A Passive House or Green Buildings is a highly energy efficient building standard that also promotes indoor comfort and acoustic insulation. They are constructed to use as little energy as possible, but also provide superior indoor air quality, comfort, and a feeling of lightness and openness in the interior.
What is a Passive House?
Passive House is a new, energy-efficient building design that aims to make homes more comfortable and improve their environmental performance. It does this by using passive solar heating and cooling systems, high levels of insulation, and efficient use of natural day lighting. Here's what you need to know about Passive Houses.
Passive house Principles
Passive house principles are a way of working towards sustainable, low-energy homes. These principles are intended to optimize the energy efficiency of buildings to improve energy performance and reduce environmental impact. This guide will explain how passive house design is different from traditional building designs, and how you can start working towards a passive house.
1. General strategies for Passive House
The Passive House / Green Buildings approach is a whole house approach. This means that the high energy efficiency can only be achieved through the interaction between the different energy measures: the whole is more than the sum of its parts. It is a design task to optimize the building as a whole in its orientation, layout, compactness and finally the quality of components to achieve high thermal comfort under the given local climate conditions.
The general idea is to keep the heat inside in cold climates and the heat outside in warm climates, which can be achieved by applying the following principles (beside a good orientation):
2. Insulation for Green Buildings
A continuous insulation layer throughout the thermal envelope, including the slab, is the starting point. Only in certain cases, an uninsulated slab may be beneficial, as the earth can then be used as a seasonal buffer. This, together with the optimal insulation thickness for the specific climatic requirements and characteristics of the project, can be defined through the energy balance calculation.
For insulation, it is also important to consider elements such as fire humidity and wind protection, and how the insulation will be fixed to the wall: low conductivity fixing (e.g. plastic fasteners like on the picture right) should be used.
3. Windows/doors for Passive House
Depending on the climate, single, double or triple glazing may be needed. For instance, if there is a high temperature difference between the interior of the building and the outside, glazing with a low U-value will be required, for example, triple glazing. Noble gas filling and low-emissivity coating (which suppress heat radiation to escape), can further reduce heat losses/gains.
Another important characteristic value of the glazing is the g-value, also called total solar energy transmission. It defines how much energy is transmitted from direct solar radiation and from secondary heat emission from the outside towards the inside. In heating-dominated climates, the g-value should be between 50 and 60%, to let in enough solar energy in the winter.
However, in hot climates where solar gains are unwanted, the g-value should be significantly lower, around 30% and windows should be shaded with moveable or fixed shading devices, preferably on the outside. The different glass panes should be separated using low conductivity spacers (e.g. plastic spacers) and the frames should have at least 2 airtight seals. Furthermore, it is best if the insulated frame is slim, to allow for more daylight (and solar gains in heating climates).
By installing windows and doors aligned to the insulation layer of the wall system, the installation thermal bridges can be reduced. In hot climates, this should be evaluated against locating the windows aligned to the interior of the wall to increase shading – the most beneficial in terms of the energy balance should be used.
4. Air-tightness for Green Building Design
One single continuous air-tight layer on the thermal envelope is needed to improve living comfort. This prevents undesired infiltration of outside air and humidity, drafts, entry of pollutants into the room, and making controlled ventilation possible as well as enhances noise protection. This layer would be usually on the interior surface in heating dominated climates, while in hot and humid climates it may be more beneficial to have it on the exterior.
In solid construction, concrete surfaces can be considered airtight, but masonry is not airtight by itself. In this case, applying a sufficiently thick plaster layer will be needed. It is important to apply it also in hidden spaces (e.g.: behind WC and equipment) and to make sure any perforations are sealed (e.g.: sockets). Connections between different airtight surfaces or at the edge of components penetrating the envelope like ducts and pipes should be made airtight by using tapes and other products designed for this purpose. In all cases, manufacturer instructions must be followed to guarantee the correct installation of the airtightness products.
Passive House air-tightness levels can reliably be achieved once designers have gained some experience. To verify the airtightness level achieved in practice, a test must be carried out. It is recommended that the air-tight layer is still accessible to allow for improvements during the test.
