Thermal Store and Condensing Boiler

Discussion in 'Plumbers' Talk' started by Ballcocks, Jan 9, 2005.

  1. Water Systems

    Water Systems New Member

    In the summer time when DHW only on , the
    store temperture will be controlled by the
    he latching relays . In the winter time when

    <snip>

    Have a heat bank (thermal; store using a plate heat exchanger). Have two operating temperature, one fixed one variable. The hotter section at 75C in the top half of the cylinder supplying DHW only. The bottom half being variable temperature supplying CH. Each section has its own flow and return pipe. Internal spreaders are used on the two flow pipes and two return pipes to prevent mixing between the two sections. Each flow has its own pump with check valve to avoid crossing. The CH circuit(s) is/are taken off the lower section, with TRVs on all rads and a Grundfoss Alpha auto variable speed pump used.

    The lower CH section is controlled by a weather compensator, with an outside temp sensor and sensor detecting the lower cylinder water temp. The compensator switches the boiler on and off directly. Cheap DHW weather compensators are available. The Honey is well north of £500.

    The setup is DHW priority.

    Start from cold:

    DHW in the upper section calling for heat, so the lower CH pump is off and the DHW pump on with boiler on max temp supply only the top DHW section. Could have a blending valve on the upper section flow/return to ensure only 75C water enters the cylinder. This should be a very quick warm up.

    DHW is satisfied with 75C reached.
    The DHW pump is switched off
    CH is calling for heat.
    The CH pump is switched on (the two cannot be on at the same time)
    The weather compensator calculates that the flow (rad temps) should be 50C as it is 10C outside. Boiler cycling is minimised because the compensator has boiler anti-cycling control, the boiler may have as well, and the mass of water only changes temp slowly.
    The boiler fires.
    The boiler is switched off at 50C by the compensator.
    The weather compensator determines the flow temp should be 40C as it is warming up outside.
    The boiler stays off and only comes on to maintain the temp the compensator dictates.
    The rads are sized for 60C flow, 40C return, giving a very low return temperature fed into the cylinder lower section.
    When the boiler fires it is fed with low temperature return water promoting condensing efficiency.
    The upper DHW section cools as DHW has been drawn off.
    DHW demands heat.
    The CH pump is switched off
    The DHW is switch on
    The boiler fires to full temp and re-heats the DHW ASAP.

    Cheap simple and promoting condensing efficiency using a cheap boiler and cheap weather compensator.

    With UFH. A third temperature section could be added below the rads section, also with its own flow/return and pump and weather compensator. Have the rads at 60C with no compensator controlling. Priority: DHW, rads, UFH. Or just extend the lower section and have the UFH flow and return pipes at the very bottom of the lower section, and use a blending valve on the UFH supply. Low temperature operation is guaranteed.
     
  2. Scousemouse

    Scousemouse New Member

    8C? must be cheapo, or just about to pack up.
    I suggest you try a few cylinder stats. Hysteresis is pretty wide on all of them. "Your" Honeywell L641 is 10C.


    going. So obvious, yet most people don&#146;t think of it.

    It isn't done because it feels horrible! You might as well say use a piddling rate shower and move yourself about under it!


    I'm not impressed by the general approach -
    suggesting 300mm insulation in a loft in this
    country! WOrk out the saving on the middle 100mm, let
    alone the top 100.

    Saving in heating bills?
    Hardly, do the sums. It would take 20 years to get back the saving from using 300mm insulation in a loft compared with 100. And your loft gets smaller.
    COuncils only give a grant for 100mm.
     
  3. Water Systems

    Water Systems New Member

    I'm not impressed by the general approach -
    suggesting 300mm insulation in a loft in this
    country! WOrk out the saving on the middle 100mm,
    let alone the top 100.

    Saving in heating bills?

    Hardly, do the sums. It would take 20 years to get
    back the saving from using 300mm insulation in a loft
    compared with 100. And your loft gets smaller.
    COuncils only give a grant for 100mm.

    Do the sums again. See "Eco House - A Design Guide". They literally say stuff in as much as you can, it will pay for itself. The expensive part is the sructure to hold the insulation. A loft is the easiest and cheapest place you can put insulation. Playback calcs are flawed because they rarely take into account inflation and fuel price rises. Also insulation keeps the heat out too. Superinsulate the place and a no full heating system is needed.

