Record High Temperature for my System

[Ivan]

11 Aug 2007 - end of day temperature of 77.6°C in my 250litre hot water cylinder (30 tubes 70mm single walled panels, on long piperun (16mx2)). The highest I had seen previously was 74°C.


Ivan

[WyeSolar]

3rd Sept weather couldn't have been better.

30 x 47mm tubes facing SE.
Pipes are 15mm with 19mm thick Armaflex with 16m to the collector and 14m back.
210Ltr unvented Megaflow with ultra tight bespoke twin retro fit coils (first centrally mounted, second in the bottom).

Start of day tank read 16 C (S2) and 39C (S3)
5pm SMAX shutdown with 75 C (S2) and 76 C (S3) !!!!

Collector then maxed out at 104 C before going into shadow at 5:15pm

This is my idea of perfection as I only fitted my system 5 days ealier

All good stuff,

Uncletig

[Ivan]

Sounds excellent!

Were the retro-coils provided by Navitron? I assume you have flow into the top one and out of the bottom one. Where have you fitted S2 sensor?

[Flamethrower_]

Hi Uncletig,

Where did you source your retro coils for your Megaflow ? extremely interested !

Regards

Rob

[WyeSolar]

Hi Ivan - Yes I got my retro fit coils through Navitron! Where else would I go?

I specified the exact sizes I needed and supplied you (John actually) with the blanking plates for your guys to make them up. Well pleased.

Flow enters into the middle of the cylinder then into the bottom (both horizontal).

I've positioned S2 about 6" from the bottom.

Attached picture shows emmersion coil locations and position of S2 (behind black duct tape patch)

Rob, If you let me know your Megaflo model I can help you specify the correct coil length(s) for your cylinder. Also I have one blanking plate that you could use to make up a coil - if its right for your model.

Today sun mostly hiding behind clouds but still got 210Ltrs from 24C to 56C !

Still good stuff

Uncletig
(Now AKA WyeSolar)

[Ivan]

9 February 2008

Nice, sunny day, approx 12C at hottest. My 260litre cylinder base temperature started at 15C, and finished at 42C. The wood stove boosted the top half of the cylinder from 43C to 60+ later in the day.

My system has long pipework (16m of 15mm each way.....before you tell me that I should be listening to my own recommendations of 10mm pipework, please bear in mind this is one of the ways I found out!!). The long pipework virtually switches off solar gain from about Mid October to Mid February, so it looks like we are starting to come online again!

[Flamethrower_]

Uncletig,

By chance this morning I saw your reply to my request (20/9/2007) Yes I'm still interested in retro coils for various megaflows got family interested in solar and they all have different size megaflows and it becomes a expensive project to go to a Solar MegaTech so the retro coils would be the way to go! What is the performance like?

Regards

Rob

[O MidKnight]

15C to 42C Not bad at all Ivan.

I sometimes wonder if my 54 metres of 10mm pipe and 315 metres total of integral tubeways in the flat plate panels are too restrictive. Including some 22mm header pipes, that makes it a distance of over 375 metres the heat transfer fluid has to travel

[Ivan]

O'Midnight,

If you have that length of pipework in series, and it seems to work well, it's a real vote of confidence for 10mm pipework. I've noticed that most installers fitting german supplied equipment tend to fit flowsetters, to restrict the flow rate. I still haven't found a justification for this, but if they are all reducing the flow rate of 15mm systems, then it suggests that 10mm might be closer to their 'ideal' flow rate conditions. The more I see of 10mm installations, the more it appeals to me. Shame that I'd have to rip up an attic floor to fit 10mm to my system, otherwise I'd give it a go. Having said that, almost all of my pipework is in living space rather than cold attic, so the pipe heatloss I experience in winter will be mostly contributing to spaceheating.

Incidentally, today, 10th February, also sunny, but not quite so good as yesterday, managed 36C at base of tank. (top of tank figure is meaningless as it would be heat generated by woodstove last night). Like O'Midnight, I don't get any sunshine on my panels until around 11.30am.

[David]

I am waiting with interest to see how my 10mm pipework behaves in summer. No problem in winter and theoretically it should be fine in summer.

As well as reducing heat loss it is much easier to install. Thread on the insulation, tape joints in the insulation together and that's that. A few clips to keep it all in place.

[Paulh_Boats]

David,

10mm is fine. In a test my 30 tubes went from 100C down to 60C with 10mm + retro coil, at 1pm on a hot summers day.

You can put flow and return inside 15mm Armiflex which saves time and space.

-Paul

[dhaslam]

What is the collector  size limit  for 10mm pipe, could it take two 30 tube panels (10 metre pipe run approx) ?

[wookey]

You run up against flow-rate limits somewhere around there. See http://c-zero.co.uk/pmwiki/pmwiki.php?n=Main.PipeSizingCalculations

60 tubes implies a flow-rate somwhere around 6l/m to give a temp rise of 10C. In 10m of (straight) pipe that is a pressure loss of 7.5psi in 10mm (or 0.8psi in 15mm).

So you need a pump that can deliver 6l/m at 8psi drop to use 10mm pipe. A pegler TC5 on speed 2 will just about manage this. Low-power pumps will be nowhere near.

If the pump cannot deliver the flow-rate then the temp-rise across the panels will be higher. I'm not sure how much of a problem this is, but higher temp in the pipe from the panel increases losses. Optimising flow-rate and panel temp rise is actually quite a tricky question, especially if you also include pump energy use. I know ericw has thought about this. Anyone worked out how to do the sums (or the practical experiments on existing systems)?

[Paulh_Boats]

Wookey,

The dominant factor is the ratio of energy lost in the pipes to energy absorbed by the heat exchanger. That factor defines the steady state heat loss and you can calculate it with 4 temperatures measured either side of manifold and coil.

Changing the flow rate from speed 1 to speed 2 made little difference to my 30 tube system, short 10mm pipes, retro-coil. I was getting less than 1C drop along pipes, manifold 5C to 10C above tank depending on sun strength.

However the transient heat loss is heavily dominated by the volume of water in the pipes. After a cloudy patch the water in the pipes must be heated up before useful heat gets into the cylinder. Therefore in marginal weather or winter the volume of the pipes is critical.

So you want:
1) Shortest, thinnest pipes possible.. ideally zero volume that would produce zero transient heat loss in poor weather (e.g. the average day  )

2) A heat exchanger that absorbs at least say 20 or more times the heat lost through the pipe insulation. That keeps steady state losses below 5%. Its relatively cheap and easy to add more pipe insulation around the Armiflex.


There is a point when the flow rate is too low but there is plenty of evidence that 10mm and a speed 1 pump is ok. Bear in mind some people used to say you needed 22mm... then a lot said you needed 15mm.....now its 10mm.....but microbore central heating uses 8mm on medium sized radiators!

cheers
Paul

[dhaslam]

Thanks,    I think I will go with 10mm. Since we only have about 60 sunny days and 300 cloudy days each year  the smaller amount of water to heat makes sense.   
(Replaces previous post lost in changeover)