5 Powerful Principles of Passive House Design

What is a Passive House?

Passive house or Passivhaus is a philosophy and a design strategy for creating high performing and thermally comfortable homes using construction and scientific methods. 

In other words, a building that stays cool in the summer and warm in the winter.

They are a design approach that allows a building to be heated and cooled whilst only using 10% of energy. This gives them a “factor 10 rating”, whereas typical new builds average only a 25% energy saving. 

The aim is downsizing your heating system by upgrading thermal efficiency.

If we can produce a building that does not need to be heated much or at all by mechanical means by retaining heat, recovering heat and ensuring everything is thermally sealed, then even body heat can be enough to heat the home. 

However, Passive house is much more than just a low energy home. 

Passive House encompasses all areas of comfort within the home whilst addressing ecological concerns of sustainability.

Fresh and stale air is exchanged, whilst using far less oil per sq metre of living per year than your average home. 

Let’s explore Passive House further by boiling this design philosophy down to 5 main principles:

the Principles

1.      Superb Thermal Performance

2.      Heat Recovery and Moisture Recovery

3.      Excellent indoor air quality

4.      Passive heating and cooling strategies

5.      Thermal Comfort

1 Superb Thermal Performance

Key building elements such as external walls, ground floor and the roof along with other building elements must have a U-Value of 0.08-0.18 W/m2k or better.

This includes mitigating thermal bridges by creating airtight and wind tight buildings.

The energy demand does not need to equal 0, mainly due to economical matters and difficulty in building to such a high standard is not practical.

However, what is important is having a heating and cooling system that will run as efficiently as possible, afterward each room can be calibrated to the desired comfort level.

2 Heat & Moisture Recovery

Our bodies create heat through activity and movement which can be significant in heating homes when the thermal performance of the building fabric is superb.

Mechanical ventilation heat recovery systems allow you to redistribute heat to other areas of the house.

Heat can also be lost through the ventilation system; it makes sense to recover heat that would otherwise be wasted, by using a mechanical ventilation heat recovery system (MVHR).

From a comfort and hygiene standpoint the system will provide fresh air to be heated or cooled, as the heat exchanger system can work both ways!

Conventional heating and cooling systems can be used too; however, the thermal performance of Passive Homes has the benefit of being so efficient that buildings can be heated through air supply only.

3 air quality

Touched on previously with the Heating and Cooling systems, integrated systems facilitate the inflow of filtered air from outside.

It is important to create a constant input and output of fresh and stale air.

Heat can be redistributed without the contaminants in the air through means of exchanging the air supply.

The heating and cooling system must also be able adjust the humidity within the rooms to ensure comfort levels are optimised.

Purge ventilation is also a useful method of both expelling heat and providing fresh air as a comforting choice for the user in the summer, although this wouldn’t be the best energy efficient solution in the winters especially, however there is something comforting about opening a window from time to time.

In terms of air purity and hygiene the mechanical ventilation system will be the best way to achieve this.

4 Passive Heating and Cooling

Harness the power of the Sun by calculating the correct aperture size of the window.

This can be determined by how the sunlight will impact the space inside in relation to the outdoor environment.

Window sizes do not need to be large, however they will need a U-value of 0.8 W/m2k or better.

Controllable Shading devices can provide excellent cooling during hot summers by changing the angle of shading throughout the day as the sun changes position.

The occupants, office or household appliances, and heat extracted from the exhaust are also heat sources that can be utilised and redistributed.

Natural shading devices like balconies or canopies and use of negative spaces are excellent ways to create cool spots during those hot summers.

Natural ventilation such as purge ventilation can be utilised as an extra measure for cooling.

Space planning can impact the efficiency by planning electrical and plant items in the core of the building.

5 Thermal Comfort

Comfort within homes and offices can be determined by a few factors.

The first being air temperature being an average of 21 degrees, and with the option adjust between 18-24 degrees.

Additionally Surface temperatures should not exceed more than 3-4 Kelvin either way, for example ideal floor temperatures are comfortable between 19-26 degrees.  

The second being air humidity with the home should be around 40-70%, as medically speaking humidity levels below 30% are considered unhealthy.

Air movement within the home should not exceed 0.08m/s to ensure ideal flow of air between rooms, and to avoid draughts.