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Author Topic: Setup and tuning a new Solar Thermal system  (Read 1581 times)
Westie
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« Reply #15 on: June 29, 2018, 01:37:11 PM »

I is an engineer. I can read'n'rite proper me  Grin
😀😀yousa (not so) dimengineer.
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4kwp south facing array  SMA 4000TL grid connected.  2x30tube Navitron solar thermal panels (east/west). Arada 5kw S/C WBS. 25000Ltr underground rain water tank. KTM E-Bike  Cool
finnercy
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« Reply #16 on: June 30, 2018, 03:08:06 PM »

cheers for that info, as an experiment I am going to try the sensor in the last panel to see if it makes any difference.
The panels are in parallel BTW.
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Jaspi Econature 40 Log boiler, Laddomat Loading unit, Jaspi 1800L oval tank, 6KW backup immersion, Automix servo controlled heating temp mixer, Navitron 4 x 2.5M flat plate collectors, Navitron pumping station and STDC3 controller, feeding 24KW solar coil in Jaspi accumlator.
finnercy
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« Reply #17 on: July 02, 2018, 01:53:07 PM »

right I tried another senor in the last panel and give or take a few degrees it was the same as one I have in the first one. I have reduced the trigger temp to be the tank senor + 8 degrees, noticed again the pump start at an indicated solar sensor 68 degrees (tank at 60c) then temp of the solar senor ramped up to 82 degrees before it stabilized and started to drop.  I did hear some gurgling noises around the pump, leading me to believe there may be  air in the system. As the sensor position is in the top of the panels I am thinking it could be air trapped round the sensor pockets insulating them and causing the under reading. Either that or it is the panel design.  Will have a go bleeding it again, thought I had all the air out but guess not!
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Jaspi Econature 40 Log boiler, Laddomat Loading unit, Jaspi 1800L oval tank, 6KW backup immersion, Automix servo controlled heating temp mixer, Navitron 4 x 2.5M flat plate collectors, Navitron pumping station and STDC3 controller, feeding 24KW solar coil in Jaspi accumlator.
kristen
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« Reply #18 on: July 02, 2018, 06:02:07 PM »

I always set the temperature to switch on at 5 degrees above tank and off at about 2 otherwise you will  not be heating the water most of the time.

I would look at the temperature drop from panel, through store, back to panel, because at 5M each way there will be some cooling ... and if the panels cool by too much (first thing in the morning / more so in mediocre conditions Spring / Autumn) the thermostat will trash and each Off will further allow the water in transit to cool, such that you may not get any/much hot stuff to the accumulator.

You might want to reduce differential in Summer and increase again Autumn-through-Spring.

Quote
That is a huge tank and it will be extremely difficult to get the water really hot because at high temperatures the tank losses are probably 5 kw.

Yeah, we started in similar vein. 6 x Navitron ET panels and 2,500L accumulator (which was 50% of the winter central heating accumulator-pair). DHW created by a pair of coils, low (pre-heat, if any heat low down, but when there is reduce stratification effect) and high "finishing" coil.  Most of the time the accumulator got to 65C during the day, but fell to 60C by tomorrow (baths etc.) so a cloudy day was borderline.

The solution was to install ad dedicated DHW (solar) tank and prioritise heating (both boiler and Solar) to heat that first.  Probably only takes a few minutes early morning mid-summer Smiley but on marginal days it does the job perfectly. The old pair of coils in accumulator are preheating the mains inlet to DHW tank, so quite a lot of the time replenish water is arriving into DHW tank at at 60C from accumulator Smiley

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I hope you do not have a circulating pump sending water to all the hot taps in the house because that will loose all the heat you generate

When we moved in here the DHW system had a gravity loop, "pumped" by towel rails in the bathrooms. Previous owner had the boiler on 365/24/7. Having put boiler on an E7 timer the DHW tank was stone cold by mid morning ...

... we put a circulation pump on the loop and that sorted that problem. Initially we used a pressure-drop switch (turn on tap, turn off, wait, then run hot water) but it came on for all sots of reasons. Flushing a loo ... water board doing something weird in the middle of the night [I only knew that because everything was bristling with logging sensors] ... so we replaced it with switches. Can take 5 whole minutes to get the far end of the loop warm though. probably worth putting a 1kW electric "tube" heater on the loop (rather than cooling DHW tank with the return)

Home Automation is a wonderful thing. Button by the bed now labelled "hot water", just reach for that in the haze of waking up and water at the tap is toasty by the time I stumble into the bathroom Smiley

when the threshold to start the solar pump is reached and the pump starts, the senor temperature increases by a good 15C  and it takes a few minutes running before the temperature starts to drop down to a stable level.

We had something similar. In our case it was because the installer had plumbed it wrongly (and what should have been a return was going back round the loop). We had three rows in parallel each with two panels in series, with an option to go down the middle first and then back through the other two rows. The one in the middle was looping hence the sensor never saw any cold water ...

