What is the Passive House (Passivhaus) Energy Efficiency Standard?

Passive house (German: Passivhaus) is a voluntary standard for energy efficiency in a building, which reduces its ecological footprint.  It results in ultra-low energy efficiency buildings that require little energy for space heating or cooling.

Contents

The Passivhaus standard

• Typical Passive House windows.
• Design considerations
• Airtightness
• Ventilation
• Ventilation heat exchanger
• Heating demand
• Heat Recovery
• Primary Energy Consumption
• Power Generation

Passive House Examples & Construction Specifications

• The Saskatchewan Conservation House (1977)
• The world’s first Passive House (built 1988)
• The Hanssen-Höppener Passive House (2018)
• Steve Giroux’s house, Hinesburg, Vermont (built 1984)
• Canolfan Hyddgen Offices, Machynlleth, Wales (Built 2008)

Benefits of living in a passive house

References for further reading

The Passivhaus standard

• Use up to 15 kWh/m2 (4,755 BTU/sq ft; 5.017 MJ/sq ft) per year for heating and cooling as calculated by the PHPP (Passivhaus Planning Package), or a peak heat load of 10 W/m2, based on local climate data.
• Use up to 60 kWh/m2 (19,020 BTU/sq ft; 20.07 MJ/sq ft) per year primary energy (for heating, hot water and electricity).
• Leak air up to 0.6 times the house volume per hour (n50 ≤ 0.6 / hour) at 50 Pa (0.0073 psi) as tested by a blower door; or up to 0.05 cubic feet per minute (1.4 l/min) per square foot of the surface area of the enclosure.

In Passivhaus buildings, the cost savings from dispensing with the conventional heating system can be used to fund the upgrade of the building envelope and the heat recovery ventilation system.

With careful design and increasing competition in the supply of the specifically designed Passivhaus building products, in Germany it is now possible to construct buildings for the same cost as those built to normal German building standards, as was done with the Passivhaus apartments at Vauban, Freiburg.

The standard is based on five principles: airtightness, ventilation, waterproofing, heating and cooling, and electrical loads.

Passivhaus buildings employ superinsulation to significantly reduce the heat transfer through the walls, roof and floor compared to conventional buildings

In Sweden, to achieve passive house standards, the wall insulation thickness would be 33.5 centimetres (13.2 in) (0.10 W/(m²·K)) and the roof 50 centimetres (20 in) (U-value 0.066 W/(m²·K)).

Typical Passive House windows.

To meet the requirements of the Passivhaus standard, windows are manufactured with exceptionally high R-values (low U-values, typically 0.85 to 0.70 W/(m²·K) for the entire window including the frame).  These normally combine triple-pane insulated glazing (with a good solar heat-gain coefficient, low-emissivity coatings, sealed argon or krypton gas filled inter-pane voids, and ‘warm edge’ insulating glass spacers) with air-seals and specially developed thermal break window frames.

Design considerations

In Central Europe and most of the United States, unobstructed south facing windows are usually incorporated into the design where the heat gains from the sun are, on average, greater than the heat losses, even in mid-winter.

Airtightness

Building envelopes under the Passivhaus standard are required to be extremely airtight compared to conventional construction. They are required to meet either 0.60 ACH50 (air changes per hour at 50 pascals) based on the building’s volume, or 0.05 CFM50/sf (cubic feet per minute at 50 pascals, per square foot of building enclosure surface area). In order to achieve these metrics, recommended best practice is to test the building air barrier enclosure with a blower door at mid-construction if possible.

Ventilation

Passive house is designed so that most of the air exchange with exterior is done by controlled ventilation through a heat-exchanger in order to minimize heat loss (or gain, depending on climate), so uncontrolled air leaks are best avoided.  Another reason is the passive house standard makes extensive use of insulation which usually requires a careful management of moisture and dew points.  This is achieved through air barriers, careful sealing of every construction joint in the building envelope, and sealing of all service penetrations.

Use of passive natural ventilation is an integral component of passive house design where ambient temperature is conducive, either by singular or cross ventilation, by a simple opening or enhanced by the stack effect from smaller ingress with larger egress windows and/or a skylight.

When ambient climate is not conducive, mechanical heat recovery ventilation systems, with a heat recovery rate of over 80% and high-efficiency electronically commutated motors (ECM), are employed to maintain air quality, and to recover sufficient heat to dispense with a conventional central heating system.  Since passively designed buildings are essentially air-tight, the rate of air change can be optimized and carefully controlled at about 0.4 air changes per hour. All ventilation ducts are insulated and sealed against leakage.

Ventilation heat exchanger

In addition to the heat exchanger (centre), a micro-heat pump extracts heat from the exhaust air (left) and hot water heats the ventilation air (right). The ability to control building temperature using only the normal volume of ventilation air is fundamental.

Heating demand

In addition to using passive solar gain, Passivhaus buildings make extensive use of their intrinsic heat from internal sources—such as waste heat from lighting, white goods (major appliances) and other electrical devices (but not dedicated heaters), as well as body heat from the people and other animals inside the building.  This is because people, on average, emit heat equivalent to 100 watts each of radiated thermal energy.

