27 Nov 2012

The Gas Saver

Condensing boilers are no longer news. They first appeared in the 1980s and for years were known as energy-saving boilers. They work by having a secondary heat exchanger which is used to take a load of heat out of the flue gases from the main boiler. This makes them more expensive to build and a little more expensive to install. Hence, they were seen as something of a green curio, an expensive option for those who cared about the planet, or the size of their gas bills. By 2004, they had achieved a market penetration of just 3%. Although a condensing boiler could be shown to have a very short payback (less than 5 years), people didn't want to spend an extra £250 for a condenser.

But then the building regs changed. In April 2005, Part L (England & Wales) was amended to make condensing boilers all but compulsory. Today, condensing boilers have over 95% of the new boiler market. That, ladies and gentlemen, is a prime example of government intervention raising the bar. What is more, you can source an A-rated Baxi Solo condensing boiler for just £450 (plus VAT). We were paying that much for ordinary boilers back in the 1990s. So competition and economies of scale have eroded the price differential (though some cynics will argue that quality has also been engineered out).

All in all, it makes a powerful argument in favour of legislation as the best way of increasing energy efficiency. If condensers hadn't been made compulsory, I bet that they would still cost £250 more and that market penetration would be sticky at around 3%.

Which brings me on to Zenex's Gas Saver. This is a new(ish) device which you attach to a condensing gas boiler and it draws even more heat from the flue gases and uses it to pre-heat the water going into the boiler. It is, if you like, a tertiary heat exchanger. The generic name for this is Passive Flue Gas Heat Recovery Devices (PFGHRDs) and the inventor, Chris Farrell, started Zenex to develop and market it.

In some ways, it's been a splendid success. Fitting a PFGHRD to a boiler has been demonstrated to bring about gas savings of up to 40% for hot water generation and consequently PFGHRDs are a ground-breaking British technology, recognised in Building Regulations, recommended by the Energy Saving Trust and recognised in the Green Deal.

Better still, two of our major boiler manufacturers, Baxi and Alpha, now market Zenex's Gas Saver with their own offerings. Indeed Alpha have a built-in version (The In Tec GS) so that you can install the boiler and the Gas saver in just one box.

But the Gas Saver costs. On it's own, it's over £600 to buy. Coupled with an Alpha boiler, it doubles the price of the boiler. And just like the condensing boiler pre 2005, it has a tiny market penetration. There are around 1.5million new boilers fitted in the UK each year (about 90% of these are replacements) and only a tiny fraction have Gas Savers fitted to them.

How best to change this situation? Though the savings appear to be real enough, and the payback period is again probably less than five years, the uplift in price between a condensing boiler and a condensing boiler plus Gas Saver is enough to put most casual buyers off — that's if they ever get to hear about it in the first place. Maybe the Green Deal will come into its own here, as PFGHRDs appear to meet the Golden Rule. But I can't help feeling that the answer lies in building regs enforcement.

14 Nov 2012

At last: a Passiv Wood Stove

In the rarified world of Passivhaus design there has been a small problem gnawing away at many enthusiasts, especially the selfbuilders. Wood stoves. They may not need them, but they want them. Focal point fires. Comfort. Neolithic TV. Call it what you will, but fires have a certain pull. And a pellet boiler just won't do.

There are — or have been — a couple of problems. One is that you need so little heat in a Passivhaus that the smallest wood stove is still too big. It's hard to make a wood stove that doesn't emit at least 4kW of heat, because that's what a log gives off when it's burning well and it seems a bit pointless to start burning kindling. That's not too big an issue — after all, as Passivhaus devotees keep saying, you can always open a window to make the room a bit cooler if you get too hot. Or you can start using the stove to heat hot water — but maybe not, as here things start to get a little bit more complex.

The next issue is the fresh air supply. Opening that same window is not really an acceptable failsafe option. And you can't fall back on the traditional, permanently open, ventilation grill — not when you've gone to so much trouble to make the place so airtight in the first place. In a draughty old pile, it's not really a problem because there is plenty of fresh air coming at you from all corners, but in a Passivhaus that's not the case. The supply air problem is usually addressed via an air duct piped directly into the stove. It's still not ideal, as it creates a cold bridge with the outside and another potential air leakage path — remember, all penetrations are bad news. But it's sort of on the right lines. It makes the stove room-sealed.

But another niggly little issue concerns spillage, the term given to the cloud of smoke emitted from the stove every time you open the door to re-load. In a draughty old pile, it quickly gets lost in the background, but in a Passivhaus the smoke will hang around until it's drawn away into the MVHR system, where it will end up clogging up the filter.

