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.

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.

Awwwwwwwwwwww

A bit late but...

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

GANL,

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...
http://www.johnsonandstarley.co.uk/warm-air/overview.asp
Maybe I'm missing something (I usually do !)
so would be fascinated to be "filled in" on this one !

gg

Using Air to Transfer heat Around Home (!)

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.

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.

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!

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'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.

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.....

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.

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!