Welcome to the Solar Collector
Brainstorming and Development Page!


 

Home

Hot Air Collector

Hot Water Project 1

Hot Water & Space Heating

Solar Electric

Solar Construction 101

FAQs

Best Collectors

Simply Solar
Sign up Calendar Latest Topics
 
 
 


Reply
  Author   Comment   Page 1 of 12      1   2   3   4   Next   »
cwwilson721

Registered:
Posts: 303
Reply with quote  #1 
As you know by now, stagnation occurs in collectors when the pumps shut off for some reason, and because there is no water flow, temps inside the collector rise to incredible levels. If you're lucky, you catch it in time, and can do something about it. Melting of insulation, instant steam in the piping inside, and catastrophic failure of the entire collector can, and does, occur. Considering the time ,effort , and money you've made to build the system, it can be very painful.

To prevent this from occurring, we use controllers and temp probes and constant power via a PV panel or some other method and trust that we can restore "cooling" to the inside of our panels in time.

What if you're not home? What if your pumps run on 110/220 AC, and the power goes out? 

For my 'solutions', I'm assuming you have a DC power source near the panel, whether PV panel or battery backup, whatever.

There are two 'easy' routes I can think of. You can use one or the other, or both. Both also require 'building in' while constructing the collector

  • A temperature controlled 12/24v DC actuator that lifts the "top" edge of the glazing panel, to vent air out rather quick. 2-4 inches should vent it rather well. This approach requires a "hinge" on the glazing part of the collector ( Think like the glazing/etc is a lid to a box, with one end hinged). When the temps get too high in the collector, either a controller or snap switch turns on the actuator, which lifts the "lid", venting the too hot air out. Getting it back down is rather easy, too, but even if you only accomplish this part, it would save the collector.
  • Vents on the 'top' and 'bottom' framing plate of the collector, with insulation on the inside, held closed by springs. When the selected temperature is reached, small actuators open the vents, allowing the hot air to escape. Use of small DC powered fans would help in this. Again, would be fairly easy to wire this to close again after the temps have reduced, but, again, even being stuck open is better than a mass of melted goo.
Can you think of anything else? A possibility in the 'vent' idea is using bimetal strips that 'push' the vents open if too hot. But top and bottom would have to open to really get the heat out.

Addition:

Results, so far (4/5/2014). This is a spreadsheet of all ideas so far, with pluses and minuses.
Pick and choose. Picture first, and a xls file at the very end.
Ideas.jpg 

xls Ideas.xls    

Ky-Jeeper

Avatar / Picture

Registered:
Posts: 199
Reply with quote  #2 
This shold work for me. Is yours a closed loop?

Attached Images
jpeg CAM00871.jpg (836.39 KB, 134 views)

Garage_Hermit

Avatar / Picture

Registered:
Posts: 2,240
Reply with quote  #3 
(some) aircraft wheels use "fusible plugs" - if the wheel rim overheats, say a brake drum has seized, the plug blows and lets the heat (and the pressure) out, and prevents the tire from bursting...

A similar fusible plug could be built into a collector, but it would need calibrating.

You could use a meltable material such as beeswax that melts at 60°C (say).

A simple method would be to have a spring-loaded flap, somewhere in the top of the frame, that is normally held shut by a bead of beeswax (or paraffin wax) sealant. When the wax melts, the flap will spring open and let the heat out...

For an hydronic system, I posted on this someplace else, just recently...
FWIW, will dig out the link and update this...

http://simplysolar.supporttopics.com/post/stagnation-event-avoidance-vertical-collector-6764919?pid=1281622837&highlight=stagnation#post1281622837


G_H

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

Registered:
Posts: 303
Reply with quote  #4 
There's cases where no TPV blowoff, but still bloated piping damage, melted glazing/etc.

It's even possible in a drainback.


Even a very small amount of water turning to steam can do alot of damage.

There are quite a few people with all CPVC systems, too. The heat trapped alone inside a collector like that in full sun can cause distortion, softening, etc.

