Columns of precision air conditioning machine room still need to do air conditioning

Precision air conditioning refers to the machine room can fully meet the requirements of environmental conditions of the machine room special precision air conditioning machine (also known as constant temperature and humidity air conditioning), is in the last 30 years gradually developed a new type of machine. Early comfort air-conditioning machine room use, often due to improper control of environmental temperature and humidity parameters caused by unstable operation of equipment in the machine room, data transmission interference, static electricity and other problems. Computer room special air conditioning and ordinary comfort air conditioning difference between the computer room on the temperature, humidity and cleanliness have more stringent requirements, therefore, the computer room special air conditioning in the design of the traditional comfort air conditioning has a great difference, as shown in the following five aspects: 1. Traditional comfort air conditioning is mainly designed for the personnel, the air volume is small, the enthalpy difference between the air supply is large, the cooling and dehumidification at the same time; while the computer room is obvious Heat accounts for more than 90% of all the heat, which includes the heat generated by the equipment itself, the heat generated by the lighting, the heat conduction through the walls, ceilings, windows, floors, and the sun's radiant heat, the heat of infiltration through the gaps in the wind and the heat of the new air, and so on. These heat generated by the amount of moisture is very small, so the use of comfort air conditioning is bound to cause the relative humidity in the room is too low, so that the internal circuitry of the equipment components surface accumulation of static electricity, resulting in discharge and thus damage to the equipment, interfering with data transmission and storage. At the same time, due to the cooling capacity of (40% to 60%) consumed in dehumidification, making the actual cooling equipment to reduce the amount of cold a lot, greatly increasing the consumption of energy. Machine room air conditioning in the design of strict control of evaporation pressure in the evaporator, increase the air supply so that the evaporator surface temperature is higher than the dew point temperature of the air without dehumidification, resulting in all the cold used to cool down, improve efficiency, reduce the loss of moisture (air supply, air supply, enthalpy difference reduction). 2. comfort air conditioning air volume is small, low wind speed, only in the direction of the air supply local air circulation, can not be in the room to form the overall air circulation, the cooling of the room, the air circulation, the cooling of the room. The air circulation in the machine room is not uniform, so that there is a regional temperature difference in the machine room, the air supply direction of the regional temperature is low, and the temperature in other areas is high, the heat generating equipment due to the placement of different local heat accumulation, resulting in overheating and damage to the equipment. The machine room air conditioning air supply volume is large, the machine room air exchange number of times (usually 30 to 60 times / hour), the entire machine room can form an overall air circulation, so that all the equipment in the room can be cooled on average. 3. traditional comfort air conditioning, due to the air supply volume is small, fewer air exchanges, the air in the machine room can not ensure that there is a sufficiently high flow rate of dust will be brought back to the filter, and in the machine room equipment within the resulting Deposits, adverse effects on the equipment itself. And general comfort air conditioning unit filter performance is poor, can not meet the purification requirements of the computer. The use of computer room air conditioning air supply volume, air circulation is good, at the same time, because of a special air filter, can be timely and efficient filtering off the dust in the air to maintain the cleanliness of the computer room. 4. Because most of the electronic equipment in the computer room are running continuously, long working hours, so the requirements of special air conditioning in the design of the computer room can be large loads of year-round continuous operation, and to maintain a very high degree of reliability. Comfort air conditioning is more difficult to meet the requirements, especially in winter, the computer room because of its good sealing and heating equipment and more, still need air conditioning unit normal refrigeration, at this time, the general comfort air conditioning due to the outdoor condensing pressure is too low has been very difficult to work properly, the machine room air conditioning through the controllable outdoor condenser, can still be normal to ensure that the refrigeration cycle. 