043. The 2009 Solar Decathlon winner is Team Germany

A little diversion away from our house building story. I had the pleasure of visiting the first Solar Decathlon competition in Washington DC back in 2002 and now I try to follow it "virtually". The winner of the 2009 competition is Team Germany from the Technische Universität Darmstadt with their surPLUShome. Incidentally, Darmstadt is the home of the Passivhaus Institut I've mentioned on this blog before.

Here is a description of the event from Wikipedia:

The international and biennial event is sponsored by the United States Department of Energy and the National Renewable Energy Laboratory (NREL). Competing colleges and universities build solar powered homes and operate them on the National Mall for 3 weeks every other year.

The point of the competition is not to create new building technologies. On the contrary, entrants have to use commercially available products to demonstrate that a sun-powered home can be commercially reproduced.

Link → US Department of Energy's Solar Decathlon Homepage
Link → Team Germany Homepage

042. From Minergie to Minergie-P (rejoice!)

Figure 33. The new calculated energy balance for the house. The numbers are in kWh/(m²). Compare to figure 23.

Back in April I had started to write a little about the calculations of the projected energy usage that had been done based on the components making up the house. Since then much has changed and the structure of the house is now going to be made entirely of wood[1]. The windows have been upgraded to have better energy performance. We also have a new energy planner who is a better fit for our project. He changed the heat pump to a better-tested model, added 4 m² of solar collector (for hot water) and an Erdregister (earth tube heat-exchanger). The result of all these changes is that we now have an optimized system with lower numbers. Numbers that put us firmly in Minergie-P territory!! Read on for more information...

First, the quantities listed in the diagram above are:

- Q_iP: heat generated by the residents.
- Q_iE: heat generated by the electrical equipment.
- The total internally generated energy is Q_i = Q_iP + Q_iE.

- Q_S: heat delivered by the sun.
- The total gain Q_g = Q_i + Q_S.

It is assumed that only 60% of Q_g can be used by the house:
- Q_g,u = 0.60 Q_g
- Q_V is the energy lost through the ventilation system.
- Q_t is the energy lost via transmission through the shell.

Also back in April, in post 021, I had written about the requirements of Minergie. Here again is the relevant equation (refer to the old post for details):

With the new construction plan, the various energy demands are computed to be:
Q_H,eff = 13.9 kWh/(m²·a)
Q_WW = 6.7 kWh/(m²·a) and the rest is met via solar energy
Q_V = 2.51 kWh/(m²·a)

This gives a weighted energy demand of 20.7 kWh/(m²·a). The limit for Minergie-P is 30 kWh/(m²·a), so we are comfortably within this requirement. This is great news!

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[1] In the earlier plan, the lower level was going to be made of concrete and bricks, and the upper level out of wood.

041. The excavation

Figure 31. The excavator operator checks his work against the plans from time to time. Figure 32. The trench for the sewer pipes has been dug.

040. Preparation of the construction site

Figure 30. View from the south-west, looking at the excavator sitting on the north part of the land.

A lot of things have happened over the last couple of months but I wanted to wait until the dust settled (so to speak) to do an update. It's high time for it now, as yesterday the ground preparation work started.

We hadn't had the land mowed in months and the ground cover was really quite dense so the first thing that was done was that the sod was turned over using this excavator. I think most of the top layer will be stored on the site, to be used to fill in after the construction ends. The material that is dug out from lower down will have to be transported away and dumped.

039. Back to the heat pump

There was a misunderstanding somewhere and it appears that the overall cost for the district heating system would exceed that of the version with a heat pump. I still don't understand this clearly so I obviously cannot explain it. So, it's back to the air-source heat pump, though perhaps not the one by Heliotherm.

I'm looking at some of the results of performance tests of these devices done by independent labs[1] to see if I find a favorite. One new issue that I've become aware of is that our technical room[2] is a little on the small side. The heat pump and its associated plumbing will fit, but we really could use the space if we can save it. Also, this type of installation requires large openings from the room to the outside and because this room is partly underground, construction elements called Licht- or Kellerschächte[3] have to be used. I have a great aversion to these things, partly from the maintenance point of view. To circumvent both these problems, I think a unit that is installed outside the house is called for (we had been considering only internal units so far). I have yet to find any indications that they're less effective than the ones installed inside.

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[1] One such facility is in Switzerland → Wärmepumpen-Testzentrum WPZ.

[2] Here's a link to an old sketch → Figure 7g. The lower level.

[3] I'm not sure these things even exist in the same form in the Anglo-world. You can do an image search with the keyword "Kellerschacht" or "Lichtschacht" to see some examples.

038. District heating instead of a heat pump

Back in March (link to the post here), I had written that we would be using a heat pump made by a company called Heliotherm to heat the house and warm water. That model had been suggested to WA by the company that did the first round of energy calculations for us. Since then, there have been some significant changes in the construction elements, and a new energy calculation is being done by a different firm. Also, a new opportunity became available in May, that of district heat[1]. Earlier in the year REFUNA, the company that runs this network, was in the process of adding capacity and they couldn't promise that they could serve us. By May they were able to give us a positive answer.

The advantages of this type of heating system is that they're generally more energy efficient and cleaner than local systems and boilers. They take up less room for installation and are very low maintenance. Wikipedia had a good write up on it, see the link in the footnotes below. In our case, the costs associated with the installation and hook-up should be below that of what it would be for the heat pump system because a lot of the necessary earth removal work will have to be done for the other connections anyway.

I'm actually very pleased about this development as I was not so happy about the air-source heat pump. At very low ambient temperatures, they basically become electric heaters.

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[1] District heat is also known as waste heat, or utility-supplied heat. The term in German is Fernwärme, literally "distance" heat or warmth. REFUNA gets its heat from the waste heat of the nuclear reactor in Beznau near where we'll be. The Wikipedia article mentions this → District heating

037. Design consideration: wall finish

This is a case where we've had a really big change in our opinion, catalyzed by the suggestions of WA. Our original thought was plaster walls painted white (or in shades somewhere between white and grey in some rooms) with a dark industrial-type floor (more about the floor in another post).

