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.

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.

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.

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.

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

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

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

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 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.

Limits on the overall heat transfer coefficient through the building envelope

Figure 3. A simplified representation of the heat transfer coefficient limits for a few specific building components.

In general, the first step towards reducing energy consumption in a house is to use a lot of insulation. The lower the heat transfer through the building envelope, the better. One limitation to this is that the thicker you make your shell, the smaller you make your interior area. In the case of our house, we're probably looking at a minimum of 35 cm (≡ 14") thick exterior walls. This is for timber construction[1], construction in masonry or concrete usually ends up being thicker for the same insulating properties.

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[1] Actually, it is more appropriate to say "mixed" construction. About a quarter to a third of the shell will probably be of concrete because our building land is on a slope.

Two things the label does not include

A couple of points that I think are important to note. - The label certification is based on the projected energy consumption of buildings. There is no oversight of the actual construction and subsequent usage. The good news is that a study[1] in 2004 (see graph below, remember that 1 MJ ≡ 0.28 kWh) carried out by the University of St. Gallen of about 500 certified buildings showed that single family homes (SFH) and renovation projects typically were better than the standard prescribed. Newly constructed larger residential units (MFH) fell short, though not by much. There have been a lot of developments and many lessons learnt since the time the study was conducted, and I think things are much improved. Figure 2. Results of a survey of Minergie-certified residential units conducted by the University of St. Gallen in 2004.

- A second important point for me is that the requirements say nothing about the consumption per person. They just set a limit on the amount consumed per heated square meter of floor space. To make an extreme comparison, person A can have 300 m² to himself or herself while family B with 4 members can live in a 180 m² house and both houses can be Minergie certified. For a vision of a per person consumption limit see, for example, the 2000 Watt society project.

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[1] A copy of a presentation of the results (in German) can be downloaded here: Minergie Praxistest 2004.

Simple representation of the basic points

Figure 1. A simplified representation illustrating the main points of a Minergie house.

The current maximum for the weighted energy demand of a single family house is set at 38 kWh/m² per year in the Minergie category. The weighting involves the type of energy source that is chosen to meet the heating demands. Direct solar energy is highly preferred while electricity from the grid[1] is not. More about this later.

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[1] I make this distinction because electricity generated via a photovoltaic system is viewed favorably.