Passive House - why bother?!

Just do it

I´m not on a mission to convince people to build smaller.
But I think what I said explains a bit as why you might need additional heating.
It´s everyones own choice whether to go for the extra expense of wanting a big house with the, lets call it disadvantage, having to put in a wet heating system even though you achieve 15KW/m²/a - passive criteria.
In my opinion it´s not a fault of the Passive House principle.
It´s more like: you buy a car that goes 70mls / gallon. Now you´re pulling a huge trailer all the time and wonder that you are down to 35mls / gallon.
Or so...

@sinnerboy:
PHPP7, 2012 Handbook.
Page 28
3.4 Calculation method, conditions, standard reference
Quote:
" Occupancy rates: 35m²/person, deviating values are permitted if the reason is given (actual occupancy or design parameters) whithin the 20-50m²/person range. "

As this is not a "cast in concrete" criteria like ACH0.6, 15Kw/m²/a or 10W/m², houses can be certified even if they do not stick to the 35m²/person rate.

But may need additional heat sources.

BryanF wrote: »

mvhr contributing to energy ?
maths?
wha?

Maths:
If you meet Pasisve House criteria Heat load 10W/m² than:

140m² house needs a max 1.4KW heat input. Can be contributed by pre-heating air at MHRV unit

400m² house needs a max. 4KW heat input. Cannot be contributed by a single MHRV unit

Both Passive, both 10W/m² but different total heat load.

just do it wrote: »

Same number of occupants but half the m2 of the current design brings it into the 30-35 m2/inhabitant.

Unfortunately it is not that easy.
If you just shrink your house to half the size, your solar gains shrink proportionally together with other factors changing.
It´s pretty sure you are not left with 3KW/m²/a but that you will stay somewhere in the region you are now ( 13KW/m²/a)
But your total heat demand / heat load will be about halfed.

What is a bit absurd is that m² price decreases if you build big. Unless you have an extravagant shape, it will be a bit easier to achieve 0.6 ACH and the ratio external envelope / volume becomes more advantageous.

Still, if I had a budget of 250k I´d rather build 150m² for 1.6k/m2 than 300m² for 0.8k/m²
But thats a matter of taste...

27 Oct 2011

On 2011 UK Passivhaus Conference
Monday and Tuesday this week saw me at the 2nd UK Passivhaus Conference at the Barbican Centre in London.

There were around 250 attendees consisting of a fair smattering of old AECB-heads, a fair few BRE types, a sprinkling of academics and a good gaggle of "people who had come to learn." Consequently, the conversations ranged from the basic "This is what a Passivhaus is" through to the arcana of extreme building physics. The Passivhaus Trust itself would seem to be in rude health, energised by the fusing of the AECB's enthusiasm with the BRE's clout and professionalism.

Not everyone in the sustainable building arena buys into Passivhaus as a concept. Some decry its enforcement of MVHR (mechanical ventilation), others are suspicious of its cult-like qualities — it's very much the brain child of Wolfgang Feist and he gets to decide who and what gets certified, as well as remaining the owner of the PassivHaus Institute. But the beauty of PassivHaus is that it's a relatively simple standard, it appears to be based on solid building science, it's been shown to deliver what it says on the tin, and it's an internationally recognised standard, thanks mostly to the tireless promotional work of Feist himself. And in the UK in particular, Passivhaus still represents a giant leap forward on current building standards, even low energy ones, so it's not hard to see why the green building movement (OK some of it!) is so keen to promote it.

Day Two was for me the more interesting. It delved into a variety of technical topics and it would have been good to be able to sit in on them all, but the nature of the breakout sessions was that you had to choose one from three. Mark Siddall was particularly impressive on the subject of thermal by-passes and wind washing, a topic that lies beyond the confines of Passivhaus, but goes a long way towards explaining why low U value walls and roofs don't perform as designed. I also sat in on a good session given by Paul Tuohy (Strathclyde Uni) and Prof Chis Tweed (Cardiff) about the problems of post-occupancy monitoring. Everybody and their aunt calls for more of it, but the process is fraught with difficulties and the results are sometimes meaningless because there are so many incidental factors at work. Co-heating, in particular, was singled out as being hugely unreliable which is interesting because the practice involves keeping the temperature in a building constant over a long period and measuring the resultant heat loss, which reminds me of the tests run all those years ago by Actis to show that their multifoil was the equal of 250mm mineral wool.