WA suggested that this combination is a dime a dozen and that a much better choice for our house would be to leave the wood of the construction elements visible. Our first reaction to this was quite negative as the examples we had seen so far were too rustic and we didn't really like them except maybe in small chalets surrounded by fields of snow and pine trees. This discussion kept coming up and we kept shaking our heads and finally we went to see a house with an application similar to ours. Actually, if I understand it correctly, ours will be one grade higher than what we saw. The manufacturer, Pius Schuler[1], has recently started producing panels with knot-free, A-grade wood on the visible side which is quite smooth and we were pleasantly surprised and agreed that it does look very nice and airy. The company also has a planning service and they're (re)designing the walls for our house right now. I'll put up detailed drawings once the design is decided. Quite possibly the energy performance will be much better than that of the version I had written about before. More on that topic later.

Figure 28. A close up of a AB-grade Pius Schuler panel in spruce and fir. One half of the panel has been treated with a UV protectant to prevent darkening. Figure 29. Interior of a house built using Pius Schuler panels in larch. Our version in spruce or fir should be lighter, and have less variation in the strips. More images can be found at the Schuler website.

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[1] Pius Schuler is well-known in the Swiss low-consumption wood construction circles → Examples of houses built using Pius Schuler wall elements

036. Design consideration: window shades

I've mentioned a few times already that it is crucial that a good plan be made for shading the (transparent elements of the) house from the sun in the summer to avoid overheating. Generally speaking, this topic is especially relevant in these times of rising global temperatures and there is a strong effort underway to find the best (low-energy) solutions. Organizations such as the European Solar Shading Organization (ES-SO) have some information in English on their websites[1]. Minergie in Switzerland provides guidelines for good practice. See Figure 22 in Post 29 to get an idea of the size of the problem for our house, as calculated for a particular set of parameters.

The German Institute for Standardization (DIN = Deutsches Institut für Normung) provides a useful listing of the rough efficiency factors for different types of shading systems as given in Table 4 below (visit the ES-SO link to see illustrations of these systems). Of course, the actual numbers will vary with the details of the type of materials used. In general, the best systems are those that are installed outside the glazing. For residential applications, roller shutters[2] seem to be the usual choice over here. Aesthetically they're not my favorite as I find them chunky and obstructive. A better alternative are external venetian blinds, with adjustable louvers that allow a view of the outside. They're rather high-maintenance from a cleaning point of view but WA assure us that in our locality we won't have to clean them more than once every couple of years.

Table 4. Solar gain reduction factors for different window shading systems. Smaller is better. Source: DIN 4108-2

	Reduction factor
Type of shade	Fc
No shading	1
Internal installation or between the glass panes
White or reflective surface with low transparency	0.75
Light colors or low (less than 15%) transparency	0.8
Dark colors or high transparency	0.9
External installation
Rear-ventilated adjustable louvers	0.25
Blinds and materials with low transparency, rear-ventilated	0.25
Blinds, general	0.4
Shutters, roller shutters	0.3
Overhangs	0.5
Awnings, ventilated	0.4
Awnings, general	0.5

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[1] A nice list of the different types of shading systems can also be found at their site → European Solar Shading Organization

[2] Actually, I'm not sure this is the right term for the objects I'm thinking of which are called Rollläden in German

035. Design consideration: roof and facade

There are so many details of the house under consideration right now that it doesn't make sense to talk about them until we come to some sort of agreement. I'm going to try to write updates as we get close to decisions, to keep a record of the evolution of the process. First up, a discussion of the choice of roof and siding material.

The unusual angular shape of our house demands a smooth transition between the roof and the walls. Ideally, the cladding should be of the same material and this limits the choice to slate, metal or fiber-reinforced cement board[1]. Factor in the cost, and only the last option remains.

In Switzerland there is only one[2] supplier for this material: Eternit. Eternit cladding stock is composed (by volume) of 40% Portland cement, 11% limestone powder and similar, 2% reinforcing fibers such as PVOH[3], 5% process fibers, 12% water and 30% air in the form of pores. The precursor to this material used asbestos fiber, but since 1991 all Eternit products have been asbestos-free. For more information on asbestos cement, see the report at the link at footnote 2.

I haven't been able to find a good example of an unconventional house completely clad in Eternit boards in a way similar to what we're considering, so below are a couple of examples in slate where the roof-wall differences are eliminated. The details here are not important (for example, our house will definitely have gutters), the point is that the same material covers all the surfaces and the format of the tiles is uniform over the two building elements (roof and walls).

Figure 26. House in Wallis by Nunatak Sàrl Architects[4].

Figure 27. House in Basel by Luca Selva Architects[5].

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[1] Faserzement in German, I'm not sure of the generally accepted English translation. Fiber cement board and fibrated concrete are some of the terms I've come across.

[2] An Austrian named Hatschek invented fiber cement (using asbestos) and patented it in 1901. He licensed the production method to only one manufacturer per country and it seems to remain that way. More information can be found in this report which deals with the asbestos aspect → The Tragedy of Asbestos

[3] PVOH is a synthetic polymer → Polyvinyl alcohol

[4] Details at ArchDaily → Zufferey House

[5] Details at ArchDaily → House in Lupsingen

034. The one that got away

I should say: the one we let get away.

Once in a while, I like to look back at my collection of notes to see how things have come along since we embarked on this house project. I had mentioned before that our architects had originally (in November 2008) presented us with two distinctly different designs to choose from. In the interest of keeping complete records, here are a couple of drawings of the one that we decided against.

Figure 25a. Plan B upper level.
Figure 25b. Plan B lower level.

There were many things we liked in this plan, but in the end we happened to like the other one better. I would have selected this design if we had neighbors living closer to us. In that case, the secluded garden and courtyard would have been more desirable. What is not apparent in these drawings is that the garden and courtyard are actually on different levels (the stairs are not drawn in).

Given the particulars of our land, with the open southern exposure, we think that the design we chose (click here to go directly to the post where I discuss that) makes better use of it. I particularly like that all the rooms, including the main bathroom, have views out on that side.

Which one might you have chosen? Feel free to leave a comment.

