heat pumps / ground source heating.

[Penners]

Did you say discarded? Copper price today is $6779.50 per tonne.

I got a hell of a shock when I bought a few lengths of 15mm tube the other day.

Is here are prospect of prices falling, or is this a case of China and India sucking in ever larger quantities?

 

[biffvernon]

Is here are prospect of prices falling, or is this a case of China and India sucking in ever larger quantities?

Anyone who knows the answer to that could make a lot of money trading on the LME

 

[Penners]

Damn! I thought I had a direct line to the oracle.

 

[NT]

Would a steel radiator (painted black of course) absorb heat as well as copper?

No, it is a poorer conductor of heat so the surface would get hot and reradiate before it has chance to conduct to the water inside. However, you try finding copper radiators for the same price as steel!
(if you really want to improve performance then the panel should be made from silver! and then painted black)

Its the black paint on the surface that absorbs the heat. The metal under it then conducts that heat to where its wanted. The temp drop across the steel of the rad would be too small to be of any significance.

The 1st downside of using steel rads is the volume of water they hold, so they wont react effectively to short bursts of sunshine between clouds, and their early morning startup is delayed a bit. The other issue is they rust.


NT

 

[NT]

PS. Did you say dicarded? Copper price today is $6779.50 per tonne.

Perhaps we'll start seeing copper coated steel again.


NT

 

[biffvernon]

Steel prices have gone up as well, of course. Tessa Jowell was using that as part of the reason for the rising costs of the Olympic build. I don't see why they don't make it all out of timber.

 

[NT]

Steel prices have gone up as well, of course. Tessa Jowell was using that as part of the reason for the rising costs of the Olympic build. I don't see why they don't make it all out of timber.

Steel is still well below copper prices, plus stell pipes can have thinner walls, if coated both sides with copper.

NT

 

[NT]

Steel prices have gone up as well, of course. Tessa Jowell was using that as part of the reason for the rising costs of the Olympic build.

Am I the only one that thinks the supposed misakes made in the initial pricing by a supposedly expert organisation are laughable? Or were the initial costs were deliberately tweaked to get the bid past?

If you bought a window from an expert joiner, would you believe it when told later 'oh we forgot about the vat, we'll have to charge you twice the price now... and it might even rise to 3x' ?


NT

 

[skier-hughes]

I think I must have heard this wrong, but I'm sure they said on the news that

"The company who were in control of getting the project through on budget had raised their costs"

Graham

 

[Moo]

You're right - they did.

Beggars belief, dunnit?

 

[Penners]

were the initial costs were deliberately tweaked to get the bid past?

How could you possibly imagine that this honest, upright, open Government would stoop to anything as low as misleading the public?

Shame on you, sir!

 

[Me!]

it will be plumbed into our existing heating system via a second indirect cylinder that will pre-heat the water before it reaches the existing cylinder

I had thought of using this idea (not that I've actually got around to doing anything about it yet!) but I was unsure if it would work? As I understand it, cold water normally enters the cylinder at the bottom and comes out at the top (not the heating coil, the actual tankfull). But, if I pre-heated this cold input to the existing tank with a solar heated second tank as you describe, would this hot input stream try to rise as soon as it gets into the second tank, cause circulation currents, and leave me with a whole tank of warm water rather than hot at the top and cold at the bottom?

 

[biffvernon]

I don't think it would have any more mixing effect than the hot currents rising from the heating coil near the bottom of the tank in a standard system. It's a tried and tested arrangement in the diy solar world.

 

[Penners]

Sorry to nag on about this, but I'm still unclear about how the relationship between the two cylinders is designed.

Presumably the water that's circulating through the solar panel forms the primary circuit (ie: in the coil) of the secondary cylinder. So this heats the secondary water in the secondary cylinder.

What then happens to this secondary water? Is it fed into the intake port on the secondary side of the primary cylinder? If so, how do you persuade it to take precedence over the cold water coming from the header tank?

Sorry to be thick.

 

[skier-hughes]

You're not thick at all Penners, I'm wondering exactly the same. I suppose if I sat down and drew it out and put my physics head on I could work my way round it, but it's been so long......... I can't find a pencil and paper

 

[biffvernon]

Is it fed into the intake port on the secondary side of the primary cylinder?

Yes

If so, how do you persuade it to take precedence over the cold water coming from the header tank?

Cold water from the header goes into the bottom of the lower, solar heated tank and leaves out the top, but instead of going to the taps feeds into the bottom of the upper tank to be further warmed (if needed) by the boiler and the immersion heater before leaving the top of that tank and heading tapwise.

 

[Penners]

Aaah - gotcha. So there's no cold water feed from the header into the upper tank at all.

Many thanks, Biff.

 

[Mark]

When I have asked the question before, I have always been told that having a single larger tank is better than a chain of tanks feeding each other.

There are suppliers of tanks which will take three or four heating elements. I suppose the other thing to look at is the thermal store. I have never been totally convinced about them from an efficiency point of view but they seem popular so presumably work as claimed?

I have seen a device which is sort of a very small tank which takes in cold water from the bottom of the hw tank and is heated by a solar coil, its output then is designed to feed in near the top of the hot water tank. The idea being that the solar (even inefficient panels) will quickly heat a small volume to a higher temp than a coil in a large tank and deliver it to the top of the main tank allowing a very quick heat up of small volumes - so for a shower for example.

Ive not seen any results so dont know if it worked or not.

 

[biffvernon]

When I have asked the question before, I have always been told that having a single larger tank is better than a chain of tanks feeding each other.

That may be true in a new build, but I have already got a tank and want a bigger one to increase thermal store and allow two people to have a bath in a short space of time, bearing in mind the demise of bathwater sharing on the cleanest first dirtiest last principal. I thought it cheaper and more ecologically sound to daisychain a couple of tanks rather than throw away a perfectly good tank and buy a bigger one.

 

[NT]

Regarding the small external tank idea...

Flat panels lose efficiency badly as water gets hot, so its always best to use those to heat the coolest water in the system, ie taken from the bottom of the main tank. What temp flat panels put out depends on the weather and design, and can be anything from hot to not even lukewarm, so you dont want to feed this into the top of your main tank. Doing that would work in summer afternoons, but off solar peak it would mix non-hot into the hot at the top of the tank. Better to feed this in at the middle.

Vacuum tubes are different, since they dont lose a lot of efficiency at hot water temps. But again in midwinter theyre not likely to produce hot water, so... it doesnt sound an ideal system. OTOH a small tank is relatively cheap, which does help with payback.

Trouble is there are so many options, and none are ideal.


NT