Winter optimised solar to drive underfloor heating - many urgent questions

[billt]

For perspective, that's the annual heating requirement for 87 m² of Passivhaus.

And, without knowing more system details, it's difficult to dismiss the idea, supported by dhaslam's figures, that quite a bit more heat would be available at low temperatures.

Unfortunately my house is not a Passivhaus, though I've done my best with insulation.

Water temperature has a minor influence on energy extraction, unless the pipe insulation is poor. There was an excel spreadsheet on the Navitron site that let you calculate the effect of various levels of insulation that was very enlightening, but I can't find it on the site now.

In the winter my the 120 x 58mm tubes were feeding a very well insulated 200l solar cylinder; when that got to 63 C the output was switched to the 2500l Akva thermal store. Controlled by a Resol E.

Here's my data for January. You can see that there is a good correlation between sun and harvested energy, and no correlation between water temperature and harvested energy.

[djh]

My 120 58mm tube system produced 1314 kWhr from the 15th of October 2010 to the 31st of March 2011, ...

For perspective, that's the annual heating requirement for 87 m² of Passivhaus.

Indeed but its perhaps worth adding that it would still need a very big store to use it for that purpose. The storage is the tricky bit, not so much the collection.

[EccentricAnomaly]

Billt, many thanks for that data. It's nice to see information which hasn't been averaged out of all usefulness. A few quick questions:

1) Can you confirm that the "power (watts)" column should really be titled "energy (watt·hours)". I think it must be but it's worth checking.

2) How do you measure insolation? Have you got a separate meter? What's its orientation (and what's the orientation of your panels, for that matter)?

3) What period is the average insolation averaged over? It's too high to be over 24 hours but it's not obvious what shorter period it would be. Sunrise to sunset? The time the pump was running? The time the insolation meter detected any insolation?

[wookey]

Duncan - it's pretty clear now that you are not a spammer. Try names, rather than links,  and the spam police might let us have a meaningful conversation. Failing that I suggest you try again on the Green building forum which is (somewhat) less trigger-happy (a link-full first post will still generate opprobrium).

It _is_ possible to collect useful solar heating in the shoulder seasons in the UK, but as many have pointed out it's not easy. This concept works a great deal better in places like Austria which are much further south and have sunnier winters.

But people are making systems that store summer heat for use later in the year. Check out Viking house's website and 'Tony's House'. Both of those are passive houses though. It really is largely futile in the UK unless you have very good insulation levels. You talk about 180mm of cork, which isn't bad (what U is that overall?), but if it's a retrofit then it does depend how well you've dealt with thermal bridges as well as plain insulation levels.

Did you mean consolar for the large expensive tank? I'd agree with others that flat plates in winter are pretty-much useless - only vacuum tubes will be any use (although it is true that central European combi-systems usually flat plates). If you haven't read it already take a look at the papers here:  http://www.elle-kilde.dk/altener-combi/dwload.html which has lots of good stuff. There have been other IEA solar programmes which include a lot of useful research, including practical details on how to build systems that actually work.

The eningeering and design details really matter where it's relatively marginal such as in the UK.

[billt]

1) Can you confirm that the "power (watts)" column should really be titled "energy (watt·hours)". I think it must be but it's worth checking.

2) How do you measure insolation? Have you got a separate meter? What's its orientation (and what's the orientation of your panels, for that matter)?

3) What period is the average insolation averaged over? It's too high to be over 24 hours but it's not obvious what shorter period it would be. Sunrise to sunset? The time the pump was running? The time the insolation meter detected any insolation?

1- Yes, sorry - it should have said watt hours.

2 - I use the Resol CS10 sensor. I've no idea how accurate it is, but it seems to be consistent, which is good enough for me. It's aligned in the plane of the panels so
the readings aren't comparable to a pyranometer, which I believe should be mounted horizontally. The panels are 15 degrees W of S and at an angle of about 50 degrees, to try and improve the spring and autumn output.

3 - It's the time that the CS10 detects any insolation. Seemed to be the simplest way and should have the virtue of a reasonable degree of consistency. I suppose it would probably be better to do a 24 hour average, but that would make the winter figures much worse than they are already!