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Principle Analysis Of The Monitoring System Of Cold And Heat Source Equipment

Apr 14, 2020

Principle analysis of the monitoring system of cold and heat source equipment


The building automatic control system is an integrated system platform, where many subsystems have diverse functions and complex engineering. What is the principle of the cold and heat source equipment monitoring system, which is one of the many subsystems of the building automatic control system? The following editor will explain to you in detail the principle of the monitoring system for cold and heat source equipment.


Principle analysis of cold and heat source equipment monitoring system


(1) Principle of monitoring cold source system


1. Chiller: The working principle of the water-cooled heat pump unit under refrigeration conditions is exactly the same as that of the chiller, and the control of the air-cooled heat pump unit is simpler (no cooling water circulation system, and the outdoor unit of the air-cooled heat pump unit is responsible for water cooling The cooling water circulation function of the heat pump unit, and the outdoor unit is controlled by the heat pump unit with its own controller).


2. Chilled water circulation: The chilled water circulation of the building air-conditioning cold source system is shown in the left part of the figure. It sends the high-temperature chilled water circulating from the air treatment equipment on each floor to the chiller for cooling, and then supplies it to each air treatment equipment.


3. Cooling water circulation: The cooling water circulation of the building air-conditioning cooling source system is shown in the right part of the figure. Its main task is to release the heat absorbed by the chiller from the chilled water circulation to the outside.


4. Inter-equipment linkage and group control of chillers: The chillers are the core equipment of the air-conditioning cold source system of the entire building, and the chilled water circulation and cooling water circulation are controlled accordingly according to the operation status of the chillers.


5. Control scheme for frequency conversion of the secondary water pump of the chilled water circuit: As mentioned above, in the case of a constant flow water pump used in the chilled water circuit, to balance the contradiction between the variable flow on the load side and the constant flow on the chiller side, prevent low load In the case of (the load side coil water valve is closed at the same time) the impact of the pump on the pipeline and the pump itself, a bypass circuit should be added to the chilled water supply and return main pipe, and the balance water pipe pressure is controlled by the opening of the bypass valve.


6. Ice cold storage system: The basic idea of ice cold storage is to use the night trough electricity price period to make ice cold storage, and to melt the ice during peak daytime for cooling.


Chiller control:


1) Chiller start / stop control and status monitoring.


2) Chiller failure alarm monitoring.


3) Monitoring of the manual / automatic control status of the chiller.


4) Monitoring of chilled water outlet / return water temperature, etc.


Cooling tower control:


1) Cooling tower fan start / stop control and status monitoring.


2) Cooling tower fan failure alarm monitoring.


3) Manual / automatic control status monitoring of cooling tower fans, etc.


1) Start / stop and status monitoring of the cooling water pump.


2) Cooling water pump failure alarm monitoring.


3) Monitoring of the manual / automatic control status of the cooling water pump, etc.


Chiller system control:


1) First of all, when an additional chiller needs to be started, it is necessary to determine which chiller to start, and the same is true when a chiller needs to be stopped.


2) Secondly, when it is necessary to start or stop a chiller, it is necessary to determine how many and which chilled water pumps, cooling water pumps and cooling towers should be added or stopped.


(1) Refrigeration unit priority control strategy: Only operate the refrigeration unit when the air-conditioning load is less than the capacity of the refrigeration unit, and only when the air-conditioning load is greater than the capacity of the refrigeration unit, the shortage is supplemented by the cold storage device.


(2) Ice storage priority cooling supply control strategy: When the air conditioning load is lower than the maximum ice melting ice release capacity of the ice storage equipment, the ice melting bears the load first, and when the air conditioning load is greater than the maximum ice melting ice release capacity, the refrigeration unit is put into operation to supplement .


(3) Fixed proportional cooling control strategy: This control strategy refers to the ice storage device and the refrigeration unit outputting a cooling load according to a fixed ratio to meet the building air conditioning load demand.


(4) Optimized control strategy: This control strategy is based on the dynamic prediction of load, under the constraints of constraints (including the maximum cooling unit output cooling load constraint, the maximum storage capacity constraint of ice storage equipment, the maximum ice melting rate constraint, etc.), Optimizing multiple control objectives (including daily operating costs, air conditioning load, remaining ice volume in one cycle, and number of starts and stops of refrigeration units, etc.).


