//The article is a close observation of the first Passive House in Kranichstein in the winter of 2022/23. The original article, written by Prof. Dr. Wolfgang Feist, is in German and can be found here: Das Passivhaus Kranichstein im Winter 2022/23 besonders sparsam heizen //

Original article: Das Passivhaus Kranichstein im Winter 2022/23 besonders sparsam heizen (German) by Dr. Wolfgang Feist

The passage of an Atlantic low-pressure system has been announced for today – and there is even hope of rain. For days now, the outside temperatures have been permanently in the range where completely passive operation – no heating and no active cooling – is possible in a Passive House. Now operation is very conventional: if we feel that it is rather “warm”, we open the windows a little; if we feel rather “cold”, we close the windows again. This means that under typical Central European summer conditions, the temperatures in occupied rooms are between 21.8 and 24 °C (with the exception of the “server room”, which sometimes reaches 25.6 °C).

Under extreme weather conditions with hot, humid air that does not cool down to below 20 °C even at night, this standard mode of summer operation does not work because the cooling potential is absent also at night. Such conditions have been rather rare in Central Europe so far - but unfortunately, this will likely change due to climate change. The summary charts for June 2023 show that during the conditions prevailing between the 19th and 22nd June there was no significant cooling down at night. The days up to 22nd June could still be “managed”, so to speak, due to the high thermal inertia of the Passive House – we only put the climate split system into operation on one day, 22nd June, for around 9 hours, consuming a total of 3.04 kWhel (see blog entry for 23rd June). Since then, the active systems have been turned off again. The electricity generated by our own PV system totalled 453.5 kWh in June. The active cooling system consumed around 0.7% of this. In comparison, my computer consumed around 18 kWhel in the same period and the entire home consumed around 208 kWhel.

Charts: Overview of June 2023; top: available solar radiation; centre: outdoor air conditions; bottom: room temperature profile. Active cooling was operated for just 9 hours in June.

For the first few weeks of July, the weather forecasts predicted continuation of the cooler weather, meant that purely passive operation could continue. However, as the measurement data from previous years shows, only a small amount of energy is required for active cooling in the Kranichstein Passive House, even in extremely hot weather – the maximum in one summer month was 45 kWhel . Based on this experience, cooling in summer does not play a significant role in energy consumption in a well-insulated Passive House building – even if the number of tropical nights were to increase significantly in future. Another reference value: so far, the electricity consumption for heating in winter using the split heat pump has been between 665 and 1072 kWhel; this is the highest individual consumption in this building – although the Passive House standard places particular emphasis on low heating loads .

The interesting finding is that contrary to often heard views, even in a Passive House in Central Europe the heating demand is far more relevant than a potential summer cooling demand, simply because of the electrical energy required. However, what is even more important is that a potential cooling demand only ever arises if there is already excess PV-generated electricity. The demand for heating energy, on the other hand, may be at its maximum in winter precisely when there is a shortfall throughout Germany and wind energy also contributes very little electricity – the little PV electricity generated is then already needed for other applications. Heating is therefore the critical requirement in the future, even in energy-efficient buildings; this is another reason why it is advisable to reduce the heating demand of buildings – this is by far the most cost-effective measure for avoiding high loads in winter. The use of an efficient heat pump for space cooling therefore no longer constitutes a 'climate sin' today.

We now often hear apprehensions, particularly from many concerned citizens, that the tipping points of the climate system will be exceeded in 2, 3 or 5 years. The bad news is that if that really is the case, then we can no longer prevent this in Europe.

Is this really the case then? Currently, no one knows with certainty when exactly which tipping points will be reached. At present, it cannot be ruled out with certainty that this will already happen in the next few years. However, as far as I know from the current debate, this is rather unlikely (2 to 8%?) . Incidentally, we can reduce this probability by actually burning fewer fossil fuels now , but already we can no longer reduce the risk to “zero”. If we simply carry on as before then the probability will increase every single year on account of the rising CO2 content of the atmosphere - and over the course of around 40 years, reaching tipping points will even be quite certain. This is the reason why “construction” is not an acceptable solution at all, because it will almost certainly lead to tipping points.

More likely than a tipping point in the next few years is that the “boiling frog syndrome” will continue as before, resulting in more and more heat-related deaths in summer, wildfires, extreme weather, climate refugees and crop failures, and then in one to two decades we will barely be able to comply with the reparation measures. These are the typical collapse scenarios already depicted in the Club of Rome's world models. These are not very encouraging unpleasant prospects – but with one very important difference: we can still prevent this today! …and also reduce the remaining risk of catastrophes occurring earlier.

There is also a second equally serious risk: these are tipping points in the political situation. A large number of people lean strongly towards the increased prosperity model; so much so that they are even prepared to give up fundamental democratic principles to achieve this. This limits the speed and scope of truly comprehensive changes.

What else can be done?

1. As always in the event of danger: keep calm. Misdirected aggression very often exacerbates the situation additionally.
2. Be careful with communication: nothing will be achieved at all if 'climate activists' come across as preachers of doom à la “the end is nigh…” for a large majority of people.
3. Continue to be careful with communication: it must not be denied that there is a serious problem (the most serious problem of all). The sensible message is: “We have a major problem, we recognise the problem. However, we can still solve this problem; for that we must act sensibly to some degree. And some things that we have become accustomed to must be done better in future.”
4. Careful communication must continue: the message “we can still change that” (very specifically!) is a necessary part of communication, otherwise it will have the exact opposite effect, namely aggression on the part of the faction concerned about prosperity, and fatalism on the part of those concerned about the climate .

How can this be done?

1. Certainly by spreading awareness that one can also carry out errands on foot, not as a demand , but rather as a paradigm, by making it attractive. I personally have been using a bicycle for all local journeys for the past 50 years consistently. In terms of costs, it is barely of consequence if a split air conditioning unit has to be fetched via taxi, which does not happen so often.
2. Consistent shift from less efficient subsystems to highly efficient systems at EVERY available opportunity. These opportunities arise more often than most believe. These highly efficient systems are available and are no more expensive than the respective conventional renewal that is necessary anyway, and they generally bring a 50% reduction in CO2 emissions, often significantly more for the respective subsystem: more than 85% in the case of electric light vehicles compared to SUVs.
3. Consistent and rapid expansion of renewable energy (electricity) generation, at every opportunity . We need to work on this, and again: we must communicate this positively and make it attractive.
4. The swift transition to a plant-based diet is certainly also possible in a “step-by-step” way; that might be too slow, but at least it's a start. Here too, it is crucial that this is attractive, and it is also necessary to make vegetable cultivation attractive for farming.

If the will is there, some of the points mentioned can also be achieved very quickly where necessary. There will hardly be any shortage in production and materials s in this regard. Note: There are also some other approaches, but these simply aren't fast enough:

• the development of a nuclear fusion supply system has not even been technically demonstrated yet (an overly optimistic estimate is +7 years); planning a demonstration in earnest (+7 years); implementation on a broad scale (+10 years)

• the same is true for e.g. travelling wave reactors; the industrial manufacturing base for this would also have to be developed first

• the same is true for the extensive substitution of natural gas by hydrogen (completely new distribution infrastructure, which is already far more expensive than the natural gas network on its own; a maximum of 12% of the previous energy flow “passes” for hydrogen; and then twice as many wind turbines?)

• I won't explain any further approaches here; everything that requires enormous investments in infrastructure usually takes time, apart from all the concrete and steel which will always be required.

• Consistent application of the principle “if you do it, do it right”; e.g. roof renewal ONLY with an excellent level of thermal insulation AND PV – unless precluded due to shading. A subsidy for each, precisely for this purpose, and ONLY if consistent improvements are actually made; NOT for the total costs . Incidentally, this amounts to lump sums – e.g. £80 per m² of roof if the material requirements are met; not 20% of the (almost always) inflated total costs, which can easily amount to more than £1000/m² if the respective luxury solution is chosen .
• Support independent consultants . Unfortunately, the market is currently controlled by those who are able to spend the most money on advertising their products .
• “NOW” impulse programme for all measures that can be implemented quickly: e.g. cavity insulation (cheap, easy, effective, etc.) or solar energy systems for balconies (extended to solar panels on bus stops, PV on motorway noise barriers, etc.).
• A ban on combustion-based central heating systems : by the way, this was a fatal communication failure, also because many did not understand that this ONLY meant replacement in the case of already due renewals . Whether this would apply in 2024 or 2025 or 2026 is actually not decisive . The decisive factor is that the available alternatives should be attractive. And: they can be made far more attractive. Here is our clear analysis again: our advice to people is to stop relying on boilers that burn carbon fuels when the heating system is due for renewal. In other words, we now advise against coal- , oil and gas boilers, as well as biomass-fired systems. This will all become very expensive in the future because there will be no way around a carbon tax2 price, and a “renewable substitute” for these fuels will not be available to the required (enormous!) extent. So what remains on the positive list? At the top of the list is the heat pump, which allows the use of electricity, a considerable share of which will come from renewable energy, and some from “stop-gap” power plants, especially in winter. This is precisely where CCGT power plants can be used, the waste heat from which can be utilised via heating networks. Heat energy from a municipal network is therefore also a solution that we recommend. Addendum: We have analysed the effects on the electricity supply structure in more detail here: “ Increase in electrical load due to heat pumps (German) ”.

It will be 37°C in Darmstadt; today the thermometer already reached 34°C. A maximum indoor temperature of 23.5 °C was reached – again without any active cooling – in the top floor room on the western side (“home office”). Again, this was due to the fact that it cooled down really well last night (14° outside early in the morning). During the night from Saturday to Sunday this will be different, there will be very little potential for window ventilation at night. However, the internal heat storage of the building still has absorption capacity (now around 22.5 °C).

