Energy systems…

Energy Systems

Designing appropriate energy systems for low-energy is quite a complex task really.  The electricity side of things, for grid connected houses, is relatively straightforward; generate what you sensibly can and export any surplus.  If that generation is large then the capacity of the grid, particularly in distributed rural areas like our own, which wasn’t designed to integrate decentralised sources of ‘microgeneration’, can be an issue.  Solar PV is the only electricity generating technology we can employ in our instance.  That is a pity because high up in rural Northumberland our wind resource is fantastic but despite having a little bit of land we just don’t have a suitable location within our own title.  We had hoped to buy a small patch of land from the farmer just big enough in the neighbouring field for the footprint of a turbine about 150m from the house on a ridge line where  the turbine would have enjoyed sweeping winds from 360 degrees but ran into complications unfortunately.  We now just look enviously across the valley at a neighbouring farm which has installed a micro-turbine that would appear to be harvesting energy with abandon!  Wind turbines may be emotive but onshore wind remains the cheapest form of renewable electricity available in the UK and at a micro level turbines rarely have the sort of visual impact which so many find upsetting either.  Instead though we’re opting for a solar photovoltaic array, keeping it below the 4kW mark so as to benefit from the maximum feed in tariff and not trouble the grid capacity.

Designing heating systems for low-energy houses would appear to be a bit more complicated.  Passivhaus design, founded as it is on principles of reducing energy demand, is obviously a good place to start, aiming as it does to do away with the need for space heating altogether.  Confirmation that a house will attain Passivhaus standards still requires the use of Passivhaus design software – the Passivhaus Planning Package (PHPP) – and of course good craftsmanship to ensure that the final building fabric meets the quality specified on paper.  Once achieved though the space heating in essence takes care itself.  More problematic are instances such as our own where factors beyond our control – our south facing elevation is primarily a very large existing solid stone wall – prevent us achieving a passive level of design, meaning supplementary space heating is required, yet the demand, relative say to a house that simply meets building regulations, is still very low.

We have used PHPP, but the further one gets away from Passivhaus levels of performance, the less reliable the model becomes.  Naturally we are obliged to carry out a SAP assessment (SAP or Standard Assessment Procedure is the government endorsed methodology that underlies building regulations and the like) so the house will be modelled at that stage too but SAP is known to be a rather blunt instrument.  The house has also been modelled using Integrated Environmental Solutions (IES) software, again not ideal because IES seems to be geared much more towards commercial buildings than one off houses.  Depending on how exactly the model was set up IES software indicated, using Passivhaus standard u-values (i.e. 0.15W/m2K for walls and roof, and .8W/m2K for windows), that the peak heat load was between 6.6 kW and 9kW.  Using similar u-values in the PHPP but alternating between an airtightness figure of 0.6 and 1.2 ach@50 Pa because we’re concerned about meeting the lower airtightness figure due to the conversion element of the build we got figures of 4.5kW and 5.2kW respectively for peak heating load.  Thus relatively there’s quite a lot of variation in these figures which makes designing the heating system tricky – you don’t want to install excess capacity yet you don’t want to leave the property under-heated.  This is a really important element of the house to get right though; obviously thermal comfort is dependent on it but also we don’t want to be coming back and having to make major alterations because we didn’t get it right at this stage!  I’ll post more on the heating system in due course…

Advertisements

Construction system

So it probably appears that since my posts in December there hasn’t been much happening on the project.  That’s because most of that time has been spent exploring the feasibility of using previously blogged about Brettstapel as our construction method.  Pursuing a system no UK fabricator or contractor has used to build a house has been a time intensive process.  Architect Dan, who has been as attracted as me to the sustainability qualities of the system, and I, did manage to establish that it was possible to put together a supply chain.  We were able to source appropriate domestic timber, we had a company in line to mould the timber, we had expert support – and thanks should go to Dainis Dauksta of Woodknowledge Wales and Deb Turnbull of Edinburgh Napier for their help – but we couldn’t get a fabricator/erector to consider taking on the task at a reasonable rate.  Perhaps understandably given the innovative nature of the product we found that people either didn’t want to touch it or they wanted to attach a considerable premium to it.

That’s not to say there aren’t companies interested in pursuing this system.  It was interesting to learn for example, through the Brettstapel Network at the Edinburgh Napier Centre for Offsite Construction + Innovative Structures about MAKAR, a closed panel timber frame specialist who are looking to integrate Brettstapel production into their conventional manufacturing processes.  In reality though for Brettstapel to become a more mainstream option it is going to need a great many more forward thinking companies to get behind it, and for a more projects, and certainly initially those with more accommodating budgets than our own, to consider specifying it.  I continue to hold the opinion that it is a fantastic system with excellent sustainability credentials and is therefore to be much encouraged.

Our thoughts are therefore turning toward a more conventional timber build system.  Intriguingly Mark Siddall, another north-east architect, who was behind Steel Farm Passivhaus, and who I heard speak at Ecobuild, is of the opinion that on the whole you should use whatever system and materials local contractors are familiar with, which in the north-east is masonary.  I can’t say I’m convinced by that.  If we are to take a holistic approach to sustainable building then the embodied carbon of the building fabric has to be given consideration in which case timber frame will inherently be more attractive than masonary.  Cob, straw bale etc. could come into consideration but given what we’re trying to achieve in terms of a contemporary open plan living area within a vaulted roof sapce they just don’t seem practical.  A more standard timber frame obviously has its benefits.  People are obviously more familiar with it giving a wider choice of manufacturers/contractors which in turn should translate into lower costs though initial estimates from one or two timber framers suggests this isn’t a given.