5. machine room air conditioning is generally equipped with special humidification system, high efficiency dehumidification system and electric power supply, and the air conditioning system can be used in the machine room. High-efficiency dehumidification system and electric heating compensation system, through the microprocessor, according to the sensor feedback data can accurately control the temperature and humidity in the room, while the comfort air conditioning is generally not equipped with a humidification system, can only control the temperature and lower precision, humidity is more difficult to control, can not meet the needs of equipment in the room. In summary, the computer room special air conditioning and comfort air conditioning in the product design there are significant differences between the two for different purposes and design, can not be used interchangeably. Computer room must be used in the computer room special air conditioning. At present, many domestic industries, such as finance, postal and telecommunications communications, television, oil exploration, printing, scientific research, electric power, etc. have been widely used to improve the reliability of computer, network, communication systems in the computer room and the economy of operation. Scope of application machine room precision air conditioner is widely used in computer rooms, program-controlled switching machine rooms, satellite mobile communication stations, large medical equipment room, laboratories, test rooms, precision electronic instruments production workshop and other high-precision environment, such an environment of air temperature, humidity, cleanliness, air distribution and other indicators have high requirements, must be 365 days a year, 24 hours a day, the safe and reliable operation of the Specialized machine room precision air conditioning equipment to protect the characteristics of significant heat large machine room installed hosts and peripherals, servers, switches, optical transceivers and other computer equipment, as well as power protection equipment, such as UPS power supply, will be heat transfer, convection, radiation to the machine room to emit heat, the heat only caused by the temperature rise in the machine room, belonging to the sensible heat. A server cabinet heat dissipation in a few kilowatts per hour to a dozen kilowatts, if the installation of blade servers, heat dissipation will be higher. Medium and large computer room equipment heat dissipation in the 400W/m2 or so, installed density of higher data centers may be 600W/m2 or more. The ratio of sensible heat in the computer room can be as high as 95%. Latent heat is small does not change the temperature in the room, but only change the humidity of the air in the room, this part of the heat is called latent heat. There is no humidity dispersal equipment in the computer room, latent heat mainly from the staff and outdoor air, and large and medium-sized computer room is generally used to separate the man-machine management mode, the computer room enclosure sealing is better, the new air is generally after the temperature and humidity pre-processing into the computer room, so the latent heat in the room is small. Large air volume, small enthalpy difference in the heat of the equipment is transmitted to the machine room by conduction, radiation, the equipment is concentrated in the area of heat concentration, in order to make the temperature and humidity uniformity of the regions in the machine room, and control in the allowable base and fluctuation range, there is a need for a larger amount of wind will be the residual heat away. In addition, less latent heat in the room, generally do not need dehumidification, the air through the air conditioner evaporator does not need to fall below zero temperature, so the temperature difference between the air supply and the enthalpy difference is required to be smaller, in order to take away the residual heat in the room, the need for a larger volume of air supply. Uninterrupted operation, year-round refrigeration equipment in the room is a steady state heat source, uninterrupted operation throughout the year, which requires a set of uninterrupted air conditioning protection system, the power supply in the air conditioning equipment also has high requirements, not only need to have a dual-channel utility power inter-commissioning, but also for the protection of important computer equipment air conditioning system should also have a generator set to do the back-up power supply. Long-term steady state heat source caused even in the winter room also need cooling, especially in the southern region, more prominent. In the northern region, if the winter still need refrigeration, in the selection of air conditioning units, need to consider the unit's condensing pressure and other related issues, in addition to increasing the proportion of cold outdoor air intake to achieve the purpose of energy saving. Send back more air conditioning room air supply depends on the room heat source and distribution characteristics, for the equipment in the room, dense arrangement of cables, bridges, more as well as alignment and other characteristics of the air conditioning air supply is divided into the lower send back, send back up, send back up, send back up the side, side send back. Static pressure box fan room air conditioning air supply and return usually do not use the pipeline, but the use of the lower part of the raised floor or ceiling space as a static pressure box to send back the wind, the formation of the static pressure box pressure regulator layer can make the air supply uniformity, so that the static pressure of each point in the space is equal. High cleanliness requirements of electronic computer rooms have strict air cleanliness requirements. Dust in the air, corrosive gases, etc. will seriously damage the life of electronic components, causing poor contact and