High energy prices and global climate changes are forcing us to change our energy consumption habits. Since buildings use 40% of the total energy in the US and European Union, energy efficient houses are becoming more and more interesting. Number of ongoing governmental and local society projects are focusing on human continence and ways to change consumer’s behavior. For example:
- use public transport (buses, subways, trolleys, trains, …)
- buy smaller and environment friendly cars
- turn off electronic devices that you are not using (TV, computer, …)
- when shopping for new electronics, favour products with low energy use (labeled with A++, A+, A, B)
All those recommendations and suggestions are suitable to decrease energy consumption, but it is very difficult to change consumer’s habits. On other side, there are many ongoing projects with goal to optimize (reduce) energy consumption without having big impact on consumer’s way of life. For example we can optimize car engines to get same power with less fuel or we can build energy efficient buildings and houses. In this article we will focus on energy efficient houses.
ENERGY EFFICIENT HOUSES
Energy efficient house is any type of house that uses less energy than a regular one. Optimization of energy consumption and best possible use of available energy is not new idea. Similar to modern time, in the ancient time people dealt with a problem of constructing buildings with appropriate thermal comfort, and the main question was how to make a house warm during winter and cool during summer. This concept was first studied by Socrates, a classical Greek philosopher, almost 2500 years ago. In early literature this concept is known as “Socratic House”. “Socratic House” is a hypothetical description of energy efficient house. The essence of Socrates’ studies was influence of the Sun movement to the shape, form and construction of a building. “Socratic House” base plan is trapezoid with base oriented to south and roof falling toward north to avoid wind blasts. North wall is massive because in that time there was no thermal isolation. South oriented porch was projected to block high summer sunshine, but also to allow low winter sunlight to get deep into rooms.
House on northern hemisphere should face to south and in southern hemisphere to north to get most of the solar energy. On other side, back wall should be isolated very well to avoid energy losses.
Today, there are five main categories of energy efficient houses:
- low energy house
- passive house (ultra-low energy house)
- zero-energy house (or net zero energy house)
- autonomous building (house with no bills)
LOW ENERGY HOUSE
There is no global definition for low-energy house. Because national standards vary considerably, ‘low energy’ developments in one country may not meet ‘normal practice’ in another. In Germany a “Low Energy House” (Niedrigenergiehaus) has an energy consumption limit of 50 kWh/m² per year for space heating. In Switzerland the term is used in connection with the MINERGIE standard – no more than 42 kWh/m² per year should be used for space heating. Right now, it is generally considered that low-energy house uses around half of energy mentioned in those standards for space heating, typically in the range from 30 kWh/m² per year to 20 kWh/m² per year.
Low-energy buildings typically use high levels of insulation, energy efficient windows, low levels of air infiltration and heat recovery ventilation to lower heating and cooling energy. They may also use passive solar building design techniques or active solar technologies. These homes may use hot water heat recycling technologies to recover heat from showers and dishwashers.
PASSIVE HOUSE (ULTRA-LOW ENERGY HOUSE)
Definition of passive house is: “A Passive House is a building, for which thermal comfort can be achieved solely by post heating or post cooling of the fresh air mass, which is required to fulfill sufficient indoor air quality conditions – without a need for recirculated air”. Some countries have their own standards that define passive house in more strict way. In Germany the term passive house refers to the rigorous, voluntary, Passivhaus standard for energy efficiency in buildings. In Switzerland is in use similar standard – MINERGIE-P. It is estimated that the number of passive houses around the world range from 15,000 to 20,000 and the vast majority have been built in German-speaking countries or Scandinavia.
The Passivhaus standard for central Europe requires that the building fulfills the following requirements:
- The building must not use more than 15 kWh/m² per year in heating and cooling energy.
- Total energy consumption (energy for heating, hot water and electricity) must not be more than 42 kWh/m² per year
- Total primary energy (source energy for electricity and etc.) consumption (primary energy for heating, hot water and electricity) must not be more than 120 kWh/m² per year
To get some perspective on those requirements, we can compare house built to meet Passivhaus standard with houses build to meet local regulations in some countries:
- In the United States, a house built to the Passive House standard uses between 75 and 95% less energy for space heating and cooling than current new buildings that meet today’s US energy efficiency codes. The Passivhaus in the German-language camp of Waldsee, Minnesota uses 85% less energy than a house built to Minnesota building codes.
