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  1.  
    The Beast aka Vigas 40s wood boiler is going to be replaced by an oil-fired boiler. I was intending to also remove the Akvatherm 2000 litre thermal store but the heating guy suggested I consider keeping it, which would mean I would need a smaller capacity oil-fired boiler. Just wondered what the pro's and con's were.

    We do not have any UFH nor intend to put it in because even though we will be insulating the inside of all the external walls with 100mm Kingspan I think that the house will still be relatively inefficient from a heatloss perspective.

    The current system is vented and we are on a private water supply and so no mains pressure to consider. Or take advantage of!
    • CommentAuthortony
    • CommentTimeMar 5th 2017
     
    Where do the heat losses from it go? Into your house or not?
  2.  
    If the oil boiler modulates low enough to cope with your lowest expected demand with out loosing too much efficiency then you can do away with the TS
    As Tony says where does the heat loss from the TS go - if it is into the heated envelope then perhaps keep the TS if the new boiler is more efficient with it, but how is your DHW produced? Will this come off the TS - which means you need to run the TS outside the heating season when the TS losses will be real losses wherever the TS is located.
    If the decision about the TS is marginal then do you have alternative use for the space and is the resale value a factor (as you will know a 2000ltr tank is a big bugger and expensive to boot)
    • CommentAuthorowlman
    • CommentTimeMar 5th 2017
     
    This situation may be one I'm faced with in the not too distant future as my log gas boiler reaches the end of it's life. I am also looking at other solutions too.
    My similar sized accumulator is housed inside the heated envelope so makes sense to keep it, plus I have a heating system I like, whereby the CH remains on 24/7 for the whole of the heating season and having that buffer is necessary for this regime.
    If I returned to oil, as you, my problem would be finding an efficient simple oil boiler that "likes" the batch burns to recharge the store, similar to the log boiler.
    I have a plate heat exchanger for winter DHW and solar thermal for summer DHW. My solar thermal also pre-heats the input to the PHx during winter.
    It'a all on a sealed system.
  3.  
    Posted By: owlmanIf I returned to oil, as you, my problem would be finding an efficient simple oil boiler that "likes" the batch burns to recharge the store, similar to the log boiler.

    Not quite - If your wood boiler stuffs in 40kw for say about 8 hours and this is sufficient for a once a day firing to meet the needs then surely an oil boiler that put in 16kw for 20 hours or a different boiler that did 80kw for 4 hours would not either also fill the need. So you could go for a small boiler running all/most of the time feeding into the TS or a batch burn oil boiler to mimic the wood burner.
    I suspect the small boiler would be more efficient and cheaper to install
    • CommentAuthorcountryman
    • CommentTimeMar 9th 2017 edited
     
    Apologies for the delay in replies ...can't see how to switch on 'Notification of Replies'.

    Just come off the phone to a chap who's put in an oil-fired boiler with a heat store. This is his rationale. It actually makes a fair bit of sense to me but interested to hear others thoughts.

    1) Condensing boilers are only at their most efficient (the 90%+ that the makers claim) when they are condensing. But condensing stops around 65 degrees which is way below were most boilers are set. Ergo oil-boilers setup with a high temperature than 65 degrees are much less efficient. Significantly, he claims.

    Anyone else agree with this ?

    2) Boilers also work best when they are working hard.

    3) Boilers wear and tear improves when they run constantly and not cycling on and off.

    So he has a heat store that is heated by an oil boiler. The heat store then supplies the heat required by the underfloor heating and radiators. He has two sensors on the tank. One at the top set to around 70 degrees or so and one at the bottom set to around 50 degrees. When the top temperature is reached the boiler switches off. It restarts when the lower temperature limit is reached. So between those two 'events' the boiler remains off. (He did admit that he got a little bit of cycling towards the end of the heating phase).

    The size of the boiler is small. Much smaller then the one specified for a 'traditional' system and he's thinking that even the one that he has is a bit over-sized.

    It does mean that his radiators are running cooler than their design temperature and I've not got my head around that one yet...seems to suggest that larger radiators in each downstairs room would be needed in the absence of UFH. So there's a trade-off there to be worked out.

    For DHW (domestic hot water) he has a coil in the bottom part of the tank and this forms a complete insulated secondary return system which constantly circulates his DHW. So no dead legs. No wasted water and instant hot water.

    Of course his heat store is only three years old and so significantly better insulated then my 2002 fibreglass wrapped monster.

    Thoughts anyone ?
    •  
      CommentAuthordjh
    • CommentTimeMar 9th 2017
     
    Posted By: countrymancan't see how to switch on 'Notification of Replies'.

    There's no such facility on this site. There is an RSS feed you can use. Otherwise just come back and see the state of All Discussions whilst you're logged in.
    •  
      CommentAuthorSteamyTea
    • CommentTimeMar 10th 2017
     
    Posted By: countrymanIt does mean that his radiators are running cooler than their design temperature and I've not got my head around that one yet

    It is just multiplication really.

    https://ostroykevse.com/Otoplenie/31En.html
    • CommentAuthorgravelld
    • CommentTimeMar 10th 2017 edited
     
    Posted By: Peter_in_HungaryIf the oil boiler modulates low enough to cope with your lowest expected demand with out loosing too much efficiency then you can do away with the TS
    I didn't think oil boilers modulated at all...? Some sort of buffer is therefore useful for oil boilers, and a TS can fill this need.
  4.  
    Posted By: gravelldI didn't think oil boilers modulated at all...? Some sort of buffer is therefore useful for oil boilers, and a TS can fill this need.

