1.？ Overview?
For a long time, urban residents in northern China generally charge heating fees according to the living area rather than the actual heat consumption, which leads to poor energy-saving awareness of users and serious waste of resources. Obviously, this measurement method is not scientific. In developed countries such as Europe and America, the use of heat meters has been quite common in the early 1980s. Heating companies use heat meters as the basis and means of pricing and charging, saving energy by 20% ~ 30%. As a basic measure of building energy conservation, the Ministry of Construction has included heat metering charges in the Ninth Five-Year Plan and the 20 10 Plan for building energy conservation. The work of installing heat meters and related regulating equipment and charging by households in central heating civil buildings has achieved results through the pilot project of 1998 and started to be popularized. In 2000, it was implemented in new residential areas in key cities, and it was implemented on 20 10. Therefore, it is very important to develop a heat meter for heating pricing. ?
1988, the international organization for legal metrology issued the world's first international standard document: OIML—R75 International Recommended Heat Meter. 1997, Europe * * officially adopted the unified standard for heat meters, and its code name was EN 1434. These two documents give the definition of heat meter, its measurement principle, working environment, measurement accuracy and other specific provisions. It can be seen that advanced heat meters generally have the following characteristics?
1)? The overall accuracy reaches Grade 4 standard specified by OIML—R75; ?
2)? Accuracy and error of flowmeter
3)? The temperature sensor adopts platinum resistance temperature measuring element, which conforms to IEC-75 1 standard and has accurate matching. When the temperature difference between supply and return water is 6? Within the measurement error range
4)? The integral calculator has enthalpy and mass density correction function or program, and the error is less than 0.5%; ?
5)? Micro-power design, built-in battery can work continuously for 5 years; ?
6)? The design structure is compact, the appearance is exquisite and the supporting series is complete. ?
At present, the technology of foreign heat meters flooding into China market is mature and standardized, but it is expensive. Especially in China, there is a huge demand for heat meters, so it is imperative to develop low-cost heat meters that meet international standards. However, at present, although the cost of domestic heat meters is low, its measurement method is too simple and its accuracy is difficult to meet international standards. This paper summarizes the heat metering principle of heat meter, introduces several specific heat metering methods, and analyzes and compares their advantages and disadvantages, so that the K-coefficient compensation method of online complete compensation of temperature and pressure at the same time has higher calculation accuracy. In addition, the rapid development of computer technology makes it possible to realize this method.
3、
temperature sensor
The classification standard of heat meter grade is as follows:
First, the measurement accuracy.
The heat meter * * * is divided into three precision grades, namely, the first-class meter, the second-class meter and the third-class meter. First of all, it should be noted that the accuracy grade of heat meters cannot be described by a fixed error number, such as 2% or 5%, because even heat meters with the same accuracy grade have different error requirements under different working conditions.
1) Measurement accuracy of integral calorimeter
Because the metering components of the integral heat meter are logically inseparable, its accuracy must be given by the standard device at one time, and its error limits are given by the following formulas respectively:
Level 1 table: e = 2+4 Δ tmin/Δ t+0.01qp/q.
Secondary table: e = 3+4 δ tmin/δ t+0.02 qp/q.
Three-level table: e = 4+4 Δ tmin/Δ t+0.05 qp/q.
Where: e- relative error limit, %[ 1]
Δ δtmin—— Minimum temperature difference,℃.
Δ t —— temperature difference within the use range,℃.
Qp- ordinary flow, m3/h.
Q—— Flow within the scope of use, m3/h
2) Measurement accuracy of split heat meter
The metering accuracy of the split heat meter is determined by the metering accuracy of the three components that make up the heat meter: the flowmeter, the temperature sensor and the accumulator, and its error limit is the arithmetic sum (that is, the sum of absolute values) of the respective errors of the above three components. Among them, the error limit formula of each part is as follows:
Error limit formula of flowmeter:
Level 1 table: E= 1+0.0 1qp/q
Secondary table: E=2+0.02qp/q
Three-level table: E=3+0.05qp/q
Where: QP- general flow, m3/h
Q—— Flow within the scope of use, m3/h
Error limit formula of paired temperature sensors: e = 0.5+3 δ tmin/δ t.
Where: Δ tmin-minimum temperature difference,℃.
Δ t —— temperature difference within the use range,℃.
Error limit of integrator: e = 0.5+δ tmin/δ t.
Where: Δ tmin-minimum temperature difference,℃.
Δ t —— temperature difference within the use range,℃.
It can be seen that in the split heat meter, because the accuracy of flowmeter is divided into three grades, the metering accuracy of split heat meter is also divided into three grades.