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Garage_Hermit

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Reply with quote  #31 
aplogies to all, I saw the period, but I think in comma's...[redface]

(watts wrong with that ?) [rolleyes]

I still think it could be a good investment, if it's protecting one's solar fleet...

(the city of Nice spends 8,000,000 (yes, that is Eight Million...) EUro's per year on city-wide surveillance cameras, staffed by 700 (!) operators...  One camera per 450 head of population...

Now *THAT* is what I call waste of resources...)

G_H
(no, not gigahertz, garage hermit...)

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(1)  "Heat goes from hot to cold, there is no directional bias"
(2) It's wrote, "voilà" unless talking musical instruments...

cwwilson721

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Reply with quote  #32 
Hmm...

http://www.builditsolar.com/Experimental/44-31-%20Harrison1Stagnation-temp-control.pdf
Garage_Hermit

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Reply with quote  #33 
CW,

That looks like it, then - the problem is solved !

thanks for that -- better late then never [cool]

G_H

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(1)  "Heat goes from hot to cold, there is no directional bias"
(2) It's wrote, "voilà" unless talking musical instruments...
cwwilson721

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Reply with quote  #34 
Quote:
Originally Posted by Garage_Hermit
CW,

That looks like it, then - the problem is solved !

thanks for that -- better late then never [cool]

G_H


Yeah..."solved"..by Professor Proton and Sheldon.

Note the details.

What did they use?
Where can you source it?
What is the cost?


Academics..Meh

And note they vented under the plates/tubes.

About all this paper proves is a proof of concept, but no details

Let's keep looking.
Garage_Hermit

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Reply with quote  #35 
CW,  guess I'm not as skeptical !

To me, it looks like an OK approach - I mean, he fought it off against a "reference collector", and it did the business !

Thinking back further up this debate, for an hydronic collector, I was thinking along the lines of venting the boiling FLUID, but he chooses to vent the HOT air - I think that is *COOL* (so to speak...) (much neater and less messier !) (and less expensive as regards anti-freeze...) (particularly if latter kills one's prize roses...).  This AIR approach also means -- per se -- that one could also use the same device on an air collector...

============
 
Quote:
For the purpose of testing, a sample valve assembly was constructed based on the use of shape memory alloy (SMA) springs, (Otsuka and Wayman, 1998). The SMA springs
could be fabricated  to exert a force at a preset temperature, thereby opening the valve assembly, allowing the natural convection of air through the cooling channel located below the absorber plate of the solar collector.


I suspect he actually means, "simple valve assembly", as sample don't make sense...


(I also suspect there is anothter typo, earlier, as he says:

"it was concluded that the most practical and reliable means of increasing the heat-loss characteristics of a solar collector during stagnation was to incorporate cooling a channel under the absorber plate".

(I guess this means, "was to incorporate a cooling channel" but mebbe I'm just nit-picking on this one...)

========================
His "simple valve assembly" is shown in Fig. 5 - guess it's a rotating flap or vane...

Driven my his "secret spring"...

Guess that as it's not a commercial document, he saw no need to state his supplier or the price of the springs...

So I did a lookaround for SMA Spring, & found this...



(a video speaks louder than words...)

Mebbe this might make it easier to source (and price) one ?

G_H

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(1)  "Heat goes from hot to cold, there is no directional bias"
(2) It's wrote, "voilà" unless talking musical instruments...
cwwilson721

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Reply with quote  #36 
The advantage to venting the air in the collector before the superheat situation happens in the transfer medium (whether water or air) would mitigate the 'after affects', like dead roses. If the transfer medium never gets hot enough to cause damage, there will be no damage.

Also, a vent is REAL cheap to build into the frame (I'm partial to a aluminium or lightweight metal frame anyway, due to hauling the collector up a ladder, or wrasslin' the dang thing into position on a mount). Just a holesaw, some insulation, and a way to hinge.

SMA springs seem to be the real answer here..They expand an contract at whatever temperatures...And, we KNOW they exist at the temps that we need...

But, now, where do we find the miracle springs?
cwwilson721

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Reply with quote  #37 
Actually, searching for Thermal Mechanical Actuators came up with this:

http://rostravernatherm.thomasnet.com/item/all-categories/thermal-actuators/pn-1021

Supposedly, they will do what we want. Stroke length/etc can be changed with a hinged arm or whatever.

that they are already manufactured, in a rather small size, and heat range, and SOLD, is AWESOME.
cwwilson721

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Reply with quote  #38 
I sent a request to the company, asking for more information, including where to buy.

I'll post here when I find out.
Quote:
We are trying to make a non-electrical powered, temperature driven 'venting system' to allow us to vent and avoid, a stagnation event from happening in solar flat-plate collector systems. The risk of dangerous (to the system, and people) temperatures, in case of power failure and loss of cooling fluid circulating in these panels, is of concern to many.
We feel these actuators, coupled with lower and upper vents in the frames of these units, would work wonderfully. We need a solution that would keep the vent closed during normal operating temperatures, but open at stagnation temps (Approx 200f). The weight of the vent 'doors' are minimal, but the 'drag' of a linkage going from 'top' vent to also open a 'bottom' or 'cold' vent may be of concern
 
We need to know:
Expansion temperature(s)
Closing temperature(s)
Size
Mechanical force max
Travel/stroke/diam or shaft
Place that we can purchase
And possible pricing (small lots)
 
Thank you


EDIT:NOTE: I just said flat-plate collector as a 'generic' term. This should work with ANY glazed solar collector, whether flat-plate hydronic, or screen air.
Also, these same actuators CAN be mounted in a water-pipe. Why? No idea. But someone may come up with a possibility..Maybe open the vents if the water gets too hot? Or some other use in the plumbing system
GaryBIS

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Reply with quote  #39 
Hi,
I bought an automatic foundation vent that opens and closes automatically with temprature change to see if it might be adapted to provide stagnation venting for solar air heating collectors.


I've done a bit of testing on it that is shown here: 

http://www.builditsolar.com/Tests/StagVent/StagVent.htm

The testing was somewhat encouraging.  
The bimetallic spring provides about 1 inch of stroke between 150F and 240F -- probably enough to drive a carefully made vent louver.  

Using the whole foundation vent (with modifications to the spring mounting) does not seem very workable as its pretty large, and made of low melting point plastic.  But, using a bimetallic spring similar to what is in it with a homemade vent louver seems like it might be workable?


What do you think?

Anyone know where one might buy the bimetallic spring alone?

Gary

gbwillson

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Reply with quote  #40 
Isn't a bimetallic spring what's in a mechanical dial thermometer? How much weight are you trying to move? Could you use more than one spring?

Greg in MN[comp]
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