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    • CommentAuthorJeff B
    • CommentTimeMar 12th 2020
     
    Back in 2007 we bought our retirement home. A 4 bed, detached, dormer bungalow so the family can come and stay whenever. C/H and DHW was originally provided by an oil fired combi-boiler but we wanted to move away from oil and so invested in a wood pellet boiler. At that time (pre-RHI) wood pellet boilers were a novel concept so to some extent I was a “pioneer” as indeed was the small, fledgling green energy company I used to design and install the system. In addition to the wood pellet boiler (25kW model) we installed solar thermal panels at the same time and later on, solar PV.

    A lot has happened in the following 13 years! The design/installation company went out of business many years ago and I have been left to my own devices to sort out the vastly overcomplicated system. (The boiler room looked like the flight deck of a jumbo jet). I have learned a lot, in no small measure from the vast pool of expertise on this forum! When the RHI scheme came along we changed the boiler for a so-called self cleaning machine but we were sold a bit of a pup unfortunately but that's another story. (This was from a different company BTW).

    Originally the system was designed around a 300 litre thermal store (TS) which was supposed to provide DHW and space heating via the C/H. The TS has a solar coil. The reality was this simply did not work - we had tepid water at the taps and tepid water in the radiators! The system was then modified by installing a separate 180 litre tank with solar coil just for DHW and this has been a big help.

    One huge snag with the pellet boiler is that it cannot be remotely started (as a normal boiler would) when there is a demand for C/H. The boiler will only start when it senses a drop in temperature of the return water to 40C, so there is a long lag phase. When it does decide to start up it first goes through a lengthy rigmarole of ash clearance, air purging, pre-ignition etc which can take about 20 minutes! So in order to heat the house in the morning or evening the timer on the boiler has to be set about about 30 minutes in advance of the C/H timer. If these get out of synch and the boiler reaches the cut out temperature (75C) quicker then it shuts down before the C/H has had time to warm the place. All the heat from the TS is rapidly extracted and it cools, so when the boiler does restart it not only has to heat up 12 radiators but a 300 litre tank of water too!

    Hence my question - do I need a thermal store any more? IMO it is purposeless now.

    I would be very grateful for any advice/ideas on this.
    •  
      CommentAuthordjh
    • CommentTimeMar 12th 2020
     
    Posted By: Jeff BOne huge snag with the pellet boiler is that it cannot be remotely started (as a normal boiler would) when there is a demand for C/H. The boiler will only start when it senses a drop in temperature of the return water to 40C, so there is a long lag phase.

    It seems to me that sorting out the control system of the boiler might be a better plan than scrapping the thermal store and dealing with the consequences. If the boiler has been off overnight or at least for an extended period, which I assume is the case, why is the return water still warm?

    Perhaps a diagram showing all the components and connections, together with the brand/model names will help.
    • CommentAuthorGreenPaddy
    • CommentTimeMar 12th 2020 edited
     
    time overlap with DJH above

    First thoughts are...

    - you need a buffer for a pellet boiler, which the TS acts as.
    - 300 litres is a bit on the small side, but can be made to work fine, even without the DHW cyl.
    - a lot has to do with what point the various systems (CH/DHW/boiler) connect into the TS
    - I don't like the sound of the activation for the pellet boiler being linked to CH return temps, and deff not when CH is switched on. The boiler should be controlled by temp inside the TS, so the boiler's job is to keep the TS hot, irrespective of who or what is using energy.
    - sometimes if there is not a clear understanding of the functionality of an entire system, an the differing demands it can be subject to (winter/summer, low use/high use), then people can just try to make it work the way they've always done it (like a gas boiler systems), and just add more bits to mask the underlying poor logic.

