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Last summer I lived in the largest passive house settlement in the world, in Heidelberg, Germany, and the main complaint is the heat in the summer. Even with cooling down the apartment to 20°C with open windows all night, and closed windows and window blinds all day, the apartment would be back at 28°C when returning after work. Basically it is too hot in the apartment from May to September. In a survey nearly 60% of the people living there complained that it is too hot in summers, so it doesn't seem to be an isolated problem to the specific building I lived in.

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Nighttime cooling only works if you have a big thermal mass inside the insulation envelope to cool down to store your 'coolth' in. In general the problem with lightweight stick frame construction is that it is too quick to respond to temperature changes so it not a good fit for this. Ideally you build off a big concrete slab which is sat on top of non compressible insulation. The houses on page 36 of this magazine use this technique.[0]

[0] https://issuu.com/passivehouseplus/docs/ph_uk_issue_23_digit...

cooling down the apartment to 20°C with open windows all night

This sounds like mainly the air cooled down while a lot of heat was still trapped in the building itself. There are ways to make this better though. So you could say that particular building is not overly well designed. 28°C is just too much. Though no matter what you try, unless you're under ground, if you have 10 or more consecutive days with temperatures rising well over 30°C, you won't really be able to stop that. Anyway it's been a while I looked into this but some things I recall: a lot of mass on the roof, like a garden, will keep much of the heat out there. More mass in general as well IIRC becasue it just takes longer to heat (but again, once all heat is in and it's too much, you're going to have to wait before it is all gone again). Avoiding direct sunlight on the walls also helps. Reflecting glass, outer blinds (blinds inside doesn't do all that much, that's basically too late because sunlight has entered the interior already).

ICF (Insulated Concrete Form) construction takes this approach tempering the indoor temperature. My brother just moved into a brand new ICF house in Salt Lake City (relatively cold winters and hot summers) and it is remarkably efficient.

One more cool idea: setting translucent Phase Change Materials (PCM) directly against your windows. PCMs are wax-like material that have a high latent heat of fusion (energy it takes to change the phase of material i.e solid -> liquid). Because latent heat change occurs at a constant temperature, the PCM acts as a thermal storage when solar energy or ambient temperature increases, and then releases the heat during the evenings.

At my (architecture/research) office, my colleague coded a 3D FEM to model the way this interacts with different geometries so we could investigate how to regulate the thermal storage capacity of a PCM surface. I'm fascinated by PCMs, although he seems to think that the resulting temperature dampening is too little[1] to have broad application in architecture...

[1] Liquid -> gas phase change has a higher latent heat of fusion and might be a way to solve this I think. It would require larger volumes, or a way to safely contain higher pressure, but similar to fridge or AC systems, this should provide a couple of orders of magnitude greater heat storage.

Are you talking about this place?

http://www.heidelberg-village.de/

I’m not totally up on my passive house knowledge but it seems to me that the passive house community might have some complaints about this block of pretty conventional looking apartments calling themselves passive houses. I see no effort at all in controlling summer thermal gain [except for some extremely narrow solar awnings]. Are they using special window coatings?

Edit: and my god, all of the floor to ceiling windows in their publicity shots are on a street that faces southwest. Of course it’s gonna be hot in the summer. And those trees won’t solve the problem for thirty years.

Yeah, any heat that comes in through the windows in the form of sunlight stays in a passive house. You need effective awnings, otherwise you are doing something silly.

I saw some construction pictures of this site that make it look like the windows are a sun-porch style arrangement, not unlike a typical passivhaus design. From the artist drawings it just looks like a stereotypical modern glass midrise.

But there's something still off about it. I'm not sure what I expect a multifamily unit to look like but the fact that this one gets complaints of being too hot doesn't surprise me.

Controlling the sunlight is important, but it's important to remember that the outdoor ambient temperature, and interior heat gains from occupants and equipment will play a large role in interior temperature - especially in larger buildings that tend to have a low surface to area ratio.

And in that case it's not just about controlling the solar energy that's coming in, but also having an actual cooling strategy, like natural ventilation, or night cooling.

I live in the Heidelberg/Mannheim area of Germany and this problem is most definitely not restricted to passive houses.

I know several people with top floor apartments that regularly come home to 32°C apartments after work in the summer. Summers here are hot with little air movement and even sleeping with open windows it's impossible to get it cooled down in the night.

If I didn't live in a rental place I would definitely invest in air conditioning.

Are window a/c units not a thing in Germany? If you can buy one of those, you can take it with you when you leave.

AC is not really a thing in private homes almost anywhere in Europe.

Windows also work differently here in Germany than in the US, so the same models definitely wouldn't work. I'm not sure if there are versions for our windows.

There are freestanding versions, which have a flexible tube which you put out the window for dumping heat.

