Passivhaus carbon emissions

There is a perception that Passivhaus buildings use hardly any energy because of all of the insulation they contain. Whilst this construction standard provides unrivalled comfort and massively reduces the heat load required it does not necessarily mean the house uses much less energy for anything else.

In a conventional house the heat losses during the winter months are such that you need a significant amount of heat input to maintain a sensible temperature internally. Even when it’s not that cold outside the strong winds that we’ve been having mean that lots of heat is lost from drafts. Additional gains from the sun and waste heat from appliances are relatively insignificant and so are mostly ignored.

At Passivhaus levels of insulation and airtightness the amount of additional heat energy required is minimal (so far this winter the Silverton Passivhaus has used 260kWh of heat or about £13 worth of gas). However, this is not to say that no heating is required at all as you do still need to heat and you still need energy for appliances. It is simply that everything else done inside a building that produces heat becomes the heating instead.

From one angle this is obviously a big benefit as the carbon emissions from each dwelling can be reduced enormously but with a large caveat. Gas is widely used for heating and, in a modern condensing boiler, has the lowest carbon emissions per unit of heat produced of any of the fuels.

In the move towards ever more energy efficient buildings we are becoming more and more dependent on electricity as an energy source. Modern homes are ever more packed with electrical devices for security, ventilation and environmental controls, all of which demand ever more electricity and create a much higher base load for the building. We are at risk of substituting low carbon heating energy for much ‘dirtier’ (from a carbon perspective) electricity in the drive to lower our heating bills.

Grid electricity currently produces around 0.55kg of CO2 per kWh and natural gas produces around 0.185kg per kWh. To illustrate the point, the average UK home consumes 16,900 kWh of gas and 4000 kWh for electricity. This would give a combined CO2 production of 5326 kg. Whilst me and my family may not represent an ‘average’ household our gas usage has reduced to around 7000 kWh but our electricity is around 10,000 kWh. This means that our energy usage produces 6795 kg of CO2.

Our heating/water heating requirement now costs about 75% less than our old cob house (which was also 1/3 the size of the new Passivhaus) but our electricity bill is slightly higher, even though we have LED lights everywhere and A+++ rated appliances. I assume this to be because of the higher base load from ventilation and control gear which we hadn’t anticipated.

To summarise, Passivhaus and other low energy standards provide un-rivalled levels of comfort and vast reductions in heating requirement but they do not necessarily provide the reductions in CO2 emissions that one might expect.  Unless the design is kept simple and the temptation to install the (often vast) array of controls and systems that are stuffed into ‘Low Energy Buildings’ is resisted we may not be reducing our impact as much as we think. Until grid electricity becomes cleaner and lower carbon we should rely on it rather less to achieve our goals.

 

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Unger Licensing Course

Today (4th December) we’ve finished another very successful Unger licensing course. This is a two day course on all of our Unger-Diffutherm wood fibre insulation systems and was the first time we’ve used our new office for these events. Amazingly, it all seemed to work very well with everyone well fed and watered in between each theory and practical session.

The course is fairly intensive for our participants and is a mixture of learning the theory behind the products and the practical installation of them. Sabine Groeneveld from Unger (and NaturePlus) in Germany came over and discussed in depth how the systems work, how it is so important to be able to manage moisture in buildings (especially in our maritime climate) and also the importance of correct detailing with all of the systems (again, because of our maritime climate!!).

Each time we run the courses I am amazed by the level of detail that Unger use to ensure that the systems work correctly and do not get damaged or cause damage to the building to which they are fitted. The thoroughness with which each component has been selected and how it is used is very reassuring, both for the installers and for me as a retailer. After all, we selected Unger a a supplier from the various manufacturers on the market because of this. They also innovate and put their money where their mouth is by offering their own 15 year warranty on some of the systems.

All of our participants came away excited and enthused about what systems they can use on current and future projects. They now have a realistic understanding of the complexities of installing insulation and how it completely changes the dynamics of buildings. These installers realise that you cannot just ‘slap it on’ and hope to achieve a decent, long lasting result and now have the skills to create high quality installations and can offer the Unger 15 year warranty.