I’ve always been attracted to structural insulated panels (SIPs) as a system.  They’re extremely simple as a concept.  Structural panels are formed by sandwiching insulation between two layers of wood sheet material, typically OSB eg. Kingspan Tek.  They lend themselves to creating very low u-value walls, with their large spans and uniform nature aiding in the attainment of very good airtightness levels.  Cut to precision off-site they seem to lend themselves to a quick and efficient construction on-site with minimal material wastage.  I am though struggling a little to determine the differences between the insulating cores used by different manufacturers and I’d want to do a little more research before settling on this route.

A further option, brought to my attention again by our visit to Ecobuild is a hybrid system like Val-u-therm that takes advantages of the benefits of both timber frame and SIP panels.   As with SIP panels Val-u-therm is able to deliver very low u-values – all the way down to .09W/m2K in fact – and enable very airtight construction.  One particularly attractive quality of this hybrid system is that the timber studs used internal of the sandwich sheet materials allow longer spans than the conventional SIP which could be particularly useful in terms of the creation of our contemporary open plan vaulted roof living space.  Additionally the insulating material used in the val-u-therm is a bio-based polymer derived from recycled vegetable oil giving reassurance that the insulation is environmentally considered too.

In summary, pros and cons to each; a decision will be made no doubt when the current cost estimates are firmed up…

Ecobuild 2014

Dan and I headed to the Ecobuild conference at the London Excel centre last month.   It seemed a good and fun opportunity to research the industry for new and relevant products and to speak to various experts.  It didn’t disappoint.  Although I was concerned to find that the event appeared quite a bit smaller than when I last attended we did find some really interesting products and were able to make some useful contacts.

The most interesting – and I thought it was a very understated launch given the potential of the product – was a cement-free concrete called Cemfree.   Cemfree purportedly uses 95% Ground Blast Furnace Slag (GGBS), seemingly overcoming previous complications when replacing higher percentages of Portland cement.  Given the carbon intensity of cement manufacture – regularly cited as being responsible for approximately 5%-8% of global CO2 emissions alone – this is a really exciting development.  Cemfree themselves report that their product reduces the carbon legacy of concrete from approximately 312kgs to 31kgs per m3.  It would appear to have additional benefits over traditional cement based concrete as well; improved durability, no need for jointing, reduced requirement for reinforcing, improved thermal mass qualities and lower water demand.  One further benefit that Cemfree didn’t appear to be pushing but which I think very attractive from a specifying point of view is that its’ natural finished colour is light and present, almost a creamy colour.  The premium in terms of price appeared absorbable at a suggested 10% though whether that is accurate in reality remains to be tested.  All in all it is a product we will most definitely be investigating.  It is a pity a polished concrete floor isn’t perhaps the most practical for house intended to accommodate the elderly otherwise it would be interesting to explore using the slab as the finished floor surface!

Other products of note included a greywater harvesting system with integrated heat recovery called reaqua+ that I’d not come across before.  I am much more familiar with rainwater harvesting products than greywater – the former seeming to have established a better reputation than the latter.  The ability to reduce water consumption whilst also benefiting from the recovery of heat from greywater is an attractive one.  There are still calculations to be run in terms of cost benefit over rainwater harvesting.  Rainwater harvesting offers an opportunity to reduce water demand further than greywater recycling.  However the shower heat recovery products that I’ve come across are on the whole extremely expensive and simply not worth the investment.  The only reasonably priced product, though still not cheap, that I’ve come across is the Zyhpo shower heat recovery system.  This combination is likely to be at least £1000 more expensive than the neat and compact reaqua unit, probably more once the additional building costs of burying the rainwater tank are taken into account, so whether it would be worth the investment is questionable.  I’ll certainly be running calculations.

There were other finds; some promising contacts in the windows department.  Central to the design of the building is a large corner window on the first floor which captures the views right back down the valley.  The plan is for the window to be frameless with a butted silicone joint.  Finding a manufacturer capable of doing this at a reasonable price is going to be a challenge.  It was also interesting to come across the construction system Val-u-therm.  This is a closed panel hybrid system encompassing principles of timber frame and structural insulated panel (SIP) systems.  I’ll discuss this more in due course but it could be a really attractive option for us.  Cladding, flooring, lighting options, the list goes on.  All in all a worthwhile visit and I’d recommend to anyone considering or planning their own build.

A word on our Architect

I don’t think I’ve stated yet that the architect we selected for the project is Dan Kerr of MawsonKerr, a small but growing practice in Newcastle upon Tyne.  Though a relatively young firm MawsonKerr have a solid portfolio, including work delivered under their own name but also at former practices.  As a certified Passivhaus designer Dan fitted the bill in terms of what we were looking for in terms of sustainability design led by first principles.  He was commissioned over other equally qualified and perhaps more proven architects because of his displayed passion for the job and an anticipation that he would make the best fit at a personal level on what was always going to be an ambitious and challenging job.  We’ve not regretted making the decision on that basis at all; over what was a testing and protracted planning process Dan demonstrated continual enthusiasm and commitment to the project.  We’re subsequently very much looking forward to continuing the relationship now that it’s time to deliver.