Common problems during debugging of refrigeration and air conditioning systems

Common problems during debugging of refrigeration and air conditioning systems

The refrigeration and air-conditioning system is large in scale, with many equipment and variable working conditions, but the design, construction, debugging and management operation level is limited, which causes many problems in the refrigeration and air-conditioning system in the building, so system debugging is an indispensable part. For general refrigeration and air-conditioning engineering, the debugging content includes: inspection of the electrical equipment and wiring of each link of the system; operation test of refrigeration and air-conditioning equipment; debugging of each link of the automatic control system; measurement and debugging of airflow parameters in the refrigeration and air-conditioning room, etc.

　　 One. Common problems during debugging of refrigeration and air conditioning systems

　　 1. The local effect of the refrigeration and air-conditioning system is not good during debugging. Reasons for formation:

　　 1) The system is blocked by foreign matter.

　　2) The system design is partially unreasonable and cannot be adjusted normally.

　　Improvement measures: remove foreign objects and clean them fully, adjust the slope of the pipeline. Ask the design unit to modify the design and make partial corrections.

　　2. The vibration and noise of the water pump are large when it is rotating. Reasons for formation:

　　1) The axial and radial deviation of the coupling of the equipment itself is large.

　　2) The pump flange is too large and the anchor bolts are not evenly stressed.

　　3) The natural vibration frequency of the pump and the pipeline is close to cause resonance.

　　Improvement measures: adjust the axial and radial deviation of the coupling. Adjust the natural vibration frequency between the pump and the pipeline, and install related soft connection parts. Replace the flange and make the anchor bolts evenly stressed.

　　 3. The cooling capacity of the chiller does not reach the rated value. Reasons for formation:

　　1) The water temperature of the cooling tower cannot reach the specified cooling parameters.

　　 2) The pump output is insufficient.

　　3) The condenser isolation pad is misplaced and cannot be cooled down.

　　4) The pipe in the condenser is blocked.

　　Improvement measures: repair the cooling tower to meet the water temperature and water volume requirements. Remove foreign objects in the pipeline and check whether the condenser isolation pad is misplaced.

　　4. The discharge pressure of the condenser refrigerator is too high. Reasons for formation:

　　 1) The amount of cooling water is insufficient.

　　 2) Severe scaling in the condenser heat transfer tube.

　　3) The cooling water temperature is too high.

　　4) Too much air in the system.

　　Improvement measures: repair the cooling tower, clean the condenser heat transfer tube, and remove the air in the system.

　　 5. The refrigeration and air conditioning unit is severely frosted during operation. Reasons for formation:

　　 1) The return air filter is clogged.

　　2) The exhaust air volume is not enough after the fan belt is loose.

　　3) The return air valve is opened too small.

　　Improvement measures: clean the return air filter and adjust the fan belt. Adjust the size of the return air valve.

　　 2. Several issues that need to be paid attention to during the commissioning of refrigeration and air conditioning systems

　　 1. Pay attention to the preparation before debugging

　　The preparatory work before debugging is an important part of the debugging process, it will affect the whole debugging process, generally including the following steps:

　　1) Leak detection of wind pipe system. The leakage volume of the air duct system is detailed in the national standard GB50243-97, which is roughly divided into high, medium and low pressure systems. The air volume leakage value per hour per square meter of the air pipe is different under different pressures.

　　 2) Visual inspection of the piping system. The main content of this work is to inspect the piping system to ensure that the various valves on the diffuser, branch pipes and main pipes are fully open to ensure that the piping system is fully open.

　　3) Preparation for debugging equipment. Before commissioning, prepare the required test equipment including those required to test temperature, humidity, pressure, speed (flow), and speed.

After completing the above tasks, the commissioning can be started. However, since the commissioning of the refrigeration and air-conditioning system is a very practical work, various preparations are often different due to different piping systems and their preliminary installation work. This should be paid attention to in work.

　　2, cold water system debugging

　　 The general steps of cold water system debugging are:

First, close the fan coils on each floor and the inlet and outlet pipes of the cooling equipment, and open the connecting valve between the supply and return pipes of the cold water branch pipes on each floor. Some large-scale chillers are also designed to supply and return water to protect the evaporator. Connecting pipe. At this time, the inlet and outlet valves of the water supply and return pipe of the chiller should also be closed, and the connecting pipe should be opened;

　　 Start the cold water pump to clean the pipeline, the time is at least half a day;

　　Drain the water in the cold water pipe and clean the filter at the inlet of the cold water pump. If time permits, you can install the filter back and refill the system for cleaning.

　　 When designing the cold water and cooling water systems of centralized refrigeration and air-conditioning, a bypass pipe with a valve must be installed at the end of the large-scale equipment and the main cold supply pipe of the floor to facilitate system cleaning.

　　 If the water pump is not turned on, and the pipes are cleaned only by water injection and discharge, for most systems (except for systems with strict construction supervision and clean pipes when the construction is completed), it will not meet the pipe cleaning requirements at all. After the pipe cleaning is over, the refrigerator can be turned on for debugging. The supplier usually assigns special personnel to be responsible for the startup and debugging of the host, which will help both parties reduce contract disputes.

