Thermal store help needed

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Ok will try keep this short.. basically our plumber did a runner left us with a poorly plumbed system and left us to pick up the pieces.

Having a large supply of free wood on our doorstep we thought it logical to get a log burner with back boiler installed. We were quoted the following

We are a family of 4 in a 4 bed house.

Bosch Greenstar 18/25 Oil boiler - plumbed in as pressurised system.
210Litre Thermal store. (2 internal coils, one for DHW one for boiler to heat Thermal store indirectly)

Boiler was plumbed to the heat store via the secondary coil so not heating mass direct

Log burner back boiler (17kw to boiler) installed, heating via gravity to thermal store mass with basic heat leak circuit.


The logic applied to the heater control:

Hot water - stat on thermal store actuates valve to heat thermal store only(Boiler+Pump activates and water diverts through thermal store coil)

Central heating - room stat actuates valve to diver water direct to central heating.

Now - this isn't what we wanted as we wanted the log burner to supply our hot water and central heating.

As above the log burner only heats the mass of thermal store which in turn gives us hot water, and the central heating is heated from the boiler direct. There is no link between the thermal store and the central heating currently.

Current config
Boiler - heats central heating and/or thermal store for hot water
Log boiler - heats thermal store for hot water only


Can anyone help here on how i correct this?


Basically i want the log burner to be our primary source for hot water and the boiler be our secondary source here.

What do i need to do to correct this to make it right without starting again without spending unlimited cash here, the H2 Panel looks like it offers all the logic i would like but how much to install. Your thoughts appreciated.
 
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First off, 120 litres is a useless size for a thermal store. You'll only capture about 3kwh.
Second, (but with a 120 litre store there's no point) you'd need to retube so that the heating feed and return connect to the mass of the thermal store and fit another pump.
You'd need at least 1 thermostat on the thermal store.
Control circuit- temp of store drops below whatever threshold you set= valve to store coil open, pump on, fire boiler (subject to timeclock).
Heating demand= fire up 2nd pump, if you're clever the heating demand timeclock will override the boiler time clock so when store temp drops below threshold the boiler fires up.
Hot water demand- governed by thermal store temperature
You could use an additional NC stat on the gravity flow to lock the boiler out if you wanted to
 
Thanks for your input here much appreciated.

My apologies typo there it's 210 litres. Is that enough?
We already have a variable stat belted to the thermal store which currently switches boiler on/off for hot water logic.

"You could use an additional NC stat on the gravity flow to lock the boiler out if you wanted to" - This is a great help thanks, i see how this could prevent the boiler firing up thanks.

Just to check because the back boiler is from an uncontrolled heat source i can i can't pump this circuit even though the system is vented? Im just concerned the back boiler gravity circulation is slow to heat the thermal store this way, and im sure the h2 panel has a pump integrated?
 
210 is still a bit undersized. Re the woodburner, did your cowboy fit and plumb it & was he HETAS or similar registered? Has he done the Building Control notifications?
Still re the woodburner, are the pipes from it to the store 22mm (naughty) or larger? How far above the woodburner is the store & how far away laterally?
Pumping from woodburner to the store- you musn't just stick a pump in line, you really don't want to obstruct the gravity circuit in any way. If your woodburner has 4 pipe connections you could in theory plumb a 2nd pumped circuit to the heat store (you'd need another 2 taps on the store, another pump and another thermostat required on the gravity return set so that pump will not operate if return is at less than 50 deg to prevent condensation). Talk to an accredited wet stove installer.
 
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No he wasn't HETAS he was Oftec i believe dont think he notified anyone as he was too busy plugging leaks.

Pipes between store and Log burner are 28mm, although they come straight out of the burner at horizontal :( they do rise after about 30cm up to the thermal store.
Height difference is about 1metre between Log store to Thermal store.
Thanks for your advice v much appreciated.
 
