1 Introduction
The heat dissipation and operating environment of equipment in high-voltage frequency converter applications directly affect the operational safety of the frequency converter itself. As the power of frequency converters continues to increase, the investment and operating costs of their auxiliary cooling systems are receiving increasing attention. Adopting professional air-water cooling devices for high-voltage frequency converters to improve equipment safety and stability, and reduce the operating costs of auxiliary cooling systems, has become one of the important issues to consider in high-voltage frequency converter applications.
The following is a comparative analysis of the economic indicators of common room air conditioning cooling and dedicated high-voltage frequency converter air-water cooling devices.
2. Economic Analysis of Air Conditioning Cooling
2.1 Cooling Power Calculation
Taking the cooling of the high-voltage frequency converter of the primary air fan of a 350MW unit in a Huaneng power plant as an example. The two high-voltage frequency converters of the primary air fan have a power of 1600kW each and are installed in the same high-voltage frequency converter room with a room area of 9m×6.5m×4.5m (length×width×height).
Based on the southern climate, the required cooling capacity is calculated at 180w/m2, and the self-cooling loss of the house is:
qf = s × 180 = 58.5 × 180 ≈ 10.53 kW
Where: s – house area
Rated total heat generation of the high-voltage frequency converter for the primary air fan: qb = p × 4% = 1600 × 4% × 2 = 128 kW
Where: p—rated output power of the high-voltage frequency converter. Therefore, the minimum effective cooling capacity required for the primary air fan high-voltage frequency converter room is: q = qb + qf = 128 + 10.53 = 138.53 kW
2.2 Calculation of Air Conditioning Cooling Power Consumption Index
Based on the above calculations, the effective cooling capacity required for the high-voltage inverter room of the primary air blower is 138.53 kW. Considering that the system heat exchange efficiency of the high-voltage inverter room cannot be 1, meaning that the cooling capacity of the air conditioner must be fully utilized for equipment cooling to achieve 100% exchange, and taking into account factors such as the placement of the air conditioner according to the surrounding environment, air supply distance, and circulation speed, the cooling power is calculated based on a typical system efficiency of 70%.
In the formula: η—efficiency
Based on the air conditioner's specifications and energy efficiency ratio parameters, and considering that the high-voltage inverter cannot operate at 100% load for extended periods, a 12p air conditioner with a rated cooling capacity of 28kW per unit is selected.
Number of air conditioners:
In other words, to achieve ambient temperature control in the high-voltage inverter room of the primary air blower, at least seven 12p air conditioning units need to be installed.
Air conditioner energy efficiency ratio = cooling capacity : grid-side power consumption = 2.5
When the primary air fan room is cooled by air conditioning, the unit power consumption on the grid side is:
That is, the daily power consumption of the high-voltage frequency converter room of the fan is 1881.6 kw·h when cooled by air conditioning once a day (24 hours).
Based on an annual effective operating period of 210 days for the unit, the annual energy consumption for cooling the high-voltage frequency converter room of the primary fan is c = 395136 kWh, which is equivalent to RMB 146,200 at an electricity price of RMB 0.37/kWh.
Based on a cost of 25,000 yuan for a 12p air conditioner, the total investment for equipment using air conditioning cooling is 175,000 yuan.
3. Economic Analysis of Air-Water Cooling System
3.1 Cooling power calculation
The calculations above show that the rated heat output of the two 1600kW high-voltage frequency converters is 128kW. When using an air-water cooling system, the system achieves heat exchange for all the hot air discharged from the high-voltage frequency converters through the air-water cooling device, and then returns the cool air to the room. Therefore, its airflow circulation efficiency is greatly improved, approaching 99%. Unlike air conditioning, which cools the room before cooling the equipment, the latter achieves the goal of controlling the indoor environment of the high-voltage frequency converter by absorbing the heat generated by the equipment. Its system efficiency is naturally improved, and it avoids the energy consumption required for ambient cooling.
Considering the heat generation under extreme operating conditions, as well as factors such as high water temperature and system exchange efficiency, the design margin of air coolers is usually selected as 1.15 to 1.2 times. That is, the heat exchange power of the air cooler should not be less than 73.6 kW/unit, and the actual selected air cooler power is 75 kW per unit.