At around 3:00 p.m., the temperature had actually reached 37°C in the shade. However, by around 6:00 a.m. in the morning, the night-time temperature had dropped to 15°C once again. This meant that we could keep the core temperature below 22.3°C in the morning by opening the windows – under such conditions, the building remains reasonably cool during the day, despite the heat outside. Now, in the evening, it is 24°C in my “home office” under the roof; with only 53% relative humidity, this leads to a “predicted mean vote” PMV for thermal comfort of 0.0 according to the comfort standard, based on my clothing . Spot on! The indoor climate couldn't be better – without any active cooling, on the hottest day of the year so far. However, a tropical night has now been predicted, and it is expected that it will stay hot tomorrow and even on Tuesday. So things remain exciting: maybe I will operate the split unit again at some point in the next few days. However, it is already easy to recognise the summer pattern: under the current climatic conditions in the Upper Rhine Lowlands (Darmstadt), active cooling is only required occasionally on a few days to achieve optimal thermal comfort in a Passive House building. Even if we didn't have this, the temperature would only exceed 27°C for a few hours and would never reach 28°C. With an air conditioning unit, the temperature can be kept below 25°C on a sustained basis, and in addition, the unit is rarely in operation, with a power consumption that is still negligible. 25°C results in a PMV of +0.2 with the same clothing and Comfort Category A is therefore still achieved. To summarise: under the current summer climate, living in a Passive House building designed using the PHPP is usually very comfortable even without an air conditioner. If there is one, even the few days with temperatures above 25°C (up to 27°C) can be managed, and that with very little energy and costs, energy which, by the way, comes entirely from the building's own PV system, as does all the electricity during the daytime in summer. A surplus still remains, which is fed into the grid.

The ventilation system here conveys almost exactly 100 m³ of fresh air into the living areas every hour. This means that the air quality remains continually good, regardless of whether windows are opened or not (with three people in the home). This also proves successful in summer: while we leave the windows open at night (with the desired cooling effect), we close them in the morning when the outside temperature exceeds the inside temperature. It doesn't matter whether it's 1 degree up or down, because with such small temperature differences, the effects are only minor, so there's plenty of room for manoeuvre. Incidentally, the supply air from the ventilation system only reaches 26°C even at an outside air temperature of 37°C. This is because in this case the heat exchanger of the heat recovery system channels the heat from the outside air back into the outgoing exhaust air – the exchanger now works, to put it plainly, as a “cold recovery system”.

However, this time the night was really nice and cool here at this location. In the morning, after the nighttime ventilation the temperature in the house was around 23 °C everywhere, cool enough to comfortably cope with the following very hot day without any active cooling. The air conditioner therefore remained on “off”, despite an outside air temperature of 33 °C in the shade around midday. At around 4 p.m., the outside air thermometer even climbed back up to 36 °C. Once again it is clear: whether active cooling is at all necessary depends primarily on whether it cools down at night. If tropical nights follow hot days, passive measures alone may not suffice during the heatwave. This has long been evident from experience gained elsewhere . Incidentally, this is no different in the case of existing buildings; the only difference is that due to the shorter time constants, the series of hot days leads to quicker heating up, as a result of which the internal heat storage capacity is already 'used up' by the afternoon of the first hot day.

This came up in a discussion session with some highly committed climate-aware people: “Well, a room temperature of 15°C in winter is comfortable enough for me. Why can't we just do that everywhere in future?”

I want to address this question as objectively as possible here . Incidentally, I believe that we can indeed do that exactly, there is neither any reason to be afraid of that , and nor is it the only solution available to us without which the world would face destruction. From a purely thermodynamic and physiological perspective, this is technically 'doable' . I will also discuss what such a 'sufficiency measure' would actually achieve (spoiler alert: with the average condition of buildings currently, this would result in around 50% energy savings if 'everyone' did it on average) and why it cannot be rated as a** completely unacceptable, absurdly anti-social approach** from the outset, which is perhaps surprising for many. This becomes apparent as soon as we analyse exactly how such a 'new normal level of comfort' could be implemented technically, i.e. in terms of clothing. It will then also become clear why discussion on this is not 'permitted' in modern society even on a theoretical basis. Finally, I will discuss how this compares to other approaches and how it can be combined with them, at least to some extent.

First, the physiological facts: 15 °C, how cold is that?
With the dress code (winter, indoors) common today, 15°C results in an average comfort rating of 'cool' (minus 2.2) for seated persons; this leads to over 85% of the people in such a room complaining actively. This can mean considerable dissatisfaction, and those responsible will then be under so much pressure that they will try to heat the room additionally using all available means. Fanger once put it this way: “This can be discussed at length in theory. But the people affected won't be interested in this discussion. They will just complain – and the vast majority of them will agree that it is 'much too cold here'. A differentiated approach is used to discuss this in the following sections. However, we should always bear in mind that the current dress code is what it is – and would have to be deliberately changed. No one is talking about this publicly at present, and as most people know, there are good reasons for this.

The measurement and evaluation of thermal comfort perception is a well-established science: interestingly, it is very well documented and there is scientific consensus on it; keyword: Ole Fanger
The basics of assessing thermal comfort were brilliantly clarified in Ole Fanger's work “Thermal Comfort”. In it, Fanger established the generally recognised “comfort equation”, which is still the basis of the internationally introduced ISO 7730 norm today. We have explained these interrelationships in detail elsewhere: Thermal comfort zones. It is worth taking the time to study this in order to understand these relationships. After all, Ole Fanger not only made subjective standards quantifiable, he even provided a good model for understanding these phenomena and quantified the number of people who would find an indoor climate unacceptable.

Another interesting observation: Fanger's work triggered international research efforts, mainly because in many places researchers originally had quite different perceptions and did not really like Fanger's results. They therefore reviewed the evaluation tests carried out in their countries particularly critically and carefully: and they (all!) arrived at the same conclusions as Fanger, regardless of the skin colour, nationality, gender, age and social status of the individuals. Again, this will surprise many even today – but it becomes immediately clear as soon as we make a sincere effort to understand it

Thermal comfort and clothing: surprise, something's up
With some reflection, the relationship is immediately readily apparent: the temperature/comfort level depends crucially on clothing, and also on physical activity. This is undisputed, based on careful research studies. This relationship can even be quantified quite well: clothing is classified based on its thermal resistance, the modern unit for which is “m²K/W”, which is precisely the reciprocal of the thermal transmittance of the clothing . Fanger introduced his own “illustrative” new unit of measurement for this, which he called “1 cloth” and which corresponded to the average winter dress code in his state which was common at the time (which definitely included a jacket in winter). Without doubt, a society can agree on dress codes that keep people much warmer. In one form or another, initially this is by no means disadvantageous in objective terms: it is debatable whether I could still work properly at my PC in 10 cm of puffy polar gear – at the least, it would become 'awkward' at some point. Let's first take a sober look at what “dress code” would be required for a room temperature of 15°C in winter. For this, we will we use ISO 7730 to determine the appropriate clothing for 15°C. Two other pieces of information are required for this: the difference between the radiation temperature and air temperature, and the activity of the person. For the temperatures, we will assume for the sake of simplicity that radiation and air are in equilibrium and are approximately the same . For the activity, we will assume a “sedentary activity” because this is a frequent case at any rate. At 15 °C, the comfort equation then gives a thermal resistance of 1.85 cloth for the clothing. “1.85 cloth” – what does that mean in practice? Compared to 'normal' values in winter today (around 0.8 to 1.1 cloth), this is 'twice as thick' clothing, illustrated specifically by the following example outfit: “Long johns, long-sleeved undershirt, warm (flannel) shirt, flannel trousers, thick jumper, jacket, gloves (!).”

Let us take a look: it is immediately clear that first of all, almost everyone will answer “of course, that's how it's done” if we ask whether 15°C is acceptable. This comment is then somewhat cynically exaggerated: “Then we'll sit in the living room in long winter coats.” We know from personal experience that we can adapt to very cold conditions by wearing thick clothing. And that's exactly the point: after decades of doing things differently, this “new dress code”, which is perceived as extreme, is seen as unreasonable. That is people's predominant assessment in this regard – let us not fool ourselves, most of those who find it unreasonable are by no means extreme so-called 'unconventional thinkers', rather, they are mostly very good-natured, but are generally upset about this type of 'solution'. There is also a less good-natured segment of society, which is not that small, as we can see today; this segment will communicate this 'unreasonable demand' loudly and aggressively – and in doing so, will score points with many other people . This is a danger that I very specifically recognise and which I would try to avoid whenever reasonably possible. But now for my very personal 'assessment' regarding such an approach: over the last 70 years or so, prosperity has increased enormously for the vast majority of people living in highly industrialised societies . For example, the living space available per person has risen from less than 20 m²/person before 1960 to over 47 m²/person. Almost all of these spaces are now heated using comfortable central heating systems – which isn't really a 'cheap solution', but we have been able to 'afford' these almost without problem. Today, homes hardly ever have extremely cold single-glazing and are no longer equipped with furniture that has been mended several times inherited from great-grandparents. In other words, the promise of prosperity has actually been fulfilled to a very high degree. Against this backdrop, this kind of mass withdrawal of a component of prosperity by lowering room temperatures to 15°C would be completely anachronistic. It becomes even more so when we realise how little this really 'achieves' in terms of the problems we face today (see section below) and, above all, what alternatives to sacrificing comfort are available: alternatives that actually increase comfort and at the same time really solve the problems caused unintentionally due to unthinking material growth.

