Passivhaus

HRS have worked on a number of Passivhaus schemes, so have extensive practical and technical experience. A Passivhaus project and an award winning building that HRS were heavily involved in is the prestigious Passivhaus Interserve Offices in Leicester.

The HRS Passivhaus air testing consultancy service will ensure you get the right advice at the right stage to achieve the Passivhaus standard. It is crucial if you are working to the Passivhaus standard that you contact HRS early – it never to soon to contact us.

Passivhaus (or ‘Passive House’) is the fastest growing energy performance standard in the world. It is said that the Passivhaus standards strengths lie in the simplicity of its approach; build a house that has an excellent thermal performance, exceptional air tightness with mechanical ventilation.
The objective for a Passivhaus building is that thermal comfort 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.
Passivhaus is often compared and confused with the Code for Sustainable Homes and BREEAM ratings for non-domestic buildings. They are not the same: Passivhaus is a specific energy performance standard that delivers very high levels of energy efficiency, whilst the Code and BREEAM are overarching sustainability assessment ratings which address a large number of environmental issues.
No. It is a misconception that the Passivhaus standard only applies to residential dwellings. The Passivhaus standard can also be applied to commercial, industrial and public buildings.
The Passivhaus standard was developed in Germany in the early 1990s by Professors Bo Adamson of Sweden and Wolfgang Feist of Germany and the first dwellings to be completed to the Passivhaus Standard were constructed in Darmstadt in 1991.
There is often confusion over the Passivhaus standard as it can be confused with the more generic approaches to passive solar architecture, as it does shares some common principles.

Where the Passivhaus standard is not the same as the more generic concepts is in Passivhaus’s ability to reduce the permitted space heating demand and primary energy consumption. This means it can be considered as both a robust energy performance specification and a holistic low energy design concept.
Passivhaus thermal comfort is achieved to a greatest practical extent through the use of passive measures. Please see the list below – this can be applied to the residential dwellings, commercial, industrial and public buildings:

  • Good levels of insulation with minimal thermal bridges
  • Passive solar gains and internal heat sources
  • Excellent level of airtightness
  • Good indoor air quality, provided by a whole house mechanical ventilation system with highly efficient heat recovery

There are no strict requirements with respect to domestic hot water, lighting and appliance consumption. The standard imposes an overall limit on the Primary Energy consumption which promotes energy efficiency in all of these areas.

The Passivhaus standard is a comprehensive low energy standard intended primarily for new buildings. The following energy performance targets define the standard and must be met in order for certification to be achieved.

Energy performance targets and air changes per hour
Specific Heating Demand ≤ 15 kWh/m². yr
Specific Cooling Demand ≤ 15 kWh/m². yr
Specific Heating Load ≤ 10 W/m²
Specific Primary Energy Demand ≤ 120 kWh/m². Yr
Air Changes Per Hour ≤ 0.6 @ n50

 

It is possible to achieve the Passivhaus standard when refurbishing buildings, although this can be a lot more costly.

The standard requires that the Primary Energy demand target is met in all cases, this figure must include the space heating, domestic hot water, lighting, fans and pumps and also all of the projected appliance consumption. In addition to the primary energy demand the standard permits that either the Specific Heating Demand or the Specific Heating Load must be met.

Yes – the energy balance of the proposed building must be verified using the Passivhaus Planning Package (PHPP) using the appropriate regional climatic dataset. Either the monthly or the annual method may be applied.

If the Specific Heat Demand is ≤ 8kWh/m².yr or the ratio of free heat gains to heat losses is greater than 0.70, it is recommended that the monthly method is used to ensure accuracy.

The standard provides limiting backstop values for the glazing specification, ventilation systems, air tightness levels and thermal bridging, as these factors should not exceed these limits in order that the thermal comfort criteria can be maintained.

The following table illustrates the elemental backstop values which should not be exceeded in order for the Passivhaus certification criteria to be met.

Design Component Limiting value
Walls, Roof, Floor (U-values)* ≤0.15 (W/m²K)
Glazing unit ≤0.8 (W/m²K)
Installed glazing ≤0.85 (W/m²K)
Doors ≤0.8 (W/m²K)
Infiltration (ach-1) ≤0.6 @ n50
Thermal bridging (linear ψ value) ≤0.01 (W/mK)
MVHR coefficient (η HR) ≥0.75
Ventilation electric limit 0.45 Wh/m3
Appliances High efficiency recommended
Lighting High efficiency recommended
On site renewables No requirement but SHW typical

* please note opaque U-values are only recommended targets and are not critical to certification.

The backstops above apply to moderate weather regions only, for warmer climates the performance values could be reduced. Please consult your building certifier for more information.

A refurbished building can be certified as a “Quality-Approved Passivhaus” if the certification criteria for Passivhaus are met when refurbishing a building – this is based on the same criteria as for new buildings. It can however be very difficult to achieve the Passivhaus standard for older buildings for various reasons.

If you are able to use Passivhaus technology for all relevant building components in your existing buildings, it will lead to substantial improvement in respect of thermal comfort, structural protection, cost-effectiveness and energy requirements.

If a building is refurbished using Passivhaus components and largely with exterior wall insulation, it can be certified to the EnerPHit standard. This will then show evidence of quality assurance and verify achievement of the specific energy values.
The designation EnerPHit+i is used if more than 25% of the opaque exterior wall surface has interior insulation. It will be likely that moisture analysis will be needed where opaque elements are insulated internally.

The standards have slightly relaxed certification criteria, as indicated below:

Criteria Passivhaus EnerPHit
Specific Heat Demand ≤ 15 kWh/m².yr ≤ 25 kWh/m².yr
Primary Energy Demand ≤ 120 kWh/m².yr ≤ 120 kWh/m².yr *
Limiting Value n50  ≤0.6-1 n50  ≤1.0-1

* PE ≤ 120 kWh/m².yr + ((SHD – 15 kWh/ m².yr) x1.2)

As with new build projects, the energy balance of the refurbished building must be verified using the Passivhaus Planning Package (PHPP). For calculation of the specific space heat demand, both the monthly as well as the annual method can be applied, see the Outline Specifications above for further details.

Thermal Bridging and Passivhaus

Thermal Bridging also exacerbates heat loss from buildings.  In modern buildings that are well insulated and reasonably airtight, the thermal bridging losses can account for a significant percentage of total building heat loss.

Calculation of thermal bridging losses (psi values) can be calculated using thermal modelling software.  HRS has dedicated experts to help analyse details, provide quantitative analysis and highlight potential solutions to meet required targets.

Thermal bridging analysis can assist with meeting Fabric Energy Efficiency targets for Building Regulations and also Code for Sustainable Homes ENE 02 criteria.  Strict energy targets required for the Passivhaus standard may also require thermal modelling.     

If you are unsure of the Air Tightness services you require please call 0800 030 4391 or email info@hrsservices.co.uk and one of HRS Air Tightness Consultants would be happy to guide you through the process.

HRS carried out Passivhaus testing at Interserve Leicester

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CASE STUDY: Centre For Medicine, University of Leicester. BREEAM, Thermography, Air Tightness Consultancy & Testing to Entire Building and Floor Plenums – pdf »

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