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UK diy (uk.d-i-y) For the discussion of all topics related to diy (do-it-yourself) in the UK. All levels of experience and proficency are welcome to join in to ask questions or offer solutions. |
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#1
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Today's solar heat
There was such a hard frost last night that the frost-stat on the ch boiler
came on for a short time. There was thick ice on all the open water in the garden and all roofs were white. But it's been sunny today (although cold) and I did three machine loads of washing and we still have a cylinder full of water at just short of 60C. Scoffers can scoff away but we're very happy -it's just a foretaste of what's to come :-) Mary |
#2
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Today's solar heat
Mary Fisher wrote:
There was such a hard frost last night that the frost-stat on the ch boiler came on for a short time. There was thick ice on all the open water in the garden and all roofs were white. But it's been sunny today (although cold) and I did three machine loads of washing and we still have a cylinder full of water at just short of 60C. Scoffers can scoff away but we're very happy -it's just a foretaste of what's to come :-) What sort of panels? I'm contemplating doing something with the old radiators, bus windows, and polystyrene sheet that I've got lying around. Currently I'm wondering how hot you could get with silly (say 5 panes) amounts of glazing, with a system to suck air through the panes. So that light absorbed in the panes is not lost. Also wondering what the possible ratio of a fan assisted panels radiator/panel size is. |
#3
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Today's solar heat
"Ian Stirling" wrote in message ... What sort of panels? A commercial product but self-installed. Mary |
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Today's solar heat
Mary Fisher wrote:
"Ian Stirling" wrote in message ... What sort of panels? A commercial product but self-installed. Mary elaborate :-) |
#5
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Today's solar heat
Ian Stirling wrote:
Mary Fisher wrote: There was such a hard frost last night that the frost-stat on the ch boiler came on for a short time. There was thick ice on all the open water in the garden and all roofs were white. But it's been sunny today (although cold) and I did three machine loads of washing and we still have a cylinder full of water at just short of 60C. Scoffers can scoff away but we're very happy -it's just a foretaste of what's to come :-) What sort of panels? I'm contemplating doing something with the old radiators, bus windows, and polystyrene sheet that I've got lying around. Currently I'm wondering how hot you could get with silly (say 5 panes) amounts of glazing, with a system to suck air through the panes. So that light absorbed in the panes is not lost. Also wondering what the possible ratio of a fan assisted panels radiator/panel size is. Hmm sounds overkill to me. A one metre square panel that I made myself works well enough to give 200 litres plus of water at 80C from around five hours in the sun. Traditional construction of a single panel steel radiator with an aluminium frame, polyurethane insulation, single glazed in 4mm glass. Did anyone see the Dick Strawbridge thing? His solar panel design was utter pants, a double panel radiator using corrugated PVC glazing. |
#6
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Today's solar heat
On Mon, 10 Apr 2006 17:50:54 +0100 someone who may be "Mary Fisher"
wrote this:- But it's been sunny today (although cold) and I did three machine loads of washing and we still have a cylinder full of water at just short of 60C. Excellent. Now the days are longer you should get a fair amount of hot water. Scoffers can scoff away but we're very happy -it's just a foretaste of what's to come :-) Perhaps you should sell hot water to the neighbours in the summer:-) -- David Hansen, Edinburgh I will *always* explain revoked encryption keys, unless RIP prevents me http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54 |
#7
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Today's solar heat
"David Hansen" wrote in message news On Mon, 10 Apr 2006 17:50:54 +0100 someone who may be "Mary Fisher" wrote this:- But it's been sunny today (although cold) and I did three machine loads of washing and we still have a cylinder full of water at just short of 60C. Excellent. Now the days are longer you should get a fair amount of hot water. More than we use, I suspect. Scoffers can scoff away but we're very happy -it's just a foretaste of what's to come :-) Perhaps you should sell hot water to the neighbours in the summer:-) Can't be bothered! They can jolly well get their own systems!! Mary |
