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Application of summer energy meter in air conditioning

by:Sure     2020-06-23
Centralized cooling public buildings are increasingly using central air conditioning household metering technology. On the one hand, through measurement, users can be encouraged to use air conditioning reasonably, saving energy and avoiding waste; on the other hand, through reasonable metering cost allocation, property management companies can be resolved With regard to the difficulty of charging, users 'use more and pay more, use less and pay less', so that the charges are based on evidence.    The deeper meaning is to evaluate the actual cooling capacity of the refrigeration unit through the reading of the energy meter, establish a database based on historical data, and study the energy saving potential of large public buildings through actual data analysis, so as to implement energy-saving renovation of large public buildings.   Although 'cold' has the same commodity attributes as water, electricity, and gas in a market economy and society, in terms of measurement, it is more complicated and difficult to measure and charge than water, electricity, and gas that have entered the market and achieved success. Large-area space (same owner) air-conditioning measurement is mainly based on energy meter measurement. The principle is: install a temperature sensor (paired use) on the air-conditioning supply and return pipe that undertakes a certain measurement area to measure the supply and return. For water temperature, install a flow meter on the return pipe to measure the temperature and flow rate of the coolant-water inlet and outlet, and then compensate for the density and enthalpy value and calculate the integral to obtain the amount of 'cold' consumed value.    At present, in the application of energy meters, according to the different types of flowmeters, there are three main types, which are mechanical, ultrasonic, and electromagnetic. Their main difference lies in the principle and structure of the flow sensor. First of all, a comprehensive analysis and comparison of mechanical, ultrasonic, and electromagnetic products from the perspective of technology and the actual situation of application, and then from the perspective of economic investment to analyze the life cycle cost, providing selection of air-conditioning measuring instruments solution.    1. Application of mechanical flowmeter in household energy meter The mechanical energy meter measures the flow of chilled water by the speed of the impeller. The mechanical energy meter is mainly divided into single-flow beam type and multi-flow beam type according to the internal structure of the flow sensor, and is divided into dry flow according to whether its counter is in contact with hot water. And wet. The speed of the impeller of the dry sensor is usually transmitted to the counter through magnetic coupling. At present, the imported mechanical energy meter adopts the inductive conduction method, that is, the non-magnetic method, which can reduce the influence of rust in the water on the meter. Application of    energy meter in air conditioning measurement   Due to technical and price reasons, most of the early my country used a variety of mechanical energy meters, including imported and domestic brands. However, in recent years, the use and research practices have shown that using mechanical energy meters to measure the cooling capacity of air conditioners has a series of problems, such as the problem of narrow range and too large starting flow rate, and the difference in chilled water flow coefficient. As the air-conditioning chilled water generally has many problems such as many impurities, many scales, and unstable flow patterns, it is easy to produce large measurement errors or non-measurement phenomena, resulting in measurement disputes, which brings trouble to property management. At the same time, the maintenance of mechanical energy meters is large. Usually, the air conditioning system needs to be shut down to drain the water, the flowmeter is cleaned, and the flowmeter must be replaced when the wear is large. In addition, the current operating conditions of air-conditioning systems in China also put more stringent requirements on energy meters than foreign heat metering, such as the poor water quality of circulating water; various reasons cause the water not only to contain a lot of harmful chemicals, but also various The flow sensor has destructive small particle impurities. These problems will still exist for a long time. Therefore, for the mechanical energy meter, due to its inherent limitations in structure and principle, whether it can operate normally and accurately within a verification cycle (five years) is a very serious challenge.    Second, the application of ultrasonic technology in household energy meters   In the measurement of air conditioning, some items use ultrasonic energy meters. Ultrasonic energy meters measure the time difference of ultrasonic waves propagating in a thermal medium (sound waves propagate in a fluid, the sound wave propagation speed increases in the downstream direction, and decreases in the reverse flow direction, and the same propagation distance has different propagation times). Use the relationship between the difference in propagation velocity and the measured fluid velocity to find the velocity to derive the flow rate. Since there are no moving parts inside the measuring cavity, there are no strict requirements on the composition or impurity content of the medium.    Therefore, in terms of life cycle cost, reliability and accuracy, ultrasonic energy meters are superior to mechanical energy meters. However, before 2000, due to price reasons, mechanical energy meters still dominated the household energy meters. Now that the defects of mechanical energy meters are recognized, they are basically eliminated. Application of    energy meter in air conditioning measurement    But in the process of practice, some people have entered a misunderstanding, that is, the imported ultrasonic heat energy meter is simply used to measure the cooling capacity of the air conditioner. From the perspective of engineering practice, the effect is very unsatisfactory, and even the system is running poorly. The reasons are as follows: First, imported heat meters (mostly European brands) are mainly used for household heating measurement in foreign countries, and the operating conditions of heating are 'large temperature difference (temperature difference is generally 15°C) and small flow rate', The cooling condition is 'small temperature difference (maximum temperature difference is 5 ℃) large flow'. In the heating environment, the ultrasonic heat meter has been widely used, and the technology is also very mature. When used for cooling, the condensate will be attached to the body. The integrated structure of the ultrasonic heat meter makes the condensate easily penetrate into the body It destroys electronic components and consumes a large amount of batteries, and the battery is used up within half a year. (Ultrasonic heat meters generally have their own batteries and can be used for 6 to 10 years). The larger the caliber of the ultrasonic energy meter, the higher the price. Sometimes the caliber of the energy meter is one size larger, and its selling price will be much higher, so the investment cost is a factor to consider using the ultrasonic energy meter. In addition, the type selection is more complicated. The main parameter of the energy meter is the system flow rather than the system pipe diameter, and the model of the energy meter is determined according to the flow size (so that the minimum flow of the selected energy meter is less than the minimum flow of the system pipe, energy meter The maximum flow rate is greater than the maximum flow rate of the system pipes), which makes the installation complicated and requires reducing measures.    3. Application of electromagnetic induction technology in household energy meters   Mechanical energy meters are generally considered unsuitable for air conditioning measurement. While applying ultrasonic energy meters, electromagnetic energy meters have appeared. Electromagnetic energy meters mainly use electromagnetic flowmeters. Its working principle is: based on Faraday's law of electromagnetic induction, when a conductive liquid flows through a measuring tube surrounded by a magnetic field, an induced electromotive force E proportional to the average flow velocity V is generated in the direction perpendicular to both the flow direction and the magnetic field. Electromagnetic flowmeters include pipeline type and plug-in type. Application of    energy meter in air conditioning measurement Summary: With the increase in basic energy demand and its price adjustments, the operating expenses for high-energy-consuming equipment such as central air conditioners are also increasing. If measurement assessment is not taken or management energy conservation awareness is strengthened, central air conditioners will become energy-efficient in buildings. The part with the largest consumption rate. Therefore, in appropriate occasions (such as the large-scale use of central air conditioning), energy meters are used to scientifically measure central air conditioning, so as to achieve a reasonable allocation of central air conditioning operating costs, prompting users to use as needed and pay according to consumption.
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