short circuits, etc., so the special air conditioning requirements of the computer room can be in accordance with the relevant standards for the circulation of air dust, filtration. In addition, it is necessary to supplement fresh air to the computer room to maintain positive pressure in the computer room. According to the "Design Code for Electronic Computer Rooms", the dust concentration of the air in the host room, tested under static conditions, the number of dust particles greater than or equal to 0.5m per liter of air should be less than 18,000 particles. The pressure difference between the host room and other rooms, corridors should not be less than 4.9 Pa, and the static pressure difference with the outdoor should not be less than 9.8 Pa. Component parts of the main components of the precision air conditioning system in the server room, the controller, including the compressor, the evaporator, the heater, the air-cooled condenser, the controller, the humidification tank, the thermal expansion valve, the liquid-viewing mirror, the filter drier, the strainer, and other components. For the water-cooled series, the indoor unit also includes a plate heat exchanger, water flow regulating valve, and water solenoid valve[1] . Cooling requirements in order to determine the capacity of the computer room precision air conditioning machine to meet the requirements of the computer room temperature, humidity, cleanliness and air supply speed (referred to as the four degrees of requirements). The heat load of the computer room must be calculated first. The heat load of the room mainly from two aspects: one is the heat generated within the room it includes: indoor computers and external equipment heat, room auxiliary facilities and room equipment heat (electric heat, steam water temperature and other heat generators). These heat generation sensible heat, latent heat is small; lighting heat (sensible heat); staff heat (sensible heat is small, latent heat is large); due to moisture evaporation, condensation of heat generated (latent heat). The second is the heat generated outside the server room it includes: conduction heat. Heat intrusion through the body of the building, such as from the walls, roofs, partitions and the ground into the room heat (sensible heat); radiant heat (also known as radiant heat). Heat that enters a room directly from a glass window due to solar irradiation (sensible heat); heat generated by convection. From windows and doors and other gaps in the invasion of high-temperature outdoor air (also contains water vapor) generated by the heat (sensible heat, latent heat); in order to make indoor staff to reduce fatigue and conducive to human health and the introduction of fresh air generated by the heat (including sensible heat and latent heat). In short, the heat released by the human body, the heat invaded by the gap wind and the heat brought in by the air exchange, not only makes the room temperature rise, but also increases the humidity content in the room, and therefore the need for dehumidification. This part of the heat load is called latent heat load, and all the equipment in the room emits heat just indoor temperature rise, this heat load is called sensible heat load. With general hotels, offices, conference rooms and other latent heat occupies a large proportion of the difference is that the computer, programmable control machine room heat load is dominated by sensible heat load. Therefore, different types of air conditioners should be used for different heat load conditions. Usually use the apparent heat ratio (SFH) as an important indicator of the air conditioner. Rough calculation (also known as estimation) in the initial design stage of the computer room, in order to select the capacity of the air conditioning machine faster, this method can be used, that is, the unit area required for the estimation of the cooling capacity. Computer room (including program-controlled switch room): when the floor is high, 250-300kcal/m2h when the floor is low, 150-250kcal/m2h (according to the density of the equipment to make the appropriate increase or decrease) Office (duty room): 90kcal/m2h simple heat load calculation computer room air conditioning load, mainly from the computer equipment, external equipment and equipment in the computer room of the heat generation. About 80% of the total heat, followed by lighting heat, conduction heat, radiant heat, etc., which are calculated in the same way as the general air conditioning room load calculation. Computer manufacturers, generally can provide specific values of the heat generated by the equipment. Otherwise, according to the computer's power consumption to calculate its heat. a. Calculation of external equipment heat Q = 860N? (kcal/h) where: N: power consumption (kW);? : simultaneous use coefficient (0.2 ~ 0.5); 860: the heat equivalent of the work, that is, lkW of electrical energy all converted to heat energy generated by the heat. b. Host heat calculation Q = 860 × P × h1 × h2 × h3 where P: total power (kW); h1: simultaneous use coefficient; h2: utilization factor; h3: load work uniformity coefficient. c. Host heat calculation Q = 860 × P × h1 × h2 × h3 where P: total power (kW); h1: simultaneous use coefficient; h2: utilization coefficient; h3: load work uniformity coefficient. The total power of various equipment in the computer room should be based on the maximum power consumption of the equipment in the computer room, but