Together with the comprehensive energy conservation measures taken, this means that a conventional central heating system is not necessary, although they are sometimes installed due to client skepticism.

Instead, Passive houses sometimes have a dual purpose 800 to 1,500 watt heating and/or cooling element integrated with the supply air duct of the ventilation system, for use during the coldest days. It is fundamental to the design that all the heat required can be transported by the normal low air volume required for ventilation.  

Heat Recovery

The air-heating element can be heated by a small heat pump, by direct solar thermal energy, annualized geothermal solar, or simply by a natural gas or oil burner.  In some cases a micro-heat pump is used to extract additional heat from the exhaust ventilation air, using it to heat either the incoming air or the hot water storage tank. Small wood-burning stoves can also be used to heat the water tank, although care is required to ensure that the room in which stove is located does not overheat.

Beyond the recovery of heat by the heat recovery ventilation unit, a well designed Passive house in the European climate should not need any supplemental heat source if the heating load is kept under 10 W/m².

Consider also daylighting, passive daylighting, active daylighting, and ecological footprint.

Primary Energy Consumption

To minimize the total primary energy consumption, the many passive and active daylighting techniques are the first daytime solution to employ.  For low-light days, non-daylighted spaces, and night-time, the use of creative-sustainable lighting design using low-energy sources can be used. Low-energy sources include ‘standard voltage’ compact fluorescent lamps or LED lamps.

Power Generation

Solar powered exterior circulation, security, and landscape lighting – with photovoltaic cells on each fixture or connecting to a central Solar panel system, are available for gardens and outdoor needs. Low voltage systems can be used for more controlled or independent illumination, while still using less electricity than conventional fixtures and lamps. Timers, motion detection and natural light operation sensors reduce energy consumption, and light pollution even further for a Passivhaus setting.

Passive House Examples & Construction Specifications

1, The Saskatchewan Conservation House (1977)

• Consumed 85% less energy than an average 1970s home
• Contained one of the first residential heat recovery ventilators (HRV) for space heating
• Equipped with a grey water heat exchanger for water heating
• Originally built with solar energy collectors to assist in generating electricity for HRV and water heat exchanger
• Sided in dark-brown cedar to absorb heat from the sun
• Designed with insulated window shutters

The Saskatchewan Conservation House helped establish basic design principles for energy-efficient housing, such as:

• Tight air-vapour barrier construction
• High (but economically justifiable) levels of insulation
• Housing designs that optimize passive solar gains
• Controlled and efficient air management
• Tight, well-insulated windows and frames (many window manufacturers now build triple glazed windows with argon filled cavities)
• Well-insulated exterior doors with excellent draught seals

2, The world’s first Passive House (built 1988), a Passive House with four units in Darmstadt-Kranichstein, Germany.

A subsequent measurement of the airtightness in October 2001, for example, gave a pressurisation test air change rate (n₅₀-value) that was still less than 0.3 h^-1. Thermographic images showed that the building components were actually free of thermal bridges.

• The hot water is heated using solar vacuum flat collectors (5.3 m² per household or 1.4 m² per person).
• Natural gas is used for secondary heating. The flat-collector thermal system covers about 66% of the dhw consumption.

Because the provision of domestic hot water represents the greatest energy requirement of this house, an efficient domestic hot water system is of great importance. The heat distribution and circulation pipes have therefore been placed inside the thermal envelope and are well insulated.

Ventilation (Heat Recovery)

A Passive House in the Central European Climate can only function with a controlled ventilation system with high efficiency heat recovery, because the average annual ventilation heat losses are 35 kWh per square meter of floor space, this is more than twice the Passive House heating demand. This was already known due to the investigations during the preparatory research project.

Thus in Kranichstein a balanced supply air and exhaust air ventilation system with a highly efficient counterflow air-to-air heat exchanger was used – but it had to be specially adapted for this purpose because at the time, the fans used had a very high electricity consumption.  This continuously operating comfort ventilation system provides a constant supply of fresh air to each accommodation unit.

• In this project, DC fans with electronic commutators were used for the first time (known as EC motors).
• During operation, a heat recovery rate of over 80% was measured after optimisation of the flow geometry.
• At the lowest setting, 100 m³/h of fresh air is supplied to the living and sleeping areas in each unit. This means, that with a four person household, the specific quantity of fresh air would amount to 25 m³ per person per hour. The unit then operates constantly at this rate independent of the actual number of people in the building (for the best as shown by experiments with complex ventilation controls that were not worth it). Users can, however, manually change the setting if the choose.
• At the highest setting, between 160 and 185 m³/h are supplied.

Extract air is drawn away from the humid rooms like the kitchen and bathrooms in corresponding quantities. Such high-efficiency ventilation systems had not been available before the Passive House.  Today these units typically display the following characteristics:

• heat recovery efficiency of more than 80%,
• electricity consumption of less than 0.4 Wh/m³ transferred air

These ventilators in the Passive House functioned faultlessly for between 13 and 15 years, until they were replaced during the course of routine renovation work by newer products from the same manufacturer.