Another observation was the ever growing interest in natural building materials and breathable fabrics. This is another area on which Passivhaus is silent: it emphasises airtightness above almost everything else, but has nothing to say on vapour permeability or embodied energy. Should these be included? Is there good practice to be passed on here or is it just getting too complicated?

And, more than once, the subject of quality control came up. Much of the success of Passivhaus is down to ensuring that the building is designed right and built right and the official or certified Passivhauses have to go through an expensive (like £2,000) and fairly rigorous auditing process. The materials need to be checked off, invoices examined, photographs taken. All very anal and tedious but critical in delivering quality. Some people are of the opinion that the certification process lies at the very heart of Passivhaus and is the main reason for its monitored success, but others feel that it's much too expensive and the certification cost needs to be reduced. It's a political point as well because Feist's PassivHaus Institute is resolute in insisting that they remain the police force here and they fear that any move away from this will inevitably lower standards. The UK Passivhaus Trust is firmly in Feist's camp but other countries (notably the USA) are taking a more relaxed view, claiming that the standards should be open and usable by all.

In one sense they already are. Anybody can look up what the Passivhaus standards are, anyone can purchase the design package (the Passivhaus Planning Package), anyone can claim to build to these standards. But where is the quality control? Without some form of rigorous certification process, how can you really know you have built a genuine Passivhaus and not a pale imitation that doesn't deliver energy savings as designed? It's a big issue, arguably the biggest one surrounding the Passivhaus movement. And it's interesting to note that of the 30,000 Passivhaus buildings constructed to date around the world, only about 10% have been through the official certification process.

Which brings me onto my final point, if it's the certification process which is the BIG THING, then maybe there's nothing much wrong with our building regs as they now stand, if only we built them properly.

just do it wrote: »

And therefore stays the same when measured per m2? (rather than absolute value)

It will not stay exactly the same per m², but to keep it simple you could say yes roughly. It´s not like dropping to 3KW/m²/a or suddenly increases to 30KW/m²/a.
For precise numbers the house needs to be calculated again with PHPP.
As mentioned before, other perimeters change as well.

sinnerboy wrote: »

Perhaps a misunderstanding. The PHI is nowhere suggesting that an MVHR installation will "provide" heat.

Good point, good to clarify. In so far a misunderstanding as I didn´t make clear enough what I meant, apologises.
Of course I do not refer to the MHRV system as such. I randomly called it "boost", or "pre-heating air at MHRV" or else.
Not very precise language, I admit.

Typically those "post-heating of fresh air masses" devices (give me the corrct technical term and I will use it!) are installed somewhere around the MHRV unit and some manufacturers offer it as a package or add on to their system. Hence my "boost at MHRV system" stumble.

sinnerboy wrote: »

Yes , yes , yes - but the point I seem to have to hammer home is

Hammered home successfully!

I still read it that the 35m²/ person is the occupancy rate at which numbers fall in place neatly, PH has started with, PH will perform at its best, comfort is met and PHI recommends.

Again, occupancy rate is stated in the PHI Certification Criteria you posted, this time as: "The following boundary conditions or calculation rules should be used in the PHPP"
"Occupancy rate: 35m²/person..." blabla...

Give me the point that it is in the certification criteria at least as a "soft criteria" to meet the comfort.

To do some more hairsplitting:
30m³ / person or min. 0.3 airchanges/hr for ventilation.
For 400m², 2.5m high = 1000m³ / hr
For 5 person thats 200m³ per hour as opposed to 30m³
You might get the warning: " risk of overly dry air " or so.
Comfort ISO 7720? ( I better read it soon if I want to stay in the discussion...)

Quite enjoying this conversation and happy to learn!