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Green Building Bible, Fourth Edition
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    Slept on it. Realised the downside (well upside really) of going wet and free (virtually) wood is that he now can save some money on insulation and for sure airtightness. It is clear good airtightness is going to cost in labour and all those stretchy collars etc can't be cheap either, but mainly the time to plan, draw, supervise, redo and just the sheer extra hours required to be careful. A super insulated roof is thick and actually not very pretty, reducing the thickness of the roof insulation will save money not just the insulation but also transport and of course copper (valances and eve's coverers (don't know the correct term). Bottom line is if he works at it and gets a 4 or 5kW instant heat load or doesn't and gets a 8kW instant heat load it makes almost no difference to the cost of the wet system (a 1000 ltr TS instead of an 800 ltr and a 10kW WB instead of a 6kW) - all other heating system costs are the same both initially and for the future - even if he sold his business and didn't get free wood the extra cost of the wood might be 100E/pa.

    Fault that logic dear friends.
    • CommentAuthorringi
    • CommentTimeApr 30th 2016
    Think about quality of life as well….

    Sitting in a draft is not nice; therefore a reasonable level of airtightness is worth having.
    Sitting next to a cold window or wall makes you feel cold even if the inside air is warm.

    However I would be going for “wet” system for all the reasons you have listed. Along with reasonable levels of insulation and air tightness, e.g. double glazing rather than triple unless a window is very large.
    Yes Ringi - I am not throwing out insulation or air tightness just going to suggest he applies a little of the 80/20 rule. Good point about 3G on a big window - looks like they will have a big picture window for the rather spectacular view across to Assisi.
    • CommentAuthorgyrogear
    • CommentTimeApr 30th 2016
    well done - in the end the solution was as sisi as that...:bigsmile:

    Awwwwwwwwwwww :cry:
    • CommentAuthormike7
    • CommentTimeMay 1st 2016 edited
    Posted By: Gotanewlife eve's coverers (don't know the correct term).

    Fig leaves traditionally.
    • CommentAuthorgyrogear
    • CommentTimeMay 1st 2016
    A bit late but...

    Using Air to Transfer heat Around Home (yes seriously!)


    I know I'm generally slow on the uptake, but why the ("yes seriously"!) in the title ?

    As if using air to transport heat around a home is "unusual" ?

    (I thought that many US homes use this method, with their ducts & boilers ??)
    Not to mention whole house fans etc.
    I even found a link...
    Maybe I'm missing something (I usually do !)
    so would be fascinated to be "filled in" on this one !


    Using Air to Transfer heat Around Home (!)
    Mike7 - how did I miss that?! Well punned!:bigsmile:
    • CommentAuthorEd Davies
    • CommentTimeMay 1st 2016
    Posted By: gyrogear(I thought that many US homes use this method, with their ducts & boilers ??)
    At high temperature - as hot as you can get it without causing smells from scorched dust. If you want to move useful amounts of heat at the small temperature differences you'd want in rooms then you need to shift a lot of air.

    The specific heat capacity of air is around 1000 J/kg·K (slight over that, actually) and the density at normal temperatures and pressures about 1.3 kg/m³ (slightly under that so tending to cancel) so the volumetric heat capacity is 1300 J/m³·K. Suppose GaNL's friend's wood-heated living room is at 22 °C and a bedroom is at 17 °C so 5 K difference so each cubic metre of air swapped transfers 6500 joules.

    To have the equivalent of a 650 W heater in the bedroom you'd need to transfer 1 m³ every 10 seconds or 360 m³ per hour. For a 3 m × 4 m, 2.4, m high room that's 12.5 air changes per hour. People worry about noise for a nominal 0.4 AC/h.
    • CommentAuthorGotanewlife
    • CommentTimeMay 1st 2016 edited
    djh said PH is 10W/m2 max instant heat requirement. So say friend (Leonardo actually) achieved 15W/m2 (that's 50% worse) then that 3mx4m room needs (12m2 x 15W) 180W of heating so 3.5 ac/h. And the Centra on high trickle (9l/sec) delivers well over that and nearly manages on low trickle (6l/sec) at 10dB@3m, before you even take into account the MVHR ) using your figures Ed.