033. Choosing planners

Over the last few weeks, our architects — I'll refer to them as WA[1] from now on — collected bids from various planning firms for specific aspects of the house. It seems that construction activity around Switzerland, at least in the part where we live, is still quite intense and several of the companies that WA have worked with in the past decided not to submit bids for our project. Even so, WA made sure there were at least two bids in each category and we had a meeting last week to make the final selections. The categories we covered were as follows:

- the Bauingenieur: the people who calculate things like the statics of the building, in particular the parts in the ground which must be executed in concrete
- the Holzbauingenieur: the people who will do the details of how to construct the house in wood
- the HLS-Planer: Heizung (heating) Lüftung (ventilation) Sanitär (sanitation)
- the Elektroplaner: responsible for planning the electrical network

Once these "third-party" plans are in, they'll be sent out for bids from firms that actually do the work, such as build concrete structures and install plumbing. Meanwhile, WA are looking at every detail of the house and re-evaluating them, looking for the best solutions. New ideas are still being considered. I'll be giving updates here as things are finalized. We had not realized that so much designing would be done after the Vorprojekt (initial project) phase and I must say that we're really, really pleased with all the effort. This is our first experience working with architects and so far it has been excellent!

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WA → Walker Architekten

032. Our provisional Minergie certificate

Figure 24. Our provisional Minergie certificate.

Earlier this week we received a provisional approval from the Minergie certification agency of Aargau for the proposed construction plan for our house.

We will meet with our architects next week. In addition to working on the details of the house, they've been collecting bids from specialized planners for things like the concrete construction and the electrical network. With the help and advice of the architects, we'll choose the planners we want to work with.

031. The energy balance

Figure 23. Illustration of the calculated yearly energy balance for our house. The numbers are in kWh/(m²).

In posts 027, 028 and 029 we looked at the heat flow into, and heat flow out of, the house on a monthly basis. The information is then put together for the year to calculate the yearly energy demand of the house. A depiction of this can be seen in figure 23 which is an illustration based on one generated by a software package called NOVA[1] which is what our energy planner used. Note that the diagram is not to scale!

The quantities listed in the diagram are:

- Q_iP is the heat generated by the residents.
- Q_iE is the heat generated by the electrical equipment.
- The total internally generated energy is Q_i = Q_iP + Q_iE.

- Q_S is the heat delivered by the sun.
- The total gain Q_g = Q_i + Q_S.

Only 69%[2] of Q_g can be used by the house:
- Q_g,u = 0.69 Q_g

- Q_V is the energy lost through the ventilation system[3].
- Q_t is the energy lost via transmission through the shell.

The box labelled WRG (Wärmeruckgewinn) represents the heat recovery aspect of the ventilation system. I think the term E_hww represents the electrical energy required to run the heat pump and related equipment that we have planned. Q_r and Q_L must give an indication of the amount of energy that is extracted from the environment (the air in the case of our air source heat pump).

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[1] NOVA is made by → Plancal AG

[2] I don't know how exactly this number is computed.

[3] This number is calculated using an Aussenluftvolumenstrom of 0.37 . I will try to explore this on the blog at some later point.

030. US Passive House Institute

I just stumbled upon a sort of companion site in the US to the German Passivehaus Institut. Complete with a discussion forum. It never came up on my Google searches for some reason. Lots of good ideas about construction, even if you're not planning a passive house.

The site is here: Passive House Institute US
The discussion forum is here: PHI-US bulletin board

029. The energy balance of the house: losses and gains

Figure 22. Heat lost and gained by the house.

At the simplest level considering conservation of energy, once we have the house at a temperature we're happy with, we want to balance the heat gain and the heat loss so as to maintain a steady state on the inside. In figure 22[1] the blue line represents the total heat energy that is lost from the house through ventilation and transmission (details at → post 028) and the red line depicts the total heat energy that is added to the house, mainly through solar gain (details at → post 027).

It is clear from the graph that in the winter months more energy flows out of the house than flows in. In order to maintain a constant temperature[2] we must add heat and the blue shaded regions represent roughly the amount of heat that must be added[3]. In the summer, the situation is reversed unless some action is taken to suppress the gain. For example, by shading the windows as they're responsible for the largest amount of gain in our case[4]. Another way to cool the house is to bring in cooler air from the outside during the nighttime. Both of these can be automated to reduce "user error", e.g. a situation where we forget to close the window shutters when we leave the house one summer morning.

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[1] The numbers here are raw numbers in that I have not included the effect of some weighting factors and such. They make a small difference.

[2] It is not true that we maintain the same temperature throughout the year. In the winter the temperature is taken to be 20°C (68°F). Exactly what the maximum summer temperature is taken to be, I do not know yet, however 22°C to 24°C (71°F to 75°F) is probably not unreasonable.

[3] The gain is pretty much maximized in this case. However there is room to play in the loss side of the equation, i.e. more insulation and reduction of heat bridges. As with most things, it's a matter of optimizing the system within the parameters of affordability.

[4] If we happened to run a computer farm at home, we'd have to implement some additional cooling methods.

028. The energy balance of the house: losses

Figure 21. Heat lost from the house.

In the previous post I showed the calculated heat gain for the house. Here we have the calculated heat loss, based on walls and roof (opaque elements, as they're called) with a heat transfer coefficient, U, of 0.13 W/(m²·K) and windows (transparent elements) with a heat transfer coefficient of 1.3 W/(m²·K). One item under discussion at the moment is window upgrades. About 43% of the heat that is lost, is lost through the windows. Reducing the heat transfer coefficient of the windows could have a significant effect on the total heat loss.

027. The energy balance of the house: passive gain

I've been slowing working my way through the results of the energy calculations that the energy planner did for the house based on the provisional plans. The document is about 60 pages long. Parts of the input information and intermediate steps in the calculations are not in it so I first have to try to reconstruct it. Then I can put the information together in a format I want for the purposes of posting here. Let's start to look at the calculation of the energy balance of the house in parts. I won't go into a discussion of the details right now there are already sites[1] where that's done.

Figure 20. Heat gained by the house passively.

Figure 20 shows the passive heat gain predicted for the house, broken down by month. I believe this is before the sun-shading system is taken into account for the summer months. It is clear that without the proper system to suppress the heat gain in the summer, the house would become unbearably hot. Note the drop in June. This must be related to the input data (see figure 16[2] in post 024) and my first reaction was to think this can't be real. However, I've found a similar thing in a plot on another site[3] so it's still an open question for me. On the other hand, it's not really very important.

