In his blog, Martin identifies the most challenging issue in creating a passive house: the design of its mechanical systems–particularly in terms of managing excessive heat gains.
As the lively array of comments that follow the blog confirm, passive house mechanical design is on the mind of everyone involved in the process. Moreover, the passive house knowledge base is growing, and the tools are evolving, to address issues related to unique climates and dynamic conditions.
“Back to the PHPP update: be aware that if you still use the older versions of PHPP (2007 through 2012) for your passive designs, it is very likely that your results may not be as accurate as they could be. You should consider upgrading. If you are working in more complex and challenging climates (very cold climate zones starting at 8 as well as mixed humid, hot humid, hot and dry climate zones, plus all zones with very high solar radiation) PHIUS very strongly recommends to use a dynamic model in addition to PHPP (or to use WUFI Passive which does both calculations — passive static verification and dynamic modeling).
“Some caveats: The stated improvements/changes in the algorithms in PHPP 2013 are a great step – it marks an acknowledgement that cooling latent issues were indeed not properly addressed until now. But, these changes for cooling and latent have not yet been verified in the various North American climates. Moreover, with more built examples and data now available, the larger question is: How accurate can a limited static representation relying only on monthly climate data really be? It is very likely that it does not afford enough granularity to accurately predict very complex interactions of buildings with a multitude of climate factors.
“For those more complex climates with heating, cooling, latent and solar climate factor combinations dynamic modeling appears to be quite a bit more accurate, allowing designers and consultants to limit the inherent risks in modeling: under or over-predicting performance as well as verifying that comfort conditions are assured throughout all rooms and spaces.”
Clearly Martin enjoys stirring the pot. He selects a somewhat obscure quote from a German Passive House website to set up, in my opinion, a straw man: “A passive house is a building in which a comfortable interior climate can be maintained without active heating and cooling systems. The house heats and cools itself, hence ‘passive.’”
In my experience, including passive house consultant and builder training, and training in WUFI-Passive, no one has ever suggested such a thing. No passive house I’ve visited did not have a heating and cooling system.
On the other hand, the title “passive house” is curious at best, if not confusing–and–a marketing bummer. When I introduce the topic to someone who is not familiar with the term, very likely confuse it with passive solar design–or make a snide reference to a passive–aggressive syndrome. But we are stuck with it.
All in all, thanks to Martin for stimulating a lively dialogue.