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Author Topic: Inline heater syphon not working?  (Read 4207 times)
RussJ
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« on: October 05, 2014, 11:00:24 AM »

I have a 4Kw solar array and last year I fitted a Solar iBoost to recover some of the exported electricity.
I also installed an external in-line heater to make the best use of available power.
Its all working well but I still have the problem of "liquid steam" at the taps but coolish water lower in the DHW tank.
My understanding was that the in-line heater avoided this problem by setting up a syphon which mixed the hot water at the top with the cooler at the bottom of the tank.
Watching the display on a nice sunny day shows the power being directed to the in-line then there is a click as its thermostat closes, the iBoost stops redirecting power, then a 30 seconds later the cycle is repeated presumably as the water in the heater cools. Thus the heating is in a series of pulses rather than a continuous run.
Is this how these heaters should work or have I got a problem?
I'm wondering whether the syphon is working as it should.
When I plumbed the heater in, I joined the lower tank connection to the heater using a 300mm flexible hose as my pipe bending skills leave much to be desired. Although this is a nominal 15mm, in fact the bore is only 10mm so I'm thinking whether this is too restrictive?
Would appreciate any comments or thoughts.
Russ
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knighty
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« Reply #1 on: October 05, 2014, 02:55:56 PM »

could you put up a few photos of the heater/tank ?

they'll help diagnose the problem :-)
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A.L.
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« Reply #2 on: October 05, 2014, 03:18:20 PM »

hello,

My understanding was that the in-line heater avoided this problem by setting up a syphon which mixed the hot water at the top with the cooler at the bottom of the tank.


- this arrangement encourages stratification, which is generally a good thing but the low flow rate through the in-line heater is as you suspect causing the water at the top of the tank to be to hot and the heater to cut out reducing your ability to use excess PV electricity

- so yes the 10mm is probably to restrictive, can you go to 22mm flexible hose?

- something similar here http://www.willis-renewables.com/immersion-how-it-works.htm



-
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asorton
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« Reply #3 on: October 05, 2014, 04:35:38 PM »

As has been said the pipes are probably slowing down the circulation, the tank will heat from the top down so you should have the external heater nice and low like in the picture in the link above.
Some pics will really help.
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marcus
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« Reply #4 on: October 05, 2014, 07:59:41 PM »

don't know what power your heater is but if it's 3kw then I'd opt for 28mm copper (~26mm ID) or equivalent for a decent thermosyphon, though you may get away with 22 if the pipes are short with little horizontal run.
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RussJ
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« Reply #5 on: October 06, 2014, 11:00:25 AM »

Pictures attached.
First is a shot of the upper connections. Pipe coming in from the right is the hot water supply from the tank.
In-line heater output is connected about 200mm above that and the pipe then continues up to vent over the cold water tank in the loft.
Second is an overview - sorry about all the towels in the way. My wife insists on keeping every towel we or the kids have ever owned ready for instant action even though there is just the two of us at home now!
Third is the lower connection with the flexi.
Hope this helps.
Interested that others agree about the inlet restriction though.
I cant see increasing the pipe beyond a 15mm bore (ie a 22mm flexi) will help since the tank flange and both heater connections are 15mm.
Willis recommend using 15mm copper to plumb their version in.
Thanks again for your help.
Russ


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dhaslam
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« Reply #6 on: October 06, 2014, 11:07:38 AM »

The flexible connections  may have much internal diameter.  I have a similar one with 1/2" connections and it is only 1/4" inside.   In any case 1/2" is far too small  for a gravity heater outputting 3 kW, it leaves no margin for error.     I cannot understand why they are approved.
« Last Edit: October 06, 2014, 11:09:19 AM by dhaslam » Logged

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knighty
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« Reply #7 on: October 06, 2014, 11:11:28 AM »

where the water out of the heater goes up to the vent pipe of the tank, it should be connected in under the tank connection, not above it!
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Andy_WSM
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« Reply #8 on: October 06, 2014, 11:13:41 AM »

where the water out of the heater goes up to the vent pipe of the tank, it should be connected in under the tank connection, not above it!