As I understand, these detailed calculations are usually only done for passive houses, i.e. houses with energy demands that are about half —15 kWh/(m²·a) instead of 38 kWh/(m²·a)— of what ours is going to have. These houses have such low heating needs that the heat generated by people[4] and appliances have a substantial influence. In the graph the lowest two lines represent these internal heat gains. The heat output of a person is taken to be 70 W and a daily 12 hour presence is assumed. The appliances are estimated to contribute 15 kWh/(m²·a). The heavy grey line at the top is then the sum of the solar heat gain and the internal gain. In my next post, I'll talk about the other side of the energy balance (the losses) and the need for additional heating.

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[1] One good example is here (in English) → Energy Balances Passive House

[2] Direct link to figure 16 → Solar data from Buchs

[3] PHPP → Passive House Design Package

[4] One passive house joke is that if you feel your house is too cold then you can invite a few of your friends over for dinner to warm it up. We'd have to invite a dozen or so.

026. Reworking one version of the American Dream

Figure 19. Michelle Kaufmann's mkSolaire house with a 'nutrition' label (see text).

Here's another little aside while I put together another post. To a small extent, I've been following the housing industry in the US over the past couple of years and one of the few names that come up in discussions of environmentally-aware construction is that of Michelle Kaufmann[1]. She's an architect based in Northern California and she aggressively pursued a plan to design and build high-quality, energy-efficient homes in a kind of modular framework. In the last five years her company realized some 40 single family homes in this style. Sadly, the economic downturn has forced some of her supplies to close and has made this aspect of her work unsustainable. In her own words, as published on her blog[2]:

“However, we have always known that to pull off our mission, it requires scale. We always believed it would be our company to do the scaling. We were well on our way to do so. However, in this current economic climate, scaling for a small company has proven to be difficult.”

A visit to her site makes clear her commitment and thoughtfulness to improving building quality. While there are not a lot of hard numbers on her site, last year she published a white paper[3] presenting the idea of what she called 'nutrition' labels for houses (similar to the European Union energy label[4]). Figure 19 above shows an example of this. With her dedication and her interest in this area, I'm certain she'll be forging ahead with her new projects.

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[1] Her website is here → Michelle Kaufmann Designs

[2] The blog post is here → The end of one dream and the beginning of another

[3] The PDF can be downloaded here → Nutrition Labels for Homes

[4] Wikipedia entry → European Union energy label

025. The land in May

Figure 18. A cat's view of the land from the street, looking towards the south.

I've been involved in several different tasks at the moment and haven't been able to spend much time on the house project. To let you all know that I'm still involved with the blog, here's a recent photograph of the land with the Bauprofile poles in the ground. They'll be removed the first week of June.

024. Solar radiation intensity over Switzerland and our region

Figure 15. Annual solar radiation over Switzerland.

Solar radiation is a major source of energy for our house. Here is an overview of how much energy is actually available to us from the sun. The map in figure 15 (pvgis-solar-optimum) shows the yearly sum of irradiation available to optimally inclined collectors in different parts of Switzerland. The high intensity regions in brown in the south are the Alps. Our house will be in the north near Zürich, in one of the least sunny areas of the country. But, there is still quite a bit of energy to be gained as can be seen in the graph in figure 16.

Figure 16. The monthly solar radiation measured at our reference weather station in Buchs, broken down by the cardinal directions. That drop in the intensity in the south in June is strange. Must look into that.
Figure 17. The average monthly temperature.

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Data and calculators covering most of Europe is available here → Photovoltaic Geographical Information System

023. Where our electricity comes from

Figure 14. Breakdown of the electricity sources in our locality.

As our plans currently stand we will be using electricity to cover the parts of our energy demand that are not met by either solar gain or the energy extracted from the environment via the heat pump.

In the locality where we're building the major share of the electricity supply is from nuclear power plants. About three-quarters of that is generated domestically while the remainder is purchased from abroad (most likely France). In the hydroelectric and renewable group, hydro actually accounts for most of it. Only about 0.01% of the total supply comes from sources such as wind, biomass and photovoltaic arrays.

About 2.7% of the supply comes from waste. There are facilities that incinerate garbage (Kehricht-verbrennungs-anlage = KVA, aka Müllverbrennungsanlage in Germany) and use the energy from the process to produce both electricity and also provide heat for direct use (Fernwärme which can be translated as district heat). One such facility in the region is in Turgi near Brugg and they serve a total of about 200,000 people. They generate 7.7 MW of electricity and 18 MW of thermal energy for the Fernwärme system. District heat could have been a possibility for our house[1]. The problem is that the connection costs are rather high.

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[1] Using district heat would lower our weighted energy demand to 33.2 kWh/(m²·a) from the 35.7 kWh/(m²·a) calculated → here

022. Approved

Figure 13. The stamp of approval.

A short update on what's been happening: Our building application has been approved by the local building commission. Now we get down to the real details.

021. Calculation of our energy demand (Minergie-Nachweis)

We received a copy of our Minergie-Nachweis (der Nachweis = certificate), computed by an energy planning firm, several weeks ago and since then I've been busy with the different aspects of it. What this is is the calculation of the projected energy needs of the house and how they are to be met. It's a detailed document with inputs ranging from the location and orientation of the house (to calculate the solar gain and also heating needs based on the average monthly temperatures) to the construction details of the connection between the walls and the foundation (to calculate the amount of heat lost through thermal-bridges[1]). Not all the details are finalized yet; however no subsequent change should increase the heat demand so let's take a look at the end results of the calculations. I'll explore the individual parts of the work-up later as time permits.

I'll start off by referring to these two old posts where I had talked about the Minergie limit on the weighted energy demand: The weighted energy demand The weighted energy demand, part II

We had the following relationship (click on the equation to see a larger version) which states that the weighted energy demand of a standard Minergie house may not exceed 38 kWh/(m²·a). So per year,

where (i) Q_H,eff is the amount of heat required to maintain a comfortable indoor temperature (usually taken to be 20°C) (ii) Q_WW is the amount of heat used to prepare hot water, and (iii) Q_V is the amount of energy required to run the ventilation system.

