Common problems of heat exchanger unit and their elimination methods

I. Explanation of Special Terms for Heating Units

1. Primary side: refers to heat source, such as hot water or steam in boiler room.

2. Secondary side: refers to heat users, such as floor heating, radiator, central air conditioning and so on.

3. Water supply: whether it is the primary side or the secondary side, hot water is the water supply, that is, the pipeline with high temperature is the water supply.

4. Backwater: whether it is the primary side or the secondary side, the cold water is backwater, that is, the pipeline with low temperature is backwater.

5. High-temperature water: water with a temperature higher than or equal to 100 degrees. The national standard is 130/80 degrees, that is, the supply water temperature is 130 degrees and the return water temperature is 80 degrees.

6. Low-temperature water: water whose temperature is lower than 100 degrees, the national standard is 95/70 degrees, that is, the supply water temperature is 95 degrees and the return water temperature is 70 degrees.

Note: High-temperature water and low-temperature water are defined for the primary side system.

Second, the unit normal operation parameters display rules

1. The water supply temperature is higher than the return water temperature and the water supply pressure is higher than the return water pressure.

2. The difference between the primary water supply pressure and the return water pressure should be greater than or equal to 0.05MPa.

3. The difference between the inlet and outlet pressure of the secondary side of the plate heat exchanger should be less than or equal to 0.15MPa.

4. If the primary side is hot water, the temperature difference between the supply water temperature and the return water temperature cannot be higher than 40 degrees.

5. If the primary side is low-temperature water, the temperature difference between the supply water temperature and the return water temperature cannot be higher than 25 degrees.

6. If the secondary side is heated by a radiator, the temperature difference between the supply water temperature and the return water temperature cannot be higher than 25 degrees.

7. If the secondary side is floor heating or air conditioning heating, the temperature difference between water supply temperature and return water temperature should not be higher than 14 degrees.

Three, common faults and troubleshooting methods

1. The unit fault indicator is on, that is, the yellow indicator on the control cabinet is on. What should I do?

The fault indicator light indicates that the corresponding pump is overloaded, and the motor current exceeds the rated current, and the thermal relay plays a protective role. The release method is to press the reset button on the thermal relay to reset. Note that the thermal relay must be cooled before it can be reset, otherwise the reset will be invalid.

2. There is pressure in the system, but the pressure gauge shows 0. What's the matter?

If the needle valve of the pressure gauge is closed, the pressure gauge will always show 0. During the operation of the system, ensure that all needle valves of pressure gauges are fully open.

3. What is the secondary side overpressure? What about overpressure? How to prevent overpressure in secondary system?

When the system is in initial operation, the secondary temperature is relatively low. After the make-up water reaches a constant pressure value, the pressure of the secondary system will also rise with the rising of the temperature. At this time, it is necessary to exhaust more air and drain water. When draining, open the drain valve of the secondary return water pipeline. After the system temperature stabilizes, the pressure will not rise again.

4. How to judge whether the filter is blocked?

If the temperature difference between the primary water supply temperature and the primary return water temperature is large, the high-temperature water exceeds 45 degrees, the low-temperature water exceeds 30 degrees, and the secondary water supply is not hot, please check whether the filter at the primary water supply is blocked.

If the temperature difference between the secondary water supply temperature and the secondary backwater temperature is large, the floor heating temperature difference exceeds 15 degrees, the radiator heating temperature difference exceeds 30 degrees, and the pressure difference is small, please check whether the filter at the secondary backwater is blocked.

5. How to judge whether the heat exchanger is blocked?

If the water pressure difference of the primary side supply and return water or the pressure difference between the inlet and outlet of the secondary side heat exchanger exceeds 0.15MPa, and the temperature of the secondary supply water is not hot, please check whether the heat exchanger is blocked. The inspection method is to disassemble and wash the heat exchanger.

6. What are the reasons why the system is not hot? How should it be analyzed?

The secondary water supply is low in temperature and not hot, which is analyzed for the following reasons:

Insufficient flow of primary water supply:

Check whether all valves of primary water supply and return pipelines are open.

Check whether the primary water supply filter is blocked.

If all valves are open, judge the pressure difference between water supply and return again. If the pressure difference is less than 0.05MPa, ask the heating company to increase the flow rate. If the water pressure difference between the primary side supply and return water is greater than 0.15MPa, please clean the heat exchanger.