these power consumption is not all converted into heat, therefore, it must be corrected with the above three coefficients, which in turn are related to the system structure of the computer, function, purpose, working condition and the electronic components used. The total coefficient is generally taken between 0.6 to 0.8 for good c. Lighting equipment thermal load computer room lighting equipment, part of the power consumption into light, part of the heat. Part of the light into the light is also absorbed by the building and equipment, etc. and become heat. Calculation of the heat load of the lighting equipment is as follows: Q = C × Pkcal / h where, P: nominal rated output power of the lighting equipment (W); C: per output lW of heat (kcal / hW), usually incandescent lamps 0.86, fluorescent lamps 1.0. d. Human body heat heat in the body of the human body is through the skin and respiratory organs put out, this heat because it contains water vapor, and its heat load should be the sensible and latent heat load. The heat load should be the sum of sensible heat and latent heat load. The heat emitted by the human body varies with the working condition. The staff in the machine room can be treated as light work. When the room temperature is 24℃, the sensible heat load is 56cal and the latent heat load is 46cal; when the room temperature is 21℃, the sensible heat load is 65cal and the latent heat load is 37ca1. In both cases, the total heat load is 102cal. e. Conducted heat of the enclosure The conducted heat that enters into the room through the roof, walls, partitions and other enclosures is a heat load that is related to the season, time of day, geographical location and the angle of sunlight, etc. The heat load of the room is the same as that of the room, geographic location, and the angle of sun exposure, among other quantities. Therefore, it is a complicated problem to accurately find such a quantity. When the indoor and outdoor air temperature to maintain a certain steady state, the heat transfer from the plane shape wall into the machine room can be calculated according to the following formula: Q = KF (t1-t2) kcal/h where, K: thermal conductivity coefficient of the enclosure (kcal/m2h ℃); F: enclosure area (m2); t1: temperature inside the machine room (℃); t2: calculated temperature outside the machine room (℃). When calculating the enclosure structure that is not in direct contact with outdoor air such as partitions, the difference between the indoor and outdoor calculated temperatures should be multiplied by a correction factor, the value of which is usually taken as 0.4 to 0.7. The thermal conductivity of commonly used materials is shown in the following table: Material thermal conductivity (kcal/m2h℃) Material thermal conductivity (kcal/m2h℃) Ordinary Concrete 1.4 to 1.5 Gypsum Board 0.2 Lightweight Concrete 0.5 to 0.7 asbestos cement board 1 mortar 1.3 soft fiberboard 0.15 cooked gypsum 0.5 fiberglass 0.03 brick 1.1 galvanized steel 38 glass 0.7 aluminum 180 wood 0.1 ~ 0.25 f. solar radiation heat from the glass penetration when the glass is irradiated by the sun, part of the sunlight is reflected, part of the glass is absorbed, and the rest of the through the glass into the engine room into heat. The heat absorbed by the glass increases the temperature of the glass, part of which enters the room through convection and becomes a heat load. Through the glass into the room heat can be calculated according to the following formula: Q = KFq (kcal / h) where, K: solar radiation heat penetration coefficient; F: the area of the glass window (m2); q: through the glass window into the intensity of solar radiation heat (kcal / m2h). The value of transmittance coefficient K depends on the type of window and is usually taken as 0.36 to 0.4. The intensity of solar heat radiation q varies with latitude, season and time, and with the angle of solar irradiation. For specific values, please refer to local meteorological data. g. Heat load of air exchange and outdoor intrusion In order to continuously replenish fresh air for the staff in the computer room, as well as to maintain the positive pressure of the computer room with air exchange, it is necessary to send fresh outdoor air to the computer room through the fresh air outlet of the air-conditioning equipment, which will also become the heat load. Through the door, window gaps and switches and the amount of outdoor air intrusion, with the degree of sealing of the room, the number of people in and out of the number of times and the outdoor wind speed and change. This heat load is usually very small, if necessary, it can be split into the room's air volume to determine the heat load. h. Other heat load in the machine room, in addition to the above heat load, in the work of the use of the show being a device, soldering iron, vacuum cleaner, etc. will become a heat load. Since the power consumption of these devices is generally small, it can be roughly calculated by the product of its rated input power and the heat equivalent of the work. In addition, a large number of transmission cables are used in the server room, which are also heat generators. The calculation is as follows: Q = 860Pl (kcal/h) in which 860: the heat equivalent of the work (kca1/h); P: the power consumption of each meter of cable (W); l: the length of the cable (m). In short, the heat load of the machine room should be determined by the sum of the heat load of each of the above a-h.