5. Ventilation for Green Buildings
To ensure occupants receive enough fresh air, a good ventilation strategy is needed. Instead of relying only on natural ventilation through windows and possible openings in the façade, the Passive House concept includes mechanical ventilation with controlled air flow rated to ensure a fresh and filtered air supply at all times. Depending on climate, the ventilation system may be only for extract air or a combination of supply and extract with heat recovery or heat and humidity recovery. In milder climates, using a ventilation system without heat or energy recovery may be sufficient, since the temperature difference between the inside and the outside may not be enough to justify the additional investment cost required for such a unit. In hot climates or cold climates, a ventilation unit with heat/humidity recovery will reduce the heating and cooling demand while keeping a high indoor air quality.
Each unit should have efficient fans (electric power < 0.45 Wh/m³), suitable air filters (F7 / G4), and a heat recovery rate higher than 75%, where applicable. The system should be designed to prevent any noise transmission between the different rooms and the ventilation unit itself should also produce limited noise.
6. Thermal bridges for Passive House
A thermal bridge is an interruption of the thermal insulation layer - a localised area of the building envelope where the heat flow is different (usually higher) in comparison with adjacent areas. These “weak” points should be avoided because they increase the energy demand, especially in climates where the difference between the indoor and outdoor temperatures is high.
Thermal bridges can be minimized following these rules:
Connection Rule: the insulation layers from different building components merge into each other without interruption when these components connect with each other.
Avoidance Rule: prevent any interruption of the insulating envelope where possible (e.g. use a balcony with a separate structure or limit the number of corridors)
Penetration Rule: If penetration is unavoidable, the thermal conductivity of the penetrating material should be as low as possible and the cross section as small as possible (e.g. plastic or stainless steel brackets)
While the concept is the same, the strategies must be adapted according to the different climate conditions. The strategies recommended in heating and cooling dominated climates as well as in temperate climates are described below.
Strategies for admirable passive house energy performance
1. Strategies in heating-dominated climates for Green Buildings
In heating-dominated climates like Srinagar, the main objectives are to keep the heat inside the building and to take advantage of solar and internal heat gains. A compact building design proves to be a very significant factor in terms of a building’s energy performance and should be optimised first before applying energy-efficiency measures such as insulation. If a small Area /Volume ratio is combined with an optimised orientation and window size, financial and energy benefits can be achieved more easily. In addition, less insulation also means energy savings in terms of the production of the materials and their installation.
Besides adequate insulation levels and the avoidance of thermal bridges, double to triple glazing with high solar transmission is recommended in most cases. Most windows should be on the South front. Furthermore, a good airtightness and heat recovery ventilation will help to limit heat losses through the air flow.
2. Strategies in cooling-dominated climates for Passive House
Three of the five climate zones in India can be considered as cooling dominated. The warm and humid climate zone features high humidity levels and thus requires a focus on reducing the energy need for dehumidification. In the hot and dry climate zone the main design task is less on dehumidification but more on protecting from the high outdoor temperatures. The composite climate zone also has some cooler winter months and calls for balanced design choices that provide comfort during both the cold and the warm seasons.
Most importantly, heat loads should be limited, as the need for cooling is related to unwanted heat in the building. Both internal and external heat and humidity loads affect the need for cooling and dehumidification. Internal heat gains can be limited by choosing energy efficient appliances and electronic devices, and paying attention to the electrical efficiency of the fans.
In addition, warm water pipes and tanks should be insulated to avoid unwanted heat in the rooms – in hot climates it might be best to install the hot water tank outside the building envelope. To limit external heat gains, sufficient insulation levels in the thermal envelope are needed. Using light colours or even reflective coatings or “cool colours” (absorptivity lower than 0.2) for the roof is recommended.
Air-tightness is also important to limit unwanted heat and humidity gains through leaks. Installing fixed or movable shading is an essential factor in limiting limiting solar heat gains. In general, large windows to the east or west should be avoided. Depending on the climate, double or triple glazing may be needed, coatings for solar control to achieve a low g-value are recommended. Finally, an efficient ventilation system with heat and/or humidity recovery will also be helpful.
