Re: Energy alternatives for the UK.

In message <oonvd155a3bbp3mb0s433r2pdsgun1a3ao@xxxxxxx>, sylva@xxxxxxxxxxxxx writes 
On Wed, 20 Jul 2005 21:15:18 +0100, David Hansen
<SENDdavidNOhSPAM@xxxxxxxxxxxxxx> wrote:


I love the idea but the cost per Watt is high and the dc pump probably
more expensive.

And less reliable. Anybody know of cheap, robust efficient small DC pumps to pump 1 to 3 litres pen minute ?

I know one chap who made his own (not that reliable), and one who's experimenting with pond pumps...


Yes, so I think. Given that my house is poorly oriented for mounting
the panels I am in a quandary, given the choice of SE or WSW facing I
wonder if the WSW mounting would produce enough heat toward the
evening. Given that I only expect the panels to contribute from spring
till autumn. To my mind if the hot water tank is well insulated then
heat losses per day are low,


Call it 2.5 kWh / day ?


so any period when water is solar heated
should be acceptable as long as the tank ends up hot.

I don't have great data to back this up, but my feeling is that is you have to choose between SE and SW, SW is the better bet because SE is hampered by morning mists in spring and autumn which 'burn off' by lunch time, and if you use most water in the evening, you should also have fewer storage losses.


This is the sort of thing to try, in the old days with lagging added
after hot water cylinder was installed I would run my hand under the
lagging to feel the temperature over the cylinder and then judge
whether or not it was hot enough for a bath. With the little foam
covered one I cannot.

You can always trim away a lump of foam so you can poke a finger down, or better yet, stab a hole tangential to the cylinder edge so you can get a K thermocouple down there.


Depending on your boiler it can be cheaper to use an immersion
heater for topping up, especially if it uses White Meter/Economy 7
rates. Running a boiler and many metres of heat losing pipe in the
summer is an expensive way of warming water compared to a 100%
efficient immersion heater.

I think I disagree but would like to see your figures for this.

Depends on 'dry cycling' and other effects I guess, but boilers can be horribly inefficient if they keep starting to run, but keep going off because of high return temp.


I
think off peak rates only become more economic if >1/3 of your use is
during the off peak period.


Probably.  Depends when you use your water, losses from cylinder etc...


It may be the ideal shape but it is small, under the current gas
regime this is not a problem as recovery from cold is ~20mins. I have
no space for a bigger one though I could fit a similar one adjacent,
if I could figure how to plum 2 to make best use of the panels.

Common strategy is to use first cylinder for preheat second for gas. Works well where demand is high and preheat temp less than required temp. Less well when preheat temp can exceed required temp and second cylinder might be left to cool etc.


In
fact I suspect a means of having a variable capacity hot tank with a
full capacity able to meet 3 days hot water demand would be better.


At last !!  Somebody else thinks variable capacity is a good idea !

Was starting to think I was the only one on the planet. Only issue in common domestic installation is the variable weight causes variable ceiling deflection, and also the cost of the control gear because domestic consumers don't want to mess with all those nasty valves and levers...


Provided it is big enough for a standard coil then this is no great
problem. If it is not big enough then you will need to make a
suitable coil. This can be an advantage anyway as you can tailor it
for the application.


Of course one coil from the gas heated circuit is there already, I
need an efficient heat exchanger below this. Wookie mentioned plate
heat exchangers which makes sense in getting the very last degree of
heat transferred.

Tricky to use to get heat into cylinders though. You can't really depend on convection, but if you pump it you trash any stratification. What's worse, without efficient flow of cooling water, the primary loop tends to overheat making the panels inefficient.


Cheers, J/.
--
John Beardmore
.

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