Home Appliance Testing is a systematic monitoring process centered around the operational principles of devices, primarily aimed at ensuring the safe and stable operation of home appliances. The quality of testing is directly related to the safety of the devices and personal safety. However, as the structure of household appliances becomes increasingly complex and the failure rate of electromechanical devices rises, the difficulty of this testing work has increased. To effectively improve the quality of home appliance testing, establishing appliance testing laboratories and production lines is essential. Among these appliances, washing machines play a crucial role in people’s lives.
Currently, regarding the classification of washing machines, they can be divided into three types based on the washing method: agitator type, pulsator type, and drum type. The working principle of washing machines involves using detergents and water to emulsify and dissolve stains on clothing, employing mechanical actions such as impact and agitation to remove the stains. Common detergents like washing powder and liquid laundry detergent contain a large number of surface-active agents that effectively reduce the binding force between stains and fabric by promoting stain swelling. Additionally, when the hydrophilic group comes into contact with water, the hydrophobic group forms a monomolecular layer that aids in further dissolving the stains. Under the mechanical force of the washing machine, the stains separate from the fibers of the clothing, achieving the washing effect.
Regarding washing machine testing, it includes three aspects: electrical performance testing, washing performance testing, and other quality performance testing. Electrical performance testing encompasses power consumption detection, overflow insulation testing, and waterproof testing. Washing performance testing includes rinsing performance testing, clothing cleanliness rate testing, and dehydration performance testing. Other performance quality testing techniques include drainage time and noise testing.
The establishment of the washing machine testing laboratory combines modern control theories and methods to develop a performance testing environment that prioritizes energy efficiency, high testing accuracy, and short transitional times for working conditions. The performance testing laboratory primarily provides the necessary environmental conditions for washing machine performance testing, ensuring the required water temperature and pressure according to technical specifications. It also incorporates a modern data acquisition system that automatically outputs parameters such as water temperature, water intake, power consumption, and energy usage of the washing machine. To accurately detect the cleanliness rate of the washed fabric, a temperature and humidity-controlled storage room for the fabric is constructed. During the performance testing process, testers only need to input the laboratory environmental conditions, set the water temperature and pressure for the washing machine, and the testing system can quickly reach the required conditions and enter an automatic control mode to collect and record parameters, determining whether the experimental results meet national standards.
The design of the washing machine testing laboratory includes aspects such as cooling systems, air handling systems, constant temperature water systems, data acquisition, and electrical control systems. The cooling system utilizes an air-source refrigeration system that belongs to low-grade energy sources. Compared to water-cooled systems, it does not require cooling towers or chilled water devices, making the cooling system simpler and more energy-efficient while stabilizing the control system. The cooling system consists of four subsystems: lubrication oil circuit (to ensure good lubrication, sealing, cooling, and energy regulation inside the compressor), liquid injection circuit (to adjust the liquid injection valve based on the return gas temperature to avoid excessively high suction temperatures), and the main refrigeration circuit (to complete the working conditions by reasonably controlling the refrigeration flow).
The air handling system is designed to manage the laboratory’s specified working conditions. This system comprises an air handling unit, air-cooled refrigerant unit, circulating fan, electric humidifier, electric heater, temperature and humidity sensors, regulators, converters, and actuators. The airflow organization is designed for upward supply and downward return, using a perforated plate for uniform air distribution. To reduce the temperature gradient in the working area, a stable pressure layer is added between the supply air plates to enhance the uniformity of air distribution. To meet the conditions of dry bulb temperature and relative humidity, the evaporator cools the air, which is then heated to the required control temperature using electric heaters. PID control is employed to adjust the heating amount (15 kW) using a SCR three-phase power regulator for precise control of the dry bulb temperature. Relative humidity control is achieved by combining the electric humidifier and evaporator. Under the worst conditions (dry bulb temperature of 21°C and relative humidity of 60%), the humidity of the air is approximately 16°C. The evaporator operates at an evaporation pressure of about 0.4 MPa and an evaporation temperature of around 3-4°C, using a 7.5 kW Carel electrode humidifier for humidification, thus completing the relative humidity control.
