Applications |

SOWAKAM Inverter in central air conditioning water system

Central air conditioning water system includes:

(1) The chilled water circulation system is composed of a freezing pump and a cold water pipe. The low-temperature chilled water enters the room for heat exchange, takes away the heat in the room, and lowers the temperature in the room.

(2) The cooling water circulation system is composed of cooling pumps, cooling pipes and cooling towers. The chilled water exchanges heat with the indoors, taking away the heat and transferring the heat energy to the cooling water to increase the temperature of the cooling water; the cooling pump will heat the heated water. The cooling water is sent into the cooling tower, and the heated cooling water and air in the cooling tower perform heat exchange to reduce the temperature of the cooling water, and then the cooled cooling water is sent back to the host machine.

(3) Host. Including refrigerators, indoor fans and temperature and humidity sensors.

SOWAKAM frequency drive VFD in Central air conditioning control system

Freezing pumps, cooling pumps, and water tower fans adopt open-loop control, which are adjusted by maintenance personnel according to seasonal changes and load changes; temperature closed-loop control is used to control the fans, and the temperature difference of the temperature sensor (the difference between the set temperature and the actual temperature value) as the feedback value of the temperature closed-loop control system, thereby adjusting the fan speed, so that the actual temperature of the controlled environment changes with the set temperature.

The cooling water system adopts frequency conversion control, and the energy saving effect is also relatively significant. Under the condition that a certain amount of cooling water flows out of the cooling tower, the cooling water flow rate is adjusted by controlling the output power of the frequency converter. When the outlet temperature of the central air-conditioning cooling water is low, the cooling water flow rate is reduced; when the central air-conditioning cooling water outlet temperature is too high, the cooling water flow rate is increased. In this way, the purpose of energy saving and efficiency improvement can be achieved while ensuring the normal operation of the central air conditioning unit.

For the central air-conditioning water system, the places that consume a lot of electricity and are rich in energy saving include cold water pumps, refrigeration pumps, air blowers and compressors, etc.

A：Refrigeration pump modification

The refrigeration pump and chilled water pressure that exchange heat and cold with the refrigerant of the compressor host are related to the normal operation of the main compressor of the air conditioner and the normal equipment. However, due to changes in climate and temperature, the indoor demand for cooling and heating is also different. Although there are also indoor Thermostat, but not as good as it could be.

The best way is to automatically adjust the flow of chilled water according to changes in temperature to make the air conditioner as comfortable as possible, and use a frequency converter temperature closed loop to detect the temperature difference between the inlet and outlet of the chilled water, and automatically adjust it according to the required outlet or inlet water temperature. The purpose of energy saving, automatic control, and temperature adjustment can be achieved by adjusting the motor speed.

The transformation of the refrigeration pump can not only reduce operating noise and maintenance costs, but also make the indoor temperature more comfortable. Energy saving is more than 25%.

The simplified diagram of freezing pump system modification is as follows:

In this solution, the control system will run automatically and can be run manually through the original starting system. The system automatically maintains pipe pressure for adjustment. It will have sufficient capabilities to protect against water shortage, pipe network rupture, blockage and other common faults.

This system solution is suitable for projects that modify the original system.

B: Cooling pump modification

The cold water pump that cools the compressor host is related to the normal operation of the entire air conditioning system. However, due to changes in climate and temperature, the circulation volume of cooling water should also change. The current method is to manually adjust it through valves (in many cases, there is no regulating valve). The use of frequency converters can automatically control the motor speed by detecting the temperature difference between the cooling water inlet and outlet according to the actual situation, which can not only meet the requirements of the air conditioning system, but also save power between 25% and 50%.

The cold water pump can achieve the following advantages after modification:

Motor soft start, no starting impulse current; power saving between 25%-50%;

Reducing the speed of the water pump ensures the reliable and stable operation of the entire system, and greatly reduces the maintenance cost of the equipment;

It can automatically adjust the operation without requiring frequent operator actions;

The simplified diagram of cooling pump system modification is as follows:

In this solution, the control system will run automatically and can be run manually through the original starting system. The system automatically maintains pipe pressure for adjustment. It will have sufficient capabilities to protect against water shortage, pipe network rupture, blockage and other common faults. This system solution is suitable for projects that modify the original system.

Analysis of energy saving principles and investment effects:

AC-DC inverters are currently the most stable inverters, and their working efficiency is also very high. Its energy-saving principle can be simply understood as the inverter sends as much electric energy as the load requires, and the motor speed is adjusted by adjusting the frequency (bandwidth). Thereby achieving the purpose of energy saving.

It can be seen from the working principle of the water pump: the flow rate of the water pump is proportional to the speed of the water pump (motor), the lift of the water pump is proportional to the square of the speed of the water pump (motor), the shaft power of the water pump is equal to the product of the flow rate and the head, so the shaft power of the water pump The power is proportional to the cube of the pump's speed (that is, the shaft power of the pump is proportional to the cube of the power supply frequency). According to the above principle, changing the speed of the water pump can change the power of the water pump.

Basic formula for flow:

Q∝N

H∝N2

KW=Q*H∝N3 (Q represents flow, N represents rotation speed, H represents head, and KW represents shaft power.)

For example: reduce the power supply frequency from 50HZ to 45HZ, then P45/P50=(45/50)3= 0.729, that is, P45=0.729 P50;

Reduce the power supply frequency from 50HZ to 40HZ, then P40/P50=(40/50)3= 0.512, that is, P40=0.512 P50.

Water pumps are generally considered based on the maximum working condition requirements of the water supply system during design. In actual use, the water system may not necessarily reach the maximum amount of water for many times. Valve adjustment is generally used to increase the resistance of the system to throttle. , causing power loss of the motor, while using a frequency converter can make the system work smoothly and stably, adjust the water supply by changing the rotation speed, and recover the investment by reducing the rotation speed and saving energy. From the figure below, we can vividly see the comparison of the three flow control methods.

Comparison table of measured power consumption of three 100KW flow control methods:

In the parameters of the frequency converter, the "lower limit frequency" cannot be set to zero, because the water pump motor may stall. Once the air conditioning circulating water stops flowing, the temperature value detected by the temperature sensor loses its practical significance. The principle of setting the "Lower Limit Frequency" parameter is: the water pump motor continues to run at the "Lower Limit Frequency". Heating is not enough to make the temperature of the air-conditioned room reach the required temperature. Similarly, cooling cannot make the room temperature drop to the appropriate value. At this time, The temperature difference between the real-time temperature and the set temperature increases, the control signal output by the thermometer increases, the frequency converter output frequency increases, the circulating water flow increases, and the indoor temperature is adjusted. Thereafter, the frequency converter adjusts the speed and flow rate of the water pump at any time according to the change in the temperature difference between the outlet water and the return water and the size of the output signal of the thermometer to control the stability of the temperature in the air-conditioned room.