensions of 40 cm × 50 cm × 40 cm, and a window with an area of 6 cm × 6 cm was designed for bilayer membrane installation. When light from the solar simulator illuminated the surface of the bilayer PML-PC NFM, the moisture in the indoor air was pumped by bilayer PML-PC NFM and simultaneously transported outdoors in the form of water vapor. The moisture actively moved from a high-humidity to a medium-humidity environment and also from a high-humidity to an ultra-high humidity environment through bilayer PML-PC NFM under sunlight irradiation. This is a unique advantage in terms of the dehumidification ability of the novel NFM-based moisture pump compared with traditional desiccants.  When the device was placed in an environment with an ambient humidity of 46%, the indoor RH was reduced from 70 to 48.9% within 2 h using bilayer PML-PC NFM.  When the device was placed in an environment with an ambient humidity of 80%. The indoor RH in the house model steadily decreased from 70 to 58.3% within 2 h using bilayer PML-PC NFM.  These are lower humidity ending points than that of the NFM without a photothermal layer. (Super hygroscopic nanofibrous membrane-based moisture pump for solar-driven indoor dehumidification)

Source: (Super hygroscopic nanofibrous membrane-based moisture pump for solar-driven indoor dehumidification

Now, what if night falls or clouds obscure the sun?  Since the experiment used a solar simulator of 1 kw/M2, which is the maximum amount of sunlight that can be had at the equator on a cloudless day, that would be a pretty intense artificial light needed to keep dehumidifying through the night or clouds.  For these reasons, this material would work best in an area with a high percentage of sunlight year-round, and lots of need for dehumidification (like the tropics).  Is it affordable?  Although the information in this paper is now 3 years old and other water-harvesting MOFs have been created, we don’t see any commercial applications yet, sadly.  Making such a technology affordable will do a lot to improve air quality in homes where energy (and dehumidifiers) are relatively expensive, since it doesn’t require electricity to condense humidity or regenerate the desiccant.  It could also allow many people to have access to clean drinking water by “pulling it out of thin air”.  We think it’s just too cool of an idea to keep to ourselves!

As for “natural” dehumidifiers, there are many materials that are hygroscopic: rock salt, calcium chloride (DampRid), baking soda, even sugar and honey.  The most efficient material we’ve seen is rock salt, most of all because it can be recycled: simply retain the liquid, let it evaporate in a pan outside in the sun, and break up the chunks to reuse it again (be sure to protect animals and children from drinking it by placing a screen over it!).  The downside to a rock salt dehumidifier is that it will only draw humidity down to 75%, which is the humidity that causes the salt to dissolve.  Also, using it in basements or porous/non-sealed areas is quite a lot of work for the results, as moisture is constantly being replenished from the ground through the concrete.  Finally, if you don’t recycle it, the liquid is quite toxic to vegetation, animals and can damage some surfaces.  

Some plants also act as natural dehumidifiers.  Check out the videos of the desert plant T. aphylla, native to the Middle East, which moves salts from the local soil to its branches and uses them to harvest water from the air!  The salt crystals on its branches change from a crystal structure during the day (low humidity) to drops of liquid at night, which it can absorb through its foliage.  If you have a normal “green thumb”, check out this article for a list of indoor plants that dehumidify.  Of course, we are all for natural, non-toxic and low-energy ways to improve the air in our homes!

Photo by Vivint Solar on Unsplash

How to keep MILDEW out of your CLOSET

How to keep MILDEW out of your CLOSET

Closet doors are meant to keep closed, right?  Unless you are Martha Stewart, it’s likely your closet doors don’t stay open very long–if they close to begin with!  The problem comes when humidity and closed doors combine for a stinky problem: mildew and mold.

