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      CommentAuthortatwalsh
    • CommentTimeJul 2nd 2015
     
    Hello, everybody,
    Our home was originally plumbed with an indoor Firebird Oil Fired Boiler, situated in a cupboard under our kitchen counter-top. This supplied the heat for our central heating, which is split up into 4 zones, with TRVs on all of our 31 radiators. It also heated our Domestic Hot Water via a Heat Exchanger and an 80 gallon Storage Tank (Insulated Copper Cylinder).
    Now, we have installed a new Multi-Fuel Boiler in our shed along with a 2000 litre Buffer Tank, which is tee-d into the old system. (Please see the attached drawing). This new system is wonderful, we have heat all over the house with loads and loads of hot water. Our home is a Bed and Breakfast and needs a constant supply of hot water and heat most of the time.
    Our old oil fired system would cost a bomb to come near the comfort the new system offers. It’s amazing! It is set up in a way that allows for the oil boiler to come on should the temperature at the top of the Buffer Tank fall below 45 degrees C. (this can be adjusted to suit our needs, but we have it set to 45 degrees C.)
    Should the temperature at the top of the Buffer Tank fall below 45 degrees C. Thermostat T4, at the top of the Buffer Tank (on the drawing), opens MV1, closes MV2 and switches on the Oil Boiler (OB), thus isolating the Multi-Fuel Boiler (MFB) and Buffer Tank (BT).
    The cartridge in the Laddomat (L) is 63 degrees C. and the Multi-Fuel Boiler is set at 65 degrees. With these settings the Temperature Gauge (TG1) at the top of the Buffer Tank normally reads around 70 degrees C., with the bottom Temperature Gauge (TG2) normally reading around 60 degrees C.
    We have one problem, though, when we have no heating on (during warm weather) the heat in the Buffer Tank can go up to 80 degrees C. at the top and up to 70 degrees C. at the bottom. This can cause the Domestic Hot Water to become very hot and, at times, cause the water in the Storage Tank (ST) to over-heat and push hot water up the Expansion Pipe (DHW/EP). At this stage the water in the taps becomes dangerously hot and is a worry. We certainly don’t want anyone getting scalded.
    Thermostat T1 for the Heat Exchanger is set to 60 degrees C. and Thermostat T2 is set at 55 degrees. Thermostat T1 switches on the Heat Exchanger Circulating Pump (P1) when the temperature reaches 60 degrees in the flow pipe from the boiler. Thermostat T2 switches off P1 when the temperature at the bottom of the Storage Tank (ST) reaches 55 degrees C.
    We are also afraid of children touching the radiators when they come on with 80 degree water in them. There’s something telling me that we need to fit a mixing (blending) valve between the flow and return at the house side of the Buffer Tank. Would I be correct in saying this?
    I would really appreciate any help or advice on this.
    Thanks.
    Tom.
      Plumbing Diagram2.jpg
  1.  
    It is usual to have a mixing valves on both the heating circuits and the DHW. The mixing valve on the heating circuit would mix the return into the flow to maintain the pre-set maximum flow temp and the mixer on the DHW would mix the mains cold with the DHW from the storage tank down to a safe temperature
    So yes I would say you need 2 mixing valves.
    •  
      CommentAuthorcrosbie
    • CommentTimeJul 2nd 2015
     
    Check out a 4 way mixing valve for your radiator circuit, such as the Termomix CS: http://www.marji.jo/Portals/Portal1/Upload/Products/PDF/TermomixCSDS.PDF

    And you can stick a constant temperature controller on it.

    Thus what happens is that when the CH pump is on, the water circulates around the radiators at your desired temperature say 50C, and only takes water from the buffer tank (whether 50-90C) in order to raise the return from the the rads, say 40C, back up to 50C (returning that fraction of 40C water to the buffer tank as it takes the same fraction of hot water).

