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!

---

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).

---

[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.

---

[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.

---

[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.

---

[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.

---

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.

---

[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):

---

[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

---

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

Climate Cent Foundation → Stiftung Klimarappen