Heat dissipation of electrical control cabinet (cabinet)
In the installation process of electrical equipment, more and more electrical control cabinets are installed on site or near mechanical equipment, which can save installation costs and reduce the complexity of the installation process.
However, the environment of industrial sites is different, and some are ideal, but the environment of many sites is relatively harsh, such as high temperature, dust, and water vapor. In addition, with the increasing popularity of new technologies such as variable frequency speed regulation and in order to meet various control needs, the use of heating elements in electrical control cabinets has become more and more common, such as: inverters, solid state relays, transformers, various rectifier modules and many more. In order to ensure the normal operation of various components in the electrical control cabinet, it is necessary to adopt various methods to ensure that a certain temperature is maintained in the electrical control cabinet.
Currently, fans (filter fans), heat exchangers, industrial air conditioners, etc. are generally used.
1. Fan (filter fan):
Fans (filter fans) are especially suitable for economical discharge of high heat loads. The use of fans (filter fans) is effective only when the temperature in the cabinet is higher than the ambient temperature. Fans (filter fans) are the most commonly used method.
Because hot air is lighter than cold air, the air flow in the cabinet should be from bottom to top. Therefore, under normal circumstances, the bottom of the front door or side wall of the cabinet should be used as the air inlet, and the top as the exhaust port.
1) If the environment of the work site is ideal, and there is no dust, oil mist, water vapor, etc. that affect the normal operation of the components in the electrical control cabinet, the air inlet can be equipped with a fan (axial fan), and the air outlet if possible Install a decorative panel. For safety and beauty, a fan decorative panel can be installed on the outside of the air inlet.
2) If the environment of the work site is not ideal, containing dust, oil mist, water vapor, etc., which affect the normal operation of various components in the electrical control cabinet, then L series filter fan sets should be selected at the air inlet and the exhaust outlet Filter grid to prevent dust, oil mist, water vapor, etc. from entering the electrical control cabinet. GU is simple and convenient, and the filter mat can be easily replaced. Filter mats are generally divided into non-woven fiber filter mats and fine filter mats. The non-woven fiber filter mat is used to prevent dust particles above 10 microns, and the fine filter mat is used to prevent dust particles below 10 microns.
The selection of the fan (filter fan) can be selected from the fan characteristic curve table based on the difference between the temperature in the cabinet and the ambient temperature and the heat loss in the cabinet.
2. Heat exchanger:
When the air circulation inside and outside the cabinet requires isolation, heat exchangers can also be considered.
According to their cooling medium, heat exchangers can generally be divided into: air/air heat exchanger (cooling medium is air), air/water heat exchanger (cooling medium is water). According to the installation method, they can be divided into: wall-mounted and top-mounted.
The air/air heat exchanger has two isolated air flow spaces, one is connected to the electrical control cabinet and the other is connected to the outside space. The hot air in the cabinet is sucked into the heat exchanger, and the heat of the hot air is passed through the heat sink. The heat pipe is transferred to the other end of the heat exchanger, and then the heat is discharged to the atmosphere through the flow of outside air. The prerequisite for using this heat exchanger is that the ambient temperature must be lower than the temperature in the cabinet.
The working principle of the air/water heat exchanger is the same as that of the air/air heat exchanger, except that the cooling medium is water. Its advantage is that it is specially used in places with a lot of dust, oil and high heat load. The power of the heat exchanger can be changed by adjusting the inlet water temperature and flow rate. However, there must be a water source.
The selection of heat exchangers is similar to the selection of fans and air conditioners.
3. Air conditioner:
Fans are suitable for the cabinet temperature higher than the ambient temperature, but when the ambient temperature is higher than the cabinet temperature or the ambient temperature is higher than the required temperature in the cabinet (generally 35 ℃), then you should consider using industrial air conditioners. In addition, when the air circulation inside and outside the cabinet is required to be isolated, industrial air conditioners should also be considered.
