nrg710
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« on: October 11, 2010, 11:56:15 AM » |
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Given a 250 ltr TS and the weekend we've just had (9th/10th Oct 2010- quite sunny) and 54 deg N, without any use at all, how easy is it to say what kind of temperature readings I should be getting in my TS?
I have 20 Navitron evacuated solar tubes on a south facing roof, with about 4m of insulated tube between the collector and the TS. I have no idea if this is enough information to predict what kind of temperature rise in my TS I should be getting...?
I was away from the house for over a week, and was expecting to come back to a TS that was about 60 degrees. To find the max temp in the TS as 36 degrees was a bit of a surprise.
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martin
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« Reply #1 on: October 11, 2010, 12:01:41 PM » |
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If you're talking 20x47mm tubes, I'd reckon you're severely "under-tubed", and would need to at least double the amount for the relatively large 250 litre tank. (I'm running 20x47 mm tubes feeding a vented 115 litre tank, and it's certainly not "over-specified") - I'm sure other people will clarify that with temperature readings
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Unpaid volunteer administrator and moderator (not employed by Navitron) - Views expressed are my own - curmudgeonly babyboomer! - http://www.farmco.co.uk |
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desperate
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« Reply #2 on: October 11, 2010, 01:12:25 PM » |
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nrg Yep Martin is right, you need more tubes, we have 60*47mm into 216 litres and we are still (just) heat dumping at 75 deg c ( no legionaires here). I would guess that 36 degrees in your cylinder sounds about right, sorry  Desperate |
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nrg710
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« Reply #3 on: October 11, 2010, 03:14:16 PM » |
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Interesting. My installer said that 20 tubes would be fine. He even said that it was heat dumping through the rad the other day...
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dinitro
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« Reply #4 on: October 11, 2010, 04:48:33 PM » |
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nrg
Please check your system ie temperatures at the panel and associated pipework at the thermal store.
Although my array is larger I had a series of problems that only manifested themselves during the day when I was at work.
I would recommend as a basic to touch pipes on sunny days to see if they get hot along their length to and fro from the TS and panels.
also check your controller settings. You may benefit from changing them. Early on in this forums life there were many wierd and wacky settings for controllers.
However I have learnt that it all depends on your local situation.
Please do not despair.... please check everything first.
dinitro
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1x 20 x 58mm panel NEE, 4x 20 x 58mm panels south, Navi-Newark 320 litre thermal store direct boiler/ rad tap by boiler, retro coil, solar coil, termovar 61, S. circuit 30m+30m flow/ return. NEE 5m flow, 5m return. S. panel 52 degrees. NEE 45. http://sunscribe.homeip.nethttp://agni.homeip.net |
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Brandon
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« Reply #5 on: October 11, 2010, 09:05:35 PM » |
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Interesting. My installer said that 20 tubes would be fine. He even said that it was heat dumping through the rad the other day...
name and shame? I would put at least 50 47mm tubes on that, and would be happy with 70 or more if an adequate heat dump was installed. |
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changing the world, one roof at a time ..."We can't be B&Q astroturfers. That's one conspiracy theory too far. You should cut down on the pot." - Wookey |
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KLD
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« Reply #6 on: October 11, 2010, 09:22:03 PM » |
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A 20 tube 47mm panel will produce a peak output of around 550W. Let's be optimistic and say you got 550W output for 6hours on both days. So, that 6.6kWh harvested. Put these 6.6kWh into a 250L store that starts out at 20°C, where do you get to? With a heat capacity of water at 4200 (J/L °C) or 1.17 x 10^-3 (kWh / L °C) I calculate a temperature rise of about 22°C. Subtract a little heat loss from the system, and 36°C sound perfectly feasible.
As all the others said: whoever sold you 20 tubes with a 250L store didn't inform you honestly about the possible / expected solar gains. Name and shame?
Klaus
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wookey
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« Reply #7 on: October 19, 2010, 05:28:12 AM » |
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Peak output should be more like 950W? 550W might be an avarage output over the day?
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Wookey
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Ian_HJ
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« Reply #8 on: October 19, 2010, 10:40:33 AM » |
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Does anyone know if there is a chart, guide, spread sheet out there that gives a quick reference to how many tubes of what size you need for what size cylinder (TS) with ideal South facing ?
Ian
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Tigger
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« Reply #9 on: October 19, 2010, 10:46:20 AM » |
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Ian_HJ, if you take a look at this link you'll see some info from Antman about sizing/tube qty etc. http://www.navitron.org.uk/forum/index.php/topic,276.msg1526.html#msg1526Ian. |
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30 tubes, south facing gable wall (Navitron Fornax Trial System). Hunter Herald 8, integrated boiler hooked up with Oil Boiler via Dunsley Neutraliser. Scrounging fire wood wherever possible  |
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brackwell
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« Reply #10 on: October 19, 2010, 11:31:35 AM » |
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I would just like to point out that with in reason the no. of tubes v tank size is not critical from the aspect that the available energy is being captured. Therefore it is a question of tank size v hot water usage.
With a small tank you will have hotter water but run the risk of running out.
With a large tank you will have to add additional heat in order to gain satisfactory temp. which is wasted if not used before the heat losses get it!
From my experience 5L per 47mm tube is about right so if you need more hot water than this you need more tubes as others have said. However i am convinced that to have the back up of feeding this hot water through a inline heater be it combi boiler or electric is the ultimate.
In my case i use the captured energy in my solar tank to prefeed the hot water tank.
Ken
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KLD
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« Reply #11 on: October 19, 2010, 09:58:12 PM » |
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Peak output should be more like 950W? 550W might be an avarage output over the day?
Wookey, In our system, 40x 47mm ET feeding into a 210L thermal store, I get a peak power of 1.2kW. See attached plot. The 550W is a quote from the SPF site.Klaus |
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« Last Edit: October 20, 2010, 12:11:09 PM by KLD »
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billt
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« Reply #12 on: October 20, 2010, 09:46:31 AM » |
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The SPF report (scf728) gives the peak output of the Navitron SFB20 (20 x 47mm tubes) as 980W at 1kW/sq.M. irradiance.
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KLD
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« Reply #13 on: October 20, 2010, 12:10:09 PM » |
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Billt, You are absolutely right!  Thank you for spotting that! Sorry for the error. If only I knew where I got that figure from then... Anyway, edit the previous post to reflect this correction. Even worth, now I need to go hunting through my system to find the missing 400W per panel  Klaus |
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nrg710
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« Reply #14 on: October 26, 2010, 07:06:48 PM » |
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Interesting replies. Particular thanks to KLD for the calculations.
I won't name and shame my installer because he pretty much arrived at the same conclusion. Also, we spec'd my system on the basis that it was just me living in the house, and I'm away for long periods of time. In other words, the 250L TS has LOADS of time to heat up between usages. I don't use huge amounts of hot water (I tend to shower rather than bath. Add to that 1 bowl of washing up water a day and maybe 1 washing machine load every week, and it doesn't amount to a lot). So I still think that the 250L TS was a good decision.
20 tubes, though, maybe that was a mistake. Can always add to them though, and I will definitely look at doing this.
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