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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    • CommentAuthorringi
    • CommentTimeOct 31st 2015
     
    I think that for a retrofit MVHR, just getting the entry points spread round the house and not next to the exit point is good enough. In improvement with having MVHR is so great, that you don't need a design that is 100% correct.

    For our ITHO HRU ECO4, I did it all in 150mm rigid ducts, as they were easy to install in the loft of our bangolow under the loft insulation. If you use 150mm ducts then the lengths are not important apart from costs.
  1.  
    The room vents do a good job mixing the air so def not worth any hassle getting right to optimum position - but I mean vents that are specific for supply and extract not the generic cheap as chips 'a vent is a vent' ones. But in any even when talking retrofit I wholeheartedly agree with ringi - just getting one in the room is more than 80% of the battle
    • CommentAuthorwookey
    • CommentTimeNov 1st 2015
     
    Hmm. BES have 'supply and extract vents' which are one thing. Is there some fancier supplier I should be using that has different in and out vents? It hadn't occurred to me that it mattered.
    • CommentAuthorGotanewlife
    • CommentTimeNov 1st 2015 edited
     
    I used these and they have a very different design. Def recommend!

    http://www.i-sells.co.uk/extract-valves-ku

    http://www.i-sells.co.uk/supply-valves-ki

    I also bought some for under a fiver I think - def not recommended! I binned mine.
    •  
      CommentAuthordjh
    • CommentTimeNov 2nd 2015
     
    I think it's definitely worth having specific supply valves. The ones I used are here, though I expect you can get cheaper elsewhere:

    http://www.phstore.co.uk/ubbink-diffusing-air-valves-125mm.html

    The point about the supply ones is that they stand away from the wall or ceiling and blow air parallel to the surface. The parallel flow reduces drafts in the room; the stand-off reduces dirt staining of the surface.

    I wouldn't put an extra supply terminal in the living room unless you need it to balance flow rates. The extract in the kitchen will be larger than the extract in the bog, so I'd put the flow in the corner furthest from the kitchen if possible.

    I don't think length of ducts is a big problem unless it causes too much back pressure for you MVHR to cope.
  2.  
    Ringi, checking out MVHRs on ebay I noticed your Itho HRU ECO4 is badged as a Heatrae Sadia on ebay. I have installed the same at home.
    Can anyone recommend a MVHR for a small space of 45m2?
    • CommentAuthorringi
    • CommentTimeNov 9th 2015
     
    I would not use the Itho HRU ECO4 again, as there is no longer any worthwhile support due to Heatrae becoming their UK "office".
  3.  
    Cheers ringi, I wasn't aware of that. I bought the unit/system 5 years ago when they had their offices in Staffordshire. Do you get your filters from Heatrae now?

    Anyone with a suggestion for a MVHR unit for a small space ca 50m2?
    • CommentAuthorGotanewlife
    • CommentTimeNov 10th 2015 edited
     
    <blockquote><cite>Posted By: chippyclaus</cite>Anyone with a suggestion for a MVHR unit for a small space ca 50m2?</blockquote>
    Chippyclaus - Yes for you this one:

    http://www.ebay.co.uk/itm/SALE-Heat-Recovery-Unit-Fan-Whole-House-Ventilation-System-Only-20-left-/281161726627?var=&hash=item41768b7aa3:m:mfZTsoJXZRxF_-xEuQRkCFQ

    EDIT: just watch out for overall pressure drop as this unit really not powerful, so don't use flexible ducting for example.

    Highly rated MVHR (ie up in SAP Q quality) don't really exist in the just above single room size without buying something much bigger and hence more expensive that you need.

    You could do worse than flick through these short threads.

    http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10852&page=1#Item_17

    http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10860&page=1#Item_5

    Any other questions and I probably have a thread that answers it - but start another thread as we are stealing this one!
    • CommentAuthorwookey
    • CommentTimeNov 24th 2015 edited
     
    OK. So I have spent way longer than I intended understanding reynolds numbers, laminar/turbulent flow, major and minor friction coefficients and so on, and have made a spreadsheet for doing the calcs, as I failed to find one online that did this, and the various engineering calculators were all far _too_ flexible, and you needed to know your kinematic velocity and reynolds number before you could calculate anything, with a lot of looking up magic numbers in clever diagrams, or it was all American in stupid units and designed for heating so with epic flow rates.