#8
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Today's solar heat
Steve Firth wrote:
Ian Stirling wrote: snip Also wondering what the possible ratio of a fan assisted panels radiator/panel size is. Hmm sounds overkill to me. A one metre square panel that I made myself works well enough to give 200 litres plus of water at 80C from around five hours in the sun. Traditional construction of a single panel steel radiator with an aluminium frame, polyurethane insulation, single glazed in 4mm glass. That does seem rather unlikely, unless you're starting from something quite warm. 5 hours * 1.3Kw/m^2 (sunlight falling on top of atmosphere) = 23.4MJ 200l of water has 4400J/K/Kg * 200Kg = 880KJ/K. 23.4/0.88 = 26.6K temperature rise. I'd be astonished if you got a real 20C rise out of it. Your numbers do however work out perfectly for a panel of reasonable construction on mercury |
#9
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Today's solar heat
"Mary Fisher" wrote A commercial product but self-installed. More info please. We are having a new boiler system put in and though we can't afford a whole solar system, can't quite stretch to Jupiter ;-) this year we are specifying a solar compatible dual coil tank with a view to self installing the rest next year. So as we are trying to find out about other peoples experiences a few questions please. What brand/type/supplier/cost please? Did you buy a complete kit or did you self source mix and match? And did you find it easy to fit? TIA Jake |
#10
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Today's solar heat
HI Jake
On Mon, 10 Apr 2006 22:47:39 +0100, "Jake" wrote: "Mary Fisher" wrote A commercial product but self-installed. More info please. We are having a new boiler system put in and though we can't afford a whole solar system, can't quite stretch to Jupiter ;-) this year we are specifying a solar compatible dual coil tank with a view to self installing the rest next year. That's what we did when we moved here 5 years ago. So as we are trying to find out about other peoples experiences a few questions please. What brand/type/supplier/cost please? Did you buy a complete kit or did you self source mix and match? And did you find it easy to fit? My local installer sold me a complete kit (less the copper pipe !) - which came with a pretty comprehensive diagram, and the offer of 'hand-holding' if necessary. It consists of an array of Thermomax evacuated collectors and their header assembly (got the installer to fit that lot on the roof for me and provide pipe stubs through into the loft space). He also supplied the controller and all the necessary brasswork, pump etc. After I'd done the necessary plumbing and wiring for the controller - he came back and commissioned the system for me - took about an hour. Been running fine ever since - with the occasional slight topping-up of the circulating water. Don't really know how much money I saved by doing the plumbing myself - but ISTR that the total kit cost just over £2k. Plumbing wasn't particularly complicated, and the (3) sensors for the controller fitted into metal sleeves (supplied) and the wiring was pre-terminated with plugs - so that was easy. In terms of performance, I've never formally recorded it - but I know that from about May to September we're not needing much input from the immersion heater to get the DHW up to temperature. Becomes more complicated to assess in winter because the woodburing stove gives priority to the DHW ..... I'd say go for it ! Have tried a complete 'home-brew' system in the past - old radiators, glazed collector etc - but the Thermomax-type tubes are reckoned to capture more heat for a given illumination.... Hope this helps Adrian Suffolk UK fwiw there's a picture of the collector at http://www.inspired-glass.co.uk/bungalow.htm - 4th photo down.... ======return email munged================= take out the papers and the trash to reply |
#11
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Today's solar heat
On Mon, 10 Apr 2006 22:47:39 +0100 someone who may be "Jake"
wrote this:- More info please. We are having a new boiler system put in and though we can't afford a whole solar system, can't quite stretch to Jupiter ;-) this year we are specifying a solar compatible dual coil tank with a view to self installing the rest next year. Mary used a Solartwin panel, for which you wouldn't need a new cylinder, though the existing one must have proper insulation. For DIY this has the advantage of minimum installation time and effort. For a more involved DIY project Navitron are one source of useful bits. -- David Hansen, Edinburgh I will *always* explain revoked encryption keys, unless RIP prevents me http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54 |
