In article ,
Andy Dingley wrote:
On 9 Sep, 12:21, Gordon Henderson wrote:
I've just done the solar panel thing (Navitron evacuated tubes) - still
need to burn gas as the weather recently hasn't been that good, but only
for 10 minutes each morning now rather than the hour or so before.
Hard experience is always interesting. I assume this is your £2k total
self-installed system?
Yes.
Biggest difference is probably the triple insulated tank
Can you give any more information on your store (as it's easy to spend
£2k on one of those alone!) What is it? Did it have internal coils
already, did you add them yourself and were they designed specifically
for solar use? Are you monitoring tank temps in this system? Do you
see good stratification of hot & cold water, did you attempt to
encourage this, and do you think it's important in an efficient
system?
I got the kit from Navitron and they made (or arranged to be made) the
tank for me. I had an idea what I wanted, and arranged the details on
the phone with them.
I started with this kit:
http://www.navitron.org.uk/product_d...ID=40&catID=86
and made adjustments on the phone.
The tank is essentially one of these:
http://www.navitron.org.uk/product_d...ID=85&catID=90
It has 2 internal coils - one for the solar loop to dump heat into the
tank, and one for the hot water extraction - this is a coil that enters
at the bottom, spirals up the full height of the tank and exits at the
top. I wish I'd taken some photos through the hole for the immersion
heater now (which I fitted with a blanking plug - might put in an
electrical immersion heater in the future)
It has 2 other pairs of connectors for direct heating - 22mm and 28mm
for the conventional boiler and cooker boiler respectively. These are
approx. 1/3 down for the entry and 2/3 down for the exit, just above
the inlet for the solar coil.
And finally, it's got a cold feed and expansion bottom and top,
respectively which is connected to a small conventional F&E tank in
the loft.
So it's a thermal store as opposed to a heat bank. There is no external
heat exchanger and associated pump - it's all done via the internal coil
which is finned for maximum heat transfer. We live in a soft water area,
so I'm not concerned about anything scaling up. (8 years and the kettle
is still clean)
The cost from Navitron for the kit just was just over £1,700 - tank,
panel/tubes, pump, controller, expansion vessel and some pipe insulation
In addition, I bought 15mm and 22mm copper pipes, a few bags of elbows,
sleeves, etc. and other misc. items - everything's soldered where
possible. I upgraded some existing valves to full-bore levers, changed
some leaky pump isolators and so on. (Screwfix to the rescue!) I was able
to recycle a lot of old copper tubing from the old setup as I went though.
I have 2 temp sensors in the tank - it came with 10mm tubes fitted to
put the sensor into the middle of the tank (they're sealed at the
far-end!) The bottom one is in-between the entry & exit of the solar
coil, (which in in the bottom quarter of the tank) the top one just
under the hot-water exit. There is a 3rd sensor at the solar panel, and
that plus the tank bottom sensor is used by the controller to turn the
solar loop pump on. (Simple difference which is all programmable in the
controler) The 3rd sensor goes into the controller too, but isn't used
for anything right now, other than to display it.
I plan to use the top sensor to turn on a heat-dump pump during the summer
when the tank temp exceeds 90C to stop it boiling. (The controller can
do this)
The tank does seem to naturally stratify and I think this is good. When
it's low on heat, reducing the hot water flow makes the most of what's
left in it - the cold entering the bottom through the coil does take what
little heat is left in the bottom of the tank while leaving the top as
hot as possible. I've seen the bottom at 25C and the top at 50C when
looking. (I got the cheap controller TDC3, so I can't put it on the
house LAN to remotely check it)
Other than convection from the solar coil, water in the tank only gets
agitated by the boiler pump - so 10 minutes in the morning, and even
then, the bottom of the tank doesn't see much of an increase. (I have
the pump set to slowest speed) I've yet to see how the cooker boiler is
going to affect it though - I've only done one trial run of it so-far,
but we'll be cooking this weekend, so will find out more.
It's still very early days for this yet, so still getting "used" to it
and working out how to make maximum savings. E.g. the run to the bathroom
takes 20 seconds and it's in 22mm pipe which I can't practically change,
so we've decided that we'll wash hands in cold water rather than waste a
long 22mm pipe of hot, but we're not afraid to take hot when we need it -
the kitchen is much closer and piped in 15mm from the tank, so minimal
lag to get hot water.
Not tried filling the bath up yet - I suspect it may require a gas burn
if it's not been sunny...
Gordon