    The spreadsheet is here:
    opendoc (libreoffice/gnumeric): http://wookware.org/files/MVHR.ods
    ISO29500 (excel): http://wookware.org/files/MVHR.xlsx

    I've made my head hurt in the process, so some reality checking would be good at this point:

    1) Do I need to allow for pressure drop due to height changes (e.g. dropping up/down 1 floor)?
    This seems to be the dominant pressure-loss, and it's mostly not mentioned in other docs. It also produces a negative drop for a short leg that mostly just drops down. I'm not sure what to make of that in terms of balancing.

    When a pipe goes up and back down again it clearly doesn't matter, but one that just drops a floor gets a pressure diff (Pascals) of (I think): density x g x height difference. so 1.18 (Kg/m3) x 9.81 (m/s2) x -2.4m = -28 Pa. Is that right - it seems high in comparison to the other components?

    For major friction loss I get numbers like 0.14Pa for 70m3/h flow in 4m of 150mm dia rigid galv pipe (@1.1m/s). i.e bugger-all.

    For minor friction (bends, outlets etc), I get 8Pa for the same pipe with 2x90 and 2x45 degree bends. i.e some, but still dwarfed by dropping one floor.

    Does that sound plausible? i.e. a total pressure drop for a run of major friction (pipe) , plus minor friction (fittings) plus(minus) height-difference pressure? typically 0.15+6+/-30.

    2) How much does it matter if my extract piping is much shorter than my supply piping? In the best spot the machine is within 1m of both kitchen and bathroom so there is approx 1m of duct each. But the supply ducting needs to go across the loft for bedrooms so they are all 8-11m. Is that going to make it hard to balance?

    3) What am I actually trying to optimise? So now I have a number for pressure drop to/from each outlet/inlet (in the range -17 to 41 Pa for the nominal 70m3/h which is 0.3 ach). Do I want to make the worst one as small as possible, or all of them similar, or all as small as reasonable?

    4) Is there such a thing as too-slow airflow? Some of my flow (to the smaller rooms) is laminar even in 100mm duct (<0.4m/s). Is this just good because that's efficient and quiet or should it be avoided for some reason?

    5) With the machine in a cupboard I can only get the external exhaust/supply cowls about 1m apart. Is that enough?

    I may have forgotten some things but that'll do for now.


    The sheet, for anyone that cares:

    You can all laugh at my low-tech solution to the problem of iterating the Colbrook-white equation. This made the spreadsheet hard, because you can't just put in a function in the normal way: the thing you want is on both sides so you have to iterate it. Turns out that Gnumeric doesn't do recursive solutions the way excel can, and if I stuck in a python solution it wouldn't work anywhere else. So, I just did it with a 6-step array iteration on a second sheet, which will work anywhere even if it's not at all pleasing to the programmer's eye :-)

    The sheet isn't perfect yet by any means (e.g. it uses hydraulic diameter where it should, but that's still set to just 'diameter' for now - it needs to look up whether square pipe is specified and if so use the correct Dh, and it currently assumes that your air is somewhere near 20C, and that your house is HxWxD). But it is probably a useful design tool, or would be with a bit more work to make it less cryptic to use. A neater way of describing the tree structure of ducts would be nice, and the multitude of ways of picking ventilation rates could do with rationalising. It should work correctly with round or square ducts in a range of materials, and of any size, and correctly deals with laminar/transitional/turbulent flow.
    •  
      CommentAuthordjh
    • CommentTimeNov 24th 2015
     
    Posted By: wookeyHow much does it matter if my extract piping is much shorter than my supply piping? In the best spot the machine is within 1m of both kitchen and bathroom so there is approx 1m of duct each. But the supply ducting needs to go across the loft for bedrooms so they are all 8-11m. Is that going to make it hard to balance?

    I expect you'll want to tweak the fan speed settings to cope with that. Mine does it automatically so the supply and extract volume rates are the same whatever the duct resistance is, but I believe some other MVHR units require you to adjust the flow rates manually.

    3) What am I actually trying to optimise? So now I have a number for pressure drop to/from each outlet/inlet (in the range -17 to 41 Pa for the nominal 70m3/h which is 0.3 ach). Do I want to make the worst one as small as possible, or all of them similar, or all as small as reasonable?

    I think you need to (a) make sure that the worst isn't so bad that your MVHR can't blow/suck enough air to it, especially given that you then (b) need to restrict the flow down/up the other ducts to increase their resistance to roughly the same point so you can fine tune the balance with the vents. You don't want to be using the vents to provide most of the resistance because that is one way to make it noisy.