#12
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Today's solar heat
Ian Stirling wrote:
Mary Fisher wrote: There was such a hard frost last night that the frost-stat on the ch boiler came on for a short time. There was thick ice on all the open water in the garden and all roofs were white. But it's been sunny today (although cold) and I did three machine loads of washing and we still have a cylinder full of water at just short of 60C. Scoffers can scoff away but we're very happy -it's just a foretaste of what's to come :-) that it works was established long ago. What sort of panels? I'm contemplating doing something with the old radiators, bus windows, and polystyrene sheet that I've got lying around. Rads are limited by their high water capacity, making for slow response. So solar pv as a control mechanism is out with these. Concentration improves this a lot, and is easy to do with all metal radiators, eg with greased silvered mylar film. Even ali foil works for a while. Concentration improves heat availability in poor weather, financial efficiency or ROI, and system reliability (less plumbing failure points). Greeenhouse poly could be used under the glass to provide cheap double glazing. Glass absorbs uv which helps the poly last longer, plus it protects it from mechanical stresses. How long its life would extend like that I dont know, but its easy to replace if your panels are ground or wall mounted rather than roof. Currently I'm wondering how hot you could get with silly (say 5 panes) amounts of glazing, with a system to suck air through the panes. So that light absorbed in the panes is not lost. I think you'll find its counterproductive. ISTR double glazing gaving the best temp rise for one scenario I calculated. But the real point is output per pound in, not per square metre, or in your case per material use. If you have a lot of glass, how about a hot air collector with one sheet of glass and one poly? Also wondering what the possible ratio of a fan assisted panels radiator/panel size is. I still cant see what you mean there NT |
#13
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Today's solar heat
"Jake" wrote in message ... "Mary Fisher" wrote A commercial product but self-installed. More info please. We are having a new boiler system put in and though we can't afford a whole solar system, can't quite stretch to Jupiter ;-) this year we are specifying a solar compatible dual coil tank with a view to self installing the rest next year. So as we are trying to find out about other peoples experiences a few questions please. What brand/type/supplier/cost please? Did you buy a complete kit or did you self source mix and match? And did you find it easy to fit? We're in UK. www.solartwin.com All information is there. It's just for domestic hot water - not house heating. We bought the kit, including a pv panel which powers the pump and all the silicone piping necessary. It was easy to fit, I can send pictures. If the company had done it it would have been quicker for a straightforward connection to an existing tank but we didn't have one so it was more complicated. And Spouse hates having anyone doing things in the house :-) The company was friendly, professional and helpful from start to finish, even when we were just thinking about it for six months. The paperwork they provided was excellent. It's the way to go, I think the capital costs will reduce too but I wish we'd done it years ago when we'd have had more time to enjoy the benefits. Mary |
#14
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Today's solar heat
Ian Stirling wrote:
Steve Firth wrote: Ian Stirling wrote: snip Hmm sounds overkill to me. A one metre square panel that I made myself works well enough to give 200 litres plus of water at 80C from around five hours in the sun. Traditional construction of a single panel steel radiator with an aluminium frame, polyurethane insulation, single glazed in 4mm glass. That does seem rather unlikely, unless you're starting from something quite warm. 5 hours * 1.3Kw/m^2 (sunlight falling on top of atmosphere) = 23.4MJ 200l of water has 4400J/K/Kg * 200Kg = 880KJ/K. 23.4/0.88 = 26.6K temperature rise. I'd be astonished if you got a real 20C rise out of it. Your numbers do however work out perfectly for a panel of reasonable construction on mercury it does seem optimistic, I wonder if Steve meant the panel was only 1m^2 but had a large external concentrator of some sort? NT |
#15
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Today's solar heat
Ian Stirling wrote:
Steve Firth wrote: Ian Stirling wrote: snip Also wondering what the possible ratio of a fan assisted panels radiator/panel size is. Hmm sounds overkill to me. A one metre square panel that I made myself works well enough to give 200 litres plus of water at 80C from around five hours in the sun. Traditional construction of a single panel steel radiator with an aluminium frame, polyurethane insulation, single glazed in 4mm glass. That does seem rather unlikely, unless you're starting from something quite warm. 5 hours * 1.3Kw/m^2 (sunlight falling on top of atmosphere) = 23.4MJ 200l of water has 4400J/K/Kg * 200Kg = 880KJ/K. 23.4/0.88 = 26.6K temperature rise. I'd be astonished if you got a real 20C rise out of it. Your numbers do however work out perfectly for a panel of reasonable construction on mercury Gee thanks. I'd suggest that the water in the cylinder is stratified. Your figure of 23.4 MJ on the atmosphere is higher than the actual insolation with is about 24MJ/8H according to the local Uni. I estimate that we should get about 95 litres of water at 80C from this over the day, as I say in practice after 5h water delivered is at 80C. I presume it's possible that the cylinder remains hot over night, it's difficult to eyeball a cylinder and know how much heat is in it. |
#16
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Today's solar heat
Steve Firth wrote:
Ian Stirling wrote: Steve Firth wrote: Ian Stirling wrote: snip Also wondering what the possible ratio of a fan assisted panels radiator/panel size is. Hmm sounds overkill to me. A one metre square panel that I made myself works well enough to give 200 litres plus of water at 80C from around five hours in the sun. Traditional construction of a single panel steel radiator with an aluminium frame, polyurethane insulation, single glazed in 4mm glass. That does seem rather unlikely, unless you're starting from something quite warm. 5 hours * 1.3Kw/m^2 (sunlight falling on top of atmosphere) = 23.4MJ 200l of water has 4400J/K/Kg * 200Kg = 880KJ/K. 23.4/0.88 = 26.6K temperature rise. I'd be astonished if you got a real 20C rise out of it. Your numbers do however work out perfectly for a panel of reasonable construction on mercury Gee thanks. I'd suggest that the water in the cylinder is stratified. Your figure of 23.4 MJ on the atmosphere is higher than the actual insolation with is about 24MJ/8H according to the local Uni. snip Yeah - I was mainly doing the numbers as they seemed surprisingly good, and diddn't accord with what I remembered. I presume it's possible that the cylinder remains hot over night, it's difficult to eyeball a cylinder and know how much heat is in it. But, if in practice it gives you enough hot water |
#17
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Today's solar heat
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#19
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Today's solar heat
"David Hansen" wrote in message ... On Mon, 10 Apr 2006 22:47:39 +0100 someone who may be "Jake" wrote this:- Mary used a Solartwin panel, for which you wouldn't need a new cylinder, though the existing one must have proper insulation. For DIY this has the advantage of minimum installation time and effort. For a more involved DIY project Navitron are one source of useful bits. Thanks for the info. My parents did a while back briefly consider the Solartwin system but didn't go ahead in the end. Think because they had a combi fitted and this made the system impossible or less practical. It's a good idea but we are going for the indirect style system. Jake |
#20
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Today's solar heat
"Mary Fisher" wrote We're in UK. www.solartwin.com All information is there. It's just for domestic hot water - not house heating. We bought the kit, including a pv panel which powers the pump and all the silicone piping necessary. It was easy to fit, I can send pictures. If the company had done it it would have been quicker for a straightforward connection to an existing tank but we didn't have one so it was more complicated. And Spouse hates having anyone doing things in the house :-) The company was friendly, professional and helpful from start to finish, even when we were just thinking about it for six months. The paperwork they provided was excellent. It's the way to go, I think the capital costs will reduce too but I wish we'd done it years ago when we'd have had more time to enjoy the benefits. Mary Thanks for the info Mary, it's much appreciated. Regards Jake |
#21
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Today's solar heat
"Jake" wrote in message ... Thanks for the info. My parents did a while back briefly consider the Solartwin system but didn't go ahead in the end. Think because they had a combi fitted and this made the system impossible or less practical. It's a good idea but we are going for the indirect style system. Hang on - why is it impractical to use when you have a combi system? We have a combi boiler too, the two systems work well together. Remember that you can't guarantee all the hot water you want every day of the year from solar, at those times the 'boost' on the combi boiler controller can heat the water in the cylinder for as long as you like up to an hour, or on 'over-ride' for as long as you want - through the indirect system. It's a wonderfully versatile arrangement! Mary Jake |