How can the potential of lowered room temperatures be categorised?
It has already been shown above that for an average residential building in Germany today (total building stock), lowering the temperature from around 22 °C to the mentioned 15 °C would result in a saving of around 50% in the heating demand. That is actually quite a lot – and this would reduce emissions even further, because the coverage ratio of renewable energy can then be increased and low-carbon fuels can be favoured (see here to find out how these values were calculated).

What about implementation in practice? Or, to put it another way, what percentage of the population is willing to go along with this, and to what extent? Since the summer of 2022, this is no longer a purely theoretical question in Germany: due to the stoppage of gas and oil supplies from Russia, the energy suppliers, the federal network agency and federal and state governments in Germany have explicitly called for “very economical behaviour”. This has never been seen before in this drastic form in the Federal Republic of Germany. In our blog post for 5th April, we explained that households and other “small consumers” have now actually achieved savings of around 15% in heating – in terms of total savings, which also include, for example, switching to wood-burning stoves or retrofitted insulation of pipes. Let us assume that this was actually due mainly to a reduction in room temperatures in the evenings. That would be a reduction of around 2 degrees, which would actually be a quite good “saving performance” . But what I also see is that, under the prevailing conditions, it is unrealistic to expect “more” of this, and certainly not on a permanent basis. Under enormous pressure due to circumstances, perhaps more may well be enforced for a short time – but at what cost?

Is there another way?
There are other approaches that allow less carbon to be burned for heating purposes which offer high potentials:

• Occupants can, for example, switch from gas heating to wood-burning stoves; some individuals have already done so. However, we now know that this tends to increase the environmental impact. More importantly, the potentials for total available biomass are low and have already been practically exhausted in Germany. The share of biomass heating will have to decline in the future , mainly because the use of scarce biomass potential for other applications has priority.

• Connection to local or district heating: we generally recommend this if such an option is available. However, heat generation for these networks will no longer be based predominantly on natural gas in the long term, there are significant still changes to be made. Germany currently has a district heating share of around 15%; this can be roughly doubled if a very committed approach is used. This therefore has a potential that is also roughly on a par with the contributions achieved through temperature reduction in winter 2022/23. The good thing about this potential is that it can be implemented sustainably and can be a permanent solution – without anyone having to worry about feeling cold at some point . However, it only 'solves' 15% of the problem; it is a contribution, but not a decisive one.

• Retrofitting heat pumps: in principle, this is possible for almost all of the 56% gas and 18% oil heating systems in Germany. Contrary to some perceptions, this cannot be done overnight, nor can it be done for everyone within e.g. six years – simply because the capacity of the relevant trade disciplines alone is nowhere near sufficient ; accelerating the rate of conversion beyond the already required replacement investments also does not make sense, because scrapping a boiler renewed in 2012 for example is not advisable in ecological terms – and it certainly is not economically feasible. In most cases, retrofitting takes place when the boiler is already due for replacement anyway. That precisely is the time for switching to a heat pump which we strongly recommend: it would be really unwise to install another fossil fuelled boiler again. Such a change will reduce the net CO₂ emissions of the relevant building by an average of around 75% over the next 26 years. This is much more than any of the measures already mentioned, around five times as much as the temperature reduction achieved in 2022/23 in particular, and even more than could be achieved by a general reduction to just 15°C. Thus there is no question: we recommend the change to a heat pump. One downside is that the practical solutions commonly chosen today are often quite expensive; financial support is only part of the solution here. Work needs to be done to make the solutions more cost-effective, and that is possible, as we have demonstrated using a whole range of solutions .

• Thermal protection of the building: based on our evaluations of modernisation projects, this has a potential of 75% on average and can also be implemented in almost all existing buildings (with the exception of listed buildings and new buildings constructed after 2002, as these are simply not “due” for modernisation yet). This measure also brings considerably more benefits than even a drastic temperature reduction. Thermal protection is also associated with improved comfort. It facilitates the subsequent switchover to heat pumps and makes it possible in the first place, and in any case, it is less time-consuming and more cost-effective. If well-conceived and implemented at the right time, thermal protection is an economically attractive solution. The ENBIL energy consulting software can be used for a specific building to quickly check which measures are suitable in each individual case and how much they reduce energy costs.

All of the other solutions mentioned here can of course also be combined with the “sufficiency measure” temperature reduction. The percentage savings achieved will then be even higher than with fossil fuel heating: heat pumps run more efficiently at lower (flow) temperatures, and with better insulation, the heating demand decreases even further than before with each degree. This is also documented under “What can temperature reductions achieve?”.

Conclusion: Temperature reduction may contribute to an overall reduction of perhaps 15 to 20% realistically; on its own, it cannot solve the problem. Ultimately, there is no alternative to switching to heating systems that no longer rely on fuels. These can be local/district heating connections or heat pumps, and on a smaller scale, a few rather exotic systems (less than 5%). However, the transition to heat pumps on a broad scale must be prepared and supported through improved thermal insulation, otherwise the electricity grid will be under strain in winter and even extremely accelerated expansion of wind power will not be able to keep pace. However, with step-by-step improvement of thermal protection, this is possible, but then the expansion of wind power should be implemented faster than originally planned . Comment added in 2025: the discussion about “extremely economical heating” has now been forgotten - after just three years. Room temperatures on average are not being lowered any further – they are being raised again. This is one example of the short-lived nature of issues in these stimulus-saturated times: short-lived reactions to events that are currently being exaggerated. If effective action was taken (e.g. by replacing the heating system or installing thermal insulation), the achieved saving would still be lasting; some are doing this, but we need to work on ensuring that more people do this.

In the evening on 11th July, the long-awaited thunderstorm arrived with some rain, loading the air with a lot of moisture; it did not cool down significantly since it remained cloudy throughout the night. It was not particularly hot during the day, with temperatures between 24°C and 28°C, but humidity in the air (around 66%) still remained high for a long time. This also had an effect indoors – and since the house did not cool down at night either, the room temperatures settled between 23°C and 25°C. The air conditioner was operated between 10:10 and 20:00, mainly to reduce the humidity; this had a favourable effect on our well-being under the prevailing conditions. Dehumidification operation consumed 2.02 kWh of electrical energy today – 15% of the 13 kWh supplied by the PV system. Evaluation: cooling operation essentially would not have been necessary because it cooled down quickly in the evening and the humidity of the outside air also decreased significantly; there would have been a few hours with temperatures slightly above 25°C, by no means uncomfortable, but it would no longer have been Comfort Category A because the air was a little too humid. However, I felt that the 2 kWh roughly were well worth it to keep a 'cool head'. Here it is also clear that in a highly efficient building with a heat pump and PV system, users can act in very different and flexible ways, whether it is just opening the windows wide, operating a cooling device or even a full-fledged heat pump, we could almost say that everything works. Neither the environmental impact nor the operating costs are relevant for this.

Consistently pleasant temperatures inside the house – without operation of any active systems. Finally: the location and date of the next Passive House Conference have been confirmed: From Friday 5th to Sunday 7th April 2024 in Innsbruck The Call for Papers was published today, see 27th International Passive House Conference, the focal theme of the conference will be “Retrofit - have an impact!”. There are many examples of this in Innsbruck, not least due to the EU projects SINFONIA and OutPHit, even including a conference venue that is a certified EnerPHit building. The conference is being organised by the Passive House Institute in close cooperation with the University of Innsbruck.

Let's start with the weather in Darmstadt: today, several storm cells passed through and it actually rained a few times; in the early morning, it was even cool with 15°C, so night-time ventilation worked perfectly; during the day, the thermometer rose to 29°C in the shade. The temperature inside the building remained consistently comfortable, never exceeding 24°C – and the split unit remained switched off.
There is news of an extreme heatwave coming in from southern Europe: it was 43°C in Athens today, the Acropolis has been closed to visitors. And it is set to get even hotter. Water temperatures in the southern Mediterranean are more than 5°C above the long-term average for July.

Although the daytime peak temperatures in the last few days were still high at 26°C, 27°C and 29°C in the shade at this location, the nights were cool enough with 17°C, 12°C and 11°C. Under such conditions, it is easily possible to keep the Passive House building comfortable with the help of night-time ventilation: active cooling then isn't necessary. This is how it has been over the past few days: the split unit has remained consistently “OFF”. According to the weather forecast for the region, this will remain so for the rest of July and there will be no further need for cooling.

…not nearly enough, not even to supply enough water for our small garden with raspberry bushes and a few herbs – let alone replenish the groundwater a little.

Temperatures rose to 30°C outside at 3 p.m. – which we already perceive to be quite bearable – and fell to 14°C during the night. Ideal summer conditions for a reasonably well-insulated building; night-time ventilation allows the room temperatures to cool down to 19°C to 22°C at the start of the day, and in the evening it is between 22°C and 24°C – all within a comfortable range; active cooling is then unnecessary. In southern Italy, the heatwave of the century has arrived today as forecast; in Cagliari (Sardinia) and Trapani (Sicily), the thermometer climbed to above 40°C, which is unusually hot even for Italy. The residents of Phoenix, Arizona, are particularly affected: for the nineteenth day in a row, daytime temperatures have been above 43°C, and even at night it does not cool down below 32°C. The current record heatwave in China is also continuing – I just saw that it is 29°C in Beijing at the moment (it is now 3:30 a.m. in the middle of the night).

Although all these values are records for the places mentioned, it is not life-threatening yet for healthy people, even though it is extremely unpleasant at present. However, we must expect that the peak values will continue to increase in the future – an additional degree or so at these locations is already certain due to CO2 emissions. It will be even more if mankind continues to burn coal, oil and gas as we have done before. It is now imperative that as many people as possible realise that we must change the course of the energy supply system: away from fossil fuels. Two measures are effective in this regard: significantly improved use of energy (see Energy efficiency – the big picture), and the rapid expansion of renewable energy, especially wind energy.