    5) With the machine in a cupboard I can only get the external exhaust/supply cowls about 1m apart. Is that enough?

    I would try to get them a bit further apart but I would guess that there won't be much problem as long as the cowls direct the exhaust away from the intake. And the problem isn't life and death.
    • CommentAuthorEd Davies
    • CommentTimeNov 24th 2015
     
    Posted By: wookey1) Do I need to allow for pressure drop due to height changes (e.g. dropping up/down 1 floor)?
    I'd think not if the air was all at the same temperature. E.g., if you take air in via a vent into a ground floor cupboard then push it upstairs out of a vent in a bedroom then you wouldn't need to worry about the height change because the syphon would be completed by the rest of the house to wherever you extract whether that's in an upstairs bathroom or downstairs kitchen.

    However, the point of the whole thing is that the air is not all at the same temperature (otherwise you'd just open a window) so, at least in principle, you ought to care that the pressure differences will be affected by density. Rearranging PV/T = k with ρ = 1/V for 1 kg of air:

    ρ₁ = ρ₀·T₀/T₁

    If outdoor air is just about freezing (273 K) with a density of 1.2 kg/m³ and indoor air is around 20 °C (293 K) then indoor air will have a density of a tad over 1.118 kg/m³. If that's near floor level downstairs then the pressure difference between a ceiling vent in the bedroom 4 metres above and outside will be (ρ₀ - ρ₁)·g·h = 0.082 × 9.81 × 4 ~= 3.22 Pa which sounds like it's in the ballpark of what's significant for these purposes.

    But that's an extreme case as the house as a whole should be well enough sealed to act as a syphon. Still, I think being a bit careful about the temperatures of the air might help, particularly if you're doing PassivHaus-style duct heating where the incoming air is significantly warmer than the exhaust air.
    • CommentAuthorEd Davies
    • CommentTimeNov 24th 2015 edited
     
    Wookey, I'm confused by your minor loss calculation. E.g., cell M80: “=L80*I80^2/2*gravity”. Shouldn't that be density, rather than gravity? I'm looking at the .ods version. (L80 is the minor loss coefficient and I80 is the velocity.)

    PS: on further reflection - I think you're muddling up the pressure-loss and head-loss forms of the minor loss equations.

    Actually, I think even if it was the head loss it'd be “L80*I80^2/(2*gravity)”. Reading the Engineering Tool Box page literally:

    http://www.engineeringtoolbox.com/minor-pressure-loss-ducts-pipes-d_624.html

    it would be as you wrote it for head loss but with the usual mathematician's sloppy make-it-up-as-you-go-along notation I think they really mean to divide by g as they do here:

    http://www.lmnoeng.com/minorloss.php

    It's divide by gravity because, for the same pressure loss, Matt Damon gets three times the head loss.
    • CommentAuthorwookey
    • CommentTimeNov 27th 2015 edited
     
    I expect you'll want to tweak the fan speed settings to cope with that. Mine does it automatically so the supply and extract volume rates are the same whatever the duct resistance is, but I believe some other MVHR units require you to adjust the flow rates manually.


    OK. took a while to find, but there is a (manual) supply/extract relative speed pot to adjust on the Itoh HRU4, so that should be fine.

    you then need to restrict the flow down/up the other ducts to increase their resistance to roughly the same point so you can fine tune the balance with the vents. You don't want to be using the vents to provide most of the resistance because that is one way to make it noisy.
    .

    Sound sensible. So one should put dampers back up the pipes for 'main balancing'? Do we know any rules of thumb for how much difference there should be between runs before it's worth adding a damper? e.g (Assuming Ed is right about it being right to ignore height) then I have pressure losses at nominal rate of:
    Inlet: 2.8, 3.7, 2.5, 2.3 and outlet: 1, 1.1, 1.3 [edited from bigger numbers]

    So that's a worst case of 1.4 extra pascals needed to equalise runs (assuming use of supply/exhaust ratio adjuster). Does that make a noisy vent? (I assume I'm dealing in absolute values here - i.e 1.4 Pa not 60%)
    • CommentAuthorwookey
    • CommentTimeNov 27th 2015
     
    Ed, thanks for taking a look at the sheet.

    I agree with you about thing nominally being a closed system so up/down shouldn't matter, as it doesn't within a pipe ( helpful diagram on: http://www.pipeflow.com/pipe-pressure-drop-calculations/pipe-elevation-changes ). In theory we have one 'pipe' with an extremely large diameter section (the house) in the middle, and narrow bits (the inlet and outlet) at either end.

