1、 Background of Passive Buildings
Reducing carbon emissions in the construction industry is an important part of China's carbon peak and carbon neutrality strategy. Improving building energy efficiency and reducing the demand for fossil fuels in buildings are fundamental solutions for the low-carbon transformation of the construction industry. In the context of the large-scale development of ultra-low energy buildings, promoting the healthy and sustainable development of ultra-low energy building standards, and achieving the goal of quantifying carbon emissions in the construction field, China introduced the high-efficiency building passive ultra-low energy building technology in 2011. So far, more than 23 million square meters of ultra-low energy buildings have been built (under construction), becoming an important means to improve building energy efficiency and reduce building carbon emissions. Promoting the large-scale and high-quality development of ultra-low energy buildings is of great significance for implementing the carbon peak and carbon neutrality strategy goals, fundamentally breaking energy and environmental constraints, and building an ecological civilization.
With the improvement of energy-saving standards, the application of passive doors, windows, and curtain walls is becoming increasingly widespread. The heat transfer coefficient K of the profiles of the exterior door and window frames of buildings should be determined according to the current national standard "Classification and Testing Methods for Thermal Insulation Performance of Building External Doors and Windows" GB/T 8484, and comply with the requirement of K ≤ 1.3W/(㎡· K). This regulation not only ensures that the overall heat transfer coefficient of the external window can be controlled within a certain range, but also ensures that the surface temperature of the profile on one side of the interior in winter is higher than the dew point temperature during use. So far, only wood or plastic profiles are available for material selection in the market.
The local standard "Design Standard for Energy Efficiency of Residential Buildings" DB11/891-2020 in Beijing requires a heat transfer coefficient K value of ≤ 1.1W/(㎡-K) for external windows, balcony doors and windows, curtain wall penetrations, and roof skylights. The energy-saving level in the Beijing Tianjin Hebei region has reached 80%, achieving five steps of energy conservation.
The "Technical Standard for Near Zero Energy Buildings" GB/T51350-2019, which was introduced in 2019, specifies that the heat transfer coefficient of doors and windows in cold regions should be K ≤ 1.0W/(㎡. K).
2、 Energy saving solution for passive sunrooms in a certain foreign country
The following is the overall design concept and energy-saving solution for a passive sunroom abroad.
The project is located in a farm villa area in Montreal, Quebec, Canada. The focus of this project is the owner's expectation for ultra-low energy consumption in the sunroom. A passive sunroom will be built on top of the existing swimming pool, which not only requires good lighting, but also ensures the ability to swim in winter, in order to relieve the owner's previous troubles of having to release water every winter and not being able to swim.
Due to the relatively short summer and long winter seasons in Montreal, Canada, the summers are hot and humid, with temperatures exceeding 30 degrees Celsius. The winters are extremely cold and snowy, with temperatures dropping below minus 30 degrees Celsius, and can last for up to six months. The wind pressure in the area must be able to withstand a wind speed of 120 kilometers per hour, and the snow load design requirement is to be able to withstand at least 47 pounds per square foot. The main materials of this project, such as glass, profiles, aluminum veneers, and auxiliary materials, are all made in China and processed domestically. They are then shipped to Canada by sea and assembled on site, and must comply with relevant requirements such as the Canadian National Building Energy Efficiency Code NECB-2011.
After relevant structural calculations and thermal analysis according to the owner's requirements, the overall K value of the sunroom should not exceed 0.5 W/(m2 · K). Ultra low energy consumption is the biggest challenge in the design of this project.
（1） Main keel solution:
If we want the overall K value of the system to reach 0.5W/(㎡-K), traditional steel keels and aluminum alloys are basically unable to achieve it, even if aluminum alloys use PA66+GF25 insulation strips, it is difficult to achieve. After conducting research on current domestic system windows, the aluminum alloy insulation profile adopts the 100 series, the insulation strip is 52mm, the glass adopts three glass double silver double low-e film, and the double 12/16 argon gas layer+warm edge partition strip. The K value of the entire window can reach below 1.0, but it is still difficult to achieve 0.5. Here we introduce a new material called basalt fiber composite profile.
Firstly, let's understand what basalt fiber is. The main component of basalt fiber is basalt, which belongs to silicates. It is composed of oxides such as silicon dioxide, aluminum oxide, calcium oxide, magnesium oxide, iron oxide, and titanium dioxide. Basalt stone is melted at 1450 ℃ to 1500 ℃ and then rapidly drawn into continuous fibers using specialized equipment. It is a new type of pure natural, green and environmentally friendly inorganic non-metallic material. Basalt fiber can be used to make basalt fiber cloth, basalt fiber felt, and basalt fiber composite materials. This material has been widely used in modern military, aerospace, bridge, ship, automobile production and other national economic production activities. Basalt fiber, carbon fiber, glass fiber, and aramid fiber are known as the four major fibers in China. As is well known, basalt is a rock formed by the solidification of volcanic magma. Therefore, compared with other fibers, basalt fibers have excellent properties such as high strength, high modulus, high temperature resistance, oxidation resistance, radiation resistance, thermal insulation, electrical insulation, corrosion resistance, and adaptability to various environments. It is reported that the estimated storage capacity of basalt in China is 18 billion tons, and China's basalt fiber production technology is also at the forefront of the world. Therefore, compared with other materials, basalt fiber has better cost-effectiveness. In addition, the production process of basalt fiber is very environmentally friendly, with no harmful substances released in the smoke and dust, which will not cause pollution to the atmosphere. There is no industrial wastewater or exhaust gas generated, and the product can be directly degraded in the environment after disposal, without any harm, making it a truly green and environmentally friendly material.
（2） Selection of Glass:
The glass used in this project is 6low-e+9Ar+5 (insulated)+9Ar+6Low-E double hollow argon filled insulated tempered Low-E glass, and the middle layer of 5mm glass is insulated glass.
Insulated glass and low-e glass have the same basic function of insulation, blocking ultraviolet rays, and extending the service life of furniture. But there is still a difference between the two.
Firstly, the production processes of the two are different. Insulated glass is produced by changing the structure of recombined molecules and atoms through physical means to achieve thermal insulation, while LOW-E glass is produced through chemical means to meet certain experimental conditions and be processed. Simply put, heat-insulating glass is made by adding some chemical materials such as silicates and phosphates during the glass production process to give the glass insulation properties. The Low-E glass commonly used in our current market is coated with one or more layers of Low-E film on the surface of the glass through online or offline methods. Low-E glass is a coated glass with high reflectivity for far-infrared rays with wavelengths ranging from 4.5 to 25um, and it has low emissivity.
Secondly, the two are not completely identical in terms of efficacy. Insulated glass mainly blocks near-infrared radiation, while Low-E glass mainly blocks far-infrared radiation. The former has a slightly higher blocking rate for ultraviolet and infrared rays than the latter.