The load calculation formula of computer room air conditioner

The load calculation formula of computer room air conditioner

How to obtain heat and cooling load in the computer room and how to calculate the cooling capacity required in the constant temperature and humidity room. To

　　 1. The heat and cooling load of the computer room

　　 (1) Heat in the computer room:

　　 Under the influence of indoor and outdoor heat and humidity disturbances, the total heat and humidity entering an air-conditioned room at a certain moment are called the heat gain and humidity gain at that moment. If the heat gain is negative, it is called heat consumption. According to different properties, the heat gain is divided into sensible heat and latent heat, and sensible heat includes convective heat and radiant heat.

　　1. The source of apparent heat in the computer room:

　　 (1), the solar radiant heat that enters the room through the external window;

　　(2). Pass the heat inside the room through the enclosure structure;

　　(3), equipment heat dissipation;

　　 (4), human body heat dissipation;

　　(5), lighting heat dissipation;

　　(6), the heat dissipation of fresh air.

　　2. Source of latent heat in the computer room:

　　(1), the amount of heat dissipation from the human body of the staff;

　　(2), the heat dissipation of the infiltration air and fresh air ventilation.

　　(2) Cooling load of the computer room:

　　 In order to maintain a stable temperature and humidity in the room at a certain moment, the amount of cold that needs to be supplied to the room air is called cooling load. On the contrary, the heat that needs to be supplied to the room to compensate for the heat loss in the room is called the heat load. The amount of humidity removed or added from the room to maintain the relative humidity in the room is called the humidity load.

　　Cooling load and heat gain are sometimes equal in quantity, sometimes not equal. The thermal characteristics of the envelope structure and the type of heat gain determine the relationship between heat gain and load. The latent heat gain in the instantaneous heat gain and the convective component in the sensible heat gain are the heat directly dissipated into the room air, and they immediately constitute the instantaneous load. Most of the heat dissipation of the computer in the computer room constitutes an instantaneous load. For example, the CPU heat sink is in direct contact with the surface of the CPU. The heat on the CPU surface is transferred to the CPU heat sink through thermal conduction. The cooling fan generates airflow to take away the heat from the surface of the CPU heat sink through thermal convection. , And the flow of air in the chassis is also through thermal convection to take away the heat of the air around the CPU heat sink to the outside of the chassis.

The radiant components in the sensible heat gain, such as the instantaneous solar gain and the radiant heat of the external window, cannot immediately constitute the instantaneous cooling load, because the laser heat is absorbed and stored by the surface of various indoor objects through the air. Once the surface temperature is higher than the indoor air temperature, they will radiate the stored heat to the air in a convective manner.

　　 2. How to calculate the cooling capacity required in the constant temperature and humidity room

　　In order to determine the capacity of the air conditioner to meet the requirements of the room temperature, humidity, cleanliness and air supply speed (referred to as the four-degree requirement). Must s* the heat load of the computer room first.

　　 (1) The heat load of the computer room mainly comes from two aspects:

　　1. The heat generated inside the computer room includes:

　　 (1) The calorific value of indoor computers and external equipment, the calorific value of auxiliary facilities and equipment in the computer room (electric heating, steam water temperature and other heating elements). These calories are large in sensible heat but low in latent heat; lighting generates heat (sensible heat);

　　 (2) The fever of the staff (small sensible heat, large latent heat);

　　 (3). Heat (latent heat) due to evaporation and condensation of water.

　　2. Heat generated outside the computer room, including:

　　 (1), conduction heat: the heat invaded through the building body, such as the heat (sensible heat) transmitted into the computer room from the wall, roof, partition and ground;

　　 (2), radiant heat (also called radiant heat): the heat (sensible heat) that enters the room directly from the glass window due to the sun's rays;

　　 (3), heat generated by convection;

　　 (4) The heat (sensible heat, latent heat) generated by the high-temperature outdoor air (also including water vapor) invaded from the gaps in doors and windows;

　　(5) The heat (including sensible heat and latent heat) generated by the fresh air introduced in order to reduce fatigue of indoor workers and benefit human health.

　　 In short, the heat emitted by the human body, the heat invaded by the crevice wind, and the heat brought in by the ventilation will not only increase the room temperature, but also increase the humidity in the room, so dehumidification is required. This part of the heat load is called latent heat load, and the heat dissipated by all equipment in the computer room is only the increase in indoor temperature. This heat load is called sensible heat load. Unlike general hotels, offices, conference rooms, etc., which account for a large proportion of latent heat, the heat load in the computer and program-controlled computer room is dominated by sensible heat load. Therefore, different types of air conditioners should be selected for occasions with different heat load conditions. The sensible heat ratio (SFH) is usually used as an important indicator of air conditioners.

　　 (two) rough calculation (also called estimation)

　　In the initial design stage of the computer room, in order to quickly select the capacity of the air conditioner, this method can be used, which is to estimate the cooling capacity per unit area.

　　 1. Computer room (including program control exchange room):

　　 (1) When the floor is higher: 250～300kcal/m2h;

　　 (2) When the floor is low: 150～250kcal/m2h (appropriate increase or decrease according to the density of the equipment).

　　2. Office (duty room): 90kcal/m2h.

　　 (3) Simple heat load calculation

Computer room air-conditioning load mainly comes from the heat generated by computer equipment, external equipment and computer room equipment, accounting for more than 80% of the total heat, followed by lighting heat, conduction heat, radiant heat, etc. These calculation methods are the same as those of general air-conditioned rooms The load calculation is the same. Computer manufacturers can generally provide specific values ​​for the heat generated by the equipment. Otherwise, calculate the calorific value according to the power consumption of the computer.

