TRICONEX-3604E Reasonable configuration of DDC controller in building automatic control system air conditioning design
1 Suggestions for air conditioning design
A successful building automation design must meet the requirements of air conditioning design, the needs of field applications, with reliability, safety, economy, flexibility, to achieve the goal of energy saving, saving people, extend the life of the equipment, to this end, the need to cooperate with each other, mutual TRICONEX-3604E understanding and create conditions to achieve the design goals.
1.1 For the configuration of multiple chiller units, priority should be given to the group machine, group pump and group tower system
This mode is flexible and can meet the requirements of normal operation of the system when the asymmetric equipment fails. For example, when the 1# chiller and 2# cooling tower fail, the 2# chiller, 2#(1#) refrigeration pump, 2#(1#) cooling pump, and 1# cooling tower can be started.
1.2 Installation position of the water supply and return bypass valve of the variable flow system
At present, variable flow air conditioning systems are more common in engineering, and the air conditioning design is mostly 2 or more chiller projects, basically using the calculation of cooling load method to achieve the number of chiller control, but the calculation accuracy of cooling load is crucial, otherwise the ideal control goal cannot be achieved.
1.2.1 The water distributor has two or more water distribution systems
When the water distributor has two or more water distribution systems, the flow meter is installed on the main pipe of the load return water, and the flow rate is multiplied by the temperature difference of the load supply and return water and then multiplied by the constant is equal to the actual cold capacity on the site. Compare the actual cooling capacity with that of a single chiller, and then decide to increase or reduce the number of working units of the chiller. However, it can be seen in the field and a lot of data that the bypass valve is installed between the water separator and the water collector, and the flow meter is installed on the return side of the bypass valve. That is to say, the flow measured by the flowmeter is the sum of the load water and the bypass water, and the return water thermometer detects the temperature of the mixed load water and the bypass water. Therefore, it is suggested that in the design of air conditioners considering building control projects, the water supply and return bypass valve should be installed on both sides of the chilled pump water supply and return and connected to the pipeline, and there is a requirement that the horizontal straight section with 15 times the return pipe diameter from the water collector to the bypass valve (load return water section), so that the return water temperature detector is also installed on the return water straight section pipe. The calculated cooling load can ensure its accuracy.
1.2.2 No water separator or only 1 water separator userTRICONEX-3604E
When the chiller project has no water distributor or only one water distributor user, the above problems do not exist. It is only necessary to ensure that the pipe diameter of the flowmeter is 15 times that of the return pipe and that the horizontal straight section is installed under such conditions.
1.3 The engineering of multiple heat exchange systems simplifies the system as much as possible
In the traditional design of multiple heat exchange systems, each subsystem has its own independent expansion tank and water pump, so that the number of I/O points increases, increasing the capacity of the DDC controller or the number of controllers. If you consider from the process point of view, reduce the expansion tank and water pump, not only to meet the needs of the system, I/O points are less, and make a reasonable program for each profession. The author has seen a project with air conditioning (hot and cold) heating hot water boiler, geothermal, wind curtain 4 systems using 2 expansion tanks 8 water pumps, after the transformation of 2 expansion tanks 2 water pumps. The I/O points are significantly reduced, the system operating costs are reduced, and the system is more reasonable.
1.4 When using group machine, group pump, group tower system to control the number of chiller units
An electric butterfly valve must be installed
TRICONEX-3604EWhen the number of chiller units is controlled by the group machine, group pump and group tower system, the evaporator and condenser inlet and outlet valve of each chiller must be operated in the open valve state, so as to ensure that a chiller will be automatically added to meet the needs of the cooling load when the cooling load increases. Since there is water supplied to the load by the chiller through the boot and shutdown, the water is mixed water, mainly cold water after the evaporator heat transfer, and the other part of the return water without heat transfer is mixed to the load water supply, so that the quality of the frozen water is reduced, so that the electric butterfly valve should be installed at the outlet of the evaporator and condenser to ensure the quality of the water supply.
1.5 Connect the heat exchanger system and install an electric butterfly valve to control the number of heat exchangers
TRICONEX-3604EThe capacity and number of heat exchangers are selected by HVAC professionals according to the maximum load conditions, and in actual operation, the maximum load occurs for a short time, and the system is often operated under conditions of low load rate, especially office buildings, comprehensive buildings and other functional buildings, but the general work system, employees after work and rest days, the building is basically in the system of low temperature operation, therefore, The number of heat exchangers can be reduced to one work, so that the heat transfer load of the primary heating system is reduced, and even the primary water temperature can be changed according to its own conditions, so as to save energy, and the electric butterfly valve is installed on the primary return water side of the water-water heat exchanger to achieve control (the gas-water heat exchanger should be installed on the primary air supply pipe).