Navitron Renewable Energy and Sustainability Forum

WIND TURBINES => Direct Heating Systems => Topic started by: biff on October 09, 2012, 10:26:12 AM

Title: Immersion coil Idea,
Post by: biff on October 09, 2012, 10:26:12 AM
Hi folks,
        There have been some exellent posts on different types of immersion heaters.These have included different ranges of DC voltage immersions, Different ranges of three phase immersions and different ranges of ac immersions.
  Now we have the combined water heated coil and immersion heater going in the same entry at the top of the tank.At the present the width of the coil is goverened by the diameter of the boss on the immersion.At present these coils are bunched up against the immersion heater but some have long leads,(pipes) going down into the bigger tanks away from the immersions and spreading the heat better.
  It did occur to me that the diameter of these coils could be a lot bigger and still be managable to fit into the boss.If the leads (pipes)to this proposed coil were long enough and the coil was apart from the immersion,still connected by the flow and return,it would be quite easy to take one end of a large spiral coil and screw it through the boss at the top,so long as the immersion which was to follow could be held carefully intact while dropping the coil down into the tank and ensuring that it did not snag on an existing boiler coil.So there would have to be some way to balance the proposed coil so that it dropped down the centre of the tank and spun round freely while the immersion was being screwed up tight.This could be done simply by suspending the coils using a heavier copper during manufacture.The operation is entirely possible and capable of being done in a reliable and professional manner but it requires a bit of tweaking and donning the thinking cap.Its there.!! Any takers,?

Title: Re: Immersion coil Idea,
Post by: Philip R on October 13, 2012, 01:47:58 AM
I have been giving the idea some thought also for the last couple of years, but I have not been motivated to make such a device because I purchased a twin coil Gledhill solar cylinder for solar, and gas heat inputs along with E7 and top mounted immersion heaters just in case the gas boiler should pack up.

As you say, the boss diameter could be seen as limiting the size of the immersion coil. Using microbore type tube could be flow limiting unless one uses a multiple parallel bundle to increase surface area and reduce flow resistance.

Back along, I recall being able to purchase a coils conversion kit for a direct hot water cylinder, making it an indirect unit. Threading it though the immersion heater pentration and deftly engageing the end through side hole drillings in the tank. Goodness knows what happens if it got dropped.

Back to your idea: Such a device could be shaped like a giant corkscrew. With an outer major diameter greater than the 2.25" diameter of the immersion heater boss. The pipe secrtion could be microbore or 12mm/15mm section. The bending done by sand filling and then bending round a circular mandrel ( knee or a decent piece of wood).

As you say, interference with an existing boiler coil must be avoided.

Also , moving away from large diameter coils to those of a lower diameter could increase temperature differential across the coil, allow better matching to index circuit resistance of heating circuit, hence better matching to pump characteristic of conventional pumped CH systems ( Many using a gate valve to throttle & proportion flow between heating and Hot Water in Y or S plan systems.

Title: Re: Immersion coil Idea,
Post by: biff on October 13, 2012, 10:48:43 AM
Aye Philip R,
           Some five months ago I installed a tripple coil tank with all the bells and whistles,The two boiler coils immediatly being used,leaving the bottom solar coil for my next project ,a ground mounted Flatplate solar collector for which I have the ideal spot.
  So ,One would think that i had plenty of coils to play with but i did not take into account the size and distance the coils were from the head of the tank where the dump load immersion is located.Because this immersion is a good 600mm above the top of the coil it cannot heat the expansion pipe enough to heat the stat to trigger the circulation pump and send the excess heat round the C/H/S.This is why I feel it necessary to find some way to cool down the head of the tank.Several time now,we have had extremely hot water come out of the taps during a force 6 and I will have to find some way to either circulate this hot water downward to the bottom of the tank,or just run it off.I considered using the solar coil as a heat exchanger but thats my future project scuppered.It would be the simplest move and all the relevant pipes are handy.I am still mulling it over.I do have a mixer valve sitting in its box but I am rather unhappy with the thought of the temperature climbing uncontrolled at the head of the tank,sooner or later something will give if it is left to itself.

Title: Re: Immersion coil Idea,
Post by: Philip R on October 13, 2012, 08:29:59 PM
Hi Biff

Just had a read on your hot tank top and getting some heat to the bootom of the tank.

Using a top boss mounted Surrey Flange or Warix Flange, extend the dip pipe (Used for air bubble free shower take off) and extend this in length with some copper tube to nearly reach the bottom of the tank. Using a bronze bodied secondary circulation pump, (CH Pump might rust away) recirculate the water when the top of the tank is hot, to warm up the bottom and even out the temperature.

Or, using a circ pump and NRV, connect a loop between the tank hot water take off at the top and the cold feed at the bottom. The NRV should prevent cold feed bypassing the tank, cooling the outlet hot water.

