Research on energy-saving design of prefabricated cabin for modular intelligent substation

introduction

Modular and intelligent prefabricated cabin substations are safe and reliable, have a small footprint, a short construction period, beautiful appearance, long service life, no radiation, low noise, flexible layout, waterproof, dustproof, earthquake-resistant, fire-resistant, corrosion-resistant, low-temperature-resistant, and impact-resistant. They have gradually been widely recognized by the market during their application. With the large-scale promotion of prefabricated cabin products and the diversification of use areas, in the face of special use environments such as high temperature, high cold, and high humidity, in order to improve the thermal environment of the prefabricated cabin of the substation, it is necessary to improve the energy utilization efficiency of the HVAC system, fundamentally improve the situation of energy waste, and contribute to the realization of the national energy-saving and environmental protection strategy and the implementation of relevant policies and regulations.

1. Substation general layout design

1.1 Towards basic principles

(1) The general layout design of the substation should try to make the main structure length (longer side) of the modular intelligent substation prefabricated cabin face north-south to avoid east-west sunlight.

(2) According to the local hydrological conditions of the project site, fine-tune the substation orientation so that the substation can obtain sufficient sunlight in winter and avoid the dominant wind direction, and can utilize natural ventilation and solar radiation in summer. Generally, the basic orientation of the urban building complex in the project area can be used as a reference.

(3) The constraints of social history and culture, topography, urban planning, roads, environment, etc. should be fully considered, and the pros and cons of each factor should be weighed to further optimize the substation orientation.

1.2 Summary

The orientation of the general layout design of the substation has a profound impact on the energy saving of the prefabricated cabin of the modular intelligent substation. When designing the general layout of the prefabricated cabin of the modular intelligent substation, the substation orientation should be fully considered. On the premise that the main body of the prefabricated cabin of the modular intelligent substation is oriented north-south, the best orientation or near-optimal orientation of the project site should be selected in combination with local geographical and hydrological conditions, as shown in Figure 1.

2 Energy-saving design of prefabricated cabin structure

(1) The prefabricated cabin walls and roofs are made of a relatively complex multi-layer composite structure. The thermal insulation performance of the wall is further consolidated through the structure, material, and thermal insulation gasket. In addition, a sealed and breathable air insulation layer is designed in the composite structure to further improve the thermal environment of the cabin and enhance the thermal insulation performance of the cabin, as shown in Figure 2.

(2) The thickness of the insulation material and the air insulation layer is calculated based on the HVAC environment of the project site, and the optimal insulation thickness design is selected in combination with factors such as economy, applicability, and spatial rationality, as shown in Figure 3.

(3) In order to avoid heat loss through the bottom of the prefabricated cabin, the bottom of the cabin must be insulated, and the bottom insulation should be made of materials with high water repellency and good sealing performance to prevent the insulation material from becoming ineffective due to moisture and moisture from entering the cabin, so as to achieve complete isolation of the bottom from the external environment.

(4) Appropriate breathing holes are set on the top eaves, bottom or walls of the cabin to ensure that the air can be breathed but does not cause the air temperature to assimilate with the external environment.

1) Due to the physical property of air expansion and contraction, the breathing port can exhaust and inhale air in a timely manner to maintain the balance of internal and external air pressure, avoid changes in air thermal conductivity due to changes in air pressure, and thus affect the thermal insulation performance, as shown in Figure 4.

2) During the gradual heating (cooling) process, the air inside and outside the cabin interacts freely through the breathing port, automatically balancing the internal

The ambient temperature can delay the start-up time of the air conditioner and reduce energy consumption.

3) When the temperature rises (drops) to the start-up temperature of the industrial equipment, the breathing port inside the cabin is automatically closed, so that the air insulation layer forms a closed air insulation cavity, as shown in Figure 5.

4) If necessary, the breathing port can be opened even when the equipment is started to breathe and rotate the air inside the wall to avoid air pollution, as shown in Figure 6: The cable layer is properly heated (cooled) so that the air temperature in the cable layer also maintains a fresh air environment, thereby ensuring the service life of the cable.

(5) Type test of prefabricated breathing cabin:

1) Test purpose: To verify the fireproof and thermal insulation performance of the "breathing prefabricated cabin" and the "conventional prefabricated cabin", to compare and analyze the thermal insulation performance of the "breathing prefabricated cabin" more objectively and scientifically, and to provide a more convincing theoretical basis for the selection of the structural system of subsequent projects.

2) Objective conditions of the test: same address, same sunshine environment, similar sample dimensions, and consistent industrial equipment power.

The sample manufacturing process and structural characteristics are shown in Table 1.

3) Test results:

Without turning on industrial equipment, according to the comparison in Figure 7:

① The breathing prefabricated cabin uses the free breathing function to ensure that the temperature inside the cabin changes relatively smoothly during the temperature rise and fall process:

②The temperature of the breathing prefabricated cabin is up to 8°C different from that of the conventional prefabricated cabin.

Figure 7 Schematic diagram of cabin temperature change curve

When the air conditioner is turned on and the temperature is set to 25℃, the power consumption of the two cabins for a whole day is shown in Table 2.

Table 2 Comparison of power consumption of test sample cabin

3. Impact of the exterior surface of prefabricated modular smart substation on energy consumption

(1) Color matching is very important for product appearance design. The modular intelligent substation prefabricated cabin is the main building of the entire substation. The color matching of the prefabricated cabin often attracts attention at the first time. If the color matching is appropriate, the product will stand out. Different designers, different owners, different companies, and different regions all have their own ideas about the color matching of the substation prefabricated cabin. They want to make the appearance design more corporate and more recognizable, but designers often ignore the impact of color on the energy consumption of the cabin.

(2) Research (cement residential buildings in Guangzhou) shows that different colors have different solar radiation absorption coefficients, as shown in Table 3, and the impact of different radiation absorption coefficients on the annual average room temperature of the building is almost linear. The annual average room temperature difference between white and black is nearly 3°C, as shown in Figure 8.

Table 3 Reference table of paint color absorption coefficient of solar radiation

Note: Light colors refer to light blue, light green, light red and other light colors

Figure 8 Annual average basic room temperature for different solar radiation absorption coefficients

(3) If the prefabricated cabin of the modular smart substation is made of steel, the solar radiation absorption coefficient is much higher than that of cement, so the annual average room temperature difference will be far more than 3°C, as shown in Table 4.

(4) According to the characteristics of different materials, the outer wall surface of the prefabricated cabin of the modular intelligent substation should preferably be made of non-metallic materials with relatively low thermal conductivity (for example, GRC cement mortar materials). Considering the long-distance transportation and hoisting assembly operations after factory prefabrication, building steel can be appropriately selected as the outer wall material to ensure reliability and stability.

(5) When designing the color matching of the outer surface paint of the prefabricated cabin of the modular intelligent substation, in order to achieve energy-saving design of the substation, the selection of different colors should be fully considered on the basis of taking into account factors such as aesthetics and corporate characteristics.

1) Areas with hot summers and warm winters: It is recommended to use white as the main color of the prefabricated cabin body, and light colors as matching colors to design the appearance of the prefabricated cabin body.