    If you draw up a reasonably detailed schematic, and post it, I suspect we can help get it running correctly for you. Diagnosing by written word is not ideal.
    • CommentAuthorRigmarole
    • CommentTimeMar 12th 2020 edited
     
    I'm not sure if it's helpful or not but our thermal store needs to be kept at 80 degrees c for decent long showers. The gas boiler kicks to heat it in when it drops to 70 degrees, then heats back up to 80 (good for efficient boiler condensing, apparently - I forget the name of this temperature difference thing on the thermostat). The gas boiler can heat the store pretty rapidly, so for us, this temperature difference on the thermal store thermostat works.

    I have a timed system when the temperature of the store drops to around 55-60 degrees c when we only need central heating.

    When the store is at its lower temperature: The hot water reaches the tap at around 55 degrees for a short while then soon cools. Perfect for rinsing out a tea cup or two during the day.

    When the store is at the higher temperature we never find we 'run out' off hot water, and my wife has ludicrously hot showers.

    Our store is 300L like yours. The temperature reading wells are at the bottom (for the thermostat), if yours are higher up you may need a lower temperature then us. The hot water comes quite high off the top of the store.

    The water pressure of the hot water is 3 bar.

    The reason I run it at two temperatures is because I figure it's pointless running a really hot thermal store when the cooler store setting provides our heating sufficiently. We crank it up when we have showers and the gas manages that fine in short time (actually I have a timer for the usual time we have a shower, but now and again we do need to override it).

    Yours will be different because of the delay of the pellet boiler (I guess, though I've never used one) but hopefully there above will help.
    • CommentAuthorArtiglio
    • CommentTimeMar 12th 2020
     
    My mums system has a 1000l buffer tank, boiler is controlled by the buffer tank temp, when buffer has dropped to 60c boiler kicks in and raises temp to 80c, boiler is on all the time. Heating controls used to draw from the buffer.
    Works well.
    Boiler is constantly lit , it feeds a few pellets to keep alight, so the time to reach full output is low. As installed the system losses due to poor insulation of buffer and pipework were substantial, over time i improved the insulation and in doing so reduced pellet use by over 5kg a day in winter.
    • CommentAuthorJeff B
    • CommentTimeMar 12th 2020
     
    djh/GreenPaddy/Rigmarole/Artiglio – thanks for your comments. As these overlap to some extent, let me make a joint reply. I need to explain the set-up a bit better I think. I agree a drawing is best but that will take some time, so for now this is how it is at present. There are two completely separate circuits but with the TS at the heart as it were:

    1. The boiler heats the thermal store and DHW tank both indirect (via coils inside the TS and the DHW tank). This is a sealed pressurised system incorporating an expansion vessel. It operates at 1 bar pressure. Both the TS and the DHW tank have an additional coil for solar thermal input. There are two pumps at work – one, lets call it Pump 1, in the loop at the rear of the boiler (back end protection circuit) and one, say Pump 2, which pumps the hot water over to the TS and DHW tank.

    2. The C/H takes its heat from the thermal store, again indirect via a coil in the TS. This again is a sealed pressurised system incorporating an expansion vessel. It operates at 1 bar pressure. It has its own circulating pump, say Pump 3, controlled by a room stat.

    So the return water that the boiler “sees” is that coming from the TS, not the C/H system. Hence in the morning the return water is warm as the TS stays hot overnight. However Pump 2 will not start until the boiler water reaches 60C. This is a good thing because if it started at a lower temperature the hot water from the TS would be pumped over to the boiler and the whole system would be cooled with the boiler acting as a large radiator. Conversely if Pump 3 starts too soon it will rapidly deplete the TS before Pump 2 starts!

    GreenPaddy – your comment “The boiler should be controlled by the temperature inside the TS, so the boiler's job is to keep the TS hot, irrespective of who or what is using energy” immediately rang an alarm bell. Currently Pump 2 is only activated at the same time as Pump 3 is activated, so this means the boiler is not pumping hot (>60C) water over to the TS as early as it could be. Hence the problem of the boiler getting to 75C and shutting down BEFORE the TS has had a chance to get heated properly. I think I will try wiring Pump 1 and Pump 2 together and see what effect that has, what do you think?