    Now I have a (non-room-sealed) small woodburner, so this definitely isn't actually true here. Not sure how to allow for that. I guess it can be generalised to 'there is some leakage in the really fat part of the pipe'. And extra air with either come in or go out, depending how much pressure difference the ventilation system (ignoring outside wind) is generating. So now the height-difference does matter, as it affects the pressure along the pipe, doesn't it?

    And you are right to observe that temp matters. That's why passive/chimney ventilation works. The air in the vertical pipe generates a pressure difference due to a density difference due to a temp difference and airflow occurs. My sheet does not yet take this into account. I'll have a bit more of a think about that. But with a max difference of ~2Pa (all my pipes are within 2.4m) on a very cold day it's not going to render my design fatally flawed.

    Minor loss calcs:

    O dear, yes foo/2*gravity != foo/(2*gravity). That's a rather major typo. That would make the minor losses ~30% of the major losses, not a factor of 5 bigger. So pipe length _and_ bends matters, not just bends. Good catch.

    I think you're muddling up the pressure-loss and head-loss forms of the minor loss equations.


    Erm, yes, quite possibly. I found it all quite confusing (There was a reason I switched to computer science after one year of engineering - computer science was child's play in comparison to all those bloody sums, and more importantly working out exactly _which_ sums applied).

    As you observe, the engineering toolbox notation is horribly sloppy.

    But yes, in fact I want pressure not head, so I reckon it should be: km * v2 * density/2
    i.e. M80*(I80^2)*(density/2)

    from ("If you have valves, elbows and other elements along your pipe" about half way down:http://engineersedge.com/fluid_flow/pressure_drop/pressure_drop.htm )

    So, having got that a lot more right, 'minor' losses now come out between 50% and times-5 of 'major' losses (except for very short pipe with a grille which is nearly all minor loss). Plausible. I guess calculating 'equivalent lengths' too, would give a better handle on plausibility.

    So ignoring height diff, as discussed above, my total pressure drops from machine to outlet are around 3Pa. That seems a bit low?
    •  
      CommentAuthordjh
    • CommentTimeNov 27th 2015
     
    Posted By: wookeyNow I have a (non-room-sealed) small woodburner, so this definitely isn't actually true here. Not sure how to allow for that.

    I'm definitely not an expert on wood burners so hopefully somebody who knows will come along, but I don't think wood burners and MVHR mix well. The problem is the need to ensure there is always greater pressure outside the stove than inside it, to prevent blowback of nasty gases and particulates. I have this horrible fear that the regs say you need a huge hole in the wall of the room. What does your BCO say?
    • CommentAuthorwookey
    • CommentTimeNov 27th 2015
     
    My woodburner is small (4kW) and therefore (at the time of fitting) did not need a big hole in the wall. It might do were I to refit it now (because it's done rather more sensibly on airtightness, rather than burner size), but bollocks to that - it's an idiotic 'solution'. I do have a CO meter which has never moved off 0, so either everything is fine or the meter doesn't work ;-) If it proves to be problematic the stove will have to get an external supply, but as things stand adding some ventilation should make things better rather than worse. Erring on the side of blow rather than suck is clearly smart.

    I'm not going to ask my BCO about it. He can concern himself with my extension and nothing more. The rest of the house is my problem :-)

    This is mostly a distraction from the important matter of getting my sums right.
    • CommentAuthorgravelld
    • CommentTimeNov 27th 2015
     
    Where is the wood burner? If there's an inlet in the room, wouldn't that mean the room is positively pressurised?
    • CommentAuthorwookey
    • CommentTimeNov 27th 2015
     
    On the matter of pipe selection. Everyone rates the galv metal piping, but it's very expensive. What is wrong with PVC ducting? That wouldn't suffer from rusting ever and appears to cost about half as much.

    I get that unless I buy the 'safe' galv stuff all joints need tescon-taping which is no doubt a big faff but this is DIY so I'm not that bothered about faffy things.

    Professionals seem enthusiastic about the semi-rigid pipe with plenum, but that seems mostly to be because it's much quicker to fit. Not sure how well it would work for retrofit.

    Also what do people do about insulating round pipe. In the loft just putting it all on the warm side and making sure there is no gappage should be good enough.