The weather has been pretty much as forecast – the last few days have been cloudy with occasional showers, with temperatures in this location ranging from a minimum of 14 °C in the morning to a maximum of 26.5 °C in the late afternoon. Under such conditions, a Passive House building in the “purely passive mode” permanently offers optimal thermal comfort; at night, the windows are opened and all the heat accumulated during the day is vented, causing the temperatures inside the building to drop to between 19°C and 22 °C. During the day, the temperatures rise slowly, driven by internal heat gains and passive solar energy gains despite the venetian blinds. In this way, maximum indoor temperatures between 22.5°C and 24°C are reached. Despite the sky not always being clear, the PV system's yield was between 8.5 and 13.6 kWh/day, which is still more (even on the least favourable day) than the electricity consumption of the entire building: this Passive House building is therefore more than self-sufficient in the summer .

Degree of self-sufficiency?

With the existing, not overly large PV system and a 4 kWh battery, it be would even be easily possible to achieve full, stringent self-sufficiency in summer: the battery would be charged with the surplus electricity generated during the day; on a summer night, electricity consumption has never exceeded 3.3 kWh here. The original meaning of the term “autarky” is that there is no longer any dependence on an external energy supply – this would be achievable here between May and September with very little effort. However, this becomes more difficult during the winter period, as two climate-induced circumstances come together: from the end of September to mid-April, the PV electricity is not even sufficient to cover household electricity consumption (washing machine, dishwasher, refrigerator, cooking, lighting, PC, etc.), let alone the much higher consumption of drive power for the heat pump; we therefore draw electricity from the grid for this purpose. This can be conveyed via the existing grid without any major problems (this output was never higher than 500 watts, compare the entry for 23rd March this year) and the electrical energy required is so low that it could also be covered by the wind power plants that are already installed, at least if all buildings with heat pumps are as well insulated as this building. However, a Passive House Basic or Passive House Plus is not considered “autarkic” yet.

The term “degree of self-sufficiency” is often used to describe such a situation; however, in logical terms this description is questionable because the building isn't self-sufficient after all. And as long as electricity still has to be drawn from the grid due to the demand in winter, residents will continue to be dependent on the electricity supply. In economic terms, a higher “degree of self-sufficiency” may hardly bring any advantages, because the grid still has to be regulated, maintained and billed, and these costs remain almost constant, regardless of how little and how rarely electrical energy is consumed. So long as large local seasonal storage facilities do not become significantly cheaper, this problem cannot be solved: a Tesla Powerwall lithium battery with 9 kWh lasts for just about one day. However, an additional 700 kWh would have to be available in winter for electrical operation of all systems: that would mean 77 such batteries – even with a significant reduction in the cost of battery storage, it is apparent that this cannot work as a 'solution for everyone': wind power is required and seasonal storage must work with a different technology . Renewably generated fuels are appropriate for this, but to be able to use these sources and storage technologies for buildings, an electricity grid is still necessary. Most buildings in general will not become entirely self-sufficient. Furthermore, this actually facilitates the energy transition: the electric heat pump works with both self-generated solar power (for cooling in summer and also for some heating in spring). Most importantly however, an electricity connection is a prerequisite for making the surplus electricity inevitably generated in summer available to other users. If surpluses still exist in the entire electricity network, then these can be fed into storage facilities – preferably into all storage facilities that are accessible from the network; these can also be storage facilities operated by industrial companies and thermal storage facilities for heat supply networks. Even if one's building has its own battery storage for example, it would make sense to fill this storage facility when there is an abundance of renewable energy available in the electricity grid – and then discharge it when the grid otherwise requires expensive condensation power plants with high CO2 emissions. All the reasons mentioned here,

• easier solution for winter with wind power supply
• feed-in option for PV electricity that cannot be used by the owner
• grid-friendly utilisation of any existing individual electricity storage

speak in favour of a grid connection, at least for the electricity grid. Truly autarkic solutions, even for winter, necessitate seasonal storage additionally. This is technically possible and has already been demonstrated – but it makes more economic and ecological sense if many consumers connect to the grid, because not everyone has their hot water heater or oven on at the same time – and the supply profiles of renewable electricity generation also vary over time and also spatially. Solar power from Eastern Europe may already be available hours before sunrise, and Portugal can feed in power for two hours longer in the evening; there is rarely extreme calm in wind energy occurring at the same time in the Aegean Sea, Norway and Ireland. A supra-regional network would therefore greatly facilitate the supply of renewable energy. Nevertheless, truly self-sufficient solutions aren't impossible – and in some locations they are even advantageous. In these cases, the rule “insulate first, then install” is particularly important: every kWh saved in winter through a high level of energy efficiency reduces the capacity needed for seasonal storage, which is quite expensive, especially if it has to be set up individually for each building.

Today it is almost continuously cloudy – outdoor and indoor temperatures are within the comfortable range. On days like this, almost all buildings can be kept comfortable “passively” with little effort. Under these conditions, neither heating nor cooling is necessary.

Hard to digest: Why nuclear deterrence cannot work in the long term The new film “Oppenheimer” is thought-provoking. Regarding the significance of nuclear weapons, it has been repeatedly said that “the existence of these weapons will end the threat of war from now on, out of sheer fear of the incredible destruction.” This statement can also be found at the end of another video linked here. Is that true? Scepticism has always been voiced by some – J.R. Oppenheimer was one of them

Think about it objectively The probability of an accident (and it doesn't have to be as serious as the fire in Heisenberg's laboratory) is never zero. Incidentally, many such near-catastrophes have happened – and we have been incredibly lucky on several occasions. The probability that a new reckless dictator like Hitler, threatened with defeat, will act irresponsibly in a mixture of megalomania and paranoia, is also never zero. The world has seen such individuals at all times in history. Therefore: the stockpiling of nuclear weapons by bitter enemies at the level of nation states cannot be a solution in the long term . Is there a solution? Yes, there is: the world had already identified it at the end of the Second World War: the United Nations . But we have lost sight of the big picture and have not made any progress in giving such an organisation the instruments and influence it needs for this purpose. So here we are again – with a growing threat to our existence. Yet another threat, alongside and in addition to the one we are systematically generating year after year, so to speak, by releasing more and more CO2 into the Earth's atmosphere. Addition (1 August 2023): the NBC documentary linked here contains interviews with many of the contemporary witnesses of the use of atomic bombs in Japan at the end of the Second World War:

This documentary sheds light on the considerations and motives of many of those involved. These were difficult decisions – there was clearly a combination of several very unlucky storylines, even those relating to the dynamics of the war itself . For example, the extent to which a prudential decision in Japan to end the essentially lost war, avoiding any casualties, was hindered. The statement right near the end of the film (1:21:30) is particularly noteworthy: “It's clear that we must never have another war. There's no other choice.” The generation born and raised in the aftermath of these events had precisely these words in mind – these are the logical consequence of the incalculably destructive threat posed by these weapons. It is particularly interesting that Edward Teller shared this position and was proud to have made a decisive contribution to ensuring that there could be no more wars with the development of the “Super”. As could have been expected , this conviction has eroded over time. The scale of warfare below the 'nuclear threshold' has gradually increased: first in smaller military operations, then in two disastrous proxy wars in Southeast Asia, and finally in conventional invasions by the major nuclear powers in the pursuit of 'important interests'. It almost seems as if the world is trying to find out to extent which war is 'permissible' again, despite a nuclear Armageddon actually precluding a war. The statements of senior officials have been forgotten: “There was war, and war brings death and destruction. It changes the way people think and act; truth has always been the first casualty of war.” (Also documented in the linked film). These statements provide one of the prerequisites for stabilisation due to nuclear armament as assumed by Teller for example: through guaranteed mutual destruction . It becomes even more clear that we have failed to do something in the 78 years since the end of the Second World War: the establishment of a world peace order and an accepted international authority capable of maintaining this order. People such as Oppenheimer, W. Shurcliff, Russel, Einstein, Szilard and Cyrus S. Eaton have worked tirelessly to limit the severity of this threat to humanity posed by humanity itself. Today, this is more important than ever before – because it now seems that many people are no longer aware of the fire we are playing with here. Perhaps the film about J.R. Oppenheimer came out at just the right time after all.

Here is the result for operating power consumption of the split air conditioning unit in the Passive House building in Darmstadt Kranichstein for July 2023:

A total of 5.5 kWh of electrical energy was consumed for active cooling for the whole apartment (note: this is NOT the value “per m²”, but the total value read on the sub-meter for the entire 156 m² living area, including the “standby consumption” of the unit). In the table below we have shown this in relation to the other energy flows measured in July:

Just 1.4% of PV electricity generation was used for cooling; altogether, even in this rather unusually moderate July in terms of solar energy availability, PV electricity generation was almost twice as high as the self-consumption: net 173 kWh could be made available to other customers on the electricity grid.

This result is due to the continuously rather cool summer weather at the location since 13 July. Such weather periods have typically always occurred in summer in Central Europe; in the past decade they were less frequent and of a shorter duration. Under these conditions, active cooling is not necessary in a Passive House building; the home can be easily adjusted to a comfortable temperature by occasionally opening the windows.

In the seven years in which the device has now been in operation, the maximum monthly electricity consumption for cooling was around 45 kWhel in August 2018, but even this is a negligible amount, less than 1% of the total annual consumption of all energy sources.

