This excellent post is reprinted from a June 16th, Building Capacity blog posting. See original here.
Passive House: Isn’t it a bit of overkill? James Jenkins, Certified PH Consultant responds
Jenny Nakao Hones of Three Frogs Design asks the question: Passive House seems like it could be a great idea for places that have extreme weather conditions, with significant temperature swings. I’m wondering about more temperate climates though, such as the West Coast. Isn’t it a bit of costly overkill?
Great questions, Jenny. For those unfamiliar with Passive House (PH) it’s a green building standard originating in Germany, gaining popularity worldwide. It’s based on predicted performance and results in very low-energy buildings that maintain comfortable temperatures with minimal input. The name is a bit of a misnomer; the German word “haus” translates directly to shelter or building – not house. So it applies to non-residential projects as well as homes. PH’s technical focus is on Energy and IAQ.
The principles found in the PH Standard actually have deep roots in the super-insulation movement of the US mid-west decades ago. Many of these projects failed because moisture and ventilation were not well considered and the same R-values were used universally, independent of climate. PH has taken the idea and infused it with building science to ensure that the problems of the past are not those of the future.
The beauty of this new and improved approach to passive technology is that it addresses what many believe is the biggest threat we face today – climate change and maintaining a habitable planet – in a way that leverages lessons learned about how buildings actually perform, and provides multiple “side” benefits to the building owner (more on that later).
Achieving PH’s strict energy requirements is typically done through a super-insulated envelope, nearly air-tight construction, and a heat recovery ventilator (HRV) to provide continuous fresh air. There is no prescribed approach beyond meeting the maximum energy consumption targets, however. Katrin Klingenberg, Director of Passive House Institute (US) recently completed a post occupancy evaluation of her personal residence in Illinois. Passive House Planning Package (PHPP), the rating system’s energy modeling software, proved to be accurate within 10% of her actual energy consumption and 70% lower than the typical American home.
In another study of a low income housing project, Katrin concluded that the cost per kWh saved was 7 cents when building to PH standards. By way of comparison, this is slightly less than the cost of purchasing a kWh from the Seattle City Light (around 8 cents per kWh). Thus it is cheaper to save the energy than to purchase it. Bearing in mind that in Seattle energy is relatively cheap today, but isn’t expected to stay that way, the long term cost justification for PH will only get stronger. There are several PH projects under construction in the Seattle area, and like other green certified buildings, reported first costs are all over the map – ranging from 0% to 18%. Given this wide range, it does not seem that PH is the driving force where first cost premiums exist.
Let’s discuss your first concern, whether super-insulation is cost-effective in mild climates. It’s important to keep in mind that the PH system includes little reliance on conventional technologies. This is the key to it being cost effective. We need to insulate passive buildings only to the extent that we can minimize or eliminate the traditional heating and cooling equipment found in typical buildings. Precisely calculated insulation values allow the internal and solar gains in a building to be roughly the same as the heat loss through the walls and windows in any climate. Super-insulation may not be necessary, or appropriate, in all climates. In general, higher indoor to outdoor temperature differentials will require higher insulation values in heating dominated climates, moderate climates such as Seattle might require R-40 walls in a single family residence. (This is roughly twice the Washington State Energy code minimum; in colder climates, you’ll see wall values of R-50, 60, or even higher.)
And let’s not forget windows! Even at their best, windows are the single largest source of heat loss in all buildings. PH requires the indoor surface temperature of a window be 64 degrees F, based on the low design temperature for the climate zone. In the Puget Sound area that’s roughly U-.19. The bottom line is that PH projects in milder climates can use less expensive windows and less insulation when compared to more extreme conditions.
An even more important aspect to PH is air tightness. PH details achieve .6 air changes per hour at 50 Pascals (ACH50). This significantly improves energy savings in two ways, by reducing air infiltration, and by redirecting heated air flow through the HRV where it can be of use.
With proven operational savings and a cost-effective design approach, PH is a financial boon to green designers, builders, and building owners looking for answers in this lean and mean economy. But that’s not all the system offers. There are several additional owner benefits, including:
- Predictable long term ownership cost;
- Passive survivability in cases of lengthy power outages or energy disruptions;
- Protection against likely carbon taxation;
- Lower replacement cost of mechanical equipment due to less complex systems requirements; and
- Future readiness for net zero energy capability.
Designers thinking about employing PH should know that the modeling protocols for PH are not accepted by other rating systems (such as LEED) at this time. Its proven accuracy suggests, however, that it’s a great tool to optimize designs. Designers will be able to identify the least cost strategies required to meet an energy savings target. PHPP software can be used to find just the right window u-values, insulation R-value, and window placement for your project.
For builders wondering how they can make the case to owners, understand that when we design the envelope precisely and with the goal of eliminating the traditional mechanical system, added insulation and better windows are not added first costs but costs that can be offset. The key challenge to the contractor will be meeting the aggressive air tightness requirements. Even at its best, current practice rarely generates anything below 2.0 ACH50. However, this challenge also serves as a tremendous opportunity for the business-savvy contractor to add value to their building projects. Quality assurance on a PH project is critical. Better buildings will be the result. That means fewer callbacks, and better referrals – as well as experience you can transfer to other projects.
James Jenkins, CPHC, CSBA, LEED AP BD+C, and Homes, is a Project Manager at O'Brien & Company, consulting on residential and non-residential green building projects. He is a Certified Passive House Consultant and currently serves as Vice-President of Passive House Northwest. Linda Whaley provided the construction photo. You can see more in-progress shots at her blog Existing Resources.
Posted on October 18, 2010