    Meanwhile I will try and draw a schematic for the whole system – would be a good exercise anyway to help get things clear in my head!

    P.S. Artiglio - did you ever get my whispered comments about finding a biomass engineer?
    • CommentAuthorGreenPaddy
    • CommentTimeMar 12th 2020 edited
     
    Deff need a schematic of this. I'm not even sure what the thermal store does, in terms of it being and actual thermal store, since everything is in its own closed loop via coils - kind of defeats some of the simplicity of having a thermal store, but no doubt the schematic will make it all clear.

    I would not rewire anything, until you have an absolutely crystal clear philosophy of what the system needs to do for you, and how you'll make that happen. Then, think it over twice more looking for every weird way it could possibly not do what you'd expect, and finally implement. I've unpicked quite a few nonsense heating systems. The end result always looks so simple, I wonder why it took me hours to suss it.

    Other comments about running a condensing boiler more efficiently at 80oC sound unusual to me, and water @ 55oC not being very hot...that should be giving skin damage. Most people would shower at around 42oC, almost certainly not up to 50oC. First thought is the DHW coil is undersized, as the heat transfer can't keep up with the cold mains flow, but that's not based on any detailed info.

    Temp stats or controllers positioning on the TS are absolutely vital, or you can be asking the boiler to do the wrong thing. These systems can be very simple, but can also be very simply screwed up.

    All the right bits are likely there with your system, just need to be arranged correctly.
    • CommentAuthorJeff B
    • CommentTimeMar 12th 2020
     
    GreenPaddy - thanks for your further comments. Can I just add that originally the C/H was direct i.e. the whole contents of the TS were part of the overall C/H water content. This required a huge amount of Fernox additive plus the system was gravity fed from an expansion tank in the attic which was also problematic. The TS is from Newark Copper Cylinders and the design is such that it could be operated either direct or indirect.

    The TS isn't really a TS, it is just a buffer tank of water at atmospheric pressure, dosed with chlorocresol to prevent mould/algal growth.

    I'll make a start on a schematic by the weekend.
    •  
      CommentAuthordjh
    • CommentTimeMar 12th 2020
     
    What is an "actual thermal store"? My thermal store is just an open-vented bucket of water with some plumbing and I believe that it is a thermal store.
    • CommentAuthorCWatters
    • CommentTimeMar 12th 2020
     
    <blockquote>So the return water that the boiler “sees” is that coming from the TS... </Blockquote>

    Does the boiler to TS loop pump run continuously so the boiler can monitor the return or does it just run briefly at intervals?

    If it runs continuously even when boiler is off then the TS might be heating the boiler!
    • CommentAuthorJeff B
    • CommentTimeMar 13th 2020
     
    Artiglio - when you say the boiler is constantly lit, do you literally mean it is burning pellets 24/7? I have tried keeping my boiler on 24/7 but it soon modulates down to 20% of rated output (i.e. 5 kW) and holds that for a while but eventually will turn itself off because the standing losses are minimal and the boiler temperature reaches the maximum permissible (75C). When heating is called for it takes an age to fire up again, as I described above. Once it has passed all the prolonged preliminary stages, then like your Mum's boiler, it doesn't take very long to get up to full temperature.

    I know you say that you have reduced the pellet consumption by 5kg per day, but can you tell me what the daily pellet consumption rate is on that boiler? Mine generally uses between 20 and 24 kg per day during the winter months.

