Navitron Renewable Energy and Sustainability Forum

SOLAR PHOTOVOLTAIC => Solar Photovoltaic Systems => Topic started by: charlesd on May 15, 2019, 08:50:12 PM



Title: Immersion advice
Post by: charlesd on May 15, 2019, 08:50:12 PM
Hi,
I've only had my solar pv working for a couple of days and I'm diverting the excess to my immersion via a solid controller.
I have however noticed that while it works well I'm only heating the top of the tank. It's an 18 inch immersion. Now I understand that the ideal would be an immersion in the bottom of the tank but changing the tank is not an option at this point. The next best option seems to be to install a longer immersion but before I do I thought I'd see if there was a better (and cheap)option so any ideas?
Cheers
Charles


Title: Re: Immersion advice
Post by: Iain on May 15, 2019, 08:56:25 PM
Hi

one option
Accelerator tubes have been discussed before. worth a search.

https://www.navitron.org.uk/forum/index.php?topic=22510.0

Iain


Title: Re: Immersion advice
Post by: Paulh_Boats on May 15, 2019, 11:39:21 PM
I wouldn't worry about heating top down.

On the average day a small amount of water is heated to a useful temperature.

But heating at the bottom a large amount of water is heated to lower temperature, which wont be useful. More so in winter. That requires extra energy to raise the temperature to a useful level.

The heat will slowly conduct down anyway, especially if you increase insulation. I built a thin plywood box around our cylinder and packed it with itch-free insulation from b&q.

I also monitored drop in temperature overnight, and concluded a large amount heat could be lost. So add extra insulation and its win, win, win.

I have a retro coil connected to a 30 tube solar thermal panel. Years ago Ivan declared me the winner for highest temperatures during winter.

Like you I thought a new cylinder was too expensive/not worth the hassle.

Hope that helps.

Paul


Title: Re: Immersion advice
Post by: nowty on May 15, 2019, 11:44:06 PM
Destratification pump, easy if you have an unused secondary return on the tank.


Title: Re: Immersion advice
Post by: brackwell on May 16, 2019, 06:57:11 AM
Just get a longer heating element. 24" is common but you can get them even longer.

Heating just the upper section can be an advantage as Paul says if your not using the whole of the tank which i doubt you are.  If you want more hot water you can of course just up the thermostat temp which after mixing with cold gives more volume. In winter i have the thermostat set to max 80C, but in summer it is set to a temp c58C, which in practice gives a next morning temp of c43C, and a shower temp 40C which requires a touch of cold at the mixer.  You need to find the temps that apply to your system. Make sure you are properly lagged.

Ken


Title: Re: Immersion advice
Post by: charlesd on May 16, 2019, 07:07:03 AM
Thanks for the ideas guys some interesting thoughts.
Unfortunately the tank is quite new and already has a lower secondary coil connected to the boiler on the wood burner so I don't think I can fit an extra immersion anywhere. It looked like on sunny days I'm going to have quite a bit of spare pv. Last couple of days I'm estimating at least 20kwh and I think thats enough to get the whole tank hot.
A small circulating pump might be practical but I'd have to use the current connections and tee off them with some non return valves in the correct places. My plumbing skills are pretty good so that might be a practical and cost effective idea.
Long term the tank will be replaced as I want to move completely away from oil fired heating but that's not in the budget for the next few years.
The immediate cheapest option looks like a 20quid 36inch immersion and turn the stat up to max so I'll try that first.
Cheers
Charles


Title: Re: Immersion advice
Post by: pantsmachine on May 16, 2019, 07:34:45 AM
It looked like on sunny days I'm going to have quite a bit of spare pv. Last couple of days I'm estimating at least 20kwh and I think thats enough to get the whole tank hot.
The immediate cheapest option looks like a 20quid 36inch immersion and turn the stat up to max so I'll try that first.
Cheers
Charles

That'll work. Enjoy the benefits! :)
Last couple of days our iboost has placed 13kwh into our tank. Two people, couple of power showers, dishwasher etc, all good. Only caveat is watch out if you have small kids and type of taps. 70 deg water must be treated with respect.


Title: Re: Immersion advice
Post by: biff on May 16, 2019, 02:02:49 PM
You really don't realise just how bad steam can scald until you get a couple of dabs of it.
   You see you don't  pull your hand away quick enough because your brain does not register the weight  of the water on your fingers. it can come out of the tap in high pressure splats.
 Remember to keep your hand under the cold tap for five minutes even after it has stopped hurting. That is important. Better still don't take chances 
      Biff.


Title: Re: Immersion advice
Post by: pj on May 16, 2019, 04:10:47 PM
Remember to keep your hand under the cold tap for five minutes even after it has stopped hurting.
Just like to mention that current NHS/NICE guidelines call for 20 minutes under cool or tepid running water for scalds and burns.


Title: Re: Immersion advice
Post by: biff on May 16, 2019, 04:31:16 PM
Thanks Patrick,
                 I should have got that right but still I stand corrected and rightly so.
                                  Biff