#22
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Today's solar heat
HI Jake
On Tue, 11 Apr 2006 15:56:03 +0100, "Jake" wrote: "Adrian Brentnall" adrian-the papers and the wrote in message ... HI Jake On Mon, 10 Apr 2006 22:47:39 +0100, "Jake" wrote: "Mary Fisher" wrote A commercial product but self-installed. More info please. We are having a new boiler system put in and though we can't afford a whole solar system, can't quite stretch to Jupiter ;-) this year we are specifying a solar compatible dual coil tank with a view to self installing the rest next year. That's what we did when we moved here 5 years ago. So as we are trying to find out about other peoples experiences a few questions please. What brand/type/supplier/cost please? Did you buy a complete kit or did you self source mix and match? And did you find it easy to fit? My local installer sold me a complete kit (less the copper pipe !) - which came with a pretty comprehensive diagram, and the offer of 'hand-holding' if necessary. It consists of an array of Thermomax evacuated collectors and their header assembly (got the installer to fit that lot on the roof for me and provide pipe stubs through into the loft space). He also supplied the controller and all the necessary brasswork, pump etc. After I'd done the necessary plumbing and wiring for the controller - he came back and commissioned the system for me - took about an hour. Been running fine ever since - with the occasional slight topping-up of the circulating water. Don't really know how much money I saved by doing the plumbing myself - but ISTR that the total kit cost just over £2k. Plumbing wasn't particularly complicated, and the (3) sensors for the controller fitted into metal sleeves (supplied) and the wiring was pre-terminated with plugs - so that was easy. In terms of performance, I've never formally recorded it - but I know that from about May to September we're not needing much input from the immersion heater to get the DHW up to temperature. Becomes more complicated to assess in winter because the woodburing stove gives priority to the DHW ..... I'd say go for it ! Have tried a complete 'home-brew' system in the past - old radiators, glazed collector etc - but the Thermomax-type tubes are reckoned to capture more heat for a given illumination.... Hope this helps Adrian Suffolk UK fwiw there's a picture of the collector at http://www.inspired-glass.co.uk/bungalow.htm - 4th photo down.... ======return email munged================= Thanks for the info, very informative. No problem! Nice house by the way, bit out of our price range though. Lovely area down there and somewhere I wouldn't mind living even if such an idea is blasphemy for a Norfolk boy :-) You're right - it's a very nice area g Don't worry about being from Norfolk - they're very broad-minded down here and let all sorts of people 'in' GG I had a stand at an exhibition last Sunday - big notice on it saying 'Cheques welcome - also Hungarians, Australians and people from Norfolk' Corny, I know - but it raised a few smiles.... ! Good luck with your solar Adrian Suffolk UK ======return email munged================= take out the papers and the trash to reply |
#23
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Today's solar heat
"Mary Fisher" wrote in message t... "Jake" wrote in message ... Hang on - why is it impractical to use when you have a combi system? We have a combi boiler too, the two systems work well together. Interesting, how does the system heat the water if there isn't a storage cylinder? I'm puzzled. Jake |
#24
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Today's solar heat
Jake wrote: "Adrian Brentnall" adrian-the papers and the wrote in message ... HI Jake On Mon, 10 Apr 2006 22:47:39 +0100, "Jake" wrote: "Mary Fisher" wrote A commercial product but self-installed. Thanks for the info, very informative. Nice house by the way, bit out of our price range though. Lovely area down there and somewhere I wouldn't mind living even if such an idea is blasphemy for a Norfolk boy :-) You could still support the Caneries, just don't shout to loud. Brian (another old Norfolk boy) |
#25
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Today's solar heat
"Jake" wrote in message ... "Mary Fisher" wrote in message t... "Jake" wrote in message ... Hang on - why is it impractical to use when you have a combi system? We have a combi boiler too, the two systems work well together. Interesting, how does the system heat the water if there isn't a storage cylinder? I'm puzzled. You getastoragecylinder. They're not expensive :-) Mary Jake |