    Did you ever get the whispered message I sent to you some time back regarding a biomass specialist? Just wondering how you got on.
    • CommentAuthorJeff B
    • CommentTimeMar 13th 2020
     
    <blockquote><cite>Posted By: djh</cite>What is an "actual thermal store"? My thermal store is just an open-vented bucket of water with some plumbing and I believe that it is a thermal store.</blockquote>

    Just a matter of semantics then?
    • CommentAuthorJeff B
    • CommentTimeMar 13th 2020
     
    <blockquote><cite>Posted By: CWatters</cite><blockquote>So the return water that the boiler “sees” is that coming from the TS... </Blockquote>

    Does the boiler to TS loop pump run continuously so the boiler can monitor the return or does it just run briefly at intervals?

    If it runs continuously even when boiler is off then the TS might be heating the boiler!</blockquote>

    I believe the TS loop pump only runs when the C/H calls for heat, so it runs at intervals. This is why I would like to wire it into the boiler pump so that the TS loop pump only runs when the boiler is on. GreenPaddy suggests that I should wait until I have sketched out a schematic and see exactly what's what, which seems reasonable!
    • CommentAuthorCliff Pope
    • CommentTimeMar 13th 2020
     
    I've some experience as a user of a small commercial-scale pellet system, and it was explained to me as follows:

    There are in effect two entirely separate and independent systems.
    1) There is a large thermal store, extremely well insulated. The central heating and hot water are drawn or circulated from this. Any demand for water at any time is therefore available from this. The size was specified so as to be able to meet any foreseeable demand.

    2) The boiler's only job is to monitor the temperature of the TS and to keep it topped up. It doesn't need to know what is being taken from the TS and when. The man down in the bowels of the battle ship just keeps shovelling coal into the boiler - he doesn't need to know what the captain is doing on the bridge.

    In practice, the boiler timing can be modified based on experience. It runs more efficiently at full blast than when trickling out heat, so it is wasteful to let it keep running all night making tiny additions to the TS - better to shut down and then come on say at 6am to get the TS up to capacity.
    • CommentAuthorJeff B
    • CommentTimeMar 13th 2020
     
    Cliff - thanks for your input. That is my understanding too. I have wrestled with this business of do I run the boiler 24/7 or just on a timer. I have found that having insulated all the pipework and the TS as far as I possibly can, I do not need to run the boiler 24/7. As you say it is definitely wasteful on pellet usage - I know from recording the amounts used overnight (my boiler display gives me a reading of the amount of pellets remaining in the side hopper). The tricky bit is getting the on/off timings of the boiler and the C/H just right.

    I am hoping that I can get some ideas from the folk on the forum as to how this can be managed better. I am working on a schematic diagram which I trust will provide the necessary info!
    • CommentAuthorArtiglio
    • CommentTimeMar 14th 2020
     
    Afternoon Jeff, no I didn’t receive a message ended up using a chap who travelled from south wales. The boiler remains constantly lit , once it has satisfied the buffer tank demand it feeds just a handful of pellets every 20 minutes or so thus keeping a small burn going but this is only getting air via convection so really just smoulders, once the buffer wants heat again the fan kicks in and it feeds more pellets, then once the boiler detects an increase in exhaust temperature it ramps up to full power then modulates down once buffer is upto around 75c, then going back to a “slumber mode” once it reaches 80c. This gets the boiler running flat out in about 5-10 mins max.
    On occasions the boiler will have extinguished entirely (usually in strong winds that draw too much air past the pellets) in which case the boiler doesn’t detect the exhaust gas temp increase and so instead goes through an ignition sequence. If this happens then it takes upto 20 mins to reach full output.

    Over the 5 years the system has been in the average pellet use is 8.6 tonnes a year, on a cold windy day it can get through about 50kg but usually a winter day is nearer 30kg, in summer where it only satisfies hot water , 5-10 kg depending on how many people are in the house.

    But there are also 2 wood stoves in the house and mum burns about 8-10 tonnes of wood a year.

    House is 250m2, main section is 600mm stone walls , insulated to building regs in 1994 ( so very poor) the various extensions and add ons over the years similarly not brilliant.