The g terms are the weighting factors for the particular type of energy source chosen and the η's (eta) are (or are analogous to) the efficiencies of the devices used. Small g's and large η's are good, for lists of some of the commonly used ones see the old posts.

For our house, the energy demands are computed to be: Q_H,eff = 31.4 kWh/(m²·a) Q_WW = 13.9 kWh/(m²·a) Q_V = 3.02 kWh/(m²·a)

You will note that this adds up to (31.4+13.9+3.02) kWh/(m²·a) = 48.3 kWh/(m²·a). This exceeds the limit of Minergie, but this is not yet weighted. Let's do that now. Some additional information specific to the heat pump chosen for the house is necessary for this step. The heating device is an air-source heat pump which runs on electricity and covers 100% of the room heating needs (η_H = 3.88) and 80% of the hot water needs (η_WW = 3.04). The remaining 20% of the hot water needs is covered by an electrical heater (η_WW = 0.9). Some of you might recall that the weighting factor g for electricity is 2.0. The weighted energy demand is then calculated to be 35.7 kWh/(m²·a) and thus satisfies the Minergie requirement. Here it is written out in equation 2 (click on the image to enlarge it):

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[1] Wikipedia entry on thermal bridges → Thermal bridge

020. Canton Aargau doubles subsidies for solar collectors and more this year

If you're thinking of building or renovating in canton Aargau, then this might be of interest. This year the subsidies for solar collectors and photovoltaic cells for homes have been doubled. In addition, there's now a subsidy to replace electrical heating systems with underfloor heating systems which use water as the heat transfer medium. Furthermore, for renovations of existing homes, the canton is doubling the subsidies given by the Klimarappen Foundation! The following is an overview of the items relevant to new construction. For more information, visit the links at the very bottom of the post.

Solar thermal collectors

Flat plate systems (Flachkollektoren)
CHF 3000.- for 4 m² to 8 m²
CHF 1250.- plus CHF 220.- per m² for installations between 8 m² and 15 m²

Evacuated tube systems (Röhrenkollektoren)
CHF 3000.- for 3 m² to 6 m²
CHF 1250.- plus CHF 280.- per m² for installations between 6 m² and 12 m²

Solar cells (Photovoltaic)

CHF 3500.- per kW_P for an integrated system
CHF 2900.- per kW_P for an add-on system
CHF 2500.- per kW_P for a free-standing system

Heat pumps (Wärmepumpen)

CHF 3000.- for either a ground-source or groundwater-source unit up to 20 kW

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Aargau Departement Bau, Vehrkehr und Umwelt → Fachstelle Energie (Aargau)

Climate Cent Foundation → Stiftung Klimarappen

019. A simple ventilation plan

This post follows from an earlier one in which I mentioned the Komfortlüftung mit Wärmerückgewinnung (comfort ventilation with heat recovery) system. The primary consideration for the indoor air quality in terms of designing a ventilation system is the amount of CO₂ in the air. On average, a person produces between 30 and 40 grams of CO₂ per hour. According to current Swiss building code, the concentration of this gas should not exceed 1000 ppm.

Figure 12. A simple ventilation scheme for a residential unit.

A schematic of the ventilation plan is depicted in figure 12 above. There are two parts, the supply and the exhaust and there's a heat exchanger (a topic for several other posts, no doubt) through which upto 90% of the heat of the stale air can be transferred to the fresh air. There's no physical mixing of the gases and an optional filtering system can remove pollen and dust from the incoming air. Odors though are another matter. The exhaust vents are installed in the kitchen and the bathrooms so that the air from these areas isn't dragged through the house. Fresh air is let into the living areas and the bedrooms. The system is configured to operate continuously during the heating period with an option to also run during the summer. People who live in noisy areas, such as near heavily used streets, can choose to run the system during the summer as well so that they can keep out the noise.

Based on the limit on the CO₂ concentration in the air, the recommendation is for an hourly intake of 22 m³ to 36 m³ of fresh air per occupant. A different method of calculating the intake that is independent of the number of occupants is to assign an hourly replacement rate of 30 m³ per room, except for bathrooms and kitchens which are designed to have a higher rate with a minimum of 40 m³ per hour. The sums of the supply and the exhaust must equal each other so that there's no pressure difference between the inside and the outside of the house, and so the higher rate of the two is chosen. This is best explained with an example: Consider a unit with 3 bedrooms and a combined living/dining room which is counted as 1.5 rooms, so a total of 4.5 rooms → 135 m³/h of fresh air coming into the unit. If there are 2 bathrooms and a kitchen then the exhausts from those add up to 120 m³/h. In order to not create a pressure difference between the house and the outside, the exhausts should be raised from the prescribed 40 m³/h to 45 m³/h per room.

I haven't mentioned anything about humidity in this post, though I have mentioned in the previous post that too much of it is a serious problem during the heating months in our current apartment where we must manually ventilate to avoid problems such as mildew associated with high humidity and cold surfaces on which condensation can occur. With the ventilation set-up described in this post, the usual result is that the air is too dry in the winter. Plants can help and there are certain types of heat exchangers that also recover some of the humidity from the outgoing air. Humidifiers are not recommended due to issues of hygiene and the additional energy usage.

Exactly how the system is going to be for our house is not yet defined.

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Much of the information here is based on that at the following site → Luftwechsel: Die Platform für Wohnungslüfter

018. Peter Zumthor receives the 2009 Pritzker Prize

Figure 11. Entrance to the Saint Benedict Chapel in Sumvitg, Switzerland. Photo by Luke Stearns.

I would be remiss if I didn't acknowledge this bit of news, even if it is a bit off topic. I've been meaning to visit some of his works for a while now but given their relative remoteness I haven't made the trips yet.

Entry on the Pritzker Prize website: 2009 Laureate, Peter Zumthor.

017. Ventilation in air-tight buildings

The air-tightness of buildings is great from the energy loss point of view but there are serious negative consequences on the indoor air quaiity that must be mitigated. Our personal experience in the conventional 1980s built apartment we currently occupy is that during the winter (i.e. the heating period when we normally have the windows closed) we get the best result by opening all the windows for about 5 minutes, usually twice a day. 'Best result' in terms of our own perceptions of things like humidity and staleness: we haven't done any tests to monitor the actual air quality and things like VOC[1] build-up. A little guide which came with our apartment suggests that we air out the place 'several' times a day, an expectation which we find a tad ridiculous. Not only is this impractical from a scheduling point of view, it also results in the loss of a heat energy through the replacement of the warm indoor air with the cold outside air. While this used to be an acceptable form of ventilation for Minergie homes, as of 2009 mechanical means of ventilation are required.

