Passive House designers: do you know what version of designPH you are using? It’s important you are using, if not the latest version (2.2.24 at time of writing) then 2.1.15 or later. Otherwise your shading factors may not be accurate.
We identified this issue last year and issued a brief advisory in our November email newsletter. Here’s the background explainer for anyone interested. When certifying Passive House projects, we do spot checks on the shading factors between designPH and PHPP. This is to verify that the correct site/self shading and shading settings have been used.
A designer on a certification project late last year found a discrepancy between shading factors in different versions of designPH. Our team confirmed the error by checking the file in both v2.1.11 and v2.2.20 and it was confirmed by designPH developers. They tracked the issue to updated climate data (from NZ1002a to NZ1002b), which included some small adjustments to the global horizontal radiation. This update was included in designPH 2.1.15.
Morale of the story: keep your software up-to-date! Especially for projects seeking certification.
The difference in results is relatively small; the largest difference we found in spot checks was four percent. However, we can’t verify your designPH file is correct unless the numbers match up. Passive House designers and certifiers both need to be working from the same climate data.