IN SHORT, HOW DOES A PASSIVE BUILDING WORK?
Imagine a perfectly insulated building, as if it had been covered with a coat that protects it in both winter and summer. It’s nice inside, as you keep it occupied and release heat into it. If, in addition, the weather is sunny, it’s even better, and you don’t need to heat anymore. But it is necessary to avoid that the sun enters there in summer, to avoid overheating.
WHY”PASSIVE”? HE DOESN’T DO ANYTHING?
The concept of the passive building is that the heat released inside the building (living things, electrical appliances) and that provided by the outside (sunlight) are sufficient to meet heating needs. An occupied building that does not lose internal heat does not need heating to remain pleasant to live in. In a traditional building, heating is only used to compensate for heat loss.
WHAT IS THE PROBLEM WITH THE HEATING?
Pollution. To heat, you have to use energy. And we can turn the problem around in all directions, the use of energy generates pollution. More or less depending on the energy used, but the only way to reduce pollution is to consume as little as possible.
The pollution of the atmosphere by the various emissions, while the most important, is not the only one: noise, visual and olfactory pollution accompany all traditional heating systems.
Do you like radiators? There are those who make noise, those who smell the burnt dust, or those who take up an inordinate amount of space. There are also building-integrated heating systems, but they also create other problems in terms of layout, maintenance, etc.
Hot and cold areas If you heat, you create hot spots. And so, logically, cold areas. The more you heat, the greater the difference between hot and cold areas. To the point that the comfort zones in the dwelling shrink as the heating increases. What a waste!
Cost Finally, you have to pay for the heating. Energy, the cost of which will inevitably increase, is a significant item. The heating system, too, represents a significant investment. There are better things to do with this money.
HOW TO KEEP THE HEAT IN?
Insulation. It is quite obvious that to keep heat in a building (or leave it outside when it is hot), it is necessary to insulate the walls well. Because the main losses occur when heat passes through these walls: first of all the roof (hot air rises), then the walls and finally the floor. Doors and windows are considered as particular walls (transparent and/or opening).
In addition to effective wall insulation, particular attention must be paid to eliminating the passage of heat through particular points in the structure, called “thermal bridges” because it is passages (bridges) that promote thermal losses. In practice, external insulation should be preferred, as it eliminates these crossing points.
Doors and windows, which are less insulating than fixed opaque walls, must also achieve a higher level of insulation. The use of triple glazing is recommended or even necessary to achieve sufficient insulation performance in a passive building.
Ventilation and sealing To avoid heat loss, a passive building must avoid any air passage. You know those unpleasant cold air streams in poorly finished buildings? Before the advent of controlled ventilation, these passages allowed the renewal of the air, which was essential for the well-being of the inhabitants. They are now to be eradicated, as they jeopardize thermal performance and can cause damage to the envelope.
In addition, the ventilation of a passive building is the only “forced” passage of air, and no longer through “leaks”. Like insulation, waterproofing is therefore an essential passive criterion. It should be noted that the air that passes through a dual flow ventilation system is filtered, which allows passive buildings to benefit from excellent Indoor Air Quality (IAQ).
Outgoing heat recovery A passive house, like any modern and comfortable house, is (very) well ventilated. But since ventilation sucks in outside air and then releases it outside after passing through the hot zone, there is no question of heating this incoming air and eventually throwing this heat out. When the insulation is satisfactory, ventilation becomes an important channel for heat loss. The idea is therefore simple: we recover the heat from the outgoing air (not the air itself, just its heat) to heat the incoming air. In cold weather, no more frozen air coming in!
For this purpose, passive constructions are most often equipped with a so-called “double-flow” ventilation system (incoming and outgoing flows pass through the ventilation system) with heat exchanger. To fit into a passive building, this system must be able to recover more than 75% of the heat from the exhaust air and transfer it to the incoming air (efficiency calculated on the exhaust air).
It is now possible, to save even more money, to recover heat from “grey” water (dishwasher, washing machine, shower, washbasins) to preheat incoming water from the network (or incoming air).
ARE THE PASSIVE BUILDINGS WEIRD?
No, a passive building is not weird. Nothing looks more like a passive house than a house that is not. The same goes for schools, offices, supermarkets…. It is an energy performance that is required, not a specific shape or aspect. From the most classic to the most eccentric, architects can design passive buildings like traditional ones.
Climate and regional clothes remain the main influences on the architecture of passive buildings. However, they often have thick walls, due to the amount of insulation required. You will also often see large windows facing south to take advantage of the solar gain and few windows to the north to avoid wastage.
Similarly, it is advisable to design compact buildings to reduce the surface area of the envelope to be insulated. Again, climatic and economic constraints influence design, as is already the case in traditional regional architecture.