In the climates of Lucknow, Aurangabad and Bhubaneswar it will prevent air at high temperature and high humidity from entering the building through the fresh air flow. For similar reasons it is also recommended to use a recirculation instead of extract hoods in the kitchen. Window ventilation is an important passive cooling measure but only when outdoor conditions are similar to or cooler than the indoor climate (especially night flushing). Open windows during hot and humid periods is counterproductive as it will lead to an increase in temperature and humidity levels.
If all these passive strategies are not enough to limit the overheating frequency to 10% of the year or less, then active cooling is needed. But the remaining cooling demand and cooling load will be much smaller than in conventional buildings once the strategies described above are implemented – thus allowing for smaller and alternative active cooling systems. In most cases the fresh air provided through the ventilation system may be enough to supply the cooling load without the need for recirculation.
There are different possibilities for active cooling systems, the most common being split-units. In any case it is important to ensure a high overall system performance. If split units are being used they should have a high COP, variable air volume, noise protection and a standby power consumption below 1 W. In efficient buildings with lower cooling loads, cooling systems can operate at lower air speeds and supply air at higher temperatures, thus ensuring more comfort at lower operational costs.
It is of critical importance to understand the dehumidification need of a building and the sensible heat ratio (i.e. the fraction of sensible and latent cooling needs). The lower the sensible cooling need in an highly energy efficient buildings, such as Passive Houses, the higher the relative fraction of dehumidification. Additional dehumidification may be required, especially during monsoon seasons. For most efficient solutions it is recommended to use an active cooling system that allows independent control of sensible cooling and dehumidification.
3. Strategies in temperate climates for Passive House Design
In temperate climates like Bengaluru, the requirements are usually lower: A few centimeter's of insulation and single to double glazing with solar protection may suffice.
Thermal bridges should always be avoided, but would have less of an impact than in more extreme climates. Reflective coatings are recommended for the roof. With the appropriate passive design strategies, very little active cooling will be required in such climates to keep temperatures between 20 and 25°C. As mentioned previously, using a ventilation system without heat or energy recovery may be sufficient in such climates e.g. a simple extract ventilation approach.
Passive House / Green Buildings FAQ
Q: Is the passive house approach only for houses? - Passive house is a building design that uses the least amount of energy possible. - It's used for new construction and renovations. - It can be used in commercial buildings, as well.
Q: Does it cost is more to build a passive building compared to a conventional building?
- It costs more to build a passive building. - Passive buildings use less energy than conventional buildings. - Passive buildings are better for the environment.
Q: what is Thermal Comfort? - Thermal comfort is the temperature at which you feel comfortable. - It's measured in degrees Celsius or Fahrenheit. - The higher the temperature, the more uncomfortable you will be.
Q: what is passive design in building? - Passive design is a method of building that uses the natural forces of wind and gravity to create an environment that is comfortable, healthy, and safe. - It's about creating a space where people can live in comfort.
Q: Why is building insulation important? - Insulation is important because it keeps the heat in your home. - It also keeps the cold air out. - It can help you save money on your energy bill.
Q: Why shading is important in designing a building? - Shading is important in designing a building because it helps to create the illusion of depth. - It also helps to make the building look more interesting and realistic.
Q: Why ventilation is important in designing a building? - Ventilation is important because it helps remove the carbon dioxide and other harmful gases from a building. - It also keeps the air fresh and clean. - It prevents mold, mildew, and bacteria from growing in a building.
Q: How do you use the thermal mass of a building? - Thermal mass is the ability of a material to absorb and store heat. - It's used in buildings to keep them warm in winter and cool in summer. - It can be made from concrete, bricks, or wood.
Q: What is the need of energy efficient building? - Energy efficient buildings are more comfortable and cost less to run. - They use less energy, which means they are cheaper to operate. - They can be built in a shorter time frame than traditional buildings.