Which Dessicant is Best?

air home use? in the room?

you'll need plenty of it, wheel barrows unless you have a super dry land climate there.

A less known, but superior is MOLSIV. But for in the house I personally wouldn't use any.

Thank you for your suggestion of MOLSIV, do you know the comparative between different dessicant?

Do you have a closed cycle or open cycle in mind?

Molsiv is probably one of the most expensive: you need heat AND vacuum to get it to work. On the other hand, it comes in many varieties - balls and pellets and also with different structures. From 2 Angstrom to 20 and even more. Depending on the size it takes more than only moisture out of the air.

There are also many variations on the cited products. I have the impression that silicagel is still the most used product (cheap) and easy to regenerate.

In case of moisture in clean air also a long lifetime can be expected.

We have used active carbon mostly to adsorb solvents (easy to regenerate with steam). But it works also to fight diarrhea.

How about a dehumidifier using a refrigeration/reheat process?

I was thinking about a more energy efficient humidity control system, i.e., using solar heat to dry the dessicant to 'refresh' it on repeated cycle.

HRV (Heat Recovery Ventilation) systems do wonders and are much more energy efficient than a dehumidifier.

Explanation

HRV

Using desiccant is asking for trouble (especially in a high humidity country and in an environment like a building that is not a sealed environment where desiccant works best!). You would need quite a bit over a large area and even then the humidity reduction effect is going to be small.

Are you trying to get rid of mold in wardrobes or other enclosed spaces where a dehumidifier is impractical?

Jack - An HRV owner.

GA. I have that in mind for a retirement cabin I'm contemplating.

In the right climate, Bravo88's idea of solar heat sounds promising for regenerating a desiccant; but not in my location.

Not to get rid of mold, but for cooling.

In our climate, plenty of solar heat. My idea of keeping cooled without using compressor type air-conditioner is to keep humidity low. With good house insulation and sealing , a low humidity air and fan ventilation , it should provide good natural cooling.

using solar heat to dry the dessicant to 'refresh' it on repeated cycle.

Why do you insist on wasting the water? Collecting the water dropped out as the humid air is chilled, and using that to irrigate container-grown vegetables in a window garden makes a lot more sense. Cut your food bill while you make yourself comfortable. I use dollars, not thermodynamic equations, to measure efficiency.

The air is not chilled, chilling requires refrigeration mechanism, which use electricity. Sun energy is plentiful in my place.

The air is not chilled, chilling requires refrigeration mechanism, which use electricity. Sun energy is plentiful in my place.

That plentiful sun energy can make the electricity for Peltier effect cooling so you can collect the water for growing food, especially if you are in an area where the dew point is above 15 C. much of the time.

A Peltier based generator that can generate enough power to run a refrigerant based humidity control system will be very funny , not to mention very expensive !

Energy efficiency and monetary efficiency are not the same thing. Most solar processes are not very energy efficient, but occasionally they can be monetarily efficient--if the capital costs are not too high for recovering the "free" energy.

My idea is more or less similar to yours. Thank you.

We use Lithium Bromide only as a refrigerant for a vapour absorption cycle. Its affinity for water is very high, but it is highly corrosive with water.

We use Lithium Bromide only as a refrigerant

How is LiBr a refrigerant, since it has a melting point of 552ºC?

It's the water that is the refrigerant.

I know. Just trying to urge clarity in replies.

Hi pritam,

Thanks for the info. The concept I see has been around for quite some time. RV refrigerators are a good example.

Now, if I am to understand it, I need to spend some time on research...

Thanks!

Mike

Lithium Bromide is not the refrigerant in absorption cooling system, but water.

Guys,

i am a potential buyer of dessicants, primrily for toolbox and similar uses.

I am trying to avoid tools going rusty or losing their edges.

I buy it in small quantities but without knowing which chemical I am buying!

I could do with a primer or two, but have always searched for Silica Gel, can I do better by widening the search? Any pointers will be useful,

Also refresh of said chemical is important, heating usually, I understand to drive the water out, colour change also useful to see whether the dessicant has passed its useful life etc

Thanks,

Sleepy

You get another GA from me. For a primarily closed container anhydrous CaSO4 can't be beat in my book, since it goes through a stepwise hydration all the way to CaSO4.7H2O.

