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.




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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.”


“. . . . 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

It’s catching (on): as heard on BBC

Some recent excitement: at very short notice I was contacted by a producer – John Neal – of You and Yours from the BBC.  He’d heard from Touchwood Homes that they had a client who made money from his fuel bills – a real headline catcher!

The long and short of it is that we were then contacted by a reporter – Bob Walker – who came to Porter’s and spent couple of hours with us. This got edited down to some 7 minutes.  Despite our nervousness at the sheer novelty of such an experience, we were not made to sound foolish. Instead I think Bob did an excellent editing job and succeeded in extracting the essence of what it’s all about.

See what you think:

This has kicked a minor flood of friends saying how good they thought it was – clearly You & Yours has an even larger audience than we thought.

Now let’s get this in perspective.  Almost anyone with  a full set of PV panels (4kWp) is likely to have negative electricity bills.  We actually use more electricity than we did in our old, inefficient house, because everything that doesn’t depend on wood or sunlight uses electricity.  We do all our cooking with electricity instead of most of it by gas.  The MVHR uses about 1 kWh a day.  And there’s a (OK, quite small) pump with the solar thermal system.  But even with the less generous Feed-in-Tariff, as explained in the post Autumn (and Summer) 2013, you’ll have to be pretty reckless with the electric to have bills more than what you get paid.  The important point is that the house is efficient, so it doesn’t really matter what you use to heat it with – you don’t use much of it.  Thank you, BBC, for keeping that in.

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Wood usage

The wood store is relatively impressive – or so people have been kind enough to say. Essentially it’s the space between the two sheds with a corrugated plastic roof over it  and a slatted back so that the air can move through it.  Over the spring and early part of the summer all the driest wood I’d collected, from whatever source, got cut up and/or split and stacked in this space so that for the second half of the summer it got a final drying.  There were 55 builder’s barrow-loads.  The quality of the wood is extremely variable.  There’s some really good oak and ash there.  Plus some very worm-eaten pine – which had spent quite a lot of time on the ground before being dealt with and had been very well attacked by some wood-boring grub which made deathwatch beetle look positively benign.  And lumber right down to a couple of hardboard-on-cardboard doors.  These take space and burn well – but not for long!

The logburner in use

The logburner in use

There were two evenings in April when we had to light the log burner.  Here it is shown alight.  The pile of logs to the left is about 3 barrow-loads and the black thing on the wood is a glove which came with the stove.  The only bit of the stove which gets really hot is the door on the front – the top and sides are fine to touch.

The Autumn article covers the generation and use of electricity.  It could be argued that the Solar PV is nothing to do with having an low energy house.  More important in purist terms is how the space heating is performing.

Below is the chart showing when we lit the log burner since mid year until the end of last week and how many barrow-loads of logs have been used in the same period.

Log burner use and consumption 2013

Log burner use and consumption 2013


We’ve used 21 barrow-loads of wood in this period.  This, as mentioned elsewhere, has provided us with all the hot water we need (for showers, washing up, etc. – the usual DHW – and we certainly do not belong to the cold shower fraternity!) and has kept the house warm as well.  It’s been good to note that there was no need to light the fire on either 19th or 28th December.  These were lovely sunny days and warmed both the house and the thermal store to meet all our needs for that day and night.

And, while we use the wood saved over the past few years and the lumber left over from building the house itself (there are quite a few pallets to be got through yet) it has cost nothing but my effort and some electricity to drive the saws.  The builders, Touchwood Homes, calculate that, if we had had to buy wood in it would have cost £371 based on a cost of 4.2p/kWh.  I’ve never bought firewood, so I can’t validate this.

We’ll keep on counting though the rest of the winter and spring so that there’s a full year’s worth of data on wood usage.

Comments welcome – and Happy New Year!

Posted in The project history, Thermal Store, Zero Carbon House | 14 Comments

Autumn (and Summer) 2013

July, you’ll remember, was very hot.  After a winter that went on and on, there was a very short spring and suddenly we were in summer.  The thermal store got up to 95°C and the solar thermal panels were about to switch themselves off, because 95°C is the maximum temperature that the system was set to.  The panels would have emptied themselves into their expansion tank.

The thermal mass did its job of preventing the house heating up too quickly during the day and yet keeping it warm at night.  In the really warm weather the house did eventually get too warm, so we opened the skylights and let the hot air out.

Late summer 2013

Late summer 2013

By the end of October, we’d been in the house a full year and can therefore provide full year figures for electricity generation and consumption.  The house is on Economy 7, so there are two meter readings for electricity imported. Over the period 19th October 2012 to 1st November 2013 we bought in 1112 kWh at night and 2748 kWh during the day – a total of 3860 kWh. Over the same period the PV system generated 4009 kWh. The EFD Blue+Price Promise 2013 tariff we were on charged 18p/day standing charge, 11.32p/kWh day rate and 5.92p/kWh night rate. So we paid ((365+13) x 18 + 1112 x 5.92 + 2748 x 11.32) x 1.05/100 = £467.19 (inc VAT) for just over a year.

For the PV we received  the payments shown in the table below:

Period                           FiT payment
28.9.12 – 1.12.12         105.32
1.12.12 – 1.3.13              96.73
1.3.13 – 1.6.13              255.81
1.6.13 – 1.9.13              343.20
Almost a year              801.06

So the electricity bill was (roughly) minus £333.

