The determination of fresh air volume in computer rooms and the composition of the fresh air system, as well as the impact of fresh air on the air conditioning purification system in computer rooms.

1、 Standardize the regulations for new air volume in computer rooms

1. It is generally believed that the new air volume in a computer room should be calculated based on the maximum value of the following three criteria:

1) 5% of the total air supply volume in the computer room;

2) Each person has a capacity of ≥ 40m ³/h;

3) The amount of fresh air required to maintain positive pressure in the computer room (positive pressure between the main room and the corridor or other rooms ≥ 4.9Pa, and positive pressure outside ≥ 9.8Pa).

2. The first rule is that the fresh air volume should be 5% of the total air supply volume, which is not reasonable because the total heat load of the computer room is not proportional to its area. Although some computer rooms are not large in size, due to high power density, the total heat load of the computer room is large, and the total air supply volume of the air conditioning unit is large. The fresh air volume determined according to this requirement is often too large, resulting in a large air conditioning load required for processing fresh air; For example, there is a 140m ² computer room with a total heat load of 360KW and a total air supply of approximately 100000 m ³/h. If calculated at 5%, the fresh air volume would be 5000m ³/h.

The purpose of introducing fresh air into the computer room is to meet the needs of people and maintain the required positive pressure value for the computer room; In the first edition of the air conditioning design manual (edited by the 10th Design Institute of the Ministry of Electronics), it is believed that the fresh air volume for turbulent flow clean rooms should not be less than 10% of the total air supply volume; In the second edition, it is stated that the reason for this provision seems insufficient, and there is no such provision in the "Design Code for Heating, Ventilation and Air Conditioning". Therefore, it should be supplemented with indoor exhaust and maintain indoor positive pressure values according to 1); Ensure that the indoor fresh air volume per person is not less than 40 m ³/h, and the larger of the two items determines the fresh air volume.

The computer room can be regarded as a turbulent flow clean room with low cleanliness requirements (British 500000 level). The computer room has no exhaust and should maintain the required positive pressure value and a fresh air volume of no less than 40 m ³/h per person in the room.

It is difficult to calculate the amount of fresh air required to maintain positive pressure in the computer room. To maintain a positive pressure of ≥ 4.9Pa between the computer room and the corridor (or other rooms), the air outlet velocity through gaps such as doors and windows in the computer room should be ≥ 2.8 m/s, and the fresh air volume should be the product of the total gap area and the air outlet velocity; Due to the difficulty in calculating the total area of gaps, the amount of fresh air required to maintain positive pressure in the computer room cannot be calculated.

2、 The Influence of New Air Volume in Computer Room on Air Conditioning Purification System

1. Advantages and disadvantages of large fresh air volume

Advantages: 1) It is easier to maintain positive pressure in the computer room; 2) Can provide more fresh air for the staff.

Disadvantages: 1) In many regions of China, the heat and humidity loads of fresh air in summer are relatively high. If the fresh air volume is large, it will increase the burden on the air conditioning system; For example, in summer, if 5000 m ³/h fresh air is processed into the computer room (temperature 23 ℃, relative humidity 55%), the cooling load in Beijing is 57.5 kW, and in Shanghai it is 72 kW.

2) In colder regions, if there is a large amount of fresh air in winter, both humidification and heating are required. For example, in winter, if 5000 m ³/h of fresh air is processed into the machine room (temperature 20 ℃, relative humidity 55%), a humidification rate of 43.8 kg/h is required in Beijing; The humidification capacity of each dedicated air conditioner in a large computer room is only 8-10kg/h, and if there is new air volume, it will add a great burden to the air conditioning system.

In colder regions, if a large amount of fresh air is directly sent into the computer room without heating during winter, condensation may occur when the temperature of the fresh air is lower than the dew point temperature of the computer room. At this time, the fresh air must be heated before being sent in; If the fresh air volume is large, a large amount of heating is required, resulting in energy waste.

3) The fresh air volume is large, requiring a large number of fresh air filters, and the initial investment and maintenance workload are both significant.

2. Advantages and disadvantages of low fresh air volume

Advantages: 1) The air conditioning load required for processing fresh air in summer is small, and the humidification and heating required in winter are also small, saving initial investment and operating energy; 2) The required number of fresh air filters is small, and the initial investment and operation maintenance costs are relatively low.