Could this increase even more in the future as a result of climate change, due to the higher outside temperatures? That is quite certainly the case. The “PHPP” planning tool even allows the maximum future value for this to be calculated: under the most unfavourable circumstances, this results in around 90 kWhel. The existing PV system alone, with a battery storage capacity of around 5 kWh, would still be able to easily cover this and all other demands in the building.
We repeat the assessment made earlier: today and in the coming decades, even with climate change, the electricity demand for potentially increased active cooling in a Passive House building in Central Europe is negligible and can be easily met at any time by the surplus solar electricity already available today.

Comment on climate protection: problems could still be solved in an acceptable manner with a little effort; unfortunately, the overriding impression currently is that there is a refusal to implement solutions

To paraphrase Carl Sagan, it could be said: “there is no hint that help will come from elsewhere to save us from ourselves.” We will have to do it ourselves, and as has often been said in the past, it is now “high time”

• The solutions are all technically available; the problem is that currently they are not being implemented to the extent necessary (EnerPHit renovations wind power expansion, electric traction in transport, heat pumps, less meat-based diets, circular economy).
• In fact, there is a massive disinformation campaign instead (unfortunately!), which is explicitly and massively directed against the mentioned effective solutions.
• A part of this campaign aims to create chaos and confusion in addition by fuelling fears about the shift away from fossil fuels.
• There are even approaches that do not mean a decline in prosperity, such as the Passive House and EnerPHit standards, and choosing electric vehicles.
• Disinformation campaigns apparently promoting pseudo-solutions also contribute to the confusion: one example is the renewed hype surrounding nuclear fusion. I have argued elsewhere that nuclear fusion could well play an important role in the distant future (in five decades, for example) for interstellar space travel for example – that is, if mankind is able to bridge such a period as a functioning civilisation. Within these five decades, nuclear fusion will not be able to make any relevant contribution towards bridging this gap – it will definitely be too late for that. On the contrary, if, as is currently the case, the nuclear fusion hype is primarily used as a political tactic to hinder serious attempts at finding a solution or to declare them 'superfluous', then this hype, like many others, is contributing to the prevention of a realistic solution.
• Equally unhelpful are the doomsday scenarios that have become increasingly common lately: whether in the extreme form, with the incorrect statement that the catastrophe is already underway today, which completely trivialises what is going to happen in just a few decades if serious action is not taken; or in the form of arbitrarily set and then 'indispensable' warming limitation targets that have not been thought through in terms of their operational feasibility, or in the variant with arbitrarily set targets for limiting global warming which are later declared 'mandatory', the operational achievability of which is not well thought through and which are often completely unrealistic .

But there is one problem: at present we are still racing towards a global catastrophe at an accelerating pace. If we continue as before, it will not be a question of whether our grandchildren's generation will perhaps enjoy slightly less prosperity than we or our parents have done. Rather, it will be a question of whether the society in which they will then be living will still deserve to be called a “civilisation”.

No, this catastrophe is by no means already happening: that would constitute trivialisation of what is coming ahead. True, there are indications: glaciers are disappearing, permafrost mountain ridges are collapsing, forests are burning down, entire regions are being flooded, heat waves that are unbearable for the human body. Each one of these now on a scale we have never seen before. But: all of these, even taken together, do not constitute an inevitable and irreversible catastrophe. Not yet. That is still to come, and no one can say exactly when: probably in a few decades. However, the problem is that if we begin taking reasonable action only then, it will be too late – once the avalanche starts rolling, it cannot be stopped.

No, at this point in time, all is not lost yet. We know how emissions can be rapidly reduced to zero over the course of 15 to 30 years – the programme for this is already outlined above. However, implementing it must not be delayed any longer now.

Ceterum censeo: we must significantly reduce carbon combustion starting now. My colleague Lloyd Alter has published a similar analysis today, climate-doomism. Rating: worth reading!

The kind of day that we always found annoying as children: too cool for summer, with one rain front after another passing through, so that going to the outdoor swimming pool wasn't very appealing. Do many people feel like that today? Looking at the comments on TV, weather reports and the so-called social media, we get the impression that this is the case. In summer, we love it when it's really sunny and warm – for decades, we Central Europeans have been travelling to the Adriatic Sea to swim, which was the holiday preferred by the majority of people.

It is August 2023. Something has changed, at least for most people in my immediate circle, to whom I shall refer to as 'we' here. First of all, in one way or another we have suffered from the extreme drought in recent years, even directly in our daily lives – and what's more, we know that such a prolonged drought will pose problems for Central Europe: agricultural production will decline, become more costly, and the corresponding products will become more expensive. The garden must be watered constantly – and we even feel guilty about that, because water is scarce. Added to this are reports on the consequences of falling groundwater levels. It is now clear to everyone in my immediate circle: rain is needed, it is long overdue and will help greatly. We have now understood this, at least rationally . However, this is where opinions quickly tend to differ: as every maths teacher knows only too well, rational insight does not necessarily mean that the knowledge is actually accepted and absorbed, let alone put into practice . In addition to the general problem of putting abstract knowledge into practical application , there is also an emotional resistance to the genuine acceptance of what has been learnt rationally. There is even a trendy word for this: popular psychology refers to it as “cognitive dissonance” .

The equally wrong response from people who have grasped somewhat more the extent of the problems, their seriousness and the catastrophic consequences of continued inaction is that they are now resorting to increasingly 'mind-numbing' means to make humanity (often seen as the 'dumb masses') finally realise the direness of the situation. I consider this response to be utterly wrong because it completely misses the point of the task at hand and, seen in the light of day, actually makes perception and solution more difficult; I will explain why this is so:

The problem of perception is not that the threat posed by climate change is not being communicated sufficiently, or that to some extent the frightening aspects of the impending catastrophe are not being painted in vivid detail. Almost everyone has been confronted with these horrific images for decades now . Many have put on an armour of ignorance, which they reinforce even further with every dire warning – they don't want to (and perhaps even can't) hear any more of it: forests are burning (where exactly)? Hail the size of tennis balls is falling. Which part of Pakistan has been under water for months already?

• This defensive armour is (still) working quite well currently. In particular, as long as these events still remain within the scope of occurrences of which there really hasn't been any shortage even in the past: there were forest fires in the past too, just like there were some years of drought , and floods, storms and landslides have also occurred in the past. Although it is again rationally correct that objectively these events are becoming more frequent and are already increasing in severity today – but as an intellectual insight, this just bounces off the full armour.
• If the current extreme events are now increasingly being constantly communicated, painted in vivid colours and elevated to the same level as the actually impending catastrophe, then all this noise will primarily only reinforce the defensive armour and strengthen it further.
• It is even more devastating when overblown protests also provide the established ignorance with a personified target for all the frustration of their cognitive dissonance: the activist who prevents you from picking up your child from nursery on time – he practically offers himself up as a target for aggression. The activist is not a result of climate change – but in that moment, he is infinitely more disruptive than climate change itself. The fact that the activist is carrying signs mentioning climate change even speaks directly against the seriousness of the problem clearly existing for the affected motorist (in this state of cognitive dissonance). The fundamental explanatory pattern here is: “There have always been religious sects preaching the approaching end of the world, and they have always demanded reflection and repentance. The only thing that will help against this is the long-practised attitude: 'It's best to ignore it'. It's harder to do that when they're sitting on the road right in front of us, so the conclusion is: “How can they do that? With due respect, this is definitely going too far.”
• As a direct consequence, mainstream society has been discussing the 'lawfulness' (it is indisputable that these actions are breaking the law) or the 'legitimacy' of various types of action for months now (incidentally, it is undeniable that almost everything that has happened in recent months falls into the category of 'basically quite harmless'. Harmless, but extremely annoying. And above all: it definitely shakes the foundations of the emotional side of cognitive dissonance – which, however, does not resolve it, but rather, even reinforces it most cases). My point here is that simply the fact that we have been engaged in personalised debates about the types of action for months now, instead of finding constructive ways forward, is damaging any real chance of effectively countering the actual impending climate catastrophe .

Another difficulty here is the long delay elements in the planetary climate system. The damage builds gradually, step by step. CO2 emissions increase the concentration in the atmosphere – and this remains at an elevated level for a long time, even if there were no more emissions; it takes many decades for the effects to be reversed .

The long delay elements mean that the emissions we release today will continue to drive climate change for decades to come. The events that will then occur cannot be 'stopped' if we only then start to actually reduce emissions. The extent of climate change in the coming decades is already being determined by us today. If we want to protect ourselves from even more intense heat waves, storm surges and forest fires in the 2030s, we must reduce emissions now and ensure that between now and 2033, significantly less CO2 is emitted than would be the case if we continued on our current course. Incidentally, I have repeatedly noticed in discussions on this topic that many people clearly find it very difficult to understand the effect of this type of delay element in a control loop .

The fact that the really serious consequences of climate change will most likely only become apparent in a few decades does not mean that we can wait until these consequences actually become apparent. It is clear that taking action only when these events occur would definitely be far (much, much) too late. Here is a comparative example: if a homeowner piles up straw bales soaked in heavy oil in the attic and around the house year after year – thereby increasing both the probability and the extent of a devastating fire each year – then reducing or stopping the storage of the fire load during a fire will be of little use in the event of such a fire.

I readily admit that such thoughts may also be too difficult to understand for many people today. I don't think everyone needs to understand all the details of every single process in the global system – a certain level of basic understanding would be entirely sufficient. This basic understanding must be enough to gain the insight that what really matters is that starting now, we must significantly reduce emissions as effectively as possible while taking into account the continued stable functioning of the global economy and of societies around the world.

