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Passiv Haus Summary

Introduction to Passivhaus

The Passivhaus (PH) standard originated from a chat in 1988 between Professors Bo Adamson and

Wolfgang Feist. Their overall concept was to create buildings with much lower energy use compared to

existing stock (and minimum building standards). The first PH residences consisting of four terraced

houses built in Darmstadt, Germany, in 1990. Feist then went on to found the Passivhaus-Institute, also

in Darmstadt in 1996. There are currently thirty people working at the Institute. There are estimated to

be more than 30,000 buildings constructed to the PH standard, mostly located in Germany and Austria

[1].

Overview of the Passivhaus Standards

Most PH resources define a Passivhaus according to the numerical standards. However, according to

the definition of PH in the Passipedia (created by the Passivhaus Institute and International Passive

House Association), it is not an energy standard but an integrated concept and is defined as:

“a building, for which thermal comfort (ISO 7730) can be achieved solely by post-heating or post-cooling

of the fresh air mass, which is required to achieve sufficient indoor air quality conditions – without the

need for additional recirculation of air.” [10]

This definition is valid for all climates. The concept also adopts the mantra that any low energy building

needs to be airtight and all airtight buildings required a ventilation system. In PHs, the ventilation

system can also be used to heat the space and thereby avoid the need for a separate heating system

(which I assume is a central heating system with separate ductwork, fans etc). The definition of a PH on

the Passipedia [10] goes on to state that rather than pay for a ventilation system plus a separate heating

system, that either a simple exhaust system coupled with a conventional heating system could be used

or a ventilation system that incorporates additional heating (over and above the heat recovered from

exhausted air) could be used. The PH concept adopts the latter approach. By reducing the capital cost

for a separate heating system, the savings can be used to offset the costs for extra insulation and

achieving airtightness.

The PH concept is then progressed to calculate the maximum amount of heat that can be added to the

preheated supply air [10]. This calculation is independent of climate. The amount of fresh air that

needs to be supplied to a building to ensure good indoor air quality is 30 m3

per hour per person. The

specific heat of air is 0.33 Wh/m3/K. The supply air can be heated up to a maximum temperature of 50

degrees (otherwise it can generate burnt odours from the dust in the air).

30 m3/h/person x 0.33 Wh/m

3/K * (50 – 20) K = 300 W per person



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Note, the temperature of 20 degrees assumes 100% heat recovery between the exhaust and supply air

but currently the most effective heat exchangers achieve 75 to 80% heat recovery. If a lower efficiency

is assumed, the temperature would be slightly less and the result would increase slightly.

Therefore heating of the preheated fresh air can supply up to 300 Watts per person. Assuming 30m2 of

living space per person, the maximum heating load cannot exceed 10 W/m2.

Based on the climate in Central Europe, the maximum heating input of 10W/m2

corresponds to an

actual space heating consumption of 15kWh/m2/year to maintain the building at 20 degrees [3].

According to this reference, the space heating consumption for current building stock is around 220

kWh/m2/year, so the PH standards result in a 93% reduction in energy for space heating.

In addition to setting a maximum energy use for space heating, the PH concept also specifies that the

total energy usage (space heating, hot water and appliances) must be less than or equal to 120kWh/m2/year [2]. This figure seems to be quite high and there seems to be some inconsistency in this

standard. There is a graph of total energy use which indicates that the maximum total energy use in a

Passiv Haus is around 40 kWh/m2/year [2, 3]. Add actual data from CEPHEUS etc in Germany and

milder European climates to demonstrate the range in measured data.

The PH energy standards are typically achieved by super insulation, minimising thermal bridging,

extreme airtightness (less than or equal to 0.6 air changes per hour at 50 Pa), high performance

windows and efficient heat recovery in the ventilation system.

It has been found that a compact heat pump is a cost effective means of adding heat to the supply air in

the ventilation system and also for supplying domestic hot water. This is often supplemented withthermal solar collectors. The heat pump extracts the remaining heat from the exhaust air after it has

preheated the fresh air. In addition, the fresh air can be preheated underground.

Initially the PH standard has focused on countries like Germany and Austria, where the concept was

predominantly focused on reducing heating load. The PH concept is now being expanded to other

climates, such as southern Europe, where cooling is also required. The cooling may also be done by the

heat pump.

In summary the Passiv Haus standards are [2]:

Space h eat demand <= 15 kWh/m2/year

Heating load < = 10 W/m2

Primary energy demand (inc electricity) < = 120 kWh/m2/year (although this seems very high!)

Excessive temperature frequency <= 10% (>25 degrees)



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Certification against Passivhaus Criteria

To be certified as a residential PH, the Passivhaus Planning Package computer modeling software must

be used to calculate the first three standards stated previously (either of the first two standards must be

met). If active cooling is provided, the cooling load must also be below 15 kWh/ m2/year and the

primary energy demand remains at 120 kWh/ m2/year. In addition a pressurization test must be

conducted and the result must be less than or equal to 0.6 air changes per hour (at 50 Pa). Details of the

construction techniques including detail drawings of all junction of the thermal envelope and details of

materials of construction (manufacturer, U value etc) must be provided. A concept for efficient

household electricity consumption must also be supplied. Photographs documenting the construction

process must be provided.

Passiv Haus Standards Compared to Actual Data at 4 Clutha Place.

The table below compares the PH standards to our current home at 4 Clutha Place South Hobart.

Obviously the PH standard is based on the climate in Central Europe (eg Germany).

Standard Passiv Haus 4 Clutha Place South Hobart

Maximum heating input

(W/m2)

10 W/m2

*This assumes 30m2

per person

53 W/m2

(This assumes that our 8kW heat pump

running flat out continuously would heat

the house to 20 degrees- we have never

tried it!)