    You can also get controllers that adapt the rad temperature to the outdoor temperature, e.g. 70C in freezing temps, and 50C in cool temps, e.g. LK Acaso Automix 10 http://www.zelenaenergija.org/blobs/96ff27a8-329e-498b-98f0-2a4b3e4cd100.pdf

    Incidentally, it seems you have two heat exchangers on the DHW tank, i.e. the coil inside, and the external HE. Isn't one of them therefore redundant?
    •  
      CommentAuthorcrosbie
    • CommentTimeJul 2nd 2015
     
    On the DHW side of things, it seems to me you'd ditch the external heat exchanger, and simply pump the buffer tank water into the bottom of the DHW coil, while the top of the DHW tank was less than 60C (but only if the buffer tank water was hotter than the top of DHW tank).
    • CommentAuthorowlman
    • CommentTimeJul 2nd 2015
     
    What the others said, you need a couple of mixing valves.
    When you order them make sure they are able to accommodate the high temps 80C+ of your buffer tank, some can't, read the spec carefully.
    Also the overheated water in your CH circuit may not be doing your TRVs any good, long term.
    •  
      CommentAuthortatwalsh
    • CommentTimeJul 5th 2015
     
    Thank you all for your advice and recommendations. Thank you Crosbie for spotting the coil in the Storage Tank (ST) – that was a mistake I made, there is no coil in the copper cylinder (ST), just an external Heat Exchanger (HE). I have updated the drawing to what I think is needed based upon all of your recommendations and my own further research.
    I have added Blending Valves (BV1 and BV2) across the Flow and Return of the Buffer Tank (BT) and the Flow and Return of the DHW Heat Exchanger (HE). The Blending Valves (BV1 and BV2) will be controlled by temperature probes on the Flows, downstream from the valves.
    I have also added a Diverter Valve (DV) to the Return of the Buffer Tank (BT) at the connection going to the Blending Valve (BV1). This Diverter Valve (DV) will be controlled by a pipe thermostat to divert the returning hot water back through the Blending Valve (BV1) and to continue recycling the water until it is cool enough to let in to the bottom of the Buffer Tank (BT). This should help to maintain good stratification within the Buffer Tank (BT) by stopping the returning hot water from entering the bottom of the Buffer Tank (BT).
    Furthermore, I will replace the standard circulating pumps P2 and P3 with GRUNDFOS ALPHA pumps.
    I would really appreciate any further help or advice on this.
    Thanks.
    Tom.
      Plumbing Diagram with 3 Way Valve.jpg
    •  
      CommentAuthorcrosbie
    • CommentTimeJul 5th 2015
     
    The input temp at the heat exchanger can be as hot as you want. The thing is to stop adding heat to the DHW tank as soon as it is at the desired temperature, e.g. 60C at the draw off point.

    I'd consider using a cheap solar panel pump controller, e.g. to modulate the speed of P1, and turn on P3 (if T3/T4 hot enough and ST needed heat). Effectively, the boiler is the sun, and the heat exchanger is your solar panel. The only difference is, that you can turn the sun on when you need it (turn on P3).

    BV2 may help limit the max temp reaching the HE, but I don't think this is the way to limit the DHW tank temp. If T1 was 90C and T2 was 30, the water input to the tank would be ~60C.

    The blending valve to limit the radiator circuit temp should be dedicated to the radiator circuit. The documentation for the Termomix should give an idea of how it would fit in.
    •  
      CommentAuthortatwalsh
    • CommentTimeJul 6th 2015
     
    Thanks, Crosbie, I really appreciate your help. I'm not a plumber, but, I have some understanding of it! The reason I'm checking things out, this way, is local plumbers, and even the guys who fitted the new Multi-Fuel Boiler for me are not very motivated to providing a top notch job - they're happy enough to get you set up and going and don't like getting involved in anything too complicated!!
    I am very happy with the way things are working at the moment, but I know that it could be working a whole lot better and much more efficient. I had a lot of research done on this before I decided to have it fitted. It cost a lot of money to install and I was willing to spend more on it to get it working properly. I was pushing the Blending Valve scenario to the guys who installed the set up, but they insisted that there was no need.
    Anyway, thank you again for your help, and apologies for being a pain. I have come this far and I'd like to finish it properly.
    What I'm picking up from you is that there is no need for BV2 - that HE could be controlled by T1 and T2 (at the moment T1 is set to 60 degrees and T2 is set to 55 degrees, but I get a lot of water expanding up the expansion pipe and out onto the street from the overflow pipe in the attic when the Buffer Tank (BT) is above 70-ish degrees).
    I would need to get a solar panel pump controller for P1 - so, no need for a GRUNDFOS ALPHA pump here? The only thing is that the DHW is tapped off the CH circuit, whether this matters or not?
    I should use a Termomix (3 or 4 way?) to control the CH. What do you think of the Diverter Valve (DV) being used on the BT return?
    Thanks,
    Tom.
    •  
      CommentAuthorcrosbie
    • CommentTimeJul 6th 2015
     
