The Summertime Failure of Minergie and the Case for AC

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Minergie is a fantastic concept for a cold planet, and to keep cool in winter. It traps heat with ease during the morning and radiates it for the rest of the day into the night. It supplements to solar radiation heat with geothermal heat, which it gets from the heat pumps. That heat is then spread across the buidling with hot water pipes.

In winter this is fantastic because it saves on energy and provides a comfortable environment. In reality it’s not unusual for me to notice 25°c in winter, so in effect it might be too warm, for some.

It’s in summer that what makes minergie so awesome in winter becomes a death trap in summer. More than once during the recent heat waves I have had the same head ache as after cycling up to Marchairuz with a sporty cycling group. The difference is that I was sitting, in shorts, at a laptop. I was not exerting myself.

I liken living in a minergie building, especially in the attic as living in a car left in the sun from April until September or later. Within minutes it’s oppressively hot, as soon as you turn off air conditioning, if it’s too hot to open windows, and that’s one of the issues with minergie, more than with traditional buildings.

With a traditional building, if you get too hot you can open to ventilate when it’s cool enough, and the Specific heat capacity will dump the heat that had accumulated. When I lived in an apartment during the 2003 heatwave I opened a window on each side, and the cross breeze provided cooling for the entire day, and key to this, when I closed the windows to avoid mosquitos I didn’t feel radiant heat as soon as I closed the windows.

I often try to find the motivation to wake at five or six in the morning, to open all the windows, including the hallway, to attempt to get cool air into the building, and it works. I go from 29°c to 28°c or even 26°c if I start early enough, and for a few minutes it feels excellent.

The problem is that as soon as the sun hits the balcony it heats the tiles, and the huge windows that are great for bringing heat in, in winter, trap it in summer. You can’t cool from one side once the sun has made its appearance.

I still cool via the veluxes until the outside air temperature (OAT) is similar to the indoor temperature. That’s when everything needs to be closed, and that’s when the oppressive heat stroke provoking level heat begins.

The thing about this Minergie building heat stroke risk is that during the night the air is comfortably cold. It’s 19°c to 21°c. Indoors it’s 30°c or more. That means that with the nocturnal heat exchange, during summer heat waves the building could cool.

People will say “but if you keep the windows open at night you do the same thing for free, or almost, and you’re right, except that the heat is structural, not air.

The hallway that connects all the apartments is sealed from the top. Neither the lift, nor the stairs have a vent. This means that in summer the heat from outside that gets in rises, and gets trapped heating the apartment walls, but also apartment floors. This means that the apartments can be sealed from the outside heat, but if anyone has bad habits, in the floors beneath, then the heat gets trapped, and then rises, for hours at a time. It’s also worth noting that the garage, that is cool in the morning, does heat up, so heat from the garage also makes its way up the stairs.

Three Good Nights

It is important to highlight that I hate the concept of air conditioning because to me, cooling air, by heating air, is negating the entire concept. For me, a simple cross breeze is good, when possible, or taking advantage of nocturnal cooling is also good.

I slept much better three times this year, once when I used air conditioning because I was getting over Puce de Canard and this was an emergency situation. I also found that a night of storms and rain helped make sleep much better, and finally for at least one night I found that having a simple fan, to shift air provided enough of a cooling effect to make sleep more consistent.

The Minergie Standard Update

While writing this blog post I read that the Minergie standard has been updated. It states that buildings should not exceed 26.5°c for more than 100 hours per year. This means that my building should be modernised with cooling systems to match the latest norms.

Minergie is now expected to make spaces more comfortable in summer as well as winter. This means that the renovation to meet this norm is justified in a shared property, especially since I have data showing that the temperatures are currently three to five degrees higher than they should be.

The Self Regulation Optic

With normal buildings, you close windows to keep them warm, and you open windows to cool them. The structure is designed with small windows which reduces heat loss in winter, and heat ingress in summer. Minergie buildings are designed to maximise heat gains in winter, but in summer that makes them uncomfortable.

Their materials makes them hermetic. Once the heat comes in there are no drafts, and thus no cooling. This means that the structure must be able to breath and release heat. A heat efficient building is stiffling in summer, unless you open windows but the paradox is that opening windows changes internal pressure and thus the thermostat behaviour.

With a minergie ventilation only changes the air but the structure stays warm.

That’s why the 2023 amendment to the Minergie standard offers hope. From 2023 onwards buildings must be below 26.5°c. They can be above 26.5°c for 100 hours before they are not within the new norms. I see this with enthusiasm, because it could help justify upgrading the setup of the building I live in.