The painting workshop is the largest energy consumer among the four major workshops of automobile manufacturing (stamping workshop, welding workshop, painting workshop, and final assembly workshop), accounting for about 60% of energy consumption. How to select energy-saving equipment during the planning of the painting workshop and implement effective energy-saving measures during operation to effectively reduce energy consumption and operating costs is a key focus of painting workshop planning and management. 1. Equipment Energy-Saving Planning 1.1 Power Supply System Planning A reasonable power supply system plan can not only save electricity but also ensure the normal operation of equipment and extend its service life. 1) Rationally arrange the number of transformers in operation. The number of transformers should be rationally arranged according to the total load. In Chery's Painting Workshop 2 (a world-class painting workshop introduced by Chery from Dürr AG of Germany, hereinafter referred to as Painting Workshop 2), 6 transformers are distributed in a dispersed manner: 2 transformers are arranged in the pretreatment line, electrophoresis line, and PVC line area, and 2 transformers are arranged in the intermediate coating line and topcoat line area. 2) When the copper loss of the transformer equals the iron loss, or in other words, when the fixed loss equals the variable loss, the transformer efficiency is the highest. At this time, the transformer is operating under the condition of optimal load rate, and the energy-saving effect is the best. When planning the transformer, after reasonably selecting the transformer capacity and arranging the line load, and reasonably distributing the transformers, the load rate of the three 2000KVA transformers and three 1600 kVA transformers in the painting workshop reached 80%. (3) Improve the power factor of the load: ① Install a reactive power compensation controller in the low-voltage cabinet of the transformer to improve the power factor to 0.95; ② Install a power factor compensation cabinet in the low-voltage cabinet and manually compensate the power factor. 1.2 Spray booth equipment planning For the heat source of the air conditioning unit heating section of the spray booth equipment, the use of steam or natural gas has a significant impact on the layout. Considering that the power plant of Chery Company (hereinafter referred to as the power plant) has already put into operation a thermal power plant, which can provide steam as an additional product, steam is still used as the heat source of the spray booth. When controlling the temperature of the spray booth in winter, the steam heats the air and produces a large amount of condensate. The temperature of this condensate is generally around 80℃. Because the power plant is far from the painting workshop, recycling and reusing the condensate from the power plant would result in heat loss. Therefore, the condensate is directly recycled in the painting workshop. The recycled condensate, at approximately 80°C, is used to spray, heat, and humidify the air, regulating the temperature and humidity of the spray booth. This saves the painting workshop on steam and water consumption, and the power plant also saves on the electricity consumption of pumping condensate recovery. The airflow requirements for the spray booth differ between production and cleaning modes; the cleaning mode requires less airflow. Therefore, the central air conditioning unit for the spray booth needs to supply different airflows depending on the situation, requiring careful selection of the central air conditioning unit's control scheme. When the centrifugal fan's speed decreases, its power consumption drops significantly. For example, when the speed drops to 50%, the shaft mechanical power decreases to 12.5%. Variable frequency speed control is highly efficient; when the speed drops to 50%, the efficiency n≈95%-98%, almost constant, making it the most energy-efficient. Central air conditioning units with dual motors often choose a control scheme that combines soft start and variable frequency speed regulation. 1.3 Drying room equipment planning (1) Drying room equipment system composition: waste gas recovery circulating incinerator (TIU), heating section (1, 2), insulation section (1, 2), waste gas circulation fan, fresh air heating circulation fan, inlet/outlet gas seal section, strong cooling chamber, see Figure 1. In order to accelerate the heating and shorten the heating time, it is generally advisable to install a gas-fired proportional regulating burner in insulation section 2. If a direct-fired incinerator (RTO) is used, RTO is generally installed in both the heating section and the insulation section. At the same time, the combustion exhaust gas needs to be centrally incinerated and then recycled. (2) Waste gas recovery circulating incinerator system (TIU) TIU is a system that mixes natural gas, a portion of compressed air, and waste gas extracted from the insulation section in the combustion furnace to output heat. It integrates the two major functions of heat exchange and combustion. The combustion temperature is generally controlled at around 760℃, and the output hot air temperature after heat exchange is generally controlled at around 480℃. (3) Heat and air volume balance in the drying room The drying temperature used in many domestic car painting workshops is roughly in the following range: the drying temperature of the electrophoresis drying room is 185～190℃, the drying temperature of the intermediate coating drying room is 165～170℃, and the drying temperature of the topcoat drying room is 155～160℃. The continuous drying time is generally around 10 minutes, and the continuous heat preservation time is generally around 20 minutes. In order to ensure the heat balance of each functional section, it is generally required that each heating and heat preservation section can be automatically adjusted according to the set value. In order to ensure the balance of air supply and exhaust volume, adjustable air valves are generally installed on the exhaust gas circulation pipeline, fresh air supply pipeline and the air seal section pipeline after heat exchange to adjust and balance the air supply and exhaust volume. 2 Energy saving management 2.1 Control of hidden kinetic energy waste The hidden waste of kinetic energy is not easy to be discovered and is difficult to control because of its "hidden" characteristics, and the waste is also greater. For example, unreasonable production scheduling leads to an unreasonable ratio of peak, flat, and valley electricity loads; uncoordinated production task scheduling results in the welding workshop not keeping up with the painting workshop's production pace, and insufficient supply of body-in-white from the welding workshop to the painting workshop, causing the painting workshop's equipment to run idle; unreasonable process parameter settings (e.g., excessively high drying room temperature in the painting workshop, excessive welding current in the welding workshop, etc.) lead to waste. To address its "hidden" nature, different control methods were adopted. 