(I) Background
With the release of the "Interim Measures for Urban Heating Price Management" jointly formulated by the National Development and Reform Commission and the Ministry of Construction, it has become a necessary means for the modern management of heating enterprises to automatically measure and charge for urban centralized heating users according to their usage. The heat meter is a metering instrument used to measure and display the heat released or absorbed by water flowing through the heat exchange system. It is installed at the inlet or outlet of the heat exchange circuit and is used to measure the heat consumption in the heating facilities.
(II) After charging according to usage, sufficient attention should be paid to preventing heat theft
Due to the special structure of the heat meter itself, once the user installs and uses the heat meter and starts charging according to usage, some new problems will inevitably arise, which should be paid attention to.
Compared with traditional metering instruments, the sensor leads of this meter are most exposed, the two temperature probes are dragged outside, and the two ultrasonic leads are sometimes exposed outside, creating conditions for malicious heat theft.
Most of the metering instruments used for trade settlement have the phenomenon of malicious theft. For example, although the management department has been preventing electricity theft during the use of electricity meters, it is difficult to prevent electricity theft during use. Here are a few examples:
a) Replace the neutral line with the live wire, and the meter line will not be used if there is no return current;
b) The outgoing line is double-stranded, and the return line is single-stranded, and the meter line is not counted;
c) Connect the cables in parallel to split the current! One line is visible and the other is hidden, and the current is stolen through the hidden passage
d) . . . . . . .
Hundreds of ways of stealing electricity have been found.
After the implementation of heat metering and charging, the heat usage fee will be the highest expense in household energy consumption. If the various possible situations are not considered in advance, the problem will be very serious.
According to statistics, the current domestic heat charging rate is less than 5%. Although some places have installed heat meters, they are just decorations and have not been really used. Most of them are still charged according to the area of use. Once the real implementation of charging according to heat usage, there may be various ways of stealing heat, which must be prevented in advance.
The calculation formula of heat is as follows:
0t t
E= ∫K*Q*△T dt
Q=Instantaneous hot water flow (M3/h)
△T=Inlet and outlet water temperature difference (℃)
From the heat calculation formula, it can be seen that the heat value is related to the flow value flowing through the pipeline and the inlet and outlet water temperature difference. In the same time, the larger the value of Q*△T, the more heat is used, and vice versa. But if one of the values is zero, that is, the value of Q*△T is zero, the cumulative value of the heat value in this period is zero.
From the above analysis, it can be seen that the heat value of the heat meter is related to two important parameters, namely the heat value flowing through the heat meter and the water temperature value of the inlet and outlet water measured by the heat. If these two measured values are changed, the heat value will be changed.
At present, most of the heat meters on the market use ultrasonic sensors for flow measurement. If the ultrasonic sensor is damaged or the lead between the sensor and the circuit is artificially short-circuited or open-circuited, as long as one of the sensors in a pair is damaged, the heat value is zero, the heat value stops accumulating, and the meter does not move.
From the perspective of temperature measurement, there are more ways to change the temperature value of the probe detection point. One method is to use the "cooling method", that is, to artificially reduce the local temperature at the water inlet temperature probe to reduce or even eliminate the temperature difference between the inlet and outlet water. If △T is zero, the calorific value will stop accumulating. If the heat meter is not designed well, when △T is negative, the accumulated calorific value will be deducted. Another method is to use the "heating method", that is, to artificially increase the local temperature at the outlet water temperature probe. We did an experiment. As long as a candle is lit near the outlet water temperature probe, heating for 30 minutes under the condition of water flow can increase the temperature measured by the temperature probe by 20℃. If the original inlet and outlet temperature difference is 20℃, the calorific value will stop accumulating after heating for 30 minutes, and the user can use the heat for free without leaving any trace. This is a terrible thing and must be prevented and taken seriously.
(III) Another issue that should be given enough attention is the measurement error of the heat meter
Due to the general deviation of domestic hot water quality, the deviation of the heat meter after one or two years of installation and use remains to be further investigated. At present, the technical supervision department only tests the heat meter before installation, and there is only one standard for judging whether it is qualified. There has been no authoritative test data on whether the meter can still guarantee the measurement accuracy or the deviation after use. When charging according to the metering data of the heat meter, there will inevitably be a large number of user complaints. These issues must be considered in advance:
a) How to test after use? How to judge?
b) The problem of verification charges: According to the "verification regulations" of heat meters, the verification cycle of heat meters does not exceed three years, that is, it must be verified once every three years. The cost of each verification is generally between 50 and 100 yuan. Who will pay this fee in the future?
c) The workload of verification: There are 1 million households installing and using heat meters every year. Calculated as a calibration every three years, more than 300,000 heat meters are sent for inspection every year. The Technical Supervision Bureau needs to calibrate 1,000 meters every day. How many devices are needed for detection? Is there such a capability for detection?
Relevant standards should be formulated as soon as possible, otherwise it will cause a lot of disputes.
(IV) How to prevent heat theft and damage from the source
a) Physical isolation method:
Install the heat meter outdoors, add a meter box, and do not allow users to open the meter box by themselves
b) Remote meter reading method:
Remote meter reading and remote monitoring. Remote meter reading is used to monitor abnormal conditions in real time using software. Once an abnormality occurs during the heat use process, an alarm is immediately issued and timely investigation and treatment are carried out to ensure the normal operation of the heat supply fee system.
(V) Conclusion:
Charging for heat by volume is a good thing for energy conservation and environmental protection. The country has invested a lot of money, but if the specific implementation process is not considered carefully, the result will deviate from the original intention and energy conservation will only become a beautiful wish.
This article is just a starting point. I hope that experts and leaders who are enthusiastic about heat metering reform can pay attention to it.
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By:Doing