Green Building Forum - Solar warm air collectors Mon, 24 Aug 2026 07:54:38 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 Solar warm air collectors https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=11502&Focus=191034#Comment_191034 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=11502&Focus=191034#Comment_191034 Fri, 06 Dec 2013 13:30:10 +0000 Ed Davies 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.]]> Solar warm air collectors https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=11502&Focus=191036#Comment_191036 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=11502&Focus=191036#Comment_191036 Fri, 06 Dec 2013 14:08:40 +0000 Chris P Bacon
Maybe you could look at 1m2 of PV mounted vertically facing east or west in PVGIS and see what the output would be in the winter months?

I think you are building further north than I (55.3 N) and I never see the sun in the east or the west at this time of year it effectively rises East South East and sets West South West.

Our house is not optimised for solar gain the rear faces South East and I have been really surprised at how a few hours of strong sunshine can raise the temperature downstairs from 20ºC to 22ºC so I am sure that your house which is far better optimised should see a great effect of solar gain.

Makes me consider building a sun space along the back of the house to harness more of the solar gain although having said that we really don't need much more heat, I put an energy monitor on our MVHR unit earlier this week to measure how much the electric after heater is drawing and it has so far been consistent at around 5kWhrs per day to maintain at least 20ºC indoors when it has been around 4ºC outdoors.

[edit] We are also putting in around 1.5kWhrs per day via electric UFH in the upstairs bathroom and the pipework to the hot tank hasn't been insulated yet so that is leaking quite a bit of heat into the laundry room.]]> Solar warm air collectors https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=11502&Focus=191038#Comment_191038 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=11502&Focus=191038#Comment_191038 Fri, 06 Dec 2013 14:22:40 +0000 Ed Davies 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.]]> Solar warm air collectors https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=11502&Focus=191042#Comment_191042 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=11502&Focus=191042#Comment_191042 Fri, 06 Dec 2013 15:26:40 +0000 Chris P Bacon Thinking about it, on the sunny days we couldn't use any more solar gain without over heating the house and obviously on the dull days we get nothing. So 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.

Its back to the old nutshell of what you really need is short term storage to tide you over the dull spells in Winter.]]> Solar warm air collectors https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=11502&Focus=191045#Comment_191045 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=11502&Focus=191045#Comment_191045 Fri, 06 Dec 2013 16:20:23 +0000 Ed Davies 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.]]> Solar warm air collectors https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=11502&Focus=191046#Comment_191046 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=11502&Focus=191046#Comment_191046 Fri, 06 Dec 2013 16:22:25 +0000 davidfreeborough Posted By: Ed DaviesAir 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.I guess you know, but for anyone else who's reading this: adding heat to the MVHR intake will just raise the outside air temperature seen by the heat exchanger, thereby increasing the MVHR exhaust temperature. So for a 90% efficient heat exchanger, 10% of this heat will make it into the house & 90% will go out of the exhaust.

For the project linked above, they put the solar air collector in the return path from the extract terminals to the MVHR unit, i.e. on the house side of the heat exchanger. This avoids having to pass the air supply through the solar air collector & instead uses the MVHR heat exchanger to indirectly heat the supply air.

Air valves were used to bypass the solar air collector when not providing useful gain. This presents an interesting control problem as its not straightforward to predict from the collector static temperature how much heat will be available when air is passed through it. So some kind of sampling control system would be required to check the differential temperature & open the bypass when some limit is reached.

David]]> Solar warm air collectors https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=11502&Focus=191051#Comment_191051 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=11502&Focus=191051#Comment_191051 Fri, 06 Dec 2013 17:06:42 +0000 Ed Davies