    You need to look into this a little more.
     
  4. changename-12753

    changename-12753 New Member

    Internal spreaders are used on the two flow pipes and two return pipes to prevent mixing

    The spreaders, is this basically a baffle between the upper and lower section. With the flow to the lower section , tapping in just below the baffle or spreader.
    Could the division between the upper and lower sections be 2 spearate copper cylinders placed one on top of the other, joined with screwed onions,??.
    I notice the heat bank DX shows the rad circuit taken off the lower section with no internal spreader shown.
     
  5. Water Systems

    Water Systems New Member

    Internal spreaders are used on the two flow pipes
    and two return pipes to prevent mixing


    The spreaders, is this basically a baffle
    between the upper and lower section. With the
    flow to the lower section , tapping in just
    below the baffle or spreader.

    Different makers use different methods. Some have plates, others have pipes with holes that direct the water coming into, or out, of the store up or down. It depends if maintaining stratification is that important. With heat banks, using plate heat exchangers, maintaining stratification is an advantage as the hottest water is at the top ready to be draw out of the cylinder by the DHW pump into the plate heat exchanger. You have only have a small amount of 60C water at the top, with the weater beneath very cold, but this water may be enough to supply a sink.

    Could the division between the upper and lower
    sections be 2 spearate copper cylinders
    placed one on top of the other, joined
    with screwed onions,??.

    Yep. Say you bought a DHW only heat bank. Then, say in the loft zip up some unistrut and hold the DHW cylinder on the top of the rack. A normal direct cylinder with tappings added to suit, can be fitted below for the heating of the rads, another for the UFH. All cylinders can use the same primary water and fed from the same F&E tank. Speaders? DIY them. Drill out the pipe stop in a brass compression fitting and run a 22mm copper pipe right through into the cylidner with an internally capped end. Have holes drilled the length of one side of the pipe and face it up or down to suit. Cheap and easy and effective.

    I notice the heat bank DX shows the rad
    circuit taken off the lower section with no
    internal spreader shown.

    There probably is one. But the flow and return of the CH circuit will only involve the water between the two pipes.
     
  6. changename-12753

    changename-12753 New Member

    The one cylinder option should be the cheaper option to build.
    Install this system on a fixed rate non-condensing oil-fired boiler and the savings I think will be marginal. The TMV will ensure a quick boiler heat up.
    But WILL this lead to an improved efficiency on a low water content boiler, in the lets say, 19 to 40 KW range.?.???
    Veissman, as someone earlier mentioned do this on their large boiler&#146;s, anything over 60KW I believe . (not with a TMV though).
    A condensing oil-fired boiler will have an improved efficiency of about 6 or 7 percent. Will it be more efficient on the thermal store set-up. YES, it will and avoids the need for expensive compensating controls.
    Will it out weigh the extra cost of the HE (high efficiency) oil fired boiler ??
    A detailed cost /benefit analysis would have to be carried out to find out the long term payback.

    Well, I have a new build project coming up, a 4 bedroom, 3500 sq feet luxury development. And I have been looking at the different veiws on this forum over the last week and giving my own opinions also. .
    Doitall,s experience and knowledge is superior to my own and I have learnt to respect his opinions on this forum over the last few years.
    Watersystems knowledge is without question superior to my own and I am beginning to respect his input, he has an unprecendented knowledge of heating systems and will only be good for this forum. My apologies to you for some of my earlier offensive postings.
     
  7. Water Systems

    Water Systems New Member

    The one cylinder option should be the cheaper
    option to build.
    Install this system on a fixed rate
    non-condensing oil-fired boiler and the savings
    I think will be marginal. The TMV will
    ensure a quick boiler heat up.
    But WILL this lead to an improved efficiency
    on a low water content boiler, in the lets
    say, 19 to 40 KW range.?.???

    Yep. It will eliminate inefficient boiler cycling.

    Veissman, as someone earlier mentioned do this
    on their large boiler&#146;s, anything over 60KW I
    I believe. (not with a TMV though).

