Atmospheric air contains water vapour in the form of invisible droplets. The amount depends on the pressure and temperature of the air. Changes to pressure have a negligible effect, while temperature has a significant impact. As the temperature rises, the air’s capacity to retain water vapour increases, and vice versa. The vapour content of the air is measured either in absolute or in relative values.
Absolute humidity is the amount of vapour in the air at a given temperature expressed in g/m3.
Relative humidity is the ratio of the amount of vapour at a given temperature to the maximum possible amount of vapour retained in the same volume of air and at the same temperature.
φ=C/CS x 100 (%)
φ = relative humidity
C = the concentration of vapour molecules contained in the air at a given temperature.
CS = the concentration of molecules in saturation at the same volume of air and the same temperature
How does condensation work?
When the vapour in the atmosphere reaches saturation, any excessive vapour is condensed and settles on the surfaces of the structural elements as droplets. This concentrated amount of moisture is the dew, while the temperature at which the phenomenon occurs is called the dew point or dew temperature.
When the hot air in a room comes in contact with a cold surface, such as a conventional window, it loses some of its heat and cools down. As its temperature decreases, its ability to retain a quantity of vapour (Cs) decreases.
If the air’s temperature drops below the dew point, then surface condensation is observed. In the above diagram, we see that if the air temperature drops from 20ο C to 10ο C, a quantity of humidity of 7.9g /m3 will be released.
Condensation can also occur if the relative humidity of the room increases, which happens in areas with many people due to breathing, boiling water in the kitchen or a bathroom when using hot water.
When does condensation appear?
Condensation usually occurs during the winter, when the outside temperature drops to low levels and at points that appear to be the coldest, generally the windows. Below is a table with the maximum surface temperatures where liquefaction is appearing.
Observing the above table, we see that for an indoor air temperature of 20oC and relative humidity of 60%, condensation will occur in any element with a temperature below 12oC.
An energy-efficient window with a lower coefficient of thermal permeability (more thermal insulation) has a higher temperature on its inner surface than a conventional one, a fact shown in the following table.
At an external temperature of -11o C and indoor at 20o C, the conventional window has a temperature of 5oC on its inner surface while the energy efficient one has 12o C. Therefore the first will show condensation at a relative humidity of 40%, while the latter will show if relative humidity exceeds 60%.
We see that with an indoor air temperature of 20oC and relative humidity of 60%, condensation will occur on a conventional window when the external temperature drops below 9.2o C. In the case of a thermal break frame, this limit drops to -1.5o C.
A thermal break aluminium window with a single 4mm glass is no good either: there will be no condensation on the frame, but there will be droplets on the glass when the external temperature falls below 9.0o C.
Humidity harms homes and human health.
Infects and destroys building materials due to absorption.
Reduces the thermal insulation capacity of the structural elements.
Favors the growth of bacteria and the retention of microorganisms in the materials, especially when accompanied by high temperatures.
Creates a feeling of discomfort in people living or working in a humid place.
Creates an unsightly image in the space (mould).
Condensation is distinguished from other forms of moisture by the way it appears:
It is usually a temporary and periodic phenomenon.
The infestation does not go deep into the building block, but remains superficial.
It is an interior phenomenon, so it appears only on the inner surface of the house.
The proposed changes to energy efficiency do not provide a clear path towards Net Zero, which is disappointing. The knowledge, the modelling tools and the building components required for this target exist. Because of our European background, we are using energy efficiency regulations and the Net Zero Energy Buildings [NZEB] concept in Europe as reference points for comparison with Australia.
We want to draw your attention in particular to our “case study about airtightness”, and we ask you to consider making the Blower Door Test compulsory for the Certificate of Occupancy.
Energy efficiency in Europe
The research for energy efficiency technologies and products in Europe started 40 years ago. PV panels for domestic hot water were the first popular solar gain products, soon to be followed by PVC and thermal break aluminium windows, double-glazing and thermal insulation products like EPS and XPS. The Passive House Institute started researches in 1991 with great help from German institutions and the industrial sector.
Despite this background, it took Germany more than 30 years to reach 50% of the net-zero targets by 2050. The rest of Europe is moving even slower. It soon became a common perception of the need of reducing energy consumption to a level that renewable resources can cover the demand.
All new buildings in the European Union must comply with the Nearly Zero Energy Building standard [ΝΖΕΒ], which refers to a building that can offset its energy demand from on-site or close-by RES. Because renewables can only meet a small portion of current energy demands, reduction of consumption is critical. The locality of RES is essential for regions with limited investing capabilities and for those with difficulties in connecting solar farms with the grid. The latter applies to Australia.
