The glass curtain wall, commonly referred to as the "curtain wall," is a key component of modern building exteriors. With energy conservation becoming a crucial aspect of construction in China, this paper presents a technical analysis and calculation of the energy-saving performance of curtain walls, along with an economic evaluation of their efficiency.
**1. Design Principles for Energy Efficiency in Curtain Wall Buildings**
China's vast geography leads to significant climatic differences between regions. In the north, winter brings snow and ice, while the south enjoys spring-like conditions. To address these variations, the following design principles are proposed for energy-efficient curtain walls:
- In severe cold, cold, and mild regions, focus on winter thermal insulation; in hot summer and cold winter or hot summer and warm winter regions, prioritize summer heat insulation.
- Currently, there is no specific standard for curtain wall thermal design in China. Therefore, designers rely on national standards for exterior walls and windows, as well as international practices.
- The complex heat transfer process of curtain walls must be analyzed, including convection, radiation, and conduction through glass and metal frames.
- The overall heat transfer coefficient of the curtain wall depends on the building’s shape, local climate, and material properties such as the profile and glass.
**2. Thermal Design of Aluminum Profiles**
Aluminum profiles are the primary structural components of curtain walls. This section focuses on the thermal analysis of aluminum profiles, including calculations of thermal resistance and heat transfer coefficients.
- **Thermal Insulation Coefficient Calculation**: Using the formula R = δ / λ, where δ is the thickness and λ is the thermal conductivity (203 W/m·K), a solid aluminum profile with 100mm thickness has a thermal resistance of 0.0005 m²·K/W. However, hollow profiles have lower effective thickness, resulting in a higher thermal resistance of 0.002 m²·K/W.
- **Heat Transfer Coefficient Calculation**: Based on the Hot Work Specification, the total thermal resistance R0 is calculated as Ri + R + Re, which equals 0.152 m²·K/W. The corresponding heat transfer coefficient K0 is 6.58 W/m²·K.
- **Design Requirements for Heat-Resistant Aluminum Profiles**: These profiles use insulating materials like plastic to reduce heat transfer. According to DIN 4108, the basic heat transfer coefficient should not exceed 3.5 W/m²·K, and the minimum thickness of the insulating layer should be 7mm.
**3. Comparison of Heat Transfer Coefficients of Curtain Wall Glass**
Single-layer glass curtain walls have high heat transfer coefficients, leading to indoor temperature drops and condensation. Insulated glass, however, significantly improves energy efficiency.
- **Single-Layer Glass (8mm)**: Thermal resistance R = 0.011 m²·K/W, total R0 = 0.161 m²·K/W, and heat transfer coefficient K0 = 6.21 W/m²·K.
- **Insulating Glass (8+10+6)**: Thermal resistance R = 0.159 m²·K/W, total R0 = 0.309 m²·K/W, and heat transfer coefficient K0 = 3.24 W/m²·K.
- The heat transfer coefficient of single-layer glass is about 48% higher than that of insulated glass, highlighting the superior energy-saving performance of the latter.
**4. Economic Evaluation of Curtain Wall Energy Saving**
In China, cost control is often prioritized over long-term benefits. However, energy-saving measures can yield significant economic returns over time.
- A commercial building in Beijing with a 10,000m² curtain wall area was analyzed. Using single-glass vs. heat-dissipating curtain walls, the annual heating costs were calculated. The single-glass curtain wall consumed 1792kW, while the heat-dissipating one used only 980kW.
- The energy savings over 129 heating days amounted to 1,047,480 kW·h. The initial cost difference between the two types of curtain walls was 5 million yuan, but the energy savings offset this within seven years.
- By the tenth year, the economic benefit of using a heat-dissipating curtain wall would be 2.56 million yuan more than that of a single-glass curtain wall.
**5. Conclusion**
Curtain walls represent a new generation of building materials, combining advanced technologies, materials, and structures. As their usage grows rapidly in China, energy-efficient design becomes increasingly important.
This study demonstrates that energy-saving measures in curtain wall design offer substantial benefits to both investors and society. The economic return from energy conservation can be fully recovered, and the long-term advantages make it a smart investment.
The most effective way to save energy in curtain wall buildings is through heat-dissipating designs, which provide both environmental and economic value.
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