The Passive House Institute in Germany has improved upon American ideas from the 1970s and re-branded it as PASSIVHAUS. Superinsulated homes have been built in many locations in the U.S. over the last 30 years, as covered by many articles on the ASHRAE web site.
Passive houses use significantly less energy than do existing or new conventional residences. In fact, they use so little heating energy that a conventional heating and cooling system is mostly unnecessary. The house stays warm by recycling heat that is already being generated by internal sources – lighting fixtures, stoves, toasters, dryers.
Now, the Passive House Institute has developed an energy modeling program called the Passive House Planning Package (PHPP), created by Dr. Wolfgang Feist. This program calculates energy savings to anticipate the monetary payback from a superinsulated home.
Here at Green Compliance Plus we purchased PHPP to see what it was all about. It’s similar in some ways to the Title 24 modeling packages, in that it determines whether the finished residence will meet the Passivhaus energy consumption goals. However, it goes beyond Title 24 in both its reporting and intent.
Title 24 compares a project to a “standard model building” of the same size and orientation, and tells you whether the proposed design is more or less efficient than the standard model. The Passivhaus calculations require more input data than Title 24, and provides reports of the actual energy usage in kWh or therms. It also considers CO2 reductions, which is the home’s carbon footprint.
Interview with Architect and Passive House Expert Nabih Tahan
To learn more, our own Alan Hugenot interviewed SF Bay Area Architect Nabih Tahan, who recently completed construction of a Passivhaus residence in Berkeley and is a well-known speaker on the topic of passive houses.
What kind of building is adequate in our mild Bay Area climate (Title 24 climate zones 2 and 3) to meet the PHPP standard?
As with conventional Title 24-based designs, many different building envelopes can qualify, and the PHPP model is used by entering different values for the insulation, fenestration, thermal mass, etc. until the optimum design is achieved. Generally, the Passivhaus envelope is more airtight than are conventionally designed residences. In a Passivhaus, the ventilation is controlled by the continuous mechanical ventilation system, which also handles all internal heat collection and redistribution. The underlying principle is “Build tight, ventilate right.”
If a Passivhaus does not require a conventional heating system, then where does the heat for the residence come from?
Tahan: In a typical house, every light bulb, computer, refrigerator, oven, hair dryer, and toaster generates heat. [In a passive house,] This heat cannot escape because the building envelope is tightly sealed. The only place this heat can go is through the ducts of the constant ventilation system which utilizes a heat recovery ventilator to transfer this heat from the air being exhausted into the fresh outside air being supplied into the house. This provides both energy efficiency and excellent indoor air quality. Typically, a passive house reduces the heating or cooling loads by 80 to 90%. So, a backup heating system is still necessary to provide the remaining 10-20% that is required.
What efficiency levels do passive houses achieve?
There are three measurements that define a passive house:
- The building envelope is constructed so that the heating requirements will not exceed 1.4 KWh / square feet per year.
- The outside source energy requirements will not exceed 11.1 kWh / square feet per year.
- The building shell is so airtight that it will pass less than 0.6 air changes per hour at a pressure above an ambient level of 50 pascals.
More Links to Nabih Tahan’s Material
Summary of a talk he gave at BuildItGreen this past February
About the author
Alan Huguenot, Certified Energy Plans Examiner (CEPE), ASHRAE, NFPA, BCA, CABEC, U.S. Green Building Council (LEED) with over 20 years experience as a Mechanical Engineer and Commissioning Agent (CxA). As a California Certified Energy Analyst (CEA), Alan provides Residential Energy Audits and full HVAC and plumbing commissioning services, to make sure that the systems in the residence are operating at their full rated efficiency.