Precision air conditioning refers to the machine room can fully meet the requirements of the 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 the gradual development of a new type of machine. Early machine rooms using comfort air conditioning, 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 issues.
Difference between computer room air conditioning and ordinary comfort air conditioning
Computer room temperature, humidity and cleanliness have more stringent requirements, therefore, computer room air conditioning in the design of the computer room with the traditional comfort air conditioning has a great deal of difference, as shown in the following five aspects:
1. Traditional comfort air conditioning is mainly designed for the personnel design, the air volume is small, and the enthalpy difference is large, the cooling effect is very small. The enthalpy difference of air supply is large, cooling and dehumidification at the same time; while the apparent heat in the room 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 the infiltration of wind through the gaps and the heat of the new wind, 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 the (40% to 60%) consumed in dehumidification, making the actual cooling equipment much less cold, greatly increasing the energy consumption.
Specialized air conditioning in the machine room is designed to use 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 and reduce the loss of humidity (air supply is large, the enthalpy difference between the air supply is reduced).
2. Comfort air-conditioning air volume is small, low wind speed, only in the direction of the air supply local air circulation, can not form a whole air circulation in the room, the room cooling is not uniform, so that there is a regional temperature difference in the room, the direction of the air supply area temperature is low, the other areas of the temperature is high, the heat generating equipment due to the different placement of the location of the accumulation of heat in the local area, leading to overheating and damage to the equipment.
The special air conditioner for the server room has a large air supply volume and a high number of air exchanges in the server room (usually 30-60 times/hour), which can form an overall air circulation in the entire server room, so that all the equipment in the server room can be cooled on average.
3. The traditional comfort air conditioning, due to the small air supply, the number of air changes is small, the air in the room can not ensure that there is a high enough flow rate of dust will be brought back to the filter, and the equipment in the room to produce internal deposition, the equipment itself has a negative impact. And general comfort air conditioning unit filtering performance is poor, can not meet the purification requirements of the computer.
The use of special air conditioning room air volume, air circulation is good, at the same time, because of special air filters, can timely and efficiently filter out the dust in the air to maintain the cleanliness of the computer room.
4. Because most of the electronic equipment in the room are continuous operation, long working hours, so the special air-conditioning requirements of the room can be designed to large loads of continuous operation all year round, and to maintain a high degree of reliability. Comfort air conditioning is more difficult to meet the requirements, especially in winter, the computer room because of its sealing and heating equipment and more, still need air conditioning unit normal refrigeration work, at this time, the general comfort air conditioning due to outdoor condensing pressure is too low has been difficult to work properly, the machine room air conditioning through the controllable outdoor condenser, can still be a normal guarantee of refrigeration cycle work.
5. machine room air conditioning is generally also equipped with a special humidification system, high-efficiency dehumidification system and electrical heating compensation system, through the microprocessor, according to the sensor feedback data can accurately control the temperature and humidity in the room, and comfort air conditioning is generally not equipped with a humidification system, can only control the temperature and lower accuracy, humidity is more difficult to control, and can not meet the needs of the equipment in the machine 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. has been widely used to improve the reliability of the computer room, network, communication system and the economy of operation.
Scope of application
Machine room precision air-conditioning machine is widely used in computer rooms, program-controlled switching machine rooms, satellite mobile communication stations, large medical equipment rooms, laboratories, test rooms, precision electronic instruments production workshop and other high-precision environment, such an environment for air temperature, humidity, cleanliness, air distribution and other indicators have high requirements, must be 365 days a year, 24 hours a day, safe and reliable operation of the special equipment room precision air conditioning equipment to protect
Features
Significant heat
Mainframe installed in the computer room and peripherals, servers, switches, optical and other computer equipment, as well as power supply equipment, such as UPS power supply, will be heat transfer, convection, radiation, heat emitted into the room, which only cause the temperature in the room to rise, belonging to the apparent This heat only causes the temperature in the server room to rise, which is 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. Large and medium-sized 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%.
Small latent heat
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 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 enclosure of the room is sealed better, the new air is generally after the temperature and humidity pre-processing into the room, so the room latent heat is small.
Large air volume, small enthalpy difference
The heat of the equipment is transferred to the machine room through conduction, radiation, equipment, dense area of heat concentration, in order to make the temperature and humidity uniformity of all areas of the machine room, and to control the permissible base and fluctuations in the scope of the need for a larger volume of air to take away the residual heat. In addition, less latent heat in the room, generally do not need dehumidification, the air through the air conditioning machine 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
The equipment in the server room cooling 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 dual-channel utility power inter-commissioning, but also for the protection of important computer equipment, air-conditioning system should be a generator as a 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, in order to achieve the purpose of energy saving.
There are more ways to send back the air
The air supply method of the air conditioning room depends on the source of heat in the room and the distribution characteristics, for the equipment in the room is densely arranged, cables, bridges, and the way of alignment and other characteristics, the air conditioner is divided into the air supply method of lower send back, send back up, send back up, send back up, send back side to side, side send side to back.
Static pressure box air
Air conditioning in the room 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 the return air, static pressure box formed in the pressure regulator layer can make the air uniform, so that the static pressure of each point in the space is equal.
High cleanliness requirements
Electronic computer room has 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 room is required to be able to circulate air in accordance with the relevant standards of dust removal, 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. Host room and other rooms, corridors between the pressure difference should not be less than 4.9Pa, and outdoor static pressure difference should not be less than 9.8Pa.
Components
The main components of the precision air conditioning system of the computer room, the controller, including the compressor, evaporator, heater, air-cooled condenser, controller, humidification tank,
Thermal expansion valve, liquid-visual mirrors, filter drier, filters, and other components. , and other components. For the water-cooled series, the indoor unit also includes a plate heat exchanger, water flow regulating valve, and a solenoid valve for the water supply[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). Must first calculate the heat load of the computer room.