The constant temperature water system is designed to meet the system’s water temperature requirements, featuring a cold water tank with a volume of 1 cubic meter and a hot water tank with a volume of 0.8 cubic meters. The cold source for the cold water tank is a 7 HP air-cooled chiller, while the hot water tank’s heat source is a 40 kW storage-type electric water heater, with the cold water tank also using an internal electric heater. The temperature of the cold water tank is controlled by adjusting the bypass flow through a three-way valve to manage the required cooling capacity, supplemented by the heating from the electric heater. The hot water tank requires substantial heating, provided by the storage-type electric water heater, while the cooling capacity is supplied by the chiller. The temperature of the hot water tank is controlled by regulating the exchange amount of cold and hot water. To reduce testing wait times and ensure a constant water temperature for the washing machine, the cold and hot water systems are in a self-circulation state. This ensures uniform temperatures throughout the water system, allowing continuous water supply to the washing machine at the set values. The water supply pump uses a variable frequency pump, ensuring not only the water flow but also precise control of the water pressure.
The data acquisition and electrical control system primarily consists of thermistors, electromagnetic flow meters, pressure sensors, temperature and humidity sensors, data acquisition instruments, PID controllers, and PCs. The measurement and control of the laboratory and storage room conditions utilize VAISALA temperature and humidity transmitters with direct DC output, as platinum resistors are very stable and commonly used as standard temperature measuring devices. The constant temperature water tank system uses Class A platinum resistors for measurement and control. Pressure measurement of the water system employs PTX-type pressure sensors with a range of 0.5 MPa, while flow measurement uses AXF-type electromagnetic flow meters. The electrical system of the laboratory is divided into two parts: one part includes regulators, data acquisition instruments, digital power meters, etc., that receive power immediately after the system is energized; the other part consists of actuators controlled by PLC. The PLC used in the laboratory has 12 input terminals and 8 output terminals, and supports I/O expansion boards to increase the input and output terminals to meet practical operational needs. In the air handling system, adjustments are made to the supply air temperature, volume, and relative humidity, with the PLC controlling heating, cooling, and humidification amounts to regulate the speed of the refrigeration compressor, the power of the variable electric heater, and the speed of the circulating fan. Liquid level control in the water tank employs float switches for alarm purposes only. Temperature control is achieved by converting the thermistor readings, with deviations adjusted via PID control to manage the heating device and plate heat exchanger, and an electromagnetic three-way valve is added to change the heat exchange amount in the plate heat exchanger, thereby improving the energy utilization of the system. Water supply pressure is adjusted by changing the speed of the water supply pump.
Our washing machine testing laboratory meets the requirements of both domestic and international standards. It covers the water needs for energy efficiency testing for various washing machine manufacturers. The facility is designed for standardized production with mobility. Currently, there are no commercially available water treatment devices specifically for washing machine energy efficiency testing. Laboratories dedicated to product inspection often design specialized water treatment equipment during the construction phase. While such equipment meets standard requirements, it often needs to be designed and modified based on actual building conditions, leading to long construction periods, large footprints, and a lack of mobility. Our equipment does not require such design and modification, can be produced in a standardized manner, and possesses mobility. It is cost-effective and easy to operate, addressing the high costs of water treatment equipment in washing machine testing laboratories, which can be substantial for many small and medium-sized washing machine manufacturers. Furthermore, traditional equipment often involves complex operations with low automation levels, requiring testers to set up different devices separately, which places high demands on personnel. In contrast, our equipment is affordable, suitable for testing equipment investment by washing machine companies, easy to operate, and features a high level of automation with a visual interface that eliminates the need for testers to set up different devices separately. Additionally, we have our own innovations; the development of water treatment equipment for washing machine energy efficiency testing is a domestic first. This equipment is used in professional laboratories, ensuring stable water temperature, pressure, and hardness for the test water, with daily water parameters remaining stable. This reduces uncertainty factors, facilitates monitoring and recording, and allows for traceability and review, thereby achieving experimental repeatability and enhancing the impartiality and legal validity of test reports issued by inspection institutions.