    Over last few years mum has been persuaded to keep house warmer and once its upto temp and kept there ( and the walls dried out) its been noticably more stable and comfortable to live in. To the extent that i can tell when i visit if she’s only warmed it up for my arrival, having caught her out a couple of times she now keeps it warmer all the time.

    Like your place, the heating systems. ( main house and attached cottage) were on their own systems, they are now linked to the buffer via heat exchangers, as i wanted to keep them separated in the event of a leak and end up having the contents of buffer and heating systems lost /needing to be cleaned up.
    So buffer to heat exchangers to standard s plan. Its all worked very well , a few pellet feed issues and ignitor problems aside, but none have been major.
    • CommentAuthorJeff B
    • CommentTimeMar 14th 2020
     
    Artiglio - thanks for your detailed response. Sorry you didn't get the PM, I don't know what happened there. I can see it ok! Could you PM me the details of the guy you used? I live in the far west of Pembrokeshire so it may be a long way for your chap to travel.

    Wow, your mum's place uses quite a lot of fuel! As you say the insulation is probably not marvellous. We use 3 tons of pellets p.a. (Sept to April) and rely mostly on solar thermal for DHW for the summer months when the boiler is off. Occasionally we may have to use the immersion heater to top up, if we have visitors.

    My system has been mucked about with so much from the original design, which to be honest was hugely over-complicated to start with (most ordinary plumbers looked stunned when they saw it). I must admit I have done a bit of tinkering as has my brother-in-law (who is a plumber) to simplify the system. There are some really odd things going on now, so I hope to produce a schematic this weekend to share with others here on the forum and maybe get some ideas to try out.

    I don't get many problems with my boiler either. Igniters - yes - some seem to last for years, others months. The pellets are good quality and the supplier is only about 10 miles from here. We get a bulk blown delivery every summer when the price should be lower, but strangely never is! I have rigged up an automated feed system which takes the pellets from the outdoor silo and passes them over a sieve to remove dust before they get into the side hopper. My main worry is if there was a breakdown requiring new parts. It is an Ekopower 2500 and the Danish manufacturer has disappeared. There are some spares to be had in the UK but for how long? The secret seems to be regular monthly maintenance, keeping the burner pot and the ash plate clean, and lubricating the worm drive on the ash plate.
    • CommentAuthorJeff B
    • CommentTimeMar 15th 2020
     
    Attached please see the schematic diagram for our heating system. Apologies for the quality – it is a freehand jobby and is definitely not to scale!

    The boiler is an Ekopower 2500 (25kW), the low loss header is Elterm, the DHW tank is Gledhill and the TS is from Newark Copper. The three pumps are all Wilo Gold RS50's.

    Myself I don't think the Elterm is necessary as the boiler already has back-end protection. I recently changed the boiler pump (the old one died) and now the balance has been upset so that the flow temperature of the water leaving the Elterm is about 10C less than that coming in from the boiler (boiler = 75C, Elterm 65C). This is somewhat self-defeating when the whole point is to get the TS to as high a temperature as possible.

    The purpose of the "loop" with the 3 way motorised valve is to prevent a slug of cold water moving into the coil in the TS when the boiler first starts up in the morning. This is because there is a very long run of 28mm pipe from the garage to the TS.

    I am aware that there are no temperature probes/controls on the TS. In a way these are not necessary I think, as the object is to keep the TS continually topped up which the boiler will do by ticking over by modulating down to its minimum output of 5.5kW whilst the C/H is running. Unfortunately there is no way of starting the boiler remotely, so if it goes off when the room stat is satisfied, it has to cool to 60C before it will restart with the inevitable time lag that that entails due to the air cleaning and pre-ignition stages.

    Currently Pump 2 only starts at the same time as Pump 3, which is not good. Pump 2 needs to start as soon as the boiler water is up to temperature and before Pump 3 starts otherwise there is not sufficient time for the TS to be “topped up” first thing in the morning. Pump 1 will only start when the boiler water temperature reaches 60C but this can be altered by the user (via the touch screen menu). I am thinking that Pump 2 could be connected to a pipe stat fitted on the boiler flow pipe rather than wire in parallel with Pump 1, which might cause some mischief within the boiler microprocessor control system.