    Gyrogear - does that answer your question? There have been a few people asking things in and around this area and all have been thoroughly 'deflated/defeated' by the wieght of opinion here (hence my "yes seriously!" comment); more importantly, eventually someone has done the maths and common sense has prevailed - but in this particular circumstance I had a gut feeling that it was actually possible - now Ed has done the bit I couldn't do (without a lot of effort) and either I have missed something or the argument is back on again :devil:

    Where did you get that 650W heating demand figure from Ed - that's 55W/m2 for the 3x4 room?
    • CommentAuthorEd Davies
    • CommentTimeMay 1st 2016
    650 W just seemed like a plausible amount for illustration which made the arithmetic easy to illustrate that lots of air needs shifting to move much heat.

    If you really think they'll achieve 15 W/m² maximum then maybe air might be enough. Without a fairly serious effort to come close to PH I wonder if that's what'd turn out though.
    • CommentAuthorringi
    • CommentTimeMay 1st 2016
    Part of the problem is that the air being moved has to be HOT, but you don't want air that hot in the room that contains the wood burning stove.

    If the air is heated (maybe as hot as 50c) by a USA type boiler, it CAN be moved with USA sized ducts, these ducts are as much a 1 foot square, so a lot larger then what is used for ventilation.

    However all is not lost as people tent to like their living rooms hotter then their bedroom. But it is very hard to control a wood burning stove to give a constant heat output.

    If there was a wood burning stove that had air ducts built in, so you could control where the air was sent (with a fan) rather then the stove heating the room it was in, then it would be worth doing the calcs.
    • CommentAuthorGotanewlife
    • CommentTimeMay 2nd 2016 edited
    Posted By: Ed DaviesIf you really think they'll achieve 15 W/m² maximum then maybe air might be enough. Without a fairly serious effort to come close to PH I wonder if that's what'd turn out though.

    I have no idea what he could achieve. I am just aiming to give him the choices, ie that he is well informed and can decide whether to put a "fairly serious effort" into eliminating the need for a wet system. I know that the GBF is a rarefied atmosphere but it seems that many people achieve PH, and I imagine that the difficult bit is the max 15 kWh/m²/year rather than the 10W/m2 instant heat load (am I right on this?). He would only need to aim at a low max heat load and it would appear that he could be over by 50% and still save himself the right side of 10,000 Euros (plus all the other things I have mentioned previously that go with a wet system).

    To reiterate: this would only work in a modest sized house, single storey, all open plan, no palatial bedrooms, probably has implications for room layout and is only applicable where someone chooses to burn wood for heating. Having said all that, how about a little credit here: this was novel and contentious but we have proven the feasibility of an alternative that saves space in the home (a TS and manifolds), a shed load of money (5% of the build maybe), simplifies the services part of the build no end, de-risks maintenance over the life of the building, reduces all those carbon rich things that go into a house and more no doubt - all for the cost of 3 Centra fans and ensuring 7 or 8 l/s ventilation into the bedrooms if you can get within 50% of the PH instant heat load target (isn't it recommended that there is 8 l/sec into bathrooms anyway).

    Ringi - not sure you are quite up with the developing argument. The air does not have to be "HOT" (Ed's figures used 22 deg living space air and 17.5 deg bedrooms). Volumes are only a little larger than ventilation norms. You are right though, as I mentioned previously, woodburners make the immediate space too hot, perhaps it is part of what's nice about them, certainly that is normal over here and (also as I mentioned) this includes my friend. To keep a fire going with some love and close attention to the room temp automatic for most over here. Finally you mentioned WBS with built in air ducts - I covered this at the beginning - he would rather have his testicales cut off than go that route again - and if he did try then that's what his wife would do to him!
    Posted By: ringithen it would be worth doing the calcs.
    What calcs???? over the previous 3 posts to yours we have already done them and proven it is feasible!
    • CommentAuthorgyrogear
    • CommentTimeMay 2nd 2016
    Posted By: Ed DaviesTo have the equivalent of a 650 W heater in the bedroom you'd need to transfer 1 m³ every 10 seconds or 360 m³ per hour.