    But the bit that goes out of the wall is interesting. One is advised to continue the insulation through the wall so just wrapping a bit of fluff round it isn't going to work there. Some layers of karrimat-type material? What thickness is sensible? 20mm? That would require a 190mm hole in the wall for 150mm pipe which is bigger than commonly-available core-drills. I guess I just have to make a mess....
    •  
      CommentAuthordjh
    • CommentTimeNov 27th 2015
     
    Posted By: wookeyOn the matter of pipe selection. Everyone rates the galv metal piping, but it's very expensive. What is wrong with PVC ducting? That wouldn't suffer from rusting ever and appears to cost about half as much.

    Dunno - static attracting dust comes to mind but I've no idea. You could ask somebody like CVC?

    Professionals seem enthusiastic about the semi-rigid pipe with plenum

    I'm not a professional and I like it too. It is way easier to fit, IMHO.

    Also what do people do about insulating round pipe. In the loft just putting it all on the warm side and making sure there is no gappage should be good enough.

    I'd have thought so.

    But the bit that goes out of the wall is interesting. One is advised to continue the insulation through the wall so just wrapping a bit of fluff round it isn't going to work there. Some layers of karrimat-type material? What thickness is sensible? 20mm? That would require a 190mm hole in the wall for 150mm pipe which is bigger than commonly-available core-drills. I guess I just have to make a mess....

    Whatever you use needs to be vapour impermeable, otherwise you will get condensation on the outside of the pipe under the insulation. I have some of the foam insulated duct left if you want it? Apparently in an ideal world it would have thicker insulation but if your runs are short or you can add extra.

    http://www.ubbink.co.uk/ubbinkcouk/media/Ubbink-UK/Literature/UBBINK-Mass-Flow-Ductwork-listing.pdf?ext=.pdf
  4.  
    I'm with you Wookey. I used std orange drain pipe (because that's what there was locally) and got on with it very well. The only negative, that I can see, is that potentially you can get static related dust build ups. But as a DIYer, using plastic pipe has got me out of a couple of 3 situations that would have been impossible using metal pipe without significant extra work. You can also solvent weld them (if you are certain you have got it right) and they are easy to work with in terms of cutting and deburring etc. You can also heat the stuff and make a male end into a female end. I used high velocity duct sealant and I am glad I did because as a DIYer it holds just enough really quickly and can be adjusted for some time (or even disassembled), and remained flexible for several days. When I wanted belt and braces or to keep the sealant from getting on me/mess etc I used ali duct tape over the sealant - dead cheap). I did use the odd metal bit joint, for example to attach house vents to pipe and for example my attenuators were galv ended - all perfectly compatible.

    I am really not at all sure I would bother taking pipe insulation all the way through the wall! The pipes will have a down to outside fall on them for sure, so what's the worst that could happen - esp with plastic pipe? Just how much interstitial condensation will you get, surly not enough to cause a problem Core drilling is painful enough already. If you have a double skinned brick, core drill, knockout some chunks of the inner leaf with a chisel and use squirty foam to make good - plenty good enough. Ref insulation: I found pipe insulation silly money, I simply bought that awful flexible pipe (it is dead, dead cheap) and pulled out the inner liner - it then slips over your pipe easily enough. Any cuts/joints I made good with ali tape and you can force it into aforementioned knocked about hole in wall and squirty foam a good seal.

    All a bit Heath but I couldn't see any reason to be more professional in this case.
    • CommentAuthorringi
    • CommentTimeNov 27th 2015
     
    I got my plastic ducts from https://www.bes.co.uk/products/180.asp, (drain pipe are not the same size, so will not directly fit onto the outlets etc).

    For insulation, I use some silver bobble wrap from b&q, the sort that is often used behind radiators.
  5.  
    Posted By: ringidrain pipe are not the same size
    They are here, 125 and 150 anyway :bigsmile:

    The stuff behind rads is in my experience pretty thin 3-5mm really all about being reflective - is it enough?
    • CommentAuthorringi
    • CommentTimeNov 28th 2015
     
    Posted By: GotanewlifeThe stuff behind rads is in my experience pretty thin 3-5mm really all about being reflective - is it enough?


