With a series of national energy conservation policies and regulations promulgated by the central cooling public buildings more and more generally used central air conditioning metering technology, through the measurement of hand can advocate users reasonable use of air conditioning, active energy, avoid wasting phenomenon; on the other hand the reasonable measurement of cost sharing, solve the difficult problem of the Property Management Company fees, users "use more, less, less charge according to the. The deeper meaning is through energy readings to assess the actual cooling capacity of refrigeration units, according to the historical data of the database, by analyzing the data of energy saving potential of large public buildings, thus the implementation of large public building energy saving reconstruction.
Although "cold" has the same commodity attributes as water, electricity and gas in the market economy society, it is difficult and complicated to measure the water, electricity and gas in the market. A large area of space (the same owner) mainly in the energy meter measurement of air conditioning, the principle is: in the region to undertake a measurement for air conditioning, water pipes on the installation of a temperature sensor (pair), measurement of supply and return water temperature, the return pipe to install a flowmeter, respectively the coolant water temperature and flow rate of import and export, after compensation and integral density and enthalpy calculation, get the consumption of "cold" value. At present, in the application of energy meter, according to the selection of flowmeter, there are three main types: mechanical, ultrasonic and electromagnetic. The main difference between them is the principle and structure of the flow sensors.
Application of mechanical flowmeter in household energy meter
To measure the rotational speed of the impeller through the chilled water flow mechanical energy, mechanical energy table according to the internal structure of the flow sensor is divided into single beam and multi beam type, according to the counter is in contact with hot water is divided into dry and wet. The impeller speed sensor is usually dry transfer to counter by way of a magnetic coupling, and the imported mechanical energy table induction and conduction mode using part, no magnetic effects can be reduced, the water table of the rust.
Due to technical and price reasons, most of our early mechanical energy meters were used, including imported and domestic brands. However, the use and research practice in recent years show that there are a series of problems in the measurement of air conditioning cooling capacity by mechanical energy meter, such as the narrow range and too large starting flow rate, the difference of the coefficient of flow coefficient of chilled water. As the air conditioning refrigeration water generally exist impurities, scale, flow instability and other issues, it is easy to produce large measurement errors or non metering phenomenon, resulting in measurement disputes, causing trouble to the property management. At the same time, mechanical energy meter maintenance is large, usually less than a month, you need air-conditioning system downtime, water, cleaning flow meters, wear larger, but also to replace the flowmeter. In addition, China's current operating conditions of the air conditioning system of energy meter is put forward than foreign heat metering and more stringent requirements, such as the circulating water quality is poor; the reasons causing water not only contain harmful chemicals in great quantities, there are all kinds of destructive flow sensor of small particles of impurities. These problems will also exist for a long time. Therefore, for mechanical energy meter, due to its inherent limitations in structure and principle, it is a severe challenge whether it can run normally and accurately in a test cycle (five years).
Two. Application of ultrasonic technology in household energy meter
In the air conditioning measurement, some projects use ultrasonic energy meter. Ultrasonic energy is measured by ultrasonic in the thermal medium propagation time difference (acoustic wave propagation in a fluid flow direction, the acoustic velocity increases, the countercurrent direction decrease, the same propagation distance have different propagation time). The flow velocity is obtained by the difference between the propagation velocity and the flow velocity of the measured fluid. There is no strict requirement for the composition or impurity content of the medium due to its absence of any moving parts inside the chamber. Therefore, the ultrasonic energy meter is superior to the mechanical energy meter in terms of cycle cost, reliability and accuracy. However, before 2000, due to price reasons, the household energy meter or mechanical energy meter occupied the dominant position. Now, with the mechanical energy meter defects have been recognized, has been basically eliminated.
But in the process of practice, some people walked into a misunderstanding, that is, simply use imported ultrasonic heat meter to measure the amount of air conditioning cooling. From the practice of the project, the effect is not satisfactory, even the system runs badly. The reason is the import of heat meter (mostly European brands) in foreign countries is mainly used in heating heat metering, heating condition is "large temperature difference (temperature of 15 DEG C), and small flow cooling conditions is small temperature difference (maximum temperature of 5 DEG C) large flow". In the heating environment, ultrasonic heat meter has been applied very widely, the technology is also very mature, and the application in cooling, condensation of water will be attached to the body, the structure of ultrasonic heat meter integration makes the condensed water easily penetrate into the body, damage to electronic components, large consumption of battery, the first half is finished using the battery situation (ultrasonic heat meter with the general battery available for 6 ~ 10 years). The larger the caliber of an ultrasonic energy meter, the higher the price, and sometimes the larger the gauge size, the higher the price,
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