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Fig.1 : Determination chart for DINDAN cooling unit.
**Determine position from area and temperature them , if have , add the fan factor to new position.


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1. Determination chart



Determination of cooling capacity is considered by Determination chart (Fig.1)

In case of using fan as ventilator to outside their should be added ventilation factor to the determination chart , for which should be shutted off after installation of cooling unit.

The factor is depend on different temperature to ambient and size of fan.




2. Nature of heat distribution



Heat normally generated inside the cabinet controller by operating equipments. Without cooling equipment, the temperature will be higher than its ambient and the heat inside will transfer out through the wall of cabinet. The temperature will balance by heat transfer as shown in Fig. 2.1, explaining the inverter working around 50°c and the smaller working at 40°c , while the total temperature inside is 37-39°c in most of cases




Fig. 2.1 : Illustration of heat distribution in cabinet before installation cooling unit.


The top side of cabinet will shown higher temperature. How much heat transferring out depend on difference between temperature of the wall to ambient. In the case of more heat source such boiler stand at backside of cabinet making ambient only at the backside around 50°c as in Fig. 2.2 The heat will transfer in only in the area from backside of cabinet while the other side still transfer out.


Fig. 2.2 : Heat distribution of cabinet with boiler is considered.


After installation of cooling unit the temperature inside keep lower than ambient. On the other hand, the heat will transfer back from its 33°c ambient to inside which is 28-31°c. Fig. 2.3 Illustrate the cooling unit supply air 20°c to cabinet which could maintain 28°c at bottom and 31°c at top of cabinet. Regarding to lower temperature have more higher mass weight. The higher ambient 33°c will make heat transfer back to the cabinet. While the inverter may operate at slightly higher than its cabinet which is 30-35°c.


Fig. 2.3 : Illustration of heat distribution in cabinet after installation cooling unit.




3. For cabinet designer



Forecasting heat loss from equipment shall be employed when total area and average temperature are impossible. There should be consider two terms. 

3.1 We approximate heat to be lost from equipment 3-5% of its power consumption. Not consider yet whether it is full load or not.Considered as listed.



-Switching power supply, Inverter, Transformer, PLC, SCR, Monitor, Servo drive

3.2 Heat inward from outside ambient while maintaining the lower temperature inside cabinet.
Calculate the heat ransfer by the convection via the total area of cabinet.


Heat = H*A*dt



Heat = H*A*dt

H , coefficient of heat convection between air at 25°c and metal sheet
(= 5 W/m2.k)

A , Total area of the cabinet = (WxDx2)+(WxHx2)+(HxDx2) (unit= m^2)

dt, different temperature between inside and ambient , (unit= °c)


4. Proper condition


Temperature around 28-32°c should be maintain in the cabinet.As shown in fig.1 before cooling operation it is 45°c which is different to ambient 7°c and the area is 2.4 m2. As according to determination chart.

Fig. 4.1 : example of temperature data collected between befor and after operation of cooling unit


Heat load calculator


Height (mm.)

Width (mm.)

Depth (mm.)

T. inside (upper)*

T. inside (lower)*

T. ambient**

T. require***

*T. inside (upper/lower)= Temperature around upper/lower part inside the machine when all sides are covered.

Measure the machine when it has been running for at least 20 minutes.
** T. ambient= Temperature around the machine when measure T. inside
***T. require= Setting temperature inside the machine after installing cooling unit.