28mm is good, horizontal leg and only a metre rise is less good (generally 2m from top of burner to bottom of store is a decent minimum). Does it work- that stove of yours at full chat should have the store boiling in under an hour.
Any temperature gauges on the gravity flow & return (you can get cheapies from Amazon that clip on the pipe)- can give you useful info on how the thing is performing.
Did the same bod do the oil boiler as well- if he did & hasn't notified building control he's a very bad man, get on to OFTEC, if he actually is/was a member they may be able to help you
 
28mm is good, horizontal leg and only a metre rise is less good (generally 2m from top of burner to bottom of store is a decent minimum). Does it work- that stove of yours at full chat should have the store boiling in under an hour.
Any temperature gauges on the gravity flow & return (you can get cheapies from Amazon that clip on the pipe)- can give you useful info on how the thing is performing.
Did the same bod do the oil boiler as well- if he did & hasn't notified building control he's a very bad man, get on to OFTEC, if he actually is/was a member they may be able to help you

Thanks again for your time and knowledge here.
I had bought a small thermometer with probe from amazon as i had no idea what the temps were, just so happens the gauge he hacked into the thermal store insulation wasn't even belted on, in fact it was on the floor had fallen off, so i pressed it back in with the thermo probe so i have a close idea of thermal store temp.

Ran a small test this morning and for anyone else interested.
We have a Parkray Aspect80B it is a big stove. ---> 210 Thermal store (albeit poorly connected)
  • Nominal output to water = 11.3kW
  • Maximum output to water = 16kW
With quite a few seasoned logs in there Exhaust gas in flume is 400 degrees it seems to be heating the tank at about 12 degrees an hour. We are now on 63degrees (from 51.5) 60mins ago. And checked again up another 6 degrees after 30mins so its quite consistent but slow. I don't see this working even if it was connected to the rads :( Where is all that heat going!? Out the poxy chimney i guess.

So i guess we need to jack up the height in the airing cupboard (have about 800mm head room) and or add the 2nd two taps and a pump.

Going to speak to Oftec, no he didn't notify anyone, including his sparky which he promised he would (which he wired himself in the end) about this bellend he charged alot for this mess. Indeed i need an expert here. Not to mention we had Bosch out who pointed out he plumbed the boiler flow return the wrong way :(
 
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Oh dear. So your 11kwh to water boiler is delivering less than 1kwh at the moment. (energy required to raise temp of 210 litres by 10 deg c = 2.1MJoules). That is spectacularly inefficient and no it won't run the heating at all well (energy going out the radiators has to come from somewhere). I bet your 'plumber' didn't have a 28mm tube bender so just used elbows everywhere- really not clever in a gravity system. Be interesting to get some temperature gauges on the flow and return and see what the drop is. Also be interesting to check the temperature difference at the bottom and top of the flow while the system is warming up- I'm wondering how much that horizontal leg in the flow is choking the thermal syphon.

Not sure what the thermal load of your house is but if its a 4 bed probably in the 20kw area so even with 100% efficiency your woodburner/store will struggle to keep the place hot. Warm should be achievable.

You're going to need someone to check the system over for building regs anyway (doubt OFTEC will help with the woodburner side), not sure what the deal is with installers commissioning someone elses' solid fuel system, if you have any local woodburner shops they might be a decent source of good installers who can give you some guidance. It's going to cost, that's for sure- I'd start thinking about small claims/trading standards on your AWOL plumber, we're not talking hundreds here.
 
With a stove output that high it should be jumping off the ground , are you sure your wood is 20% or less moisture content when split and measured in it centre?
Whats the colour/ types of the deposits on the boiler ?
 
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Oh dear. So your 11kwh to water boiler is delivering less than 1kwh at the moment. (energy required to raise temp of 210 litres by 10 deg c = 2.1MJoules). That is spectacularly inefficient and no it won't run the heating at all well (energy going out the radiators has to come from somewhere). I bet your 'plumber' didn't have a 28mm tube bender so just used elbows everywhere- really not clever in a gravity system. Be interesting to get some temperature gauges on the flow and return and see what the drop is. Also be interesting to check the temperature difference at the bottom and top of the flow while the system is warming up- I'm wondering how much that horizontal leg in the flow is choking the thermal syphon.

Not sure what the thermal load of your house is but if its a 4 bed probably in the 20kw area so even with 100% efficiency your woodburner/store will struggle to keep the place hot. Warm should be achievable.

You're going to need someone to check the system over for building regs anyway (doubt OFTEC will help with the woodburner side), not sure what the deal is with installers commissioning someone elses' solid fuel system, if you have any local woodburner shops they might be a decent source of good installers who can give you some guidance. It's going to cost, that's for sure- I'd start thinking about small claims/trading standards on your AWOL plumber, we're not talking hundreds here.

