意大利GM安全栅 D1043Q 常州吉盟（华东总代理）

of Electronic Equipments in the Cabinet

All electronic equipment operate using electrical power Ａnd dissipate part of it into heat which is generally removed by the surrounding

ambient air Ａnd determines an increase in the operating temperature. High operating temperatures reduce their life Ａnd increase the

probability of failures according to the Arrhenius criteria, for example an operating temperature increase from 25 to 50 °C can cause a

failure rate ten times higher.

In a cabinet air circulates Ａnd removes heat by convection (natural convection cooling) or, more effectively, by forced ventilation (fans)

or even more effectively by refrigerated forced ventilation (air conditioning). Installation of electronics in cabinets restricts free air

movement Ａnd rises their internal temperature. These effects can be reduced in two concurring lines of action:

• by limiting the power dissipation Ａnd the heat produced inside the cabinet

• by encouraging air circulation (and exchange of heat) inside the cabinet

A simple way to improve air circulation is to provide sPACe between the isolators, also installing isolators in horizontally oriented DIN rail

rows with the enclosure main surfaces oriented vertically allows better air circulation inside the enclosure Ａnd significantly improves

heat exchange.

What ultimately determines the operating temperature rise inside a cabinet is the total power dissipation Ａnd the provisions available

for removing the heat with cool air (natural convectionＯrforced cooling). The maximum power consumption of each type of isolator is

specified in the corresponding data sheet so by summing the power of each unit in the cabinet the total power Pmax can be easily

found. In normal operating conditions however the power dissipated by the installed equipments is not likely to be the maximum value

specified for all of them Ａnd at the same time, the value of the effective power Peff can therefore be considered smaller (typical 70 %)

than the value Pmax:

Peff ≤ Σ Pmax * 70 %

1) Closed Cabinets with Natural Convection

Closed cabinets are preferred in dustyＯrharsh environments where they offer a better equipment protection but their heat / power

dissipation capability is modest. Heat is removed by air flowing internally Ａnd exchanged with the walls of the cabinet, the calculation of

the maximum allowed power dissipation in this type of cabinet is:

Pmax = Δt * S * K

where: Pmax [W] maximum allowed power dissipation

Δt [°C] maximum allowed temperature rise

S [m²] free heat emitting surface of the cabinet

K [W/m² * °C] thermal conductivity coefficient (K=5.5 for painted steel sheets)

As an example a cabinet sized 600x600 mm Ａnd 2000 mm high has a temperature rise of 10 °C for an installed power of 250 W.

2) Open Cabinets with Natural Convection

Open cabinets must operate in clean environments, their heat / power dissipation capability is medium.

Heat is removed by air flowing through the equipment, circulating from bottom to top of cabinet (convection). Depending on the type of

engineering (freedom of cool air to enter at the bottom of the cabinet, to circulate vertically around the equipment extracting heat Ａnd to

exit at the top of the cabinet), the power dissipation improvement can be two times better than case 1.

The cabinet must be equipped with inlet Ａnd outlet louvers in the lower Ａnd upper ends of the cabinets, vertical air flow inside and

outside the cabinet must be kept free from obstacles to enhance the “chimney effect” air circulation.

As an example a cabinet sized 600x600 mm Ａnd 2000 mm high has a temperature rise of 10 °C for an installed power of 350 W.

3) Open Cabinets with Forced Ventilation

Open cabinets must operate in clean environments, their heat / power dissipation capability is high with forced ventilation

Air is forced into the louvers on the bottom of cabinet, flows through the equipments, Ａnd finally exits at the top of the cabinet, where

generally is forced by oneＯrmore fans. The calculation of the required airflow is:

Q = 3.1 * Peff / Δt

where: Q [m³/h] is the required airflow

Peff [W] is the dissipated power (typical 70 % of the maximum power dissipation)

Δt [°C] is the maximum allowed temperature rise in the cabinet

As an example a cabinet sized 600x600 mm Ａnd 2000 mm high has a temperature rise of 10 °C for an installed power of 500 W.

4) Closed Cabinets with Forced Ventilation Ａnd Heat Exchanger

Closed cabinets with forced ventilation are preferred in high dissipated power Ａnd harsh environment where natural convection

cabinets cannot be used. Hot air is extracted from the cabinet by a fan, cooled by a heat exchanger (using a cooling fan with ambient

air) Ａnd forced back into the cabinet; depending on the type of engineering the improvement can reach a 5 times higher power

dissipation than in case 1.

As an example a cabinet sized 600x600 mm Ａnd 2000 mm high has a temperature rise of 10 °C for an installed power of 1000 W.

5) Air Conditioned Cabinets

Air conditioned cabinets are preferred in hot climates Ａnd /Ｏrharsh environments.

Cabinet temperature can become equalＯreven lower than the ambient temperature. A specific refrigerating systemＯrthe existing air

conditioning system can be used for cabinet conditioning.

As an example a cabinet sized 600x600 mm Ａnd 2000 mm high has a temperature rise of 10 °C for an installed power of 1000 W.