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    • CommentAuthorJeff B
    • CommentTimeOct 3rd 2017
     
    Is it OK (i.e. safe) to put an NRV in the flow and/or return pipework from a wood pellet boiler? The reason I am thinking this is to prevent thermosyphoning from the thermal store back to the boiler when the latter is not on e.g. overnight. I have put a loop and an NRV in the C/H circuit and this has worked very well in preventing thermosyphoning.
  1.  
    I would be concerned about the residual heat in the pellet boiler in the event of a power cut. Read the installation instructions of the pellet boiler to see if any gravity flow is required to cater for residual heat, if yes then no NRV. And also ask the manufactures of their opinion.
    • CommentAuthorJeff B
    • CommentTimeOct 5th 2017 edited
     
    Peter - OK I checked - installer says no to an NVR but suggests adding a normally closed valve and buffer tank thermostat to switch the circulating pump on and off (i.e. the pump between the boiler and the buffer tank). I'm wondering if that's correct though because wouldn't that be effectively the same as an NRV i.e. when the buffer tank is up to temperature the valve will close and the boiler will keep on running?
  2.  
    I agree with you that a normally closed valve would be no better than a NRV (or even worse as electrically operated valves go wrong or stick more frequently than NRVs)

    How is the circulating pump controlled now? And what causes the boiler to fire up?

    How much gravity circulation are you getting now? The thing about gravity circulation is that there needs to be a heat loss or lower temperature above the heat source. When the TS is up to temp. then (providing the pipes are insulated) you should only get gravity circulation whilst the boiler temp. is higher than the TS temp. when the boiler temp. drops (e.g. due to the gravity circulation) I would expect the circulation to stop.

    Is the boiler next to the TS and both within the heated envelope?
    • CommentAuthorJeff B
    • CommentTimeOct 6th 2017
     
    Peter - thanks for your comments and questions.

    The circulating pump (i.e. the pump between the boiler and the TS) is controlled by a master controller Model WLM2 made by OJ Electronics (which I have just discovered has been discontinued - great!). I have recently found out, as part of a grand investigation into the very complicated heating system I have here, that the pump is linked to the motorised valve on the DHW cylinder. When the DHW thermostat is satisfied, the MV closes to stop boiler flow to the DHW cylinder and at the same time the MV microswitch opens and cuts the current to the circulating pump. This would be ok except that when that happens the thermal store stops receiving boiler flow too because the circulating pump has stopped, so if the central heating is on at the same time then this quickly “drains” all the heat from the thermal store because the C/H system has its own circulating pump!

    The boiler will fire up when the boiler temperature falls to below 60C. Currently it is set to run at an operating of 75C. There is no electrical connection between the boiler and the rest of system – it is strictly a stand-alone system i.e. there is no possibility of remotely starting the boiler.

    It is interesting what you say about gravity circulation. It seems to me that when the boiler goes off and cools down that there is thermo-syphoning back from the TS to the boiler because the boiler flow/return pipes at the TS end stay very hot for sometime after. However I admit that this is only a subjective observation on my part – I really need to monitor this properly with my IR thermometer.

    Re: locations. The boiler is in the garage and the TS is in a cloakroom inside the house. They are about 8 metres apart in terms of horizontal distance but about 12 metres apart in terms of length of pipework as we live in a dormer bungalow and the pipes from the boiler go up into the space behind the dwarf walls and then back down again to the thermal store at the other end. They are very well insulated.
  3.  
    If the pipes to and fro the TS are well insulated I would expect them to stay hot for a good while. If they cool down eventually in advance of the TS cooling then You don't have much (any) gravity circulation.

    How does the TS call for heat from the boiler? From your description it sounds like that the boiler will switch off when the DHW is up to temp.

    What I would expect is that both the DHW tank and the TS would have a thermostat switch that could call for heat from the boiler so that either can start the boiler. When the DHW calls for heat the same signal would operate the MV so that DHW would have priority over the CH. I would expect the DHW thermostat to turn off the boiler and the MV leaving the TS thermostat to call for heat if needed. The pump should be operated by either the of the DHW thermostat or the TS thermostast calling for heat or perhaps an 'up to temperature' signal from the boiler (done to prevent the pump running if the boiler is out) (sorry about the alphabet spaghetti).
    • CommentAuthorJeff B
    • CommentTimeOct 8th 2017
     
    Peter – thanks for your latest reply. The fundamental snag with my system is that the boiler is a completely stand-alone unit i.e. there is no facility for remote starting. When I bought the boiler (3 years ago) I was promised that a software modification to allow remote starting was “on its way” – this has never materialised. The boiler has its own internal time clock (I can set up to 4 on and 4 off periods per 24 hours) and the rest of the system has a separate time clock which I set to start about half an hour after the boiler has fired up and to stop about half an hour before it shuts down.

