Three year logburner record

In these posts I’ve argued for some time that the Solar PV is a “nice to have” but is not really part of the performance of the house – that is due to the air tightness and insulation. So whether one has solar PV or not affects the energy bills, but not how the house behaves.

When the visitors come on the International Passive House Open Days – see https://passivehouse-international.org/index.php?page_id=262  – it will be interesting to hear what they say about Solar PV.  See the slightly earlier post – we are ID5042 and seem to be the only Passive House in Essex (indeed, most of East Anglia) which is open this year.

Anyway, the Feed-in-Tariff isn’t anything like as attractive as it used to be, even though the cost of the panels has fallen considerably, so the sort of payback that we’ve been getting is no longer obtainable.

On the other hand the Solar Thermal panels and the Logburner, both working with (into?) the Thermal Store are key to the thermal management of the house – not forgetting the big, south-facing windows.

So it may be of interest to publish the graphs for the last 3 years showing the number of times we had to light the logburner and how many barrows of wood we used.  I regret that we didn’t make a notes for the first winter we were here but it would not have been representative anyway as it was the end of October (just over 4 years ago now) when we finally moved in – into a cold, damp house.  I remember that we burnt quite a lot of wood at the beginning getting the house up to temperature and to begin to dry it out.

So here are the three graphs

slide1

slide2

slide3

I’m sorry that they are not clearer – this seems to be the best I can manage within my limited understanding of WordPress.

In table form

Year Fires Barrows
2013-14 96 35
2014-15 89 33
2015-16 103 39

And I note, with mild interest, that in every year we had to light the log burner in Week 42. And we’ve just done so again this year.  Wasn’t 42 the answer to life, the universe and everything?

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Now – Porter’s is a certified Passiv Haus!

Hurrah!  We’ve just received formal agreement that Porter’s meets the Passiv Haus – Passive House – standard.

So now we’re passive house ID5042.  And the PH organisation across the country is holding Open Days, on Friday 11th to Sunday 13th November.  So you can go to see Passive Houses near you.  And we’re opening Porter’s on all three afternoons. Go to https://passivehouse-international.org/index.php?page_id=474 , click “Come and have a look!” which will open the list of buildings – several hundred. More detail on each if you click it. And there are flyers to download (small and large).

Dr Roderick Williams has been working on our behalf with WARM, which is one of the few UK based Passivhaus Certifiers working on behalf of the Passivhaus Institut, Germany, to achieve this certification.  It would have been easier and almost certainly quicker to have done this as the house was being built.  But we were under considerable financial pressure at the time and the additional expenditure did not seem a good idea then.

BUT – we’re not a zero-carbon house – not quite, so we’ll have to relinquish this claim. While it’s certainly true that we get all our heat and hot water from sunlight and wood, when you look at the electricity power balance from the records of the last three years, it isn’t really possible to say that we generate more electricity than we use. And if the electricity we use from the mains isn’t all from a carbon free source, then we’re not zero-carbon.

Could we become so? Ignoring, for the moment, the argument about taking our electricity from an all-renewable source supplier, such as Ecotricity, or from a nuclear source supplier such as EDF, then the answer is, almost certainly, no.  The PV panels, limited to 4kWp without special permission, simply don’t generate enough electricity over the course of a year to achieve this.

The figures show that although we generate more electricity in a year than we draw from the mains supply, it isn’t possible to show that we generate more than we use.  So we’re not self sufficient in electricity.  We’d probably need a PV system twice the size to achieve this.

With the present PV system, to achieve a balance, I think we’d need to use less than 4,000kWh/a. And as the Klargester package sewage system uses about 1kWh a day, as does the MVHR, that’s over 700kWh/a used already.  It wouldn’t be comfortable – not enough cooking- too many cold meals!

 

 

 

 

 

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Now 2016 and just over 3 years

Yes, over 3 years now and still going strong.  Now starting to burn some of the -relatively little – left-overs from building the house which I cut down to size and stacked last spring. The off-cuts from the cladding – rebated Thermowood weatherboard – is particularly good kindling, so it’s just as well that the DWD – the external airtight cladding – does not support flame.

