(NickW) wrote in message . com...
Lets have a think. Oil heating costs about 1.4 pence / kwh.

Are you sure? I dont know, its just that gas is more than that.

Not certain but FWIW, this is my source:
http://www.chic-info.org.uk/electric.html

I took a quick look, and the prices there are a fair bit off what we
pay here. I'd check out your leccy and gas bills, and factor in
efficiency for each heating type. Roughly speaking leccy = 100%, gas =
80% efficient.


I havent done the maths here, but ave of 1/8 kW per sqm sounds much
too low.
I dont know what kind of collector youre considering, all I can say is
big trackers can pay back according to previous calcs. But it does
depend how you design them. Somewhere I've got detailed figures on
this one: want me to mail them? Might be of interest.

Yes please.

Will do.

Right. I'd be tempted to just run it slower, by using a series
impedance or transformer. Sounds pretty lousy tho if its crapping out
already.

It was making a nasty whining noise, obviously too much back pressure,
I have a 1/4 hp one on order though.

Sounds like that one was rock bottom stuff. Have you got a filter on
it btw? I just wonder if there might be something in the pump.

You may even find 1/4hp to be more than you need, in which case you
can cut energy use/noise/increase life by reducing its run speed.
Whats your temp rise with the 1hp pump, with the present plumbing
setup and fast flow rate? It should be poss to make rough calcs from
there, if youre interested in slowing it down.

I reckon if you get more than 50% through it should gain you. Youre
really losing a lot with an open collector. It wont matter that theres
light scattering.

I did another calc on the uncovered collector at the weekend. Now that
the coil is divided into 4 circuits, the flow rate is much higher but
the temp gain seems the same. Perhaps it's just better conditions now
(mid summer, high noon, no cloud at all). I got 10kw! If there is 800W
/sqm available then from my 25sqm collector, that's an efficiency of
50%. Given this, do you think the polythene will still benefit?

Yes, definitely. Youre losing loads as it is. I'm surprised to see you
getting 50% off such a collector though, I would have expected a fair
bit less. Your low water output temp will be helping a lot, but
plastic pipes and no cover would generally hit efficiency quite hard.

Well I'd be curious to see what happens if you ever space the pipes
out and put silvered mylar underneath, and polythene on top. I reckon
you'd seriously cook.

Sounds like doing the same thing for DHW has to be on the cards, thats
some heat output! If you ever do I'd efficientise it as much as poss
though, since water output temp would have to be high, so all those
extra tweaks would be much more important.

Regards, NT