#26
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Today's solar heat
"Mary Fisher" wrote in You getastoragecylinder. They're not expensive :-) They are if you haven't got the space ;-) I think there was also problems, amongst others, with access to a suitable roof. Instead they went for massive amounts of insulation well above current regulation standards. Jake |
#27
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Today's solar heat
"Mary Fisher" wrote who? They HTH Jake |
#28
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Today's solar heat
Jake wrote:
Interesting, how does the system heat the water if there isn't a storage cylinder? I'm puzzled. I think the clue was in the bit where she said "heat the water in the cylinder for as long as you like" i.e. they *do* have a cylinder. (just because you have a combi, it does not mean you can't also have a cylinder) -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
#29
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Today's solar heat
Ian Stirling wrote:
200l of water has 4400J/K/Kg * 200Kg = 880KJ/K. 4200J/K/kg shirly? -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
#30
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Today's solar heat
"Jake" wrote in message ... "Mary Fisher" wrote who? They HTH No Jake |
#31
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Today's solar heat
John Rumm wrote:
Ian Stirling wrote: 200l of water has 4400J/K/Kg * 200Kg = 880KJ/K. 4200J/K/kg shirly? Oh, you mean he's not using the standard 1:3 normal - heavy water ratio? |
#32
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Today's solar heat
Ian Stirling wrote:
wrote: Ian Stirling wrote: Mary Fisher wrote: Concentration improves this a lot, and is easy to do with all metal radiators, eg with greased silvered mylar film. Even ali foil works for a while. Concentration improves heat availability in poor weather, financial efficiency or ROI, and system reliability (less plumbing failure points). But of course, concentration works best with direct sun. well, it does improve capture with diffuse light, but not by anywhere near as much as with direct sun. Poor real world performance of concentrator systems in winter is down to their typically small collector areas. There are times a concentrator will deliver heat when flat panels wont. I was actually wondering about a scheme which was an air heater alone, for that one. You have a stack of n (where n is a large number of panes, which absorbs say 80% of incoming light before it hits the bottom. The air is drawn past these from the outside in, in a serpentine fashion, so that the inner panels are hottest, and hopefully essentially all IR radiation is trapped. I wouldn't be surprised if 2-300C was possible. But, it'd use a hell of a lot of glass, and probably take a long time to start up, due to thermal inertia. ok theres a proven system a bit like this using shade cloth. 2 or more layers of shade cloth, just one of glass. The air flow is from near the outer glass towards the inside, through the cloth, and efficiency is very high, far above any black or selective absorber system. And the cloth is cheap, unlike glass. If you have a lot of glass, how about a hot air collector with one sheet of glass and one poly? Possibly - there is an obvious tradeoff (for non evacuated panels) between power output, and maximum temperature. Obviously, adding another layer of glazing will always increase the maximum steady-state temperature, but due to absorbing some light, will decrease the power output. only above a point. Double glazing will give more power out than single, as conduction losses are less. Triple may not. Extending the dg layer below the first glazing layer also provides reduced heat loss. : ___ : |___| : | | | : | | | : | | | : | | | : | | | : | | | : |_| | : | | : | | : |___| : : in order from left to right: dots for text formatting roof/base of panel single glazing layer double glazing layer The area below the panel captures heat that flows over the single glazing layer, reducing panel heat loss further. I suspect a 'low temperature' panel, and a high temperature one may be worthwhile. this is what I've been thinking about for some time now. Each panel type performs best in different parts of the system. Eg vac tubes for the top of the tank, as theyre the only thing that performs sensibly at high temp, rads as a simple minimum cost inlet prewarmer, and flat panel for the bulk of tank heating. Also wondering what the possible ratio of a fan assisted panels radiator/panel size is. I still cant see what you mean there 2m^2 panel, 1m^2 radiator and a fan. Or 0.5m^2 radiator, ... Helps with the thermal inertia thing as well as to some extent the cost. still just as puzzled NT |