Now that we have the new offices set up we will aim to run these installers courses as often as possible for those keen to understand these amazing systems and how to install them. If you are interested get in touch here and let us know. We try and keep the sessions to 5-6 people at a time so as everyone gets very hands on training and fully understands it all. We look forward to seeing you.

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Postscript

As an addendum to my last post I wanted to add a few things. The first being that the whilst the Silverton Passivhaus is an exceptionally well performing building the occupants are still consuming fairly large quantities of energy. This appears mainly to be because of their 3 children who create large quantities of laundry and struggle with the concept of energy and water saving. The washing machine, tumble drier (yes, you can use one in a passivhaus so long as it is a condensing one) and dishwasher are in almost constant use which consumes a lot of energy.

The second point was pointed out to me by Christian Nialki from Clay UK. Passivhaus’s PHPP can still produce energy consumption estimates which are wildly different from the actual consumption. However, in all of the German examples monitored (there hasn’t been a large UK study yet) even the worst performing households are still excellent compared to existing housing stock. As he says, Passivhaus not only gives you exceptional comfort and low energy consumption but it gives you choice. You can set the thermostat to 18 in the winter and keep the windows closed or set it to 25 and open them. Even in the latter example you’ll still not be using as much energy as anyone else.

For more info see http://passipedia.passiv.de/passipedia_en/operation/operation_and_experience/measurement_results/energy_use_measurement_results or contact us to discuss it more.

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Mind the Gap/SAP – Go for Passivhaus

There is a gap between real energy consumption and consumption calculated by SAP (standard assessment procedure), known as the performance gap. In spite of this sometimes enormous gap it still used by the majority of engineers to size heating loads for homes, boiler sizes and everything else related. The savings made by adding Solar thermal and solar electric are then put forward to show what massive reduction in energy use is going to be delivered.

In the paper cited in the last blog (A Comparative Study of the Effects of Thermal Mass in New Dwellings in Scotland by Janice Foster) two identical dwellings, one of high mass and one of low mass had their energy consumption monitored and then compared to their SAP calculations. Both buildings had identical architectural designs (design layout, U-values, etc.) and were in the same location and orientation and so SAP predicted the boiler heating load for both would be 20 kWh/m2/annum. The actual consumption was 67 kWh/m2/annum for the high mass building and 89 kWh/m2/annum for the low mass.

Apart from showing how thermal mass can benefit modern, highly insulated buildings by reducing heating requirements by up to 20% it showed the monumental discrepancy between calculated and simulated energy consumption. This is very worrying given that the output of SAP is pivotal in a lot of domestic scale decisions regarding heating and lighting and also policy decisions from government.

I recently looked at the SAP (2009) calculation for the Silverton Passivhaus building and again found a very significant difference between the actual and calculated energy performance of the building. However, this time the building was using at least 30% less energy than calculated rather than the norm of using significantly more. I say at least 30% less as SAP doesn’t include cooking in it’s calculations whereas the total energy figures for the house do.

Maybe it’s time we switched over to using rather more complex modelling tools, such as PHPP (the spreadsheet used to model Passivhaus buildings) which will actually reflect the real performance of a building in most cases. The situation we are currently in appears to be that in most cases SAP does not represent the energy consumption likely.

Admittedly the reasons for this are largely due to the generally poor build quality of UK housing combined with massively variable occupant behaviour. The build quality of Passivhaus certified buildings is much higher than the norm as without this they will not achieve the levels of airtightness required. Also, the simplicity and attention to detail with which they are designed makes building them much easier from the outset.

If we are to really push our 21st century housing in to the 21st century we need to design it, model it and build it properly. It is time we stopped being apathetic about the way our housing is built and demand houses that perform as designed and don’t waste energy. Afterall, it is as important to make the volume house builders build homes that don’t waste energy as it is to demand that the energy used to heat and light them is not exorbitant.

