Zero energy homes
A Zero Energy PV home is an all-electric low-energy building.
A «Zero net energy (ZNE) building produces as much energy as it consumes over the course of a year. These buildings achieve ZNE first through high levels of energy efficiency, and then through the addition of clean, on-site renewable power generation, typically solar PV» (California ZNE Residential Action Planning Effort definition).
Passive Houses (PassiveHaus) are designed according to a strict set of low-energy standards, defined by the German Passive House Institute. They are especially intended for cold climates, and should not be confused with Passive Solar Houses.
Their secrete is in their design and standards, and their air-tightness and massive thermal insulation. They are designed to reduce heat loss to the minimum, and because of it, they do not need large heating systems to be comfortable, even in the harshest climates.
The PassiveHaus standards stress a super-insulation approach. The walls, ceilings and floors should be comprehensively insulated, without thermal bridges (points where there is unintended heat transfer).
Edges, connections, corners, and all possible air penetrations have to be taken into account with great care. Heat transfer through the elements of walls, ceilings and floors should be eliminated or minimized as much as possible.
Accordingly, Passive Houses are also highly airtight buildings, where uncontrolled leakage through gaps have to be “smaller than 0.6 of the total house volume per hour during a pressure test at 50 Pascal”.
PassiveHaus buildings also require efficient heat recovery ventilation systems, to allow good indoor air quality. In cold climates, PassiveHaus standards require that at least “75% of the heat from the exhaust air is transferred to the fresh air again by means of a heat exchanger”. See for details: Passive Haus Institute
The PassiveHaus standards are highly advantageous for cold climates. They are very strict, and should be optimized and verified according to the Passive House Planning Package (PHPP).
They are a top reference, and they influence most other energy efficiency standards for Zero Energy Buildings.
Passive Solar Houses
Passive solar houses are part of a set of principles formulated in the 1970s and 1980s, which are now being subject to some criticism, especially the use of very large glazing surfaces in the sunny side of the house or the use of high thermal mass materials.Key passive solar house principles (intended for cold and moderate climates):
- The main living areas should be located on the sunny side of the house;
- High thermal mass strategies;
- The windows (and the house) should be properly oriented to the winter sun. Windows should provide significant solar heat gains in the winter.
- The sunny side of the house should be protected with roof overhangs; they should be sized in order to protect the windows in hot weather, without reducing it in the heating season.
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