    Ed, thanks for the explanation.
    I obviously overlooked the difference between US use of boilers, and GANL's intended use of a WBS and just air circulation, so the point is taken !

    (Lived in this house 8.5 years and thanks to your explanation, just took the temp in our bedroom for the 1st time ever - it is 18.1°C -- with no heating at all (we dumped the convector the first week -- hate the things...) and never replaced it with anything. A few years ago I ran some numbers on a web-based calculator and it came out with a heat requirement of 300 W, so we never bothered).
    "we don't need much heat as we are semi-buried" :sad:

    • CommentAuthorCerisy
    • CommentTimeMay 2nd 2016
    We are getting into the twilight area of not quite warm enough in the evenings so the WBS goes on + a bit of eye candy of course, but we then have to open a window as the bedroom gets too hot. Another week or so and the WBS can be cleaned out and we'll sleep better! The heat naturally rises, but the MVHR is also pushing it around during the night - great for the couple of cold days this winter, but now ... NO!

    We love the WBS, but it's too tempting to just put it on briefly (yeah, right!) as it looks nice! We have no other option so mustn't grumble.
    I hear you Cerisy - I have had to make provision for a WBS on our lounge "just to take the chill off sometimes", despite having a massive 40kW WB and 2000 l TS. Wife also enjoys looking for 'the one' not sure she has an option under 4K! and we don't have that sort of money now - the draw of the wood fire aye. But for you MVHR does the distributing heat around thing just fine - was that a thought through calculated thing or luck or driven by an outside maybe financial imperative?

    Gyrogear - so for you too moving heat around with air (via MVHR) works! But it must depend on the outside temp no - so if it were -5 deg outside you'd have to get the nasty heater back in again I assume - it is an important point - what outside temp does the PH limit of 10W/m2 instant heat load apply to - if it is -5 deg then MVHR might manage on it's own with minor tweaks say 80% of the time - with clever control gear incl some hysteresis and anticipation on the Centra fans it could probably be organised so that the bedrooms never have the Centras on when people are sleeping (on the small part of the year when they are need at all).
    • CommentAuthorEd Davies
    • CommentTimeMay 2nd 2016
    I've poured a bit of cold water on the completely passive slab idea but I'm lukewarm about the warm air distribution ideas. As I've shown, if you want to move noticeable amounts of heat around with air you have to move a lot of air which would be a problem if you only ran the things while the WBS is lit in the evening (outside the peak-heating season) and there was no other way of moving heat. But realistically, heat's going to be conducted as well as advected and you can leave the fans running when the WBS isn't lit, though maybe not when somebody is trying to sleep.

    The difficulty might be working out the layout so it works well enough. E.g., you'd want the kid's bedroom well enough separated from the main living area to allow them to sleep earlier in the evening while the adults are still up yet closely enough connected that they get the benefit of the heat.

    Also, even with a 6 kW limit putting an electric heater on in a few rooms for a couple of hours during the worst few weeks of the winter (e.g., when there's no cooking going in) might not be terrible and a lot less capital intensive than a wet system.
    • CommentAuthorEd Davies
    • CommentTimeMay 2nd 2016
    Posted By: Gotanewlifewhat outside temp does the PH limit of 10W/m2 instant heat load apply to
    AIUI, PH works with local climate data so you need more insulation, etc, in a cold climate to meet PH. This is the North American argument that PH doesn't apply everywhere - when it's -40 °F or C outside the tradeoff between insulation and heating is different, they claim. ( <-- just an example to illustrate how PH works; if you want to discuss that, start another thread.)
    And you are usually so hot about things Ed! But a big thanks you for doing the sums anyway!

