That seems to be paywalled but one of the authors' Masters thesis on the same subject is here:

http://digital.library.louisville.edu/cdm/singleitem/collection/etd/id/833/rec/9

14 MB, 184 pages. I may be gone some time.

I cant get either of them, my Athens login says 'sorry your useless'
Ed's like says 'sorry we are useless'

Shall try later

A few days in November, almost better than our summer.

Hope this link to the paper works:
https://skydrive.live.com/redir.aspx?cid=698cc0950b10ccbd&page=self&resid=698CC0950B10CCBD!976&parid=698CC0950B10CCBD!120&authkey=!AsWa33VQq4HmTRw&Bpub=SDX.SkyDrive&Bsrc=Share

Bit to big to upload but got my Athens login working, really shoudl read my university emails.

Now I got my access back I have loads more if anyone is interested in doing a lit review.

Now read the original paper (thanks djh) and as much as I'm going to of the thesis I linked to.

Posted By: djhThinking about the design more, it basically comes down to being equivalent to efficient solar collectors plumbed in to a fairly low-temperature thermal store. So the interesting question is whether there's a significant cost saving that would make it worthwhile?

Yes, that's my take, too. From his costings I don't see how it's going to be all that competitive with conventional collectors. There might be a few circumstances where it's a bit better but the flexibility of location of the collectors and the thermal store of conventional would make them have a wider appeal and therefore probably lower costs. His figures include a weight of nearly 300 pounds which would make installation awkward - not a job for one person unlike ETs.

It's an intriguing idea though for site-built collectors. E.g., a custom design to cover the whole of a gable end without funny pixelation at the edges.

I was more interested though in the “home”-made heat pipes so I was a bit disappointed to see they used a refrigerant which is scheduled to be phased out until the Montreal protocol and so is presumably a bit awkward to handle from a legal and ethical point of view. It was nice to see that the whole thing worked OK with out too hard a vacuum in the pipes, though.

The high conductivity of heat pipes combined with their uphill thermal diode effect has some interesting possible applications.

E.g., a refrigerator/larder could be cooled using a heat pipe through the roof to poleward facing condenser/radiator on the roof. A simple thermosyphon could be used but a heat pipe would be more effective, I think.

Use of underground air pipes to precondition incoming ventilation air has often been discussed. There's always the concern about condensation and bugs in the pipes, etc. Inspired by the Siberian railway idea of sticking heatpipes in the ground under tracks to keep the permafrost there frozen I wonder if heat pipes could be used to extract heat from the ground when it's useful (ground's warmer than the air). Of course, the ground couldn't cool the air but that's a dubious thing to do anyway and the air wouldn't recharge the ground but I, for one, wonder if that would be much of a useful effect in practice anyway.

Nice thread !

Posted By: djhThe basic idea is a solar collector on a wall with heat pipes leading through the wall to a thermal store

I have already tested my ventilated slate facade with "bare PEX" and got 20% efficiency, so heat pipes look like a nice upgrade solution !

My question is, would it work with the heat pipes vertical (inside the facade cavity), but *not* penetrating the wall ?

Would tops of heat pipes need to be embedded in insulation, or would they work "bare" ?

Thanks for inputs & opinions!

gg

Thanks, Ed !

Current design as tested (November), is a PEX serpentine, inserted inside the slade cladding cavity, circulating through a barrel of water on the deck. I recorded heat difference x water volume, calculated the kilocalories, converted that to kWh, then divided that by the "estimated" sunshine over the period, and got 20%.

The slates are in 3 "layers", hooked to lathes; lathes are nailed to "rafters" on (approx) 50 cm centers; which are nailed to stringers nailed to second set of rafters fixed to blockwork (25cm block wall).

So there is a 12cm cavity between the backs of the slates, and the blocks. Access to it being through plywood bottom edge of "slate box". Could not remove slates otherwise (well not yet anyhow...).

Cavity is 1.8 m tall x 5 m wide. Rafters mean that it is divided into 6 "slots" 30 cm wide x 4 cms across.