    The flow from the boiler splits into two branches near the DHW tank – one to the DHW tank and the other to the TS which is more or less directly under it on the ground floor. This flow is maintained by a separate circulation pump. Currently this runs all the time that the system timer is on i.e. about 3 hours in the morning and 6 hours in the afternoon/evening. I am looking at ways to link this to a thermostat on the TS.

    When the DHW thermostat is satisfied, this closes the MV on the boiler supply to the DHW tank and all the boiler flow goes to the TS. There is no MV on the TS so the boiler runs until the TS is up to/close to the boiler temperature (75C) and the boiler modulates down and down until it turns itself off. Crude but effective, although I suspect I am burning more pellets than is necessary. There must be standing losses from the TS overnight as the cloakroom where it is sited is like the desert simulation at Kew Gardens. I know this is still within the heated envelope, so it’s no big deal.
    • CommentAuthordpmiller
    • CommentTimeOct 9th 2017
     
    can't you just break into wire to the boiler's timeclock to get remote control?
    • CommentAuthorJeff B
    • CommentTimeOct 9th 2017
     
    <blockquote><cite>Posted By: dpmiller</cite>can't you just break into wire to the boiler's timeclock to get remote control?</blockquote>

    I wouldn't be able to do that as the boiler functions/settings are controlled from a touch-screen, behind which is a microprocessor unit. There is no physical time clock per se.
    • CommentAuthorArtiglio
    • CommentTimeOct 9th 2017
     
    If i understand your descrition in an earlier post, the system is set up to fire the boiler when the buffer/store has dropped to 60 degrees and shuts the boiler down when it reaches 75 degrees.
    If this is correct and the buffer/ pipework (between boiler and buffer) is good, is there any great disadvantage to leaving the boiler switched on 24/7 (at least during the heating season). Effectively giving control via the central heating controls.
    Notionally there may be a slight advantage in that, (again from my understanding) hot water usage may reduce the buffer temp between boiler/heating cycles.
  4.  
    I was thinking on the same lines as dpmiller !

    It depends how old school the boiler is after the microprocessor. If the microprocessor triggers a run sequence that is controlled by thermostats and relays then it may be possible to remove the microprocessor signal to the run sequence hardware and substitute an input from the DHW and TS thermostats with if needed an external timer. Of course this would remove (some / most / all of) the function of the microprocessor which may have unintended consequences so someone who understands what the circuitry is doing shouild look at it to enable the safe rewiring of the boiler.
    •  
      CommentAuthordjh
    • CommentTimeOct 9th 2017
     
    It seems to me that the heating system is obviously incorrectly wired and/or plumbed. My first step would be to get full plumbing and wiring diagrams as designed, if you don't have them already, and compare them to the actual system to see whether they match. If not, find out why not. If they do match then ask the designer (who was that?) to explain how it is supposed to work, and specifically how it deals with the cases that have been discussed.

    Was the promise of remote boiler control made in writing? What does the boiler manufacturer say about its non-delivery?

    Posting the plumbing and wiring diagrams and the makes and models of the major components would be helpful.
  5.  
    It sounds to me as if the plumbing is OK in that when the boiler runs the TS heats up unless the DHW is calling for heat in which case the MV diverts the boiler output to the DHW. This is a standard setup with the boiler running both DHW and CH with priority to DHW.

    The wiring however..... The boiler should be able to start up from an external demand either the DHW and/or the TS. If the boiler could be made to start up from an external demand then it sounds like the issues would go away.
    • CommentAuthorJeff B
    • CommentTimeOct 9th 2017
     
    Artiglio: It seems that this is the norm on the continent according to the boiler manufacturer (Ekopower) i.e. the boiler is on 24/7. I think this would be wasteful of pellets as our house is well insulated and we don’t need the heating on all day (and certainly not all night). During the heating season the boiler is programmed to come on for 3 hours in the morning (7-10am) and then again for 7 hours in the afternoon/evening (3 – 10pm).
    • CommentAuthorJeff B
    • CommentTimeOct 9th 2017
     
    Peter - I have asked the boiler installers and apparently there is a “boiler management system” which would involve installing temperature probes on the TS to control the boiler. However this would mean I would have to connect the boiler to the TS in a direct mode rather than indirect which is the way I wanted to go (i.e. remove the F&E tank and have a pressurised system). Hence I dismissed this idea.
    • CommentAuthorJeff B
    • CommentTimeOct 9th 2017 edited
     
