Application of energy meter in air conditioning measurement<br></br>

Application of energy meter in air conditioning measurement

Central air-conditioning household metering technology is more and more commonly used in public buildings with centralized cooling. On the one hand, users can encourage users to use air-conditioning rationally, actively save energy, and avoid waste; on the other hand, they can solve the problem of property management companies through reasonable cost allocation. The problem of difficulty in charging, users "more use more, less use less", so that the charges can be based on evidence.

　　The deeper meaning is to evaluate the actual cooling capacity of the refrigeration unit through the readings of the energy meter, establish a database based on historical data, and analyze the energy-saving potential of large public buildings through actual data analysis, so as to implement energy-saving transformation of large public buildings.

　　 Although "cold" has the same commodity attributes as water, electricity, and gas in a market economy society, in terms of measurement, it is more complicated and difficult than the metering and charging of water, electricity, and gas that have already entered the market and achieved success. The measurement of air conditioning in a large area (same owner) is mainly based on energy meter measurement. The principle is: install a temperature sensor (paired use) on each of the air conditioning supply and return pipes that undertake a certain measurement area to measure the supply and return. For water temperature, install a flowmeter on the return pipe to measure the temperature and flow rate of the inlet and outlet of the refrigerant-water respectively, and then through the density and enthalpy value compensation and integral calculation, the consumed "cold" amount is obtained value.

　　 At present, in the application of energy meters, there are three main types according to the selection of flow meters, which are mechanical, ultrasonic, and electromagnetic. Their main difference lies in the principle and structure of the flow sensor.

First, conduct a comprehensive analysis and comparison of mechanical, ultrasonic, and electromagnetic products from the perspective of technology and the actual situation of the application, and then analyze the life cycle cost from the perspective of economic investment, and provide the 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 through the speed of the impeller. According to the internal structure of the flow sensor, the mechanical energy meter is mainly divided into single-stream type and multi-stream type, and divided into dry type according to whether the counter is in contact with hot water. And wet. The impeller speed of the dry sensor is usually transmitted to the counter through magnetic coupling, and the imported mechanical energy meter part adopts the induction conduction method, that is, the non-magnetic method, which can reduce the influence of rust in the water on the meter.

　　 Due to technology and price reasons, most of our country used various mechanical energy meters in the early days, including imported and domestic brands. However, the use and research practice in recent years have shown that the use of mechanical energy meters to measure air-conditioning cooling capacity has a series of problems, such as narrow range and too large starting flow, and the difference in chilled water flow coefficient. Because air-conditioning chilled water generally has many problems such as large amounts of impurities, large scales, and uneven flow, it is very easy to produce large measurement errors or non-measurement phenomena, resulting in measurement disputes, and bringing trouble to property management. At the same time, the mechanical energy meter requires a lot of maintenance. Usually, it takes less than a month to shut down the air conditioning system to drain water, clean the flowmeter, and replace the flowmeter when the wear is large.

In addition, the current operating conditions of the air-conditioning system in China also put forward more stringent requirements for energy meters than foreign heat measurement, such as the poor quality of circulating water; various reasons cause the water not only to contain a large number of harmful chemicals, but also to The flow sensor has destructive small particles of impurities. These problems will exist for a long time. Therefore, for a mechanical energy meter, due to its inherent limitations in its structure and principle, whether it can operate normally and accurately within a verification period (five years) is a very serious challenge.

　　 2. The application of ultrasonic technology in household energy meters

　　In air conditioning measurement, some items use ultrasonic energy meters. Ultrasonic energy meters measure the time difference of ultrasonic propagation in the thermal medium (sound waves propagate in the fluid, the speed of the sound wave will increase in the downstream direction, and the reverse direction will decrease, and the same propagation distance will have different propagation times). Use the difference between the propagation velocity and the flow velocity of the fluid to be measured to obtain the flow velocity to derive the flow rate. Since there are no movable 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 dominated the field of household energy meters. Now that the defects of mechanical energy meters are recognized, they have basically been eliminated.

　　 But in the process of practice, some people came into a misunderstanding, that is, simply use imported ultrasonic heat meters to measure the cooling capacity of air conditioners. From the perspective of engineering practice, the effect is very unsatisfactory, and even poor system operation occurs.

The reasons are as follows: First, imported heat meters (most of them are European brands) are mainly used for heating heating household metering abroad, and the heating conditions are "large temperature difference (temperature difference is generally 15°C) and small flow". The cooling condition is "small temperature difference (z*large temperature difference is 5℃) and large flow".

In the heating environment, the ultrasonic heat meter has been widely used and the technology is mature. When used in cooling, the condensed water will be attached to the meter body. The integrated structure of the ultrasonic heat meter makes it easy for the condensed water to penetrate into the meter body. , Destroy the electronic components, consume a lot of batteries, and run out of batteries in 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 the price will be much higher, so the investment cost is a factor to consider using the ultrasonic energy meter.

In addition, the selection of the ultrasonic energy meter is more complicated. The main parameter of the energy meter is the system flow rate instead of the system pipe diameter. The model of the energy meter is determined according to the flow rate (make the minimum flow rate of the selected energy meter less than the minimum flow rate of the system pipeline , The maximum flow rate of the energy meter is greater than the maximum flow rate of the system pipeline), which makes the installation complicated and requires reducing measures.

　　 Third, the application of electromagnetic induction technology in household energy meters

　　Mechanical energy meters are generally considered to be unsuitable for air conditioning measurement. While ultrasonic energy meters are used, electromagnetic energy meters have appeared. The electromagnetic energy meter mainly uses an electromagnetic flowmeter. 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 will be generated in the direction perpendicular to the flow direction and the magnetic field. Electromagnetic flowmeter includes pipeline type and plug-in type.

Summary: With the increase in the demand for basic energy and the adjustment of its price, the operating cost of high energy-consuming equipment such as central air-conditioning is also increasing. If metering assessment is not taken or the awareness of energy-saving management is strengthened, central air-conditioning will become the energy in the building. The part that consumes the largest proportion. Therefore, in appropriate occasions (such as the occasions where central air-conditioning is used in a large area), the energy meter is used to scientifically measure the central air-conditioning, so as to realize the reasonable allocation of central air-conditioning operating costs, and encourage users to use them as needed and pay according to the amount.