The last point is obviously a little misunderstood by some committed individuals acting as “climate protectors” and “climate change admonishers”: the current structure of the global economy consists of a system that does not function as a matter of course – and that cannot abruptly be changed over to a completely different operating method without jeopardising its essential function. The actual strength of this system's resilience is the subject of much political debate, as discussed below. But: it is indisputable that a significant collapse of the global economy would lead to truly serious problems that could also threaten the continued existence of civilisation .

This realisation has serious implications: the solution today can only consist of a structured, phased transition from unsustainable structures to ultimately sustainable structures. This is also the original basic idea behind the so-called “European Green Deal” . That there are arguments regarding the speed of transition which is “just barely acceptable” or “unreasonable and will lead to economic collapse” is very understandable; that is even a necessary and hopefully productive discussion.

Then there are a few other problems with the way this discussion is conducted: on the one hand, the enormous emotionalisation associated with it and, on the other hand, the disproportionate influence that powerful and wealthy lobby groups have on the course of the discussion. Lobby groups that represent very specific individual interests; the financially powerful fossil fuel suppliers among others, whose interest in delaying the phase-out of fossil fuel combustion for as long as possible is entirely understandable. Of course, these groups are actually all in the same boat: nevertheless, for many of them, charity begins at home; that's a problem here, and it's not the only one. Other powerful lobby groups thrive on the structural consequences of fossil fuel infrastructure: the cement industry, for example, depends on the construction of underground car parks and motorway bridges. It is therefore not surprising that some major economic sectors are putting up massive resistance to the transformation process. It is not easy to decide where the line between 'necessary change' and 'catastrophic intervention in the functioning of the entire economic structure' lies. Unfortunately, complete overdramatisation prevails in the current discussion, on both sides of the debate. As an example, a year-on-year reduction in the average weight of passenger cars, which has increased massively over the last decade (also over a period of about a decade), doesn't necessarily have to lead to the complete ruin of the German automotive industry, especially if this transition is intelligently combined with advances in vehicle efficiency and usability. Wouldn't that be an adequate answer to the problem of the transport sector's contribution to climate change? Why not actually, if it is cleverly combined with the previously mentioned improvements in efficiency and changes to the transport structure in cities (as has already been practiced in e.g. Amsterdam and Paris for some time).

However, what is actually damaging about this current debate, particularly in Germany, is that observed from the outside, it presents a picture of massive conflict and extreme disruption. The message here is quite clear: the transformation to sustainability cannot be all that attractive if it is associated with such massive confrontations. It is precisely this message that does a disservice to climate protection: our own specific contribution is more than entirely devalued if all those observing perceive it as a path to societal self-destruction. To put it another way: what we actually achieved in terms of substantial climate protection in Germany between 1999 and 2010 was not that bad. True, from around 2010 onwards we more or less stopped doing that, quite deliberately. We became irritated first about the supposed problems associated with it that had been conjured up, and then about the few activists (e.g. Fridays for Future) who reminded us that this was “nowhere near enough”. The image we conveyed was not very motivating. Could we change that? I think so! That is the subject of most of the pages on Passipedia, but I also intend to explain it in more detail in a later post.

— The above text was provocative enough to spark a debate on social media. Open debates bring additional insights. It is not uncommon for them to even change one's view of a situation or alternative course of action. In order not to complicate the debate, I won't change the content and intentions of this text from 1st August (but I will correct any spelling mistakes I find). Here I will explain any necessary changes or additions next, with reference to the relevant passage in the previous text, so that the debate remains transparent.

@masterhajoda@mastodon.social By the way, I completely disagree. People need to be made far more drastically aware of what to expect. So far, most seem to consider it fun and games. Why else do you think they are still continuing with business as usual, refusing to accept reality in the pursuit of profit? They don't take it SERIOUSLY because they don't UNDERSTAND it! #climatecatastrophe

WF: Thank you for the contradiction! We obviously see things a little differently. 'Differently' meaning different from how you present it: YES, the vast majority currently see it as a work of fiction for the purpose of entertainment. This group is even larger than you think. And YES, they really don't understand. There have been many apocalyptic films. Mostly blockbusters, excellent entertainment. And it's clearly all just “fiction”. That's all that will be achieved by inflating disasters out of proportion.

@masterhajoda That's the annoying problem with all these disaster films. The viewer thinks, aha, so that's how disaster happens! Whoosh, and then the world ends. But of course, there's none of that in reality generally. The process is too slow for human perception – but on a geological scale, it is happening at a breathtaking speed, the likes of which the planet has never seen before. #climatecatastrophe

WF: I would doubly emphasise this last post. We will see why in a moment. In particular, the last part: it took tens of millions of years for plants to remove carbon from the atmosphere and convert it into biomass; we are now extracting and burning the remaining biomass, i.e. returning it to the atmosphere. The only problem with this 'recycling' is that we are doing it within a few decades, which from a geological and evolutionary perspective is a fraction of a moment.

Jim Skea (the new head of the Climate Council) recently gave an interview (Der Spiegel) in which he expressed similar considerations: “If you constantly communicate the message that we are all doomed to extinction, then that paralyses people and prevents them from taking the necessary steps to get a grip on climate change,” he said. “The world won't end if it warms by more than 1.5 degrees,” Skea told Der Spiegel. “It will, however, be a more dangerous world.”

WF comments: In fact, the probability of the world ending is increased with more than 1.5°C; a probability that has never been 'zero' anyway and is currently noticeably increased mainly due to wars and the mere existence of nuclear weapons, according to those who really understand these things. Presumably, the greatest danger currently comes from burning excessive (far too excessive) amounts of carbon. That is why we must urgently reduce this significantly: now, not in ten years' time. We must actively promote this as far as possible – without, of course, jeopardising healthcare or global food supplies, for example, as doing both could also lead to 'the end of the world', perhaps even more quickly.

__The most important communication error today is that it is always suggested that people will suffer as a result of decisive climate protection measures. No one will suffer as a result of many of the truly effective measures – except perhaps a few very narrow-minded and unyielding profiteers in the fossil fuel industry, and not even those, if they participate in the transformation process in an active and productive way. __

… humanity demonstrated that it was now capable of ending civilisation in a matter of hours.

The linked article quantifies the human tragedy of the use of nuclear weapons in figures.

After the danger of a nuclear conflict was thus demonstrated, almost everyone on Earth agreed that it was important to avoid wars in the future. That was one of the goals of the newly founded UN. The aim was to prevent military conflicts in advance through diplomatic efforts.

Now in 2023, we have deviated very far from this path. There is a reason why the Doomsday Clock is now set to”90 seconds to midnight”. However, the Bulletin of the Atomic Scientists is not solely concerned with this obvious mechanism for humanity endangering itself: the impending massive climatic changes that we are triggering through the continued excessive emission of carbon dioxide into the atmosphere are also topics that are systematically assessed here, and this is also included in the assessment of the situation that is symbolised by the Doomsday Clock.

Will cooler heads prevail in the future? This seems to be urgently needed…

Speaking of 'cool heads': in Darmstadt, the past few days have been rather cool and rainy (outdoor climate). This is a weather situation that energy-efficient buildings can cope with perfectly in summer: in a Passive House or an EnerPHit renovated residential building there is no need for active cooling or heating in the summer under such conditions. The indoor temperatures then adjust almost 'automatically' to an optimal comfortable range; if someone feels that it is a little too 'warm', this is quickly corrected by tilting open (or briefly opening) the windows, which much faster than with an active system. If it then becomes a little too cool with the windows open, the windows are consequently closed. Because the ventilation system always provides sufficient fresh air exactly where it is needed, the windows can be kept permanently closed when outdoor conditions are unfavourable (e.g. too cold, too hot, too stormy) without any problems. The effect of the fresh air supply on the thermal conditions inside the building is very small, practically imperceptible, on account of the heat recovery system. This is one of the reasons why there has never been any need to use active heating between mid-March and mid-October during the 32 years of operation of this Passive House building.

The air masses flowing in over Spain are hot; when they arrive here, they are not excessively hot – just particularly damp. This has a number of consequences: firstly, there is some rain from time to time. Above all, however, the air feels humid, which is not surprising given an outside air temperature of around 28°C and 66.3% relative humidity . Under these conditions, the humidity level in living spaces also rises: this is mitigated somewhat due to capillary moisture absorption on surfaces; after all, there are plenty of books, other paper, fabrics and mineral materials in the rooms – but of course, the water vapour released inside the home also contributes to this. As a result, the humidity level inside the home yesterday was actually slightly lower than that of the outside air, but too high for us to find it pleasant. Another consequence of the high water vapour content is the increased absorption of heat radiation in the air at night – exterior surfaces then cool down far less effectively, and as a further consequence, night-time temperatures also remain high under these circumstances; on Sunday night, for example, the temperature remained above 20°C, which largely eliminates the potential for effective night-time ventilation and cooling (known as a 'tropical night').

Although all conditions yesterday (and today) were still within a “tolerable range” , we enjoyed the luxury of the split air conditioning unit yesterday: it was in operation from 10:52 to 21:22 (CEST) for dehumidification of the indoor air, consuming 2.35 kWh of electrical energy. In this way, temperatures below 24.5°C and humidity below 12.5g/kg were achieved; with appropriate clothing, this is “Category A” thermal comfort. On the other hand, the PV system generated 11.1 kWh of electrical energy yesterday, which is still more than the total household electricity consumption, including that of the air conditioning unit.

The question sometimes asked in this context is: although this 'small' increase in thermal comfort yesterday really wasn't vitally important, it did improve my quality of life – thus it certainly did lead to more creativity. Is the energy expenditure for such luxury still justified? We could argue as follows: if the split unit was not operated, the PV electricity from our system would have been available to other users during the relevant period –there was even a demand for electricity during that period that caused CO2 emissions of around 335 g/kWh (average value according to “Agora Energiewende”). By not operating our split unit, we could have saved around 790 g more in CO2 emissions.

