Table of Contents

 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 Code for Sustainable Homes does.

The basis of the standard is about achieving very low energy use. The actual standard is that

• the total energy demand for space heating and cooling is less than 15 kWhkilowatt hour. This is a unit to measure an amount of energy. If you run your 30 kW gas boiler for 2 hours a day you use 60 kWh per day/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[for the purposes of part C of the Approved Documents] - Any wall that does not have a separating function. 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 littlethermal 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 PassivhausSee more on the Passivhaus standard. The PassivHaus Institute has pioneered a standard for low energy buildings. It includes very low energy usage and ways of achieving this. The word is derived from the idea of buildings which are fundamentally low energy and passive solar heated rather than using extra gadgets to heat them. See Passivhaus for the UK branch of the organisation. 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 right after the MVHRMechanical Ventilation with Heat Recovery 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 (PVPhoto Voltaic. referring to the generation of electricity from sunlight ready).

There is a short primer on Passivhaus on the BREBuilding Research Establishment.  website

Comparison with SAP and CSH

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 regulationsThese are the legal regulations which govern how a house is constructed. (not to be confused with Planning Permission which is about whether you are allowed to build the house at all or what it might look like) see Building Regulations) which have built in factors in the SAPStandard Assessment Procedure - the method used in the building regulations for calculating the energy use of a house. see Part L and SAP calculation which take into account the amount of carbon emissions.

The Code for Sustainable Homes covers much more than just energy so comparing it with the Passivhaus standard is like comparing apples and oranges. However the energy saving element of a Passivhaus is roughly equivalent to CSH Code for Sustainable Homes. A standard for eco-houses developed by the Building Research Establishment. It covers a wide range of criteria  level 4. If you were then to add PV energy generation and some of the other features which count in CSH then you could reach level 6 (carbon neutral). The Larch House at Ebbw Vale is an example of this. 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 AECBthe Sustainable Building Association)  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 rather than rolling them into one as the CSH tends to do.

Design and certification

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 - PHPPPassivhaus planning package) 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. Manufacturers are queuing up to get their products approved.

see also The Passivhaus Trust for more information on the standard.

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

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