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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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      CommentAuthordjh
    • CommentTimeMay 29th 2020 edited
     
    Posted By: WillInAberdeenSeems odd, as quarter of a tonne of scalding water in an DHW cylinder above the stairs, would seem to be as hazardous as quarter of a tonne of scalding water in a thermal store, location and pressure being equal...?

    Typically they aren't equal though. DHW cylinders these days are typically pressurised, so it doesn't really matter where they are but upgrades/old designs and maybe lazy current systems are placed upstairs because that was necessary for vented systems. Thermal stores are typically vented, I believe (why would anybody have a pressurised thermal store?), and the feed/header tank can be directly above (like mine) so the whole installation is downstairs.
    • CommentAuthorEd Davies
    • CommentTimeMay 29th 2020
     
    Posted By: djhwhy would anybody have a pressurised thermal store?
    Aren't CH systems typically sealed and wouldn't you normally run the radiators directly off the water in the thermal store (without a heat exchanger)? So couldn't it become very pressurised in a failure situation?
  1.  
    DJH, no, there's no necessity for a vented DHW cylinder to go upstairs, it can go wherever is convenient, so long as the F&E tank is sufficiently above the highest connection, and any gravity loops work. Same for vented thermal stores feeding upstairs radiators. Same for bungalows and flats.


    There are requirements in building regs for vented DHW systems, such as : 19mm vent pipe, non- resetting thermal cutout, overflow, supports, accessibility, etc. But I can't see where the equivalent is written for a vented thermal store or CH system.


    Has anyone positively tested that their pressure safety valves actually work at the correct pressure? If not, what does the 'annual inspection' actually achieve?
    •  
      CommentAuthordjh
    • CommentTimeMay 30th 2020
     
    Posted By: WillInAberdeenThere are requirements in building regs for vented DHW systems, such as : 19mm vent pipe, non- resettable thermal cutout, overflow, supports, accessibility, etc. But I can't see where the equivalent is written for a vented thermal store or CH system.

    Those regs apply to 'Vented hot water storage systems', which include thermal stores as well as vented DHW cylinders and central heating buffers.

    But a thermal store has no need for a pressure head created by having the feed tank in the loft, so the feed & expansion tank can be mounted directly above the thermal store with consequent shortening of the plumbing and reduction of overflow risk.

    Posted By: Ed DaviesAren't CH systems typically sealed and wouldn't you normally run the radiators directly off the water in the thermal store (without a heat exchanger)? So couldn't it become very pressurised in a failure situation?

    If you have an arrangement as I describe above then the central heating circuit needs to be separate from the thermal store water and is likely pressurised since that will be simpler than a separate high-level header tank. But sure, you could also pressurise the thermal store. I'm not sure what failure situation you're concerned about nor what consequences that don't occur with any pressurised circuit?
  2.  
    No, those requirements are specifically for "heated wholesome water" only, not central heating.

    A thermal store needs its F&E tank to be in the loft if it is connected to radiators on an upper floor, as Ed highlights. Otherwise you'd need a separate system, unvented with expansion vessels or vented to a F&E in the loft, to exchange heat between the thermal store and the radiators, which seems an unnecessary complication, but if you're happy with your setup that's fine.


    Breaking news: I have removed the thermostat from the immersion heater, which the 'heating engineer' didn't bother to check, and found it is a cheaper type with **no thermal cutout** at all!! The immersion heater is going to remain isolated at the CU until I buy a replacement thermostat that is safe.

    Advise everyone to CHECK your thermal cutouts and don't rely on it having been fitted by someone 'competent' !!
    •  
      CommentAuthordjh
    • CommentTimeMay 30th 2020
     
    Posted By: WillInAberdeenNo, those requirements are specifically for "heated wholesome water" only, not central heating.

    "Hot water storage system means a vessel for storing:

    "a. heated wholesome hot water or softened
    wholesome hot water for subsequent use

    "b. water that is used to heat other water

    "together with any ancillary safety devices
    described in paragraphs 3.10 and 3.11 of this
    Approved Document and all other applicable
    operating devices."

    Note especially clause b. Source is https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/504207/BR_PDF_AD_G_2015_with_2016_amendments.pdf

    Your second paragraph describes one of the arrangements I already described. None of it is relevant to my setup, since I don't have wet central heating.
    • CommentAuthorMike1
    • CommentTimeMay 30th 2020 edited
     
    Posted By: djh
    Posted By: WillInAberdeenNo, those requirements are specifically for "heated wholesome water" only, not central heating.

    "Hot water storage system means a vessel for storing:

    "a. heated wholesome hot water or softened
    wholesome hot water for subsequent use

    "b. water that is used to heat other water

    "together with any ancillary safety devices
    described in paragraphs 3.10 and 3.11 of this
    Approved Document and all other applicable
    operating devices."