Sadly you are right (again) the 28mm punches through the wall from kitchen horizontal to the base of the thermal store from the log burner then bends 90 on a compression elbow vertical to the top of the Thermal store. Tip my hat to you again sir!

I have purchased a load of pipe temp gauges so will take your advice and run some checks on pipes as you say there is a significant issue here more than likely caused by a lack of height and poor routing of pipes.

Spoke to Oftec yesterday and i have to say whilst the chap sounded professional and helpful there wasn't alot they could do. Didn't seem keen to send anyone out to inspect the work and mentioned their only assistance would be to give the engineer in question a ticking off and or ask him to come back and finish the work properly, they seem to have far less power than Gas Safe, i was told the reason being oil engineers had less risk of killing someone over Gas? I'm not sure i agree with that. Oftec seem to operate the same model as checkatrade relying on income from paying Engineers, at least you can leave a review on their work on Checkatrade...(not that i in any way endorse these sheisters as they clearly also favor protecting their revenue over a customer who doesn't pay them anything).

Oftec quote - By selecting an OFTEC registered technician you are provided with peace of mind that you are choosing a skilled and qualified engineer. An OFTEC registered technician can also save time and reduce costs because they self-certify their work, avoiding the need for a building inspection and associated fees. - I disagree.

Anyway i digress. Thankyou again for your input.

Just to add we observed alot of fizzing in the horizontal section of flow pipe from Log boiler when the Thermal store was reaching hi 70's (c) and then bubbling noises in the thermal store which ran up to the header tank, which i assume is another illustration of a slow flow from the back boiler to thermal store causing the flow to overheat instead of charging the thermal store.
 
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With a stove output that high it should be jumping off the ground , are you sure your wood is 20% or less moisture content when split and measured in it centre?
Whats the colour/ types of the deposits on the boiler ?

Good question but ive already had our local log burner chap over to investigate as he discovered we were initially burning damp logs, he ran a smoke/draw test at the same time. We got a new delivery in from another source which he tested with a damp gauge. He also was the one to recommend sticking a temp gauge on the flu to ensure we are burning around 300/400c which we are most of the time, esp when conducting that test yesterday.

Glass is staying clean now, and no real deposits as such just ash. Walls of boiler becoming smoother again now.
 
Believe me I take no pleasure in being right. Your setup (woodburner level ish with the store) needs some looking at- rule of thumb is at least as much rise as there is distance to the store. If it was possible you'd improve the performance by swapping the pipework round (so the pipes start vertical out of the woodburner then track across to the thermal store with as much rise as you can get away with- there is wiggle room in compression fittings and a bit of flex in the tube, you can get about 5 degrees if you're careful- doing that would get the syphon going a bit better but probably not a lot.

OFTEC- that figures. From the sound of it the oil bit is functioning correctly anyway, just a problem with certification.

Burn temperature- hope you mean 300-400 deg F, my flue gauge reckons 400 deg C would be far too hot

EDIT The fizzing is kettling, caused by the woodburner getting a bit hot and happening because of poor circulation. Not to be encouraged but not a danger in a properly designed system in the short term (can cause corrosion if it happens a lot).
Question- the open vent, heat sink rad etc- are they vertical direct from the woodburner or do they do this horizontal dance as well (hope not, that could get a bit risky with the kettling)
 
Yes correct 300-400 deg F !

And ahh yes your assumption is correct again. They run flat on loft floor here is crude representation of current plumbing.

Not clear but bascially flow for example runs 600mm horizontal from log burner through wall to airing cupboard which sits on a slightly higher level (steps up) from ground floor. Then 90 degrees rise 1300mm to an elbow into thermal store.
 

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Is there a feed and expansion tank in the loft? Prob only small (30 litres), should be metal, usually the feed pipe drops to the return & expansion (loop over the top) comes from the flow
And have you got a spirit level- you need to make sure those horizontal legs are either horizontal (bad but tolerable) or have a slight rise towards wherever the expansion pipe comes off. If there are any negative gradients especially in the flow then kettling could get dangerous
EDIT Looking at your sketch, there is scope for improvement- if you rerun the flow & return from the woodburner so they run diagonally up then vertical you'll get a large performance boost
 
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