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G3OCR

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Reply with quote  #21 
I found the pad - it was indoors after all

Here's yesterday's results.  Temps in Celsius.  I was away from home in the early afternoon - pity, as the time between midday and 4 pm would have been interesting.  The peak of 60C (about 150F) was the temp measured about 9" from the top of the collector, which I think was quite good considering it was not full continuous sun.

The collector is facing just East of due South and is perpendicular (horizontally) at about 11:30

Time

Ambient

Inside

Collector

Out

Slab

Out

Weather

0900

5.5

6.2

10.6

9.0

Continuous Cloud

0930

6.0

6.3

13.9

9.7

Continuous light cloud

1030

5.6

6.6

13.0

9.7

Sun just visible thru cloud

1100

5.9

7.4

14.8

9.7

Sun brighter behind cloud

11.30

7.7

7.8

27.8

9.7

Bright sun behind thin cloud

1200

8.0

8.1

60

9.9

Bright sun thru gaps in cloud

1600

4.7

9.1

14.2

10

Intense cloud


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solardan1959

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Reply with quote  #22 
Stu,
   You need to start tracking slab temp also.
Dan
Scott Davis

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Reply with quote  #23 
I agree with Dan, it will be interesting to see if the relatively small collector and super tiny air conduits in the slab are able to raise the slab temperature over a period of days or weeks.
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SolarInterested

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Reply with quote  #24 
My comments here are a bit off topic for this thread. Scott feel free to move this post if you see fit.

Quote:
Originally Posted by G3OCR
I don't think there's a way to do it "direct".  The advantage of doing it by hosting the images elsewhere is that Scott's server doesn't have to handle the bandwidth every time somebody loads a page into their browser - saves him a lot of money and his provider doesn't need a faster connection to the internet backbone.  When we load a page from here, we basically only download the text from Scott's server and the big stuff (800 x 600 pixel images come from PhotoBucket's server.

A potential problem with using other image hosts is when folks let their accounts lapse and the photos are no longer available. I see this in other forums on old posts.

A work around is to attach the image then use it's url to place it inline. The image is only served once from Scott's server. This is useful when using the same image in muliple posts/threads.




This is an image attached to solardan's post

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G3OCR

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Reply with quote  #25 
Here's the Problem!


(picture of wall with collector removed)

The thermometers that I ordered didn't arrive until after the weekend, with the weather being pretty bad most of the week (rain, cloud), and I had placed the 2 that I had in what seemed to be the places where's they'd give the most important information.  I didn't think I'd lose much heat from just 3 feet of pipe that was exposed on just a small-ish part of its surface. 

However, when I fitted another thermometer to where the pipes entered the building, I could see that I was losing almost all of the heat generated by the panel in just those 3-foot lengths!  The reason that the South edges were left exposed is that the collector is slightly up-tilted (I'm most interested in collecting heat in the winter months when the sun is low but there is a gap between the bottom of the collector and the wall that will be closed-off once my experimenting is finished.


(Gap at the sides)

The addition of some spray-foam on the exposed sides of the pipes now gives me much better temperatures going into the building, though the air coming OUT of the slab is only showing a couple of degrees higher than ambient.  I'm guessing that the temperature drop between going in and coming out is being absorbed into the slab, but it looks like a need a few days of full sun to prove that.

Scott - if it turns out that the slab temperature rises once I get some decent weather, then the small pipes going through must be transferring the heat successfully (where else can that heat be going to? - the slab is insulated around the sides and from some of the comments in the email forum recently, I may get some improvement by adding more insulation at the sides).   I think the 6' x 4' collector should be big enough as with full sun last week I was getting air at the top of the panel at just over 100 degrees Celsius and the building is only 60 sq ft floor area. Note that the readings I took last week were Celsius.

I'll report further once I get some sunshine that will give me some decent output from the collector again - from the forecast, that's not going to be for several days yet, although I'm getting some quite interesting readings from the thermometer at the entrance to the slab even with moderate cloud covering the sun .

Attached Images
jpeg NoInsulation[1].jpg (133.26 KB, 79 views)
jpeg Collector_Angle.jpg (170.26 KB, 62 views)


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Scott Davis

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Reply with quote  #26 
Thanks for the update and good report Stu.  I definitely agree that your slab is absorbing your heat, which is what you want. 

Did you insulate under your slab as well.  The earth can be a pretty good heat sink and draw a large portion of the heat away.