　　 1. Calculation of calorific value of external equipment:

　　Q＝860N￠(kcal／h)

　　 where:

　　(1), N: power consumption (kW);

　　(2), ￠: simultaneous use coefficient (0.2～0.5);

　　(3), 860: The heat equivalent of work, that is, the heat generated when all lGW electric energy is converted into thermal energy.

　　2. Calculation of the calorific value of the host:

　　Q=860×P×h1×h2×h3

　　 where:

　　(1), P: total power (kW);

　　(2), h1: simultaneous use coefficient;

　　(3), h2: utilization factor;

　　 (4), h3: load work uniformity coefficient.

The total power of various equipment in the computer room should be based on the z* maximum power consumption of the equipment in the computer room. However, these power consumptions are not all converted into heat. Therefore, the above three coefficients must be used to correct them. The system structure, function, purpose, working status and electronic components used. The total coefficient is generally between 0.6 and 0.8.

　　3. Calculation of heat load of lighting equipment:

　　 The power consumption of the lighting equipment in the computer room is partly turned into light and partly turned into heat. The part that becomes light also becomes heat because it is absorbed by buildings and equipment.

　　The heat load of lighting equipment is calculated as follows:

　　Q=C×Pkcal／h

　　 where:

　　(1), P: the nominal rated output power of the lighting equipment (W);

　　(2), C: The heat per output 1W (kcal/hW), usually 0.86 from incandescent lamp, 1.0 from fluorescent lamp.

　　 4. Human body heat:

　　 The heat in the human body is released through the skin and respiratory organs. This heat contains water vapor, and its heat load should be the sum of sensible heat and latent heat load.

　　The heat generated by the human body varies with the working conditions. The staff in the computer room can handle light physical 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 37cal. In both cases, the total heat load is 102cal.

　　5. Conduction heat of enclosure structure:

　　The conduction heat entering the computer room through the roof, walls, partitions and other enclosures of the computer room is a quantity related to the season, time, geographic location, and the angle of the sun. Therefore, it is very complicated to accurately obtain such a quantity.

　　 When the indoor and outdoor air temperature maintains a certain stable state, the heat transferred from the flat wall into the computer room can be calculated as follows:

　　Q=KF(t1-t2)kcal／h

　　 where:

　　(1), K: thermal conductivity of the enclosure structure (kcal/m2h℃);

　　(2), F: Enclosure structure area (m2);

　　(3), t1: temperature in the computer room (℃);

　　(4), t2: the calculated temperature outside the computer room (℃).

　　 When calculating enclosure structures that are not in direct contact with outdoor air, such as partitions, the calculated temperature difference between indoor and outdoor should be multiplied by a correction coefficient, which is usually 0.4-0.7. The thermal conductivity of commonly used materials is shown in the following table:

　　 (1), thermal conductivity of material (kcal/m2h℃) thermal conductivity of material (kcal/m2h℃);

　　 (2), ordinary concrete 1.4～1.5 gypsum board 0.2;

　　(3), light concrete 0.5～0.7 asbestos cement board 1;

　　 (4), mortar 1.3 soft fiberboard 0.15;

　　(5), plaster of Paris 0.5 glass fiber 0.03;

　　(6), brick 1.1 galvanized steel sheet 38;

　　 (7), glass 0.7 aluminum plate 180;

　　 (8), wood 0.1～0.25.

　　 6. Solar radiant heat penetrating through glass:

　　 When the glass is irradiated by sunlight, part of it is reflected and part is absorbed by the glass, and the rest is shot through the glass into the computer room and converted into heat. The heat absorbed by the glass increases the temperature of the glass, and part of it enters the computer room through convection and becomes a heat load.

　　 The heat entering the room through the glass can be calculated as follows:

　　Q=KFq(kcal／h)

　　 where:

　　(1), K: penetration coefficient of solar radiant heat;

　　(2), F: the area of the glass window (m2);

　　(3), q: the intensity of solar radiation heat entering through the glass window (kcal/m2h).

　　The penetration coefficient K depends on the type of window, usually 0.36～0.4.

　　 The solar radiant heat intensity q varies with latitude, season and time, and also varies with the angle of the sun. Please refer to local meteorological data for specific values.

　　7. Heat load for ventilation and outdoor invasion:

　　 In order to constantly replenish fresh air for the staff in the computer room and maintain the positive pressure in the computer room with ventilation, 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. The amount of outdoor air invaded through the gaps of doors, windows and switches varies according to the degree of sealing of the house, the number of people coming in and out and the wind speed outside. This kind of heat load is usually very small. If necessary, it can be divided into the air exchange rate of the room to determine the heat load.

　　 8. Other heat load:

　　In the computer room, in addition to the above-mentioned heat load, the use of quilts, soldering irons, vacuum cleaners, etc. during work will all become heat loads. Since the power consumption of these devices is generally small, it can be calculated roughly based on the product of its rated input power and the heat equivalent of work. In addition, a large number of transmission cables are used in the machine room, which are also heating elements.

　　 Its calculation is as follows:

　　Q=860Pl(kcal／h)

　　 where:

　　 (1) 860: The heat equivalent of work (kca1/h);

　　(2) P: power consumption per meter of cable (W);

　　(3)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 loads of 1 to 8 above.