Well, as it happens, Chesney's, the wood stove manufacturers based in London, have just come up with a spillage-free stove design. Nigel True, their stove wizard, (pictured)

has been beavering away in his Whitstable workshop and has hit on a spillage-free design. "Until now, the best solution on the market has been a stove with a hinged door with an automatic closer," he told me. "We've come up with a design which diverts the air intake when the door opens so that the supply flow is redirected from an opening under the door into the stove, and away up the flue. It doesn't smoke at all"

The idea for a Passiv stove came about when they were contacted by CenterParcs with a view to supplying stoves in all their Passivhaus-standard chalets at their yet-to-be constructed Woburn site. The contract itself came to nothing, as CenterParcs later lowered their spec on cost grounds, but Chesney's carried on with the project and have now launched the resultant stove commercially. Its been through rigorous testing at Gastec in Cheltenham (the place where all UK good wood stoves get tested for smoke emissions) and has emerged with distinction. Both carbon monoxide and carbon dioxide emissions were rated as "negligible" even when subjected to worse case scenarios — i.e. forgetting to close the door.

At present, the new design has been fitted into a fairly basic 4.6kW Milan stove. It's being marketed under the name of Milan Passiv and the retail cost will be around £1150 plus VAT, which is around 25% more than the regular Milan stove. This puts it down at the lower end of what people pay for new wood burners.

As it happens, Passivhaus stove enthusiasts may have another promising development on the horizon. Poujoulat, the French chimney and flue manufacturers, are about to launch a triple-walled stainless steel flue which will work in conjunction with Chesneys new stove range. The advantage of a triple-walled flue is that the external cavity becomes the the stove intake air supply, in a the way a balanced flue works on a gas boiler. Not only does the intake air get pre-heated as it's drawn down the flue (thus increasing combustion efficiency), but the extra vent hole for supply air is eliminated. Instead of two penetrations, you have one: music to the ears of Passivhaus builders.

As of now, I don't think this product is yet on the market, but according to James Parkin, their UK technical manager, it's coming soon and anyone interested should contact him at j.parkin@poujoulat.co.uk

9 Nov 2012

Passivhaus Conference 2012

I have just returned from the UK Passivhaus Conference 2012, held in Nottingham. Two days of lectures, networking, eating, drinking and schmoozing in East Midlands Conference Centre and a night sleeping in the brand new Orchard Hotel next door, so new that it wasn't actually finished.

As is so often the case with events like this, you come back down slowly to earth with a huge swathe of unnoticed feelings and unformed opinions, and only gradually do you assimilate the drift of what was going on there.

Some obvious things stand out: Passivhaus is a success if measured by the number of projects underway in this country (75 underway or completed, up from very little last year), and the spread of people taking an interest has widened to include lots of businesses I had never heard of before. There is a surprising amount of interest from RSLs who are more concerned with whole-life costings than up front capital costs, and see a genuine payback in using Passivhaus principles if measuring over a 25 year period. Many of these 75 schemes involve several units: they are not all one-offs.

And there is also great interest from the schools sector and one or two offices. I also talked to a man who was sussing out whether Passivhaus would be suitable for a fire station.

If there was a theme this year, it was summed up by the number of presentations, especially on Day Two, on Post Occupancy Testing. Lots of figures, lots of graphs and lots of tables, all rather hard to take in slide shows if truth be told, but with one over-arching theme — Passivhaus delivers what it says on the tin. Whereas the building world has been bedevilled by many so-called green projects which turned out to be anything but, Passivhaus standards, if properly instigated, seem to hit their targets unerringly.

But, you might argue, we knew that already. Well, yes it's true: there have been lots of testing carried out in Germany and Austria and the reason that Passivhaus is catching on elsewhere is that it has been proven to be effective. Post Completion Testing is construction's equivalent of the Double Blind Trial — a little bit of scientific rigour brought to bear.

What's interesting about this is that it puts Passivhaus firmly into the enlightenment camp of people who believe in logic and science and physics in particular. Not all green construction resides here and there were many people there uneasy about some of the reductive nature of Passivhaus. If Passivhaus works, does it follow that we should be building compact, rectangular boxes, all clad in white render in a vaguely international style? Does engineering have to trump aesthetics every time? And what about if you want to build using more cuddly materials like straw bale, or turf roofs? Do they have a place?

Well of course they do, because there are already examples of straw-bale Passiv and very traditional, vernacular-style buildings as well. Passivhaus boxes clever here because it says it's not prescriptive, it's just a standard and that you are free to interpret it in any way you see fit. But that ignores the fact that it's an engineering standard more than an architectural one, a standard whose primary design tool is a spreadsheet (PHPP) not a drawing board. Elegance, in the world of Passivhaus, is simplicity not ornamentation, and whilst there is nothing to stop you indulging in architecture with a capital A, in doing so you veer away from the essential message.

That's not to say that, for all its scientific rigour, Passivhaus has all the answers. No, there are still questions to be resolved, primarily to do with resilience. The three corner stones of Passivhaus are insulation (lots of it), airtightness (v. tight) and ventilation (MVHR please). It works in models and it works in practice. But how will it work over the lifetime of a building? Will the airtightness be compromised by inhabitants putting in cables for their TV sets or cat flaps for their pets? Or just knocking houses about for the fun of it? And what about these ventilation units? Will they get adequately serviced? Will they continue to work as planned? Indeed, will a new certified Passivhaus circa 2012 still be a Passivhaus in 2022, or 2052? If a Passivhaus is difficult to design and build (it is) then it will surely be difficult to maintain?