I have inserted sheetmetal absorber troughs inside the cavity (through bottom of cladding "box"), hoping that this warms the PEX more... Steel wool packed into troughs. Troughs are 1.5 m Tall and start flush with bottom of box.

The intent would be to insert a long heat pipe also, into the absorber (with an insulated rod (= PVC tube) between heat pipe and PEX, to prevent melting !). Heatpipe 1.8 m long, so the top of it would be at extreme top of cavity.

I want to pull heat out of the cavity (it is at 37°C at the moment (solar noon + 1 hour), for 9.5°C external air temp... (This will probably be the max for today, as it is just starting to rain...).

The slates already warm the house (heat percoclates through the blocks...) Typically overnight, cavity temp would be 8°C, for a 2.5°C external air temp...) (so the blocks are obviously warming the cavity backwards !).

I can manage with 20% efficiency, sort-of, but more is better !
With 10 square meters of slates I reckon I could extract 6kWh of useful heat, over an average "winter" day (= 8 months). Obviously the slates are fixed at 90° and dead south...
I would dearly love to overglaze them, but this is problematic from planning rules (would probably need building declaration) as it is I could not get past OH authorization : hence the stealth approach.

I thought that heat tubes sounded like a great way to grab more heat...

Thanks again for your interest !

Apologies for jumbled ideas, it is in fact VERY jumbled in my head !

gg

Hey Joe,
Go for it !

I was like U, till I bought an aquarium pump and a blowlamp !

The web is your teacher !

PEX costs rubbish, and plastic dustbins make great storages!

Likely you would need Good Insulation under the PEX...

You might even get away without draining back, for 9/10ths of the year...

gg

Mildly relevant and I wanted to post a link somewhere anyway, low-thermal-mass sunspace in Montana: http://www.builditsolar.com/Projects/SolarHomes/SolarEfficient/SolarEfficient.html

Neat project. Some immediate thoughts:

The thermal mass of your blocks are probably a liability. They'll absorb heat during the day when you could make use of it and release it at night when you can't so much. If you finish up taking the slates off then putting a layer of insulation between the innermost bits of wood would probably help.

20% efficiency is pretty good. Sunlight falls on the slates and heats them up then they lose heat to the outside and into your cavity so it seems you'd be very unlikely to get more than about 50% at best unless you use a heat pump or something to make the cavity colder than the outside.

To do better passively you need to let some of the sunlight through and get it properly greenhouse-effect trapped. As you say, overglazing might work but I wonder if you could negotiate with the aesthetes to replace them with dark polycarbonate in front of cavities which are painted black inside?

PEX is typically rated for a small number of freeze/thaw cycles but I wonder if you're careful with the connections whether in practice you can get away with just letting it freeze, particularly in a conservatory where a leak is probably only a nuisance, not a disaster. Or, for the number of times it happens in a conservatory which ought not to freeze even when it goes below zero for a day or two outside, manual recovery from drain back (shut off exit valve, open vent valve, run pump, shut vent valve, open exit valve) would be OK.

Sure, use copper if you can afford it!
However, there is not actually that much difference: per one study I saw, the heat-transfer efficiency is actually remarkaby similar, irrespective of the material -- the thermal conductivity actually plays a tiny part in the equation... Gary also says about the same thing on builditsolar...

gg

Posted By: joe90Perhaps I need to start a new thread..