Maximum heating input

for a 150 m2 house with

3 people

6 W/m2

or 900 W

8000 W

(electricity consumption for this output

from the heat pump is ~ 2500W)

Maximum energy usage

for heating

(kWh/m2/year)

15 kWh/m2/year 8 kWh/m2/year

(only heat lounge room to 18 deg; much

milder climate than Central Europe)

NATHERS star rating for

Hobart climate zone

8.5

(assumes zero energy for cooling)

9

Maximum total energy

consumption

(kWh/year/m2)

120 33

(5,051 kWh from 1/9/10 to 1/9/11, this

includes solar electricity generated and

used on site. Note, there is a solar hot

water which reduces the energy

consumption for heating water)



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Buildings in Australia Designed the Passiv Haus Standards

There are no known buildings in Australia that have been certified against the PH standards. However,

there was a school gymnasium built to the standard (but has not been certified) [5].

Passiv House Planning Package

The Passivhaus Planning Package (PHPP) is a comprehensive spreadsheet used to calculate the energy

consumption of the building. The energy demand of highly efficient buildings is very accurately

reproduced [3]. The PHPP is believed to be well ground truthed with examples in Central Europe, but

not in milder climates, such as Tasmania.

Ventilation Requirements

As a building’s airtightness increases, this may negatively impact on the quality of the indoor air.

Ventilation systems are used in PHs to maintain excellent indoor air quality. Ventilation systems can

range from an extraction only system through to a supply and exhaust system with heat recovery. Key

pollutants present in indoor air include carbon dioxide (from people, combustion byproduct), water

vapour (people, plants, cooking, clothes drying) and VOCs (furniture, fabrics, paints). High levels of

carbon dioxide and VOCs are a direct health hazard. High levels of water vapour can lead to

condensation which can lead to mould growth which is also a potential health hazard. Condensation

(particularly in the roof and walls) can also lead to problems with the structure of the building. Humidity

levels that are too low will cause discomfort for people living inside.

Fresh air ingress through leaks in a house is not a good way to manage indoor air quality. During windy

conditions, the house would have intolerable draughts and probably insufficient air exchange during

calm conditions [7].

In a simulation for a bedroom occupied by two people where the airtightness met the PH standard of

0.6 air changes per hour, the carbon dioxide concentration was predicted to reach 7500 ppm within 8

hours [6]. The safe level specified by ASHRAE and the WHO is 1000 ppm.

For a house that doesn’t have ventilation, windows have to be opened at least four times a day for

purge ventilation and preferably in 6 hour intervals [7].

The simplest ventilation system is an exhaust fan system that extracts stale air from the kitchen,

bathroom and toilet. Fresh air is drawn in through outdoor air inlets into the living areas. The

disadvantage is that in cold or hot conditions, the incoming air is at an extreme temperature and heating

or cooling may be needed. At the other end of the spectrum is a ducted ventilation system where the

exhaust air is used to preheat (or cool) the incoming fresh air in a heat exchanger. In a PH, extra heating

or cooling is added to the supply air.



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It is important that a ventilation system is maintained properly. A Canadian government publication

relating to mechanical ventilation systems recommends that ductwork be professionally cleaned every

few years [8] amongst other maintenance tasks.

The amount of ventilation is stated as 10 L/s for master bedrooms and 5 L/s for other rooms [8] on high

speed (if painting etc). The low speed routine supply speed is about half of these values.

In Australia, ventilation systems are not widespread in residential buildings. Are there minimum

ventilation requirements under the Building Code of Australia?

Applicability of PH to Australia

The core of the PH concept involves adding space heating through the ventilation system. Would it bepossible to relax the airtightness to the point that a mechanical ventilation system is no longer needed?

In Australia, ventilation systems are not common. However, as buildings in Australia become more air

tight for energy efficiency reasons, the need for mechanical ventilation systems in likely to increase.

Hence it could be argued that the PH concept has merit.

PHs in Europe tend to be of lightweight construction without thermal mass whereas in Australia thermal

mass is strongly recommended for cool climates [9].

The PHPP may provide a better indication of heating needs for a low energy home in Tasmania

compared to an Australian package eg Accurate.



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References

[1] http://passipedia.passiv.de/passipedia_en/examples Accessed 6/9/11

[2] Feist, W., First Steps: What Can be a Passive House in Your Region with Your Climate? Accessed via

Passiv Haus Institute http://www.passiv.de/07_eng/index_e.html

[3] Feist. W., What is a Passive House? Accessed via Passiv Haus Institute

http://www.passiv.de/07_eng/PHI/Flyer_quality_assurance.pdf

[4] Stadtwerke Hannover, Passivhausinstitute, Final Technical Report: Cost Efficient Passive Houses as

European Standards, July 2001. Accessed via

http://www.passivehouse.com/07_eng/news/CEPHEUS_final_long.pdf

[5] Pers comm., Peter Steudle, Principal at Passive House Pty Ltd, 5/9/11

[6]

http://passipedia.passiv.de/passipedia_en/planning/building_services/ventilation/the_ventilation_syste

m_-_there_is_no_alternative Accessed 7/9/11

[7]

http://passipedia.passiv.de/passipedia_en/planning/building_services/ventilation/basics/types_of_venti

lation#controlled_ventilation Accessed 7/9/11

[8] http://oee.nrcan.gc.ca/Publications/infosource/Pub/hrv/maintenance.cfm?attr=4 Accessed 7/9/11

[9] Reardon et al, Your Home – Technical Manual , 4th

ed, 2008

[10] http://passipedia.passiv.de/passipedia_en/basics/the_passive_house_-_definition Accessed 7/9/11

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