Is the Petflap a passivhaus pet door?
With the help of the Passive House Academy New Zealand we have had the Petflap’s U-value calculated and its air leakage performance tested. The results show that the Petflap far outperforms a standard pet door, particularly the a double-ended Petflap with long trunking, which is the likely standard for a passivhaus. This doesn’t confer any official status on the Petflap as a passivhaus pet door, but the results speak for themselves.
The results are really good – even better than we’d hoped for. The Petflap provides a good standard of insulation and allows a low rate of air exchange. In other words, it’s a great choice if you’re looking for a draughtproof and well-insulated pet door.
The Petflap has been fitted in exposed areas and low energy homes around the world. It’s been fitted by people who’d given up on catflaps on windblown islands, and people looking for the best catflap for their energy efficient build. We knew anecdotally that the Petflap performed to a very high standard, and these figures prove it.
Air leakage tests
Air leakage tests were carried out by Oculus Architectural Engineering Limited in Auckland.
The Petflap was set into a specially prepared box and was taped over so that the door couldn’t move and no air could escape through it. Air was blown through the box and measurements taken. The process was repeated with no tape on the Petflap, ie just as it would sit in a house, and measurements taken again. The difference between the two measurements shows how effective the Petflap is at keeping out air.
The result was that air moved through the Petflap at a rate of 1 l/s, which is an excellent result. We knew the Petflap was effective but we were delighted to see results this good.
PDFs showing details of the sealed and unsealed tests are available to download here:
Passivhaus consultant Richard Bendy writes:
The Petflap pet door & Passivhaus certification
The headline U value of the Petflap at 3.521 W/(m²K) might not seem remarkable in a passivhaus context, but with an area of only 0.05m2 it will not be that significant as a proportion of the whole fabric heat loss area of a building. Therefore it is unlikely to make any noticeable difference to the heat demand in the Passivhaus PHPP calculation.
In addition when using the dual door design with 400mm plus extended trunking likely to be used in a Passivhaus, the U value shrinks to 1.82W/(m2K) which reduces heat loss considerably and should preclude any increased risk of mould-growth in the surrounding area.
The major advantage of the Petflap design however is its excellent airtightness; a single Petflap with standard 70mm trunking has been tested at by Jon Davies of Oculus Architectural Engineers in Auckland New Zealand (though not certified by the Passivhaus Institute) and the results show that the difference in airflow between a taped-up example and an un-taped one using the same test rig was 1 litre/second at 50 Pascals.
To put that into context: for a house with a VN50 volume of 240m3, the increased ACH due to the Petflap when un-taped with the building being tested at 50pa would be (1l/s x 3.6)/240m3 = 0.015ACH. So with a building having a target of 0.6 ACH that would be 1/40th of the total air leakage, which although not completely negligible is unlikely to be a significant factor in a borderline air leakage test and would of course be even less significant in a larger building. This test was conducted using the standard single door version so with the dual door version with 400mm plus of extended trunking, which is likely to be used in a Passivhaus, the airtightness results will be significantly better. Results to date have been about 0.45ACH, coming in well under 0.6ACH.
Finally taking all the above into account, as a cat gives off about 20 Watts when asleep on your bed in winter, your feline companion and its Petflap are probably energy cost neutral when living in a Passivhaus!
For any queries about the Passivhaus aspects of the Petflap please contact Richard Bendy at the Healthy Home Ltd – richard@thehealthyhome.uk – +447990571394
U-value
The Petflap’s U-value is calculated to 3.979 W/(m²K).
The U-value had to be a very conservative exercise. We couldn’t obtain the necessary information from a single one of our materials suppliers, so Kara Rosemeier of PHANZ used generic values for all the materials making up the Petflap. This approach creates ‘worst case scenario’ results that overestimate heat loss. In other words, you can trust that performance is absolutely no worse than these figures show, and is likely a fair bit better.
The only way of getting a really accurate U-value is to have 3D thermal analysis carried out. This is expensive and is on our wish list but likely to be out of reach for a while.
3.979 W/(m²K) is a very good result for a pet door and far outperforms all standard catflaps. A typical catflap with an acrylic flap of 2-3mm thickness has a U-value in the order of 6/6.2 W/(m²K). The lower the figure the better.
Other passivhaus standard pet doors are available, but the Petflap is by the most affordable for this sort of performance.
You can download a PDF showing the detailed calculations here.