    Djh: the whole system is a problem indeed; unfortunately the full story is a long and boring one. If you can face it, here it is:

    Originally there was just a thermal store with 3 coils, one for solar thermal input and the other two for other heat sources e.g. ASHP etc., together with an OPOP wood pellet boiler. This could be remotely started and was a very simple boiler with no frills (no fancy self cleaning features). There was no separate DHW tank. There was a weather compensator and a mixing valve, which blended the boiler flow and C/H return etc. We have an electrical diagram but not a drawing of the plumbing aspects. This combination did not work very well in that the thermal store being on the small side (300 litres) was not man enough to cope with C/H and producing DHW at the required temperature at the same time.

    So we started to think about how we could incorporate a separate DHW tank. Unfortunately in the interim the company that designed and installed the original system had gone bust so we found another green energy company to modify the system for us. We then had a separate DHW tank installed upstairs and the pipework and some of the electrics were modified accordingly. We did not get a proper set of drawings for this, so we are not sure exactly what mods were made to the original system.

    We then changed the boiler from the OPOP to the Ekopower as my wife was not amused at the idea of cleaning out the OPOP. The Ekopower is supposed to be self cleaning but this is a bit of a joke really – there is more to do with this boiler than there was with the OPOP! Part of the incentive to change was that we would qualify for RHI payments. (We bought the OPOP less than a year before the RHI cut off date – typical!).

    We discovered that the entire heating system was set up as a direct system i.e. the water in the boiler, TS and C/H system was the same throughout and the two of the three TS coils were not used. I was getting a gassing problem in the C/H system so we decided to revamp the whole lot using one of the TS coils for boiler flow and the other for C/H. In this way each part of the system is separate and pressurised (no, more F&E tank) and can be dosed with inhibitor independently. The weather compensator has been disabled as well as the blending valve, so the plumbing is very simple now. However this has thrown up some additional issues as I have described in this thread!

    There is still a mass of unidentified white cables running here, there, and everywhere and I will be checking these in due course and labelling appropriately. When this is all done I would then be in a position to do an electrical diagram and a plumbing diagram. This is something I need for my own sanity and for any new user in the event that I sell up and move and some point in the future. (No plans to do that but who knows what life can bring!).

    P.S. Yes, the offer of the remote start upgrade is in writing. Maybe time to chase up the manufacturer and see where they are at with this.
    • CommentAuthorJeff B
    • CommentTimeOct 9th 2017
     
    <blockquote><cite>Posted By: Peter_in_Hungary</cite>It sounds to me as if the plumbing is OK in that when the boiler runs the TS heats up unless the DHW is calling for heat in which case the MV diverts the boiler output to the DHW. This is a standard setup with the boiler running both DHW and CH with priority to DHW.

    The wiring however..... The boiler should be able to start up from an external demand either the DHW and/or the TS. If the boiler could be made to start up from an external demand then it sounds like the issues would go away.</blockquote>

    Maybe time to get back to the manufacturer to see if there is any progress on this!
    •  
      CommentAuthordjh
    • CommentTimeOct 9th 2017
     
    Posted By: Peter_in_HungaryIt sounds to me as if the plumbing is OK in that when the boiler runs the TS heats up unless the DHW is calling for heat in which case the MV diverts the boiler output to the DHW.

    Please reread the description of the plumbing more carefully. It isn't a standard setup.

    That's why I asked to see the diagrams; the problems will be more obvious.

    Posted By: Jeff BI will be checking these in due course

    Yes, the complicated history makes it even more imperative to get an accurate picture of the hydraulic and electric circuits before starting to diagnose the system and propose improvements, IMHO. So I would say that 'due course' starts tomorrow!
  6.  
    Posted By: djh
    Posted By: Peter_in_HungaryIt sounds to me as if the plumbing is OK in that when the boiler runs the TS heats up unless the DHW is calling for heat in which case the MV diverts the boiler output to the DHW.

    Please reread the description of the plumbing more carefully. It isn't a standard setup.

    I read the description of what was and what remains and
    Posted By: Jeff Bso the plumbing is very simple now.

    To me the remanent sounded pretty standard - boiler heats TS with priority to DHW tank

    But yes diagrams of plumbing (combined in use and redundant) and a wiring diagram including a boiler wiring diagram would be helpful
    • CommentAuthorJeff B
    • CommentTimeOct 10th 2017 edited
     
    DJH wrote: "Yes, the complicated history makes it even more imperative to get an accurate picture of the hydraulic and electric circuits before starting to diagnose the system and propose improvements, IMHO. So I would say that 'due course' starts tomorrow!"