Pretty normal in Norway, just reversed. But I’ve never seen the window version. Usually the a/c unit is mounted on the outside wall and a hole is drilled in the wall to bring in the hose to the unit inside.

> AC is not really a thing in private homes almost anywhere in Europe.

Northern Europe, no; but in Italy they're now very, very common. Temperatures there are steadily rising. Italians used to mock countries where AC has long been de rigueur (North-Africa, South-East Asia etc), but now it's a basic necessity - in areas that already felt very hot because of high humidity, they now hit 50°C year after year.

AC is generally not a thing at all in German residential properties. Usually only in stores/offices/etc and even then it's not a given, I once worked here in an office with no AC. That was a hard summer and it was horrible trying to concentrate on work.

As I think someone else mentioned European/German windows are different to American ones. American ones, lift from the bottom up I believe and an AC unit is put in the gap. European windows can be tilted to be slightly open, or completely opened up into the room much like a door [1].

There are Window units I believe but the Windows have to be modified for them I think, so it's more of a permanent change.

There are also freestanding units which have a hose to go out a window but I've been told from several people that they're not worth the money / don't cool the place down enough. And because the window has to be slightly open for the hose to aim out of more heat keeps coming back in.

[1] - http://4e9dsh1squ2a41o9at4bz989-wpengine.netdna-ssl.com/wp-c...

Most residential windows lift bottom up but we also have the other kind. Makes cleaning much easier.

German electricity prices are very high, almost $0.37 per kWh.

http://ec.europa.eu/eurostat/statistics-explained/index.php/...

I found it interesting that the new Apple HQ (space donut) won't have any are air conditioning. I find it hard to think that a string of sunny hot days won't spike the temp to uncomfortable levels.

https://www.cnbc.com/2017/05/17/apples-new-office-will-refle...

If you read the article, it's still going to have cooling, but with chilled water in the floor instead of cold forced air.

Seems like there was too much glazing (windows and doors) on the south side. It's a problem that a lot of glass skyscrapers face right now as well. They have so much solar heat gain that the AC will be running on a warm spring day just to stop the inside from getting hot.

San Francisco has a number of “luxury” skyscrapers without AC. While this might make sense at ground level, the combination of height, so much glass, and windows that barely open makes things pretty uncomfortable without it.

>Even with cooling down the apartment to 20°C with open windows all night, and closed windows and window blinds all day, the apartment would be back at 28°C when returning after work.

what was the outside temperature? I live in a fairly normal, cheaply-built and poorly-insulated canadian house without AC and in order for my house to get up to 28C by the end of the day it's got to be about 35C outside. It seems hard to believe that a building specifically designed to be "passive" could perform worse.

Last year I lived in a older mobile home in Saskatchewan (tin clad, all south-facing windows). It could definitely get up to around 28C during the day if I wasn't careful about managing things (open the windows while it was cool in the morning, close them by 10am or so, make sure shades are drawn, etc). I only had a wall-mount AC unit, and if I messed up the heat management process I had to run the crap out of it to get the temperatures back down to something manageable.

Fortunately I was working from home, so I would catch a screw-up early (when I'd realize that I was starting to sweat because of the temperature).

Winter was interesting too. The trailer wasn't all that well insulated, so the furnace had to run a fair bit. But on sunny days, even in the middle of winter, you could really feel how much the sun contributed to warming the place up.

It was an experience that really drove home the concept of solar gain though! If I were still living there, I'd be putting up carefully angled awnings to reflect the sun during the summer but still let it in during the winter (when it's lower in the sky).

That is interesting. I've had to run building energy simulations where I spent a lot of time running through similar scenarios while trying to figure out set points for an automated natural ventilation system. It went pretty much exactly as you describe, if you don't catch that heat gain at the right moment, the interior temperatures can get caught increase to a point where opening windows won't exhaust the heat anymore. Since I was working on a completely passively ventilated building at the time, that meant the heat gain would remain, and if there would be a gradual positive feedback loop over the course of a couple of days meaning everyday the interior temperature would get a hotter.

On hindsight, I wish I'd tracked the data for you :)

We were fortunate enough last year to still have quite cool nights; even if I screwed it up, opening the windows at both ends of the house would cool the place down quite well over night. The only really awkward part was when my wife would come home at 6pm, and she'd be uncomfortably warm until it got dark (which wasn't until 10:30pm or so).

Vancouver climate is a lot more temperate than most places in the world. It rarely goes below zero, and during the few months of summer, it will rarely go above 27 C. Most houses don't even have AC so passive houses seem like a great idea.

Put reflective Mylar over your windows.

im sorry but this means that the houses were not designed well. if you have a house that is well insulated, and that does not leak heat from the ventilation system, that means that it will stay the same temperature. if you go through a cycle of cooling and then coming home to a hot house and then cooling again, eventually you will stop coming back to a hot house. the only explanation is that there is a leak (poor design) or that heat is being injected into the house through sunlight or some other means. i would put my money on sunlight making its ways through poorly implemented windows.

by the laws of physics, if you have a passive house kind of house, you will not be able to come home to a hot house repeatedly.

