Combined air handling unit is a piece of equipment specially used to process air. It has the functions of cooling, dehumidifying and drying, heating and humidifying, filtering and purifying, supplying and returning air, and introducing new air. Mainly used in industry, medicine and health, large and medium-sized buildings, such as hotels, luxury commercial facilities, sports and entertainment centers and other places.
air handling unit classification:
(1) Classification according to structural form:
a) Horizontal type;
b) vertical;
c) Ceiling type;
(2) According to usage characteristics:
a) Fresh air unit;
b) Variable fresh air ratio air conditioning unit;
c) Return air handling unit;
d) Heat recovery unit;
(3) Classification according to specifications, generally according to the size of the air volume.
air handling unit consists of:
It mainly consists of primary effect filter, medium effect filter, preheating coil, precooling coil, water washing and humidification device, recooling coil, reheating coil, air supply fan, high efficiency filter, backstop electric damper, etc. .
Steam humidification:
Electric humidifier: Use electric heating to heat pure water to generate steam for humidification. When the water level in the water tank decreases, water is supplied step by step in proportion. When high humidification accuracy is required, SCR can be used to drive the electric heater to increase stability.
Electrode humidifier: Use electrodes to make ions in the water search for electricity to generate heat, heat the water into water vapor, and humidify the air. It is not suitable for humidifying pure water. It is not suitable for humidifying pure water, so it is not suitable to be used for humidifying pure water. High place.
Steam humidification: Use a steam boiler to generate steam for humidification, and use a control valve to control the amount of humidification.
Water mist humidification:
Two-fluid humidification: Use high-pressure air to atomize water and evaporate the water mist to achieve a humidification effect.
Washing and humidification: Use washing equipment to atomize water and extend the contact time between water and air to achieve a humidifying effect.
air handling unit control:
The control of the air handling unit mainly controls its various components effectively, including: cleanliness control; pressure control; temperature and humidity control; and air valve control of the air handling unit.
Cleanliness control:
Cleanliness control is the control of external air particles. The air handling unit filters the air to achieve air cleanliness. It usually includes: primary filter, medium filter, and high efficiency filter.
Primary filter: mainly used to filter coarse dust particles above 1um in the atmosphere;
Medium efficiency filter: mainly used to filter coarse dust particles below 1um in the atmosphere;
High-efficiency filter: mainly used to filter dust particles below 0.5um in the atmosphere;
The air handling unit control system installs differential pressure switches on both sides of the filter to provide a real-time alarm for the degree of pollution of the filter. When the differential pressure at both ends of the filter exceeds the set value, an alarm will be issued on site and in the central computer configuration interface. Remind property managers to replace filters in a timely manner to reduce system pressure loss.
Pressure control:
The formation of air pressure in the air handling unit is completed by the air supply fan. Its control system monitors the main status of the fan and controls the execution components in real time. The system is divided into manual mode and automatic mode.
1. Manual mode
Turn the on-site switch to manual mode, start/stop the system on-site, and set the operating frequency of the inverter on-site.
2. Automatic mode
The central computer monitors the manual/automatic status, operating status, fault status of the system and the operating status, fault status, and operating frequency of the inverter in real time through the configuration software, and performs historical storage. It can remotely start/stop the system and adjust the operating frequency of the inverter. Install a static pressure sensor at the air outlet of the air handling unit to measure the outlet static pressure, compare it with the set value, and perform real-time PID control to maintain the outlet static pressure within the set range.
Temperature and humidity control:
The outlet air temperature and humidity of the air handling unit are achieved through hot and cold coils and humidifiers. First, an outside air temperature and humidity sensor is installed in the computer room to measure the outside air temperature and humidity. It can be automatically controlled in winter and summer modes according to the absolute humidity of the outside air. According to the indoor conditions, assuming: A℃/B%, the corresponding absolute humidity Cg/kg can be seen from the enthalpy-humidity diagram. When the absolute humidity of the outside air is greater than or equal to Cg/kg, it is controlled according to the summer mode. When it is less than Cg/kg, Control by winter mode.
