Silica Gel

[Onoff]

Any merit in using silica gel to store heat / hot water?

 

Not sure where I'm going with this rather than a discussion at the mo but I can potentially get some foc. Looking at some in it's pink state mulling whether it could be "dried" and one thought led to another...it stores water...so why not "hot" water. 

 

Thinking maybe coupled with solar thermal, first as solar heated air to dry the gel out and make it "receptive" to being rehydrated. What then happens to the water being evaporated?

 

In an insulated container? Would it work better under vacuum conditions?

 

 

[Guest Alphonsox]

All you need to know...

https://link.springer.com/chapter/10.1007/978-94-009-6508-9_167

[Onoff]

20 hours ago, Alphonsox said:

All you need to know...

https://link.springer.com/chapter/10.1007/978-94-009-6508-9_167

 

Ta. Tbh I only started thinking about it on the back of the Sunamp thread. 

[Ed Davies]

Yes, there have been projects to store energy in the dryness of materials. It's not so much that they'd absorb or adsorb hot water but that they'd release heat as they turn water vapour in the air into liquid (or other non-gaseous) phases bound in the material.

 

At around room temperature water has a latent heat of vapourisation of 2470 kJ/kg (0.68 kWh/kg). The heat released by a[d/b]sorption will be different but I don't think it'll be vastly different. Still, you'd quite a lot of material to get a lot of heat.

 

Silica gel is one option. Another is various clays which absorb water readily. Like some types of cat litter. There was a system (done in the Netherlands) which used expanded clays of some sort, dried out in the summer, to absorb water vapour from ventilation extract air which was then used to warm inlet air. There was a long discussion about it on GBF started by somebody promoting it in the UK. What I couldn't see was how it wouldn't just be a complicated way of only slightly improving on a standard MHRV.

 

A calculation I did on GBF suggested that if you had a timber lined house and could get it fairly well dried out during the summer then could get it to absorb water vapour over the winter you could get something like 20 watts of continuous heat output. Small but not completely irrelevant on Passivhaus scales. But it was pointed out that that's back to front - indoor humidity tends to be higher in the summer and lower in the winter.