Remember that the PH standard is now 30 years old at least and in my opinion is light on the insulation values needed for homes of the future.

I am saying aim a lot better than PH not reduce the requirements, it is easy to build in insulation but very difficult to add it later, oil gas and eventually coal will all run out.

Over what time scale will you do the economics?

Posted By: tonyRemember that the PH standard is now 30 years old at least and in my opinion is light on the insulation values needed for homes of the future.

Have you got any numbers to say whether adding more insulation or adding more solar collectors of one sort or another is a more economical means of reducing paid-for energy use?

I don't know much about PH but AIUI it's a bit weak on the use of on-site renewables.

This is the one area of my build that is like a recurring nightmare to me.

I don't know what electricity prices have been doing in the UK but here in Sweden they have been dropping over the last two years and I recently read a commentary in the papers where the CEO of one of the large energy companies said that the current all time low prices were now "the new normal".

We have a fairly high standing charge and with the unit price plus taxes (VAT and energy tax) plus per kWh delivery fee the current price of electricity is somewhere between 9p-10p per kWh.

In a low energy build it is then very hard to justify large capital expense to reduce our energy cost below that of using direct electricity.

If I take an estimate of 3000kWh/a for DHW then the cost with direct electricity is £300/a with a water heater costing about £675.

The capital cost of installing solar thermal to supply 65% of our annual DHW is about £2,500-£3,000 to save about £195 a year at best, so 12-15 year payback.

I'm with Ed Davies in that I believe PV is probably a more worthwhile solution than solar thermal.

Our space heating demand is about 4,500kWh but the cheapest quote I have had to install a new air to water heat pump is £8,500. Running the UFH on water heated with direct electricity would cost £450/a and with a ASHP assuming a SPF of 3.0 the cost is about £150.

Assuming I do both DHW and space heating with the ASHP the saving is about £500/a against direct electricity so the payback on the HP is again about 15 years.

As ST says it is only a wild guess what electricity prices will do over that sort of horizon but at this stage I am strongly considering the lowest cost direct electricity solution.

Assuming the electricity company CEO is correct and electricity prices remain at this level for at least 3-5 years then it will buy me some time to decide what to do longer term. ASHP technology is improving all the time and you don't know what other technologies may take a big leap forward within 5 years and provide viable alternatives.

Sorry djh if that may be wandering off topic but it is my practical experience of what you describe in your OP.

As for heating the house with a battery in the ventilation system it is a possible solution for me but every instance I have heard of of people opting for this solution they appear to have regretted it.

Posted By: Chris P BaconAssuming I do both DHW and space heating with the ASHP the saving is about £500/a against direct electricity so the payback on the HP is again about 15 years.

And there's no guarantee the HP will even last 15 years.

Posted By: Chris P BaconSorry djh if that may be wandering off topic but it is my practical experience of what you describe in your OP.

No, it was a pretty broad brush question so wandering answers are perfectly suitable.

To me, the main merits of PH are that it's an independent standard, developed by physicists rather than politicians, and it has a more rigorous process to test whether you have in fact met the standard. The exact level of insulation is at least in the right ballpark, I think. But I'm not sure the cost arguments hold true.

Posted By: Ed Davies

Posted By: SteamyTeaWhat is the old mantra, a kWh saved is cheaper than a kWh generated.

Exactly, it is anoldmantra which should be re-examined once in a while as the relative costs of insulation and sustainable energy generation vary relative to each other.

It's not just the costs that need examining, it's also important to look at resource usage.

Posted By: SteamyTea

Posted By: djhit's also important to look at resource usage.

... there seems to be a global glut of conventional energy

Dave was saying what about all the other finite resources, apart from energy (and its cousin Carbon)?

Never mind individual industrial materials, which may get noticed if shortage-prices cause pain to UK plc.

'Finite resources' include systemic things like the planet's capacity to reprocess the thermal and chemical pollution that all living things (animals anyway) naturally create - and which human animals thoughtlessly spew in unmanageable quantity. We have well exceeded that capacity, more than used up that resource, since a tipping point about 1982, now accumulating an accelerating backlog of damage, with no idea what to do about that.

Another finite resource, now used up, is fossil energy extractable at useful EROEI. Useful global aggregate EROEI is a thing of the past, but again we've no idea what to do about that. Nuclear and 'renewable' energy won't help - both have low EROEI, and their growth brings global aggregate EROEI down.

Posted By: Ed DaviesEnergy doesn't matter anymore. We can use as much as we like as Lockheed Martin will have a working fusion reactor prototype by 2017 and in production by 2023.

The already under construction ITER isn't even expecting "First Plasma" till 2020!

http://www.iter.org/faq

Probably plasma-ware (like vapour-ware only hotter) but…

I was told that nuclear fusion was 20 years away, in 1970 and 71,72 ,73...
One of those predictions should be right Mr. Nostradamus

Tom, if you want a serious discussion of fusion, etc, I'd suggest starting another thread. I was just trying to point out a rather extreme case of how changes to technology could make existing assumptions about how houses are or should be built irrelevant.

Posted By: djhSo the standard explanation of why the Passivhaus standard is set at the level that it is is that it eliminates the cost of the heat distribution system. But the standard heating mechanism is via a heat battery in the ventilation system and that requires heat at 50°C or so. Which we now accept is a bit higher than ideal for heat pumps and the like, and large area emitters at lower temperatures are more efficient. Plus we all consider adding in UFH and/or towel rads in bathrooms.
So does the economic argument for the particular spec chosen for Passivhaus really hold up in the light of these variations? Is anybody aware of any published work on the economics of Passivhaus in the face of exergy?

Jon Kristinsson who built the world's first Passive Houses in 1979 always said that the heatloss from a Passive House is equal to the heatloss from ventilation. He now maintains that the "Breathing Window" cuts the ventilation heat losses in half because of the higher efficiency and because its runs 75% less throughout the year.
We've Solar Thermal down to £100/m2 so that's still a realistic option but I can't help thinking that the answer for zero energy kit houses will include a good proportion of PV.