    Any thoughts on the layout welcome!
    • CommentAuthorphiledge
    • CommentTimeMar 16th 2020
     
    The online manual for an Ekoheat 2500 shows several system configurations with and without a thermal store. The integrated controller is set up to control these various setups, or the parts of them closest to the boiler, so it may be worth having a look at those and possibly reverting to what should be a proven setup??
    • CommentAuthorGreenPaddy
    • CommentTimeMar 16th 2020
     
    Hi Jeff B,

    no way would you have explained your system in words. Good schematic, very helpful. That's a lot of bits of kit, just to make some hot water, and you say you've already simplified it!!

    A few check points;

    - I assume pump1 should point downwards, as a return to the boiler.
    - the thermo valve above pump1, is that not a 3 port at the "T", so it draws hot from the boiler, blends in some cooler from the LLH, to give the set 60oC into pump1/boiler return?
    - does the TS have any other coils in it (poss a DHW coil, even if you don't use it)?
    - you mentioned before the boiler start trigger is the "return temp". Where is that temp sensor located? Also, is it a voltfree sensor (ie. resistance like a PT100), or a stat providing a switched live?
    - does the boiler use its internal time controller combined with DHW cyl temp to make the DHW in summer?

    I'll wait till you confirm the above before adding any poss solutions. One observation would be that a 25kW boiler (albeit it can modulate to 5.5kW) seems a bit mis-matched to the rest of the system. Your TS will only take a charge of around 15kWh (even at deltaT of 50oC, which you prob won't achieve). I'd have thought the TS will be taking a 10kWh charge, so your boiler might tend to cycle, but there may be things we can do to avoid that. A worse case is in the non-heating periods, when only making DHW. You DHW cyl @ 180 litre, will run say 50oC to 80oC, so that's a an energy input of 6kWh. That's when a thermal store is of use, to reduce cycling.
  1.  
    IMO the low loss header is not needed and could be part of the problem.
    If you get rid of the LLH then pump 2 is not needed, in fact should be taken out.
    From the diagram I presume the TS is open vented and I assume the CH coil is a bit closer to the top of the water than shown and as Green paddy surmises pump 1 pumps downwards and the thermo valve is a temperature loading valve for the boiler.

    The job of the boiler should be to keep the TS and the DHW hot and as such IMO it should be switched on by the (low) temperature of the tanks and not any return temperature i.e. thermostats on the tanks. It may be advantageous to have 2 stats per tank, an upper stat to detect low temp (=boiler on) and a lower stat to detect high temp (= boiler off) in this way short cycling of the boiler is better avoided.

    I would put a 3 way valve at the T before the DHW tank where you show a motorised valve on the diagram. This valve would prioritise DHW over the TS

    For the electrical controls, either the DHW or the TS (or both) being low would turn the boiler on and at the same time the 3 way valve would select DHW over TS until the DHW is up to temperature then the TS is brought up to temp. If / when both DHW and TS are up to temp then the boiler switches off.

    DHW and TS can have different temps. but both should be lower than the top cut out temp. of the boiler.
    Pump 3 has nothing to do with the boiler or TS controls it should be switched on by the CH room stat / program controller, it just starts the load in the TS the same as the kitchen tap starts the load on the DHW

    I would construct the control circuits simply using 230v relays - easy and cheap to get and simple to wire up (especially if you are like me who stated work as a GPO tech. when telephone exchangers were all 2 motion selectors and relays !!)
    •  
      CommentAuthordjh
    • CommentTimeMar 16th 2020
     
    Posted By: Peter_in_HungaryI would put a 3 way valve at the T before the DHW tank where you show a motorised valve on the diagram. This valve would prioritise DHW over the TS