Was just getting my head around that. As it's connected it will want to push hot water up the vent!
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clivejo
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« Reply #9 on: October 06, 2014, 01:29:00 PM »

The pipe bore is far too restrictive for 3kW of heat.  You are going to have a trickle of VERY hot water which is going up your expansion pipe and being lost heating the cupboard!! If the Willis heater doesn't get rid of the heat it will tip the immersion thermostat and cut the power which is what you are seeing.

Have you seen the bore in those flexible pipe isolation values?



You have a capped off 15mm pipe there, why not use that with full bore 15mm copper,  even a compression elbow would be way better than that flexy piping in my view!  

« Last Edit: October 06, 2014, 01:36:19 PM by clivejo » Logged



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dhaslam
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« Reply #10 on: October 06, 2014, 03:15:01 PM »

If the thermostat sticks  it will go red hot and set fire to the  house.    This can  happens with  1/2 inch pipe as well because the elements can short and increase the output.   All  immersions should have  thermal cut out switch, not sure if the Willis  has  one now.     
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DHW 250 litre cylinder  60 X 47mm tubes
Heating  180,000 litre straw insulated seasonal store, 90X58mm tubes + 7 sqm flat collectors, 1 kW VAWT, 3 kW heatpump plus Walltherm gasifying stove
RussJ
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« Reply #11 on: October 06, 2014, 08:20:51 PM »

Thanks again for comments and suggestions.
Seems to be a general consensus that the flexi has got to go, so I'll replace it with 15mm copper.
I'll also re-do the upper connection so it's below the hot water take off.
Hopefully that will go some way to sorting the problem.
I'll report back in due course.
I checked the literature for the heater and it confirms that there is a safety cutout in case the thermostat sticks.
Thanks again.
Russ
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Iain
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« Reply #12 on: October 06, 2014, 08:30:04 PM »

Hi Russ

Quote
where the water out of the heater goes up to the vent pipe of the tank, it should be connected in under the tank connection, not above it!

Before you move the top connection have a look at this

http://www.willis-renewables.com/pdf/Technical_Instructions.pdf

The top connection is meant to go 500mm above the top of the tank with the solar syphon.
I would have thought yours might be similar. Worth a check first
What did the instructions say?

Iain
« Last Edit: October 06, 2014, 08:32:43 PM by Iain » Logged

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« Reply #13 on: October 08, 2014, 07:26:28 PM »

People will tell you all sorts of things, good and bad, my advice, follow the manufacturers instructions, after all they even put it in capitals so there is no doubt !

Quote
Insert a tee piece with 15mm branch on the open vent pipe at a level NOT LESS THAN 600mm above the dome of the cylinder. Connect between this branch and the top (end) of the Willis Immersion with 15mm copper tube.
« Last Edit: October 08, 2014, 07:31:26 PM by asorton » Logged

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RussJ
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« Reply #14 on: October 08, 2014, 08:52:20 PM »

Hi Russ

Quote
where the water out of the heater goes up to the vent pipe of the tank, it should be connected in under the tank connection, not above it!

Before you move the top connection have a look at this

http://www.willis-renewables.com/pdf/Technical_Instructions.pdf

The top connection is meant to go 500mm above the top of the tank with the solar syphon.
I would have thought yours might be similar. Worth a check first
What did the instructions say?


Iain

I knew there was a reason why I put the top connection so high up - but I forgot where I'd read it and couldn't find the source!
I didn't buy a genuine Willis but  got a similar heater from a company call ThermcoUK who are only a few miles away from me but it didn't come with any instructions.
The Solasyphon is a slightly different beast and I'm now wondering if the high connection is correct for an inline heater.
Probably do the job in two stages:
1 Re-do the lower connection with 15mm copper. See if it fixes the problem and if not
2 Relocate the upper connection

Russ



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