Here I would like to move straight on to what I consider to be the appropriate assessment (without having to go through other possible interpretations): the solution that is now in place in the building being used here can be implemented for everyone without too much effort – and it isn't particularly expensive: in fact, it is more cost-effective than the average combination of energy supply, technical equipment and building quality in Germany today. If the solution practised here is ultimately implemented for almost everyone , then all these people will be able to afford this level of comfort , and there isn't ANY relevant environmental impact .

This is what we can consider a “sustainable solution” – a solution that is fed entirely by natural energy flows (solar radiation), with a demand that is permanently available to all people and does not generate any negative environmental consequences. This example also beautifully illustrates the fact that such solutions do allow for a certain degree of luxury – because it is naturally still possible to live healthily and comfortably even under Category C“ comfort conditions. This example illustrates why people need not worry about a decline in comfort or prosperity before the transformation to a sustainable economy, because in almost all areas of our lives the situation is similar to this example. Once we switch to a sustainable structure, it will often be possible to achieve a higher level of comfort than we have today, even without environmental damage.

However, I must warn against jumping to the wrong conclusion: this does not prove that every luxury we enjoy today is completely unproblematic because it can be made sustainable in the future. This is because, on the one hand, the potential of renewables is ultimately limited, especially with regard to the potential speed of their expansion. And on the other hand, precisely this expansion of renewable energy and energy-efficient usage structures must also actually take place, and we are only at the very beginning. And this is precisely what is currently being hotly debated: we still seem to be a long way from reaching a consensus that renewable energy sources should now be expanded as much as reasonably possible and that wherever energy efficiency potentials are available, they should be quickly exploited.

Economic paradigms

Almost all schools of economics today accept the tenet ”… available to all people permanently…“, but this is usually stated without the restriction mentioned above: ”…without causing negative environmental impacts“, because it is assumed that the latter is essentially almost automatically the case.

This is one of the accepted axioms: an ongoing scarcity of natural resources due to the laws of nature does not exist, or it is so far off that it does not play any serious role. Scientists from various disciplines have questioned the validity of this axiom and directly refuted it in an increasing number of cases. There is no doubt today that, for example, the reserves of oil, cobalt and the resilience of the atmosphere are limited and that, in some cases, we as a civilisation are operating close to the limits or have most likely already exceeded them. However, this fact is clearly hard to digest for some schools of economics. If the limitlessness of resources leads to the assumption that there is no need for regulation beyond the self-regulation of the market, thereby calling into question the legitimacy of democratic structures, then awareness of the objective limitation is quite definitely disturbing. This is obviously noticeable – which is why reactions to publications such as 'The Limits to Growth' [Meadows 1972], [Global 2000] and the film 'An Inconvenient Truth' [Gore 2006] were so strong. My theory is that the dissonance with reference to precisely this issue is the main reason for the increasingly ideological trench warfare.

On the Passipedia website we have put together numerous building blocks that can be used to overcome this dissonance. At the moment, it would not even be necessary for the disputing sides (“unlimited resources” vs. “planetary limits”) to agree on this very issue for all time, so to speak. It may turn out in a few decades that, taking certain 'local limits' into account, the resource situation on a cosmic scale is indeed 'almost unending'. However, hardly any economist today would deny that such local limits have always existed and have had to be 'circumvented' through repair, conservation, substitution or completely innovative solutions.

There can be no serious doubt that we are now forcefully pushing one of these limits, namely the compatability of high levels of CO2 combustion products with climate stability. The huge additional emission of CO2 into the atmosphere must cease to a large extent – and this must be achieved within a few decades. It can even be achieved within a few decades: the key instruments for this are large-scale expansion of renewable energy sources, the consistent utilisation of untapped energy efficiency potentials, and the careful optimisation of some material flows (e.g. metals as well as cement).

In Efficiency NOW, we have outlined specific solutions for key sectors. These solutions all have one thing in common: they do not decrease prosperity or cherished comforts – we discussed this in detail in our post for 16th August, using the example of building cooling.

Now, one thing is true: the suggested proposals will lead to enormous shifts in the turnover of some economic sectors. For example, it is obvious that in order to avoid CO2 emissions, there must be significantly less combustion of coal, oil and gas. Nor can it be denied that, regardless of the method ultimately used to avoid carbon combustion, this will always lead to adaptations in the sectors mentioned. In principle, there is also no doubt that such shifts, including those involving a high level of value creation, have occurred repeatedly throughout history and have been successfully mastered.

In the present case, too, it is possible to master these tasks. In particular, the potentials offered by efficient energy use are especially helpful in this regard because they can be accessed with the least overall effort, because these are integrated in natural cycles and allow for a smooth transition and because the development of a renewable energy supply system is facilitated .

This transformation is possible – even if it is still being opposed today by some people who depend on fossil fuels. Incidentally, such opposition only consumes additional resources. In numerous contributions to the Passive House conferences, we have even described instruments for a specific path towards such a transformation. These instruments have also already been tested, with good results.

However, the widespread implementation of this transformation has stagnated since around 2009 – here it was no different than in other sectors, with the wind and solar industries being particularly affected. This halt was demanded by key players and enforced by a certain overall political consensus – in Germany, this restricting policy was driven by the extreme expansion of the natural gas infrastructure. As recent analyses have shown, this had more to do with the very specific interests of very specific “global players” . As is often the case in such matters, some of these players ultimately ended up harming themselves the most. Constructive cooperation on real solutions to the problems would create noticeably better conditions for almost all of the stakeholders involved. However, it is inevitable that carbon combustion must be reduced quickly and drastically.

At 2 p.m., it is already 30°C in the shade – with an air humidity of 58%. These are hot and humid climatic conditions; initially unavoidable, they also have an effect inside if active dehumidification does not take place here. In these conditions the skin feels sticky and there is buckling of paper.

This exactly is where the split air conditioning unit performs really well: the indoor unit dehumidifies the inside, removing water vapour from the air in the home. Incidentally, this works quite reliably for the entire flat, as long as the interior doors are kept open. I am currently measuring 24.6°C and 61% relative humidity in my attic study. This lowers the dew point temperature by 4 degrees – and actually means that nothing 'sticks' anymore and we feel perfectly comfortable and productive.

The split air conditioning unit requires electricity to operate. The unit consumes around 250 watts at present, which is still less than the PV system generates currently. Also the costs for installing this unit weren’t high; it has been with us for 6 years now – and, as described above in this blog, it also allows us to heat our home in winter almost entirely using renewable electricity .

Sustainable solutions such as this one, namely a well-insulated building with a split unit, therefore not only make sense in ecological terms – they also prove particularly cost-effective and allow for significantly improved thermal comfort, especially during extremely hot, sweltering external conditions.

In the article 'Installation of a split unit', we describe how such solutions can be implemented in practice and what they can contribute: it is surprising how much difference this can make, even in an average existing building. If the owner then implements the long-overdue thermal insulation measures for the building, this contribution will be even greater – in the end it may even lead to a completely sustainable solution, even in an existing building. This is an example of a specific solution that can be implemented step by step, almost anywhere, at reasonable cost and with reasonable effort, and with many other advantages.

The smoking gun? “SMOKING GUN EVIDENCE”
When a scientific article has a headline like this, it is a serious indication that the research may not have been conducted with particular scientific diligence. The real background is perfectly clear: it's all about sensationalism. The aim here is to attract attention – this does not necessarily mean that the content is completely untrustworthy in all cases; especially ambitious researchers are often genuinely convinced that they have stumbled upon something 'exceptionally important' – many professors are familiar with this problem and advise 'moderation' in such cases. This will quickly be clear to anyone with a little background in critical thinking .

https://youtu.be/XHcTtTB2Iho?t=204

Anton Petrov is right: …something that's actually become a huge issue in the last few years has become much more common in recent years…in most of these cases at least the actual discoveries were somewhat real, maybe not as groundbreaking as the title makes its sound but still real nonetheless … we also had titles like this: “Scientists confirm major breakthrough in nuclear fusion” or “Superconductor breakthrough could represent biggest physics discovery of lifetime”. These huge claims were either disproven almost right away … or are going to be eventually disproven with time, although for that fusion claim it's really more of a representation of what its actually for, I mean we're talking about a weapons research facility, not something that is trying to create clean energy. … This sensationalism in science has actually reached a completely new level of absurdity. We've reached the point where it is very difficult to tell what's real and what's not. Several science communication channels including technically I guess myself have now started to slowly become 'debunkers', not really presenters of new discoveries… …so when I see an article like this with the title 'Smoking gun evidence for modified gravity at low acceleration from Gaia observations of wide binary stars', it sort of makes me go 'Huh? What? What exactly are they talking about?… A couple of months back I read separate articles that basically seemed to state the opposite, so I guess the question is: how exactly should we approach these articles and who do we actually believe? Well, the obvious answer for scientists would be: “Time will tell.” I mean, obviously, as Carl Sagan said many times: “Science is not just a body of knowledge, it is a way of thinking.”

For those interested in this specific scientific question, it is really worth watching Anton Petrov's entire video.

Deliberate confusion by populists

I would like to highlight one aspect of this development which Anton Petrov also alludes to: the purposes behind such sensationalist “clickbait”. I am quite certain that there has been another extreme increase in the frequency and exaggeration of such 'reports' over the past year or so. It is easy to see what some of these sensational headlines are actually aiming to achieve: namely, to cause maximum confusion and at the same time destroy trust in science. This is the tried and tested 'populist method' that has proven so successful in the political arena. Emotionalising an issue in such a way that a lot of people take the bait; often this is actually trivial nonsense , but more often it is massive and intended deception . That's the first category of such reports.