Disadvantage: It is difficult to maintain the required positive pressure value for the computer room. If the positive pressure value of the computer room is low or even negative, it is difficult to maintain the temperature, humidity, and cleanliness of the computer room; Untreated outdoor air enters the computer room directly through gaps such as doors and windows, causing high relative humidity in humid areas during summer and low relative humidity in colder areas during winter. Due to the unfiltered outdoor air entering through gaps, the cleanliness of the computer room cannot be guaranteed.

3、 Determination of New Air Volume in Computer Room

A suitable fresh air volume should be determined for the computer room. If the fresh air volume is too small or too large, it cannot meet the temperature, humidity, and cleanliness requirements of the computer room. It is recommended to calculate the new air volume based on the higher of the required positive pressure value for maintaining the computer room and the requirement of ≥ 40m ³/h per person.

Due to the difficulty in calculating the required fresh air volume to maintain positive pressure in the computer room, based on experience and reference to the design of clean rooms, the fresh air volume can be calculated at 1-2 air changes per hour. If the sealing of the surrounding protective structure of the computer room is good, the new air volume can be calculated using ≥ 1 air change/hour; If the sealing is poor, the ventilation rate can be appropriately increased and sealing measures can be taken. The most effective and energy-saving method is to take sealing measures for the surrounding protective structure, especially paying attention to the sealing under the raised floor and inside the ceiling. After all pipelines passing through the computer room enclosure structure are laid, the holes should be tightly sealed to prevent air leakage.

4、 Methods for handling fresh air

1. The dedicated air conditioning unit for the computer room is a high air volume, low enthalpy difference air conditioning unit, with an enthalpy difference of about half of that of a comfort air conditioning unit; This is because sensible heat accounts for the vast majority of the total heat load in the computer room, and measures have been taken to prevent condensation in the computer room.

Due to the small enthalpy difference and large air volume of the dedicated air conditioning unit in the computer room, the high surface temperature of the evaporator is not conducive to dehumidification. In humid areas during summer, dedicated air conditioning units often have compressors and electric heaters working simultaneously for dehumidification purposes; It consumes electrical energy, increases the working time of the compressor and electric heater, and reduces the lifespan of the air conditioner. In this operating state, the configuration of the air conditioner also needs to be increased.

2. To prevent the above-mentioned operating conditions from occurring, it is best to use a comfort air conditioner to preprocess the fresh air, mix it with the return air in the computer room, and then enter a dedicated air conditioner for processing; Avoiding the simultaneous operation of compressors and electric heaters in summer can save energy, reduce the operating time of air conditioning units, and extend their service life.

3. To maintain the cleanliness required for the computer room, it is necessary to:

1) To maintain the cleanliness required for the computer room (British 500000 level), it is necessary to maintain a positive pressure in the computer room to prevent untreated dirty outdoor air from entering through gaps; To maintain positive pressure, it is necessary to introduce a certain amount of fresh air as mentioned earlier and seal the surrounding protective structure.

2) Fresh air must undergo good filtration before being sent into the computer room, and the cleanliness of the filtered fresh air should be better than the cleanliness required by the computer room; The fresh air sent in is cleaner than the air inside the computer room. Clean fresh air is used to dilute the dust inside the computer room, and the positive pressure of the computer room is used to discharge some dirty air through gaps such as doors and windows outside the computer room.

4. Fresh air system. In summary, the fresh air system should include a fresh air filtration device and a fresh air temperature and humidity pretreatment device:

1) Fresh air filtration device. There should be at least two levels of air filters, with the second level being a sub high efficiency air filter, in order to ensure that the cleanliness of the computer room meets the required standards.

2) Pre treatment device for fresh air temperature and humidity. Pre treat fresh air with comfort air conditioning units for cooling and dehumidification in summer, and heat pump air conditioning units can also be used for heating in winter; In colder regions, when the winter heat pump air conditioner cannot generate heat or has insufficient heating capacity, an additional fresh air heater needs to be added to prevent condensation after fresh air is sent into the machine room.

3) The fresh air system is divided into two types: floor standing and concealed installation inside the ceiling.

① The concealed installation in the ceiling has a small volume and weight, and does not occupy any area; But maintenance is inconvenient, and due to limited volume and small filter area, it is easy to clog. After clogging, replacing the filter needs to be done inside the ceiling.

② A floor standing ventilation room can be built, and maintenance work is carried out inside the room; And it can increase the area of the filter, increase the dust holding capacity of the filter, prolong the use time of the filter, and reduce maintenance workload; In addition, due to the large area of the filter, the resistance of air passing through the filter is reduced, which can lower the pressure head and noise of the fan; But the floor standing design needs to occupy a certain area. In places where conditions permit, it is better to use floor standing construction