Sorry, but what's the height of the system got to do with anything?

Posted By: wookey
If you do pick 10mm copper remember to buy inserts for all compression joinst otherwise you'll regret it...

posted by: Borfin
Will the insert (which will reduce the bore at the fittings), have any impact?

The inserts go into the compression fitting around the outside of the pipe so they dont reduce the effective bore of the pipe.

Where at all possible dont use compression 90'bends as this adds a lot to the resistance of the flow. You can get very cheap 10mm pipe benders that give a radius of about 50mm.

Posted By: borpin...............Ah, Ok. All inserts I have ever used (including plastic 10mm) went inside the pipe (hence insert). Cheers.

I guess OUTsert's then Brian.

Posted By: joe90sorry no! they are inserts for the fitting, you put them in the compression fitting then insert the pipe. They effectively make the OD of the pipe up to the ID of the fitting.

Ah OK I'm with you. I would call that a reducer as it reduces the dia of the fitting to suit the pipe. Used them years ago in my Dad's house that had a microbore system and some was 10mm and some 8mm IIRC. Most fittings were 10mm so we used these reducers for the 8mm pipe.

<blockquote><cite>Posted By: borpin</cite>
Anyway, what pressure / temperature is needed for Solar installations? </blockquote>

UK solar systems seem to run at around 1 to 2 bar from what I've read. The boiling point of 50% glycol solution is around 107 deg C at atmospheric pressure, but this would increase under pressure to be around 120 to 130 deg C at 2 bar. From what I've read, solar collectors tend to be self-limiting in temperature to some degree, because the losses increase as the temperature increases. Nevertheless, there is evidence that they can get up to around 200 deg C under extreme conditions.

I'd suggest that it might be risky to use pipe rated to only 114 deg C, as it would seem that there is a fair chance that this could be exceeded.

Posted By: JSHarrisAs wookey rightly says, small bore pipe has a lower surface area, so lower heat loss. By the same token, smooth pipe will have a lower surface area than corrugated pipe, so will have lower heat loss.

It's not just the surface area; it's also the volume. Unless your pump is running continuously, there is a slug of hot water in the pipe that cools down when the pump stops. And a [the same] slug of cool water that runs through the tank heat exchanger when the pump starts. Both effects waste heat, so minimising the volume of water in the pipe is beneficial.

Posted By: owlmanThe big suppliers PAW, Resol, Meibes all seem to put DN16 fittings on their connecting unions. So I would guess the clue as to which dia pipe to use is there. Perhaps it's because they use standard components, like Grundfoss and Wilo modulating pumps in order to keep the costs of the whole assambly down.

Well they have to choose some size to fit - it isn't sensible to have different models just with different size unions. And for some installations (big ones) you do need bigger pipes, so you need to make sure the flow for those situations isn't restricted. And as has already been described, it's quite easy to reduce from a larger union down to a smaller pipe. So I don't think the union size says anything at all about the best pipe size.

<blockquote><cite>Posted By: borpin</cite>
Surprised in someways that the system does not require to be pressure tested if such extremes can occur.</blockquote>

I think it's normal to fit a pressure relief valve that lets the steam out if it boils, so making it no different to a pressurised hot water system in principle. Presumably this is the way they avoid the need for pressure testing.

Is high temp insulation available for 10mm microbore for this application?

Posted By: borpin..........................Surprised in someways that the system does not require to be pressure tested if such extremes can occur.

It is, as part of the filling procedure,

Posted By: owlman Normally part of the pumpstation, it ejects the glycol into a collecting vessel.

Any idea what pressure this is set to?

Posted By: borpin..............Any idea what pressure this is set to?

Operating pressure depends on the array manufacturers recommendation usuually 1.8 - 2.3 bar. Pumpstation PRVs normally "crack" at 3 bar. When the system is filled and tested it's quite mormal to raise pressure to 6 bar to check joints for weeping and leakage.

I'm not anti microbore wookey I guess I don't really see the point of beating yourself up over only a few metres of pipework, in some cases. I don't know what intensive research has been done to validate the use of microbore in a "holistic" system sort of way. For instance is the research just all about pipework temp losses and fluid transmission, or are these gains perhaps negated by the venturi effect of "choking" down pipework and then opening it up again over and over again. After all the pump, the cylinder coil, the manifold, are all larger capacity/bigger bore. Perhaps PAW, Meibes etc have done their sums and come to the conclusion all in all it's better to use the slightly larger pipe, and keep the flow even. Having said that, "annular " construction flexible SS pipe does have a disadvantage in that it can create current eddies hence the use of slightly larger bore pipewark. The better, some say, is " flexible SS pipe with a " helical "construction but it's harder to find, and I guess it's more expensive. The not inconsiderable advantage as Gotanewlife says and you allude to, is in the ease of fitting. When you're balancing on a roof or awkwardly on your back in a loft trying to thread pipework, undamaged, through a convoluted space you'll quickly realise that pre-insulated, pre- wired pipe is a boon. Microbore soft copper gets it's flexibility from reduced wall thickness 0.7mm as opposed to 0.9mm in normal more rigid microbore, so again as Gotanewlife pointed out the risk of "kinking" is greater. then as joe90 points out there's the insulation, can you get say 20mm wall thickness neoprene for 10mm microbore and once it's on, will you see any kinks in the pipe. Given all that I'm happy to be steered by the pumpstation manufacturers, most new domestic pro installs are done with DN12 or DN16 and I'm happy with that and I've absolutely no complaints about my install.

Posted By: JSHarris...then the volume difference means absorbing an extra 0.03 kWh int the working fluid each time the system starts from cold, or around 11 kWh through the whole year.

That's assuming the system starts and stops once per day. On the more marginal days (which are the ones we care about) it'll probably stop and start many times per day as the cloud comes and goes.

<blockquote><cite>Posted By: Ed Davies</cite><blockquote><cite>Posted By: JSHarris</cite>...then the volume difference means absorbing an extra 0.03 kWh int the working fluid each time the system starts from cold, or around 11 kWh through the whole year.</blockquote>

That's assuming the system starts and stops once per day. On the more marginal days (which are the ones we care about) it'll probably stop and start many times per day as the cloud comes and goes.</blockquote>

But if the pipe insulation is good, would the temperature really change by 60 deg during cloudy periods during the day? TBH I don't know, but would guess that the fluid doesn't have time to change temperature by a lot during the day, particularly for the many times during the year when the air temperature is relatively high, reducing the temperature differential from the 60 deg C all year around simple approximation I used. If anything I suspect my 1% guesstimate is probably on the high side when the whole year is taken into account.

The losses would be a lot higher if bigger pipe was used, though, and I heard mention somewhere of systems being plumbed with 22 mm copper. That would make a much bigger difference, as 10 m would hold around 3.8 l, increasing the loss to maybe 6 or 7 % when compared to 10 mm pipe.

It seems that there's really not much to choose between 10 mm, 12 mm or 15 mm pipe work (accepting that smaller is generally slightly better in most cases), but it looks as if there's a potentially a much bigger loss if using 22 mm pipe.