Suggestions on safe and intelligent control of air conditioning and ventilation systems during epidemics

Suggestions on safe and intelligent control of air conditioning and ventilation systems during epidemics

Under the epidemic situation, rework is imminent. We have carefully studied the relevant regulations and guidelines newly implemented in the country during the epidemic period, combined with relevant national regulations, and provided targeted air-conditioning and ventilation system epidemic prevention measures for customers in need, and worked with building operation and maintenance personnel to create A safer and higher quality office environment.

　　 The recent resumption of work is the peak period, and many companies have started work one after another. However, in the past few days, there have been cases of infection of returning employees in Guangzhou and Shenzhen.

On February 15, the management office of Tianying Plaza, an office building next to Tianhui Plaza, a well-known commercial center in Guangzhou, notified that it received a notice from the government on the morning of February 15 that a worker in one of the units on the 13th floor of the East Tower of Tianying Plaza was diagnosed For the new crown pneumonia!

　　 It is understood that all the staff of the company have been isolated and stopped working on February 14, 2020. At the same time, the management office and the CDC have come to the door to conduct a comprehensive disinfection of the floors and units. The notice of the office property management company mentioned that it had implemented various epidemic prevention and control work in accordance with the government's implementation requirements on January 28. One of them mentioned, "Every public location on the floor and public air conditioning vents and air cabinets , The filter screen is fully sprayed and disinfected, and the air-conditioning volume is increased to each unit every day." According to the recent release of the “Operation of Air-Conditioning and Ventilation Systems in Offices and Public Places During the New Coronary Pneumonia Epidemic The Management Guidelines stipulate that the need to continue to use the centralized air conditioning and ventilation system must meet the operation and management requirements, and the centralized air conditioning and ventilation system should be inspected, ventilated, cleaned and disinfected regularly.

　　 It can be seen that office buildings should adopt effective air-conditioning and ventilation systems to prevent epidemics. For building operation and maintenance personnel, how should they create a safer and higher-quality office environment?

As a leader in the smart building and building automation industry, Honeywell’s products, software and technology have been used in more than 10 million buildings around the world, helping commercial building owners and users’ facilities to be safe, energy-efficient, sustainable and high productive forces. At the same time, Honeywell is also a cooperative research partner of the American Lung Association. With hundreds of years of experience in air purification treatment, we provide air quality improvement solutions for many building users.

　　 Under the epidemic situation, rework is imminent, Honeywell provides targeted air-conditioning and ventilation system epidemic prevention measures for customers in need, and works with building operation and maintenance personnel to create a safer and higher-quality office environment.

　　 1. The operating status of air conditioning and ventilation systems

　　 There are three main forms of mainstream air-conditioning systems in general public buildings in China:

　　 1. Fan coil FCU + fresh air system (PAU unit)

　　2. Constant air volume full air system (AHU unit)

　　3. Variable air volume air conditioning system (AHU+VAV BOX)

Generally speaking, public buildings in severe cold areas (such as cities in Northeast China) use central air conditioning for cooling in summer and heating systems in winter; public buildings in cold regions (such as Beijing, Xi’an, Taiyuan, etc.) use central air conditioning for cooling in summer. Central air-conditioning is used in winter to combine central heating and heating system heating; public buildings in hot summer and cold winter areas (such as Shanghai, Nanjing, Wuhan and other cities) use central air conditioning for cooling in summer and central air conditioning for central heating in winter; southern regions (such as Shenzhen) , Guangzhou, Haikou and other cities) use central air-conditioning for cooling in summer. In winter, except for some star-rated hotels, most office buildings have no heating. Only the air conditioning units are turned on to achieve ventilation in the building.

　　 We learned that many buildings that use fan coil + fresh air systems, the fresh air unit does not open, or open time is short, generally do not have a centralized mechanical exhaust system. The constant air volume AHU unit fresh air ratio is generally around 30%, and the VAV system fresh air is fixed air volume + CAV dynamic adjustment, which can generally reach 50-60%. In recent years, the fresh air standard of air-conditioning system has been improved, and it can generally meet the requirement of 70% fresh air. The full air system is generally exhausted through the AHU unit. In addition, the air conditioning system is rarely cleaned and disinfected in strict accordance with the national standard frequency. For this epidemic, we recommend that we make targeted adjustments based on users in different regions.

