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welshboy

Collect lots of low grade heat. Solar Trickle Collector

In one of my thinking moods I ran a hosepipe which was running by gravity from our spring into a bit of drainpipe which was placed horizontally on a black zinc roof of an outbuilding on our smallholding.
I had drilled some holes in the drainpipe to correspond with the corrugations of the zinc.
The total run on the roof was about 17ft at a fairly gentle slope and I put some troughing in the bottom of the roof to collect and tip the water into a bucket.
I measured the temperature change.
On a sunny day with no wind at the end of March the water was entering at 12c and in the bucket it was 26/28c average after I let the experiment run for a few hours.
I worked out that if on the whole roof 30 ft wide by 17ft fall the flow rate was about 350 gallons an hour or about 27kw worth of extra heat captured per hour.

If the zinc was covered with polycarb or polytunnel sheet it would be better.

Can anyone suggest practical uses for this low grade heat ?
I can use it in the heating season but it is wasted in the summer.
Justme

Re: Collect lots of low grade heat. Solar Trickle Collector

welshboy wrote:

about 27kw
Can anyone suggest practical uses for this low grade heat ?
I can use it in the heating season but it is wasted in the summer.



27kwh not 27kw.

27kw is huge, over an 8 hour sunny day its 216kwh.

You wont get any where near that amount of heat in the "heating season" more like about 2kwh

Your roof is about 56m2 at 1000w/m2 & 80% efficiency (average efficiency of a bought system) you should get 46kwh of heat in summer. Your system is doing ok at about 50% but in winter like all flat panel systems it will suffer due to thermal conduction losses & lack of insulation, wind, less radiation available etc.

You could use it to heat a pool or spa they are used more in summer.

If you fit a thermal store with mains pressure hot water coil (vented system) you could pre heat your hot water before it goes to the boiler. With insulated storage you could even use the water directly for an outside shower (or inside with pumping).
TopCat

You could have a look on this site and see if anyone can come up with any suggestions?
Its a good forum for all things Solar/Wind/Water etc

http://gotwind.forumco.com/forum~FORUM_ID~2.asp

Regards
Tom
Justme

Oh & its only low grade heat cos of lack of insulated storage. Sort that out & you should get some nice hot temps.
welshboy

Thanks Justme
I thought that the per hour bit covered the 27kwh. 27kw thingy .
"about 27kw worth of extra heat captured per hour."

I don't want to give the impression that this is all my idea but this link explains where I got to thinking about it and trying an experiment.
http://www.ece.vill.edu/~nick/Solar_Heat.pdf
It definitely reduces the oil bill in the comparable buildings.

As far as the heating season goes we are hothouse plants and tend to run the heating from Oct to May although I must confess to switching it on a couple of times this July !
As a result we can make get a useful contribution to our heating costs for 3 months of the year and a little in the winter. I pre heat the incoming water to the groundsource heat pump giving it less work to do.

Having said that I wish it would work like this guy has done
http://www.builditsolar.com/Proje...ceHeating/SolarShed/solarshed.htm

I had thought about the pool idea but that means building a pool !

I am trying to get my head around interseasonal stores.
Topcat Thanks for the link
Justme

No.

Per hour means its doing 27kw for every hour (is that what you meant? IE as powerful as a gas boiler). Or is what you meant that during all day you collected 27kwh (which is a tidy amount & not to be sniffed at a sit would cover most peoples hot water use).

How did you calc it as 27kwh?

The calc is

total water volume in Litres / 860 x (deg in c raised in total over measuring period) = total kwh collected over time period.
(1kwh will raise 860L by 1 deg c)

As you quote flow & not volume I cant do the sums.

(looking at what you have said in the first post again & I think you are not recurculating the water so flow can be used)

14c rise in temp
1557L volume
1 hour time

1557 / 860 x 14 = 25.34kwh which is close to your 27kw per hour.


If so thats some power.

I am getting about 5kwh per day from my 1.5m2 of tubes (shaded till 11ish). If I increased my area to match yours it would gather 190kwh per day or about 350 if unshaded. So your sums seem about right at 27kw x 8 hours = 216kwh per (good sunny) day.

Its suprising aint it how much you can get for free. For better performance in less sunny days does cost mind.
Justme

Yeh that solar shed is good but our winters are not like his.
welshboy

Justme
yes thats how I calculated it 350 gal= 3500 pounds raising average 15 c  
= 3500 *15/5*9 /3400.

I work in old money !

I was just thinking about bangs for bucks and what I can do with what I have got with minimal investment so yes almost for free.

The measurement experiment was on a perfect day  clear sun and no wind to cool the roof.

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