A method for controlling the on / off sequence of refrigeration equipment in a refrigeration station

Abstract

The present invention discloses a method for controlling the startup and shutdown sequence of refrigeration equipment in a freezing station. The method performs differentiated startup and shutdown sequence control by judging whether the chiller to be started is the first unit and whether the chiller to be shut down is the last unit. Before starting a chiller other than the first unit, the chilled water pump and cooling water pump corresponding to the chiller are kept running at the lowest allowable frequency. After all electric valves are fully opened, the water pump frequency is rapidly increased to the same frequency as the running water pump frequency before the chiller is started. If the chiller to be shut down is not the last unit, after the chiller is shut down, the electric valve corresponding to the chiller is closed, and then the water pump is reduced to the lowest allowable frequency. After all electric valves are fully closed, the chilled water pump, cooling water pump and cooling tower fan corresponding to the chiller are shut down. Thereby, the fluctuation amplitude of the chilled water outlet temperature during the startup and shutdown process of the chiller is significantly reduced, and the energy consumption of the freezing station operation can be effectively reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of refrigeration and air conditioning, and in particular relates to a method for controlling the on / off sequence of refrigeration equipment in a freezing station. Background Art

[0002] The refrigeration system of the freezing station mainly includes four functional modules: chillers, chilled water pumps, cooling water pumps, and cooling towers. Each module is connected by multiple devices. The chillers, water pumps, and cooling towers maintain different switch combinations according to different load requirements. In order to achieve automatic control, electric valves are set in the inlet and outlet pipes of the cooling tower, and electric valves are set in the evaporator and condenser inlet pipes of the chiller, and water flow switches are set in the outlet pipes; in order to achieve energy-saving operation, the chilled water pump, cooling water pump, and cooling tower fan generally adopt frequency conversion regulation. Generally, there are two types of system layout forms for each functional module: one is that the chiller, chilled water pump, cooling water pump, and cooling tower are connected in series one by one to form a complete set of refrigeration devices, and then connected in parallel to form a complete refrigeration system of the freezing station, that is, the series-parallel form. This form may cause all refrigeration devices in the freezing station to fail to operate normally due to failures of cooling towers, cooling water pumps, or chilled water pumps in different refrigeration devices. The other is that multiple devices in each functional module are connected in parallel and then in series with other functional modules to form a refrigeration system for the freezing station, that is, the parallel-series (many-to-many) form. The advantage of this form is that when the refrigeration system is partially loaded, each functional module can flexibly select different equipment to be put into operation, so as to avoid the problems existing in the first arrangement.

[0003] The existing large and medium-sized refrigeration stations used in commercial central air-conditioning and industrial refrigeration generally adopt the parallel-series form.

[0004] The normal startup sequence of this type of refrigeration station is to first open the electric valves of the water circuit of the chiller to be started and the water inlet and outlet pipes of the cooling tower, then open the chilled water pump and cooling water pump corresponding to the chiller, and then start the chiller. Since there are usually several minutes of self-checking and system preparation time before the chiller is started, if there is a chiller running before a chiller is started, as the opening of the electric valve of the evaporator water circuit of the chiller to be started gradually increases, the chilled water flow through the evaporator of the unit will also gradually increase. After the electric valve of the evaporator water circuit is fully opened, the chilled water flow of the evaporator of the running chiller will be reduced by 50% in a very short time (several seconds to tens of seconds) because half of the water is taken away by the chiller to be started; and as the chilled water pump corresponding to the chiller is turned on, the chilled water flow of the evaporator of the running chiller will increase to the previous flow in a short time (several seconds to tens of seconds). That is, during the startup of the chiller, the chilled water flow rate of the evaporator of the existing chiller will experience a large change from 100% to 50% and then to 100% within tens of seconds, and the chilled water outlet temperature of the chiller will fluctuate significantly due to the large change in water volume. Since the control system of the chiller generally increases or decreases the load of the compressor based on the deviation between the measured value of the chilled water outlet temperature and the set value, this obvious fluctuation of the chilled water outlet temperature rapidly decreasing and then rapidly increasing can easily cause the compressor to reduce the load first and then increase the load, resulting in unstable operation of the chiller, and even alarm shutdown due to too low chilled water outlet temperature.

