Posted By: eniacsWill; Its not economical to do because we use only about £100 of hot water per year through our combi gas boiler. Ok this may increase, but not to the point that i will recover my investment of circa £2.5k.

£2.5k sounds an awful lot for the marginal cost of ST on a new-build (or nearly so). If you're messing with the roof and messing with the plumbing anyway (e.g., scaffolding in place) and don't care about MCS/RHI enough ST for DHW shouldn't cost more than half that, even with a professional install, I'd have thought.

Posted By: eniacsi also have to consider whether to go for a system boiler or with the combi boiler approach

Wouldn't it be nice to save the money on not having either. Apply here for details.

You're either an early adopter or a follower-when-safe. Ask the question another, less defensive way.

'My house' is a rented cob farmhouse oil heated with window cracks you can see thro - so not an exemplar!

With a physicist/engineer colleague we're in process of modelling year-round space heating by solar incl Dec/Jan, with two near-PH house projects on site to apply our findings to, using industry-standard bits but 'not as we know it'. Extended year-round contribution to DHW too. The issues are
1) quantifying solar radiation incident on potential collector areas, for the site location (weather data) and horizon shape as seen from the collector areas
2) choice or development of collectors optimised for ultra-lo thermofluid temp and minimisation of standing and start-up losses, given intermittent collection
3) duration/size of heat storage depending on period between sunny patches, from analysis of weather data
4) means of ultra-lo-temp heat input to interior.

Most of this we've mastered but work continues, and at present is unique to each project, until a body of experience is built up. In principle, no doubt that it's do-able, and our clients are convinced.

Fuel-less space heating 'for all' is the goal, leaving out all that costly apparatus, but of course substituting other apparatus.

Top marks to eniacs for opening his/her plans up to public disection on the forum. Itll be more energy effective than my renovation.

I hope 1) s/he gets positive suggestions, which would educate the rest of us and 2) nobody else is put off sharing their plans for fear of negative reaction.

PS ... two posts up should read "how warm" not "how how"

Each to their own life-flavour.

Posted By: Ed DaviesTony actually put in UFH pipes as an insurance but hasn't ever connected them to anything

It cd be important to develop ways to input ultra-lo-temp solar-derived heat to near-PH houses, that aren't UFH.

With UFH the possibility of taking advantage of coupling the interior to subsoil mass via uninsulated slab (perimeter downstand insulated instead) is eliminated. That leaves the walls e.g. inside face of external walls as candidate for very large heat emitters.

Even in a near-PH the emitters have to be v large in order to run at ultra-lo temp e.g. 1C above target room temp at the wall/emitter's room face. That ultra-lo temp is essential in order that the collectors can run at ultra-lo temp e.g. 25C in order to minimise simultaneous re-radiant loss from collectors to cold scenery/sky in Dec/Jan. That re-radiant loss (when collectors run hotter than that) is the reason for the conventional wisdom that it's unfeasible to collect solar thro Dec/Jan.

Up till now, full-PH has been able to rely upon incidental gains - solar thro windows, occupants' heat, cooking, electrics - to provide the tiny bit of heat still needed, with 'backup' heating system only for exceptional moments. That calculation is coming to an end, as new technology begins to reduce the two largest contributors to insignificant.

LED lighting is already here; enormous reductions in appliances consumption esp on standby are continuing (over-balanced at present by increasing nos of appliances); and lo-energy cooking is in the wings.

Present PHs will find their 'supplementary' heating systems (often on-peak electric) working harder, and future PHs will need another more full-time source of Dec/Jan heat - solar (other than thro windows) - which PH as a method is presently ill-equipped to calculate.

With such 'free' solar heat available, the fullest rigours of full-PH are no longer necessary, which will be a great relief to eco-builders, and to the cost of retrofitting the nation's building stock.

It would be interesting to see plans or photos of the house now because modifying an existing house is a totally different kettle of fish than designing a new one.

Posted By: eniacsThe walls on this property are 60mm cavity with blown fibreglass and 100mm phenolic giving U = 0.15. The ceilings are 220mm phenolic and some floors will be upgraded during the build to 100mm phenolic. How is this a poorly insulated fuel guzzler?

Is the phenolic wall insulation external or internal? Was there any particular reason for going for phenolic for the ceilings instead of thicker levels of mineral wool as that must have cost quite a lot more. Sounds like an interesting building, have you had any SAP modelling done on the current/proposed build?

Ed i think Tonys house is fantastic. I read that thing through years ago and was very impressed. However he was lucky enough to build his own house. Somthing i would like to do, but cannot at this stage.
Additionally Tom is talking about no heating at all, even PH houses end up having some kind of heating. Thats what i mean, I am going for practical in my house, I am happy to insulate alot, but i know that however well i do, it will still require some kind of heating system...

Yes the roof insulation was expensive indeed, and i am still doing it. But i hate rockwool with a passion. Have insulated one too many lofts with it and its the devils material!

Tom i dont have anymore space for huge solar collectors. The end wall is large enough for maybe 10m2 but thats about it?

Atomic, there are a couple shots from summer 2011 when we bought the place here:
http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=8142&page=1#Item_12

Sorry i should have stated more clearly, that Tom is talking about a house without any external inputs (other than solar) for all space heating.

Tom to what end are you doing this, redesigning the roof? Lets guess at the cost of replacing the roof at £10k, this would therefor never pay back in my lifetime the miniscule savings on an already energy effiecient well insulated house.
I appreciate that you are trying to make a point that it can be done, but to what end?

Isnt this the whole problem with PH and green houses, that 90% of energy is saved with only 10% cost, the remaining 90% of cost is trying to save the reminaing 10%, and then coming up with an ever more complicated system for heating it during the coldest 20 days of a year.

A recent German study showed a 67% reduction in running costs when a 40m2 solar roof was installed on a 150m2 house with average insulation and double glazing.
We reduced the heating demand of this Passive House by 90% with 16m2 of Solar http://www.viking-house.co.uk/kilcloon-passive-house.html

The way I look at is;
Save 90% of the energy with Passive House Insulation levels and Airtightness.
Reduce it by a further 8-9% with Solar heating.
Use Electricity for the last bit.

Posted By: eniacsIsnt this the whole problem with PH and green houses, that 90% of energy is saved with only 10% cost, the remaining 90% of cost is trying to save the reminaing 10%, and then coming up with an ever more complicated system for heating it during the coldest 20 days of a year.

Yeah but we're all working on it, finding rationalisations even in the midst of 'ever more complicated system'. Long way to go, massive savings potential. Everyone can choose to be an early adopter, or let others do the legwork and come in when it's safe. Don't say we're stupid.