Airtightness and air quality

The insulating materials are airtightly separated from the interior by continuous interior plaster or vapour membrane without any gaps.  

Due to particularly well-insulating and airtight sliding shutters as temporary heat protection, it was even possible to operate one of the accommodation units as a “zero-heating-energy house” without any heating in the years 1994 to 1996.

3, The Hanssen-Höppener Passive House (2018)

The calculated annual heating demand is 14.24 kWh/m². The building is equipped with a heat recovery ventilation system (heat recovery rate 95%) and a 50 metre long upstream geothermal heat exchanger.

The small remaining demand for heating the house is met by a radiant heat pellet stove. The wood pellets that are produced from untreated by-products of the wood-working industry are completely CO2-neutral. The CO2 released during combustion is no more than that released during the natural decay of wood in forests, for example.

Domestic hot water is provided by an air/water heat pump with an integrated 250 litre storage tank.

A 3.2 kWp photovoltaic system on the roof produces electricity which is fed into the grid (cost effective battery storage are now available).

4, Steve Giroux’s house, Hinesburg, Vermont (built 1984)

The attached deck is on the home’s south side (a typical detail in Vermont, where sun is usually welcome). The small size of the south windows is a clue that Giroux favored the superinsulation side of the solar vs. superinsulation debate

Therefore, if your house design or refurb relies on a large amount of glazing for solar gains, it should be possible to close this area off to the rest of the building at times of low sun heat cold weather. Inversely, if it is very hot in summer, it should be possible to vent the solar gains part of the building.

Canolfan Hyddgen Offices, Machynlleth, Wales (Built 2008)

•  space heating demand (14.8kWh/m2/yr) is almost exactly what was projected (15kWh/m2/yr). Space heating demand (measured, average over 4 years): 9 kWh/m2/yr.
• the building’s primary energy demand (80kWh/m2/yr) is almost half that projected (144 kWh/m2/yr), mainly because computer use has been lower than expected.
• The gas heating boiler was the smallest the team could find at 9-22kW. Temperature control, TRV’s
• Heat load (PHPP): 4.8kW (PHPP – Passive house planning package)
• Carbon emissions (measured): 48.4 kg CO2 m2/yr
• Airtightness (at 50 Pascals): 0.249 ACH
• Ground floor: Slate finish with 150mm Regen GGBS slab under this, followed underneath by 300mm Jablite 70 EPS insulation. U-value: 0.122
• Walls: European larch cladding counter battened to 22mm Bitroc sheathing board externally, followed inside by 195mm stud insulated with Warmcel, 9mm OSB, 50mm service cavity, 25m Gypsum plasterboard, Gypsum Plaster skim finish. U-value: 0.18
• South roof: build up features 300mm of Warmcel with 50mm uninsulated service cavity inside this, and finished internally with 13mm Gypsum plasterboard and Gypsum Plaster skim finish. U-value: 0.125
• Windows: thermally broken triple-glazed Internorm Edition windows with Krypton filling. U-value: 0.78
• Heating system: Heating system: 24-9kW Broag Remeha low NOX condensing gas boiler, providing 4054 kWh/yr (PHPP)
• Ventilation: five Drexel & Weiss Aerosilent Business units, with 85% heat recovery according to VDI 2071
• Electricity: 7kW solar photovoltaic array with Fronius inverter. Producing 19.38 kWh/m2/yr. Projected to produce 5250kWh/yr but monitoring found it producing 6493 kWh/yr in 1st year due to cold bright sunny winter weather. Average dropped back over four years when two milder overcast winters and a very wet summer were included.
• Green materials: recycled concrete blocks, cellulose insulation, timber frame elements, GGBS

Benefits of living in a passive house

Fresh, clean air:  Note that for the parameters tested, and provided the filters (minimum F6) are maintained, HEPA quality air is provided. 0.3 air changes per hour (ACH) are recommended, otherwise the air can become “stale” (excess CO2, flushing of indoor air pollutants) and any greater, excessively dry (less than 40% humidity).  This implies careful selection of interior finishes and furnishings, to minimize indoor air pollution from VOC’s (e.g., formaldehyde). This can be counteracted somewhat by opening a window for a very brief time, by plants, and by indoor fountains.

Very small heating and hot water energy bills and a low environmental footprint building.

Homogeneous interior temperature: it is impossible to have single rooms (e.g. the sleeping rooms) at a different temperature from the rest of the house. Note that the relatively high temperature of the sleeping areas is physiologically not considered desirable by some building scientists. Bedroom windows can be cracked open slightly to alleviate this when necessary.

Slow temperature changes: with ventilation and heating systems switched off, a passive house typically loses less than 0.5 °C (0.90 °F) per day (in winter), stabilizing at around 15 °C (59 °F) in the central European climate.

In the United Kingdom, an average new house built to the Passive House standard would use 77% less energy for space heating, compared to the circa-2006 Building Regulations.

Passive house Trust Awards

https://www.passivhaustrust.org.uk/passivhaus_awards/awards/

References for further reading

https://www.passivhaustrust.org.uk/

https://passivehouse.com/

https://passipedia.org/