Passive House and Net-Zero Building
A Passive House is a home or other building that conforms to rigorous energy efficiency standards. Essentially, passive houses are designed so that they lose little or no heat to the outside world. This means that a passive house theoretically does not require a traditional heat source to remain comfortably heated. Passive Houses can get enough heat just from body heat, heat generated by electrical appliances, heat trapped by windows and other non-traditional heat sources. Because they do such a great job of retaining heat, Passive House projects are famous for being incredibly comfortable as much as they are for saving money on heating bills.
While Net-Zero homes are also designed to be comfortable and highly efficient, they go a step further by demanding that all the energy a house uses per year must be renewable and generated on-site. This means that, on top of being designed to prevent heat and energy loss, renewable energy systems like solar thermal, solar PV and geothermal and wind are used. The result is a home that is either entirely self-sufficient or one that gives back as much energy it consumes from the grid per year.
Passive House Projects
The first Passive house was was built in Germany in 1990 and was known as a Passivhaus. In 1996, the Passivhaus Institute was founded. The institute functioned both to promote the actual building of Passive Houses, but also to create and control some standards that define what it means to be a Passive House. Standards include how much energy the houses are permitted to use for heating over the course of a year (not be more than 120 kWh/m2) and the amount of air a home loses to the outside world per hour (no more more air than 0.6 times the house volume per hour when measured by a blower door).
In practice, passive houses use virtually every trick in the book to prevent heat loss to the outside world. An airtight envelope is created around the home, with heat recovery ventilation normally used to circulate fresh air without losing much heat. Triple glazed windows are used as standard. Thick layers of insulation are installed in the walls, roof and often floors of a home, again preventing as much heat loss as possible. When being constructed, passive houses are usually orientated so that, in Winter, as much sunlight as possible through the windows and heats the home. This orientation is also important for the Summer months; Passive houses do not use air conditioning systems, and therefore should be shaded from the Sun in summer to prevent them from getting too hot.
While a Passive House can be understood as a home that prevents energy heat loss at all costs, net-zero homes take things in a slightly different direction and seek to use only renewable energy produced on-site for all energy needs. This goes beyond heating and also includes electricity use. If a net-zero home uses non-renewable energy at any time, it must pay the grid back with an equivalent amount of renewable energy. For example, a home that uses a lot of electrical appliances at night can take energy from the grid and pay it back the next day using solar PV panels connected to the grid. What is important for net-zero homes (although there are many definitions for what makes a home ‘net-zero’) is that they can generate all necessary energy needed over the course of a year from on-site renewable energy sources.
Net-Zero homes use a lot of the same methods as Passive House homes to conserve energy. Lots of insulation is used as standard, as are double or triple glazed windows. A tight envelope around the home is also used to prevent heat loss. Along with these heat conserving methods, net-zero homes need to generate a lot of renewable energy. This usually comes from a variety of sources, chiefly solar PV for electricity and either solar thermal or geothermal for heat generation. Wind, biomass and other renewable energy systems can also be used when appropriate. Net-zero homes are therefore both environmentally friendly and cost-effective, saving hundreds of dollars on monthly heating and electricity bills, while also maintaining a high level of comfort for homeowners.