Gahl Sorkin Spanier, MBA, CPHT, CPHC, LEED AP BD+C Business and Market Analyst, Association for Energy Affordability, Inc., Founding member, New Jersey Passive House
Since I spend my days working on Passive House, one of the things I find more challenging is how to explain Passive House (PH) to someone who isn’t familiar with it. I am so immersed in the subject, I sometimes find it difficult to slip into the shoes of someone who isn’t very familiar with PH, or to whom energy efficiency and air quality, aren’t, yet, high-priority considerations. For sure, it doesn’t help that Passive House has a confusing name translated from German, eluding to the fact that it may not be appropriate for larger or varied-use buildings, or that in the U.S., two certification paths exist, PHIUS and PHI, which though very similar, have a few key differences. When I was first introduced to PH and researched the subject online, I was utterly confused.
So, how do I work this out - how do I explain Passive House to people who want to know more about it? In my work life, I often need to do so and it depends, of course, on what the other person already knows about buildings in general, and about energy efficiency and Passive House in particular. What I personally appreciate most about Passive House beyond its ingenious individual components, is how these components interact. With that in mind, I usually explain PH using 2-component, 3-component or 5-component outlines.
If I want to keep it simple, I say Passive House is a Fabric First System: a building system featuring a very high-performance building envelope, basing the design of the mechanical systems on this high performance. Economically, it means the envelope, the most rigid and long-lasting component of the building, with an EUL (Expected Useful Life) of at least 50 years, is made much better and even longer lasting. This allows you to reduce the size (and thereby the cost) of your mechanical systems, saving money twice: Now, on initial capital cost, and again in 20-25 years when the EUL of the mechanical system has elapsed or technological improvements make it sensible to replace them. The economic focus of this system makes it a good choice to explain PH in financial contexts.
At the level of the building owner or user, I often find it’s better to make the concepts less abstract, and I break PH down as: superior insulation, outstanding air sealing, and high-performance heat recovery ventilation. It is a better way to explain to someone who really thinks about living in a Passive House, giving me the platform to explain how insulation and air sealing complement each other in cutting heat loss via conduction and convection. I can then dispel the fear of suffocation, by explaining how heat recovery ventilation allows much more and better ventilation with way less associated energy loss – and yes of course you can open the windows. If relevant, I can even continue to a higher level, explaining how controlling the flow of air through the envelope helps increase air quality and reduces the risks of moisture accumulation within the walls.
To someone who really intends to be involved in building a Passive House, I usually take the time to explain PH using the 5 components. It is about breaking the insulation component of the 3-component system above (Insulation, air sealing and heat recovery ventilation) into three parts. For someone who wants to realize or pay for a PH, the breakdown is important. High level insulation is still crucial, but it must be clear that all fenestrations must have equally high-performance. It’s essential also to address thermal bridges. What good is an amazing bucket if it has a bunch of medium holes in it (fenestrations) or a lot of very small holes (thermal bridges)? As anyone can tell, in either case it will not be a good vessel to carry liquid. If a typical PH wall can have a nominal R value of 25-40, most double-pane windows’ R values are only between 2-3 (an R3 is an amazing double pane window). there’s no way to describe the heat flow through such windows other than a bucket with holes. Triple pane PH windows are only R7, still a very weak point in the envelope, but since heat flows at a finite speed, this is usually enough for a conditioning system to undo the heat loss (or gain) faster than it occurs. This bucket analogy helps because thermal energy flows a bit like liquid and will flow much faster through a thermal bridge even if (in fact, somewhat because) its sectional area is extremely narrow. Still, a Passive House isn’t complete without outstanding air sealing (I am still looking for a better word to describe air sealing that is 10 times tighter than typical codes), and its twin component, the mechanical heat recovery ventilation, which complements it in ensuring the building is adequately ventilated at minimal energy loss. Most people who aren’t familiar with PH need an explanation of what heat recovery ventilation is – the simplest way I do this is by saying it’s a machine that lets the outgoing and incoming air streams exchange thermal energy, with the direction dependent on whether it’s cooling or heating season, but DOES NOT mix the air particles in the process – thus ensuring an indoor supply of oxygen-rich clean air with little energy investment.
Finally, Passive House has a cap on the amount of overall energy used in the building for space conditioning and for anything else that is happening in it. Depending on whether the building is certified via PHI or PHIUS, this will be measured by energy per treated floor area (TFA) or per number of persons using the space, but it will be so incredibly low compared to typical buildings that you would have to make an effort and keep very close accounting of your energy-using components- a good practice anyway.
If you are looking for some visual resources on explaining Passive House:
Passive House in 90 Seconds Video by Hans-Jörn Eich
PH Principles videos by Adam Romano, a colleague and fellow member of New Jersey Passive House.
Got another good way to explain Passive House, A PH project or story to share, we would be happy to hear for you. Email us at Hello@njpassivehouse.com