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Garage_Hermit

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Reply with quote  #27 
Hi Scott,

I actually avoided asking this question before, to G30CR, thinking what was the point, as he had already done the slab. Still, I guess the discussion might be of use for anybody else going down this same track...

It's pretty certain that if there is no insulation under the slab, that is exactly what risks happening, the earth will eat up a good portion of the heat. Probably not catastrophic, but once it's done, it's done...

For house construction (and let's remember that this a radio shack & not a house...), I believe that at least 100 mm of insulation is required under a slab and preferably 160.  Not just under a slab, but under (and around...) a wall footing also...

However, even 20 mm under a slab is better than none... And just as important, is the vapour barrier: if you don't use a vapour barrier, all the water just runs straight out of the concrete, into the ground, instead of evaporating slowly through the mass, upwards like it should,  so the concrete does not cure properly.  Again, this is not a bridge structure so guess the structural side is almost negligible in this case...  In any case, I am sure that G30CR *did* use a vapour barrier

I put 60 mm of extruded polystyrene under my portico (wood) floor, and some days I feel like ripping it all out and starting again ! Maybe I will, one day when I have the inclination...

There is some discussion about slab insulation here:

http://www.garagejournal.com/forum/showthread.php?t=5942

In the event, the only solution, apart from breaking up the slab, would be to inject underneath it - this would require some pretty severe civil engineering, most certainly far more expensive than the cost of the saved energy...

In any event, with the speed that heat moves through thermal mass, especially an uncured concrete slab, I reckon that G30 should not be looking to see any spectacular temp difference in the slab for at least 2 years and perhaps even three...

Garage_Hermit

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solardan1959

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Reply with quote  #28 

Garage_Hermit said,
"In any event, with the speed that heat moves through thermal mass, especially an uncured concrete slab, I reckon that G30 should not be looking to see any spectacular temp difference in the slab for at least 2 years and perhaps even three..."

Hope not but by then maybe I'll have my ION generator up and running and be able to provide free heat and power for all"
Dan

G3OCR

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Reply with quote  #29 
Hi Hermit,

I thought I'd already covered the construction of the slab, but there's a vapour barrier of heavy "1000 guage" (construction grade) plastic sheet under and all around the slab - not glued or taped but a single continuous sheet.  There's also 5cms (2 inches) of polystyrene both under the slab and around the sides.  Having read recent discussions in the email forum, I may look at adding some more insulation around the sides both above and below the ground level, at a later date.

Yes, I'm stuck with the 18 narrow pipes through the slab, but from the apparent absorption of all of the heat between the  input to the slab and the exhaust, it would appear that part of the system is working okay.  Yes, I'm aware that the slab probably contains a lot of moisture, and that will take some time to drive out.

There's no "wall footing", as the construction is of stud walls, insulated with fibreglass matting ("loft insulation") between the studs and with twin-wall 10mm PVC cladding over the OSB on the outside, the stud walls being built on the top of (and bolted through to) the concrete slab.

Today's weather wasn't too helpful, with cloud, rain, and just a couple of short periods of broken sunshine, but there was surprisingly good solar heat being generated, and on a clear day I've had the air out of the collector reaching just over 100 degrees C (212 degrees Fahrenheit!).

If I was to do it again, I'd run bigger channels through the slab, probably with bare concrete walls to these instead of PVC pipe, and thicker insulation under and around the slab but, as you say, there's not much I can do about it now and just have to learn (and hopefully help others to learn) from my mistakes.  BTW - the concrete had almost a year to cure, so it should have "chemically" cured, but I'd not be surprised if there's not still some moisture left in it that will have to dry out (although the RH inside the building is not excessively high when the fans are running)

Stu

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Garage_Hermit

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Reply with quote  #30 
Hiya, G30CR,

Thanks for the update - reassuring to hear about the insulation, must admit !  I read your string up & down, several times, but obviously missed that bit !
You'll be right about the curing, and after a year a lot of the moisture will already be out.
Even then, once all the moisture is out, there is still the "normal" transmission time of heat through the thermal mass to consider, and this will be slower, the lower the temperature swing between your normal day and night temperatures.  I guess that will not be very great in your part of the world, to say the least... However, because the heat is trickling in, it will certainly trickle out !

Regarding extra insulation around the slab, go for it, extruded polystyrene, down to same depth as your ground sheet, and as thick as you can afford !

Hope you get some good sun to bump that floor temperature up some more !

Cheers,

G_H


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