15 kWh/m²/y.

Of course, the North American argument is that in very cold climates even going down to this level is a waste of money.

If you're looking at carbon emissions then, considering the embodied carbon in PUR and the like, when U values get below about 0.1 W/m²K you start to lose out over reasonable periods of time (30 to 50 years). With mineral wool (which has lower embodied carbon per unit of thermal resistance) it makes sense to go lower but then you get a very thick wall with associated structural costs and, in some cases, planning footprint considerations.

Something to consider is that buildings tend to need heating at just the times of year when in future we might expect energy to be expensive (unlike, for example, cooling which tends to be needed when PV is producing so energy is likely to be cheap). Suppose everybody lived in a Passivhaus but all consumed their 1500 kWh, or whatever, as electricity in the same six weeks of the year. Roughly 1.5 kW per house (6 weeks is 1008 hours). With something like 25 million dwellings in the UK that's an extra 37 GW or so. Smart meters are likely to really rack up the prices during that period.

(Obviously it'd really be spread over a longer period with a ramp up and down but this serves to illustrate the sort of peak that'd be involved).

But will energy prices have risen a lot in thirty years? The price of renewable energy is falling dramatically and is having a downward pressure on electricity costs in many parts of the world already, even with today's low fossil fuel prices. Nimbyism, excessive constraints and poor government policy are keeping them up here, compared with many other countries (Eg the USA where wind power is being built for under 2p/kWh) but even so I wouldn't bet on large increases.

Ed

I believe that the key to the passive house figure of 15 kWh/m²/y is that is removes the costs of having a heating systems. But it assumes lights etc give out enough heat, yet we are now getting lights that give out less heat.

But I don’t like XX kWh/m²/y at all, as having a smaller home with a higher XX kWh/m²/y can use fewer resources to both heat and build. I expect by better design we could reduce the size of homes “self builders” believe they need for a given quality of life.

Whenever I take a close look at energy prices across Europe and the US, I find they amount to 5% (or there about) of household income. This has been pretty steady for the last two decades.
So it is really just a matter of working out the marginal costs of reducing energy usage via increased insulation, better airtightness/MVHR, better appliances and lighting.

What is hard to do is work out an average figure as houses are different sizes, different shapes, have different occupancy levels.

One of the problems is that for those in or close to energy poverty their proportion of household income is higher or step changes to zero when they have to choose to heat rather than eat.

I cannot see renewables being implemented quickly enough to prevent very rapid energy price rises as oil and gas run out.

They are a finite resource and we are still using them at an increasing rate. The only reason that they won't run out is that they will become too slow and too expensive to extract from the ground.

Posted By: fostertomSaudi is rich and nimble enough

…and tends to get a bit of sunlight.

Posted By: Ed DaviesSomething to consider is that buildings tend to need heating at just the times of year when in future we might expect energy to be expensive (unlike, for example, cooling which tends to be needed when PV is producing so energy is likely to be cheap). Suppose everybody lived in a Passivhaus but all consumed their 1500 kWh, or whatever, as electricity in the same six weeks of the year. Roughly 1.5 kW per house (6 weeks is 1008 hours). With something like 25 million dwellings in the UK that's an extra 37 GW or so. Smart meters are likely to really rack up the prices during that period.

That's why I think it makes some sense to design dwellings to 'overheat', so that more of their energy demand is for cooling in the summer rather than heating in the winter. It would tend to balance demand somewhat and be beneficial to the extent that energy was derived from sunlight.

Note that I said 'dwellings' because larger commercial building typically behave in this way already.

I can see the PHI view that an air conditioner plus PV system versus no air conditioner and no PV system is added complication. I can also see their view that you have to have windows to admit light and so you may as well optimise them for heat transfer too. But I think their overall treatment of PV is fundamentally flawed.