[0005] The normal shutdown sequence of this type of refrigeration station is to first control the chiller to shut down, confirm that the chiller is shut down, first shut down the matching chilled water pump and cooling water pump, and then shut down the chiller's condenser water circuit electric valve, evaporator water circuit electric valve and the corresponding cooling tower water inlet and outlet electric valve. During the period from the shutdown of the chiller's pump to the shutdown of the electric valve, if there is still a chiller in operation, the chilled water flow of its evaporator will also experience a large change from 100% to 50% and then to 100% within tens of seconds, and similar problems may occur as described above, such as unstable operation of the chiller, resulting in alarm and shutdown due to low cold water outlet temperature. Summary of the invention

[0006] The present invention aims to solve the above-mentioned technical problems existing in the prior art and provides a method for controlling the on / off sequence of refrigeration equipment in a freezing station.

[0007] The technical solution of the present invention is: a method for controlling the on / off sequence of refrigeration equipment in a freezing station, wherein the freezing station is provided with a chiller module, a chilled water pump module, a cooling water pump module and a cooling tower module, each module being arranged in a system in which the modules are first connected in parallel internally and then in series, and the evaporator and condenser water inlet pipes of each chiller in the chiller module are respectively provided with electric valves, and the water outlet pipes are respectively provided with water flow switches, and each cooling tower in the cooling tower module is provided with a cooling tower fan and the inlet and outlet pipes are respectively provided with electric valves, and the following steps are sequentially performed:

[0008] Step 1. Determine whether there is a need for a chiller unit. If not, proceed to step 2. If yes, proceed to step 3.

[0009] Step 2. Determine whether there is a need for a cooling water unit. If yes, proceed to step 6. If no, return to step 1.

[0010] Step 3. Determine whether the chiller to be started is the first chiller to be started. If yes, go to step 4; if no, go to step 5;

[0011] Step 4. First, simultaneously open the evaporator water circuit electric valve, condenser water circuit electric valve and cooling tower inlet and outlet water electric valve corresponding to the chiller, and after confirming that the electric valves are fully open, simultaneously start the chilled water pump and cooling water pump corresponding to the chiller and keep them at the lowest set frequency. After the corresponding chilled water flow switch and cooling water flow switch are both in the closed state, control the chiller and the corresponding cooling tower fan to start, and return to step 1;

[0012] Step 5. First, open the cooling tower water inlet and outlet electric valves corresponding to the chiller to be started, and then keep the working state of the cooling tower fan consistent with the running state of the cooling tower fan, and then start the chilled water pump and cooling water pump corresponding to the chiller to be started and keep them at the lowest allowable operating frequency, and then open the evaporator water circuit electric valve and condenser water circuit electric valve corresponding to the chiller to be started. After confirming that the electric valves are open, quickly adjust the chilled water pump frequency corresponding to the chiller to be started to the same as the running chilled water pump, and quickly adjust the cooling water pump frequency to the same as the running cooling water pump. After the chilled water flow switch and cooling water flow switch corresponding to the chiller to be started are both in the closed state, control the chiller to start, and return to step 1;

[0013] Step 6. Determine whether the chiller to be shut down is the last chiller. If not, go to step 7. If yes, go to step 8.

[0014] Step 7. First, control the chiller to shut down. After confirming that the chiller has stopped, close the evaporator water circuit electric valve, condenser water circuit electric valve and cooling tower water inlet and outlet electric valve corresponding to the chiller. At the same time, reduce the frequency of the chilled water pump and cooling water pump to the minimum allowable frequency. After the evaporator water circuit electric valve, condenser water circuit electric valve and cooling tower water inlet and outlet electric valve are completely closed, close the chilled water pump, cooling water pump and cooling tower fan corresponding to the chiller, and return to step 1.

[0015] Step 8. First, control the chiller to shut down. After confirming that the chiller has been shut down for several seconds, turn off the corresponding cooling water pump and cooling tower fan. After confirming that the cooling water pump has been completely shut down for several seconds, close the condenser water circuit electric valve and cooling tower inlet and outlet water electric valve corresponding to the chiller. After confirming that the chiller has been shut down for several minutes or the chilled water outlet temperature is higher than the set temperature, turn off the chilled water pump. After confirming that the chilled water pump is shut down, close the evaporator water circuit electric valve and return to step 1.