The heat load of the computer room mainly from two aspects:
One is the heat generated within the room
It includes: indoor computers and external equipment heat, the room auxiliary facilities and the 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); 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 intruded through the body of the building, such as from the walls, roofs, partitions and floors into the server room (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. The heat generated by the hot outdoor air (also including water vapor) intruding through windows and doors and other gaps (sensible and latent heat);
The heat generated by the fresh air introduced to reduce fatigue of indoor workers and to benefit human health (including sensible and latent heat).
In short, the heat released by the human body, the heat intruded 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, for different heat load conditions should be selected for different types of air conditioners. Usually use the apparent heat ratio (SFH) as an important indicator of the air conditioner.
Profile calculation (also known as estimation)
In the initial design stage of the room, in order to select the capacity of the air conditioning unit faster, this method can be used, that is, the unit area of the required cooling capacity for the estimation.
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 increases or decreases)
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 room heat, accounting for more than 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, in general, can provide specific values of the heat generated by the equipment. Otherwise, according to the computer's power consumption to calculate its heat generation.
a. Calculation of heat generation from external equipment
Q=860N¢ (kcal/h)
Where: N: power consumption (kW); ¢: while using the coefficient (0.2 ~ 0.5); 860: the thermal equivalent of the work, i.e., l kW of electrical energy all the way to the heat produced by thermal energy.
b. Calculation of heat generated by the host Q = 860 × P × h 1 × h 2 × h 3
In the formula, P: total power (kW);
h 1: coefficient of simultaneous use;
h 2: coefficient of utilization;
h 3: coefficient of uniformity of the work of the load.
The total power of the 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, so it must be corrected with the above three coefficients, which in turn are related to the computer's system structure, function, purpose, working condition and the electronic components used. The total coefficient is generally taken between 0.6 and 0.8 is good
c. Lighting equipment heat load calculation
The power consumption of the lighting equipment in the computer room, part of the light into a part of the heat. The part that becomes light also becomes heat because it is absorbed by buildings and equipment. Calculation of the heat load of the lighting equipment is as follows:
Q=C×P kcal/h
In the formula, P: the nominal rated output power of the lighting equipment (W);
C: the heat of each output of l W (kcal/h W), usually since the incandescent lamps 0.86, fluorescent lamps 1.0.
d. Human body heat
The heat of the human body Is released through the skin and respiratory organs, this heat contains water vapor, its heat load should be the apparent heat and latent heat load and the sum.
The heat emitted by the human body varies with the working condition. The staff in the room can be treated as light work. When the room temperature is 24℃, its sensible heat load is 56cal, latent heat load is 46cal; when the room temperature is 21℃, its sensible heat load is 65cal, latent heat load is 37ca1. In both cases, the total heat load is 102cal.
e.Conduction heat of enclosure structure
The conduction heat that enters into the room through the enclosure structure of the roof, wall, partition, etc. is a seasonal and seasonal heat load. Conducted heat is a quantity that is related to season, time of day, geographic location, and the angle of the sun, among other things. Therefore, it is a complex problem to accurately find such a quantity.
When the indoor and outdoor air temperature maintains a certain steady state, the heat transfer from the plane-shaped wall into the machine room can be calculated according to the following formula:
Q=KF(t1-t2) kcal/h
In which, K: the thermal conductivity of the enclosure structure (kcal/m2h℃);
F: the area of the enclosure structure (m2);
t1: temperature inside the room (℃);
t2: calculated temperature outside the room (℃).
When calculating the enclosure structure that is not in direct contact with the outdoor air, such as partitions, the difference between the indoor and outdoor calculated temperature should be multiplied by a correction factor, the value of which is usually taken as 0.4 to 0.7. Commonly used materials thermal conductivity is shown in the following table:
Materials Thermal Conductivity (kcal/m2h℃) Material Thermal Conductivity (kcal/m2h℃)
Ordinary Concrete 1.4 ~1.5 Gypsum board 0.2
Lightweight concrete 0.5~0.7 Asbestos cement board 1
Mortar 1.3 Flexible fiberboard 0.15
Cooked gypsum 0.5 Fiberglass 0.03
Bricks 1.1 Galvanized steel sheet 38
Glass 0.7 Aluminum sheet 180
Wood 0.1~0.25
f. Solar radiation from the glass
When the glass is irradiated by sunlight, part of it is reflected, part of it is absorbed by the glass, and the rest of it shoots through the glass into the room and is converted 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.
The heat entering the room through the glass can be calculated according to the following formula:
Q=KFq (kcal/h )
In which, K: the solar radiation heat transmission coefficient;
F: the area of the glass window (m2);
q: the intensity of the solar radiation heat entering through the glass window (kcal/m2h).
The value of the coefficient of transmission 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 sun exposure. Please refer to local meteorological data for specific values.
g. Heat load of air exchange and outdoor intrusion
In order to continuously replenish fresh air for the staff working in the computer room and 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, and this fresh air will also become a 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 air volume to determine the heat load.
h. Other heat load
In the room, in addition to the above heat load, in the work of the use of the show was used, soldering iron, vacuum cleaner, etc. will become a heat load. As the power consumption of these devices are generally small, can be roughly calculated by its rated input power and the product of the heat equivalent of the work. In addition, the computer room uses a large number of transmission cables, also is the heat generator. Its calculation is as follows:
Q=860 Pl (kcal/h)
In the formula, 860: the heat equivalent of the work (kca1/h);
P: the power consumption per meter of cable (W); l: the length of the cable (m).
In short, the heat load of the computer room should be determined by the sum of the heat load of each of the above a-h.