    Yes. If you set the boiler stats to 70C, only 70C water leaves the boiler.

    On a normal boiler, on start up, a boiler may raise the water temp say 40C at most. If the system is 15C, then only 55C water will be at the flow until the system warms up. This may create condensation in a non-condensing boiler. Not what you want. One method in commercial systems, was always to have a modulating 3-way valve on the return, so the boiler pumps back on itself from flow to return until either the return is above 60C or the flow is at a setpoint design temp.

    The TMV on thermal stores or heat banks ensures that only water of a high temp is leaving the boiler and that the return is below dew point promoting condensing. All the store water only enters the boiler in one pass. This ensurers a rapid heat up with hot usable water being dumped into the upper part of the cylidner, available virually instantly for DHW puposes. Eliminating the TMV and putting a pump on that runs wild, may mean that the water may circulate through the boiler 1.5 or 2 or 3 times.

    Non-condensing boilers are designed to not condense. All the peripheral equipment around the boiler, rads and cylinder coils were designed to run at 10C delta T (temp differential). This ensures a high return temp to avoid condensing. With condensing boilers this all goes to the wall. The opposite is required. Larger lower running temp rads with high delta Ts are required. Large quick recovery could in cylinders to take all the boilers output. too. You engineer the system to have low return temperatures.

    The makers of non-condensing boilers always state to run the boiler at max, usually 82C. This ensures no condensing in the boiler - condensing is a bad thing, so running at max avoids it. Running the boiler at lower temperatures improves efficiencies. Adding a TMV on the return to ensure the return is &#147;just&#148; above dew point will improve efficiency.

    A condensing oil-fired boiler will have an
    improved efficiency of about 6 or 7 percent.
    Will it be more efficient on the thermal
    store set-up. YES, it will and avoids the need
    for expensive compensating controls.
    Will it out weigh the extra cost of the HE
    (high efficiency) oil fired boiler ??
    A detailed cost /benefit analysis would have to
    be carried out to find out the long term
    payback.

    Oil condensers are far more expensive than non-condensing units. Yet the efficiency hype is not great when compared to gas. You have to work out the figures to justify the oil condenser.

    Well, I have a new build project coming up, a
    4 bedroom, 3500 sq feet luxury development.
    And I have been looking at the different
    veiws on this forum over the last week and
    giving my own opinions also.
    Doitall,s experience and knowledge is superior
    to my own and I have learnt to respect his
    opinions on this forum over the last few years.
    Watersystems knowledge is without question
    superior to my own and I am beginning to
    respect his input, he has an unprecendented
    knowledge of heating systems and will only
    be good for this forum. My apologies to
    you for some of my earlier offensive
    postings.

    No problem. I am terse and direct when I see fallacies and old wives tales and unjustified dogmatic claims. If you believe something is a certain way then justify it. Don&#146;t make things up or listen to the old plumbers codgers down the caff.
     
  8. Agile

    Agile Member

    I really find some attitudes amazing on these forums! Its like drivers in their cars, otherwise very mild mannered people honk their horns so agressively.

    DIY has spent 46 years on plumbing, many on up market systems, in multi million pound homes, yet here he is told that he has no idea what he is talking about.

    Clearly Water Sys has a very good knowledge of heating systems yet he seems to have no regard for politeness or respect for others views. Take him away from his closed computer room and he is probably as likeable as anyone!

    Is anyone here within driving distance of NW London or Bath and likes Indian meals?

    Tony Glazier
     
  9. Water Systems

    Water Systems New Member

    I really find some attitudes amazing on these forums!
    Its like drivers in their cars, otherwise very mild
    d mannered people honk their horns so agressively.

    DIY has spent 46 years on plumbing, many on up market
    systems, in multi million pound homes, yet here he is
    told that he has no idea what he is talking about.

    BY what he states here I would say so. Seniority is no proof of competence.

    Clearly Water Sys has a very good knowledge of
    heating systems yet he seems to have no regard for
    politeness or respect for others views.

    Where did you get that from? Counter me and you beter justify it. Simple. Just explaining things in a sensible technical manner would do.

    Take him
    away from his closed computer room and he is probably
    as likeable as anyone!