[0016] When the chiller needs to be increased or decreased, the present invention performs differentiated start-up and shutdown sequence control by judging whether the chiller to be turned on is the first chiller and whether the chiller to be turned off is the last chiller, thereby ensuring that the cold water flow rate of the running chiller is basically stable during the start-up and shutdown process of the chiller, avoiding unnecessary increase or decrease of the load of the chiller due to the fluctuation of the cold water outlet temperature, and thus ensuring the stable operation of the chiller. At the same time, the time used in the start-up and shutdown process can be shortened to the maximum extent, effectively reducing the energy consumption of the refrigeration station. Implementation

[0017] The present invention discloses a method for controlling the on / off sequence of refrigeration equipment in a freezing station. The freezing station is provided with a chiller module, a chilled water pump module, a cooling water pump module and a cooling tower module. Each module is arranged in a system in which the modules are first connected in parallel and then in series. The evaporator and condenser water inlet pipes of each chiller in the chiller module are respectively provided with electric valves, and the water outlet pipes are respectively provided with water flow switches. Each cooling tower in the cooling tower module is provided with a cooling tower fan, and the inlet and outlet pipes are respectively provided with electric valves. The difference from the prior art is that the control method is performed in the following steps in sequence:

[0018] Step 1. Determine whether there is a need for a chiller unit. If not, proceed to step 2. If yes, proceed to step 3.

[0019] Step 2. Determine whether there is a need for a cooling water unit. If yes, proceed to step 6. If no, return to step 1.

[0020] Step 3. Determine whether the chiller to be started is the first chiller to be started. If yes, go to step 4; if no, go to step 5;

[0021] Step 4. First, simultaneously open the evaporator water circuit electric valve, condenser water circuit electric valve and cooling tower inlet and outlet water electric valve corresponding to the chiller. After confirming that the electric valves are fully open, simultaneously start the chilled water pump and cooling water pump corresponding to the chiller and keep them at the lowest set frequency of 25HZ. After the corresponding chilled water flow switch and cooling water flow switch are both in the closed state, control the chiller and the corresponding cooling tower fan to start, and return to step 1;

[0022] Step 5. First, open the cooling tower water inlet and outlet electric valves corresponding to the chiller to be started, and then keep the working state of the cooling tower fan consistent with the running state of the cooling tower fan (that is, whether the running cooling tower fan is in the open state with an operating frequency of 40HZ or in the closed state, the working state of the cooling tower fan is consistent with it), then start the chilled water pump and cooling water pump corresponding to the chiller to be started and keep them at the minimum allowable operating frequency of 25HZ, and then open the evaporator water circuit electric valve and condenser water circuit electric valve corresponding to the chiller to be started. After confirming that the electric valve is open, adjust the chilled water pump frequency of the chiller to be started to the same as the running chilled water pump within 2 seconds, and adjust the cooling water pump frequency to the same as the running cooling water pump within 2 seconds. After the chilled water flow switch and cooling water flow switch corresponding to the chiller to be started are both in the closed state, control the chiller to start, and return to step 1;

[0023] Step 6. Determine whether the chiller to be shut down is the last chiller. If not, go to step 7. If yes, go to step 8.

[0024] Step 7. First, control the chiller to shut down. After confirming that the chiller has stopped, close the evaporator water circuit electric valve, condenser water circuit electric valve and cooling tower inlet and outlet water electric valve corresponding to the chiller. At the same time, reduce the frequency of the chilled water pump and cooling water pump to the minimum allowable frequency of 25HZ. After the evaporator water circuit electric valve, condenser water circuit electric valve and cooling tower inlet and outlet water electric valve are completely closed, close the chilled water pump, cooling water pump and cooling tower fan corresponding to the chiller, and return to step 1;

[0025] Step 8. First, control the chiller to shut down. After confirming that the chiller has been shut down for several seconds, turn off the corresponding cooling water pump and cooling tower fan. After confirming that the cooling water pump has been completely shut down for 10 seconds, turn off the condenser water circuit electric valve and cooling tower inlet and outlet water electric valve corresponding to the chiller. After confirming that the chiller has been shut down for 30 minutes or the chilled water outlet temperature is higher than 15°C, turn off the chilled water pump to fully release the cold contained in the low-temperature chilled water for room cooling. In this way, the chiller can be shut down several times in advance before the commercial building closes or the office building closes, so as to reduce the energy consumption of the refrigeration station. After confirming that the chilled water pump is shut down, turn off the evaporator water circuit electric valve and return to step 1.

