Energy Efficiency

Passive House

Published on January 14, 2021

Dowell ThermaLineTM

The main difference between a passive house window and a standard window is that the windows within a passive house play an important role by reducing the heat loss from the house. Passive windows are insulated and trap solar gains within the building. Passive homes require double low-e or triple glazed windows to ensure the correct U-value is achieved. Insulated frames are also used to minimise heat loss and ensure the occupants comfort within the building.

Standard windows don’t have insulated frames and sometimes only have single or double glazing, by using these windows in a passive house the occupants will not be comfortable due to the huge temperature difference between the window and the wall, there might also be problems with thermal transfer and condensation.

The ‘Passive House’ standard requires that the building fulfills the following requirements:

  • 1. The building must be designed to have an annual heating and cooling demand as calculated with the passive house planning package of not more than 15 kWh/m² per year (4746 btu/ft² per year) in heating and 15 kWh/m² per year cooling energy, or to be designed with a peak heat load of 10W/m².
  • 2. Total primary energy (source energy for electricity) consumption (primary energy for heating, hot water and electricity) must not be more than 120 kWh/m² per year (3.79 × 104 btu/ft² per year).
  • 3. The building must not leak more air than 0.6 times the house volume per hour (n50 ≤ 0.6 / hour) at 50 Pa (N/m²) as tested by a blower door.

Passive solar design can also be used to optimise the free energy from the sun. Depending on the expanse of glazing, orientation and available shading, it is likely that the window specification (glass and frame) required will be Uw 2.0 or below.

Of the three defined, a typical passive house accounts for as much as 50% of the heating and air-conditioning loads, and accounts for most of the discomfort due to draughts or excessive heat gains. A typical Australian home built before 2000 would likely achieve an airtightness test result in the realm of 10 air changes per hour (ACH), measured in a pressurised building (to 50Pa), and in many homes this can be up to 25 ACH.

Zero Energy Building

A zero-energy building, also known as a zero net energy (ZNE) building, is a building with zero net energy consumption, meaning the total amount of energy used by the building on an annual basis is roughly equal to the amount of renewable energy created on the site. These buildings still produce greenhouse gases because on cloudy (or non-windy) days, or at night when the sun isn’t shining, and on short winter days, conventional grid power is still the main energy source. Because of this, most ZNE buildings still get half or more of their energy from the grid.

Buildings that produce a surplus of energy over the year may be called ‘energy-plus buildings’ and buildings that consume slightly more energy than they produce are called ‘near-zero energy buildings’ or ‘ultra-low energy houses’.

Traditional buildings consume 40% of the total fossil fuel energy in the US and European Union, and are significant contributors of greenhouse gases. The zero-energy goal is becoming more practical as the costs of alternative energy technologies decrease and the costs of traditional fossil fuels increase.

The development of modern ZNE buildings became possible, not only through the progress made in new energy and construction technologies and techniques, but also improved by significant scientific research, which collects precise energy performance data on traditional and experimental buildings and provides performance parameters for advanced computer models to predict the efficacy of engineering designs.

Heating and insulating buildings
Architects need to know how well different materials will insulate the building they design. To help them with this they need to know the U-values of different materials.

A U-value of 1 W/(m2 ºC) means a 1 metre square area of the material with a 1ºC temperature difference across the material will conduct heat at a rate of 1 joule per second.

U-values measure how effective the properties of the insulating materials are. The lower the U-value the better the material is at insulating.

U-values for windows (Uw-values)

Dowell ThermaLine™ windows and doors have been designed to allow building designers to achieve energy efficient designs. They are efficient in terms of Uw-value and also air leakages rates to minimise heating and cooling loads.

Reference source; 1. Building Connection Magazine (Winter 2014 Issue), ‘Building a Passive House’; 2. Passive House Builders [online] Available: (13 November 2014)

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