There are six different standard solutions to choose from and we are probably going to install what's called Komfortlüftung mit Wärmerückgewinnung (comfort ventilation with heat recovery), illustrated in Figure 10. I should mention here that the list also includes an automated window ventilation system, in which the windows are opened and closed by computerized motors and which does not incorporate heat recovery.

Figure 10. Schematic of a ventilation system which incorporates a heat recovery system.

Some people here have an aversion to centralized ventilation systems as they expect them to cause draughts throughout the house and harbor mold and bacteria in the ducts. The first issue is an easy one to address as the rates of flow in a properly dimensioned system are too low to be noticed and this is easily experienced by spending a couple of hours in a house with such an installation. The second one isn't quite so easily answered and one has to convince oneself that a duct system built and maintained to the current recommendations will provide good air quality. More about all this in the next post.

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[1] About volative organic compounds at the Minnesota Department of Health → VOCs in your home

016. An air-tight building envelope

We've already seen that the first step in making energy efficient buildings is a thick layer of insulation. Once the heat loss via conduction through the building shell is minimized, the amount of heat that is lost via air leaks in the shell becomes notable. Not only that, there's also increased risk of condensation around the areas of the leaks and consequently increased possibility of mold growth. With current technology, it turns out to be energetically favorable to make the shell 'air-tight' and incorporate a mechanical ventilation system equipped with a heat exchanger to replace the indoor air. More about this in the next post.

The air tightness of a building is quantified by measuring how many times in one hour the entire volume of air in it is replaced when the building is subjected to a pressure difference of 50 Pascals (1 Pascal ≡ 0.0003" of mercury). The test is called the Blower Door Test[1] and the quantity measured is called the air exchange rate and is denoted as n_L50. This test is mandatory for Minergie-P houses where n_L50 must be shown to be less than 0.6 [1/h]. In other words, it takes about 2 hours for the air in the house to be replaced by air from the outside. A mechanical ventilation system is required to refresh the air and I'll talk about in the next post. For plain Minergie houses this test is not required but it is expected that the level of air-tightness be less than 1 [1/h]. For comparison, consider that a 1989 survey of 35 Swiss timber homes done by EMPA[2] showed that they had an average air exchange rate of about 7 [1/h]. Current construction without special consideration to air tightness is somewhere around 3 [1/h].

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[1] About the Blower Door Test on Wikipedia → Blower Door Test

[2] Kropf F., et al. Luftdurchlässigkeit von Gebäudehüllen im Holzhausbau → EMPA Bericht 218, 1989

015. The Baugesuch

Figure 9. The Bauprofile marks out the edges and corners of the building.

The application (Baugesuch or Baueingabe in German) for our building permit (Baubewilligung) was recently submitted to the local building commission. It includes blueprints of the house, plans for the connections to the water, sewer and electricity supply lines and an analysis of the energy usage (Energienachweis). In addition to these things one is also required to physically mark out the corners of the proposed building on the land as shown in figure 9 above. This is known as the Bauprofile (aka Baugespann or Bauvisiere and it allows the commission and other interested parties to visualize the building and easily ascertain that none of the building limits are exceeded. As part of the approval process a period of time, usually two or three weeks, is set aside to give the neighbors the chance to file objections or concerns. There's a form for this and the objections (Einsprache) have to be submitted in writing. Naturally, we're hoping that there will be none against our plans. It's an interesting process.

The weighted energy demand, part II

Yesterday's post was about the calculation of the energy demand of a house and the weighting factors assigned to different energy sources. Another factor that must be taken into account is the efficiency of the particular device, e.g. a furnace, used to produce the heat energy. A note on terminology: In the case of heat pumps, the word efficiency is not accurate and the phrase coefficient of performance[1] is used instead.

It is important to note that these are the "standard" values accepted in the Minergie system. There are heat pumps which beat these numbers and our architects have recommended one of the best performing models on the market. The COPs for the air-source heat pumps made by this company[2] are claimed to range from 3.56 to 4.2, depending on the particular model. I plan to write a post about these systems before too long. Update 23 August 2009: Instead of a heat pump we will probably use district heating. Please see post 038.

Table 3. Efficiencies or coefficient of performance (COP) for a selection of different heat generating systems. Larger is better.

	Heating	Warm (hot) water
Source	ηH	ηWW
Oil or gas furnace	0.85	0.85
Oil, condensing furnace	0.91	0.88
Wood-fired furnace	0.75	0.75
Wood pellet furnace	0.85	0.85
Waste (district) heat	1.0	1.0
Electricity	1.0	0.9
Heat pump, outside air	2.3	2.3
Heat pump, ground source	3.1	2.7
Heat pump, ground water	3.2	2.9
Photovoltaic	0	0
Solar collector	0	0

The effect of this weighting system can be seen in figure 8 below. The standard values for the weighting factors for the different energy sources have been used here to compare the different results for the same house. I've left off the numbers on the graph because I just want to give an idea of the relative differences. A process of optimization leads to the the best solution for a particular house.

Figure 8. The weighted energy demand calculated using different energy sources.

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[1] Read about COP at this Wikipedia page → Coefficient of performance

[2] The company is Heliotherm → Heliotherm air-source heat pump

The weighted energy demand

All this talk of insulation, but I haven't yet gone over the fundamental point of Minergie which is to reduce the energy demand of buildings, in this case our house. I've mentioned several times that the limiting value for houses is 38 kWh/(m²·a). Then the question is how this energy demand is defined. Different systems of certification (e.g. the German KfW-40) have different ways of calculating this and in the Minergie system under consideration here it is a weighted sum of the energy required to
(i) maintain a comfortable indoor temperature (usually taken to be 20°C), call this Q_H,eff
(ii) to heat water Q_WW and
(iii) to run the ventilation system[1], Q_V.

We have the following relationship (click on the equation to see a larger version):

In Equation 1 the g terms are the weighting factors for the particular type of energy source chosen and the η's (eta) are (or are analogous to) the efficiencies of the devices used. You can see from the inequality that small g's and large η's are good.