Financially this was very encouraging, although it has to be admitted that the EDF tariff we were on was quite competitive.  We’re now on Blue+Price Promise 2014, which on a similar usage means that the price of the electricity bought in is about 25% more (and people moan about 9% increases!).  The rates have become 6.81p (15% increase) and 14.73p/kWh  (30% increase) for night and day rates respectively. What was that switching site?

(Update: now on EDF’s Blue+Price Promise April 2015 – a good deal better!)

During last winter (i.e. 2012-13) we failed to record when the log burner was lit and how much wood we used.  This autumn and winter, however, we have been doing so – having spent quite a lot of time sawing and splitting 55 barrow-loads (builder’s barrow) of dry wood during the early part of the year.  (Keeps me fit!)  Much of this had been collected over some years, saved on the basis that anything thicker than my thumb was firewood – and anything thinner got shredded and put into a compost heap.  The information on this is discussed in a separate article.

Getting up to date at last: thanks for your patience!


Posted in Electrics, Solar PV, Solar thermal, Thermal mass, Thermal Store, Uncategorized, Ventilation | 2 Comments

Winter and Spring 2013

More grovelling apologies.  I’ve been sitting on this for months without publishing it and now (round about Christmas 2013) have finally got round to doing something about it.

Well, quite a winter (meaning early 2013)!  This was a severe test of the performance of the house, with long periods with the temperature close to, and often below, 0°C by night and often day.

The house has done well.  A first experience of living in this sort of house makes a few notes worthwhile – how has it performed?

The original calculations suggested that the house would need 48 kWh a day to keep warm. Using the log burner – the Woodfire F12, which puts 10 of its 12 kW into water, we found that burning it for 4 hours an evening during the really cold patch – well below freezing at night and not over 2°C during the day (and a keen east wind – you (if local to Essex) will remember!) provided all the hot water we needed and kept the house warm (~20°C) for the next 24 hours.  And used much less wood than I’d expected.  So we’re well pleased. And half that when the weather was milder. We didn’t need to burn the stove at all for the second half of April – first half of May.  Then there was very grey patch and we had to light the stove briefly to be sure of enough hot water for showers – the house itself was kept warm from lower temperature heat and the solar gain through the windows. The May BH weekend was very sunny.  The temperatures in the thermal store read 72, 72 and 60°C (top, middle and bottom) and it’s a good thing that the water to the hot taps is mixed down to a lower temperature.

The thermal mass also seems to be doing its job.  Again over the Bank Holiday, the main bedroom got up to 23.5°C during the day but only lost a degree over night.  Visitors to see the house – who often take their shoes off – comment that the floors do not feel cold.  As mentioned elsewhere in this site, we do have underfloor heating but have not yet used it.  So the floor slab has picked up the temperature of the house and holds it.

Interesting effect: those of  a certain age – including me – may remember the pretty patterns on the inside of windows, formed by the condensation freezing in very cold weather.  We have had similar pretty patterns on the outside of the outer layer of the triple glazing this winter.  The insulation provided by the windows is that good!

The decking has been laid at the front – well, it’s actually the back, being the other side of the house from the front door – but is on the south side.  And the ground work has been done at the front and sides of the house.  And sheds for tools etc.  Curious, we still seem to be very busy when somehow we expected to be able to relax a bit by now.

Better publish this and get on with the next installment

Posted in Foundations, Solar thermal, Thermal mass, Thermal Store, Underfloor heating, Windows | Comments Off on Winter and Spring 2013

Week Thirty one to end October ’12

There were apologies here because I hadn’t kept this up to date.  So some progress now (end May 2013) at long last! Last autumn and winter we really got very busy indeed and keeping this up to date was a task too far.

When the stairs got unpacked it was found that the spindles were the wrong size – which meant that the banister and bottom rail were also wrong.  Replacements were promised in 2 weeks (which I thought was pretty slow for what I strongly suspect are ex- stock items) but in the event took 3 1/2 weeks to come. So by the time the builders came back to install it a full month was lost.  We then had to wait two weeks for the last day’s plastering. This in turn held the 2nd fix electrics of all this area and its decoration.  One way and another we lost 2 months in 2 months. Very unhappy.

But done now

Since then everything has been done – 2nd fix plumbing (some delay because the Multi-Board (instead of tiles – another make is Mermaid) was most unlike the brochure picture, so that had to go back and Simon has done a good job on the bathrooms.  The 2nd fix electrics has been done and the wiring certified.  The MVHR installed and the air flows balanced – and almost everything has been painted (there’s some skirtings which have still to be finished).  And carpets!

We had 2 Open Days – one for the Uttlesford Sustainable Homes Network when all sort of people interested in these things turned up and were able to meet our architect Jenny Bishop, (Green Architect), the main builder Touchwood Homes, the designer  and installer of the heating systems Dragon Contracts and the plumber Simon King. Rod Williams who calculated the Passivhaus heat equations and designed the ventilation was also there. And the following day we had another one for local friends and acquaintances who were interested.  Both days rather passed in a blur, spent talking.

And the following week we moved in (October 25th)!

Sometime!  Happy New Year

Posted in Electrics, Ground Floor, Plumbing, Solar PV, Solar thermal, Ventilation, Zero Carbon House | Comments Off on Week Thirty one to end October ’12