A similar standard is gaining momentum in the US and Canada, however, NZEB there stands for Net Zero Energy Building.
A house certified to the Passive House standard has an energy demand of 15kWh/m2 per annum for heating, cooling and hot water. Compared to a conventional building, PH has approximately 80-90% lower demand. Computational modelling is done through the Passive House Planning Package (PHPP), which is a comprehensive and sophisticated tool that takes into account thermal insulation, mechanical ventilation with heat recovery and an airtight building envelope and also complying with many building standards:
Thermal comfort calculation according to ISO 7730
Indoor air quality according to DIN 1946
U-value of window frames and thermal bridges according to EN/ISO 10077-2
U-value of glass according to EN 673
G-value (solar transmission of glass) according to EN 410
Mechanical services as per AHSRAE’s guidelines
We believe that NatHERS is an empirical model without serious scientific backup, presented in a complicated manner.
Three random examples:
The concept of the “average R-value” does not base on any building physics standard. How will double thermal insulation outside a bedroom help the thermal comfort in another bedroom on the opposite side?
Thermal bridges are under consideration. With many modelling software available (Flixo, Heat3, THERM, Psi-therm), we expected to see relevant calculations incorporated in the NCC.
The standard treatment of thermal bridges is to wrap exposed surfaces with insulation and not to “resolve thermal bridges with air cavities”. Who is supposed to understand this description and document it? The domestic builder?
The future of energy efficiency in Australia
There are many constraints in Australia developing its path towards carbon-free buildings:
With 0.322% of the global population, the size of the Australian economy is relatively small, making overseas investments in R&D non-feasible.
While the rest of the developed world is buying expensive energy, Australia is exporting fossil fuels. Any changes to this industry will cause political and social side effects. Unless statutory changes (like the NCC) are drive towards net-zero, there is no reason to expect that developers and builders will do that voluntarily.
There is a bipartisan policy to prioritise trade qualifications versus University Degrees. The current status sees trade qualified builders designing, overseeing and to some extend certifying their works. We cannot see how Australia can compete with countries where engineers and architects drive research and production.
«Tracking towards 2020: Encouraging renewable energy in Australia» lapsed in 2020, and there is no official policy following up.
Solar farms have had difficulties connecting to the old and sensitive grid since 2019.
Conflicting messages are sent to the public:
The Premier of Victoria confirmed three years ago that the State «has enough renewable energy projects on the way», assuring that «soon we will generate enough energy to power every home in Victoria».
In April 2021, «renewable energy from sources like wind, solar and hydro provides about 21% of Australia’s electricity supply».
Daniel Westerman (CEO, Australian Energy Market Operator) announced Australia’s transition to 100% Renewable Energy Resources by 2025.
Combining the global status towards net-zero with the proposals about upgrading 6-star to 7-stars in Australian buildings, we don’t see Australia reaching net zero within this century.
Comparing Passive House with NATHERS
60,000 buildings around the globe have been tested and certified.
Requirement for continuous thermal insulation layer around the building envelope
The “average R-value” concept balances local poor insulation by additional insulation in another area.
Maximum of 0.6CPH and this is tested during construction.
NatHERS assumes 10CPH
Mechanical ventilation with a minimum of 75% heat recovery.
Heating & hot water energy demand
<15kWh/m2 per year, alternatively, 10kW/m2
No validated data is provided.
<15kWh/m2 per year + dehumidification contribution, or 10kW/m2 cooling load
No validated data is provided.
Primary energy demand
<120kWh/m2 per year
Linear and point thermal bridges calculated according to EN-ISO 10211.
Case study about airtightness
A three-bedroom certified Passive House in Melbourne with a floor area of 120m2 and ceiling height 2.70m has an air volume of 324m3. The Blower Door test measured 0.6CPH during the certification process, while the PHPP confirmed an energy demand of 15kWh/m2/annum.
This demand equals 54MJ/m2/annum, which, as per the NatHERS star band criteria classifies the house at 8-star.
We drill one hundred and twenty eight holes in the external walls where we put toilet fans to all of them. Half of the fans blow 50m3/h and the other half extract 50m3/h.
We have now created an air circulation of 64 X 50m3= 3,200m3per hour, increasing the air changes to 10CPH.
This house is not a Passive House anymore, but it still is 8-stars in NatHERS.
Energy efficiency in Australian homes is some decades back from Europe.
While Europe and the USA use dynamic analysis in energy efficiency modelling, double-glazing is still a voluntary and luxurious feature in Australia
The discussion about upgrading the minimum requirement from 6 to 7 stars is outdated. In global terms, the NatHERS system is a primitive tool, and results will still be very far from energy efficiency as is meant in the rest of the world.