    Yup, I don't think BV2 is helpful. Limiting the temp to the HE will limit the temp of ST, but you end up pumping 80C water round a loop just so a 60C fraction can be taken off. You might as well transfer more heat from 80C into the HE to faster heat the ST.

    The issue is limiting the temp of the ST, not the HE. That's why it may be worth considering a solar pump station controller, because you can have several temperature sensors in vital places and control the operation & speed of one or more pumps (motorised valves, etc).

    As to overflowing from the expansion pipe, I would assume you had an insulated high temperature F&E tank rather than just a pipe, and presumably, there would be a cold feed to the bottom of the ST from that F&E tank. What do you have at present for cold feed? A cistern with float valve?

    Although your diagram may reflect your current installation (with the DHW tapped off the CH circuit), I think you need to separate the CH circuit from the DHW/HE circuit, at least logically, in order to more clearly see how to insert the Termomix 4 way.

    I'd minimise the circuit length and the rate of circulation for high temperature water. Hence, ideally the Termomix CS would be close to OB/BT, and the HE would be close to OB/BT, and each circuit would be independent of the other.

    BV1 & DV don't really make sense to me.

    As to choice of pumps, your existing pump is most likely able to be speed modulated by a solar pump controller, but you can check to be sure.
    •  
      CommentAuthortatwalsh
    • CommentTimeJul 6th 2015
     
    Our house was purposely built as a B&B, 30 years ago. At the time en-suite bedrooms were starting to become a necessity - before this, all rooms shared a bathroom at the end of a hallway, in a typical B&B. We were ahead of the game, back then, with power showers in each of our 8 en-suite bedrooms. Our plumber did a great job of installing the system, I think, for 30 years ago?
    He installed the external Heat Exchanger to give the attic-tanks-fed (gravity) copper cylinder (80 Gallons) a chance to heat without the CH robbing it. We have 5 large storage tanks, with a ball valve, in our attic feeding our system.
    In a B&B the most important thing to have is HOT WATER all day! This system allowed us to have this, provided we monitored the CH. The CH is zoned (4 zones), which we could switch on and off, as we needed.
    On a typical morning we would set the system to come on around 6 o'clock (CH and DHW). At 7 o'clock we would switch off the CH and leave the DHW going to satisfy the draw off for showers, for people having breakfast a 8 o'clock. We would make sure to keep the ST hot, top to toe, so when we'd switch the CH on in the evening it wouldn't rob the ST. Before we'd go to bed at night we'd make sure that ST was full of hot water so as not to have it robbed by the CH again, the next morning. We also have a Secondary Return on the DHW to all rooms.
    It all worked a treat for us, but, we could not afford to have people staying with us during the winter months - it would rob us in oil, trying to heat the house - it's a fairly big house (300 sq. mts.)!!
    The Oil Boiler (OB) is installed in the kitchen, under the counter. The hot-press with the ST is situated at the other end of the kitchen - that's where the HE is tapped off the main flow (CH). The return from the HE is brought back to just outside the OB. In order to separate the CH and HE we would have to rip out the kitchen (which we're not going to do at this stage - we're getting too old for all that craic!).
    We had to build a new shed (25 metres from the house) for the new boiler (MFB) and Buffer Tank (BT). We also had to rip a channel through our tarmac-ed drive for the pipes and cables. So, we're fairly limited to options when it comes to lengths of circuits.
    I just thought, after a lot of research, that by adding BV1 to the flow from the BT it would re-use the return to cool down the flow and, at the same time, preserve the hot water in the BT. Then, by adding the DV, set to, say, 45 degrees, the DV would not let anything hotter than 45 degrees into the bottom of the BT. This would be diverted back to the flow, again. This, in turn would help the Stratification of the BT – rather than pushing hot water into the bottom of the tank to upset Stratification.
    By maximizing Stratification in the BT, I thought it would be of benefit to the workings of the Laddomat (L) and boiler (MFB) – minimize short cycling of the MFB. The MFB is soot-ing up and tarring up at the moment and I would like to run it hotter to stop this. The MFB is set at 65 degrees with the water in it at about 71 degrees. The temperature gauge at the top of the MFB reads about 80 degrees. If I raise the MFB temperature to 70 degrees this raises the BT temperature to over 80 degrees and leaves the DHW where you couldn’t put your hand under it without getting scalded.
    Sorry for the long winded replies, but, I just needed to explain the situation to you. I am not looking for perfection, but I would like to maximize what I have.
    Thanks,
    Tom.
    •  
      CommentAuthorcrosbie
    • CommentTimeJul 6th 2015
     