…and untenable promises The nuclear fusion article cited by Petrov is an example of the second category. Many will have noticed this already: starting in early 2022, articles with clickbait headlines promising “breakthroughs” have become increasingly common; another such article appears in the playlist almost every day. There could be two reasons for this: the first is that this area of science is currently making “giant strides” forward . The second is that it has something to do with the current situation in highly developed industrialised countries. On the one hand, we have seen a very sharp rise in energy prices due to events in world politics. At the same time, it is also becoming abundantly clear that “we are now being presented with the bill for our failure to protect the climate” . If people were to take a step back and try to view the situation more objectively with detachment, they would find it relatively easy to see that we have gone a little too far in terms of energy consumption and energy production – a realisation that is not new by the way , and for which there are reasonable solutions . It is now really time to take these proposals seriously and implement them consistently .

Nevertheless, it is clear that consistent implementation of these proposals would lead to significant reductions in coal, oil and gas consumption relatively quickly – which is precisely what these proposals are designed to achieve. Especially now, with global consumption of fossil fuels at an all-time high, this would be a major change in precisely these markets. The amount of CO2 emitted is a measure of this: per capita of the world's population, we are adding 4.7 to 4.9 tonnes of this gas to the atmosphere. That is more than 60 times our body weight, every year. Behind this also are tonnes of precisely these consumed fossil fuels, whose carbon content is converted into CO2 through combustion. These tonnes of fossil energy resources represent by far the largest material turnover in our civilisation; the highest turnover of renewable materials is that of grain, which at around 380 kg per capita is a good ten times lower .

It will bring a noticeable reduction in the consumption of coal, oil and gas. However, these still account for over 90% of primary energy worldwide, and their sale contributes significantly to the gross national product. The revenues, profits and even taxes from this trade are of great importance: for the companies that engage in this trade – but also for other important parts of the national economies . Against this backdrop, it is easy to see why precisely this development is causing alarm in major rich and powerful economic sectors. It is completely understandable that these sectors are doing almost everything they can to slow the transition process at first .

This explains the second aspect of the sensationalism relating to energy technology: the vast majority of populist reports describing “groundbreaking” or “promising” breakthroughs are specifically about specific energy technologies, such as nuclear fusion, travelling wave reactors or large-scale hydrogen production. What all these technologies have in common is that they obviously promise great potential – and that they do so, at least allegedly, on a large-scale production level. As a result, these reports all appear to signal to users of energy services that “great things are coming, there is no reason to stop and think, for you everything can continue as before – and will be even cheaper, and in a short time the relevant industry will provide us with a perfectly sustainable solution for production.” But that is not the only thing that the reports currently being emphasised have in common: the other similarity is that all of the mentioned technologies presently use systems that have been demonstrated on a laboratory scale at best; or not even that in some important cases. So far, there isn't even one permanently operational nuclear fusion plant that delivers net energy to the system. All reputable colleagues in this field of research will confirm that it will take at least another 30 years before nuclear fusion can play a relevant role in energy supply on a large scale. These are precisely the 30 years within which, according to the latest findings relating to climate protection, we must already have achieved reduction of carbon combustion to “virtually zero” . In the case of nuclear fusion, this is obvious; seen realistically, nuclear fission approaches could make a (small, see International Energy Agency [IEA]) contribution, and hydrogen can make a contribution towards solutions for selected industrial sectors, but it will by no means be able to replace fuel in the entire transport sector or for heating our homes; the present consumption levels for these are simply too high (5 to 10 times higher) for that.

Despite these facts, or perhaps precisely because of them, such reports have particularly been “pushed” for some time now. For example, every day I receive at least four 'new' videos with exactly this structure recommended to me across all internet channels. There are almost as many recommendations, such as 'What most homeowners don't know: solar energy is not worthwhile' by an energy expert, or 'Stay away from heat pumps: they're expensive and consume huge amounts of electricity' or 'With an electric car, you might get 200 km and then be stranded due to a lack of charging stations'. There is a simple reason for such numbers of posts: they are generated via financially powerful advertising channels, and this serves the essential purpose of keeping the fossil fuel business model at as high a level as possible for as long as possible. Numerous political forces are also working towards this goal; in this case, this even applies to all parties, although not all politicians. Those few exceptions, however, very quickly become the subject of quite special treatment: the tried-and-tested attacks are directed at the individuals themselves; in harmless cases, it's their hairstyles, or their lifestyles, their friends or partners, and odd stories from their earlier lives .

There is only one genuinely realistic approach: the combustion of carbon-containing materials must be reduced quickly (starting today) and drastically (by a factor of 5 to 20). This applies wherever this currently occurs on a large scale, whether in the combustion engine of a motor vehicle (tens of kilowatts, tens of millions of times), in the burner of a central heating system (also tens of kilowatts, tens of millions of times), or in a lignite-fired power plant or cement kiln. The solutions, both technically and economically feasible, have been available to us for a long time: not as recently tested exotic solutions in the laboratory, but as proven technical systems that have been used in practice for decades: electric motors for vehicles, powered by batteries; thermal insulation of buildings; the remaining demand, which will then be easily manageable, can be met by means of heat pumps, as well as wind turbines and ecological building materials. These solutions can be implemented today, with immediate high contributions, at affordable costs and usually with further advantages. That's right: implementing these will rapidly further reduce the demand for fossil fuels each year. That precisely is the goal – and it is necessary to achieve this goal. The fossil fuel industry would be well advised to participate constructively in this transformation – the rapid collapse that is otherwise inevitable at some point can still be avoided if it switches to alternative investments. The millions currently being poured into disinformation campaigns will ultimately only make the situation much more difficult for this sector.

The sweltering heat continues: in fact, I didn't skip my fresh air exercise yesterday or today. Walking briskly for 50 minutes at a time, I worked up quite a sweat at 30°C and 58% relative humidity; saunas are supposed to be healthy! It certainly felt good to put on dry clothes again and return to the attic, which still achieves Comfort Category A with around 24.8°C and 59% relative humidity.

In order to maintain these indoor conditions, the air conditioning unit must now actually be operated. A purely passive method of dehumidifying the room air under such outdoor conditions does not exist – at least not with justifiable effort .

Here is the link again with tips on reducing heat stress.

It also necessary to repeat here that installing a split air conditioning unit no longer constitutes a climate sin if a modern, energy-efficient system is used. On the contrary, it can even help protect the climate. Information on this can be found here: Installing a split air conditioning unit. These units also aren't particularly expensive and can usually be installed quickly and cost-effectively. Many people are unaware that modern units of a good quality can also be operated in reverse mode, extracting heat from the outside air to use it for heating the inside. This is because these units are also heat pumps. They are powered by electricity and as a rule, a single room can be kept warm using such a unit, even in an old building. Since more than 50% of the electricity used for this purpose now comes from renewable energy sources, the CO2 emissions from this kind of heating operation are generally lower than those of a gas heating system – and it is often possible to switch off the central heating completely for a longer period of time in autumn, which also eliminates the otherwise often high radiation, conduction and standby losses.

Experiences gained with such a device are documented in the posts appearing here on a regular basis. In this very well-insulated building, it is even possible to replace the entire heating system with this; we have tested this over a period of 6 years now: simply scroll through the earlier posts above, e.g. for the total consumption for heating the building: Electricity consumption of the split unit in winter 2022/23.

If the weather forecasts are correct, today will be the peak of the sweltering heat for our location (Darmstadt); 32°C will be reached in the shade – and the air humidity is still very high (50% relative humidity in the outside air at present; this corresponds to a dew point temperature of 16.9 °C). Due to moisture buffering in furniture and building components and operation of the split air conditioning unit, the indoor values for the attic are now 25 °C and 62.3% relative humidity ; that is now (almost) outside of the range for the Comfort Category A .

The split unit consumes around 4 kWh of electrical energy per day under these conditions. This is also completely covered by the electricity generated by the building's own PV system, including all other domestic electricity.

The news from other parts of the world is somewhat different: in southern Spain, outdoor temperatures in the shade are just above 40°C (in Seville), but very dry heat prevails here currently.

The current period of heat and humidity lasted up to and including 22nd August, ending with the passage of a huge thunderstorm. From 23rd August onwards, the split unit was no longer in operation; although the air was still slightly more humid than usual, it was bearable with a temperature below 26°C in the rooms. The windows can now be left tilted open all day again; there are occasional bursts of warm air and humidity, but as soon as this becomes unbearable, the windows are simply closed again.

In total, the air conditioner consumed 27.86 kWh of electrical energy in August so far, and any further consumption (in this year) is not likely. For comparison: the electricity meter for PV electricity generation stands at 251.3 kWh, while total domestic electricity consumption (excluding the split unit) was around 147 kWh. Despite a solar yield that is rather atypical for August, it is still higher than the total consumption, and a net feed-in surplus remains.

The total operating energy for cooling this summer was therefore less than 36.4 kWhel/(m²a); this also corresponds roughly to the average summer electricity consumption of the split unit so far. With less than 0.25 kWh/(m²a), however, this consumption is negligible: it is far less than the electricity consumption of our refrigerator or dishwasher, for example.

However, what is much more important here is that the electricity demand for air conditioning occurs exclusively during the time periods with a PV surplus – and this will also be the case in future for all locations in Central Europe if the expansion of solar power generation continues at a fast pace.

If the weather forecasts are to be believed, then the recent hot spell was the last unpleasantly hot period at our location this year; of course, the weather may always bring surprises, so we will only be able to take final stock of this summer in October.

Heating the Passive House in Darmstadt- Kranichstein efficiently