If you’d like to read more about (including the SAP calculations) the Silverton Passivhaus then see the case study here.

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Thermal Mass

I was sent a very interesting thesis entitled ‘A Comparative Study of the Effects of Thermal Mass in New Dwellings in Scotland’ by Janice Foster. The paper researches how thermal mass affects overheating in buildings.

Most people would intuitively say that thermal mass would prevent buildings from overheating by absorbing the excess heat from either solar gains or internal gains and in some cases this is true. However, as with all things related to buildings and people, it is not that simple.

First and foremost there needs to be adequate night time cooling to dissipate the heat stored from the day. If this is not present then the thermal mass will exacerbate the overheating by radiating heat in addition to the other gains. Secondly, to actually work the mass need to be thermally coupled with the interior of the building. Simply, this means that the mass is in direct contact with the interior of the building and not hidden under carpets, behind service voids or in the case of ICF, not behind a layer of insulation.

The thesis also discusses how thermal mass, used correctly, is more useful in the South and East of the country where there is more sunshine and the average temperature is higher. High mass buildings typically have an internal temperature around 2 degrees lower than lightweight buildings and so as the climate changes developers and homebuyers should be looking for heavier-weight constructions.

There were two surprising points within the document, both around the cooler end of the year. One was that high mass buildings can reduce heating requirements by a staggering 20% by simply reducing the fluctuations in internal temperatures and storing heat gains from the day. The second was the gap between real energy consumption data and that calculated by modelling software such as IES and SAP. On one building SAP calculated the energy consumption to be 20kWh/m2, IES was 35kWh/m2 whereas the actual consumption of the building was 89 kWh/m2. Such staggeringly inaccurate assessments, especially by a tool which is a mandatory requirement of building control, beggars belief. How on earth can we pretend to be able to model buildings and make informed decisions on how to reduce heat loss when the output of such programs is so monumentally wrong?

The final point to make is about orientation and the difference it makes to heating and cooling requirements. South really is by far the best orientation from an overheating and a heating requirement point of view. To see a copy of the thesis contact Janice Foster at j.foster@gsa.ac.uk.

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Sustainability in the Third World

I took part in a recent conversation about how to make more people aware of sustainability and renewable energy in Zambia. This is one of the more challenging and though provoking discussions I’ve had for a while as the culture is so different from the Northern European culture I’m used to.

The main thing that came across was that the systems, materials and processes that we use in the first world will not necessarily work in developing countries for several reasons. One of the most important is that 90-95% of the population live a very rural existence and could not hope to afford to use lots of energy anyway. This also means that they will never afford solar panels and quite frankly could teach us a thing or two about how to use energy and resources wisely. Those that can afford to will tend to use the more reliable sources such as generators as they are easy to fix and parts are available.

We also discussed how best to use earth in construction globally, to improve sustainability. Earth is a fantastic building materials for lots of reasons. It keeps buildings very cool in the summer, it has enormous thermal mass, it is very cheap and abundant and earth construction has very low embodied energy.

Some thought that hi-tech inclusion and mixing of soils was the best way to get more earth used in construction. Others thought that going back to using traditional methods would be best. However, I don’t think that there is one method that will suit all cultures and all markets.

In the developed world we have infrastructure, industry and industrialised processes, methods of assessment and also a housing market where people will pay lots of money for housing. This set of conditions could cope with producing a standardised product of blended soils from various locations. It can also cope with high tech methods of construction or prefabrication.

In less developed countries where the situation is different, educating people to use what materials are abundant may work much better as high tech methods are out of the reach of most people. The growing middle classes could use local materials and processes rather than trying to emulate what we in the developed world have created. This would suit local vernacular architecture much better and prevent these countries from becoming the all consuming behemoths that we have become.

What is your opinion? Add your comments below.

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25% discount on Baumit lime plasters and renders

We will be running a 25% discount on our remaining Baumit stock from the 16th of October until the 15th of November. If you want to come straight to the shop, click here or contact us at 7 Tuns Lane, Silverton, Devon. EX5 4HY – 01392 861763.

