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gbwillson

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Reply with quote  #21 
Quote:
Originally Posted by GaryBIS
Hi Greg,
Not sure on the adjustability of the bimetallic spring vents.
I ordered one online yesterday just see how it works and see if it can be adjusted and how much.

It might be more practical to just find a place that sells the spring alone, and build the vent part.  I just thought that it would be worthwhile to just see how the commercial foundation vent works.

I'm a bit skeptical about the automotive thermostat in that the flow opening on the ones I've seen is small -- not sure enough air would get through to be effective?

Gary


Hi Gary-

I was thinking about the size of thermostats in that even the largest thermostat would likely be limited to a 2" diameter opening. While it would certainly vent the hottest air, more than one would likely be needed. The other thing to think about is if you have a metal vent located at the top of the collector it will act like a heat sink unless you have it covered with insulation. I think Ky-Jeepers greenhouse vent cylinder could be a viable solution as an insulated door could be made to open. I know they make adjustable cylinders.

Greg in MN[comp]

stmbtwle

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Reply with quote  #22 
My feeling was that the auto thermostats might be adapted to open/close a shutter, larger than the thermostat itself.  If the shutter were made of say polyiso you wouldn't have the heat sink issue.
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cwwilson721

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Reply with quote  #23 
Holy Cow!

This thread has taken a life of it's own, to say the least. Lots of ideas, possibilities, etc.

As far as the 'efficiency' issue goes, if you're stagnating, you have 0 efficiency anyway. No heat being moved, no work done. This is how to avoid catastrophe, not how to improve the collection of solar heat.

To answer another question, some don't have drainback systems, either. Here in the sunny South, where freezing temps MAY occur 2-3 times a year, a light glycol closed loop is a bit easier. So there could be liquid still in the system, still collecting heat, then a pressure change..Possible steam. Not for long, but how long would it take to cook the meat off your fingers?

The idea of motorized/electrically operated venting is very 'easy' (fans, or my idea of the glazing 'lifting' via actuators, or vents opening the same way), BUT, what if the stagnation event occurred because of a total power failure (grid or PV)? These solutions wouldn't work, then. However, they are GREAT if the stagnation event occurred because of a pump failure. They would be quick, easy, cheap, and controllable.

Of course, all vents/etc (any penetration to the outside of the collector) SHOULD be well-insulated. At least the same amount you use for the sidewalls, for example.

As far as non-powered solutions go, a bi-metal strip 'pushing' open a vent on top, and via linkages, one on the bottom, too, is fairly simple and fail-safe (if you can find the right material to do so). No electrical loss issues, and simple. It may be difficult to find the right material(s) for this, so it would only open at a stagnation+ temperatures, while staying 'closed' for normal operation, plus have enough 'strength' to mechanically open the vent(s). Using a cylinder to mechanically 'help' the spring to open a vent is a time-tested solution (that's what those foundation vents use), that could also be easily adapted to the "glazing panel" lift method.

And, by their very nature, bi-metallic springs are not adjustable. They work by the different expansion and contraction properties of the metals they are made with. Until someone actually invents Calvin's Transmorgifier Box, you can't 'adjust' this property. Thus, a bi-metallic spring needs to be found that expands at the correct theshold temperature. May not be easy, but there SHOULD be one.

Thanks to all contributing to the thoughts in this thread. I basically made it so ideas can be spread around. Are any of these methods REALLY neccessary? Not really. Good management and total design of the entire system would take care of 98% of the issue(s). But if you accidently fall into that 2% category, you may wish you had added these ideas in...




Garage_Hermit

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Reply with quote  #24 
Quote:
what if the stagnation event occurred because of a total power failure (grid or PV)? These solutions wouldn't work, then.


Well, they would not work if they were normally "off".

But if they were normally ON, then they would operate after current-loss (like a fire-door hold-open device in an office building, for example...).

http://www.secutron.com/index.php?page=shop.product_details&flypage=flypage-system-short.tpl&product_id=1721&category_id=155&option=com_virtuemart&Itemid=90

This means, having a permanent supply to the device, to hold it closed (such as a 12-V solenoid).  When the current fails, the device loses power, and  so opens, allowing the flap to open and release the hot air...