It kind of sounds like GP's was just a regular house, opening windows etc. at night and closing everything during the day is what I do with my regular house. I'd expect a passive house to handle a lot more of this without requiring those types of interventions, and be a lot more successful at it. Like...I don't think something qualifies as a passive house if it doesn't work.

Probably a design with south facing windows simply because while 28 degrees is unacceptable, so is an architecture with no windows in one or more directions.

Also, all power used inside the building must be dissipated somewhere. In a very well insulated building even just 500W idle power inside quickly adds to the air temp.

Like a fridge / freezer which is usually left on 24/7.

first of all, a house with no windows on a single side is not unacceptable. i live in a place that only has windows on one wall and i find it more than acceptable. look at all the houses that people have built with no windows on one or more faces. there are innumerable examples that prove you wrong. and on top of all that, its a completely subjective thing, whether a house needs a certain number of windows. you cant just say that leaving out windows on one side is objectively and definitively unacceptable. thats bullshit.

furthermore, there is no need to omit windows on any side, even the south side. typically, a shading structure is placed that blocks direct sunlight during the warm seasons when the sun occupies those seasonal positions in the sky. these shading structures do allow sunlight when the sun is in its cold season positions, when sunlight is appreciated inside. going even further, windows should filter out any light that is not within the useful spectrum of visibility -- this reduces heat load from the sun. movable shading can also be used to block the sun only during the warm season.

there are countless examples of houses that have lots of windows and do not get too hot.

moving on to power. the back-side of your refrigerator should be vented, not exposed to your inside environment. led bulbs produce very little heat. overall, as i have said elsewhere, you will always need some amount of cooling and heating capacity.

it remains true that a properly implemented passive house will not get too hot, despite your shortsighted observations.

I have almost no windows on the North/East because the idea is to maximize light and have as little heat loss through the windows as possible (heating here is far more expensive I’ve the year than cooling).

In hot and stable climates it’s probably common to not have large windows to the south, but in places where you have +30C in summer and freezing to -20 and dark all winter it’s hard to architect for all seasons. I wouldn’t give up the 4h daylight in my south windows in winter, even though they make the house too hot in summer. Shading that can be removed is probably the answer.

Vented rears for freezers, how does that work? Do they typically sit in an outer wall, or do they have ducts venting so they can be placed anywhere? I have never heard of those.

venting appliances that create heat is not done anywhere as far as i know. the refrigerator is the main appliance that needs this because it is essentially a heat pump that runs all the time. insulating it well and venting its hot side is very simple conceptually and is completely doable.

not venting heat generating appliances inside the house is a design flaw and does not follow passive house principles. because nobody addresses this problem, i do consider almost all passive houses to be incorrectly designed and implemented.

the reason why this problem is not addressed is because some degree of cooling capacity is usually present and can keep the house cool despite this flaw. the heat load from the appliances is relatively small and so it is overlooked -- small compared the loads encountered in old-style houses. also, heat generating appliances are a benefit during the winter, so the problem only exists half of the time.

in an ideal system, all heat generated by all systems in and around the house would be channeled and utilized correctly. we are coming closer to that goal.

True. These things are done in Travel Trailers and RV’s

You may not have to remove shading in winter. The sun is higher up in the air in summer, so an overhang can be all you need (https://greenpassivesolar.com/passive-solar/building-charact...)

I think that is more an effect of Germans hating air conditions.

I think the point of a passive building is that it shouldn't need air conditioning.

no, this is not the point of passive houses. it is a contradiction, but the point is to reduce hvac use as much as possible. you will always need hvac for perfect results because it is impossible to build a perfect hrv system. its impossible to insulate perfectly. there will always be heat leaking from the system. in some extreme cases people can do away with their hvac completely but its difficult and expensive.

Living in Germany, I have not seen a single household with air conditioning in my life.

Even in Italy and Spain, it’s extremely rare. As long as you don’t use plywood, it’s perfectly possible to live without ac.

but i would wager that they do not live in perfect conditions inside those houses

Spaniard here. While not ubiquitous, household AC is not even rare nowadays.

It depends a lot on the area though: it's uncommon in the north/west (where temperatures get pretty low during the night even during the summer), but not in the south/east where temps won't go below 25ºC for several days (and nights) in a row.

Living in Austria we have very strict building regulations and a lot of insulation and despite of this there are more and more air conditioners because it’s so hot outside in summers now that even nights are too hot. No insulation in the world can fix that, especially if heat is also created inside.

It's possible, but not well-advised. Heat deaths in areas with poor AC penetration are, without fail, higher than in those with AC deployed.

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