【 Weak current College 】 DDC auto control of air-conditioning system saving energy by method

1. introduction

Energy conservation can be said to be the floor, Word automatically control system starting point and end point. We all know, in intelligent building, HVAC (heating, ventilation and air conditioning) systems that consume energy to account for the total energy consumption in the building of the great majority proportion, generally at 50 percent to 60 percent. Especially the cold: the Eastern units, cooling tower, circulating pumps and air conditioning units, air supply unit, energy consumption. Therefore it is necessary to develop an effective energy-saving air-conditioning system, especially with a method to improve existing building air-conditioning system automation. DDC (Directdigitalcontr01) direct digital control, is a simple operation and easy control of the device, it may transfer the equipment by the interface with the load changes for system control, such as air conditioning cooling water circulation system, air conditioning, automatic volume adjustment box frequency and cooling towers cooling fans, variable frequency control, you can have the air conditioning system more efficient operation, thus, not only to property management bring great benefits, but also allows the system to better condition run, thus lengthens the service life of equipment, as well as to provide a comfortable air-conditioned environment and energy saving.

Automatic control system introduction 2.DDC

DDC direct digital control is a simple micro-computer equipment, it shall be with the other components, such as frequency, temperature and humidity sensor, enthalpy difference controller, two way valve and other components to integrate with. These components of input and output with analog signal DC0 ~ 10V or 4-20mA, low-current for signal transmission, sent to the DDC controller. The DDC built-in software for evaluation after reverse output signal to control valve parts or converter to adjust the air conditioning. DDC auto control system peripherals and control functions.

2.1 direct digital control (DDC)

Refers to a digital computer direct manipulation of a State, or a set of programs to automatically control jobs. The use of the digital computer, you can use small microprocessor can also be equipped for Central type MCU appear online jobs. Air conditioning system commonly used control components, such as wind gate switches, valves, switches, relay, etc in order, irrespective of their original for pneumatic or electric, regardless of their role in the original action to adjust the size or just on or off action, may use the DDC for automated operation.

DDC system uses hardware and software to resize the control variables or pursuant to the operator's need to control the manufacturing process. Which control variables including temperature, pressure, relative humidity, flow, etc. Control procedures and the set point can make use of the software into the computer and to the operator of an amendment on the keyboard, so you can replace the last calibration hardware controller. DDC system can also be detected such as control of temperature, pressure, and advance the variables stored in the computer hope numeric comparison, if the test number is less than or greater than the expected value, the system will send out a series of digital pulse, the pulse is with electric converters for pneumatic (electrtC-to-pneUmatiCtransducer) or electric converters for electric (electric-to-electrlctransducer) into control device for adjusting the signal, and then through a computer of its output signal, and then manipulate its converter, so that the original line pneumatic or electric components according to indication signal operation. If air conditioning controller parts, original series pneumatic, plus a set of actions to be pneumatic, electrical signals to electrical signals into the computer. The original series electric operation components are also the same. As for input, the DDC system need not be subject to any hardware device, you can make any performance control of operations.

2.2 inverter

Inverter-driven motor is the use of diode, Rectifier power be rectified, then through capacitor smoothed to convert from AC DC. Use PowerTransister, SCR (Thynstor) will replace any frequency DC, and then to AC output. Induction motor with frequency inverter-driven help avoid motor magnetic gas saturation, but will also suppress starting current, and because of the drive motor and produce the necessary torque, it must control the output voltage of the inverter, echoing the frequency changes. The inverter can be divided into voltage-and current-converter-converter. Voltage-frequency converter using SCR or diode rectifier, reusable smoothing capacitor as voltage source. On the other hand, current-converter using SCR rectifier, open reactor, they may have current source SCR. The control has a voltage control and current control.

2.3 enthalpy difference controller

Enthalpy difference control means the air supply system, when the outdoor temperature is lower than room temperature, the use of the outdoor temperature air-conditioned indoor temperature. Enthalpy difference controller is determined by comparing the outdoor temperature controller and return air temperature and low but the door shut down large, or full open and full closed. Air volume control, you can take automatic and manual dual mode, the temperature (wet) of sensing, after the throttle and the frequency of double regulation, to achieve the indoor temperature and humidity can be set.

2.4 cooling towers cooling fan thermostat

Cooling water tower fans in different cooling load under its power to maintain a certain value, causing an electrical waste. Therefore, in cooling tower fan with variable frequency motor, and utilization of cooling water outlet temperature control fan motor start and stop and high and low speed, not only host can lower cooling water inlet temperatures do the high efficiency of operation and can effectively reduce the power consumption of the cooling tower fan.

3. building air-conditioning system schema

General building common air conditioning system with CAV, VAV, VWV etc with different play mode, you can use the DDC control.