    Is that necessary or desirable given that the boiler output is 25 kW? We don't know the exact models of either DHW cylinder or TS so we don't know the capacity of the coils, but can they even dissipate 25 kW between them, let alone requiring to be fed one at a time? Wouldn't an S-plan system as existing be better than a Y-plan one?
  2.  
    Posted By: djh
    Posted By: Peter_in_HungaryI would put a 3 way valve at the T before the DHW tank where you show a motorised valve on the diagram. This valve would prioritise DHW over the TS

    Is that necessary or desirable given that the boiler output is 25 kW? We don't know the exact models of either DHW cylinder or TS so we don't know the capacity of the coils, but can they even dissipate 25 kW between them, let alone requiring to be fed one at a time? Wouldn't an S-plan system as existing be better than a Y-plan one?

    It is quoted that the boiler will modulate down to 5.5kW so I assumed that the coils individually would cope with this amount or more.
    • CommentAuthorJeff B
    • CommentTimeMar 17th 2020
     
    <blockquote><cite>Posted By: philedge</cite>The online manual for an Ekoheat 2500 shows several system configurations with and without a thermal store. The integrated controller is set up to control these various setups, or the parts of them closest to the boiler, so it may be worth having a look at those and possibly reverting to what should be a proven setup??</blockquote>

    Phil - can you provide the link to the online manual please? I have a paper version of the manual from Ekopower but it is in Danish English so not readily understandable!
    • CommentAuthorJeff B
    • CommentTimeMar 17th 2020 edited
     
    Green Paddy. Thanks for your comments. Let me answer them as below:

    I assume pump1 should point downwards, as a return to the boiler.
    Yes it does.


    the thermo valve above pump1, is that not a 3 port at the "T", so it draws hot from the boiler, blends in some cooler from the LLH, to give the set 60oC into pump1/boiler return?
    No it is like a TRV. When it opens, it blends in the return water from the LLH.


    does the TS have any other coils in it (poss a DHW coil, even if you don't use it)?
    Only the solar coil.


    you mentioned before the boiler start trigger is the "return temp". Where is that temp sensor located? Also, is it a voltfree sensor (ie. resistance like a PT100), or a stat providing a switched live?

    It must be inside the boiler itself. What happens is when the boiler temperature drops to a preset temperature (currently 65C) it fires up again.


    does the boiler use its internal time controller combined with DHW cyl temp to make the DHW in summer?

    I don’t think there is any such control as there is no connection between the DHW tank and the boiler. We turn the boiler off during the summer months as the solar thermal system generates all the hot DHW we need. The solar thermal system we have is a massive overkill – there are four flat plate jobbies (approx 2m x 1m each) made by Filsol who went bust several years ago. They are of a very simple but robust design, it was a shame the company went to the wall.
    • CommentAuthorJeff B
    • CommentTimeMar 17th 2020
     
    Peter – yes, the TS is open vented. The location of the coils in my schematic are not precise, sorry - should have spotted that! Yes it is higher in reality. Pump 1 points downwards. The thermo valve is basically like a TRV.

    I am awaiting a reply from the UK distributor for the Elterm LLH. I am thinking the same as you. Indeed it is part of the problem because since I replaced Pump 1 (the previous one died) this has done something to the flow through the LLH and return water seems to be blended with flow water, cooling it from 75C to about 65C before it sets off for the TS which is self-defeating.

    There is no way to start the boiler remotely, so there is no point in having thermostats on the tanks. The flow from the boiler splits just before the DHW tank so when the boiler first starts up both the DHW tank and the TS are heated simultaneously. When the DHW tank is satisfied the thermostat signals the MV to close, sending 100% of the boiler flow down to the TS. This does not take long actually as the DHW tank is very well insulated and standing losses are minimal.

