In another thread: http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=11497&page=1#Item_5

Posted By: davidfreeborough: “Perhaps a discussion for another thread, but do you have any details on the solar warm air collectors? Will they be connected to the MVHR system? Have you seen this?

http://www.cibse.org/content/Groups/Building_Simulation_Group/Modelling%20the%20Aerogel%20Trombe%20Wal_A%20solar%20heated%20collector%20storage%20wall.pdf

David”

Sketch of the house for orientation: http://edavies.me.uk/2012/01/house-sketch/

Basically, my thinking is that the gable ends need a ventilation space and cladding anyway. Making the cladding be twin-walled polycarbonate and the back side of the ventilation space be black with a black absorber will need only a fairly small incremental cost. These gable ends will face east and west and will get very little sun in winter but should get some in spring and autumn giving a bit of a boost to the proper collectors on the south roof.

Yes, they will be connected into the MVHR system somehow though that's a matter for experimentation and may well change on a seasonal basis. The MVHR will be in the loft of the main part of the house adjoining the porch/greenhouse with ducting just below the ridge through to the main bedroom, which is at the east end. I'm thinking that when it's warm enough air from the east gable collector would be mixed into that.

Air from the west end collector on the greenhouse would either go to warm the greenhouse directly or be fed into the input side of the MVHR.

No, I hadn't seen that article about aerogel on Trombe walls. I'm far from convinced about the Trombe wall idea (and direct solar radiation onto thermal mass in general) but if anything could make it work then an aerogel layer would, I suppose. Bit expensive for an experimental idea on a sub-optimally oriented wall, though.

Posted By: Chris P BaconHave you any way of accessing how much sunlight will fall on the gables in the winter time Ed?

As you say, I could use PVGIS but I've basically just assumed zero for actual winter time. Spring and autumn should give some, though, meaning that heat which would otherwise be needed in those seasons to feed the thermal store can help with the house and/or greenhouse.

Posted By: Chris P BaconSo If you are going for decent U values I can't see solar air being of much addition you won't need it in Autumn and Spring.

Absolutely. These solar-warm-air collectors are at most an ancillary and a bit of an experiment. Frankly, if the planners had objected they'd have been something I was willing to give up on without too much of a fight but they seem quite mellow about the idea. Still, delaying the first frost in the greenhouse and the like seem like good uses.

Its back to the old nutshell of what you really need is short term storage to tide you over the dull spells in Winter.

Yes, the 10 m³ thermal store fed by solar thermal and any excess PV is the main story. Extension of the system would probably be a small turbine (Futurenergy 1 kW is what I have in mind) followed by maybe more batteries or maybe more PV, not more solar warm air.

If the slightly warmer exhaust air from the MHRV goes into the greenhouse it's a net win, though. You also need to think about the absolute humidities of the airflows. All stuff to experiment with.