Vacuum Insulation Panels

Vacuum Packed Insulation Panels or VIP's are thermal insulators that combine high thermal performance properties with limited thickness. VIP's consist of a nano-structured open-celled core material with a composite material wrapped around it which functions as a gas barrier; all of the air is then evacuated. This structure is then tightly sealed into a low permeation barrier envelope which normally consists of either multilayered metalized polymer film or a multilayered aluminium foil.

Initial Use

Due to the high insulation properties of VIP's they were first designed for refrigeration purposes however as building designers became more aware of their high insulation properties they began to specify their use in construction projects that required highly thermal efficient elements, that minimised heat transmission through the building envelope whilst still being of limited thickness.

Advantages of VIP's

• VIP's can provide an extremely thermal efficient barrier of minimum thickness.
• VIP's provide up to 10 times higher insulation performance compared to conventional insulations.
• High quality and long product life time.
• Impermeable to moisture.

Disadvantages of VIP’s

• If the VIP gets punctured on-site then its thermal performance rating is compromised.
• More expensive than other types of insulation.
• Thermal bridging is a constant construction issue.

VIP Risks

However the use of VIP's does not come without risks and careful consideration must be taken with regards to the thermal performance of the panel, the hygric performance, the hygrothermal performance and the structural behaviour and performance of the VIP. In order for VIP's to be successfully integrated into wide scale construction projects they must first be able to demonstrate that they meet the requirements of the 1988 European Construction Products Directive. This directive specifies that construction products must be meet the following requirements:

• Structural requirements.
• Thermal requirements.
• Functional service life requirements. 
• Fire protection requirements.
• Hygiene, health and environmental requirements.
• Safety in use requirements.
• Acoustic requirements.

Thermal Performance vs. Structural Performance

Thermal performance is a critical element of all VIP's and an important point to note is that; when using VIP's in order to provide maximum thermal performance thermal bridging must be kept to a minimum. This requirement can however impact on the structural performance of the VIP as the designer seeks to minimise connection points and edge spacers which act as thermal bridges and thus reduce the thermal performance of the completed VIP structure. One way to minimise thermal bridging when using VIP's is to replace one thick panel with several thinner ones and position them in such a way that the joints of the panels are staggered. Another method of reducing thermal bridging in VIP construction is to use spacers made from low thermal conductivity materials and of limited thickness.

Functional service life vs. Thermal Performance

When designing a building it is important to choose materials with a long service life so as to increase the durability of the building in question. The functional service life of a VIP depends mainly on the rate of thermal conductivity aging inside the VIP. Some factors that are known to influence the aging of VIP panels are;

• The initial vacuum and water content.
• Water vapour.
• Temperature.
• Atmospheric pressure.
• VIP Panel dimensions.

In general, thick and large panels with a ratio of panel perimeter length to surface area as high as possible have a longer expected service life than thin and small panels so for construction details this author advises only specifying VIP's for use in large scale applications. The functional service life of a VIP can also be extended through the use of thick metal based foils to seal the panel however these foils also result in energy losses due to their high thermal conductivity, so here a catch 22 situation is presented to the designer.

Conclusions

• VIP's provide an extremely efficient thermal barrier with minimal thickness of materials.
• When designing VIP's careful consideration must be given to thermal performance, structural integrity and the functional service live of the element.
• VIP's have the potential for widespread use throughout the construction industry.

The Denby Dale Passive House.

For my case study of an international, certified Passive House, I have chosen the the Denby Dale Passive House in West Yorkshire in England. This Passive House was constructed by Green Building Store's construction division; Green Building Company for clients Geoff and Kate Tunstall. The Denby Dale Passive House  is the first certified Passive House in the UK to be built using traditional cavity wall construction.  The house has pioneered the combination of traditional construction methods with the German low energy Passive House design methodology.

www.walkergardensuburb.blogspot.com

Costs:

The Denby Dale house is a 118m² three-bed detached house with basic build costs of approximately €165,000. Not included in this initial cost were: garage, any external works, service connections, decorating, and any sun shading work.

Design:

The Tunstalls had initially wanted a rectangular shaped home but this design did not perform to the Passive House standards after modelling with Passivhaus Planning Package (PHPP) software. Instead a rectangular shape was chosen with the longest side facing south so as to achieve optimum solar gains. This new design met the desired 15 kWh/m²/annum level required for space heating. The clients also expressed there desire to have a conservatory in there new house. This is often a problem for passive houses as it is very hard to retain heat within conservatories, however this conservatory was incorporated into the building envelope as an integral solar space, with exterior brise soleil put in place to minimise overheating.

Insulation:

As heat retention was one of the primary aims of this development, the type of insulation used would be vital. In the end 100mm mineral wool batts were installed in the cavity three deep. This results in 300mm of insulation with each layer having a lambda value of 0.037. The outside of the cavity wall comprises of 100mm natural stone, with the inside comprising of 100mm block work. The Denby Dale house also uses a 500mm fibreglass quilt in the roof void and 225mm of high-performing poly foam insulation in the floor.

Cavity wall construction. www.building.co.uk

Heating:

This house requires at least 90% less heating than the average UK house. The peak heating load for this house is calculated in PHPP as being 10W/m2 when the outside temperature is -10ºC. To allow for this space heating is provided by a conventional condensing gas combination boiler. Water heating is provided by solar panels, which were accquired under a local grant.
 

Points of interest:

• Walls in the Denby Dale House have a U value of 0.1 W/m²K.

• The Ecopassiv timber windows that were used in the build are triple glazed with low-emissivity coatings and argon fill and have a whole-window U-value of just under 0.8W/m²K (and glazing U-value of 0.6W/m²K)
  
• The Denby Dale house overshot the airtightness requirement (0.6 air changes /hour @50Pa) by about 33% and  also came in well under the space heating requirement of 15 kWh/m²/annum.