The Design of Air-conditioning Control System using LabVIEW Software Platform

Abstract: LabVIEW is an innovative product of National Instruments Corporation which is a virtual instrument development environment marked by graphical software programming method and the integrated development environment. This paper focuses on the air conditioning system of venue and the audience area in a university gymnasium, and then draw the outline of the various parameters to measure branch of the monitoring and control, and the choice of components of the type of virtual air conditioning control system hardware, while uses LabVIEW software platform to develop the software of virtual air-conditioning control system, Finally commissioning and raise the entire virtual air conditioning control system. A necessary information database can use computer establishing virtual air conditioning control system for air conditioning units. The temperature and humidity of air supply, temperature and humidity indoor air conditioning room, temperature and humidity outdoor air supply speed, return air and fresh air is can be measured, comprehensive and timely through the telemetry system measurement. In this way, we can keep pace with The Times of the air conditioning system, so as to guide the operating conditions of cold and heat sources plan more effectively run the efficiency.

Key words: air conditioning control system; virtual instrument; Labview

1 OVERVIEW OF VIRTUAL INSTRUMENT TECHNOLOGY AND GYMNASIUM

1.1 Overview of virtual instrument technology

The so-called virtual instrument (hereinafter referred to as "VI) refers to the general computer function modules through the application. The user can use computer powerful graphical environment and online help function, establish Chinese or English virtual instrument panel interface. Then the system can complete instrument control; Data analysis, store and display. In this case, we can change the way in which use traditional instruments, in order to improve the function of the effective instruments of the price also greatly reduce instrument [7]. It also allows the user to define the instrument according to the needs of their functions. The basic component of virtual instrument system technology is as shown in figure 1 below.

1.2 Overview of air-conditioning system in university gymnasium

This paper focuses on the central air-conditioning system installed at venue and auditorium area in a university gymnasium. This region is controlled by 6 sets of combined air-conditioning unit. These 6 all-air units are used with combined air-conditioning whose type is 39G2226 produced by Carrier in U.S. The main technical parameters are as following: capacity of air supply is 41626m3 / h; cooling load is 364kW; heat load is 321kW; power is 22kW; pressure is 800Pa; capacity of humidification is 108kg / h. In order to describe clearly, the 6 sets of units are numbered with K3-1 ~ K3-6. While K3-1 ~ K3-4 units are responsible for the northwest stands, southwest stands, northeast stands and southeast stands in fixed auditorium stands respectively; K3-5 and K3-6 units are responsible for the east and west of venue area respectively. In this paper, we focus on K3-1 unit that is responsible for northwest grandstand in the fixed auditorium and K3-5 unit that is responsible for west venue area..

2 THE MONITORING OF HEAT AND MOISTURE PARAMETERS AND ARRANGEMENT

OF CONTROL POINT

2.1 Monitoring program of air conditioning system

In reference to the central air conditioning system in all the venues in the hall, areas in fixed were proposed based on the university gymnasium air-conditioning system in certain automatic program is as follows:

1) In the cool and refreshing coil section, the dynamic balance of electrical control valves located in export pipeline freezing water (or hot water air conditioning winter) [6]. When the load change in air conditioning room, which control the electric regulator through the setting of indoor temperature sensor or air conditioning system supply air lines, and automatically adjust the flow of hot water and cold water through the cooling coil in the air conditioning.

2) Located in the pipes of electric regulator humidification portions of the film [6]. Motorized valve is opening control and humidity measurement stadium air conditioning system, in order to control the number of humidification bloom in cold winter.

3) Differential pressure alarm device solve before and after crude filter part [6]. When the resistance of the filter is too big, it will inform operation and management personnel to clean strainer.

4) Fresh and supply/return air duct in the air conditioning system, supply/return air pipe inside the stadium and the central venue, the measuring point air speed has also been settled.

5) The CO2 concentration sensor is settled in the return air duct of air-conditioning system and venue hall, in order to control the content of fresh air in air-conditioning systems, and then save energy.

2.2 Summary of measuring/controlling-point in air-conditioning control system

In accordance with the procedures to monitor and control points, the layout of the layout of the distribution measurement/control points all central air conditioning monitoring system in the stadium as follows:

3. SELECTION OF HARDWARE IN AIR-CONDITIONING CONTROL SYSTEM

3.1 Overview of hardware selection

After completing the arrangement of the air conditioning control system test point in the gymnasium, secondly, the more important task is to select hardware system needs, make the number of every component. Because the data collection, transmission, and regulate and a series of more complex work in the whole of the control system of air conditioning system hardware realized on the basis of [1], hardware selection in appear particularly important. In this paper the gym air conditioning control system based on virtual instrument technology is, highlighting the selected parts of sensors, signal control, data collection card related virtual instrument technology as follows.