More about the η's in the next post, here I'll just say a few words about the weighting factors g. This is where the differences in the different certification systems become apparent[2]. They are basically an attempt to compare the losses associated with the conversion of the energy from different sources to heat (see Table 2 below for the list). Burning fossil fuels to generate heat is taken to have a g of unity. Using the sun directly, as in absorbing the radiation and storing it as heat 'costs' nothing so it is given a weighting of 0. Using electricity, say to run a heat pump or (horror!) a resistance heater is considered least desirable (I imagine because the electricity itself is generated from other sources and there are losses in that chain of production and in the transmission). However, in the case of heat pumps this is mitigated by the ability of these devices to extract energy from the surroundings and this should be clear in tomorrow's post. The energy source to run the ventilation system is almost certainly electricity. A typical value for the Q_V is between 3 kWh/(m²·a) and 4 kWh/(m²·a).

Table 2. Weighting factors for different energy sources. Smaller is better.

	Weighting factor
Source	g
Solar, geothermal, ambient	0
Biomass (Wood, biogas)	0.5
Waste heat	0.6
Fossil fuels	1.0
Electricity	2.0

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[1] A little aside about the ventilation system: The aspect of the building envelope that I've talked about so far, namely the insulation, deals with the loss of heat via conduction through the shell. Another very important mechanism of heat loss is the movement of warm air from (i.e. leakage) and cold air into (i.e. infiltration) the house through gaps in the shell. In a well-insulated house, this can account for upto 50% of the total heat loss. It turns out that it is possible to neutralize this effect and still have good air quality by building a very tight shell and by relying on a high-efficiency mechanical ventilation system with a heat exchanger to capture back more than 80% of the heat of the exhaust air. A topic for other posts.

[2] An entry on the German language Wikipedia compares three systems: Primärenergiebedarf

Limits on the overall heat transfer coefficient through the building envelope

I've mentioned before that the first step in reducing energy consumption is to invest in a well-insulated building shell. Just like choosing a thick and warm winter jacket. I've also stated before that in the end what is important for the Minergie specification is that the weighted (I'll talk about this weighting very soon) energy consumption per unit area be less than 0.38 kWh/m² per year. It is possible to achieve this by adjusting the different factors that play into this equation and to simplify the matter the Minergie group has come up with a set of "standard solutions". The limits given in the table below are those for the building elements. It is possible to build a Minergie house with components that exceed these values but make up the difference in other ways. In fact, not only it is possible, it seems to be often the case. This clarifies some of the confusion I had in earlier posts.

Table 1. Limits on the total heat transfer coefficient for building components.

	Separation from exterior	Separation from unheated interior	Separation from ground
	W/(m2·K)	W/(m2·K)	W/(m2·K)
Roof	0.15	0.20	-
Wall	0.15	0.20	0.20
Floor	0.15	0.20	0.20
Window	1.00	1.60	-
Door	1.20	2.00	-

Minergie vs the average building

I find it useful to remind myself from time to time what it is that we're doing that's different from conventional construction. If you haven't already, download the following flyer (in English) from the Minergie website. It seems to be a little outdated[1], but there's still useful information. Clicking on the link should start the download of the PDF file: The Minergie Standard for Buildings

The standard requires that general energy consumption must not be higher than 75% of that of average buildings and that fossil-fuel consumption must not exceed 50% of the consumption of such buildings.

So what's an average building? Rather than try to describe that, I find it easier to consider the limiting value from my third post, figure 1: The weighted energy performance value of a Minergie house must not exceed 38 kWh per m² per year. See page 4 of the flyer for more information.

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[1] E.g. In this flyer which is edition January 2008, the U-value (the overall heat transfer coefficient) limit for the walls and roof is given to be 0.20 kWh/(m²·K), while as far as I can tell the 2009 standards set it to 0.15 kWh/(m²·K).

The wheels are in motion

Figure 7a. A rough representation of how the proposed house will sit on our land.

It was almost a year ago that we found a piece of land we liked and we initiated the process of acquiring it. We also started conversations with a selected group of Minergie-specialist builders in parallel. Back in those early days we were pretty sure that we would have one of these companies design and build our home. Their publicity materials assured us that they specialize in individual solutions and the combination of that with (i) the fixed-price guarantee they can offer and (ii) the good reputation for quality they enjoy is what interested us. As our discussions continued and we visited a number of houses they had built we realized that our individual solution would cost no less than what we could expect if we worked with an architect, with possibly a rather constrained design palette. We simply saw no examples that assured us that they would really build us something special. There was no doubt that they would build us a good, solid house, it was just that we were not convinced of their willingness to push the design envelope for us.

Figure 7b. The east elevation of our proposed house. Note how the land slopes off and the rear of the lower level is underground. The rectangular opening on the side is to the carport which is integrated into the building.

In the meantime I had compiled a short list of local architects based on examples of their work that I found either in magazines or through web searches[1] or actual houses I saw around our area. It was during this time that I decided that the websites of many architects left much to be desired[2]. In many cases the navigation is too cumbersome, the images miniscule or embedded in some fancy but slow-as-molasses display presentation, the information hardly useful. But there was one that stuck out for me. Both in the accessibility of the website and the aesthetics of the houses, especially the interiors.

Figure 7c. The north elevation. This is the side at street level. It looks a little menacing with the slits for windows. I'll say it: almost bunker-like. From the energy-loss point of view though, the north side (at these latitudes) is the worst and it makes sense to minimize glazing here. It's all made up for on the south side.

So one day at the beginning of last summer I plucked up my courage and popped into the office to make an appointment with said architect. Initially we had thought that we would want to talk with at least two architectural firms but we soon decided that we felt confident that this group would build us something lovely. So here we are now.

Figure 7d. West elevation. The door opens out from the kitchen. This side borders a public path connecting the two streets that can be seen on the map view so we'll have to have some sort of structure to provide privacy.