- In the United Kingdom, an average new house built to the Passive House standard would use 77% less energy for space heating, compared to the Building Regulations.
- In Ireland, it is calculated that a typical house built to the Passive House standard instead of the 2002 Building Regulations would consume 85% less energy for space heating and cut space-heating related carbon emissions by 94%.
Building costs for passive house were in past much higher than building costs of regular house, but with technology development and higher demands for specifically designed Passivhaus building products costs are now much lower. For example, in Germany it is now possible to construct Passivhaus buildings for the same cost as those built to normal German building standards because of increasing competition in the supply of the specifically designed Passivhaus building products.
A house with zero net energy consumption and zero carbon emissions annually is called zero energy house. Zero net energy consumption means that zero energy houses can be autonomous from the energy grid supply, but in practice that means that in some periods power is gained from grid and in other periods power is returned to grid (renewable energy sources are often seasonal). To achieve this energy must be produces on-site with non polluting renewable energy sources. Zero energy houses are also very interesting from environmental point of view because renewable energy means that greenhouse gas emissions are very low.
There are several more detailed definitions of what zero-energy house means in practice, with a particular difference in usage between North America and Europe.
- Net zero site energy use – In this type of zero-energy house, the amount of energy provided by on-site renewable energy sources is equal to the amount of energy used by the building. In the United States, “zero energy building” generally refers to this type of building.
- Net zero source energy use – This zero-energy house generates the same amount of energy as is used, including the energy used to transport the energy to the building. This type accounts for losses during electricity transmission. Those zero-energy houses must generate more electricity than net zero site energy buildings.
- Net zero energy emissions – Outside the United States and Canada, a zero-energy house is generally defined as one with zero net energy emissions, also known as a zero carbon building or zero emissions building. Under this definition the carbon emissions generated from on-site or off-site fossil fuel use are balanced by the amount of on-site renewable energy production. Other definitions include not only the carbon emissions generated by the building in use, but also those generated in the construction of the building and the embodied energy of the structure. Others debate whether the carbon emissions of commuting to and from the building should also be included in the calculation.
- Net zero cost – In this type of building, the cost of purchasing energy is balanced by income from sales of electricity to the grid of electricity generated on-site. Such a status depends on how a utility credits net electricity generation and the utility rate structure the building uses.
- Net off-site zero energy use – A building may be considered a zero-energy house if 100% of the energy it purchases comes from renewable energy sources, even if the energy is generated off the site.
- Off-the-grid – Off-the-grid buildings are stand-alone zero-energy houses that are not connected to an off-site energy utility facility. They require distributed renewable energy generation and energy storage capability (for when the sun is not shining, wind is not blowing, etc).
AUTONOMOUS BUILDING (AUTONOMOUS HOUSE)
An autonomous building is a building designed to be operated independently from infrastructural support services such as the electric power grid, municipal water systems, sewage treatment systems, storm drains, communication services, and in some cases public roads. Autonomous building is much more than energy efficient house –energy is only one of resources to gain from the nature.
Energy-plus-house is house that on average over the year produces more energy from renewable energy sources than it imports from external sources. This is achieved using combination of small power generators and low-energy building techniques such as passive solar building design, insulation and careful site selection and placement. Many energy-plus houses are almost indistinguishable from a traditional home, since they simply use the most energy-efficient solutions (appliances, fixtures, etc) throughout the house. In some developed countries power distribution companies have to buy surplus electricity from energy-plus homes, and with that approach house can even earn money for owner.
Energy efficiency is important and in future it will be even more important. To achieve energy efficiency we will have to adapt to new energy sources and new ways to save energy. Energy efficient house is only one part of that. For now number of energy efficient buildings in world is very low, but when we build houses in that way we also learn how to improve building methods even more. That knowledge will be probably used in the future for all new buildings.