So, I have my PV diverter setup and running smoothly. I'm heating water up in my tank nicely. The only problem is it's a 300 litre tank and the immersion coil is nearer the top than the bottom. So although the top gets nice and hot, the bottom remains cold.
I know there have been many discussions on here about a circulation pump as a method of 'stirring' up the water. But I have a different proposal I'd like some opinions on.
When I bought my tank fairly recently (http://www.gledhill.net/page/102/Stainless-Lite-Indirect.htm) I was persuaded by a friend to get a solar tank in readiness for a solar thermal system. Well, that never happened and now I'm happy heating my water with excess PV.
So the bottom of this tank has a separate heat exchanger coil which would normally be for the solar thermal circuit. But my thinking is, could there be a way of creating my own small circuit that heats water (using excess PV) and pumps it round this lower coil?
I'd need some sort of water heater that can heat and maybe pump water round a smallish section of pipe. Does anyone have any ideas if this would be feasible / worthwhile / etc. Any suggestions of parts, etc would be helpful too.
I know a lot of you are engineers, so maybe one of you would have a good idea.
Thanks,
Allen
Re: Heating large DHW tank
Could you just fit a longer immersion heater element?
I suppose it depends on the tank geometry, but they go up to 36" at least ( http://www.ebay.co.uk/itm/GENUINE-BACKER-IMMERSION-CYLINDER-HEATER-ELEMENT-11-14-18-27-36-/181181852826 ) which might heat quite a lot more water than your current one?
Re: Heating large DHW tank
See this thread: http://openenergymonitor.org/emon/node/2422 for a discussion of exactly the same problem.
Re: Heating large DHW tank
@schism - my immersion heater is mounted horizontally, so I don't think I can just put in a longer one. I had seen something about ones with a 90 degree bend, but I can find any for sale.
@Robert - I read that thread before posting. Are you suggesting a Willis heater to circulate hot water round my lower coil? The diagrams in their website don't use it like that, but just as an instant heater for HW. I want to heat up my large tank.
Re: Heating large DHW tank
All I was suggesting was there had been a discussion - I remembered it but obviously as you didn't mention it and didn't post on the thread, I didn't know you had seen it.
I think the idea is it heats a small volume to a high temperature and that then convects and slowly fills the cylinder with hot water from the top, with minimal stirring; so stratification is actually key to the intended method of use. Their examples seem to indicate that given enough time (= energy input) it would heat the whole cylinder, which is what you want.
I think it would be well worth asking Willis whether they think it would work in your situation, either as per their diagram or as you suggest - but maybe that would need a circulating pump. I wouldn't be surprised if they say no to your suggestion, if only because they've never tried it and they're not certain it would work.
Re: Heating large DHW tank
I do know of someone in a very similar position, 210Ltr tank, prior to Robin's excellent circuit. His solution was to join the spare coil inlet and outlet with some 28mm pipe that is use to house a Towel Rail heating element. These are available up to 600W. There is no reason why more could not be connected in parallel.
The lower connection was also piped into the existing Hot Water coil circuit and the upper connection taken up to the Central Heating expansion tank. No pump required as it sets up its own gravity circulation.
Re: Heating large DHW tank
Have you seen a Kenlowe Hotstart preheater? We had one years ago for our Land Rover to bring the engine up to operating temperature without running the engine. We had ours set up on a timeswitch so that the engine started like a dream on frosty mornings and demisted the windows straight away. It runs on mains electricity and contains a 3KW heater, pump and thermostat.
http://www.kenlowe.co.uk/pre-heaters/cars/spec.html
Might be worth looking at, or maybe there is something similar made for DHW.
Andy
Re: Heating large DHW tank
Hmm, I just wonder how it would cope with lime scale? When used as intended (to pump engine coolant) it would be pumping water with a inhibiter added, but not so here. The same issue applies to the Willis element, OK in soft water areas, but having spoken with Willis's engineer, definitely not suitable for hard water areas.
Re: Heating large DHW tank
Paul,
I think the idea of the Kenlowe heater is to utilise the second coil in Allen's solar thermal tank to indirectly heat the potable water. Therefore an inhibitor could / should be used in the circuit.
John
Re: Heating large DHW tank
I think the idea of the Kenlowe heater is to utilise the second coil in Allen's solar thermal tank to indirectly heat the potable water. Therefore an inhibitor could / should be used in the circuit.
...I really must keep away from the forum whilst babysitting!
Paul