1. Summer control mode
Assume that the outside air conditions are as follows: A1℃/B1%.
During summer mode control, the preheating coil is turned off. According to the cooling capacity demand, the precooling coil and recooling coil are turned on to perform cooling and dehumidification until the absolute humidity drops to Cg/kg. The reheating coil is turned on to raise the temperature to the indoor requirement. temperature to meet the required conditions in the clean room.
2. Winter control mode
Different humidification types have different temperature controls.
(1) Water mist humidification mode (including water-wash humidification and two-fluid humidification):
Assume that the outdoor conditions are: A2℃/B2%.
Check the enthalpy-humidity diagram to know:
The enthalpy value at C g/kg/100% is Dkj/kg;
First, turn on the preheating coil and raise the temperature to the enthalpy value: D kj/kg, then wash and humidify with water, wait for the enthalpy and humidify to saturation, start the reheating coil, and raise the temperature to the indoor temperature to achieve the required temperature and humidity in the clean room.
2) Steam humidification mode
Including: steam humidification, electric humidification, electrode humidification.
A. Steam humidification: Install a temperature and humidity sensor at the air outlet of the air handling unit to measure the air temperature and humidity of the air conditioning box. By adjusting the hot water coil control valve, the amount of hot water is proportionally controlled to achieve the desired indoor temperature; by adjusting the steam control valve , proportionally control the amount of humidification to achieve the required humidity in the room.
B. Electric heating humidification: Install a temperature and humidity sensor at the air outlet of the air handling unit to measure the air temperature and humidity of the air conditioning box. By adjusting the hot water coil control valve, the amount of hot water is proportionally controlled to achieve the desired indoor temperature; by adjusting the heating rod voltage , proportionally control the amount of humidification to achieve the required humidity in the room.
C. Electrode humidification: Install a temperature and humidity sensor at the air outlet of the air handling unit to measure the air temperature and humidity of the air handling unit. By adjusting the hot water coil control valve, the amount of hot water is proportionally controlled to achieve the desired indoor temperature; by adjusting the electric voltage , proportionally control the amount of humidification to achieve the required humidity in the room.
air handling unit air valve control:
The air valve setting of the air handling unit is related to the type of air handling unit. Generally, there are fresh air valve, return air valve, exhaust valve and air supply valve.
1. Fresh air air handling unit damper control
Fresh air air handling unit are generally equipped with only supply air valves and no air inlet air valves. The operating status of the fan is interlocked with the air valve. When the fan starts, the air valve is opened first, and when the fan stops, the air valve is closed.
2. Return air handling unit damper control
The air handling unit is equipped with a fresh air damper, a return air damper and a supply air damper.
A. The fresh air valve and the return air valve achieve inverse proportional interlocking;
B. The return air valve, fresh air valve and air supply valve are interlocked with the air handling unit fan. When the fan starts, open the air valve first, and when the fan stops, close the air valve.
3. Change the fresh air ratio and control the air handling unit damper
The variable fresh air ratio air handling unit is equipped with a fresh air damper, a return air damper and a supply air damper.
A. The fresh air valve and the return air valve achieve inverse proportional interlocking;
B. The exhaust valve and the exhaust fan operating status are interlocked. When the exhaust fan starts, open the exhaust valve first. When the exhaust fan stops, close the exhaust valve;
C. The return air valve and the exhaust valve are inversely interlocked;
D. The return air valve, fresh air valve and air supply valve are interlocked with the air handling unit fan. When the fan starts, open the air valve first, and when the fan stops, close the air valve.
Washing and humidification system control:
1. Composition of water washing and humidification control system:
The water washing and humidification system consists of a pressure pump, nozzles, water replenishment valves, drainage valves, and pipelines.
The main water washing and humidification control systems include:
1. Pressurized pump control: start/stop control, operating status, fault status, manual/automatic status monitoring;
2. Water replenishment control: Install a liquid level gauge in the water tank, and control the water replenishment valve according to the liquid level to replenish water;
3. Drainage control: Install a conductivity meter in the sink and control the drainage of the washing system based on the measured value.