    Ok, so it's a little clearer how flexible your system configuration is.

    I attach an image of where you might insert a temperature controlled motorised mixing valve (if you aren't able to insert it nearer to the heat source) for the radiator circuit. Effectively when there's a need for heat, P2 circulates water around the radiators, and the Termomix slips in 70-80C water from OB/BT in order to maintain the rads at the seasonally appropriate temperature, e.g. 50C.

    If you have a secondary circuit for the DHW, then presumably this is temperature limited? E.g. to 50C?

    Yes, the MFB should burn full blast, rather than choked back. You can get different temp valves for the Laddomat if the MFB prefers a particular input temp. There's also a possibility that the MFB is being run on when the input temp from the BT is high (near capacity) and then reduces its air intake to reduce its output, and consequently generates tar/soot, etc.

    If you limit the temperature of the ST, then it doesn't matter how hot the water is at OB/BT.

    BV1 appears to be in conflict with DV, hence it doesn't make sense, i.e. either have BV1 or DV, but not both. Or if you do have both, then they need to be plumbed differently.

    I presumed you used a heat exchanger because the DHW ST is fresh water, rather than system water. Are the two other system circuits, HE/CH & MFB, open (with F&E tank) or closed (pressurised via expansion vessels)?
      tatwalsh.jpg
    •  
      CommentAuthorcrosbie
    • CommentTimeJul 6th 2015
     
    Also, are you really heating the buffer tank indirectly via coils? Or are the coils superfluous as in the ST? Perhaps the buffer tank also has a F&E tank above it?

    If there were no coils in the buffer tank, then you'd have a single system circuit.
    •  
      CommentAuthorcrosbie
    • CommentTimeJul 6th 2015
     
    In fact, if the MFB is indeed heating the buffer tank via a coil then it may well be that the return temp is too high (coil not losing heat fast enough) and this causes the MFB to choke itself. The flow rate determined by P4 will also be a factor in this.

    I'd have the MFB heat the buffer tank water directly.
    •  
      CommentAuthortatwalsh
    • CommentTimeJul 8th 2015
     
    Crosbie,

    You are correct, the Buffer Tank (BT) has no coils - sorry, my fault again!! As I said, I'm not a plumber, but, at last, I am starting to see the picture. Does the Termomix CS 4-Way (TCS) need a motor and stat to control it, or would you leave it manually set?

    Would I need to replace P2 (and/or P3) with a Smart Pump?

    All that's left to sort out, then, is the HE side of things? Would you have a recommendation for a solar pump controller?

    By the way, P1 is a NSB Salmson 30W 0.15A pump.

    Thanks,

    Tom.
      Plumbing Diagram with 4 Way Valve.jpg
    •  
      CommentAuthorcrosbie
    • CommentTimeJul 8th 2015 edited
     
    Yes, the TCS is best with at least a constant temperature controller/motor, e.g. the LK Acaso Automix I referred you to in a response above - you don't have to use its outdoor thermosensor.

    Sure, you can do without motorisation and find some happy fraction that tends to work most of the winter (perhaps tweaking it for autumn/spring), but automation is nice, especially as it's likely that the temperature in that circuit will be fairly variable.