3.2 Selection of hardware

3.2.1 Temperature and humidity sensor

Temperature and humidity sensor is the temperature and humidity sensor of conversion of electrical signals. In the temperature and humidity sensor selection, we should consider sensor structure, measurement range of temperature, humidity, sensitivity, linearity, reaction time, stability, etc. [2].

This design uses the QFA-3171 Series temperature and humidity sensors manufactured by German Siemens Company, as shown in Figure 2. Specific performance parameters are as following: type of thermal resistance (platinum resistance); temperature range (0 ~ 70°C) ; sub-degree numbers (Pt1000); output signal (4 ~ 20mA current value); operating voltage (24V AC voltage).

3.2.2 Signal Conditioner

Signal conditioner is a bridge between the sensor and the data acquisition device [2]. As the sensor type varies widely, even though the transmitter module, it built in other types of sensor signal into 4 ~ 20 graduate or 0 ~ 10 v unity, however, there are still quite a difference from voltage signal data acquisition card design requirements. This may need to be involved in signal processing module to meet the requirements of data collection.

This design uses SCC-CI20-type signal conditioner produced by U.S. NI Corporation, as is shown in Figure 3. Specific performance parameters are as following: channel number (2); input signal (4 ~ 20mA); output signal (0 ~ 5V); bias error (± 0.6mV); gain error (± 0.1%);power (100 mW).

3.2.3 Data Acquisition Card

The data acquisition card is between the computer and external interface. Its main function is to analog signal converted into digital signals external computers can handle [2]. Data acquisition card based on PCI bus can be used for as long as it is plugged directly into slot on the desktop. Data acquisition card's performance depends on its resolution, sampling rate, the channel number, flexibility and reliability, scalability, and computer platforms. [3].

This design uses PCI-M6255 data acquisition card that is produced by U.S. NI Corporation, as is shown in Figure 4. The specific performance parameters are as following: 80 analog input channels; resolution (16bit); sampling rate (2.8 MS / s); input signal (± 5V ~ ± 10V); digital output channels (24).

Through the hardware platform based on virtual instrument technology above, the live signals collected by all kinds of sensors transmit through shielded twisted pair, and then enter into the external wiring box of DAQ card by signal conditioning unit. And furthermore the signal from the wiring box enters into the computer through the special cable of DAQ card. Similarly, when the control signal has been processed from the LabVIEW program in the central computer (the IV chapter will describe more in detail), it will be dedicated from the special cable of analog output card, and then transferred to the output signal conditioning unit via external wiring box of analog output card, and furthermore shifted to move signal through actuators. And finally these signals will control all kinds of valve in the stadium.

4 SOFTWARE OF AIR-CONDITIONING

CONTROL SYSTEM

4.1 Overview of the software

The LabVIEW program of entire air-conditioning control system include eight sub-modules: data acquisition module, system description and modules instruction module, upper and lower limits setting module, limited alarm module, fault information module, trend display module, data storage module and data print module. Because the number of measuring and control points in this air-conditioning control systems in the university gymnasium is so large, tab structure is chosen as the main structure of the front panel. This can make all kinds of thermometer, anemometer, digital indicators, controllers, LED lights, oscilloscope, etc. more clearly and accurately display to the user. In this paper, the focus functional module of monitoring system will be instructed detail.

4.2 The specific description of each module

4.2.1 Introduction of data acquisition module

The fact that various types of thermal parameters in the gymnasium will be monitored real-time is the biggest functional advantage using virtual instrument technology to design the air-conditioning control system. Thus the design of this function module becomes particularly important. The 0 ~ 10V voltage signal acquired by DAQ card, through the powerful graphics processing of computer, display the real-time status of various types of thermal parameters. As is shown in Figure 5.

4.2.2 Introduction of limited alarm module

Data acquisition is the functions of this air-conditioning control system; in addition, it is a conventional fact that the upper and lower limits of various parameters can be set on the needs of the user.

4.2.3 Instruction of fault information Module

After the LED indicator in limited alarm module operate, further report on the working state of the hardware system has been made through the module. In that case, system administrators can make clearer understanding of the specific operational status in energy supply system, such as: open degrees of heating / cool coil, open degrees of fresh air valve and so forth. As is shown in Figure 6.

4.2.3 Instruction of trend display module

As we all know, thermal environment that all kinds of building energy supply system control is a process of slow changes, but the computer processing is a relatively quick process. To enable combine the two distinct data processing, and to observe the slow change trend of the thermal environmental parameters in stadium through the computer, the curve on the oscilloscope of front panel in host computer display the current status of work in air-conditioning system to system administrators, which allows administrators make greater certainty of the condition of the system in accordance with current conditions. And they can predict the trend of air-conditioning system, furthermore find the fault that may be occurred in the future. This module plays a proactive role. As is shown in Figure 7.