Well, we haven’t had the rain that the northwest – and now the north-east – has been getting but it has been very grey. And, even if mild, this means having to light the log burner to give us hot water.  Not necessarily every day because, when it’s mild, the house loses even less heat than it would normally do at this time of year.  But no sun, no hot water.

2015ytd

So here is the graph so far.  The wood so far has been very good quality (only just started using the lumber mentioned above) so not many barrow loads and relatively short-lived fires – just to generate a little heat and the hot water.  It’s a funny old winter so far.  Anybody still not believing climate change?

Posted in Cladding, Log burner, Solar thermal | 2 Comments

Will we make it to . .

. . the end of August?

It’s been pretty grey these last few days and today, 31st August, the forecast is for rain all day.  We had a fair bit of sunshine the day before yesterday and the thermal store temperatures got up to 70 at the top and not too bad below, so we have had hot water for yesterday and today – but will there be enough for a decent shower tomorrow morning?  We’ve got our younger son staying and so there’s more hot water needed!

Which prompted me to extract the data from the diaries for the last six months of last year and the first six months of this. So here’s the graph showing the number of times we lit the log burner and the number of barrows of wood we brought into the house.

Logburnerusage 2014-15

If you look back to “Another article – and wood usage update” (published in June 2014) which gives a rather different graph – the weather was clearly not the same, though, interestingly, both have a sort of gap in March – a spell of sunny weather which means that you don’t have to light the burner.  Then April needs more heat.  Ah yes – Flanders and Swann (for those of a certain age) April brings the sweet Spring showers/on and on for hours and hours.  Which explains it all, of course!

In 2013-14 we used 35 barrow-loads of wood and lit the fire 96 times – vs. the figures above of 33 and 89.  Of course if we go away for  a few days . . .

But the point I’m hoping to make is that we only lit the fire 96 or 89 times.  Out of the 365 days of the year.  All the other days – three quarters of the year – we didn’t need to. All the heat came from the sun.  Even if we were using gas – even oil(!) we would not be using much and not often.  And that’s the point of building to Passivhaus standards.

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Update for Summer 2015 – and the PV story

A few words to report what has been happening since the beginning of this year.  I suspect that visitors to the site are now as few and as intermittent as my posts on to it.  But the house is built and we’re living in it, so the excitement when everything was new and slightly experimental has, er, abated.

We finally got the Solar PV more or less sorted.  As described earlier, there are two “strings” of 9 panels side by side on the same roof.  So you would expect the output from each string as shown on the inverter display to be the same to within quite tight limits when the system is new – which they were – and to change only gradually as the panels age. It was noted that, within a year, the output from the east string was 10% below the west string.  This was reported to the contractor that installed the PV system.  The measurements were confirmed but nothing was done to rectify the matter.

By the following spring the east string had deteriorated to the point that it was 17% below the west string.  I pointed out that this was well outside the guaranteed performance – no more than 10% degradation after 10 years, no more than 20% degradation after 20 years. More measurements of the open-circuit voltages and short-circuit currents from each string were made and, after I pointed out that I would have to consider my legal position, there was even a visit from the panel manufacturers, Romag.  Romag had hoped that using a thermal camera would identify any suspicious temperature differences in the panels but this didn’t seem to work.  In the discussions it was put to me that the energy that the system had collected over the previous year was still significantly greater than the SAP performance.  I was unimpressed by this, pointing out that the SAP figure must be one which even the worst system in a year of really bad weather would be able to exceed, otherwise the industry would be receiving continuous complaints; they had to admit that this was the case.  In other words the SAP performance is a worst case figure!

But this was a red herring – the outputs were substantially different so the east string must be defective.