    So the idea (not even a plan yet) is a beefed up insulated slab, cellulose in the walls, an oversized MVHR with clever control gear, 3 x Centra fans with control gear, back up electrical heating in bedrooms, bathrooms with infra-red and/or electric under floor if tiled instead of wood floors. Room sealed WBS and big effort on getting max instant heat load as low as poss.

    Have I missed anything? Ohh yes then there is the conversation with Leonardo who's going to think this is a crackpot idea.....
    • CommentAuthorgyrogear
    • CommentTimeMay 2nd 2016 edited
    GANL, I actually don't have MVHR (yet...)
    and fortunately we never get down to minus 5°C...
    we just have a "benign climate", I'm happy to say !

    However, I *do* like the idea of warming with air...

    Posted By: Gotanewlifea beefed up insulated slab, cellulose in the walls, an oversized MVHR with clever control gear, 3 x Centra fans with control gear, back up electrical heating in bedrooms, bathrooms with infra-red and/or electric under floor

    sorry, but to me it sounds like a gasworks !

    Why not go for the KISS principle ?
    Here's an idea...

    He'd maybe have to purchase in south of France - HERE is one, it has two 6-inch air offtakes and a turbine

    Posted By: Ed DaviesAt high temperature - as hot as you can get it without causing smells from scorched dust.

    It is better if it's not that hot.

    As I have posted many times before, I have a water-to-air GSHP and it works perfectly in cold Montreal. The trick is sizing the ducts large enough to transport the heat around at a velocity that doesn't cause noise. Drafts are also not a problem with correct design. If you use too high a supply temperature, you'll feel drafts more than a cooler temperature (my system uses air at around 32C). Large ducts are also not noisy as the velocity is kept "low enough", plus they are acoustically lined to remove the sound of the fan, too. Just go to an US aircon site and read up on the calculations for duct sizing versus amount of heat (or coolth) to transport.

    Paul in Montreal.
    • CommentTimeMay 3rd 2016
    Posted By: GotanewlifeI imagine that the difficult bit is the max 15 kWh/m²/year rather than the 10W/m2 instant heat load (am I right on this?).

    It varies, depending on location and the size and design of the building. Given your friend's lack of solar gain, I suspect that you might be right for his situation. His peak load is no worse than other people's, but his yearly demand will be higher.

    The 50°C air temperature is PH-only. Other air-heating systems recirculate air and use quite a large air flow so they can use lower supply temperatures. The PH trick is to use only fresh air circulated by an MVHR unit at its normal setting so it needs to maximise the supply temperature.

    My preference for a UFH system is that we know it will work. With a custom warm air system there is the question of how controllable the wood burner is, how noisy the whole system will be (and how much that matters to the occupiers), and what the backup plan is if it doesn't work perfectly. JMHO.
    • CommentAuthorGotanewlife
    • CommentTimeMay 3rd 2016 edited
    Posted By: djhwhat the backup plan is if it doesn't work perfectly.
    Nail head go! If it were my house then I reckon I could pull it off but obviously I would be accepting the risks incl use of the back up plan. Leonardo will already be experimenting in so many other areas, being a first time self managed build (whilst working full time) for one and a wood framed house in a region devoid of them for another, so saving the money, and all the other advantages, would have to capture his imagination big time in order for him to want to pursue this course of action.

    I think a post heater in the MVHR would be the first choice back up plan. I think the noise issue is a bit of a red herring - I have installed DIY 2 x MVHR systems and they are silent and with capacity to reduce noise even further. I have installed various fans in various ways and I understand those dB figures and how they relate to the real world - the Centra fan's noise figures are class leading and 10dB is below most people's limit of hearing for example. And control gear is straightforward and dead cheap. Also let's not forget that for the majority of the heating season it is not below zero outside and the 15W/m2 is a maximum that would not be needed most of the time.

    In fact, I see the biggest risk as Leonardo setting out to do this but not getting the detailing right that is required to get down to such a low heat demand and there's no going back to fit a wet system!
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