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Passivhaus standard

Passivhaus at Denby Dale
Passivhaus at Denby Dale

Outline

The Passivhaus standard has been developed to provide a practical methodology for designing and building houses which require very little energy for heating, so little in fact that they require no central heating system, even in the coldest parts of Europe. Note that Passivhaus is about energy only and does not cover other ecological aspects in the way that, say CSH does.

The standard is now widely accepted, not only by self builders but also by local authorities and housing associations, eg the Norwich based Broadlands Housing Association plan to build a 208-home eco-development

The basis of the standard is about achieving very low energy use in conjunction with a high standard of comfort and air quality. The actual standard is that

  • the spacific heating demand for space heating and cooling is less than 15 kWh/m 2 /yr
  • the total primary energy use for all appliances, domestic hot water and space heating and cooling is less than 120 kWh/m 2 /yr

(the floor area is measured to the inside face of external walls and ignores internal wall thicknesses and certain areas which are not considered habitable such as stairs and landings)

This is achieved by a combination of –

  • very high insulation in walls, ceilings and floors – typically 300mm thick (with very little thermal bridging) with doors and windows having high values of insulation built in. Glazing is typically triple with low E coatings and argon filled. See more on Passivhaus window design
  • low air infiltration – below 0.6 air changes per hour; enough to provide very high air quality without unnecessarily cooling the building.
  • compact form which ensures a minimum of heat loss through the fabric
  • passive solar collection which is incorporated by having most of the glazing to the south and designing windows with high solar heat-gain coefficients.
  • heat recovery ventilation which is designed so that the minimum of air necessary to maintain high quality ventilation is achieved, (1m³/m² of floor area/hr). An air to air heat exchanger recovers most of the heat from the outgoing air (usually over 80%). Incoming air first goes through the heat exchanger and then an in-line booster heater which lifts the temperature up to room temperature. It is then distributed by ductwork to the various rooms in the house.

The Passivhaus Institute has an excellent web site called Passipedia which explains all the fundamental principles of the standard and the main web site for all UK things Passivhaus is http://www.passivhaus.org.uk/

Once you design to this level of energy efficiency no central heating system is necessary. Any heating which may be required is added to the incoming ventilation air either directly by an electric heater or (thanks to recent developments) via a ground source heat pump which has its heat output into the ventilation air. This combination of energy saving measures has a built in logic to it.

vent outlets ensure there is never a direct draught

The rate of air change is minimal but sufficient to guarantee a high level of air quality. It is also a sufficiently low rate to ensure that air is never moving at a speed of more than one tenth of a metre per second, the threshold at which air movement becomes noticeable. This allows a maximum heat input of 10W/m2 of floor area which is typically provided by a small heating coil or resistance heater situated after the MVHR heat exchanger. So for instance a 150m2 house would have an extra heat input on top of solar and internal gains) of 1.5kW under the severest conditions.

Although on-site generation of energy from sources such as photovoltaics is not an integral part of Passivhaus design there is no reason it cannot be incorporated additionally, possibly at a later date (PV ready). See Passivhaus Plus standard below.

The Passivhaus standard is gaining traction in the UK and several towns and cities are beginning to adopt it. Examples are Exeter and Norwich.

Comparison with SAP

Passivhaus does not prescribe what type of energy is used (except the bit about ‘primary’), or whether it is carbon based. Only how much energy is used. This contrasts with the UK building regulations which have built in factors in the SAP calculation which take into account the amount of carbon emissions.

The standard assessment procedure (SAP) which is the part of the building regulations used to calculate energy efficiency has its counterpart in the Passivhaus Planning Package. There is a bit of a debate going on as to whether it would be better to adopt the Passivhaus approach rather than the SAP approach to energy calculation. A detailed comparison of the two (originally produced by the AECB) is available here. It should be borne in mind that the continental approach to ecological building has tended to separate energy calculations from the ecological and health impact of building materials

Design and certification

PH logo

To achieve this level of low energy consumption there is a combination of computer aided design (via a large spreadsheet) and a certification procedure, all based on the experience of the thousands of existing Passivhauses which have been built already, mainly across Europe. At present both the BRE and the AECB have taken on the responsibility for administering this process in the UK and information is available on the BRE website and a demo version of  the computer design software (the Passivhaus planning package – PHPP) can be downloaded from there and also from Passivhaus.

There is a well developed certification procedure for building components such as doors, windows etc. to gain Passivhaus ratings so that these ratings can be fed into the spreadsheet which produces the final energy use values for a house.

Although the standards are very high and very strict there is (in theory) no restriction on the types of materials used or the design of components such as windows and doors, just so long as the final standards are met. While manufacturers are queuing up to get their products approved, there is still a massive lack of components made in the UK and people tend to get them imported.

see also

A list of certified Passivhaus designers can be found on the PassivhausPlaner.EU web site.

Cost

Experience in Germany, Sweden and Austria, where most of the development has been done shows that initially the cost of individual Passivhauses is quite high but that as builders become more conversant with the standards and more local manufacturers produce components then the extra price comes down to about 4 to 6 percent above normal building rates.

Passivhaus refurbishment

The Passivhaus standard for refurbishment can be slightly lower than for new buildings because it is acknowledged that certain aspects of an existing building are difficult to change, e.g. the number of windows and their sizes. This is all covered in a modified standard called EnerPHit where for instance the energy limit is ≤ 25 kWh/m²/yr rather than 15.

One of the most thoroughly thought through renovations of an old house is ‘Under the Sun‘ in Birmingham. This has been successfully brought up to Passivhaus standard

 

Under the Sun. Click the image for more info

Passivhaus Plus standard

The Classic passivhaus standard is mainly about reducing energy consumption by incorporating very high levels of insulation, excellent control of air infiltration, the use of passive solar collection (mainly through windows) and high quality MVHR. This is mostly achieved with no ‘gadjets’ or particularly high technology. A passivhaus could probably have been built 50 years ago by someone with access to MVHR technology.

Fulford Passivhaus

the first UK Passivhaus Plus house at Fulford near York

The Passivhaus Plus standard places the upper limit for total energy demand at 45 kWh/(m²a) rather than 60kWh/(m²a). It also requires a minimum of 60 kWh/(m²grounda) of electricity generation (either directly from the house site (such as PV) or if that is not possible, then investment in remotely generated sustainable electricity. See more detail on the Passivhaus Trust web site.

Volfgang Feist and some background to the Passivhaus Institute

Volfgang, a physicist, is the originator of the Passivhaus concept along with Bo Adamson, and there is an interview with him by energy consultant Peter Warm on the background and principles involved. It is in 6 parts.

Part 1 on the background to it

Part 2 on principles

Part 3 on renewables

Part 4 on the pace of implementation

Part 5 on the history of Passivhaus development

Part 6 on technical aspects

The concept is moving into the mainstream now with developments such as Camden Council’s new council house scheme for 55 new homes to be built by Willmott Dixon and designed by architects Rick Mather.

Passivhaus stove flues

There have been a considerable number of fires in Passivhauses with class 1 heating appliances (such as wood stoves). These have been attributed to heavily insulated and sealed roof areas where heat buildup has occurred, possibly due to flue fires. An article in Green Building magazine, summer 2013 describes one such very serious fire, which although the flue was twin-wall and to current building regulations. pretty much burnt the house down. A Dutch company, Metaloterm, manufacture a high grade insulated flue designed to prevent such fires.

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