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