Introduction：
The concept of HVAC includes heating, ventilation, and air conditioning, so it has a broader concept than central air conditioning. The concept of energy saving in HVAC is not to reduce the environment or suppress energy demand in exchange for energy saving, but to improve the energy efficiency of buildings through the application of integrated resource planning (IRP) methods and energy demand side management (DSM) techniques, with limited Resources and minimum energy consumption costs to obtain maximum social and economic efficiency to meet the growing environmental needs. D71 inverter has been widely used in heating, ventilation and air-conditioning systems in high-end places such as airports, radio and television buildings, hospitals, and subways.
Features：
D71 is a wall-mounted inverter, the power range is 0.75KW-500KW, the voltage level of the incoming line voltage is 380V-480V, and the control method is vector control without speed sensor.
D71 has a wealth of control devices, including 8 digital inputs (LI1-LI8), 2 analog inputs (AI), 2 relay outputs (TA), 2 analog outputs (AO), 5V auxiliary power supply for analog power supply Fixed input, 24V auxiliary power supply is used for digital input, all LI/TA, AI/AO can be freely programmed to define functions.
MODBUS interface is standard configuration of D71, no option is required. The D71 can be connected to higher-level automation systems via MODBUS.
Advantage：
Good low-frequency torque performance (1.5 times the torque output when open-loop 0.5Hz), low-frequency large torque;
It has the advantage of fast torque response, and when the load fluctuates, the current fluctuation is small;
It has good overload capacity and environmental adaptability, and has high operational reliability;
Super power grid adaptability, anti-power grid fluctuation ability up to ±15%, to ensure the stability of output voltage, current, speed
15kW and above are equipped with standard DC reactors, which perform well in harmonic control and stability, helping customers save hardware costs;
Excellent current limiting characteristics, strong overload capacity, can effectively reduce frequency conversion overload, overcurrent protection, and maximize production continuity;
It has strong environmental adaptability, and the completely independent air duct design can greatly improve the resistance to harsh environments such as oil pollution, dust and damp heat.
system introduction：
In this system, two 110KW chilled water pumps are driven by two D71 110KW inverters, and there are also several D71 inverters that drive fans (including indoor fans and cooling tower fans). In the chilled water circulation system, the signal 1 (temperature signal or pressure signal) of the water inlet circuit and the signal 2 (temperature signal or pressure signal) of the water outlet circuit are sent to the analog module to obtain the analog feedback signal of the inverter. Through the built-in PID function of the inverter, the closed-loop automatic control is realized.
Technical Parameter：
| Inverter technical parameters | Device configuration | |
 Model: D71-X | Output current: 215A | One D71 inverter |
| Input voltage: 3-phase, 380-480V | Frequency range: 0-400Hz | 110KW chilled water pump and motor |
| Input frequency: 50/60Hz ±5% | Overload capacity: 150%, 60 seconds | chilled water circulation system |
| Output power: 110KW | Ambient temperature: -10-40°C | |
| Output voltage: 0-480V (the maximum value is determined by the input voltage) | Protection level: IP20 | |
On Site Usage：
According to the on-site space situation, a D71 series inverter is installed in the control cabinet, and the inverter installation and on-site motor are as shown in the figure
Running Result：
The heating, ventilation and air-conditioning control system using D71 inverter has been put into operation for more than three years, and has achieved good economic and social benefits:
The control device operates reliably, has good environmental adaptability, can resist harsh environments such as oil pollution, dust and damp heat, and has a low failure rate;
Excellent current limiting characteristics, strong overload capacity, can effectively reduce frequency conversion overload, overcurrent protection, and maximize production continuity;
The central air-conditioning system adopts frequency conversion closed-loop control, with fast dynamic response and high degree of automation, and the entire system realizes digital and intelligent control;
The economic benefits are remarkable, the basic energy saving effect is 35% to 55%, and the entire investment increased by the frequency conversion control system can be recovered in more than one year.
Customer Benefits：
PID closed-loop automatic control reduces worker workload and improves work efficiency;
Reduced motor loss and maintenance costs;
The comprehensive protection function of the frequency converter ensures maximum production continuity;
Reduce the running noise of the water pump and improve the comfort of the building;
The economic benefits are significant, and the entire investment increased by the frequency conversion control system can be recovered in more than one year.