Solutions for cooling of equipment

Climate control enclosure can be operated for many years, however such factors as condensate, humidity, temperature drop significantly reduce the service life and stable operation of equipment. Specialists will agree that optimal temperature in an enclosure is a guarantee of safe, long-term and comfortable operation.

Cooling in climate control enclosures is divided into passive and active one. Passive cooling provides for such arrangement of internal space, which ensures free circulation of air in unoccupied space of the enclosure, which air comes into the enclosure and exits it through holes in perforated doors and walls. However not always the passive cooling is sufficient. In most cases in order to maintain operating micro-climate of the equipment the active cooling shall be arranged.

For arrangement of active cooling the following is used:

forced ventilation;

• air conditioners;
• head exchangers.
• Forced ventilation

Cooling by means of fans is efficient when temperature of ambient environment is 10 degrees lower than the temperature recommended for equipment inside of the enclosure. With the purpose of efficient air circulation the fan units will be installed on the bottom and on the roof of enclosure. Bottom fans are designed to blow cool air masses into the enclosure body whereas coolers on the roof discharge heated air outside of the structure. One more option of fan units installation is fixing them on side walls of enclosure. Longitudinal cooling of equipment will be effected this way, which also ensures effective protection from overheating.

Air flow parameter can be calculated using the formula:

V = 3.1 * Qv / ΔT,

Where, 3,1 is air constant value,

Qv – heat emission from components in control enclosure,

ΔT – difference of temperatures between maximum allowable air temperature inside of enclosure and ambient temperature.

If device requires protective way of cooling usually two basic options are distinguished: air conditioner or heat exchanger.

Air conditioners are applied in the following cases:

if temperature inside of the body is not higher than ambient temperature;

if it is necessary to reduce humidity;

if electronic system generates medium or large amount of heat.

Cooling capacity of air conditioner shall be not lower than the heat load generated by electrical equipment.

Total heat load is generated by two sources:

a) electronic components (so called internal heat load);

b) heat of ambient environment (i.e. heat exchange can significantly increase overall heat load on the system especially under high air temperature or in case the body is subject to direct impact of sun rays).

In order to calculate productivity of air conditioner the following formula shall be used:

Pк = Qv - Pr,

where Pк – air conditioner productivity;

Qv – heat emission from components in control enclosure;

Pr [Watt] – heat output through enclosure body walls (without consideration of insulation ratio).

Pr = k × A × ΔT,

k – heat output ratio;

А- wall surface area, which is in contact with the ambient environment, m2;

ΔT – difference between maximum allowable air temperature inside of enclosure and ambient temperature

Air conditioner capacity is determined as per efficiency chart, which you can see on the picture. Air conditioner efficiency shall be higher than the level of heat loss from the components approximately by 10%.

Efficiency curve for determination of air conditioner capacity

Heat output ratio is radiation power per 1 m2 of surface area. It is a constant value and depends on material:

Material	Heat output ratio, k
Steel sheet	5,5 W/m2
Stainless steel	5,5 W/m2
Aluminum	12,0 W/m2
Plastic	3,5 W/m2

Surface area is measured in accordance with VDE 0660 part 500 specification. Calculation depends on location of enclosure:

One enclosure, free standing A = 1,8H · (W + D) + 1,4 · W · D

One enclosure, wall mounted A = 1,4 · W · (H + D) + 1,8 · D · H

Utmost enclosure, free standing in a row  A = 1,4 · D · (H + W) + 1,8 · W · H

Utmost enclosure, wall mounted A = 1,4 · H · (W + D) + 1,4 · W · D

Not utmost enclosure, free standing in a row A = 1,8 · W · H + 1,4 · W · D + D · H

Not utmost enclosure, to be mounted onto wall А = 1,4 · W · (H + D) + D · H

Not utmost enclosure, to be mounted into wall, under a canopy  A = 1,4 · W · H + 0,7 · W · D + D · H

Where W is enclosure width, H is enclosure height, D is enclosure depth, measured in meters.

Difference between air temperature inside and outside of enclosure is measured in Kelvins (temperature difference in Kelvins is equal to temperature difference in Celsius).

The difference is found by deducting the ambient temperature value from the value of temperature inside of enclosure:

ΔT = Ti - Ta, where

Ti – temperature inside of enclosure;

Ta – ambient temperature.

If ambient environment temperature is below zero, for example, Ta = 10°C, whereas the required temperature inside of enclosure is Ti = +35°C, then

ΔT = 35 - (-10) = 35 + 10 = 45°K

By putting the formula of enclosure heat output into general equation the general equation of thermal balance will be as follows:

Pk = Pv - k · A · ΔT [Watt] 

Positive value of obtained capacity shows that cooling shall be applied, whereas a negative value shows that heating shall be used.

Heat exchangers are deployed for discharge of heat from body to outside atmosphere in the following cases:

if electronic equipment can operate under a temperature higher that ambient environment temperature;

if humidity level does not matter;

if the system generates small or medium amount of heat.

Cooling capacity of heat exchangers

Selection of a heat exchanger is similar to that of an air conditioner, in both cases it is necessary to eliminate internal heat load inside of electronic equipment body. Cooling capacity of heat exchanger is calculated by dividing the value of actual heat load by ΔT – difference between maximum temperature of ambient environment outside the body and maximum allowable operating temperature of electronic equipment.

Pс = (Qv - Pr) / ΔT,

Pс – efficiency of heat exchanger;

Qv – heat emission from components in control enclosure;

Pr [Watt] – heat output through enclosure body walls (without consideration of insulation ratio);

ΔT – difference between maximum allowable air temperature inside of enclosure and outside temperature.

The obtained value is the minimum cooling capacity of heat exchanger. In case no heat exchanger model is available with a nominal value equal to the obtained value, then a higher capacity heat exchanger shall be chosen.

You can receive professional consultation from our engineers.