According to our customer’s survey feedback, due to the early construction period or changes in the use of functions, the original air conditioning and ventilation system design may have some defects and deficiencies. In addition, the tenant’s secondary renovation and renovation has brought a lot of air conditioning and waterways. influences. The user's air-conditioning system has a deviation from the original design parameters and operating parameters, and the user has no overall understanding and control of his own system. We recommend contacting Honeywell's professional engineers during the epidemic to thoroughly review the design, construction, operation and maintenance of the system, and carry out detailed rectification and optimization one by one.

　　 2. System model adjustments under the epidemic

　　 For the mode management of the building air conditioning system, we generally set up three modes of heating, cooling, and transition seasons. In some projects, overtime mode and natural cooling source mode will be added according to actual operation requirements. The most critical and effective preventive measure for the air-conditioning system of this epidemic is to increase fresh air ventilation and stop the operation of the return air, triggering a series of changes in the operation strategy of air-conditioning equipment. Such as the change of equipment operating time, the change of the opening strategy of the electric damper/electric water valve, the adjustment of the comprehensive consideration of coil antifreeze, the change of the indoor ventilation and exhaust strategy, the adjustment of equipment operating parameters, etc., the design workload is relatively large.

We suggest adding "Public Health Emergency Mode" to the intelligent building control system: After all the logic and adjustments are modified in the DDC controller, global variables are added to the host computer software, and the "Public Health Emergency Mode" menu key is added. Users can One-click on the software interface to enable and disable the "Public Health Emergency Mode", the operation is simple.

　　 Three, air conditioning and ventilation system operation strategy adjustment measures

　　 1. The fresh air unit is forced to open.

　　2. It should be ensured that the fresh air is taken directly from the outdoors, and it is prohibited to take the air from the machine room, corridor and ceiling; and the fresh air intake and the surrounding environment must be clean to ensure that the fresh air is not polluted.

　　 3. The air conditioning unit runs with fresh air, the fresh air valve and exhaust valve (if any) are fully opened, and the return air valve is closed.

　　4. The linkage control mode of external window magnetism and air conditioning system is released.

　　 5. Turn off the runner heat recovery device (if any):

　　(1) The fresh air in the building and the exhaust system are independent. If the heat recovery device is used to recover the cold and heat through the runner and other heat recovery devices, turn off the runner heat recovery motor, and the fresh air and exhaust air can operate independently.

　　 (2) The fresh air and exhaust air are heat recovered through the runner unit (the unit is equipped with cold and heat treatment capacity, and the air is supplied through a centralized shaft). In this case, turn off the heat recovery motor of the runner, and the new and exhaust air will still operate normally. If there is a bypass duct, it is recommended to switch off the heat recovery and switch the bypass duct to run the new and exhaust air independently; if conditions permit, it is recommended Add new and exhaust bypass ducts. When it is not in the public health emergency mode, the bypass operation can be turned on in the transition season operation mode to save energy.

　　(3) The fresh air and exhaust air are heat recovered through the rotary unit (the unit does not have the ability of cold heat treatment, and the air is sent through the centralized shaft, and then the cold heat treatment is performed on each floor of the unit) (this is rare). It is recommended to add a hot coil in the unit to preheat the fresh air and take anti-freezing measures.

　　6. ​​When the fresh air is running, if the fan speed of the air conditioning unit can be adjusted, reduce the frequency of the unit fan (such as 30Hz, which can be adjusted according to the actual situation) to achieve low-speed fresh air supply and improve the discomfort caused by high-speed and low-temperature air supply.

　　7. It is recommended to increase the fan-coil network, which can effectively remotely control the start-stop and parameter adjustment of all terminal equipment (the public health emergency mode is more convenient for remote unified monitoring.)

8. Comprehensively check the coverage area of ​​the VAV BOX. For cross-regional FPB, if the ceiling return air is connected to several areas, it is recommended to close the FPB return air outlet; if it is not connected, only keep the air supply outlet in the area where the equipment is located, and other air outlets. The tuyere is closed.

　　9. Continue to use the unit not lower than F7 level filter or high-voltage electrostatic dust removal equipment to ensure the treatment of small particles in the air.

　　10. For units with a relatively low air filtration level, we recommend adding a filter of no less than F7 filtration level. Taking into account the characteristics of low resistance and high efficiency, it is recommended to add high-voltage electrostatic dust removal equipment to ensure the treatment of small particles in the air.