2.1.1 Rational use of time-of-use pricing: Since electricity prices vary greatly at different times of the day—peak price is 1.5 times the flat price, and peak price is 2.9 times the valley price—time-of-use pricing can be used to control hidden energy consumption. When scheduling production, if it is single-shift production, try to schedule it during the night shift (0:30-8:00) when electricity prices are lower. When scheduling specific production times, try to schedule the production time of the painting workshop, a major energy consumer, during valley hours to increase the proportion of valley hours. From December 2005 to February 2006, through reasonable production scheduling, the peak efficiency ratio of Painting Workshop 2 increased from 34.7% to 42.1%, saving over 1.7 million yuan in electricity (see Figure 2). 2.1.2 Reasonably ensuring production cycle time: On the one hand, it is necessary to balance the production of the welding and painting workshops, reducing production gaps caused by waiting between the painting and welding workshops, and reducing production gaps caused by waiting between subsequent workstations in the painting workshop and previous workstations, thus ensuring the hourly production cycle time of the painting workshop; on the other hand, by modifying equipment parameters, such as inverter parameters and motor parameters, the processing speed of each piece of equipment is accelerated, thereby increasing the hourly production cycle time of the painting workshop. After the entire Painting Workshop 2 line accelerated in April 2005, the hourly output increased by 13%–16%, and energy consumption decreased by more than 10%. Equipment planning is of decisive significance for energy conservation. When selecting equipment, leaving an appropriate margin in equipment power is key to successful speed increases. If the equipment power only just meets the original design requirements, it will be difficult to achieve speed increases later without additional investment. 2.1.3 Rational Selection of Energy Types When the No. 2 Painting Workshop went into operation in 2003, the heating energy for the drying chamber was air-mixed liquefied petroleum gas (LPG). After the national "Two Gas Pipelines to the East" reached Wuhu City, in May 2005, after analyzing the calorific value of natural gas and air-mixed LPG, as well as the matching of natural gas with the burner, the heating energy for the drying chamber was switched from air-mixed LPG to natural gas. The unit price of gas per cubic meter decreased by 50%, and the energy cost per vehicle decreased by 25 yuan. 2.2 Equipment Improvement to Reduce Energy Waste Equipment improvement is a very effective means of energy control. Through equipment improvement, energy waste can be effectively reduced. For example, during shutdown maintenance, the No. 2 Painting Workshop's self-provided air compressor can only supply compressed air to the automatic painting equipment in this workshop. If other equipment in this workshop also needs to use compressed air, the air compressor from the energy plant must be started, resulting in a huge waste of electricity. Through improvements, the pipelines of the air compressors in Painting Workshop 2 were connected to other air-consuming points within the workshop. During shutdown and maintenance, only the air compressors in each workshop need to be started to complete the maintenance tasks. 2.2.1 Improvement in Timely Start-up In Painting Workshop 2, there are interlocking mechanisms between various process equipment. The entire workshop can only operate normally when all process equipment reaches the set values ​​of process parameters. For example, the spray booth equipment must be started in advance. When the temperature and humidity of the spray booth reach the process set values, the car body can enter the spray booth to start painting; the drying chamber equipment must be started in advance. When the temperature of the drying chamber reaches the process set value, the car body can enter the drying chamber to start drying. The time it takes for each piece of equipment to reach its set process parameters varies. For example, the intermediate coating spray booth takes approximately 25 minutes to reach its set process parameters. If the line is to start at 8:00 AM, the intermediate coating spray booth equipment must be started 25 minutes earlier, at 7:35 AM. The intermediate coating drying chamber takes approximately 55 minutes to reach its set process parameters, and must be started 55 minutes earlier, at 7:05 AM. This ensures that all equipment reaches its set process parameters simultaneously, allowing for timely line start-up and preventing some equipment from running idle and wasting energy. Since 2003, data on the start-up time, parameter set point arrival time, and line start-up time of each piece of equipment has been collected in the second painting workshop. The start-up time of each piece of equipment is adjusted daily. After six months of monitoring and improvement, while ensuring that high-power equipment cannot be started simultaneously, the start-up time can be accurate to within 0.5 minutes, and the line start-up time can be accurate to within 1.5 mm. Compared to 2003, energy consumption decreased by 20% in 2004, saving 8 million yuan in energy costs. 2.2.2 Improvement of Lighting Electricity Consumption: Various workshops experienced varying degrees of waste in lighting electricity consumption, mainly manifested in one switch controlling multiple lights, or even one switch controlling lights in multiple areas; lights in stairwells and corridors often going unturned; and excessive illuminance in some areas. The lighting circuits were modified to reduce the number of lights controlled by a single switch; stairwell and corridor lights were replaced with touch-delay switches; and the illuminance of workstation lighting was measured to rationally allocate the number of lights. Taking the second painting workshop as an example: after improving lighting electricity consumption, 34,000 yuan in electricity costs can be saved annually. 2.2.3 Improvement of Process Parameters: During the trial production and debugging phase of the second painting workshop, the set value of the drying chamber temperature was higher than the actual demand to ensure the drying effect. After entering the formal production stage, the set value of the drying chamber temperature was appropriately lowered. After multiple tests, the set value of the drying chamber temperature decreased by nearly 10℃, reducing energy consumption.