[0026] Compared with the prior art, the method for controlling the startup and shutdown sequence of refrigeration equipment in the refrigeration station can reduce the average fluctuation range of the chilled water outlet temperature during the startup of non-first chillers and the shutdown of non-last chillers from ±0.5°C to ±0.2°C, and can reduce the operating energy consumption of the refrigeration station by an average of about 3%.

Claims

1. A method for controlling the on / off sequence of refrigeration equipment in a freezing station, wherein the freezing station is provided with a chiller module, a chilled water pump module, a cooling water pump module and a cooling tower module, each module being arranged in a system in which the modules are first connected in parallel internally and then in series, an electric valve is provided on the water inlet pipe of the evaporator and the condenser of each chiller in the chiller module, and a water flow switch is provided on the water outlet pipe, each cooling tower in the cooling tower module is provided with a cooling tower fan and an electric valve is provided on the water inlet and outlet pipes, wherein the method is characterized in that Follow the steps below: Step 1. Determine whether there is a need for a chiller unit. If not, proceed to step 2. If yes, proceed to step 3. Step 2. Determine whether there is a need for a cooling water unit. If yes, proceed to step 6. If no, return to step 1. Step 3. Determine whether the chiller to be started is the first chiller to be started. If yes, proceed to step 4; If no, proceed to step 5. Step 4. First, simultaneously open the evaporator water circuit electric valve, condenser water circuit electric valve and cooling tower inlet and outlet water electric valve corresponding to the chiller, and after confirming that the electric valves are fully open, simultaneously start the chilled water pump and cooling water pump corresponding to the chiller and keep them at the lowest set frequency. After the corresponding chilled water flow switch and cooling water flow switch are both in the closed state, control the chiller and the corresponding cooling tower fan to start, and return to step 1; Step 5. First, open the cooling tower water inlet and outlet electric valves corresponding to the chiller to be started, and then keep the working state of the cooling tower fan consistent with the running state of the cooling tower fan, and then start the chilled water pump and cooling water pump corresponding to the chiller to be started and keep them at the lowest allowable operating frequency, and then open the evaporator water circuit electric valve and condenser water circuit electric valve corresponding to the chiller to be started. After confirming that the electric valves are open, quickly adjust the chilled water pump frequency corresponding to the chiller to be started to the same as the running chilled water pump, and quickly adjust the cooling water pump frequency to the same as the running cooling water pump. After the chilled water flow switch and cooling water flow switch corresponding to the chiller to be started are both in the closed state, control the chiller to start, and return to step 1; Step 6. Determine whether the chiller to be shut down is the last chiller. If not, go to step 7. If yes, go to step 8. Step 7. First, control the chiller to shut down. After confirming that the chiller has stopped, close the evaporator water circuit electric valve, condenser water circuit electric valve and cooling tower water inlet and outlet electric valve corresponding to the chiller. At the same time, reduce the frequency of the chilled water pump and cooling water pump to the minimum allowable frequency. After the evaporator water circuit electric valve, condenser water circuit electric valve and cooling tower water inlet and outlet electric valve are completely closed, close the chilled water pump, cooling water pump and cooling tower fan corresponding to the chiller, and return to step 1. Step 8. First, control the chiller to shut down. After confirming that the chiller has been shut down for several seconds, turn off the corresponding cooling water pump and cooling tower fan. After confirming that the cooling water pump has been completely shut down for several seconds, close the condenser water circuit electric valve and cooling tower inlet and outlet water electric valve corresponding to the chiller. After confirming that the chiller has been shut down for several minutes or the chilled water outlet temperature is higher than the set temperature, turn off the chilled water pump. After confirming that the chilled water pump is shut down, close the evaporator water circuit electric valve and return to step 1.