It might be a mite easier & more straightforward (& cheaper...) on an hydronic system - a simple electric valve like this...
http://www.adafruit.com/products/997

G_H

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cwwilson721

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Reply with quote  #25 
Quote:
Originally Posted by Garage_Hermit
Quote:
what if the stagnation event occurred because of a total power failure (grid or PV)? These solutions wouldn't work, then.


Well, they would not work if they were normally "off".

But if they were normally ON, then they would operate after current-loss (like a fire-door hold-open device in an office building, for example...).

http://www.secutron.com/index.php?page=shop.product_details&flypage=flypage-system-short.tpl&product_id=1721&category_id=155&option=com_virtuemart&Itemid=90

This means, having a permanent supply to the device, to hold it closed (such as a 12-V solenoid).  When the current fails, the device loses power, and  so opens, allowing the flap to open and release the hot air...

It might be a mite easier & more straightforward (& cheaper...) on an hydronic system - a simple electric valve like this...
http://www.adafruit.com/products/997

G_H


While this will work, the problem I can see is having a constant power draw when in 'normal' operation. This may be a drawback for some people, (using N.O. devices such as that) especially in a watts-limited setup like PV, or if you're trying to save/eliminate as much electrical 'waste' as possible.

While the draw may be low, multiply that 'low' over time. 

Let's just assume the device(s) on all panels would have a total of a 0.5w/h draw.
And further assume that you lucked out and had a solid year of no issues.

24hours x 0.5w/h=12w/day
12w/day x 365 days = 4.380kw 'loss' over a year.

So an 'always on' electrical component may not be a good route to go (not saying 'impossible' by ANY stretch of the imagination), but at least we're all coming up with viable ideas.
Garage_Hermit

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Reply with quote  #26 
er...  I think it is more like 4380 WATTS per year !
not kilowatts !

at my prices, that is around 65 eurocents, or 1 US dollar per year - somewhat less expensive than a foot of PEX ?


G_H

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solardan1959

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Reply with quote  #27 
Hermit,
  He said 4.380 kw that is 4380 watts, oh never mind, I should have just stayed out of it. [smile]
 (your probably half asleep because it's past your bedtime)

Dan
cwwilson721

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Reply with quote  #28 
1kw=1000w
4.380kw=4380w

May not seem like much. But ask a small PV user what that is like...Cost in batteries, panels, etc.

And that's basically running ONE of those fire solenoids, approx.

If you have 4 panels, that 16kw/year (all approx)

If you're running a real tight power budget, that might make it alot less desirable.




cwwilson721

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Reply with quote  #29 
Quote:
Originally Posted by solardan1959
Hermit,
  He said 4.380 kw that is 4380 watts, oh never mind, I should have just stayed out of it. [smile]
 (your probably half asleep because it's past your bedtime)

Dan


Let's put it this way:

I've been 'lurking' in these forums for quite awhile now, and I REALLY respect BOTH of your opinions and thoughts.

All ideas have merit. I was just pointing out a possible drawback to some for using the N.O. devices.

Since I don't use PV at the present time, it wouldn't be an issue for me. (I already thought of that).

But, I'm trying to think of ideas that can be semi-universal
GaryBIS

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Reply with quote  #30 
Hi,
OK, I know this is being picky, but this is a pet peeve of mine.

The watt is a rate of using energy.

A watt-hour is an amount of energy.

A 40 watt light bulb uses energy at a rate of 40 watts.

In  24 hours, a 40 watt light bulb uses 40watts*24hours = 960 watt-hours of energy.

Your electric bill tells you how many kilowatt-hours you used over the month, no how many kilowatts you used over the month.

In the water world, watts are like gpm (a rate).
and, gallons are like watt-hours (an amount or quantity).

--
Got the automatic foundation vent late today.
The bimetallic strip comes in the form of a spiral, with the inner end of the spiral fixed to the frame, and the outer end of the spiral attached to a linkage that moves the 3 vanes that open or close.  The total stroke at the spring appears to be about half an inch.
Will try to see how adaptable it is in the next couple days.


Gary







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