WHAT IS A PASSIVE HOUSE?
What exactly is a "Passive House"? You may have heard of this term before and you may immediately think energy efficient. But how is it energy efficient? Well, imagine living in Toronto, with its hot summers and cold winters in a house with no air conditioner and no furnace. You must think that's crazy! You'll just boil to death in the summer and freeze to death in the winter. That's not energy efficiency, that's energy deficiency! Well, let's pause and think for a second. When we are so accustomed to houses with heaters and air conditioners, we cannot comprehend living in a house without them. With a passive house, even though it does not have a conventional heating and cooling system, it regulates temperature in other ways.
Here are the 5 basic principles that make a "Passive House" energy efficient.
1. Lots of Insulation
Almost all houses have insulation, but what makes a passive house different is the quality and strategic placement of insulation. It's like a thermos, whatever beverage of choice you put in the bottle, it stays completely insulated. Hot stays hot and cold stays cold. Insulating a passive house means trapping heat in all areas, especially areas that have a high heat loss. This means insulating the entire building envelope which consists of walls, roof, floor, doors and windows. When these 5 areas are sealed properly, you would feel warm inside the house without the need of a heater.
2. No Air Leakages
There should be no holes whatsoever to let air in or out of a passive house. This is like an unpoppable balloon that never loses its air. In a passive house, the air is sealed in and there is controlled air flow which almost eliminates:
heat energy loss
unwanted heat gain
infiltration of pollutants
This allows for comfortable living inside the house where the temperature is constant and you won't feel cold walking from one room to the next because of a drafty window.
3. No Thermal Bridges
Thermal bridges are a big no-no in a passive house. Yet, it exists in most houses today because eliminating thermal bridges is much easier to do at the time the house is first being built. You may wonder, what exactly is thermal bridging and why are we eliminating it? A thermal bridge is a pathway where heat travels through walls from the inside to outside. When a house is heated, right away the heat is escaping through the walls resulting in heat loss.
You can eliminate thermal bridging by having a layer of insulation between the inside wall and outside wall, just like how a thermos works. When you have hot coffee in a thermos, you won't realize how hot the coffee actually is just by holding the outside of the bottle. Only when you take a sip, you realize it's hot, hot, hot! When thermal bridging is interrupted by insulation in the thermos, heat won't be transferred to your hand. When we apply this concept to a passive house, it becomes that much more energy efficient.
4. Heat Recovery Ventilation
A heat recovery ventilation (HRV) system is a device that provides the inside of the house with fresh air without letting any heat out. It controls ventilation throughout the entire house so that you won't have to open windows for fresh air (although you still can, of course). Ventilation is important to eliminate smell, air pollutants and humidity. This ensures comfort for the occupants inside the house and protects structure of the house from moisture.
A HRV device may not sound familiar to you but you're likely using one right now. Although, we call it something else. A nose! That's right, as you are reading this, you are probably unconsciously using your nose to breathe air in and breathe air out. As this happens, heat recovery ventilation is at work. As you breathe in, cold air goes in through your nose and gets warmed up. As you breathe out, hot air goes out through your nose and gets cooled down. This helps your body to retain heat energy. A HRV device is essentially the nose of a house. It consists of two ventilation ducts where one duct carries cool, fresh air in and the other duct carries moist, stale air out. This results in better indoor air quality and lower energy use. In a certified passive home, the HRV device has to meet a minimum standard of 75% heat ventilation recovery rate to ensure energy efficiency.
5. Proper Windows
Having windows of the right thickness and orientation is essential in a passive house. Triple pane glass has a higher heat resistant (R factor) than double pane glass, which means the energy savings is far greater with a higher R value. You can generally expect triple pane glass to have a value of 9 or 10. By contrast, double pane windows tend to have an R value of somewhere between 3 and 4.
The orientation of windows is also of great importance. Windows needs to be oriented properly so the sun can heat the indoors in the winter and shade is provided in the summer. South windows are the best as it allows for maximum heat gain in the winter, whereas north windows are not about heat gain, but about heat loss to help the house cool down in the summer.
The window frame is the weakest part in the entire building envelope in terms of heat loss, which is why in passive house construction, it is important to have properly insulated frames.
Putting these 5 things together, you end up with an energy efficient passive house...
There you have it, so living in a house without a conventional heater and air conditioner is entirely doable. With its smart use of energy, you can literally heat up a whole living room with only 10 candles. A passive house requires 90% less energy than a typical house. But you may wonder, where does the 10% come from? Simple. Energy can be easily supplied to the house from the sun, body heat, light bulbs and appliances. So the next time you bake those delicious cookies on a crisp autumn day, you are not only satisfying your sweet tooth, but you are effectively heating up the house. And don't worry, the HRV device takes care of the smell without you having to crack open the window.
Believe it or not, passive house is not a new concept. The first passive house was built in Germany almost 30 years ago, in 1991 by physicist, Dr. Wolfgang Feist. It has been tried and tested for decades and is another example of German engineering at its finest. This concept is now gaining popularity in Canada for being both affordable and eco-friendly. Stay tuned for our next blog on why we think passive house is the future!
Links and References
Here is a short video by Hans-Jörn Eich that explains the concept of a passive house in 90 seconds. It visually depicts the concept quite well.
For a more detailed video, here is a good one that explains how a passive house = 90% home energy reduction.