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Heatwave performance charts

From the data that we have collected from the Silverton Passivhaus since May, the most interesting period, in terms of the house’s performance, was during the heatwave in July. We saw temperatures in excess of 32 degrees which is a good test for the Passivhaus principle but also for the design input that we as a company have had on the building. If you want to download a drawing of the house, please click here for the PDF or click here for the data.

The house contains around 120 tonnes of concrete and steel that are fully within the insulation envelope. There are also around 20 tonnes of clay boards and around 6 tonnes of Fermacell boards which also add to the mass. The house uses a lot of wood fibre insulation wool and wood fibre boards for insulation. These have high thermal mass and should help keep the house cool in a heatwave.

The charts below, apart from looking like my 2 year old daughter has had a go with some colouring pens, show how the temperature varied with time during the heatwave in July this year.

This chart shows the South elevation. You can see from sensors 3 and 4 that the outer wood fibre boards are absorbing a lot of the heat from the direct sunlight with variations of around 15 degrees at sensor 4 (40mm below wall outer surface), 5 degrees at sensor 3 (140mm below wall outer surface) but buffering it so effectively that on the interior the variation is down to around 2 – 2.5 degrees. The exterior variation was up to 20 degrees between day and night and even during the day it is likely that there was at least a 20 degree difference between the inside and outside surfaces during the day.

The East and West face data set show relatively similar behaviour but that missing data from sensors 3 and 4 on the East face makes it difficult to see clearly how the wall behaved.

This data from the North wall shows the variations well but the temperatures experienced by sensors 1 and 2 is a couple of degrees higher that the interior temperature because there is a fridge nearby heating the area. Internal temperatures tended to peak when cooking happened in the evenings as the internal sensor was located near the kitchen area.

Overall the wood fibre insulation has performed well and done what is was supposed to have by keeping the building at a comfortable temperature inspite of high external temperatures. It would be great to be able to compare this to other Passivhaus buildings built with different materials to see how much is material dependent and how much is design dependent.

For more information on the Unger-Diffutherm wood fibre products see http://www.backtoearth.co.uk/products/unger-diffutherm-woodfibre-insulation-systems.

If you can shed any more light on these charts please feel free to contact me or comment.

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Our online shop

Now that some of you have started finding it, I thought I’d better mention that we’ve opened an online shop with all of our products on it.

We’ve opened an online shop with all of our products on it.

There, said it. Actually, not all of our products are on there yet but they will appear over the next few months so as you can buy whenever you like or just compare our prices to everyone else’s!!

Simply go to the product pages on the website and at the bottom of each page you can purchase the products individually or by the pallet.

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Passivhaus performance data

We have an ever growing database of information relating to the temperature and relative humidity of a passivhaus building. Externally we’re using a Davis weather station to produce a weather file and to monitor the internal conditions at the centre of the house.

We’ve also installed temp/rh probes in to the timber framed walls. These are in the service void, in between the OSB and the UdiFLEX wood fibre wool, at the interface between the UdiFLEX and the UdiTHERM  wood fibre boards (300mm from OSB) and also at the junction between the UdiTHERM and the UdiSPEED wood fibre boards (400mm from OSB). There are a set of these sensors on each elevation (e.g. N,S,E,W). If you’d like to see the house and how it is constructed see our Flickr page.

The construction of the walls are (from the interior) 12mm Fermacell, 38mm service void, 15mm taped OSB3, 300mm UdiFLEX wood fibre wool, 100mm UdiTHERM wood fibre board, 40mm UdiSPEED wood fibre board, 7mm UdiPERL self coloured render system. The U-value is around 0.1 W/m2K.

We’ve had a few issues with stability of the connection between the sensors and the computer which is logging data but we seem to have this under control now. Apologies for the holes in the data, hopefully this will disappear from here on in.

If anyone would like the data please contact us. I’ll host it in a public dropbox and send you a link.

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