Go to Forum Home › Building Design › Passivhaus Design Question
- This topic has 19 replies, 5 voices, and was last updated 10 years, 4 months ago by Tom Foster.
-
AuthorPosts
-
-
28 September 2012 at 8:37 am #31739Anonymous
Excuse me if this question sounds to simplistic, but is the aim of the Passivhaus total maximum energy usage of 120 kWh/m2/yr restricted to using the prescribed envelope elemental values or does it allow design flexibility of these values in achieving the 120 kWh/m2/yr?
I would also like to apply this question to other low energy design guides such as Carbonlite and Code for Sustainable Homes.
Jean-Marc Bouvier
-
1 October 2012 at 7:29 pm #38700
The main target is the space heating of 15kWh/(m2.a) (or 10W/m2 peak heat demand).
This is calculated according to PHPP with Passivhaus assumptions for gains etc.
Please see the document claiming the Passivhaus Standard which can be downloaded from the Passivhaus Trust Website.
There are no prescribed elemental U values except for windows (climate specific) and that is for comfort. However you will need very good U values (0.15 or better in the UK is typical) to meet the target for most building types, especially dwellings.
The 120kWh/m2 if total primary energy value.
Same for Carbonlite, I can't help with CSH.
Nick
-
1 October 2012 at 10:17 pm #38701Anonymous
Hi Nick
So if a designer can be convinced that a wall with a value of 0.25 can produce the target of 15kWh/m2/yr then its possible to do so?
Jean-Marc
-
3 October 2012 at 9:24 pm #38702
Jean-Marc
In theory you could achieve the 15 kWh/m2.yr with a fabric U-value of 0.25 W/m2K. You could do this with a suitably large building that has a preferable surface are to volume ratio and/or a suitably warm climate (think the south of France.) As for the UK, it is likely that more often than not a detached house will need U-values in the order of 0.1 W/m2K or so.…also, it is not a case of 'convincing a designer', rather it is a case of running suitable PHPP calculations and determining what U-value is required to achieve the 15kWh/m2.yr
Mark
-
4 October 2012 at 8:48 am #38703Anonymous
Hi Mark
Does the type of wall, heavy or light, have any bearing on the u-value?
Jean-Marc
-
7 October 2012 at 5:25 pm #38704
In terms of the BS EN standards the U-value is not affected by thermal mass. (This is not to say that that thermal mass is not beneficial. PHPP does factor in the impact of thermal mass upon overall performance and generally tends to favour heavy weight during the winter and summer.)
-
11 October 2012 at 10:57 am #38705
Worth pointing out that the benefit of mass is modest and that it doesn't 'slow down' the escape of heat as some claim!!
-
15 October 2012 at 8:20 am #38706Anonymous
Does this apply to all types “mass” walls?
-
16 October 2012 at 8:51 pm #38707
Please define “mass” walls.
-
20 October 2012 at 8:25 am #38708Anonymous
I will stay with what I know best, insulated concrete forms.
-
25 October 2012 at 8:49 am #38709Anonymous
Nick,
I would like to see the document/data concerning the modest “slow down” of escaping heat and mass walls, could you point me to where I can get it.
-
11 October 2013 at 8:35 am #38710Anonymous
Nick,
Since you haven't sent me any info I thought I would send you some of mine. All links are builds with external wall u-values of 0.23, the Canadian office shows the kWh/m2/yr but the Kentucky school and office is in kbtu/sqft/yr so multiply by 3.15 for kWh/m2/yr
http://www.enermodal.com/pdf/EEL-Kitchener-AGV-1pg.pdf
http://www.hpbmagazine.org/case-studies/office-institutional/cmta-office-building-louisville-ky-
-
16 October 2013 at 8:59 pm #38711
Jean-Marc
I fail to see how these case studies address your initial query to Nick. Furthermore, Nick's comments recognised that the reported “slow down” of heat loss arising from the use of thermal mass is an inappropriate, and incorrect, proposition. -
17 October 2013 at 7:53 am #38712Anonymous
Mark
May I suggest you look into what ASHRAE have to say about mass in their new Advanced Energy Design Guides. The point I am trying to make is that u values are a poor indicator of how a wall will “perform” and that all the examples I posted are all operating at 70kWh/m2/yr or less with exterior wall u values of 0.23 and that “performance” to PHPP is doable with the added cost of insulation to “tick a box”.