The air conditioner adopts the principle of compressor refrigeration for powerful cooling to achieve constant temperature control of the internal temperature of the electrical control cabinet. Since the air circulation inside and outside the electrical control cabinet is isolated from each other, it can effectively prevent harmful and humid gas and dust from entering the cabinet.
According to their installation methods, air conditioners can generally be divided into wall-mounted (side-mounted, embedded and rack-mounted in the cabinet) and top-mounted.
The selection of air conditioners is also based on the difference between the temperature in the cabinet and the ambient temperature and the heat loss in the cabinet to determine the cooling capacity required by the air conditioner. Now it is generally selected according to the empirical formula provided by the German company. The calculation is as follows:
QE=QV-KXAXΔT
Where: QE----Total cooling capacity (W);
QV----The total heat loss of the components in the cabinet (W);
K ---- Thermal conductivity (W/m2K), its value varies according to the cabinet material, generally speaking, steel plate is 5.5, aluminum plate is 11, and plastic is 0.3;
A ----The actual heat dissipation area of the cabinet (m2). The installation method of the cabinet has a great influence on the heat dissipation of the cabinet. Rittal provides calculations for the heat dissipation area of the following typical installation methods:
(Width=cabinet width, height=cabinet height, depth=cabinet depth)
1) A single cabinet with free space around: A=1.8X height X (width + depth) + 1.4X width X depth
2) A single cabinet for wall mounting: A=1.4X width X (height + depth) + 1.8X depth X height
3) Starting or terminal cabinet with free space around: A=1.4X width X (height + depth) + 1.8X width X height
4) Start or terminal cabinet for wall mounting: A=1.4X height X (width + depth) + 1.4X width X depth
5) The cabinet in the middle, with free space around: A=1.8X width X height + 1.4X width X depth + depth X height
6) The cabinet in the middle is used for wall mounting: A=1.4X width X (height + depth) + depth X height
7) The cabinet in the middle is used for wall mounting, and the top cover: A=1.4X width X height + 0.7X width X depth + depth X height
ΔT ----The temperature difference between the inside and outside of the cabinet, the temperature inside the cabinet (usually 35°C) minus the temperature outside the cabinet (ie the ambient temperature at the work site).
Pay attention to the following points when installing air conditioners:
1) The electrical control cabinet must be sealed;
2) The top-mounted air conditioner cannot bend the top plate of the electrical control cabinet. If necessary, strengthen the top plate;
3) Be sure to pay attention to the discharge of condensate. After installation, the condensate pipe should be inserted into the outlet hole to prevent the condensate from flowing into the cabinet. Nowadays, there are manufacturers that produce air conditioners without condensate discharge (condensate vaporizes quickly).
4) A door switch should be installed. The air conditioner should be cut off when the door is opened to avoid condensation in the cabinet. At the same time, the air conditioner can be switched on again after the door is closed for 5 minutes;
5) Keep the air circuit in the cabinet unblocked and avoid obstruction at the air inlet and outlet.
With the increasing maturity of air-conditioning technology, more and more users have put forward the requirements of installing air-conditioners in electrical control cabinets, and produce wall-mounted and ceiling-mounted air conditioners of various specifications. The maximum cooling capacity can reach more than 4000 watts, which can meet various requirements. Kind of user requirements.
4. Other:
1) If the environment of the work site is ideal, there are few heating components in the electrical control cabinet, and the heat generation can be solved by the heat dissipation of the cabinet itself, heat dissipation measures may not be considered.
2) When the ambient temperature is relatively high, or for other reasons, the above heat dissipation methods are not suitable for use, it may be necessary to establish an electrical control room to place the electrical control cabinet. The electrical control room can be established far away from the site, so that it will not be affected by the site, but it will increase the cost of cable laying, civil construction, air conditioning installation, etc., and it is very inconvenient for frequent operations; it can also be established At the site, it may be affected by the site, but it can save a lot of cable laying costs, only the cost of civil construction and air conditioning installation, and the operation is convenient. The easiest way is to use aluminum alloy to build an electrical control room on site, which can basically eliminate the impact of the site on the electrical control cabinet. This is a simple and easy method.