It was confirmed that the manufacturer will replace any defective panel(s) free of charge. Just that. Their warranty does not extend to the cost of removing and replacing the defective panels – this the installer has to bear.   It would be expected that a contractor in this business would hold insurance for just this eventuality – there are bound to be occasional problems as with any installation.  Some figures (inflated in my view) of the cost of scaffolding and getting the slates removed were mentioned together with a litany of the difficulties.  Time had passed and at the end of last summer the east string was now 19% down – I was asking if the string had fail completely before the installer would accept that it was defective and do something about it!  Eventually I was forced to go to another installer – essentially as an independent assessor – to confirm that the system was defective.  The original installer, after some trouble, finally obtained some replacement panels from Romag and delivered them here.  By this time it was winter and the weather was such that, on at least two of the agreed days when the independent contractor planned to change the panel(s), it was too windy to be safe.  Interestingly, on the morning that the scaffolding was put up, there was a frost which covered the whole roof with hoarfrost – except for one patch.  This picture was taken at 8.55 am on 9th December 2014.  There was light in the sky but no sunshine anywhere on the roof

Spot the hot spot!

Spot the hot spot!

Eventually coordinating some roofers and the independent contractor was achieved and the defective panel was replaced.  There was a period of panic when it was found that the first panel on the stack of replacement panels was found to be a slightly different size and wouldn’t fit.  Fortunately the next panel was the right size!

With the benefit of hindsight I should have insisted that all the panels were checked and had all those that were “down” replaced.  While I’m certain that the panel with the hot spot was the main culprit – there were some scorch marks and evidence of some delamination nevertheless the east string is still 9% below the west string.  After a further struggle, the original installer reimbursed me for the independent contractor’s invoice.

There’s further comment to all this: had I not had two strings – and so was able to compare the outputs – but only one, I would have had no idea that the performance had deteriorated.  The normal householder, like me, does not have a light meter and other equipment to check how well the panels that have been supplied are performing. Worth a thought!

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March comes in – sunny!

Amazing what a few days’ sunshine makes.  Now that there’s a bit more oomph in the sun light, the thermal panels heat the water in the thermal store quite quickly, so that within less than a day there’s all the hot water we need and plenty in the bottom half to keep the house warm, should it need it.  And the house needs quite a lot less because the heat coming through the windows is putting warmth into the thermal mass, so that even if it gets frosty overnight, the house keeps warm well into the night before the thermostats call for heat.

So today (Monday 9th March), though it was sunny for a while this morning, the sky clouded over quite soon and only  a little heat was stored in the bottom half of the thermal store.  But there is more than enough heat from the previous two days to keep the house warm and the DHW requirements met until tomorrow – when the forecast says it will be sunny again.  We have not needed to light the log burner since 28th February!

All very satisfactory.

 

 

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Frosty Christmas

Pleased to be able to report that Porters is still performing as we’d expect as far as the house, log burner and solar thermal goes.  In contrast with last winter which was warm, and wet – and so grey with overcast skies – quite a lot of the recent weather has been clear and cold.  Again we’ve had Jack Frost patterns on the outside of the triple glazing – which I still find amazing.  The sun, though low in the sky and only really able to do anything useful between 10 am and 2 pm, nevertheless puts worthwhile heat into the thermal store and directly into the house through the big windows.  The solar thermal panel collector temperature doesn’t get high enough to do much for hot water but if we haven’t used too much from when we last lit the log burner, we can go a day without lighting it at all because there’s enough from the sun in the thermal store to keep the house warm.

We’ve put in hand the process of having the house accredited as a Passivhaus, so that’s a story which I’ll report on as we go forward.  So far we’ve had the air test repeated which has passed at 0.58ach.  It was a bit better than this when the original test was done during the building of the house and we suspect that one or two things have dried out over the intervening 2 years+ and gaps opened up.  Attention was needed where the SVP passes through the roof and also where the log burner’s flue passes through the roof as well.

As 2 years have passed it was time for the Paul MVHR to be serviced.  The matrix simply gets washed with water – it didn’t seem to need it – and the fans are sealed for life.  So there wasn’t much to be done. The filters get changed regularly anyway, the dirtiest being that in the pre-heater which is the first – and catches all the insects in the summer.  The filter downstream from the pre-heater doesn’t really need changing very often as it doesn’t get dirty.  And the filter preventing house dust getting into the system gets looked at every 90 days but again does not always need changing.

The saga of the faulty solar PV string mentioned in the previous post is still running and I’ll complete that – when it’s completed! Very soon now I do hope.

