1. Energy-saving design standards for various types of buildings in my country
The lifespan of a building can be more than 50 years. Especially in summer, the building's air-conditioning electricity consumption accounts for about one-third of the total peak electricity consumption. If the daily energy consumption of the building can be reduced, the energy-saving benefits obtained is very significant. In view of this, in order to promote the effective use of energy and without hindering the safety, health and comfort of the living environment, the benchmarks for energy-saving design of various types of buildings in our country are clearly defined.
The energy-saving design of the building envelope, in addition to referring to the climate zone, also depends on the type of the roof, the average heat transmittance (Uar), the skylight transmittance (HWS), and the visible light reflectivity of the glass to the outdoors. (GRc) and other four items should be lower than their corresponding benchmark values.
2. Management benchmark for average heat transmittance of exterior walls and roofs
The roof of a building is exposed to the sun all day long and absorbs a large amount of solar radiation heat. The absorbed solar radiation will increase the temperature of the outer surface of the roof. On a sunny summer day, the temperature on the outer surface of the roof can usually reach between 40 and 50°C. At noon when the sun is shining, it can even exceed 60°C.
With such a high temperature difference between indoor and outdoor surfaces, a roof without good insulation properties can easily become the largest source of indoor heat in summer. Therefore, my country's construction technical rules list strengthening the thermal insulation performance of the roof as a key project of building energy conservation management, and use the roof average heat transmittance (Uar) as an indicator. One of the building technical rules stipulates that the average heat transmittance of the roof should be less than 0.8W/m2.K to suppress the heat conduction caused by the temperature difference between the inner and outer surfaces of the roof; the other stipulates that the average heat transmittance of the exterior wall and the average window Thermal transmittance should be lower than the baseline value.
Thermal transmittance (U value) and thermal resistance value (R value) are two indicators used to measure the thermal performance of a building wall or roof. The R value represents the ability of the building wall or roof to prevent heat from passing through. The higher the R value of a wall or roof, the stronger the thermal insulation performance of the wall or roof; the U value represents the amount of heat conduction between the indoor and outdoor surfaces of the wall or roof, which is opposite to the meaning of the R value. The lower the U-value, the lower the heat transfer and the better the insulation effect of the wall or roof.
The thermal conductivity (k value) and thickness can be used to measure the thermal resistance (R value) and thermal transmittance (U value) of a material. For a single building material, the thermal resistance value (R value) is calculated as follows Mode:
R=d/k
in
R: Thermal resistance value, m2.K/W
d: Material thickness, m
k: thermal conductivity coefficient, W/m.K
Generally speaking, the wall or roof of a building is made of a combination of materials, and its total thermal resistance value (Rt value) is calculated as follows:
Rt = Ro + d1 / k1 + d2 / k2 +…dn / kn + Ri
in
Ro: thermal resistance of air thin layer on outer surface, m2.K/W
Ri: thermal resistance of air thin layer on inner surface, m2.K/W
k: Thermal conductivity coefficient of the component material, W/m.K
d: Thickness of basic material, m
The heat transmittance (U value) of a building wall or roof represents the heat directly conducted by the unit area of the building wall or the inner and outer surfaces of the roof in unit air temperature difference and unit time under stable heat transfer conditions. Its value is just the reciprocal of the thermal resistance value (Rt value) of the wall or roof, as shown in the formula below. The lower the U-value of a building material, the better its heat resistance.
U=1/Rt
The common PS insulation board roof structure is used to illustrate how to calculate the Uar value. From this calculation example, we can also understand the impact of the thermal resistance value (R value) of different materials on the insulation effect of walls and roofs. The thermal resistance performance of traditional RC concrete building materials is not very good. Only by using thermal insulation materials for thermal insulation treatment can good results be achieved. If the same building has different roof structures, the average heat transmittance of its roof is calculated in an area-weighted manner, as follows:
Uar=(Uar, 1×Ar, 1+Uar, 2×Ar, 2+…Uar, n×Ar, n)/(Ar, 1+Ar, 2+…+Ar, n)
3. Management standards for transmittance of windows and roof windows
Using a glass lighting cover on the roof of the atrium or walkway of a building can increase the brightness of light and reduce the electricity consumption of lighting, which is of great significance in lighting energy saving. But on the other hand, the light introduced by the roof skylight also introduces the sun's radiant heat into the room. The introduced sunlight is absorbed by the floor and turns into long-wave radiation. Due to the characteristics of glass, long-wave radiation does not easily penetrate the glass and return to the outdoors. In addition, the special position of the skylight is generally a glass window that cannot be opened. If not designed properly, these atriums or walkways can easily become a greenhouse. Increase the electricity consumption of air conditioners.
Therefore, the building technical rules stipulate that when there is a roof translucent skylight with a horizontal elevation angle less than 80 degrees, and its horizontal projected area (HWa) is greater than 1.0m2, the solar transmittance (HWs) of the translucent skylight should be lower than its benchmark value(HWsc). However, this does not apply if the exterior wall of a building has more than half of the space exposed.
4. Energy saving management indicators for various types of buildings
Our country's construction technical regulations use ENVLOAD as an energy saving management indicator for office buildings, department stores, hotels and hospital buildings.
5. Daily energy saving evaluation indicators of green buildings
The building technical rules only provide energy-saving provisions for the design of the building shell, but there are no relevant provisions for the energy efficiency of air-conditioning and lighting systems, which account for the largest proportion of electricity consumption in daily energy consumption of buildings. Therefore, the green building evaluation system integrates the three aspects of building shell energy-saving design, air-conditioning efficiency design, and lighting efficiency design to become a "daily energy-saving indicator."
In terms of building shell energy-saving evaluation, the qualified benchmark for energy consumption of the shell of a certified green building is 20% stricter than the energy-saving regulations stipulated in the Building Technology Code. Energy-saving evaluation of air-conditioning systems includes preventing over-design of main units and encouraging the use of high-efficiency equipment and air-conditioning energy-saving technologies. Air-conditioning systems can be divided into three types: central air-conditioning, window-type and split air-conditioning. For buildings using central air-conditioning, the evaluation items include host capacity efficiency HSC and air-conditioning system energy-saving efficiency EAC. Buildings with separate air conditioners can be exempted from the evaluation of air conditioning energy-saving design.
