Sat, 15 Aug 2026 23:10:25 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9627&Focus=157601#Comment_157601 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9627&Focus=157601#Comment_157601 Thu, 27 Sep 2012 01:03:01 +0100 Jeremy S Hi,

so, here's how I understand things:
1) evacuated tube collectors (ETC) maintain efficiency at higher inlet temperatures;
2) flat plate collectors (FPC) are more efficient at low inlet temperatures;
3) ETC are more expensive than FPC by both per joule and per sq_m.

what's to stop us trying to optimise using the benefits of both in a mixed system?

I'm thinking: 6-8sq_m of FPC in series with ~2sq_m of ETC.

Is there any technical constraint that would prevent this being viable? (apparently the MCS certificate can't handle it but that's bureaucracy, eh?)

best wishes - Jeremy]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9627&Focus=157602#Comment_157602 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9627&Focus=157602#Comment_157602 Thu, 27 Sep 2012 06:49:08 +0100 SteamyTea I am not sure if it is efficiency that varies really, more to do with losses (which can be calculated as efficiencies I suppose depending on what you measure).
The question is why would you want to do this if you have 10m^2 to play with.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9627&Focus=157604#Comment_157604 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9627&Focus=157604#Comment_157604 Thu, 27 Sep 2012 07:17:35 +0100 tony
ETC are better at collecting in the colder months]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9627&Focus=157609#Comment_157609 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9627&Focus=157609#Comment_157609 Thu, 27 Sep 2012 08:00:23 +0100 SteamyTea https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9627&Focus=157628#Comment_157628 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9627&Focus=157628#Comment_157628 Thu, 27 Sep 2012 09:51:15 +0100 Ed Davies
To operate with the large differentials needed for significant differences between the flat plate and ET temperatures would require a low flow rate. I suppose that's quite possible and would save a bit of pumping energy but would imagine it's a bit trickier to control. E.g., does the viscosity of anti-freeze change much with temperature?]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9627&Focus=157633#Comment_157633 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9627&Focus=157633#Comment_157633 Thu, 27 Sep 2012 10:10:24 +0100 fostertom 1) heat pipe collectors maintain efficiency (somewhat) at lower outside air/radiant scenery/sky temperatures;
2) flat plate collectors (FPC) are less efficient at lower ditto because more succeptible to simultaneous re-radiation loss to cold scenery/sky;
3) evacuated tube (non heat pipe) collectors (ETC) are just as succeptible as FPCs to simultaneous re-radiation loss, but a bit less succeptible to simultaneous conduction loss to cold outside air.

1)'s efficiency is relatively unaffected by thermofluid temp
2) and 3's) efficiency rises sharply as thermofluid temp is lowered - but how low can that go and still be useful?

I have a hunch that 2) and 3) would be more efficient, in mid winter, that 1), provided thermofluid temp were lowered to say 22C. Our theoretical calcs show efficiency of 60% in mid winter, with suitably optimised (but simple) FPC, at that thermofluid temp. At 60%, with big (but simple) collector, insolation is adequate to space-heat a near-PH building by solar alone, right thro Dec/Jan (depending on horizon obstructions).]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9627&Focus=157634#Comment_157634 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9627&Focus=157634#Comment_157634 Thu, 27 Sep 2012 10:13:13 +0100 SteamyTea Our favourite place has the answers:
http://www.engineeringtoolbox.com/ethylene-glycol-d_146.html]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9627&Focus=157643#Comment_157643 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9627&Focus=157643#Comment_157643 Thu, 27 Sep 2012 11:28:03 +0100 Ed Davies https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9627&Focus=157690#Comment_157690 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9627&Focus=157690#Comment_157690 Thu, 27 Sep 2012 15:45:35 +0100 SteamyTea