    Everyone likes me. :)

    Is anyone here within driving distance of NW London
    or Bath and likes Indian meals?

    Tony Glazier
     
  10. changename-12753

    changename-12753 New Member

    Been Thinking again. (must stop doing this )
    Are their any strict regulations governing the manufacture of vented thermal stores.
    Obviously these regulations will be less strict than compared with an unvented cylinder.
    The Elson Thermal Stores are rectangler in shape, and will easier to insulate and position. Can they make a custom made Thermal store made to order for example.?? Does the square or rectangular shape in any way represent a disadvantage over the cylindrical thermal stores as regards heat transfer from the boiler.??

    I can could be wrong but I see a potential here, given the cost of oil recently and the capability to integrate the thermal store with multiple energy inputs.
    I have a 5000 square feet workshop facility with full sheet metal cutting,folding,rolling and ,plasma cutting and Tig welding capability.
    Now before I go off and source a halt ton of sheet copper and a few skilled copper metal fabricators , would their be any severe restrictions on the production of Thermal Stores that would be detritmental to my proposition..
    The BBA (British board of Approval ) I think would be the governing body over this I think and the production would obviously only be carried out with such approval from such a body.
    Could even give some local employment as well.
     
  11. RenewableEnergyMan

    RenewableEnergyMan New Member

    R2D2

    The unvented regs only apply to thermal stores if your heat exchanger can contain over 15litres of mains pressure hot water, so in general, there are no regulations governing Thermal Stores other than WRAS regs that cover the materials and fittings used - that they should be approved for domestic potable water.

    As far as square tanks go - their advantage is that for the same height of tank, you can store more water, but when you bend the copper sheet in a tight 90 degree bedn, you stress it - almost all corrosion within elson tanks (the ones I have seen and replaced anyways) takes place at the corners - where it is stressed.

    before you run off & source all that copper sheet and skilled coppersmiths, give me a shout! We have about 120 ton of the stuff in stock, and employ a good few guys :)

    If its copper & got hot water in it, I can make it :)

    CCM
     
  12. changename-12753

    changename-12753 New Member

    Thanks for that CCM.
    Can a copper sheet not have different annealed properties like copper pipe so the stress would be less on the annealed type.
    What anout long radius corners, using a large V block in the press brake, giving say a 15mm radius.
     
  13. RenewableEnergyMan

    RenewableEnergyMan New Member

    Anneal it, and you end up working with something thats like roofing lead :)

    Cylinders are made from metal with a temper, know as 'half hard'. The sheets, when cut from the rols, are fairly rigid, and we take care to keep them that way.

    I'm pretty certain about the above, but I dont get involved in the details of the production - tech support & sales is what I do. I can check with production guys in the morning if you like.

    CCM
     
  14. changename-12753

    changename-12753 New Member

    I can check with production guys in the morning if you like.
    I will not refuse an offer like this.
    Many Thanks to you CCM and most of all to Watersystems.

    We just sold a batch of scrap copper. £1600 per ton.
    I could assume sheet copper (2.4m x 1.2m) to be double this price per ton with about 25 sheets per ton .Hmmn. About £128 per sheet. Would make about 2 x 42 inch direct cylinders . A direct copper cylinder is about £100. How is that for guesswork. Think I am way out though,it has to be cheaper or their are more sheets per ton than I estimated .It,s mined in Africa I believe or most of it is I think.
     
  15. Water Systems

    Water Systems New Member

    Been Thinking again. (must stop doing this )
    Are their any strict regulations governing the
    manufacture of vented thermal stores.
    Obviously these regulations will be less strict
    than compared with an unvented cylinder.
    The Elson Thermal Stores are rectangler in
    shape, and will easier to insulate and
    position. Can they make a custom made
    Thermal store made to order for example.??
    ? Does the square or rectangular shape in any
    way represent a disadvantage over the
    cylindrical thermal stores as regards heat
    transfer from the boiler.??

    When using a coil, a cylidner is far superior. When using a plate heat exchnager, well the suare shape is not so much a hindrance, as the pump pumps water from the square store.
     
  16. olfert

    olfert New Member

    R2D2

    the current LME price for copper is £2114/tonne. Copper is mined all over the world primarily in south america The no's of sheets per tonne would depend on the thickness of course.