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Hot September

Not said a lot here for quite a while.  It has been an excellent summer in many ways.  With so much water in the ground after the long wet winter, things have grown very well – and there’s been quite a lot of rain, very nearly as much as we had two years ago – which was a summer everyone thought terrible.  But this time most of the rain fell at night and the days were warm and sunny.

But this isn’t about gardening.  We have noticed an interesting and puzzling phenomenon here with the Solar PV.  And I, at least, am not getting any answers.  The solar PV consists of two identical strings each of nine panels, mounted side by side on the same, south-facing roof.  After a year, I noticed that the instantaneous power figures displayed by the inverter differed by about 10%, whereas they had been almost identical when the system was first installed (as one would expect).  I mentioned this to the installer – i.e. I complained!  By earlier this year, which is 2 years after the panels were first installed and about 18 months after we moved into the house, this discrepancy had widened to about 17%.  Now it is nearly 19%.

There have been visits by both the installer and the panel manufacturer. The two DC inputs to the inverter have been changed over – the difference changes to the other channel, so it would not seem to be the inverter.  Indeed a second inverter has been connected – and the figures remain different, so everyone now agrees it is not the inverter.

Repeated measurements on the DC output from the two arrays (strings) have also been made.  Open circuit voltage measurements have been made on both strings – and are reported to be closely similar.  Even more puzzling, short-circuit current measurements have also been made on both strings – and again are reported to be closely similar. Now, if cells within a panel had failed short-circuit, then you would expect the voltage to be down a very little bit – unless a lot of cells had failed, in which case the voltage would be noticeably lower.  But as the failed cells would not be generating power, the current would also be lower.  But it isn’t.  If the cells had failed open-circuit then, because an array has 3 diodes, you would expect to lose 1/3 of that array’s power – but the loss is not that large.  It’s only when the array is called upon to deliver power that the difference shows.  This does not behave in the manner I expect from what I was taught at school or university.

Needless to say, no-one wants to put up scaffolding and remove the panels since it would appear to be difficult to find the defective panel – if, indeed it is a defective panel. Oh yes, each panel is identified and its initial performance is known – and they are all initially similar to  better than 2%.

Any ideas, anyone?

On a quite separate point, the experts point out that south and west facing rooms can suffer from over-heating in autumn and, to a lesser extent, spring.  This is because the sun is noticeably lower in the sky and the shading measures (see picture elsewhere – we have a large overhang to the south) are therefore less effective.  Well, it’s true!  One room, which has windows to both south and west has got noticeably hotter during sunny days this last month than it did at the height of summer.  It’s not a problem – you open a window.  But from the thermometer in the room it has been getting 2 or 3C hotter this last month than in the fine weather of June/July.

Posted in Solar PV, Thermal mass, Windows | 2 Comments

Another article – and wood usage update

Those who follow these things will by now have seen an article on this house in the June issue of Self Build & Design magazine.  This was an interesting experience, in that the journalist, Debbie Jeffery wrote the article based on a phone conversation with us – and probably from information in this blog – and the photographs were taken by Caroline Bridges separately, taking most of a day, relatively few of which appear in the magazine.  Impressive (apart from a picture of me looking worn out!) And we were sent a complimentary copy of the magazine – and I realise that this post should have been written much earlier.  Anyway, I hope that, like the other articles in this magazine, readers found it useful.  This is not a “stunning” house not, as noted elsewhere, a “Grand Design” – we doubted Kevin would have been interested and, having talked it over, decided not to submit it.  And, as it turned out, there wouldn’t have been enough drama – thank goodness!

It just works.  Here’s the wood usage graph updated.  The log burner has been lit 5 times since the beginning of March and the 5th time only because we had a house guest and wanted to ensure there would be plenty of hot water.  And it’s interesting to see that there were only 4 weeks when we had to light it every day. All the rest of the space heating and hot water comes from the sun!