    DJH - I absolutely agree! Unfortunately my time is rather stretched otherwise I would love to get stuck into this. At the moment it's a case of just keeping the whole system going whilst ensuring that pellet consumption is kept at a reasonable level. When I do get my head around how the system works I'll do some diagrams and update the thread.

    Thank you, and Peter, and others, for your helpful inputs.

    Meanwhile, in the words of the famous Antarctic explorer....I may be gone for some time!
    • CommentAuthorArtiglio
    • CommentTimeOct 13th 2017
     
    Evening Jeff

    Whilst i can see your concern, surely so long as the boiler is controlled by the TS/buffer temperature and there is no heating demand, the boiler whilst on would not be required to fire up unless the TS temperature had dropped sufficiently through standing losses. Which if it does rather negates the point of having a buffer/ts and indicates better insulationnis required.
    The system, which i look after, is based on a basic polish boiler (ekogren but badged and marketed by trianco) this stays on 24/7 controlled by buffer temp. Average losses over a 12 hour period are around 2 degrees. The boiler can function in two modes,
    1) pellets are fed to maintain a bed of smouldering embers.
    2) the feed ceases once buffer temp has stabilised for a period of time (2 hours , i believe)

    Innthe first case , response time is much faster than the second where it takes around 15mins to relight and get ypto temperature. Extra pellet consumption in this mode seems to be negligible against the second setting, in which because the boiler needs its temperature raised further and so uses pellets to do so.

    This is all based on a system heating a stone built welsh farmhouse, which is far from being ideally insulated, ewi would ruin the external appearance of the building, internally everything is in good condition and iwi would be intrusive and disruptive to have fitted. As such the amount of pellets burnt to keep the boiler "on and warm" is an insignificant percentage of annual consumption. Which is currently around 7.5 tonnes p/a.
    System efficiency gained the most from painstaking insulation of pipework and buffer.
    • CommentAuthorJeff B
    • CommentTimeOct 14th 2017
     
    Artiglio - thanks for your response. I have got the equivalent of your scenario (2) here, in as much as the boiler seems to modulate down to 5.5kW and then "coasts" along for what appears to be an indeterminate time before switching off. I don't have any equivalent to your scenario (1) with my boiler. As you rightly say, once the boiler has turned off it takes quite a while to get back up to temperature and when it does come back on, it burns extra pellets as it does so. However I'm not convinced that this represents an insignificant percentage of annual consumption in my case since we modified the system. I'll need much more data though to be sure. I keep a daily record of the amount of pellets we use, and have done so since we had the boiler (3 years).

    We live in a 4 bedroom detached dormer bungalow in a fairly elevated, windy location near the coast in west Wales. I have put in a lot of extra insulation including IWI upstairs. I have 15 radiators with a total rated output of 18 kWh. The max boiler output is 25kW and we use 3 tonnes pellets p.a.

    I admit that whilst the pipework is well insulated, the TS has only a minimal layer of insulating foam applied by the manufacturer (approx 25 mm) so I have added two layers of the trifoil type insulation which has helped - the cloakroom where it is situated is no longer suffocatingly hot! Nevertheless the foil still feels quite warm on the surface, so maybe I could add a few more layers.

    I could add a thermostat to the TS and use it to operate a motorised valve to stop the flow from the boiler when the TS is up to temperature. In this way the boiler temperature would increase and the boiler stat would turn off the boiler. However the installer has indicated that this should not be done for safety reasons (or at least I should not install a non-return valve for the same reason but which in my opinion would be the same as having an MV?)
    • CommentAuthorArtiglio
    • CommentTime6 days ago
     
    Evening Jeff

    Our TS is 1000l , as supplied it had only a 100mm fibre jacket, that was penetrated all over for endless possible connections. Over the course time I've added,

    40 mm of foil backed rockwool
    Layer foil faced bubble wrap
    150 mm "space wrap"
    Foil bubble wrap
    100mm celotex "cap"
    Cling film ( to hopefully fully seal the insulation)

    This cut losses from the store from nearly 1 degree per hour , to less than 4degrees per day. Which saved around 4kg of pellets per day.

    You may not be so far away, LL36 .
    • CommentAuthorJeff B
    • CommentTime5 days ago
     
    Artiglio - wow, you must have doubled the diameter of the store with all that insulation!

    I have done a little bit more investigation into heat losses since I started this thread. The loop I put in plus the NRV have completely stopped thermo-syphoning into the C/H side of the system. I haven’t done anything with the boiler flow/return side as yet (still confused about MV’s vs NRV’s) but I have noticed that both the flow and return pipes are cold by the morning yet the TS is still holding its temperature pretty well (although see below). From this I conclude that thermo-syphoning back to the boiler is not an issue after all.