　　 Further debugging work is aimed at the refrigeration and air-conditioning terminal. When the water pump and the main engine are both turned on, the terminal is debugged one by one. Open the valves of the end water supply and return pipes that were previously closed, turn off the supply and return water mains and the bypass valve on the main circuit that were opened during pipe cleaning to see if the two-way valve is normal. If it is abnormal, check if there is a problem with the wiring. There is no electricity, or the coil of the valve is burned out. If the coil is burnt and there is no spare parts, the manual switch of the valve can be used to force the two-way valve to open for debugging.

　　 3. The problem of improper layout of fresh air outlets in fan coil plus fresh air system

　　The fan coil and fresh air system is commonly used in the refrigeration and air-conditioning systems of hotels and office buildings. This method not only has good refrigeration and air-conditioning effects, but also easy installation and construction. However, in the design process, the fresh air and the air outlet of the fan coil must be combined reasonably, otherwise it will affect the use of refrigeration and air conditioning.

　　 The commissioning of the fresh air system is carried out under the condition that the fan coil unit stops running (the fan coil unit itself does not operate), and the fresh air volume of each room is also measured under this condition.

However, in the actual system operation, the fan coils in each room may not be all running (independent control in the room). For the room where the fan coil is started, a negative pressure zone is formed in the return air box of the fan coil. The return air box of the fan coil unit is not in operation, which damages the air volume balance of the entire fresh air system, and makes the air volume of the fresh air branch pipes entering the room vary greatly. The fresh air branch pipes of individual fan coils that are not activated even form negative pressure. The indoor air enters the fresh air duct and is sent to other rooms, causing the air quality of each room in the system to deteriorate.

　　 When the fresh air duct is connected to the air supply section of the fan coil, similar problems will also occur. In order to avoid the above-mentioned problems, the influence of the fan coil unit on its connection system should be fully considered during the design. Independent ducts should be set up at the fresh air outlet. It is recommended that such problems should be specified in the design code.

　　4, summer heat adjustment

　　According to the standards of air-cooled heat pump chillers and hot water units formulated by our country, the rated heating capacity of the unit refers to the heating capacity of the unit when the ambient temperature is 7℃ and the outlet temperature is 45℃.

　　In actual work, due to the different ambient temperature and the different temperature of the hot water supply in the refrigeration and air-conditioning system in winter, the heating capacity of the unit changes accordingly. The heating capacity of the air-cooled heat pump chiller and hot water unit decreases with the increase of the hot water outlet temperature, and decreases with the decrease of the ambient temperature. The input power of the unit under heating conditions increases as the outlet temperature of hot water increases, and decreases as the ambient temperature decreases.

This is mainly because the condensing pressure is required to increase correspondingly when the hot water outlet temperature increases. At this time, if the ambient temperature remains unchanged, the pressure ratio of the compressor increases, and the compressor consumes more power per kilogram of refrigerant, resulting in the compressor input power increase.

When the ambient temperature decreases, the evaporation temperature of the system decreases, which reduces the refrigerant flow of the compressor. Due to the frost on the surface of the air-side heat exchanger, the heat transfer temperature difference is large. At this time, the flow decreases faster and the input power of the corresponding compressor is greatly increased. Decrease. Generally, when the ambient temperature drops below -4℃~-5℃, the auxiliary heater can be activated to heat the return water of the heating system to compensate for the attenuation of the heat produced by the air-cooled heat pump unit.

　　 5. Use computer technology to assist debugging

　　In actual engineering, many refrigeration and air-conditioning systems are extremely complex and the balancing process is difficult. Therefore, the commissioning work is divided into two stages: initial commissioning and repeated commissioning.

　　Take wind system debugging as an example. Generally, after the adjustment of each tuyere in the branch during the initial adjustment, it will have a certain impact on the air volume of other tuyere. After the initial adjustment is successful, it will enter the repeated debugging stage. If the initial adjustment is successful, most of the air outlets do not need to be adjusted or the air volume is not large at this time, and the hydraulic condition of the entire system changes little. Except for individual air outlets with unstable performance, the influence of the air outlets on each other can be overlooked.

　　 It can be seen that the initial commissioning stage is very important. The starting point of computer-aided debugging technology is that no matter which debugging method is used, the results should be satisfied: the actual air volume of each air supply outlet should be ±10% of the design air volume; the valve at the end of the system's most unfavorable loop should be Fully open.

　　 In China, because the commissioning personnel belong to the equipment installation company, they can contact the air volume adjustment device during the equipment installation process. If they can obtain the pre-adjusted opening degree of each valve through computer-aided calculation according to the air volume design requirements in advance.

　　On this basis during installation, the corresponding valve opening adjustment can be carried out, which is very helpful to improve the speed and efficiency of wind system debugging, and reduce debugging costs. This advantage will be more prominent in large-scale refrigeration and air-conditioning systems.