#33
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Today's solar heat
wrote:
Ian Stirling wrote: wrote: Ian Stirling wrote: Mary Fisher wrote: snip You have a stack of n (where n is a large number of panes, which absorbs say 80% of incoming light before it hits the bottom. The air is drawn past these from the outside in, in a serpentine fashion, so that the inner panels are hottest, and hopefully essentially all IR radiation is trapped. I wouldn't be surprised if 2-300C was possible. But, it'd use a hell of a lot of glass, and probably take a long time to start up, due to thermal inertia. ok theres a proven system a bit like this using shade cloth. 2 or more layers of shade cloth, just one of glass. The air flow is from near the outer glass towards the inside, through the cloth, and efficiency is very high, far above any black or selective absorber system. And the cloth is cheap, unlike glass. Interesting. If you have a lot of glass, how about a hot air collector with one sheet of glass and one poly? Possibly - there is an obvious tradeoff (for non evacuated panels) between power output, and maximum temperature. Obviously, adding another layer of glazing will always increase the maximum steady-state temperature, but due to absorbing some light, will decrease the power output. only above a point. Double glazing will give more power out than single, as conduction losses are less. Triple may not. Extending the dg layer below the first glazing layer also provides reduced heat loss. To restate. Adding another level of glazing will increase the maximum temperature it will reach at 0 flow. It will reduce the maximum power output at a reasonable flow to below the temperature without an extra pane, due to the lower power due to the losses from the first pane. snip I suspect a 'low temperature' panel, and a high temperature one may be worthwhile. this is what I've been thinking about for some time now. Each panel type performs best in different parts of the system. Eg vac tubes for the top of the tank, as theyre the only thing that performs sensibly at high temp, rads as a simple minimum cost inlet prewarmer, and flat panel for the bulk of tank heating. Also wondering what the possible ratio of a fan assisted panels radiator/panel size is. I still cant see what you mean there 2m^2 panel, 1m^2 radiator and a fan. Or 0.5m^2 radiator, ... Helps with the thermal inertia thing as well as to some extent the cost. still just as puzzled Ok, in more words Instead of having a 1m^2 radiator, in a 1m^2 panel, you have a 0.5m^2 radiator in a 1m^2 panel, and a fan, to circulate the air to the radiator. |
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Today's solar heat
Ian Stirling wrote:
wrote: ok theres a proven system a bit like this using shade cloth. 2 or more layers of shade cloth, just one of glass. The air flow is from near the outer glass towards the inside, through the cloth, and efficiency is very high, far above any black or selective absorber system. And the cloth is cheap, unlike glass. Interesting. IIRC The solar barn uses it at http://builditsolar.com/Projects/Spa...rn_project.htm Possibly - there is an obvious tradeoff (for non evacuated panels) between power output, and maximum temperature. Obviously, adding another layer of glazing will always increase the maximum steady-state temperature, but due to absorbing some light, will decrease the power output. only above a point. Double glazing will give more power out than single, as conduction losses are less. Triple may not. Extending the dg layer below the first glazing layer also provides reduced heat loss. To restate. Adding another level of glazing will increase the maximum temperature it will reach at 0 flow. yes It will reduce the maximum power output at a reasonable flow to below the temperature without an extra pane, due to the lower power due to the losses from the first pane. I still am not seeing how you can conclude that, since an extra layer of glazing has 2 opposite effects, not just one. First there is 5% or so absorption reducing the power output, then there is the double glazing effect reducing convention losses, which increases power out. Instead of having a 1m^2 radiator, in a 1m^2 panel, you have a 0.5m^2 radiator in a 1m^2 panel, and a fan, to circulate the air to the radiator. ahh I dont think youd need a fan. Why dont you run this past alt.solar.thermal? Lots of expertise there. When I calculated something similar, small collector plus plenty of space yielded more than the small colelctor in small box but less than the bigger in the bigger box. I think small rads in bigger boxes would make good sense, long as youre not short on glass. NT |
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