I'm just offering possible solutions above and beyond 'common practice'

Examples:
To open the 'lid'
http://www.ebay.com/itm/NEW-2-Linear-Actuator-225lb-Adjustable-Stroke-12-Volt-DC-Heavy-Duty-New-/151247258363?pt=LH_DefaultDomain_0&hash=item23370a02fb

And the vents:
http://www.ebay.com/itm/Airpax-Digital-Linear-Actuator-Model-Number-K92121-P2-S1-New-12-Volts-/171253280717?pt=LH_DefaultDomain_0&hash=item27df7dafcd





Ky-Jeeper

Avatar / Picture

Registered:
Posts: 199
Reply with quote  #5 
I have a closed loop system somewhat completed. Melting polyiso shouldnt be a problem in mine. Behind the copper pipe is and alum plate which behind it is a layer of slightly compressed fiberglass insulation which the melt point is way up there. Then radiant barrier. After that the polyiso. Inner frame is 2x4 metal studs and fully insulated and outside framed with presure treated lumber. Now all black waiting for the wood to be flashed out with white alum.

Attached Images
jpeg IMG_62412043459696.jpeg (71.48 KB, 123 views)

stmbtwle

Avatar / Picture

Registered:
Posts: 2,872
Reply with quote  #6 
Might explain why production collectors are so expensive.

I've wondered if an automotive thermostat could be rigged to open a flap or flaps to allow outside air into the collector, cooling it.

__________________
Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
solardan1959

Avatar / Picture

Registered:
Posts: 1,845
Reply with quote  #7 
Drainback, no power and the system drains, no stagnation.  Unfortunately your design may work because there are lots of places for water to settle and while it may not stagnate it will freeze.

By commercial do you mean manufactured or large specially built commercial units for factories etc.
Most smaller manufactured units are similar to what we make (without cpvc).  A manual vent should easily suffice, open in warmer weather, close in cooler.  You could also use a backup dc system as we have talked about in the past.

Dan
gbwillson

Avatar / Picture

Registered:
Posts: 2,305
Reply with quote  #8 
On a liquid system, do we need to reduce the temp of the air in the box, or the liquid in the pipes during stagnation? How much damage to the pipes occurs if the box is vented? I recall someone mentioned installing a "plug" on the top of the unit. This plug would be made of a material, such as styrofoam, with a relatively low melting point that would shrink slightly and fall out of place when the collector stagnated, thereby allowing excess heat to escape.

Greg in MN[wave]
stmbtwle

Avatar / Picture

Registered:
Posts: 2,872
Reply with quote  #9 
No, I mean commercially manufactured & sold collectors for home water heating. The two I have have copper collectors, aluminum frames and backs, heavy glass glazing, and I think fiberglass insulation. They're designed to last 20 years or so (one of them is that old) and stagnation does not bother them, even in our Florida summers. The old one will boil water if it airlocks, even in March. Can't speak for the new one but it's under pressure, so the boiling point will be higher.
__________________
Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
cwwilson721

Registered:
Posts: 303
Reply with quote  #10 
Quote:
Originally Posted by gbwillson
On a liquid system, do we need to reduce the temp of the air in the box, or the liquid in the pipes during stagnation? How much damage to the pipes occurs if the box is vented? I recall someone mentioned installing a "plug" on the top of the unit. This plug would be made of a material, such as styrofoam, with a relatively low melting point that would shrink slightly and fall out of place when the collector stagnated, thereby allowing excess heat to escape.

Greg in MN[wave]


Interesting idea..But at what temp does the plug 'melt'? If it's in the range of 'normal operation', could be detrimental.

Also, to most everyone: If you have a copper pipe collector, odds are stagnation will not be a huge issue except for possible glazing melting/deforming. If you have glass glazing, not real worries, except when the water hits the box, it may flash to steam real quick.

The ideas I put out where more for the ones of us who DIY a CVPC (or possibly, PEX) collector, and really have to worry about a stagnation event melting the collector. 

But even if I have a copper pipe collector, I may incorporate these ideas into it. Mostly because steam burns SUCK.

Think of it as wearing suspenders with a belt if you have copper pipe. Think of it as a bank guard if you have 'plastic' pipe.

Minimal expense, and great return. Safety, and for some, expense.
Previous Topic | Next Topic
Print
Reply

Quick Navigation:

Easily create a Forum Website with Website Toolbox.

 

web statistics