We sometimes think that mildew is a less toxic form of mold, but it is still mold nonetheless.  Mildew is a subclass of mold that exhibits a white or gray, flat, powdery growth, while the rest of the molds can get more fuzzy and colorful.  Both release spores, but unlike other molds, mildew doesn’t penetrate surfaces and grow into the materials it lands on (though it can still cause cosmetic damage). Instead, it grows on top of flat surfaces and often collects in places like cardboard boxes or your vintage leather jacket in the closet.  Not good!  (What is Mildew, Really? The Difference Between Mold and Mildew)

Since we know that mildew is a form of mold, we know that it needs several things to grow: a food source (ie. leather, clothing, and dust in general), moisture (even excess humidity) and air (although stagnant air is best because lack of circulation keeps humidity at surfaces high).  So, the best ways to keep mildew at bay in closets is to:

  • Clean out the dust and seal off any sources of dust

  • Keep the humidity down and ventilate

  • Store items for longevity and air circulation 

How the heck does dust get in the closet when the door’s closed?

Incredibly, some closets are like dust magnets.  If your closet is part of a tiled or vinyl floor area, dust bunnies can usually slide right under the door due to the slick surface.  If you have any penetrations in the ceiling (like a light bulb), then your closet may be part of a hidden circulation system where the framing in your walls conducts air currents throughout your home.  For example, closets near bathrooms may unknowingly supply air to the bathroom exhaust fan, if the fan’s ductwork is not sealed well in the attic or the lightbulb box is not sealed to the ceiling.  Then there are the closets that double as storage areas and HVAC equipment rooms.  If the HVAC unit is not sealed well, it just pulls air from the surrounding home into your closet.

  1. Seal

The way to keep out the dust is to seal these small air passages: at the ceiling, remove the light fixture and either use a caulk gun (less messy) or a spray foam can with a straw (very messy, be sure to cover everything!)  to seal the electrical box to the drywall.  If the closet is an upper story, you may be able to do it from above in the attic with less mess, and sealing all the ceiling penetrations may help with dust house-wide.  If you notice a lot of dust forming on the floor, it may be worth caulking the baseboards to the floor (if it’s tile or solid-surface) to seal that up as well.

  1. Clean 

Next, removing the dust should be part of a larger goal to store items properly so that cleaning will be easier and mildew will be less likely to form.  You’ll need a HEPA vacuum with brush attachments, and various storage containers.  If possible, empty the closet.  This will allow you to see all the walls and floor to see if there are any water leaks coming in that could be causing the mildew.  If not, use the vacuum to clean ALL the surfaces so you can get a fresh clean start!

It’s a great time to wash clothing and purge any items that you don’t use anymore by donating them.  Clean clothing is less likely to smell and deteriorate from body sweat and dust mites as well.

Stop right there!  If you had mildew in your closet before, you need to make ventilation changes to stop it from recurring.

  1. Ventilate/dehumidify

Mildew sometimes forms in closets because of lack of ventilation.  The great thing about moving air is that it lowers the moisture content of surfaces that come in contact with it.  If the air is not moving, the moisture content of surfaces tends to equalize with the stagnant air, and over time, mold is able to grow.  Also, if your closet is located on the corner or north side of a building, the insulation in the wall may not be sufficient to prevent warm house air from causing condensation on the cold wall.   Here are some tips:

  1. Refill the closet

Ok, you can start restocking the closet but remember this important point: maintain space between items so that air can freely circulate!  Don’t overstuff or compact items against the wall, either.  Wire shelving is great for maintaining circulation from top to bottom, too.

Storage containers matter, too–if possible, don’t use cardboard boxes because cardboard holds moisture, and it’s a favorite food for all kinds of pests: mold, roaches and silverfish like to eat it, and mice like to use it for bedding!  If you’ve cleaned and dried your clothing and excess bedding, packing them in clear storage bins is ideal so that you can easily see what’s in each.  For wool and moth-prone items, you can add cedar blocks to the bin to keep pests out.  These garment bags are great to keep dust off hanging clothes.

After mildew remediation, it’s important to check on your closet at least every few weeks until you’re sure that the changes are producing their intended effect: the ability to close the closet door without mildew taking root!

Photo by Annie Spratt on Unsplash