Navitron Renewable Energy and Sustainability Forum

SOLAR PHOTOVOLTAIC => Solar Photovoltaic Systems => Topic started by: RussJ on October 05, 2014, 11:00:24 AM



Title: Inline heater syphon not working?
Post by: RussJ 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


Title: Re: Inline heater syphon not working?
Post by: knighty 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 :-)


Title: Re: Inline heater syphon not working?
Post by: A.L. 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 (http://www.willis-renewables.com/immersion-how-it-works.htm)



-


Title: Re: Inline heater syphon not working?
Post by: asorton 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.


Title: Re: Inline heater syphon not working?
Post by: marcus 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.


Title: Re: Inline heater syphon not working?
Post by: RussJ 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


Title: Re: Inline heater syphon not working?
Post by: dhaslam 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.


Title: Re: Inline heater syphon not working?
Post by: knighty 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!


Title: Re: Inline heater syphon not working?
Post by: Andy_WSM 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!


Title: Re: Inline heater syphon not working?
Post by: clivejo 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?

(http://s1.postimg.org/l01x697h7/15mm_Flexy.jpg) (http://postimg.org/image/l01x697h7/)

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!  



Title: Re: Inline heater syphon not working?
Post by: dhaslam 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.     


Title: Re: Inline heater syphon not working?
Post by: RussJ 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


Title: Re: Inline heater syphon not working?
Post by: Iain 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


Title: Re: Inline heater syphon not working?
Post by: asorton 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.


Title: Re: Inline heater syphon not working?
Post by: RussJ 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





Title: Re: Inline heater syphon not working?
Post by: Iain on October 08, 2014, 10:28:34 PM
Hi

Quote
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.

Have you tried contacting ThermcoUK for instructions. They list it for the application, same as the Willis. So should have some recommended method of fitting.
Iain


Title: Re: Inline heater syphon not working?
Post by: RussJ on October 09, 2014, 11:09:04 AM
Tried to phone Thermco but phone constantly engaged . Have now sent them an email.
I also found this on a trade plumbing forum:

"Most of these Willis heaters use a standard 11" element which is 3kw. The savings is the ability to have small amounts water heated very hot, although it will heat the whole cylinder if wanted. They will heat very rapid, if piped right.
The drawing Tamz shows, while correct, is not the normal way most are piped. Normally the flow is joined to the cylinder vent ABOVE the draw off to taps. Simpler to pipe & works usually okay. Important that this pipe joins to vent preferably at least 2 or 3 feet above the top of cylinder, if you just joined at draw off, it will not circulate well & heater stat would cut off a lot.
I haven't a clue why they are not in rest of UK.

Edit:- just noticed on drawing that an Essex flange is used at bottom of cylinder. Esssexs are a disaster IMO, especially on a Willis, as if the heater gets a knock, so does the Esssex which will leak easily. Better using drain tapping & adding a draincock to pipe."

This guy is a plumber in Northern Ireland, where the Willis is very common.
I'm still reasonably confident that my set up will work OK once I have replaced the flexi.
Away this weekend so will attack it next week...
Russ


Title: Re: Inline heater syphon not working?
Post by: clivejo on October 09, 2014, 12:41:19 PM
Yup, Willis heaters are very common here, I'm not sure why.  But because they are common, there are a LOT of scare stories about them catching fire!  Make sure you have all the protection you can on the electrical end of things and only use the built in thermostat as an emergency cut out not for normal operation.  Also, usage of a Willis heater results in very high temperatures on the DHW draw.  It would be advisable to install mixer valves for safety (especially if you have a family!!). 


Title: Re: Inline heater syphon not working?
Post by: RussJ on October 13, 2014, 04:17:13 PM
I thought I'd report back and let you know how I got on...
Today I removed the 15mm flexi and replaced it with copper plus a "full bore" isolation valve.
Took a bit of faffing about to get the angles right and fix a couple of small leaks but is now watertight.
So I now have a genuine 15mm from tank to heater.
I decided to leave the top connection as it is for the time being and see how things go.

Not a chance of testing it via the PV as its been pi**ing down all day but I ran it on a 15min mains boost and it didn't cut out at all.
Looks like the problem is solved. exhappy:

Again, many thanks to all for your suggestions and comments.

Russ



Title: Re: Inline heater syphon not working?
Post by: clivejo on October 13, 2014, 04:47:43 PM
Looks like the problem is solved. exhappy:

Awww drats! My evil plan has failed!!  I was gearing up to sell you a 150 litre water heater with 2 x 3kW immersions in it   :hysteria


Title: Re: Inline heater syphon not working?
Post by: RussJ on May 08, 2018, 05:03:14 PM
I'm resurrecting an old post of mine as I need some more advice please and there are pictures here of my handywork!
My system has been working fine but I am  finding that on a sunny day the hot water is very hot but there ain't much of it...
The iBoost switches off well before the tank is fully heated so lots of my generation is "wasted".
Reading up it seems that stratification is occurring so that the top of the tank is 75C or a bit more and the bottom is cool.
I need to install a small 12v  pump to circulate the water so I get a full tank of hot water.
I thought of putting the pump in the lower copper pipe and forcing water through the Willis heater and controlling the pump via a standard tankstat fitted at the top of the tank.
As the water gets too hot it will switch on the pump and then the temperature should fall switching the pump off. As it heats up again the pump will be triggered and the cycle repeats.
I'm no heating engineer (as you probably can guess) but would this work?
Any better solutions please?
Russ


Title: Re: Inline heater syphon not working?
Post by: clivejo on February 10, 2019, 02:44:33 PM
How high is the Willis heater compared to the DHW cylinder?  They need to be be installed lower to be able to heat more of the DWH tank.


Title: Re: Inline heater syphon not working?
Post by: biff on February 10, 2019, 03:12:00 PM
Hello Clive,
         Welcome home, You will have to pay me a visit while we still can get about, ;D.
                                         Biff