3.2 Calculation of Air Conditioning Cooling Power Consumption Index
Each high-voltage frequency converter is equipped with an air-water cooling system, the main power-consuming equipment of which is a 2.2kW booster fan. This equipment, along with the fans on the top of the high-voltage frequency converter cabinet and the fans configured in the air-cooling system, operates in a hot standby configuration. The system adopts indoor closed-loop cooling, and the ambient temperature is controlled below 40℃. When the primary air fan uses an air-water cooling system to achieve ambient temperature control, the total power consumption of the fan配套 with each high-voltage frequency converter is 2.2kW, and the power consumption p' of the two high-voltage frequency converter cooling fans is 4.4kW.
This system utilizes closed-loop industrial cooling water from the units for heat exchange. The cooling water is recycled, with a circulating water requirement of 36 t/h per unit. Based on the total circulating water volume of the units operating on-site, the primary air system's water usage accounts for less than 2% of the total, therefore the increase in power consumption of the circulating pumps is minimal and negligible.
The total power consumption of the unit using the air-water cooling system is 4.4 kW. The daily power consumption of the high-voltage frequency converter room of the primary fan of the two units in air-water cooling operation is: 24 × 4.4 = 105.6 kW·h.
Based on an annual effective operating period of 210 days for the unit, the annual energy consumption for cooling the high-voltage frequency converter room of the primary fan is c = 22176 kWh, which is equivalent to RMB 8,200 at an electricity price of RMB 0.37/kWh.
Based on a cost of 97,000 yuan per 75kW air-water cooling system, the total investment for air-water cooling equipment is 194,000 yuan.
4. Economic Comparison Analysis
Based on the above data calculations, the economic comparison analysis between the air-water cooling system and conventional air conditioning cooling methods is as follows:
Energy saving rate:
In the formula, p0 is the grid-side power consumption p when the primary air fan room is cooled by air conditioning.
Annual electricity savings:
q=qd－qb=395136－22176=372960kw.h
Annual electricity savings: m = q × n = 372960 × 0.37 = 137995.2 yuan, approximately 138,000 yuan.
In other words, by using an air-water cooling system to cool the primary air high-voltage frequency converter, the annual electricity consumption for cooling alone can be reduced by 138,000 yuan compared to conventional air conditioning cooling. The equipment investment cost can be recovered in 1.5 years, achieving energy saving for both the high-voltage frequency converter project and the auxiliary equipment.
5. Conclusion
The high-voltage frequency converter room of the primary air fan of a 350MW unit in a Huaneng power plant adopts an air-water cooling system. In addition to bringing direct energy-saving economic benefits, it also brings the following economic benefits:
(1) After adopting the new cooling system, the equipment cooling operation cost of its high-voltage frequency converter will be reduced by about 90% compared with conventional air conditioning cooling. The operating cost is only 10% of that of air conditioning cooling system.
(2) Because the new cooling system adopts a closed cooling structure design and the air duct is used in a circulating manner, it has the characteristics of low dust, stable environment and less influence from external environmental factors. The cleaning cycle of the dust filter can be extended from the original 7-15 days to 30-45 days, which greatly reduces the workload of maintenance personnel.
(3) Due to the reduced number of devices used and in operation, and the fact that the air-water cooling system is mainly composed of mechanical equipment, its stability and safety are far superior to those of the power electronic equipment used in air conditioning refrigeration. The safety of the system is improved, and the safety of the unit operation is ensured from the auxiliary equipment.
(4) The new cooling system is designed with full consideration of safety protection measures such as equipment failure, heat exchange medium leakage, emergency bypass of air duct, ease of operation, and maintainability. It is integrated with high-voltage frequency converter equipment to improve overall safety performance.
(5) The service life of the air-water cooling system is 5 to 8 times that of the air conditioning equipment, which can greatly reduce the maintenance cost of the equipment.
In conclusion, the adoption of an energy-saving and environmentally friendly air-water cooling system in the primary air fan frequency conversion energy-saving project of a Huaneng power plant is a necessary and feasible measure. The project has significant economic advantages and is worthy of widespread promotion and application in the high-voltage frequency conversion application industry, thereby achieving comprehensive energy saving in high-voltage frequency conversion projects.
