30 x 47mm tubes with existing 117L tank

[Paulh_Boats]

Our house was built in 1985 with a 117L tank. The trend at the time was low volume tanks with quick recovery, something like 20 minutes to heat up with a gas boiler.

30 tubes is probably over the top for summer use, but ideal for the other 3 seasons. Newly commisioned last week there is no heat dump solution yet, so high temperatures are to be expected.

A larger tank would be better in the summer, although in the winter I would expect the current tank to perform the best. Since it costs £400 plus a lot of elbow grease to swap the tank I'll see how it performs in winter before deciding to replace it.


Today at 9am all the hot water was drained to give a constant 26.4C through the tank.

At 2pm after a clear sunny morning the top of the tank (TST) was 65.8C.

-Paul

[jason]

Hi Paul
what is the temperature this evening HOT! HOT! HOT!
sounds like a bit of fun to me.
keep us posted
jason

[Paulh_Boats]

Cloudy all day, some heavy rain.

TST (top of tank) started at about 60C, finished at 58C
bottom of tank finished at 39C

Not much water used.


The pump did come on once before I left for work...amazingly all I could see was a bright patch in the clouds so the panels work well in diffuse sunlight.


Recent observations.
As the hours go by the top and bottom tend to mix together, the top temperature drops and the bottom rises slightly. So today was probably neutral with gains equal to losses.

Because the system has a retro coil in the immersion socket the Resol sensor is at the top of the tank and the panel temperature must get above the hottest part of the tank to switch on. The panel has to be about 20C warmer than if it had a solar cylinder.

-Paul

[jason]

hi Paul
good to see it is working well
i have 2 x 30 x 47mm tube panels feeding in to a 200ltr cylinder and all we managed was 42c enough for a bath for the boys who had been to party on a farm and came back stinking of chocolate and cow sh** thank heavens for free baths.
all smelling sweet now
jason

[Paulh_Boats]

26th May, temperatures top/bottom

At 07:15    50.8/36.4      Clear sun

At 10:15    65.8/44.4      Patchy cloud started

At 13:35    73/41.8         Patches of afternoon rain put an end to solar gain

At 17:19    71.8/45.5      Notice the mixing of top/bottom since 13:35


Hot water use during day: one shower, hand washing, one dishwasher load (single feed of hot water only)


Facing south-east the biggest gains are in the morning, although the pump can still trigger after 5pm.

Overnight there seems to be a lot of heat loss. The old tank with thin foam and patchy pipe insulation are largely to blame I think. Need to add a cylinder jacket and pay attention to lagging every sqaure inch of pipe work.

-Paul

[Ivan]

Paul,

One of the major differences with your setup compared with a twin coil tank, is that you will to a certain extent heat from the top down, whereas a twin coil tank will tend to heat from the bottom up. This looks quite clear from the data you provide - it is quite impressive that you have useful temperature increase at the top of the tank before 10am!

Perhaps you could consider loose-fill insulation for your tank - just lock the airing cupboard, and pump it full of those little polystyrene beads?!

Ivan

[Paulh_Boats]

it is quite impressive that you have useful temperature increase at the top of the tank before 10am!

Perhaps you could consider loose-fill insulation for your tank - just lock the airing cupboard, and pump it full of those little polystyrene beads?!

Ivan,

Yes I'm very pleased with the early morning temperature rise.  Facing south east we catch the morning sun and the panel starts warming at 7am (maybe sooner).

I'm now developing a theory that an immersion coil with short 10mm pipes and a low volume tank will be useful in winter fed with 30 tubes. It can provide a small amount of hot water fairly quickly and maybe there will be no need for the boiler on a sunny day. Perhaps the ideal system can switch between 2 coils..... the lower coil for a large amount of sun that will eventually heat the whole tank, and the immersion coil for short amount of sun to heat just the top of the tank.

On cloudy days with sunny intervals my system performs well (the boiler has been off last 2 weeks), but in strong sun the top gets too hot and it would be better to store the heat lower down.


Ahhh!  Finally a use for all that polystyrene bead packaging, ..... I'm not sure how to break the news to wifey about the loss of the ariing cupboard.

The easy option for now is a cylinder quilt for £12 from the DIY sheds. I'll fit one and see how it goes, we only have 10mm foam at the moment so its bound to help.

cheers
Paul

[O MidKnight]

Paul

You will find quite a bit of difference with extra insulation. I used old continential quilts. Some of my old customers used to box the pre-heat solar tank and similiar to Ivan`s suggestion fill the box with vermiculite insulation - great until the cylinder couplings started leaking the old oil heat transfer fluid.

Rob

[Paulh_Boats]

Rob,

Thanks for the tip..I've bought a cylinder jacket and several lengths of the extra thick 22mm insulation. Should be able to fit them soon.

-Paul

[Paulh_Boats]

Today in good sunshine the tank top went from 43C to 77C, but we soon used the hot water with 2 showers, 2 full loads of washing and one dishwasher load. By evening it was 55C top and 20C bottom.


I have identified one major path of heat loss. The 22mm cylinder output rises up 15 degrees, which encourages thermo syphoning. Then the 22mm pipe goes straight up to the vent in the header tank, which convects a lot of heat up. The pipe lagging is a bit poor also and there is about 2m of 22mm pipe that can lose heat.

I'll take it all apart and bend the cylinder output down slightly to reduce thermo syphoning, then immediatly reduce the upward pipe to 15mm. This will reduce the pipe area up to the vent by 32% and I'll heavily insulate it with 25mm thick pipe lagging (which is 25+15+25 = 65mm diameter).

Ivan's suggestion of boxing the tank looks practical. The tank is in a corner so I only need to box 2 sides and the top.

-Paul

[lightfoot]

Hi Paul,

The outlet from your cylinder should NOT fall before the vertical vent pipe and it should be 22mm DO NOT REDUCE IT.  Bending the pipe down will not stop the heat going up the vent pipe but may leave air in the sitting in top of the cylinder.  The heat is really being transfered up the vent pipe by conduction and the fact that heat rises but this is not really the same as thermo-syphoning.  Lots of insulation is the only way to stop heat loss.

Hope this helps

Lightfoot.

[Paulh_Boats]

Lightfoot,

Yes insulation seems the best solution - I only planned reducing to 15mm for the overflow vent, the feed to the house will stay as 22mm.

cheers
Paul

[lightfoot]

Paul,

Do not reduce or restrict the vent pipe in any way, we don't use 22mm for fun.

Regards

Lightfoot

[Paulh_Boats]

For the benifit of everyone I've included a link to the 1999 water regulations, section G20.1

"Vent pipes from primary water systems should be of adequate size but not less than 19 mm internal diameter"

http://www.defra.gov.uk/environment/water/industry/wsregs99/guide/section8.htm


Thanks to lightfoot for pointing me in the right direction. It seems that under extreme conditions, like an immersion thermostat failing causing the tank to boil, a small pipe won't vent the steam and pressure fast enough.

-Paul

[Ivan]

I've noticed thermosyphoning in my vent pipe - so I insulated it right up to the top to try to reduce the heat loss.