Houses without Heating Systems
by: Paul Kando
Polar explorer Fridtjof Nansen in his memoir of polar research Farthest North
Whether the thermometer stands at 22 degrees above zero or at 22 degrees
below it, we have no fire in the stove. The ventilation is excellent, especially
since we rigged up the air sail, which sends a whole winter's cold in through the
ventilator; yet in spite of this we sit here warm and comfortable, with only a lamp
burning. I am thinking of having the stove removed altogether; it is only in the way.
His vessel Fram ("Forward" in Norwegian) was perhaps the first true "passive house" (PH) structure, with 15 inch-thick, multi-layered insulation inside its hull: one evolutionary step in the concept's discovery through centuries of human experience and international research.
Physical phenomena play out in a building in familiar ways: Heat flows from hot to cold by radiation, conduction, or convection. When liquid moisture is heated, it evaporates. Air absorbs the resulting vapor. The warmer the air, the more it absorbs. Warm air expands, becomes lighter, and rises above cooler air. When air is cooled, the moisture it can no longer hold condenses on any sufficiently cold surface. Indoor climate is the product of constant interactions between heat, air and moisture. To maintain comfort we must control all three.
Research has established how best to do this:
- Control the movement of heat by appropriate levels of insulation, without thermal bridges (e.g. through wooden studs in a wall), and by using thermally efficient windows (three panes, two low-e spaces, thermal bridge-free frame).
- Control air and moisture movement by airtight construction.
- Provide fresh air by a ventilation system that recovers 80-95 percent of the heat from the exhaust air and transfers it to the incoming fresh air; continually removes odors and excess moisture; and eliminates the need for a separate heating/cooling system.
- The remaining heating or cooling load can be met by renewable energy, resulting in a zero energy building. In fact, there are PH buildings that generate more energy than they use.
Research established the following maximum energy consumption limits for PH buildings: 15 kWh/m2/yr for space heating or 10 kW/m2 heating load; 120 kWh/m2/yr for all uses; and 0.6 air changes per hour at 50 Pascals indoor-outdoor pressure difference.
(My use of metric units is deliberate. They are the international standard and our use of the archaic imperial units, alone among developed nations, handicaps us by extra calculations to perform and needlessly complicated math every time we encounter advances in international research. Here are the equivalents: 1 kWh = 3412 Btu; 1 meter2 = 10.7639 square feet; 50 Pascals is the universal standard used in blower door tests. A Pascal (Pa) is a small unit of pressure. One Pa equals 2.953 x 10-4 inches of mercury (at 32°F) = 0.00014504 Lbs./square inch -- PSI.)
These targets apply regardless of a building's size or the local climate. To aid in determining the design features and materials used in individual buildings, the German Passivhaus Institute developed a PC-based design software. Available in English, it includes data bases on the thermal properties of building materials and climate.
While it is impractical to attempt to design a PH building without deep knowledge of building physics and use of this software, there is a useful lesson we can all profit from: Maximizing building energy efficiency requires systemic rethinking.
Historically we built a box and added things to it as "afterthoughts": insulation, plumbing, wiring, fans, windows, doors, heating system, air conditioning, and other elements. In case of problems, we tinkered with specific afterthoughts, which fast became someone's trade or profit center, often subject to separate regulations.
The passive house design, instead views buildings as systems expected to deliver certain services: comfort, warmth, cold and warm water, lighting, fresh air, sanitation, friendly atmosphere, and eco-friendliness, for example. Such systems need integral combinations of features to deliver these services, efficiently working together with the rest of the system.
Since a PH requires less energy for space heating than water heating, features have to be configured to deliver both; as it happens, combining both services with a third, ventilation, works best.
PH design ensures very low heating costs even as fuel prices rise. It also ensures a high level of indoor comfort, fresh air in all rooms year round, no increase in humidity or mold, and a significantly smaller carbon footprint.
Since in new buildings the marginal first cost of PH features is only 5 to 15 percent and the payback from energy savings is fast, it makes no economic sense to construct new buildings that do not meet PH specifications. The total monthly payment (financing and operation) is what matters. In a PH this is likely to be comparably low from the get-go.
The next installment on houses without heating systems will feature the PH upgrade of existing buildings.
Continue Reading: Part 1 or Part 3