For a primarily closed container anhydrous CaSO4 can't be beat in my book, since it goes through a stepwise hydration all the way to CaSO4.7H2O.

Could you share your experience why this is so good that can't be beaten , strong absorption, ease of regeneration etc?

Could you share your experience why this is so good that can't be beaten , strong absorption, ease of regeneration etc?

All of the Government, University, and private sector laboratories where I have worked, including the one I owned, used indicating drierite (CaSO4) as the dessicant of choice for dessicators or drying cabinets due to cost, drying capacity, absorption rate and time and ease of regeneration. We used CaCl2 solutions of known normality to hold an enclosed volume of gas at a known humidity for test purposes. Check CRC Handbook of Chemistry and Physics. The first hydrate formed is Gypsum, CaSO4.0.5H20, the last one is Plaster of Paris, CaSO4.7H2O.

Where I work, we have a relative humidity (RH)-controlled oven. If the requirement is for RH below ambient, a dehumidification unit can be turned on.

This unit uses compressed air and has two columns. While one of the columns is removing water from the incoming air, the other goes through a moisture purge cycle. The regeneration of the desiccant is all in the switching of the airflow.

This is a small unit with a capacity of ~8ft³. I believe this type of system could be scaled-up to accommodate home volume requirements.

I don't remember the manufacturer, but I will get it and get back to you on Monday.

There are even some off-the-shelf systems out there:

http://www.forwardthinking.honeywell.com/products/dehumidification/dehumidification_products.html

No need to reinvent the wheel!

Good link, appreciate your info on Monday.

Under good insolation conditions, I suspect that ammonia/water absorption refrigeration would be more energy efficient than desiccant regeneration. Higher first cost, though. (This is only a guess, not up on best current technology.)

ammonia/water absorption system for home use will be crazy !

My thought is, desiccant based system is ideal for home cooling .

A low humidity environment, with fan blowing , the faster rate natural body perspiration will give good cooling effect. Using Solar heat regeneration is obvious choice.

Even if a desiccant system were to take, say, twice as much/many solar collector(s)? Admittedly, I haven't yet run any numbers, but you don't even seem to be interested in doing so. And why is an ammonia/water system crazy?--it is quite commonplace in RVs.

I am not thinking of a professionally made expensive RV system. The very purpose of my post here is to find a most cost effective way of cooling .

Anyway , I think ammonia for home use is not safe enough .

I don't know for sure, but am only suggesting that absorption system may be more cost effective than desiccant systems. (Or, it could go the other way.)

Just what do you think is unsafe about sealed ammonia/water absorption systems, whether for home or RV?

This seems to be a conceptual difficulty about rather simple stuff.

It is conceptual difficulty of the monetary kind !

You would probably have considered Indirect Evaporative Cooling:

http://jbarrownews.blogspot.com/2007/09/introduction-to-indirect-evaporative.html

thanks for the link.

I think Tornado is on to it here.

A natural gas absorber for heating /cooling and dehumidification. Or focus a solar collector into the area that the flame/burn would occur and then you have free energy. Solar power to run the fan and pumps, batteries to store for off hours consumption.

I remember when Amana had the propane A/C units for heating and cooling. Packaged absorbers for the homes down to 5 tons. Very popular here in Tracy and Livermore...by the lab, out in California.

I can imagine a pair of large panels with a surface thickly covered with silica gel or similar absorber.

These panel would be mounted vertically on a swivel post and separated with insulation. The assembly would be installed in an exterior wall "window hole" with a south/west orientation.

During the day, the inside panel absorb humidity while the outside half gets dried by the sun and lower dew point air. The insulation between the two panels would prevent heat from entering the house. At night, the exterior surface would be covered by some vapor barrier. During the night it would cool down.

In the morning, one would rotate the two walls and remove the vapor barrier on the interior side to repeat the cycle.

This whole process could be completely passive with only a five minute rotation every morning and a vapor barrier installation at night.

One could even have the panel permanently covered like solar panels and use fans to force the air through. Add a small motor, a timer and some sensors and it could be automated.

yes, similar idea.

I also suggested a similar idea at #12, it looks workable.