    If by 'Alpha' or 'smart' we're talking about intelligent pumps that decide what time of day to operate, I'd only consider using one for a secondary DHW circuit. But, if you mean one that automatically backs off according to rising pressure as a consequence of closed radiator TRVs, then yes, it may well be appropriate to your CH system.

    P2 would be operated by a room thermostat somewhere (or more complicated system).

    As your DHW ST application is not quite as critical as a solar panel, you may find a cheap Chinese controller will do the job fine, e.g. http://r.ebay.com/YNV5mW put "CONTROLLER SOLAR WATER HEATER" into eBay for a variety of items.

    This will allow you to have sensors on the HE, the ST (top and/or bottom), and OB/BT, and enable you to operate P1 and P3. If you pay a bit more money you can get controllers able to modulate the speed of P1 and/or P3.

    It's then a matter of tweaking the settings such that the ST only receives heat when it needs it (<60C), and that you only attempt to provide heat from OB/BT via P3 when it's available (>40C) and can be received (OB/BT > ST).

    As to whether your P1's speed can be modulated (varied), it's highly likely, but if in doubt contact the manufacturer. The solar controller would automatically adjust P1's speed to avoid it circulating faster than heat can be provided from the HE.

    In any case, if P1 & P3 have appropriate speeds, you may not need speed control, e.g. perhaps you can simply make P3 slightly faster than P1?
    •  
      CommentAuthorcrosbie
    • CommentTimeJul 8th 2015
     
    A further observation: I trust OB is fired up, not only when T4<45 (operating MVs), but also ONLY when either P2 is operating or when ST<60C (which will operate P3 when T3 rises).

    Another thing to consider, that obviates those conditions is ditching MV1 and MV2, and putting a pump P5 into the input to the OB. Then when OB+P5 was fired up (because T4<45), it would heat the BT up until it reached 45 again.
    •  
      CommentAuthortatwalsh
    • CommentTimeMar 8th 2017 edited
     
    Thank you for all your help and sound advice. I have, at long last, come to a happy medium. I have attached an up to date diagram of the setup. I am controlling the LK 841 4-way-mixing-valve with a Thermomatic CC Actuator, which is set to 55 degrees C (4WV on diagram). I also installed an Automatic By-Pass Valve (ABV) to take the pressure off the CH circulating pump (P2).

    Lastly, I installed a thermostat (T6) to control the DHW circulating pump (P3). This is set to 65 degrees, which switches T6 off when the top of ST reaches 65 degrees C. This keeps the domestic hot water from getting too hot, as before. Everything is working as close to perfect, as possible. I'm really happy with it, thanks to you guys.

    Please don't shoot me, but I can't stop thinking that I could replace the multi-fuel boiler (MFB) with a 35 KW oil fired boiler. Is this feasible with this setup? I would appreciate any feedback.

    Thank you.

    Tom.
      Plumbing Diagram with 4 Way and By-Pass Valves.jpg
  2.  
    Posted By: tatwalshPlease don't shoot me, but I can't stop thinking that I could replace the multi-fuel boiler (MFB) with a 35 KW oil fired boiler. Is this feasible with this setup? I would appreciate any feedback.

    You can. At the end of the day the the MFB is only a heat source and can be replaced with any other heat source

    However to quote from your first post
    Posted By: tatwalshOur old oil fired system would cost a bomb to come near the comfort the new system offers.

    So if this cost issue has now been resolved or life demands have changed then putting in a new oil boiler would give you 2 oil boilers on the system. Why? If you go down this route then why not have only one oil boiler and either get rid of the buffer tank and run the whole lot on a properly modulating boiler or have the same properly modulating boiler with a small buffer tank to stop any short cycling of the new oil boiler.
    This assumes that the existing oil boiler is past its best / old and inefficient / too small to manage the system (delete as appropriate) otherwise you could run on the existing boiler
    Presumably the MFB and BT would have a resale value to consider
    •  
      CommentAuthortatwalsh
    • CommentTimeMar 8th 2017
     
    Thank you Peter.

    The existing oil fired boiler (OB) is there for nearly 30 years, and working as good as ever! It's a Firebird Popular 150 38-44 KW. It is situated in the kitchen, under the counter. The new Multi-Fuel Boiler (30 KW) and 2000 litres Buffer Tank are in a shed, 25 metres from the house.

