Pipe diameter of the solar interconnect ?

[Pip]

Hi

I am just in the early stages of research and planning my home installation, and have been monitoring this forum, and found it to be a good resource.  So far I am feeling that I will most likely start by putting in a vacuum tube array to heat hot water.

I am currently decorating the attic of our house, and need to pre-empt any major work by putting the pipe run for the solar collectors down from the roof to the, or at least close to the cylinder in advance.  I have some plumbing heating and engineering background, but would value advice as to what diameter pipe I should use to interconnects the array to the heating coil (what ever guise that will end up to be).

I have heard that it is best to keep the volume of liquid in the interconnect as low as possible to keep the thermal inertia of the transport loop as low as possible.  But as with any energy transfer, I understand that liquid volume and velocity are directly related to how much thermal energy can be transported in any given time.  Looking at the spec sheet, I see the terminals on the manifold are 22mm, so I guess that is the maximum diameter I can use, however for inertial reasons, and for ease of routing, I would like to keep the diameter of the interconnect as low as possible.  One other factor I should mention, is the distance from the would-be collector panel to the cylinder.  Our house is about 10 metes high, with the other routing limitations the pipe run lengths are likely to end up being 15 meters each way.

We currently have a 200ltr unvented mains pressure tank, and currently I expect to put between 20 – 30 tube array in.

So in summary, what dia pipe should I use, and what will the overall diameter end up being with the high temp insulation over it. (Sorry I couldn’t find the dimensions on the Navitron site).

Thanks in advance.

Pip

[NickW]

Pip

Between the solar panel and the tank I reduced the pipe down to 15mm using 22-15mm copper reducers. It hasn't caused any problems with the pump - which runs at its lowest speed anyway. Reducers are fairly cheap - 11.50 for 10 in screwfix direct. This can be offset against savings in pipe - 15mm pipe is about half the price of 22mm pipe.

Nick