    Just a very quick search "modulating oil fired boiler" gave
    Weishaupt Thermo Condens oil-fired condensing boiler (WTC-OW, 6 to 15 kW)
    Weishaupt oil-fired condensing boilers use almost all of the energy stored in the fuel, converting it efficiently into heat. A condensing boiler uses the energy which in older heating systems is lost to atmosphere with the flue gases. In so doing, nett efficiency is increased to 105 % compared to 95 % for low-temperature systems.
    .......The boiler benefits from modulating operation, having an infinitely variable response to current heat demand between 6 and 15 kW.
    .......Particularly quiet: Just like a gas-fired condensing boiler, the boiler is almost completely silent thanks to its modulating operation and innovative preparation of the fuel/air mixture.

    Of course there must be others in the market place. It would seem that modern oil boilers are up to the same standards of efficiencies as modern gas boilers. So with the quick 'for example' above I would have thought a TS would not be needed.
  5.  
    Posted By: countrymanThoughts anyone ?

    Modern oil boilers have come a long way in the last few years, some even have integrated DHW tanks. (Did I hear someone shout COMBI ? ) You also get wall hung types.

    People don't talk about the need for a TS when installing a modern gas boiler, so with modern oil boilers up to the standards of gas boilers why would you need a TS with a new oil boiler?
    • CommentAuthorgravelld
    • CommentTimeMar 10th 2017
     
    Interesting there are some developments in this area. Here's something else pertinent, PiH, which might not have come up in your search due to your location:


    https://www.worcester-bosch.co.uk/professional/news/erp-regulation-update
    The major stumbling block is on the modulation of an oil-fired boiler. Generally speaking, certainly in the UK, a domestic oil-fired boiler typically has a fixed burner, a non-modulated burner.


    But probably better to build or fix the house such that burning T-Rex bones isn't required.
  6.  
    Posted By: gravelld

    https://www.worcester-bosch.co.uk/professional/news/erp-regulation-update
    The major stumbling block is on the modulation of an oil-fired boiler. Generally speaking, certainly in the UK, a domestic oil-fired boiler typically has a fixed burner, a non-modulated burner.

    However the report goes on to say
    "A modulating burner would cost almost double the price of the present burner used in oil burners and also require an increase in controls complexity."
    And
    "All of which are relatively untried and tested so as a result we think it could signal the end of oil-fired boiler."
    After which comes
    "In what is generally a price-sensitive market, the price of an oil-fired boiler would increase significantly,"

    From which I take it that it is a cost/price issue in a competitive market. But the fact remains that modulating combi oil boilers are already on the market place and instead of comparing them to gas boilers the comparison should be made with the cost of say a gasifying wood boiler plus TS then a different comparison result arises. After all I doubt that any one with mains gas will be looking at an oil boiler, The competitive market place for oil boilers IMO is LPG and wood, pellet or as from another thread turf. Perhaps compare the price of a new pellet boiler with auto feed against the price of an oil boiler, not the mention the space demands for a pellet boiler even if there is no TS with it.

    The report goes on to say

    "Further developments
    It's not good news at present, but we are optimistic and we are lobbying hard using facts and laboratory evidence which would prove that a modulating burner and an on/off burner has virtually no difference in efficiency."

    Obviously this subject is still work in progress but the implication is that an on/off burner is not the disaster that it used to be with the 20 - 30 year old boilers.
    •  
      CommentAuthordjh
    • CommentTimeMar 10th 2017
     
    Posted By: Peter_in_HungaryThe competitive market place for oil boilers IMO is LPG and wood, pellet or as from another thread turf.

    Or a heat pump.
    •  
      CommentAuthorrichy
    • CommentTimeMar 11th 2017
     
    No Brainer, just pipe the oil boiler into the TS if there are spare ports. Thats what I did, best of both worlds,
    •  
      CommentAuthorrichy
    • CommentTimeMar 11th 2017
     
    Oops just the read the OP properly. In my opinion TS are great for combining inputs from different heat sources, but are just one big, albeit inefficient, radiator when heated by just an oil boiler.
    • CommentAuthorcountryman
    • CommentTimeMar 11th 2017
     
    SteamyTea...great link, thanks
    • CommentAuthorringi
    • CommentTimeMar 13th 2017
     
    Modem oil boiler will condense if operating with a low temperature flow, when a TS is used to heat DHW, it needs to be kept at a high temperature. Hence using a thermal store for DHW is not a good option with a modem oil or gas boiler.
  7.  
    Posted By: ringiModem oil boiler will condense if operating with a low temperature flow, when a TS is used to heat DHW, it needs to be kept at a high temperature. Hence using a thermal store for DHW is not a good option with a modem oil or gas boiler.

    Silly question - maybe - Does a condensing boiler need low temp. flow (operation) or just a low temp. return?
    • CommentAuthorgoodevans
    • CommentTimeMar 13th 2017
     
    It needs a low temp return - this is the water that does the condensing before it warms up in the boiler - ideally the flow rate needs to be as low as the boiler allows. I've seen boiler specs allow a 20 degree C raise (this allows 40 degree return, 60 degree flow for example).

    For my hot water I plan to use a simple regular condensing boiler, fix the flow to the minimum specified, mix the return with the flow to have a fixed minimum return temp into the boiler and therefore feed into the tank/store only water at the desired temperature for DHW in a single lift.
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