... OR bend the conversation (and your design) to get some HEAT PIPES in, somewhere LOL

gg

Posted By: joe90if I use pipes and not solar panels then it is heat pipes

not really !
https://en.wikipedia.org/wiki/Heat_pipe

Can't you go direct, through or under the bedroom floor ?
Or use a local batch store inside the conservatory, and pump it in one go, when full of heat.
Overnight, the batch store is cold (ready for tomorrow...) so no heat to lose to outside in any case...

gg

OK, Joe, either way, it is a great idea to grab that heat and get it somewhere safe and useful ! Depending on the roof angle, you might not get a great deal of collection in winter, though... I suspect that antifreeze also kills some more efficiency... Also, PEX does not like UV, BTW... so it might need to be under a tin sheet etc. Maybe you would be better with a sealed air caisson, with a fan in it, circulating warm air over an HEX, then just plumb to and from the HEX, with a small circulator. I'm considering this for my future "solar farm", but that *IS* hijacking the thread LOL

======
To Ed Davies :

Hi, Ed,

Obviously crossed with you in the post as we were PEXING Joe, so thanks for all the feedback!

"The thermal mass of your blocks are probably a liability".

Yes, but they *were* there first ! I think the architect wanted a Trombe wall…
He tried slowing down the outward loss by stuffing the cavity with fiberglass…
So mea culpa, I have been pulling it all out in order to insert my gizmo’s, and anyhow I hate FG (coming from a long line of lungies…).

Had not thought of dark polycarbonate for overglazing, but did think of clear (2.5mm), will have to give this a trial and see if it arouses any "negative neighbourhood issues", so it is on my list for an ASK at the building control office… (Ironic, round here everybody fits extra Velux without asking & gets away with it…). Loads of garage conversions too… Below 16 square meters, no need for building permit… But I suspect that "shiny slates" might fall foul… (we have a public monument over the river)... Only one way to find out…

Agree about PEX "elasticity" - if it did go bang in the night, like you say, it is not a catastrophe…
Otherwise, recycling the tank back through the PEX would be a way to go, good investment-wise… I’ll need a controller for all of this, it is clear…

Re drainback, thanks for the valving routine – I had considered same, but with an air cylinder (paintball size…) and appropriate valves, to give it a push to empty the lines. (With similar for mains water pressure, to prime the circuit at start-up, as the pump would not handle that…).

Finally I much like the Montana low-inertia sunspace, especially when he twins it with his Sealed Crawlspace, I have done the same (I got the idea of BIS « zone heating » article, it’s a great site.

Attached is freebie drawing FWIW ! MOD: *Deleted* (see below for later version...)

Cheers,

gg

Hi, again, was thinking of this DIY model...

https://www.youtube.com/watch?v=252zgxems04

I like this comment: "Generally, most manufacturers aim for a phase transition of around 30C for solar collectors"

The cavity temp is generally 40°C this time of year... Maxed out at 34 today (grim afternoon).

If installing inside a stagnated glazed collector, which is an option, I'd suspect that the air temp would be, say, 60°C at least - thus 20°C TD between the bottom and top ends... Enough To Pull a Draught ?

gg

Excellent feedback, Tom, thanks as usual !
Nice idea for the little PV panel - lots around here (on boats) - will go down this evening and rip one off (LOL).

Posted By: fostertom the fill/drainback could (in fact should) take a little longer than 'quickly'.

Good advice - I guess that this implies that the PEX diameter needs to be "larger rather than smaller" ?

I tested with 20mm PEX, and I have the option of 16mm or 12mm...
Also, I suspect that it means, "NO SERPENTINE", as the troughs would need blowdown assistance, in order to empty. In which case I would use "inverted U" risers...

(diagram currently in preparation...)

gg

Drainback, unless it's complicated, results in using quite a lot of energy for pumping, particularly if the top of the system is well above the drainback level.

The point of a heat-pipe system (where the top of the heat pipe heats the fluid, rather than having the fluid flow through the collector) is that a) the heat-pipe acts as a thermal diode to greatly reduce the losses when the sun goes in for a while and b) to keep the volume of fluid to a minimum so there's less heat available to be lost.

GG, thanks for the link to that video. I'd forgotten about the trick of heating the pipe to boil the fluid and get rid of most of the air. Still, I'm wondering why the air matters. Reducing the boiling point of the fluid is good because it increases the area over which evaporation can happen but air or a vacuum won't make much difference to the amount of vapour in the pipe (only about 0.5% difference). Will have to think about it some more.