    We never had much heat nor hot water with the original setup. We couldn't afford to keep the oil fired boiler on long enough, to keep the heating on, to heat the whole house comfortably. Even at that, we used to spend 3,000 to 3,500 Euros on oil every year.

    After installing the multi-fuel boiler and buffer tank everything changed. Suddenly, we had our home very comfortably heated with lots and lots of hot water. All this being heated by the buffer tank, and costing us about 3,500 Euros a year for turf (peat) to supply the multi-fuel boiler. The only drawback with the new system is there's a lot of work involved. We buy the turf in trailer loads which have to be dumped on our driveway and, later, taken in to the shed. A lot of the time the weather is wet and this makes it more difficult. On top of all this, when the fire lights up, we tend to have a lot of smoke, which can be a nuisance.

    The fact that the buffer tank is now our new boiler, I'm just wondering if it would need to have an oil boiler running all day to satisfy the buffer tank. Would anyone be able to advise me on that? There's no point in putting in an oil fired boiler to keep the buffer tank heated if it was going to cost 5,000 Euros a year for oil.

    I wouldn't be inclined to get rid of the buffer tank, but could get rid of the multi-fuel boiler. After all, the buffer tank that's doing the work, now. I know it has to be heated by a source, but would a 35 KW oil fired boiler be the job? I could take out the existing Firebird Popular 150 38-44 KW and replace the multi-fuel boiler with it, if that would make more sense? I just thought that the newer boilers are more efficient, now.

    I hope I'm making sense!

    Thanks.

    Tom.
  3.  
    Posted By: tatwalshAfter installing the multi-fuel boiler and buffer tank everything changed. Suddenly, we had our home very comfortably heated with lots and lots of hot water. All this being heated by the buffer tank,

    No - The heating is done by the MFB, the buffer tank just stores the heat from the MFB because the boiler is a batch burn device. The buffer tank will have losses during storage and there will be further losses in the 25m pipe work to the house and further losses from the MFB as it is outside the house so any heat escaping from the boiler and chimney is lost to the house.

    Posted By: tatwalshThe only drawback with the new system is there's a lot of work involved.

    Heating with wood -or in your case turf - is a life style choice. It comes with work (fitness exercise?) and mess.

    Posted By: tatwalshThe fact that the buffer tank is now our new boiler,

    Posted By: tatwalshI wouldn't be inclined to get rid of the buffer tank, but could get rid of the multi-fuel boiler. After all, the buffer tank that's doing the work, now. I know it has to be heated by a source, but would a 35 KW oil fired boiler be the job?

    The reason you have a buffer tank is to supply heating when the MFB is not alight. The tank is to overcome the operation method (limitations) of the MFB. Get rid of the MFB then you don't need the tank (unless you went for a e.g batch burn wood gasifying boiler)
    You are right when you say new oil boilers will be more efficient than your 30 year old boiler. Look at your own figures, the old boiler is 40kw and doesn't heat the place properly, the MFB is 30kw and has losses as described above and only produces 30kw mid burn i.e. on start up and towards the end you will get nothing like 30kw, in fact you probably only get 30kw for about 75% of the burn time - assuming you are using 1st grade fuel (moisture content etc.) which is what the MFB was using when the factory calibrated output was measured.

    IMO you should do the heat demand calculation for your house if you have not yet done one to determine your actual heat requirements (What about draft proofing and insulation levels?) You could well find that you don't need a 30kw boiler to supply your needs. Typically with batch burn boilers it is recommended to have at least 50% higher capacity than the heat load just to made up for the operating methods / limitations of a batch burn system. Look at the figures then look at the oil boiler options that supply the demand and you will be able to work out the annual costs. IMO running the buffer tank heated by an oil boiler 25m from your house will cost efficiency which = money. (This lost efficiency is less of a financial issue burning turf as the fuel is cheaper). Much better to replace the in house old oil boiler with a new in house oil boiler that matches the demand. If you are nervous about going down that route then get a new oil boiler to replace the old one, turn off the heating system in the shed, run on the 'in the house' new oil boiler and see how you go for a season.
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