This was brought out a couple of times by speakers relating what had happened to some of the social housing Passivhaus projects. Some of the tenants had tinkered (i.e. messed up) the MVHR settings, many of them had installed huge plasma TVs (Lord, help us), one kept a window open all winter long so that he could run an extension lead into the garden to power up the jacuzzi. And you could tell the ones that smoked dope from the state of their ventilation filters.

It all sounded just a tad Victorian as these well-meaning philanthropists bestowed heaven-on-earth (aka Passivhaus) on these poor saps, only to find that they are a bunch of undeserving ner-do-wells, intent on a lifestyle of drink, drugs, fatty foods and general sloth. I'm sure that's a total exaggeration, but as always, it's the anecdotes that you remember, not the graphs.

There was lots on retrofit. Cost and test data is still coming in from the RetroFit for the Future schemes which are now complete. It's a much more problematic area than new build because, whilst there is undoubted elegance in creating a genuinely low-energy structure, almost nothing about retrofit could be described as elegant. It's an almighty kerfuffle and it's also incredibly expensive if done to Passivhaus standards, often considerably more than starting again from scratch. This poses problem for enlightened builders because logic would seem to dictate that we would be better to demolish every inefficient house and rebuild our entire housing stock on Passivhaus principles. But of course that ain't going to happen. Not only is there extreme opposition to it from the population at large, but it's also such a vast task that no way would we be able to complete it in a sensible timescale.

What we don't know — cannot know — is what the future holds in terms of energy supply. Will we have got to grips with the supply problem by 2050? Will we have lots of low-carbon energy to burn, or will it be a precious commodity to be husbanded carefully. And how much will it cost? Without this information, we can do no more than guess at how much effort we should make to "RetroFit" our existing building stock.

1 Nov 2012

Green Deal: Reading the Runes

I spent Tuesday at the NEC in Birmingham, visiting an exhibition entitled RetroExpo. Running inside it was a Green Deal Summit which featured a number of Green Deal(GD) notables working through their PowerPoints. That's not to be disparaging about them, there were lots of very distinguished speakers, and the exhibition is to be congratulated for assembling them all together in one place. Surely, now was the chance to learn something significant about GD?

Well maybe, maybe not. I've yet to write anything enthusiastic about GD and my feelings haven't changed much as a result of Tuesday's deliberations. For a start, it's damned complicated, so complicated that presenters kept flashing up organisation charts only to quickly withdraw them because they were too difficult to explain. Not encouraging.

It seems to get a GD going, you have to start with an assessor coming to visit your property and carrying out a survey. How much will this cost? Various answers from £130 down to nothing. If it's nothing, that tends to suggest that the assessor will be a tied agent. Would you trust such a person to carry out an independent survey? I wouldn't.

Anyway, stage two is to put the survey results into effect. There is much talk of the Golden Rule which means that the works to be undertaken have to payback in 10 years. Or is it 25? Or something else? I'm afraid I still don't know. And do you have to take the GD Finance Deal (at somewhere between 6% and 8% APR — again no one can say for sure)? What if you decide to arrange your own finance, or just pay for it from savings, is it still a green deal, and will you get the guarantee? No one could answer these either.

How much will it all cost? It was here that I did learn something new although it still didn't fill me with confidence. The government has announced some kick start money to get the GD off the ground. I though this was just window dressing, but it turns out this may just be the start and that the energy companies will soon start to subsidise GD works in the way they have been doing cavity wall and loft insulation. They are required by law to undertake carbon saving measures, expressed in tonnes of carbon per annum (it's different for each company, depending on their size). Some of this carbon-saving cash is probably going to filter through to GD providers and it may end up subsidising works such as external wall insulation (EWI), which on their own are very unlikely to ever meet the Golden Rule.

So, for instance, if EWI is estimated to cost £10,000, and the expected saving is, say, £300/annum, then the householder might only have to pay £3,000 (which gets roughly a 10 year payback), with the other £7,000 being paid for via an energy company subsidy - or ECO as it's getting called. Or at least I think that's what ECO is — once again the slippery nature of the GD makes it hard to know what is what. Was ECO a fund or a mechanism? Or both?

If I am right, then you really need someone else acting as a broker, who could fit your job together with the appropriate energy company, the one who is offering the best subsidy for this kind of work.

At least, I think that may be how it will work. I could also be completely wrong. But then, if I am, I will not be alone.

I came away surprised by:
a) how much I already knew about the Green Deal — I kept thinking "I know that" — but
b) how much I didn't understand — like how is it all going to work.

I wish it well, but I don't think the runes are looking too helpful.