    Agreed. If you look up the actual regulations (rather than the approved documents), it's even clearer:

    Hot water supply and systems
    G3.—

    (1) There must be a suitable installation for the provision of heated wholesome water or heated softened wholesome water to—
    (a) any washbasin or bidet provided in or adjacent to a room containing a sanitary convenience:
    (b) any washbasin, bidet, fixed bath and shower in a bathroom; and
    (c) any sink provided in any area where food is prepared.

    (2) A hot water system, including any cistern or other vessel that supplies water to or receives expansion water from a hot water system, must be designed, constructed and installed so as to resist the effects of temperature and pressure that may occur either in normal use or in the event of such malfunctions as may reasonably be anticipated, and must be adequately supported.

    (3) A hot water system that has a hot water storage vessel must incorporate precautions to
    (a) prevent the temperature of the water stored in the vessel at any time exceeding 100°C:
    (b) ensure that any discharge from safety devices is safely conveyed to where it is visible but will not cause a danger to persons in or about the building.

    (4) The hot water supply to any fixed bath must be so designed and installed as to incorporate measures to ensure that the temperature of the water that can be delivered to that bath does not exceed 48°C.

    Posted By: WillInAberdeen
    Building Stds/regs apply when constructing or modifying, so can't impose requirements for maintenance.

    Agreed; they don't.

    However, as mentioned in my post on the previous page, your insurance company probably will require regular maintenance of an unvented system.
  3.  
    Hi again

    Thanks for all comments!
    This post grew a few interesting legs over the weeks, and I am trying to take stock!

    Given that I have existing timber floorboarded suspended floors to ground and first floor, and that raising floor levels is not practicable, my thinking is :-

    UFH heating pipes between joists, fixed from below using aluminium spreader plates with close fitted insulation under. Evidently not as efficient as pipes bedded in screed, but I do not have that option. These plates are very expensive - c £4.50/lm for two pipe section - am I being realistic in thinking this will work effectively?

    AHP serving UFH.

    Thermal Store in semi basement - lots of debate about TS or DHW - if it were a DWH cylinder it would have to be pressurised (with expansion vessel) to deliver hot water to the upper floors (no loft space for header tank) and have an indirect solar coil? Is there any consensus as to whether TS or DWH is better?

    TS/DHW heated by Solar Thermal panels and/or immersion heaters and/or AHP when not called for heat as priority?
    How to control the AHP (when not called for UFH) so that it is not competing against free solar?

    Good insulation and draft proofing generally.

    Any residual comments to any of this?

    Thanks
    • CommentAuthorMike1
    • CommentTime3 days ago edited
     
    Posted By: CharentemanThese plates are very expensive - c £4.50/lm for two pipe section - am I being realistic in thinking this will work effectively?

    As per my post on the previous page, you need some calculations to prove that it will, rather than guessing. And don't rule out having plates made up locally.

    But heat transfer plates are frequently used within a 1st floor structure - just that they are usually laid over the joists before the boarding out, rather than retrofitted from below afterwards.

    Posted By: Charentemanif it were a DWH cylinder it would have to be pressurised (with expansion vessel) to deliver hot water to the upper floors (no loft space for header tank)

    Yes, unless you put a cold feed tank within a 1st floor room and use a booster pump for the shower (or accept a weak shower).

    Posted By: Charenteman...and have an indirect solar coil?

    As previously suggested, I would choose PV, not solar thermal.

    Posted By: CharentemanIs there any consensus as to whether TS or DWH is better?

    Probably not! There are pros and cons to each. Personally I'd choose a TS in your situation.

    Posted By: CharentemanTS/DHW heated by Solar Thermal panels and/or immersion heaters and/or AHP when not called for heat as priority?
    How to control the AHP (when not called for UFH) so that it is not competing against free solar?

    The simple way is to keep DHW & space heating separate, with PV only heating DHW.
    • CommentAuthorMike1
    • CommentTime3 days ago edited
     
    dupe.
  4.  
    Thanks Mike 1
    Yes, I had meant to include PV as a further source to the TS.

    I have to say that given the floor constraints, I am becoming very uncertain about the suitability of an AHP for our heating - capital and running costs and most importantly whether it will keep us comfortably warm in a sub zero French winter!
    Perhaps I should consider a wood pellet stove although is this really a more sustainable solution than a programmable and controllable LPG condensing boiler...?
    Big and tricky decisions to make...!
    • CommentAuthorMike1
    • CommentTime23 hours ago edited
     
    Posted By: CharentemanI have to say that given the floor constraints, I am becoming very uncertain about the suitability of an AHP for our heating - capital and running costs and most importantly whether it will keep us comfortably warm in a sub zero French winter!

    If you take a look at the statistics, the Scandanavian countries are the biggest European users of heat pumps, where the winter climate is definitely colder than France - and new installations are higher in France than anywhere else in Europe. See http://stats.ehpa.org/hp_sales/story_sales/

    You just need the calculations to verify that your proposed heat pump and floor distribution pipes are capable of delivering at least as much heat to each room as those rooms are loosing through the fabric of the building and through ventilation. You'll need similar calculations for any other type of heating you might consider too...
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