    I have been monitoring the TS and have found that it drops about 6C overnight (from 10pm to about 7am) which is not brilliant I realise. I am not surprised as despite the extra insulation the surface is very warm to the touch. I do not have the room to add much more insulation as the TS is in a cloakroom. The room is 1000mm wide and the TS is currently 600mm wide! I need space to get around it as all the connections are on the back of the store but I could add some more of the foil faced bubble wrap. [I like the cling film idea!]. The TS is of course indoors, so the “lost” heat is going into the house anyway, rather than to outside. Since I have balanced the radiators properly I notice that the two in the hallway are not coming on at all, as this area, immediately outside the cloakroom, must be being heated by the TS. If I put a duct though the cloakroom wall with a fan I could create a mini warm air system!

    Our TS has an F&E tank built in on top and this will be the difficult part to insulate really well.

    What is the temperature of the water in your TS? Our’s is at about 72C.

    Jeff

    P.S. we are near St.Davids, Pembs. You must be near Towyn, so probably similar weather conditions to us.
    •  
      CommentAuthordjh
    • CommentTime5 days ago
     
    Posted By: Jeff BOur TS has an F&E tank built in on top and this will be the difficult part to insulate really well.

    Why can't it just be wrapped along with the thermal store itself?

    I'd be tempted to stuff the whole space around the thermal store with insulation (recycled plastic wool is my favourite) to stop airflow and accept that you'll have to pull it out to access the connections if required.
    • CommentAuthorArtiglio
    • CommentTime5 days ago
     
    Evening Jeff

    The store has certainly increased in size, ours is in a barn room above the boiler across the farmyard from the house, so any lost heat is totally wasted, hence the overkill. Heat losses in the colder months when it was first installed were horrendous. Still room for improvement but certainly hit the point of diminishing returns.
    The peak store temp is 80 degrees, the boiler is fired up once the store temp drops to 60 degrees. There are occasions of short cycling when the store is asked for just a little heat and gets a slug of cold water from the main connecting it to the house, this causes the boiler to fire unnecessarily as once the store restratifies the temp is often in excess of 60, this could be dealt with by adding a delay to the boiler firing , but in winter with a high heat demand this could result in the store losing too much heat, so system is staying as is.
    We opted for a low tech system/boiler under the rhi scheme , so can't expect wonders. House is certainly more comfortable and heating more efficient than the old lpg boilers.
  7.  
    Posted By: ArtiglioThere are occasions of short cycling when the store is asked for just a little heat and gets a slug of cold water from the main connecting it to the house, this causes the boiler to fire unnecessarily as once the store restratifies the temp is often in excess of 60,

    Ermm A slug of cold water, or cooler water should not cause the TS to de-stratify. That implies that there something amiss with the return, either too fast or the entry is too turbulent due to bad piping.
    •  
      CommentAuthordjh
    • CommentTime5 days ago
     
    Thermal stores don't get any water from the mains, except when they are filled. That's their whole point.
    • CommentAuthorArtiglio
    • CommentTime4 days ago
     
    Djh- apologies a poorly worded post, the ts receives a slug of cold water from the piping between the boiler room and house, a flow and return each of 40mm. The product used is described as district main a term that has stuck.

    PiH , again another poor choice of words, the initial return to the ts when the house calls for heat, enters the ts and can trigger the temp sensor that fires up the boiler when below 60 degrees. Certainly the set up could be better. Pump currently running close to its mimimum , redoing the pipework seems a bit much given the issue is relatively minor. Moving the temperature sensor to a different pocket , seems a better option, but means stripping off much of the extra insulation i've added. Currently not a high priority.
    • CommentAuthorJeff B
    • CommentTime3 days ago edited
     
    <blockquote><cite>Posted By: djh</cite><blockquote><cite>Posted By: Jeff B</cite>Our TS has an F&E tank built in on top and this will be the difficult part to insulate really well.</blockquote>
    Why can't it just be wrapped along with the thermal store itself?

    I'd be tempted to stuff the whole space around the thermal store with insulation (recycled plastic wool is my favourite) to stop airflow and accept that you'll have to pull it out to access the connections if required.</blockquote>

    Sorry not very well explained. The circumference of the F&E tank is insulated with the alu foil covered shrinkwrap but I don't want to bury the F&E as I would like to be able to inspect the contents from time to time. It has a circular aluminium lid which I have covered with polystyrene but there is just a 10mm lip which is exposed - I can live with that.
   
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