A passive house represents an innovative construction system ideal for our climate, thanks to advanced insulation and heating systems, allowing for a tenfold reduction in energy consumption for heating and cooling. Let’s explore the benefits and drawbacks of passive houses and whether construction costs pose a barrier to investing in such properties.
When we mention passive houses, we often think of some highly advanced and revolutionary construction system that is expensive, thus nullifying its advantages, at least considering our climate and financial capabilities. However, the concept of a passive house isn’t revolutionary, nor does it involve materials from NASA’s space program.
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Essentially, a passive house is designed from the ground up to minimize energy loss through high-quality insulation, achieving about ten times lower energy consumption for heating compared to conventional houses. To put it in numbers, a passive house achieves a heating energy consumption of no more than 15 kW/m2 annually, representing 80-90% less energy than a traditional house.
How is this achieved? Several key elements must be observed during construction:
- Compact Design: Ensuring the building has a compact shape to minimize its external surface area relative to its volume.
- Southern Orientation: If possible, orienting the building towards the south, depending on the terrain configuration.
- Avoiding Complex Shapes: Steering clear of complex shapes in the building’s construction to simplify insulation and prevent the formation of thermal bridges, which lead to heat loss.
One of the most crucial factors is high-quality thermal insulation. All non-transparent structures must be insulated to achieve a heat transfer coefficient of less than 0.15W/m2. In practice, this is accomplished with a layer of thermal insulation 20-30cm thick (aproximately 8 up to 12 inches). To ensure insulation is effective, airtightness must be maintained to prevent uncontrolled air exchange between the interior and exterior.
Achieving super-tightness requires careful design and execution of construction works. Airtight layers can consist of internal plaster, sealing membranes, or wood-based panels. The significance of this aspect is highlighted by the fact that conventional blinds with a strip extending from the outer shell into the house are not an option.
Moreover, windows and doors play a vital role in a passive house’s insulation system. In a passive house, windows and all glass doors must be of higher quality than those in a standard insulated building. The requirement is for the highest quality windows made from profiles without thermal bridges, meaning profiles that don’t conduct external temperatures to the inner profile surface.
PVC profiles are one of the best solutions for passive houses. The glass is typically triple-pane, with chambers between the glass filled with thermally insulating gas such as argon. The level of attention required for windows is illustrated by the fact that in a well-insulated building, windows have six to seven times worse insulation than walls per unit area.
Therefore, these are critical areas that require special attention. In well-designed passive buildings with the highest quality windows, analyses have shown that during the heating season, windows sometimes, acting like a greenhouse, contribute more to raising the temperature inside the house by allowing sunlight and light to enter, than they lose heat through poorer insulation.
System autonomously maintains temperature and air quality
At first glance, a house constructed and executed in this manner may seem unpleasant to live in because nobody wants to spend time in a hermetically sealed room. Of course, this is not the case. Hermeticity is necessary to prevent uncontrolled heat loss during winter months. As mentioned earlier, a passive house doesn’t have conventional heating systems like radiators or underfloor heating. Instead, it maintains an ideal temperature through forced air circulation.
The system autonomously maintains temperature and air quality in the house, and due to its hermetic nature and superior insulation, the energy consumption for maintaining the ideal temperature is ten times lower than in a conventional building. All energy is utilized. If the outside air temperature is zero degrees Celsius and the ideal temperature inside the house is 20 degrees, when fresh air is introduced into the house, it doesn’t enter directly but passes through a heat exchanger through which used indoor air is expelled.
During this process, the outgoing and “used” air from the interior, at a higher temperature, can transfer up to 80% of its heat energy to the incoming air. This means that indoor air at 20°C (68°F) can heat outdoor air at 0°C to 16°C (32°F to 60.8°F). The process is reversed in summer months, where the outgoing air absorbs heat from the incoming air, maintaining a pleasant temperature indoors with less need to activate air conditioning.
The minimum requirement for these heat exchange systems is a 75% transfer of heat from one air to the other. Only a few devices in the world have the ability to transfer above 88%, and a transfer of 84% is considered very good.
Despite the heat energy exchange with outdoor air, minimal additional heating is still required during winter months. The choice of heating or cooling system depends on the region and which energy source is the cheapest. Considering that the overall heating cost is ten times lower than in a conventional house, using electricity is cost-effective.
Consumption for heating and cooling is reduced
Of course, the most efficient system is heat pumps. For the same amount of heat produced, they consume three times less energy than electric heating, as previously discussed, making heat pumps the most suitable option for passive houses and aligning with the trend of significantly reducing energy consumption.
With passive houses, energy consumption for heating and cooling is reduced to such an extent through the mentioned methods that in such households, other consumers become absolutely unacceptable, thus undermining the concept itself. It goes without saying that a tiny boiler with a power of two kilowatts is completely undesirable in a house where a 100-watt light bulb can heat the room. Therefore, passive houses typically use various solar systems for water heating.
The fact is, the concept of a passive house is still distant to most average families in Serbia. Some calculations suggest that, on average, a passive house should repay higher initial investments through lower maintenance costs after eight years and then continue “earning.” Of course, even that isn’t enough at this point for a larger number of families to decide to build a passive house.
However, the fact is that the population is growing, and energy prices will only rise in the future, with some estimates suggesting even drastic increases. This will make passive buildings the only profitable construction system in the future.
Foto: Freepik