Passivhaus encourages an approach to design which considers the building as an interconnected whole. Holistic concepts should be applied to the orientation and form of the building, as well as the design of mechanical services and fabric performance.
Designers can address all these interconnected principles/requirements through their own work, for example, through their PHPP calculations. Alternatively, there are now multiple companies that offer a ‘Wholebuilding system’ approach to achieving the Passivhaus standard. This may offer a simpler approach, especially for inexperienced designers or clients, as the system providers will have undertaken much of the work to ensure compliance with the Passivhaus standard. In addition, the systems are built in state-of-the-art factories by highly skilled technicians, which allows for closely monitored quality control without the need for multiple on-site visits during varying weather conditions. However, they may not be suitable for all sites, designs or situations!
All whole-building systems should deliver on Passivhaus requirements, including the following principles:
Fabric U-value 0.08 – 0.15W/m2K
The building fabric will probably have 200–300mm of insulation, depending on the lambda value of the insulation, but still needs carefully considered design, which will reduce heating and cooling energy requirements significantly. The design should also avoid thermal bridges, which could compromise the thermal performance of the building, although the system should help as these potential bridges should already have been considered, identified and minimised.
The system should achieve the target of very airtight construction, which has four advantages:
• no draughts, and thermal comfort at lower temperatures
• fabric preservation through preventing moisture ingress into walls from inside
• energy saving
• sound attenuation from external noise.
Again, off-site fabrication should help in achieving the required airtightness level for Passivhaus.
Window U-value less than 0.8W/m2K
The triple glazed windows reduce unwanted cold down draughts by maintaining a minimum internal surface temperature of 17˚C, which is standard for Passivhaus and should be included as standard within the system. However, design decisions, such as concentrating window openings on the south facing elevation, and using appropriate shading, will help to reduce heat losses and manage solar gain.
Fresh air ventilation 30m3 /person/hour
The system should also include an efficient controlled ventilation and heat recovery system to ensure optimum fresh air while managing heat recovery from outgoing air. This should maintain the optimum internal temperature with minimal heating and cooling equipment. However, the location of the unit and the design/ layout of the ducting will still affect the efficiency of the system.