Poor secondary system:

Check whether all valves of secondary side water supply and return pipelines are open.

The secondary filter is blocked.

The pressure difference between the inlet and outlet of the secondary side heat exchanger is higher than 0.15MPa, and the heat exchanger is blocked. Please clean the heat exchanger.

7. What's the matter with the system that can't be replenished with water? The pump keeps running, but the pressure doesn't rise.

If the make-up water pump keeps running, but the pressure never reaches the set value, please exhaust the system. Poor water supply is mostly caused by gas collection in the system.

8. What is the reason why the frequency converter does not automatically replenish water and the frequency converter does not start?

Check whether the change-over switch is in the frequency conversion or automatic position. Only when it is in the frequency conversion or automatic position can the frequency converter work normally.

Check whether the start button of the water supply pump is running. Only when the green indicator of the water supply pump is on, the frequency converter can work normally.

Check whether there is an alarm code on the operation panel of the frequency converter. The number beginning with F is the fault code, and the number beginning with R is the warning code. The warning code does not affect the operation of the frequency converter. After the fault code appears, the frequency converter must be reset before it can continue to work. If there is a fault code, please press the EXIT key in the upper left corner of the inverter operation screen.

Only when the above three conditions are normal, can frequency conversion water supply work normally.

9. What should I do when the temperature of secondary water supply is too high?

If the user feels that the water supply temperature is too high and the room is too hot, the best way is to turn down the primary water supply valve. Please note that the primary water supply valve must be turned down, and the return valve is fully open.

10. What is the noise of the pump?

When the unit runs for one or two heating periods, the noise will increase due to mechanical wear. Check whether the fan cover is loose and exhaust the pump. The water pump must be regularly maintained, lubricated, wearing parts replaced, etc.

11. Make-up pump frequently makes up water, and the pressure drops rapidly after stopping. What's the matter?

If the unit frequently makes up water after a long period of normal operation, please check as follows:

Check the secondary side system for pipeline or valve leakage, etc.

Check whether the check valve in front of the make-up pump is not tight and flows backwards. The inspection method is to stop the water supply pump, close the inlet valve of the water supply pump, and then open the exhaust valve at the outlet of the water supply pump. If water is discharged, the check valve in front of the water supply pump is not strict and needs to be replaced.

12. What's going on when one circulating pump is turned on and the other circulating pump is running?

During the operation of the unit, if one circulating pump is turned on, the other circulating pump will rotate along with it, and it will rotate reversely, indicating that the check valve in front of the unopened pump is not tight, and it is necessary to replace the check valve. If it can't be replaced temporarily, please close the butterfly valves before and after this pump to prevent the water from flowing backwards.

13. If the unit is equipped with a shielded pump, how can we judge whether the pump's steering is correct?

The most reliable way to judge whether the shielded pump is turning correctly is to measure the current with a clamp ammeter, and the forward current is greater than the reverse current.

14. The start-up indicator of the pump is on, but the pump is not running. What's the matter?

Check the circuit breakers in the control cabinet, and make them all in the suction state.

Fourth, analyze the status of the system through the system parameters.

1. The pressure difference between the inlet and outlet of the circulating pump indicates the resistance value of the whole system. For example, the inlet pressure of the circulating pump is 0.25MPa and the outlet pressure of the circulating pump is 0.55MPa, which means that the resistance of the whole system is 0.3MPa, including the resistance of the unit itself. If the pressure difference between the inlet and outlet of the circulating pump has exceeded the head of the circulating pump, it means that the secondary water supply pipeline is seriously blocked, resulting in the super-high secondary water supply pressure. It is normal that the inlet and outlet pressure of the circulating pump cannot exceed the head of the circulating pump.

2. The pressure difference between the inlet and outlet of the heat exchanger is equal to the resistance of the heat exchanger. For example, if the inlet pressure of the heat exchanger (i.e. the outlet pressure of the circulating pump) is 0.55MPa and the outlet pressure of the heat exchanger is 0.50MPa, the resistance of the heat exchanger is 0.05MPa.

3. The smaller the temperature difference between the water supply temperature and the return water temperature, the greater the flow of the system and the smoother the system. On the contrary, if the temperature difference between the water supply temperature and the return water temperature is larger (exceeding the rated value), it means that the system flow is small and the system circulation is not smooth enough. At this time, please check whether the filters, heat exchangers and corresponding valves of pipelines are blocked.

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