I could also show you a hotbox test done comparing various wall types in this country showing lag times for maintaing a constant temp with a “stick frame” lag time of 2.5 hrs and an ICF lag time of 27 hrs. And the stick frame had “better” uvalues than the ICF.
For me, the only pieces of paper that are a true indication of performance are the energy bills and an ICF “outperforms' everything that I've come across worldwide.
-
17 October 2013 at 9:17 am #38713
23hrs seems a non-useful lag, re-delivering yesterday's heat at same time today. 8-12hrs is useful, re-delivering daytime heat in the evening.
To me, simple massiveness added to the walls, floor, partitions etc of a near-PH building is ineffective, being bi-directional i.e. window-collected solar heat In daytime, Out by same route reversed evening – activates only the near-100mm of the mass at best.
Mass has to be used more knowingly, so heat is input to one face of the mass and travels uni-directional through to the interior. That is the case with wall-collected solar heat, but is defeated by super-insulation, so is hard to see how ICF walls would make any difference either way; U-value alone would count.
-
17 October 2013 at 11:19 am #38714Anonymous
I'm afraid I will have to give up on this as no matter what info/data I put forward people with initials after their name always seem to disagree with hard fact. What I have found here in the UK is that you've recently gone from having no insulation in your reg's to trying teaching the world how to build efficiently, with no data to back it up but an awful lot of extraordinary misses on design and actual performance.
I will ask again of anyone, show me a system that can outperform an icf and I will switch.
-
18 October 2013 at 6:30 pm #38715
Sounds like you have something to prove – that you're more right. That makes you turn down the offer of an interesting discussion that could bring understanding. You said '23hrs' as if it's an important virtue – I'd like to know how that's a good number. Any idea?
-
30 October 2013 at 1:22 pm #38716
North America has differences from northern Europe. Many well-known cities in the NE USA are 10-15 degrees nearer the equator than English cities. Blue skies are more common in winter than they are in N W Europe.
This winter insolation makes a huge difference to the heat consumption for a given set of U-values, air leakage and for a given level of thermal capacity (assuming south-facing glazing).
Also the difference in energy performance between heavy and light construction increases (heavy consumes less) as one moves nearer the equator and/or to a climate with more moderate outside temperatures. Louisville, Ky. has a mean annual temperature of 14.6 degC it seems. Southern England averages about 9.5 degC. Big difference.
I don't think the UK has ever tried to teach the rest of the world to build well. That would be rash, given where Canada or Sweden had got to by 40 years ago.
I too find the UK treatment of thermal mass simplistic. I'm writing a book which may help rectify this.
-
30 October 2013 at 1:45 pm #38717Anonymous
The BRE may disagree with you as I know from the “discussions” I've had with some of them. My point has always been about performance and data as the examples I posted show.
-
15 November 2013 at 10:28 am #38718
treatment of thermal mass … I'm writing a book which may help rectify this.
I'll look forward to that!
North America has differences from northern Europe. Many well-known cities in the NE USA are 10-15 degrees nearer the equator than English cities. Blue skies are more common in winter than they are in N W Europe.
According to WUFI data, Seattle (cold year) seems to be not unlike Oostende, which in turn is a slightly tough climate applicable to southern England. Main difference is Seattle's wind is from SSE, Oostende's from SW.
Southern Scandinavian weather may similarly do for N Britain.
No other European or US/Canadian weather (e.g. not Vancouver) in WUFI comes close. I note this because meanie UK and Irish met offices won't release 'free' climate data for issue with WUFI, unlike all of Europe, US, Canada, and rest of world.
-
-
AuthorPosts
- You must be logged in to reply to this topic.