The Passive House vs the Net Zero House

Written By:

David Peabody, AIA, LEED-AP
Certified Passive House Consultant
Peabody Architects
Alexandria, VA

One shouldn’t think in terms of the Passive House versus the Net Zero house. Passive House defines an approach to construction and an energy certification standard. Net Zero is simply another name for buildings whose net annual energy use from fossil sources is zero or less.

There are many paths one can take to get to net zero. Most are quite expensive. The Passive House approach is simply the most efficient path. Why? Because the Passive House approach focuses upon reducing energy demand to the absolute minimum so that that only a small amount of expensive technology and renewables are necessary to get to the house to net zero.

Let’s look at the Passive House in Bethesda, 4717 N Chelsea Lane Bethesda, MD  20814. It has a projected heating and cooling cost of roughly $230/year. This is all achieved without the front end expense of geothermal, solar thermal or photovoltaic energy, but simply by building a highly efficient building envelope. The incremental extra cost to build the envelope in this manner was approximately 8% of construction cost. No other construction approach can get energy costs this low for so little extra front end investment.

How then does one take this Passive House to net zero? While the heating and cooling costs are tiny, hot water, lighting, electronics and other electrical loads increase the total energy number to roughly $1,300/year. It is primarily these other loads which must be offset by renewables in order to reach net zero.

Because the heating and cooling costs have been so minimized, domestic hot water (DHW) is the leading single energy user in Passive Houses. Therefore adding solar thermal panels for DHW and some of the heating load will move the building a long way toward net zero. With DHW demand taken care of by solar thermal panels, total energy cost goes down to $855/year.

Here is where photovoltaics , the most expensive of renewables, finally come into play. A PV array to generate that $855/year of energy will cost the homeowner, using federal and state and local subsidies, around $30,000. That is less than the cost of a geothermal heat pump.

This is why we can’t get to Net Zero efficiently without taking the Passive House approach.

Michael Kiefer
Green DC Realty Team
Phoenix Real Estate Solutions
Realtors DC/MD/VA
www.greenDCrealty.com
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