　　 11. Reasonable use of ultraviolet sterilization equipment.

　　 12. It is recommended to turn off the humidification function of the air conditioning and ventilation system.

　　 13. When a suspected or confirmed case of pneumonia with a new type of coronavirus infection is discovered, the air conditioning and ventilation system should be stopped. Under the guidance of the Center for Disease Control and Prevention, the air-conditioning and ventilation system shall be disinfected and cleaned, and it may be reactivated after passing the hygienic evaluation.

Note: After adopting all the existing measures that can increase the fresh air, the fresh air ventilation requirements are still seriously not met. It is recommended to increase the area of ​​the fresh air outlet and expand the size of the fresh air duct to meet the air volume requirements of the fresh air operation. It can also be operated to save energy.

　　 4. Operation and energy saving of air-conditioning system during non-working hours

Compared with the previous system, open the fresh air unit ahead of time (1-2h), and delay the closing 1-2h after work to fully carry out ventilation in the building. In the northern winter, it is necessary to close the unit while ensuring that the fresh air valve is closed to prevent If the group is not turned on at night, the coil will freeze out.

1. In the cooling area, open the air valve and fan of the fresh air unit in advance to achieve only ventilation, without cooling consumption, and realize energy saving. 20-30 minutes before work, turn on the fresh air unit and open the water valve to achieve pre-cooling of the building ; Close the water valve of the fresh air unit after work, and then close the fan and air valve after 1-2h.

　　2. Heating area: in severe cold areas, when turning on the unit, ensure that the water valve and hot water circulation pump are fully opened to prevent freezing. In cold areas, it can be adjusted according to the outdoor (fresh air) temperature. If the temperature is suitable, the unit can be opened in advance while ensuring the minimum flow of the water valve.

　　 5. Fresh air operation to prevent low temperature and coil antifreeze measures

　　1. If there is a heating and air-conditioning system, it is recommended to only turn on the heating to provide heating, a separate fresh air unit is forced to turn on, or to open the windows regularly (recommended not less than 2 hours)

　　 2. When the air conditioning unit is turned on, increase the air supply temperature by 2-4°C (adjustable), and the water valve is adjusted according to the air supply temperature.

　　 3. Increase the water supply temperature of the secondary side of the heat exchange station by 2-4°C (adjustable), and increase the flow supply of the primary heat source.

　　4. If necessary, install electric heat tracing in the fresh air inlet pipe, and take precautions against electricity consumption.

　　5. Comprehensively monitor the antifreeze switch, unit supply air temperature, and fresh air temperature to prevent freezing. It is recommended to keep the water circulating during non-working hours.

　　6. ​​On the premise of ensuring that the number of indoor air changes meets the requirements, the fresh air running time can be appropriately shortened.

　　 Six, ventilation and exhaust system operation adjustment measures

1. The mechanical exhaust fan (if any) of the existing system of the building is controlled online (the intelligent building control system adds point monitoring), and the damaged exhaust pipe is repaired, and the air pipe connection is sealed to prevent the exhaust air from entering other The area causes pollution.

　　2. For buildings without a mechanical exhaust system, it is recommended to add a centralized mechanical exhaust system, add exhaust outlets and exhaust ducts in each area for centralized exhaust, and remote monitoring by the building control system.

　　3. Conditional users can add air quality sensors, real-time monitoring of abnormal air data, and linkage with public health emergency mode.

　　4. When the AHU unit is equipped with return air and exhaust ducts, and the air inlet of the return air duct is open in the ceiling, it is recommended to connect the indoor return air outlet with the return air pipe in the ceiling through modification.

　　5. For the kitchen ventilation system, it is recommended to modify the local operation and add points to connect to the remote intelligent building control system to realize the forced interlocking function of the kitchen exhaust fan and the supplementary fan.

　　6. ​​For the ventilation and exhaust system of the underground parking lot, considering the large power of ventilation and exhaust equipment, the long-term stay of personnel, and the uneconomical long-term operation of the system, it is recommended to extend the operating time of the system by about 30% according to the actual situation of the project.

　　 Seven, system maintenance, cleaning, disinfection and adjustment measures

　　 1. It is recommended to clean and disinfect the entire air conditioning and ventilation system no less than once a month.

2. It is recommended to clean and disinfect the filter/filter/supply outlet and return air outlet no less than once a week (250mg/L-500mg/L chlorine (bromine) or chlorine dioxide disinfectant can be used for spraying, soaking or wiping, Act for 10-30 minutes.