Even with the 7 stars, implementation will base on the builder’s confirmation, as there is no testing requirement.
Accept the Passive House standard as a thermal assessment tool in the NCC-2022
All thermal and energy computational modelling tools must prove a minimum interior temperature of 12.6o when the relative indoor humidity is 50% to prevent mould growth.
Airtightness test must become compulsory.
Include heat recovery performance of mechanical services in the Certificate of Occupancy.
Certified Passive House Designers hold a degree in architecture or engineering. We find additional training requirements at a lower level needless.
The past decade has seen increased awareness of the need for renewable energy and reducing embodied energy in the building sector. Together with our affiliates, our global #EfficiencyFirst campaign aims to raise awareness of the foundational aspect of sustainable buildings that is too often overlooked: Energy efficiency.
Currently, 35% of global energy consumption stems from the building sector alone and the operational stage is the largest contributor to carbon emissions. The majority of this stems from heating and cooling demand. Passive House buildings provide a transparent, quality-assured approach to meeting our climate goals, while also creating a comfortable, healthy and sustainable built environment.
Over the course of 2021, the International Passive House Association-iPHA network will be running a series of activities and events with the aim of promoting the significance of an efficiency first approach to building design; wherein buildings are planned, constructed and retrofitted to have an extremely low heating and cooling demand.
Make your building work for you and live better using less energy in a comfortable, healthy, sustainable and future-oriented Passive House.
NZEB Australia will be partnering with Clinics By Design, a dedicated Design & Construction company specialising in new buildings and fit-outs for the healthcare industry, to provide Passive House Design services for their upcoming projects.
Buildings that implement the Passive House principles use approximately 80% less energy than buildings of equivalent size while providing superior air quality and comfort, two extremely important factors in any healthcare setting.
Proper thermal insulation is essential in Passive House design. Not only does thick and continuous insulation provide the crucial thermal separation between the heated or cooled inside environment and the outdoors but it also improves thermal comfort by reducing the risk of condensation.
Although this can be seen as a challenge within the Australian medical environment in which we have automatic doors and promote open windows where possible in order to create a better atmosphere for patients, it doesn’t mean your clinic will be constructed as an air tight box. The difference is that when these windows and doors are closed there is no gap for cold or warm air to escape, therefore maintaining an ambient and comfortable environment. This can be beneficial within environments that are dealing with skin or more serious medical conditions and therefore want to keep the building free from outdoor pollutants where possible. Not only do MVHR systems help to clean the air from pollution and contribute in regulating humidity they also recover warm and cool air which would otherwise go to waste.
In the summer of 2017, the island of Tilos became known through two awards it won at the EU Sustainable Energy Awards. The island won the first prize in the category for the Green Islands but also in the category for the audience award for the TILOS project.
Launched in 2015, TILOS aims at the energy autonomy of the remote island, in a project involving thirteen partners from seven European countries. The project is led by the Laboratory of Mild Energy and Environmental Protection of the University of Piraeus, while also participating HEDNO, WWF-Hellas and private sector entities active in the field of renewable energy sources.
The implementation of the project includes the installation of hybrid Renewable Energy Resources system, combining a wind turbine with photovoltaic park and the storage of electricity in advanced technology batteries. The initial goal of the program was to meet the needs of the island by at least 60-70% and later by 100% with the possibility of exporting the energy surplus to the island of Kos, through a submarine power cord.
Upon completion of the project, this power generation system will cover the needs of the island, both for the 400 permanent residents, as well as for 13,000 visitors each year. At the same time, the European Commission intends to use the project as a guide for similar projects on other small islands in the European Union, in a move that will change what we knew about electrifying island areas. This is also the reason why the European Union has largely funded the project, providing A$7mn out of the total A$9mn of the budget.
Converting energy into easily stored fuels is a good solution:
Water electrolysis and hydrogen production, potentially as intermediate storage (conversion utilisation rate of up to 63%)
Conversion into synthetic methane (3 H2 + CO2 → CH4 + 2 H2O), also called P2G (conversion efficiency rate of up to 57%). The methane is stored in subsoil storage tanks with almost no losses, resulting in an expenditure factor of 1.75 kWh/kWh.
The EPBD requires all new buildings from 2021 (public buildings from 2019) to be nearly zero-energy buildings (NZEB). According to Article 2 “nearly zero-energy building” means a building that has a very high energy performance, as determined in accordance with Annex I. The nearly zero or very low amount of energy required should be covered to a very significant extent from renewable sources, including sources produced on-site or nearby.