One of the wishes we conveyed to the architect was that we didn't want a "box". Boxes are very popular here right now, and it is true that they are more energetically favorable because the surface-area-to-volume ratio is lower than say, something enlongated. But, that's not the way we wanted to go. Actually, after our initial meeting where we set down our wants and desires and budget we were actually presented with not one but TWO very different plans. This was a very pleasant surprise. The version we decided against was also very interesting. It was more compact – it would probably have had better energy performance – and we felt it didn't make the most of the southern exposure of the land that we had. It also had a more complicated sunken-courtyard thing going on which was rather cool but we decided the simpler design would work better for us.

Figure 7e. The very important south elevation. This is where most of the solar gain will be made hence the plethora of windows. Here you can see the terraced garden on the left. The rest of the land we envision as a wildflower meadow, much as it has been until now.

It seems that issues of accessibility (as in this definition on Wikipedia) are on the minds of many people right now. It wasn't so different for us. We wanted a house where it would be possible to live on one level if necessary. So the upper floor at street level had to include a bedroom and a full bathroom.

Figure 7f. The upper-level floor plan.

A few words about the upper-level. The entrance hallway (A) can be closed off in the winter to reduce the infiltration of cold air. There's a built-in coat closet (B) with a glass inset on the stairwell side to let in light. The stairwell (C) is illuminated by a skylight. I haven't done the calculations yet (it's on my long to-do list) but my gut feeling is that a skylight provides more light per unit of heat lost through it than a similarly sized north-facing window[3]. The labels BF (Bodenfläche) and FF (Fensterfläche) refer to the areas of the floor surfaces and the window surfaces, respectively, in each room. There's a minimum ratio of 8:1 that is mandated for rooms in which people "live". As we have no real basement nor attic nor garage, we don't have many areas in which to accumulate stuff. There's a generous storage room (D) on this level which in combination with all the built-in wardrobes we have planned should cover all our storage needs and then some.

The division of the interior space was partly driven by my insistence on good natural light in all rooms, including bathrooms. Light shafts are frequently used to bring light into basement-type areas but I'm not a fan. This meant that on the lower level all the rooms had to be arranged on the south wall because all other sides lie underground, so to speak.

Figure 7g. The lower level.

The "technical" room is where the heating system, water boiler, air handling device etc will be located. It will be unheated and will lie outside the insulated hull of the house. Actually, the same is (obviously) true of the carport just above it.

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[1] Many of the architects are listed through this website: www.swiss-architects.com

[2] I'm not alone in this. See this Guardian blog post from January of 2008: Why are architects' websites so badly designed?

[3] If you know I'm wrong, please explain why.

Warm fuzzy insulation

Figure 6. The thermal conductivities of a selection of materials typically used as insulation in construction.

Generally speaking, the effective insulating value of a wall is really determined by that of the insulation used. This was the case of the wall I discussed in my last post a few days ago. The thermal conductivities, λ, of some of the commonly used insulating materials can be seen in figure 6. You can see that they range roughly from 0.025 W/(m·K) to 0.060 W/(m·K). For any given type of insulating material there's a host of products made in different ways and they can have different λ values. In some instances, the different forms are necessary for particular applications, for example, the physical requirements for flooring components are quite different from those for walls. In the graph, the areas represented by the solid colors depict the best (lowest) and worst (highest) measured products in these groups. The lone values at the top of the columns are to be used for those particular products that remain untested by an approved facility.

At the right edge of the figure I've included some other materials of interest. Things such as porous concrete have better insulating properties compared to regular concrete but they're still a long way away from what is necessary for a Minergie-type house. Walls made of them would be too thick. In the area of bricks, there are perlite-filled ones which have very good insulating properties. Poroton-T7 is one that is actually appropriate for Minergie homes. A wall thickness of 42.5 cm satisfied the required U-value limit of 0.16[1] W/(m²·K) for the Minergie-P house BE-028-P. A blog (in German) about the construction of this house can be found here.

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[1] If you're wondering why it's 0.16 and not 0.15 as I've been saying, I have to say that I don't know yet. I'm working on finding the answer.

A closer look at a wood wall

Figure 5. An example of a Minergie wall module. This one is by Isover.

I was not completely satisfied with the wall discussion from three days ago so I spent a little more time looking through the PDF of the Bauteilekatalog I had linked to. The big challenge of calculating the U-value for the type of construction I've shown here is that the layers making up the sandwich don't extend uninterrupted through the entire length. There is a lattice made of wood that runs through the assembly holding things in place and providing stability. Wood is a better conductor of heat (λ in W/(m·K) is between 0.13 and 0.18) than insulating materials such as glass wool (λ in W/(m·K) runs from 0.031 to 0.048) and these areas where there's wood instead of insulation constitute a leak for heat flow (a thermal bridge) from the warm side to the cold side of the wall. In poorly insulated walls they don't make a big difference but in well insulated ones they do. Unless these regions are taken into account, the U-value that is calculated is lower than the true U-value (remember that a lower U-value is better).

The walls for our house are currently being designed. In the meantime let's consider a Minergie-certified wall module. There are a number of these units from different manufacturers that are guaranteed to satisfy the requirements. This one is made by Isover[1], a glass wool manufacturer. It has a total thickness of 35.75 cm and a thermal-bridge corrected U-value of 0.15 W/(m²·K). (According to the product description the non-corrected value is 0.12 W/(m²·K) though my own calculations give 0.13 W/(m²·K) – I must be using wrong λ values for some of the components). Anyway, the breakdown of the components is as follows. I've looked up the λ values when not provided by Isover (the numbers in red) :

1. 12.5 mm at 0.25 W/(m·K) | Gipsbauplatte (gypsum board of some sort).
2. 40.0 mm at 0.032 W/(m·K) | Support lattice; installation space embedded in Isotwin.
3. 0.05 mm – too small to matter | Vapor retarder/air sealer Vario KM Duplex.
4. 15.0 mm at 0.12 W/(m·K) | OSB (oriented strand board is 95% wood and 5% binder).
5. 200 mm at 0.035 W/(m·K) | Isofix.
6. 30 mm at 0.06 W/(m·K) | Fiberboard.
7. 40 mm – not counted | Ventilation gap.
8. 20 mm at 0.14 W/(m·K) but not counted | Wood siding.

Isotwin has a λ = 0.032 W/(m·K) and Isofix has a λ = 0.035 W/(m·K).

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[1] Here is the page where I found the information: Isover.ch 24-201