    Copper is more suited to cylinders rather rectangles because of its low rigidity. Usually the ends are spun from flat sheet rather than pressed, to avoid the stress that CCM mentioned.

    For your project you might consider stainless steel 316 or 444 might be competative with copper but harder to fabricate. Possibly even mild steel if the contained water can be neutralised and you use a mains pressure coil for DHW (with relief valve of course). But that might get you into deeper water with regs I am not sure.


    TOF
     
  17. Agile

    Agile Member

    Where is that fellow with a degree in metalurgy?

    CCM, why do cylinder manufacturers charge disproportionately so much more to fit a larger primary coil?

    Have you ever realised that for some applications, like launderettes, its important to get the stored HW out quickly? So why do quite big cylinders still have 22 mm inlet and outlet tappings?

    Tony
     
  18. doitall

    doitall New Member

    Have you ever realised that for some applications, like launderettes, its important to get the stored HW out quickly? So why do quite big cylinders still have 22 mm inlet and outlet tappings?

    They don't Tony, commercial cylinders are what you order.

    Check out the MHS "Gemini" tappings are 42mm mormally.

    And since I'm here r2d2, if this house is for you forget the solar panels and consider ground source far better with a cop of 4-1
     
  19. RenewableEnergyMan

    RenewableEnergyMan New Member

    Where to start....

    LE is correct as posted, £2114 per ton - bear in mind that this time last year it was at approx £1200-1300/ton if I remeber right - its shot up since last winter anyways.

    The LME is just the start though, thats foir raw metal - you have to pay a mill to roll it to suit your application - the mills we use are in Italy (the last UK rolling mill closed years ago) and this can add approx £800-1000 per ton. It arrives in 2 ton coils, in various thicknesses and we cut it to length - we try to avoid scrap if possible (obviously!)

    You then also have the cost of getting circles spun into tops & bottoms - its a dirty, dangerous business so most of us use dedicated metal spinners for this.


    The sizes of connections on cylinders are generally regulated by the relevant British Standard (Bs 1566:2002) - 450mm cylinders have 28mm connections, 500 diameter have 35mm conns, and the 600 diameter have 42mm conns.

    That said, a decent manufacturer can make you a cylinder with any size of connection, in any position - they can still be kitemarked so long as the changes are customer led, and the same quality procedures are followed. The only rider to that is that the coil connections on a 600 diameter cylinder have to be 42mm to get the best connection to the 42mm coil thats inside - the other cylinders have 28mm pipe as the coil.

    The reason manufacturers charge what might seem a disproportionate amount for a larger primary coil is probably a combination of factors...your standard cylinders are made in batches of 50-100 or so, bringing the usual economies of scale - to make a one-off will add significantly to the labour, as well as the cost of the added coil. If you demand so much extra coil that we are forced to use finned coil, then this is itself hellish expensive compared to standard tube.


    I did check and the production guys think that if cooled correctly, the temper would return to the copper sheet, but they still think that there would be some stresses on the sheet if bent, even in a 15mm radius. Without having a go at the square tanks for the sake of it the corroded ones we have seen have all gone at the corners.

    CCM
     
  20. changename-12753

    changename-12753 New Member

    And since I'm here r2d2, if this house is for you forget the solar panels and consider ground source far better with a cop of 4-1

    Doi.
    A Ground source heat pump is being considered along with a wind turbine to deliver the electricity . Solar, well that is also being considered but the rear roof is westerly facing.
    The Thermal Store, well that will be reality I hope. The client has seen the set-up and I have explained the operation based on water systems technical advice.
    A few other engineers will be privy to this information along with the other couple of thousand reading this thread.

    CCP
    Appreciate the input. I think the stainless that olfert mentioned would be a better choice than copper, might be the best option on a custom built thermal store.
    As for mild steel, based on watersystems input about corrision within the system I would have confidence using material.

    We currently install German built Thermal Stores , used for heat recovery on industrial refrigeration plant.
    This store is fabricated rolled mild steel to my knowledge, but the inside is entirely glass lined.
    So it looks like a copper cylinder will be the choice for this project.
     

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