Could a surface mounted tank thermostat be located further up the tank to operate the recirc pump, or if using an electronic control, relocate the thermistor or thermocouple under the lagging onto the copper?

Recalling if I am correct, that you are off grid, It would be a real shame to have to switch off your wind generation input and not capitalise by using the surplus heat, especially if it blowing a hooly outside!


Title: Re: Immersion coil Idea,
Post by: biff on October 14, 2012, 10:57:08 AM
Good morning Philip R,
                  Yes,we are totally off grid and value the immersions contribution to out water heating .It certainly works well.The problem with recirulating down the cold feed is ,that it breaks up the stratification in the tank,The tank in question is 1800mm x 550mm and I would prefere to use a more gentle heat exchanger type method in which the same hot water is returned to the tank head.This would give a more even temperature at the hot water taps.
  I suspect that only a very light touch on the circulation pump would be need and the stat sensor could be buried under the insulation at the top.
  It all works very well at the moment but we are edging toward a system that will not need a knowing hand to tweek it and steady it.The combined immersion and coil seems an exellent idea and I will probely go that way eventually but in the meantime I will T off the hot feed,just before a NRV and pump through the solar coil,returning to a 22mm existing blank at the tank head.It will mean a bigger job when I get round to our solar hot water collector.
  There is without doubt a place in the market for a combined immersion heater and heat exchanger coil which will be able to do exactly what we described.It will have to be properly thought out with a set piece installation method,avoiding snags and faulty installation.The potential is there,even the probe sheath on the immersion can be used to house the pump stat because our immersion heaters being driven on the dump load excess cannot have a thermostat.It could all work out very nicely.

Title: Re: Immersion coil Idea,
Post by: knighty on October 14, 2012, 01:14:50 PM
biff... I know you don't like the idea of loosing your tank stratification...

but with your hot water as hot as it is... it's not going to really matter ?

if you have a pump from top to bottom, set to minimum setting, and you could even restrict it a bit more with a valve if you wanted... you'd only have slow mixing

and with a thermostat at the top of the tank the pump will kick off as soon as the top of the tank starts to cool ?

once the water gets up over 60'C it's getting too hot to use it anyway?

I'd think a full tank at 45'C would be better than a tank with the top third at 90'C and the bottom two thirds at room temperature ?

with your system working so well at this time of year, just think what it will be like in the summer when the PV really starts to kick out a lot of power... you'll have a full tank of hot water every day !

Title: Re: Immersion coil Idea,
Post by: biff on October 14, 2012, 02:16:07 PM
Good point knighty,
                       I had this notion that the stratification should not be disturbed but keeping the temperature under control is much more important especially with the danger of scalding.There is still another 1kw of pv to be added to the system when i get this sorted.So,yes there will definatly be loads of hot water.

Title: Re: Immersion coil Idea,
Post by: knighty on October 27, 2012, 03:14:31 PM
biff, what about something like this... ( ?

(with a suitable immersion in for your system - or make your own version of it)

you could have your top immersion tick off at a lower temperature... say 50'c ish, and then have one of the above start up - external to the tank, connected between the top and bottom ports... and it will naturally thermo-syphen and heat all of the tank ?

(just saw that on ebay and thought of you :-) )

Title: Re: Immersion coil Idea,
Post by: TOMSEPPINGS on October 28, 2012, 06:32:55 PM
Hi Biff

It is possible that you are thinking of my product.
When developing the SolaPlug I did play with a few other options, see the attached picture.
The heat exchanger is flexible & can be placed at the bottom of the cylinder.
( (
It's good to get solar heat right to the bottom of the tank, but I decided against marketing this because I thought most installers wouldn't want the hassle of trying to carefully place a coil round the bottom of the cylinder, ( like a snake in a basket ).
Also there could be noise issues as the coil would be touching the cylinder wall.
Navitron retails the SolaPlug, so contact them if you'd like to order one. I have tried most ways of doing this, I may have the odd prototype available as a one off.


Title: Re: Immersion coil Idea,
Post by: biff on October 28, 2012, 07:13:44 PM
Hi Tom,
        The type of immersion setup I was thinking off was one which had a 2kw dc element and a coil which could drop down the 5ft 6" to the bottom of the tank.So it would be quite complicated to make and install but I am sure there could be a save procedure for installation which would take the risk out of it.

Title: Re: Immersion coil Idea,
Post by: biff on October 28, 2012, 07:18:56 PM
Hi Knighty,
           Thanks for that.I thought I answered your last post but I can see no evidence of it remaining,I must have accidentally wiped it,
 This guy is about an hour away from me so he is handy enough and goodness the idea is very good.It can do the two jobs,,dump the excess from the turbine and circulate the water like you said.This could be the answer to the problem.