So don't rule out "plumbing" ... until you do Smiley

Moving the sensor to the last panel is a possibility

I would want it at the outlet end, not the inlet end (of anything in series) - where it will cool more quickly as cooled water arrives from accumulator.  At the outlet end it will keep the pump on until the last bit of hot water has left the panels.  I'm sure that's obvious ... and depends on the Series / Parallel configuration you've gone for.

Stick some logging sensors on it. Makes it much easier to make decisions. I put a couple of dozen on mine (1-wire things), haven't used them in years as I now know how it behaves and the novelty of looking at graphs has worn off ...
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finnercy
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« Reply #19 on: July 03, 2018, 03:53:02 PM »

Your comments on having a dedicated DHW tank are right on the money.
I have two issues with the current setup:
1.  I have to heat a huge tank when all I want is a little hot water
2. Takes a couple mins of running tap first thing to get hot water as the location of my boiler shed/shape of house mean long pipe runs.

So I was already thinking of putting a small very well insulated DHW tank in my attic,  feeding it from what used to be my hot water source (via thermal accumulator coils) and having an immersion in small tank there to cover any short fall.  That solves both my issues but does mean I would be using a small amount of "lecky"  when the sun dont shine Smiley


Cheers
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Jaspi Econature 40 Log boiler, Laddomat Loading unit, Jaspi 1800L oval tank, 6KW backup immersion, Automix servo controlled heating temp mixer, Navitron 4 x 2.5M flat plate collectors, Navitron pumping station and STDC3 controller, feeding 24KW solar coil in Jaspi accumlator.
kristen
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« Reply #20 on: July 03, 2018, 04:17:36 PM »

a small very well insulated DHW tank in my attic

Dunno what your layout is (so maybe this is moot), but my pipes from Solar Thermal go to Accumulator, and putting my DHW (Solar-type) tank right next to it made the plumbing easy, plus I preheat top-up water going into DHW tank (from accumulator).

If, say, Accumulator was in one place, and DHW in loft, then the switch-over, when DHW reaches temperature, will presumably have a slug of cold water in the pipe, and perhaps? the pre-heat opportunity will not exist?
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finnercy
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« Reply #21 on: July 03, 2018, 04:21:45 PM »

just to follow up on the plumbing question, I am confident it is plumbed correctly as I was working off the documentation provided with the panels:


<----to Accumulator-----P1(top)-----P2(top)-----P3(top)-----P4(top)--Air point
>----from pump---------P1 (bot)----P2(bot)------P3(bot)---- P4(bot)--blank plug
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Jaspi Econature 40 Log boiler, Laddomat Loading unit, Jaspi 1800L oval tank, 6KW backup immersion, Automix servo controlled heating temp mixer, Navitron 4 x 2.5M flat plate collectors, Navitron pumping station and STDC3 controller, feeding 24KW solar coil in Jaspi accumlator.
kristen
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« Reply #22 on: July 03, 2018, 04:52:09 PM »

Mine are in a different arrangement now (and not relevant), but back then I think mine were plumbed


<----to Accumulator-----P1(top)-----P2(top)-----P3(top)-----P4(top)--
                        P1 (bot)----P2(bot)------P3(bot)---- P4(bot)--<----from pump-------<-


I wonder if your arrangement short-circuits favouring P1(bot) flow to P1(top) and the flow from P4(bot) to P4(top) is slow (and therefore gets hot)

But take the opinion from folk that have way more of a clue than me
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Westie
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« Reply #23 on: July 03, 2018, 10:40:03 PM »

Finnercy's plumbing isn't self balancing, Kirstens is.

Flow will always take the path of least resistance, in Finnercys system the resistance to flow increases as the pipe run length increases for each panel. Kirstens plumbing equalises the pipe run lengths so they're the same for each panel, so the flow rates through each panel will be equal.
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4kwp south facing array  SMA 4000TL grid connected.  2x30tube Navitron solar thermal panels (east/west). Arada 5kw S/C WBS. 25000Ltr underground rain water tank. KTM E-Bike  Cool
pj
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« Reply #24 on: July 04, 2018, 01:10:46 PM »

IMHO...
The connection across the bottom of the panels, and also across the top, is quite a large bore, so there will be little dynamic pressure loss between the first and forth panels, so I don't think the different layouts will make much difference to the flow through the panels. In fact, Navitron's own data sheet says up to six panels can be connected as per Finnercy's layout.
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kristen
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« Reply #25 on: July 05, 2018, 07:50:04 PM »

Presumably the top of all P1...to...P4 have a sensor pocket , so it would be possible to put a thermometer in there and turn the pump off for a couple of minutes to give everything time to heat up, and then after turning the pump back on see whether the temperature of P1, P2, P3 and P4 fall at the same rate, or if P4 falls slower (and "slow enough" to be a potential problem)
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