Log burner usage by week

Log burner usage by week

Another few weeks and we’ll have the whole year’s record.  I have been cutting, splitting and stacking quite a lot of wood lately for next winter. I’d stored what I thought were 55 barrowloads last year in 5 stacks and we used almost 4 of the stacks – 80% of the store. But I see that the graph shows 35 barrowloads.  Hmm.  The barrowloads being brought into the house were bigger – all I could get into the barrow each time!  But much of the work is because we lost 3 large branches from the weeping willow in the storm last autumn and I’ve been working my way through this.  It’s a substantial volume, all wet of course, so it’ll need storing for at least a couple of years to dry out – and won’t be very good wood even then, being very light – probably half the value for burning that other hardwoods are.

 

 

 

Posted in Log burner, Solar thermal, Thermal Store | 2 Comments

More Publicity!

Fame (though not fortune!)  seems to have struck – again.  No sooner had the 6 minutes of BBC fame begun to die down than our local MP, Sir Alan Haselhurst, came to see the house. Together with Dunmow Broadcast reporter Sam Tonkin, the house tour was undertaken and both Sam and Sir Alan seemed interested and, dare I say it, even impressed.

This resulted in a double page(!) spread in this local paper and, once again, we were caught on the hop.  Dunmow residents get their copies delivered on the Thursday of publication, but those in the sticks of Felsted have to wait until the following day.  So I didn’t immediately connect with the ribald remarks offered on meeting Dunmow residents at a rehearsal on the Thursday evening because, of course, I didn’t know what had been published. It’s a freebie, so pretty well everyone gets it.  This is a mixed blessing. Famous for being famous? In-for-me?

More seriously, it was a useful if rather local step in trying to persuade people that it’s not difficult to build a really low energy house and not that expensive either.  Sir Alan pointed out (very reasonably) that he couldn’t remember all that he was told, so would I summarise it for him in a letter?  Of course, though curiously not easy. Rabbitting on about the technology is fun and interesting for those interested but for those with political fish to fry?

I’ve copied in parts of that letter below which others may find helpful.

” . . . . it would be good to see all new build to the standard we have achieved here as it would go far to meet the need to reduce energy consumption – and hence carbon emissions.
The principles may be summarised in 5 key points:

  1. The ground slab has 300mm of insulation under it.  The slab provides much of the thermal mass to keep the house temperature steady.
  2. The walls and roof are deeply insulated.  The house thus sits in a cocoon of insulation.
  3. The air tight layer – the T&G fibreboard we showed you – is on the outside.  This reduces the number of places that need care to maintain the air seal and minimises its vulnerability over time.  There are lobbies at the outside doors to reduce the heat loss as you go in and out.
  4. Thermal bridging is minimised by the use of thermally efficient doors and windows (which are triple glazed) and good design at the floor-wall junction.
  5. Given that the house is airtight, a mechanical ventilation system is required – and this transfers the heat from the outgoing air to the incoming air, giving good ventilation through the house with negligible heat loss.  Our MVHR is 93% efficient and uses just 44W – no need for expensive and wasteful bathroom fans, for example.”

and

“. . . . This house meets Passivhaus principles.  These differ from the UK standard – the Code for Sustainable Homes – in being simpler.  CfSH looks for sustainability not only in the work of building the property, but also in the materials with which the property is built and, finally, in the way the occupants can then live.  All of this is desirable but expensive and hence meets resistance from the commercial house-builders.  Passivhaus simply puts limits on the energy demands.  It limits the space heating requirement, which is usually the largest demand, to 15kWh per square meter per year – a 90% energy reduction from what most houses need.  This simpler requirement would, on its own, have an amazing effect on total energy requirements at a lower build cost.  Whatever you use – wood, gas, even oil – you don’t use much!

This house would meet Level 5 of CfSH – but fail Level 6 for reasons that have nothing to do with the energy performance of the house.”

OK, there are simplifications here but the principle remains true.

You’re welcome to comment!

17-Feb-14: Two days with no need to light the log burner! After that very windy night, Saturday produced quite a lot of sunshine, enough to get us through to Sunday – which was a glorious day.  Spring offering a preview? Some brightness today, more than forecast, but while that keeps the house warm, we’ll need hot water, so the fire will have to be lit this evening.

Posted in Cladding, Thermal mass, Ventilation, Windows, Zero Carbon House | 2 Comments