    I got a role of it, and wrapped it round the ducts a few times. I only needed it for the air intake duct to stop condensation on it within the "cold" loft space, I sealed it with "sliver" tape. The rest of the ducts are under my loft insulation.
  6.  
    So, yes enough for the 'cold' lost space for sure. For clarity one should mention that the main outlet after the MVHR unit contains cold air and in a warm space there can also be condensation on the outside of this pipe - so it would need insulation if under insulation if that makes sense. :confused:
    • CommentAuthorRobL
    • CommentTimeNov 28th 2015
     
    I diy installed MVHR, in a 4 bed similar house to Wookeys. Have to say, I didn't even try to do anywhere near the number of calcs he's referring to. I think there are so many difficult factors to take into account, and ultimately it's a sliding scale between noisy & thin pipes/ducts, and quiet & fat pipes. I choose fat pipes!

    I did try experiments with a CO2 meter in different occupied rooms, while the adjascent hallway window was open - to try to work out if a duct was needed in the room. My rule of thumb after this was only to put ducts in rooms that were wet, or expected more than one occupant. Is the door open/closed, what is the gap under it - all make a difference here. My now-teenage daughter now closes her door by default - so I'm thinking of adding a duct in her room - or at least remeasuring the CO2 level. Definitely recommend a CO2 meter.

    As for what ducting - I tried to use metal where I could, thinking it more likely to be biocidal than plastic. For a couple of long loft runs, the pipes are 200mm diameter. The majority of pipework is 150mm diameter, and the room ducts are all 150mm diameter. The system is quiet - I can't hear it at night, even in our quiet neighbourhood. I think the noisiest duct is the bathroom one - it's closest to the MVHR unit, so there's less attenuation maybe.

    It's difficult to get ducts where you want in a retrofit, without making a mess. So there was compromise in the livingroom inlet duct location - it's too close to the hallway door. It probably discourages heat from the stove circulating around our house a bit? Not that we light it that often, but something you'd care more about Wookey.

    I religiously went around our house measuring flow rates and adding them up, intending to adjust the supply/extract main fan speeds - but they were balanced anyway. I didn't bother adjusting individual room ducts with dampers or closing off ducts - it all mixes in the house anyway I think, and closing off ducts makes the whole thing noisier & less efficient.
    • CommentAuthorwookey
    • CommentTimeNov 29th 2015
     
    <blockquote><cite>Posted By: Gotanewlife</cite>am really not at all sure I would bother taking pipe insulation all the way through the wall!</blockquote>

    You make a good case that there is no point going through the outer leaf, and I can make as much of a mess as I like on the inside, and builders foam is good insulation.

    On balancing it turns out that the current manual (http://www.heatraesadia.com/docs/HRU_ECO_4_-_Installer_Manual_-_36006182_issue_1.pdf , p17-p18) has 3 pots, one for in/out balancing. But mine only has 2 pots, not including the balancing pot. This is dull.
    •  
      CommentAuthordjh
    • CommentTimeNov 29th 2015
     
    Posted By: wookeyOn balancing it turns out that the current manual (http://www.heatraesadia.com/docs/HRU_ECO_4_-_Installer_Manual_-_36006182_issue_1.pdf , p17-p18) has 3 pots, one for in/out balancing. But mine only has 2 pots, not including the balancing pot. This is dull.

    Sounds like you need to balance the resistance of the ducts then unless the nice folks at heatraesadia can suggest an alternative. Maybe there's some way to hack the circuit to do what you want, but the warranty may be worth something.
    • CommentAuthorwookey
    • CommentTimeDec 1st 2015
     
    They were reasonably helpful. Turns out that the pot described as 'balance pot' is actually for setting 'speed 2', and after the early models has been factory set at 'speed1+20%'. So no, no fan balancing unless I throw the innards away and put my own controller in (which was the original plan, but it might take me a while to get round to).

    I guess I'll just suck it and see.

    Next issue: Removing cross-bracing.

    I have worked out that actually a 220x100 flat tube will fit from unit to lounge in the downstairs ceiling void. (I had previously assumed there there was too much plumbing and wiring in the way for this to be practical). However this will require removing the cross-bracing that is currently in there. Should I worry about that, on 50-year old joists? The rest of the bracing will still be there, and it should be quite stable by now. Presumably people remove these from time to time and nothing bad happens?

    One could put a noggin back in above and a steel strap below to put back some bracing.
    •  
      CommentAuthordjh
    • CommentTimeDec 1st 2015 edited
     
    Posted By: wookey'speed 2', and after the early models has been factory set at 'speed1+20%'

    The table in section 2.6 of the manual you posted seems nothing like that?

    One could put a noggin back in above and a steel strap below to put back some bracing.

    That sounds reasonable to me.
   
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