    Yes, Pump 3 is indeed independent of the boiler or TS controls and is switched on by the CH room stat / program controller.

    I don’t think the system will operate without Pump 2, but I could be wrong. I suppose I say that because that is how the system has been set up and has always run. It would be easy enough to switch off Pump 2 and see what happens I suppose. I plan to have Pump 2 started up at the same time as Pump 1 using a relay as you suggest (someone I know has already suggested that because they were nervous that wiring the two pumps in parallel might cause some mischief inside the boiler microprocessor.
    • CommentAuthorphiledge
    • CommentTimeMar 17th 2020
     
    For the manual, google "ekoheat 2500 manual" and the first result at simplybiomass.co.uk should be a PDF copy in english.

    The temp sensors appear to be resistance devices. You should be able to remotely start the boiler by using a relay to switch in an external 10 ohm resistor in lieu of the return temp RTD which will kid the boilers controller that return temp is at 25 degrees. Simples!

    The controller seems to be able to do more than just manage the boiler so if the piping/pump/valve setup you have differs from ekopowers set configurations, the controller may not be able to do what ekopower intended.
    • CommentAuthorGreenPaddy
    • CommentTimeMar 17th 2020
     
    Agree with most of what PiH has said above, but there might be an even simpler control solution...I'll chuck a sketch on in a bit.

    I'm going to assume that the Therm Store DOES infact have connections for making DHW, based on the fact that it originally provided DHW, albeit not adequately, and you have since added the separate DHW cyl.

    I would do the following...

    - remove the LLH
    - remove pump2 (but insert a piece of pipe as a spool, just in case you need to reinstall it due to high pressure drop through the system, unlikely).
    - remove the MV going to the DHW cyl
    - relocate the 3port control valve to the "T" prior to the DHW cyl (just before where the MV is currently)
    - adjust the pipework so that the boiler feed goes to the DHW cyl, then through the therm store, and back to the boiler
    - connect the cold mains back onto the therm store, and then on to the DHWcyl, in series.
    - fit a temp sensor onto the Therm Store, as per the description in the Manual control set up, and input the DHW control temp to be 70oC with 20oC hysterisis (that's all in the manual and how it ought to have been set up in the first place). Here's a link to the type of sensor- NTC 10kohm@25oC. Dont worry if it's a little out at 70oC, as you ca just alter the set point to suit.

    https://uk.rs-online.com/web/p/temperature-control-cables/4388477?cm_mmc=UK-PLA-DS3A-_-google-_-CSS_UK_EN_Automation+%26+Control+Gear_Whoop-_-Temperature+Control+Cables_Whoop-_-PRODUCT_GROUP&matchtype=&pla-336861515209&gclid=EAIaIQobChMImqfN65Kh6AIVQrTtCh2gygMCEAQYBCABEgIRqvD_BwE&gclsrc=aw.ds


    What does that all mean for you....??

    - Essentially you're making the 2 cylinders into one larger therm store.
    - The boiler will keep the TS at between 50oC and 70oC.
    - you can vary those temps and range, but you want a large range to minimise cycling, which the manual suggest must be less than 1.5 hours running.
    - the DHW will always be hot, because either the boiler has heated it when it's heating the TS, or the cold mains feed will have come through the TS on it's way to the DHW cyl.
    - no new materials to purchase (apart from a £12 sensor)
    - get rid of lots of complexity
    - use the boiler controls to do its job (by the way, the manual shows the boiler does have a time control, not that you sound like you need it, though you might want to use it a bit in spring/autumn in case solar hasn't done it's job
    - by running cold mains feed through both the TS and the DHW cyl, you get the benefit of solar into both, and with 8m2 of flat plate collectors, you've loads of free energy to make use of.
    • CommentAuthorGreenPaddy
    • CommentTimeMar 17th 2020
     
    Hope this attaches
    • CommentAuthorGreenPaddy
    • CommentTimeMar 17th 2020
     
   
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