(2) Principle of heat source system monitoring


1. The principle of monitoring the heating conditions of the heat pump system: the working principle and monitoring content of the heat source system corresponding to the heat pump unit is similar to its working principle and monitoring content in the cooling state, except that the position of the condenser and evaporator inside the heat pump unit can be passed through the four-way The valves are interchanged.


2. Boiler system monitoring principle: Boiler system equipment includes 3 parts: boiler unit, heat exchanger and hot water circulation.


1) Monitor the boiler's running status and fault alarm.


2) Monitor the flue temperature and boiler pressure of the boiler.


3) Alarm signal for monitoring the high and low liquid level of the make-up tank.


4) Real-time detection of boiler oil or gas consumption.


5) Monitor the boiler primary water pump operation status, differential pressure and bypass valve opening.


6) Boiler primary water supply and return water temperature.


1) Monitor the secondary water outlet temperature and return water temperature of each heat exchanger, adjust the primary hot water (or steam) regulating valve according to the outlet temperature to ensure that the outlet water temperature is stable within the set value range, and alarm when the temperature exceeds the limit; conditional The secondary side water flow is detected to estimate the air conditioning load in winter.


2) Monitor the running status and fault signal of the hot water circulation pump, alarm when a fault occurs, and accumulate the running time.


Chiller:


Using compressors, condensers, evaporators and other equipment, artificially control the refrigerant gas-liquid state transition, and the cycle repeats, the refrigerant will continuously cool the chilled water, and at the same time, release the absorbed heat into the cooling water cycle.


Chilled water unit monitoring content:


Chilled water unit start / stop control and status monitoring.


Chilled water unit failure alarm monitoring.


Chiller's manual / automatic control status monitoring.


Cooled water outlet / return water temperature monitoring, etc.


Chilled water system:


The chilled water circulation of the building air conditioning cold source system, it will send the high temperature chilled water circulated from the air treatment equipment on each floor to the chiller for cooling, and then supply it to each air treatment equipment. The monitoring content of this loop mainly includes the monitoring of the chilled water pump, the monitoring of the parameters of the chilled water supply / return water and the control of the bypass water valve.


Air conditioner, fresh air fan, coil refrigerant is chilled water.


Chilled water system monitoring content:


Start / stop of chilled water pump and status monitoring.


Chilled water pump fault alarm monitoring.


Cooling water pump manual / automatic control status monitoring, etc.


Chilled water supply / return water temperature monitoring.


Cooled water supply / return water main pressure monitoring.


Chilled water circulation flow monitoring, etc.


Cooling water circulation:


The cooling water circulation of the building air conditioning cold source system, its main task is to release the heat absorbed by the chiller from the chilled water circulation to the outdoor. The monitoring content of this loop mainly includes cooling tower monitoring, cooling water pump monitoring and cooling water inlet and return water parameters monitoring.


Cooling water monitoring content:


Cooling tower fan start / stop control and status monitoring.


Cooling tower fan failure alarm monitoring.


Cooling tower fan manual / automatic control status monitoring, etc.


Cooling pump start / stop and status monitoring.


Cooling water pump fault alarm monitoring.


Cooling water pump manual / automatic control status monitoring, etc.


Inter-equipment linkage and group control of chillers


Chilled water unit is the core equipment of the air-conditioning cold source system of the whole building. The chilled water circulation and cooling water circulation are controlled accordingly according to the operation state of the chiller.


When starting the chiller, start the cooling tower, the cooling water circulation system, and the chilled water circulation system. When it is determined that the chilled water and cooling water circulation systems have been started, the chiller can be started.


When the chiller is stopped, the order of stopping is the reverse of the starting order. Stop the chiller, stop the chilled water circulation system, stop the cooling water circulation system, and finally the cooling tower.


The main heat source equipment of building air-conditioning system includes heat pump unit and boiler system.


The working principle of water-cooled heat pump unit under refrigeration condition is exactly the same as that of chiller unit.


The control of the air-cooled heat pump unit is simpler. There is no cooling water circulation system. The outdoor unit of the air-cooled heat pump unit assumes the cooling water circulation function of the water-cooled heat pump unit.