3.1 air flow system (ConstantAirVolume, hereinafter referred to as CAV)

For air flow system for air conditioning blowing out of the air flow must be to provide air conditioning needed in cold regions (warm). When emptyAdjusting area load changes is to change the supply air temperature with indoor and reach to maintain indoor temperature in comfort zone requirements. Commonly used for AHU central air-conditioning system (air conditioner) and cold water pipe system (FCU). Both generally to air (CAV) to supply air conditioning area, in order to meet changes in the indoor part load, AHU for air flow system to air conditioner temperature air at the beginning of the process, in general the FCU to cold water valve system ON/OFF control to adjust the supply air temperature.

3.2 VAV system (VAV)

VAV system (VarlableAirVolume, hereinafter referred to as VAV) is the air conditioners (AHU or FCU) can reduce VAV. Commonly used for AHU central air-conditioning system (air conditioner) and cold water pipe systems FCU system. Both generally to air (CAV) to supply air conditioning area, in order to meet changes in the indoor part load, AHU for air flow system to air conditioner temperature air at the beginning of the process, in general the FCU to cold water valve system ON/OFF control to adjust the supply air temperature. However, both in the air supply system on wasted energy. Because in the long term low load blowers are also wide wind speed and power, this is not only difficult to maintain a stable temperature and humidity conditions of indoor or wasting a lot of energy supply air operation. VAV system is designed for air supply system power-saving countermeasures. deficiencies VAV system can be divided into two: one for AHU wind pipes system air conditioners of VAV system (AHU-VAV system); a FCU system indoor fans in VAV system (FCU-VAV system). AHU-VAV system is in the air duct system will supply air temperature constant but to adjust blower air ways to cope with changes in indoor air conditioning load. FCU-VAV system is cold water supply, while indoors FCU installs the constant variable power controller change air, i.e. change the rate of heat FCU to regulate indoor load change. This two ways through air flow adjustment to reduce the power consumption of fan, but also can increase the efficiency of heat source equipment operation and saving heat power, so you can in the air and heat both for energy saving effect.

3.3 variable flow system (VWV)

The so-called variable flow system (VariableWaterVolume, hereinafter referred to as VWV), is to a certain temperature supply air conditioners to improve the efficiency of the heat source machine, and a special water pump to change sent, by the way reach saving water pump power. Vwv on the pump system for energy efficiency as water pump control and vary with the proportions VWV, general control way VWV stepless speed (SP) and bi-directional valve control. The above three air conditioning system is by far the most often used by air-conditioning system design. Central air-conditioning control also is the pipe, pipe fittings, valve or valves delivers centralized set control fluid cooling. So the effective combination of central air-conditioning control that can effectively control the consumption of energy, energy saving design conforms to the air conditioning system.

4. different self-adjusting device use DDC method

DDC devices in the market of the product, the manufacturer of the model, the suite are different, but similar. As long as the analogy signal input through digital processing, you can make the computer controls and settings. When these digital controlof air conditioning equipment, integration with the following:

4.1FCU used in fixed air flow system (CAV) regional air conditioning

Because it is a fixed amount of wind system, so we control water cooling system on two way valve. When the room temperature rise, indoor takes to send out signals to the controller, the controller receives a signal and set temperature, the output signal to the cold water pipe on valve. Control two way valve open, so that the circulating air is cooled into the Interior. If the room temperature drops too much, coil fan for uninstall. Indoor temperature takes to send signals to the controller to the analog input, controller and set temperature, the output analog signal to the cold water pipe on valve closed. There are also two way valve proportional type, this proportion type two way valve to control the size of the row into the cold water so that the air conditioning more flexible control, maintain the room temperature above and below the set value.

4.2AHU is used in VAV system (VAV) regional air conditioning

Building common air conditioning systems to the preset temperature and wind is control. By sending, air and gas temperature SENSOR to control the motor speed. Control procedures are as follows:

(1) the air temperature induction to the heat exchanger (set of 12 ° c), DDC control two way valve open.

(2) send the air-conditioning, cold water temperature sensor for cold water and leave the measured temperature cold-, adjust the outlet temperature conditions, continue to use DDC control AHU converter changes the motor speed out of ideal outlet temperature.

(3) when the cold water valve down to 12 ° c, DDC controller open foreign gas and return air throttle, integrated air supply temperature until external gas air door closed to most small opening to maintain 12 ° c air temperature, can be cum outside air conditioning use.

(4) the low temperature limit temperature control for induction hybrid to protect ice cold row.

4.3 do cold water host switch machine and condition records

General building air-conditioning system daily cold water host switch machine, largely artificial to manipulation. The main power on loaded programs from people to monitor more flexible. Therefore, the operations staff is important, but who want to rest will shift, therefore there is no operation of chiller hosts a set of effective management. DDC can set all switching machine procedures and standards, not relent in our class. Host control system equipped with analog signal adapter card transforms communications, together with a list of machines that can put all running in a day where displayed. In case of jump machine and instant notification technology personnel to view.

5. concluding remarks

Use DDCSystem to control the air conditioning system, the most important is not the ideal way for improvement of the control. Over the years, the domestic air-conditioning host device, in the operators in accordance with government standards high EER or COP be improved have a good product.The need for complementary measures is the integration of DDC control system, use it with load quickly and effectively adjust the fan motor speed up energy-saving targets.