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Heat Load Calculation		  
 

1. Determination chart
2. Nature of heat distribution
3. For cabinet designer
4. Proper designed

  
     
  1. Determination chart  
 
Fig.1.1 : Equivalent factor of fan cooling variation with different temperature.		 Making decision whether which cooling unit shall be installed on those cabinets
have to collect nearly exact two physical terms.

   - Totally area of the cabinet , m2
      Consider total area enclosing cabinet. For normally is
      2(WxD)+2(WxH)+2(HxD)

   - Average inside cabinet temperature , °c
     Consider average temperature of overall space
     in normally operation or full load

Determination of cooling capacity is considered by Determination chart Fig.1.2
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 as
according to Fig.1.1
 
Determination chart for LINEAR cooling unit.
 
Fig.1.2 : Determination chart for DINDAN cooling unit.
**Determine position from area and temperature them , if have , add the fan factor to new position.
     
  2. Nature of heat distribution  
 
Fig. 2.1 : Illustration of heat distribution in cabinet before installation cooling unit.

Normally of cabinet controller will generate heat
inside by the operating equipments.
nature. If they have no cooling equipment the
temperaturewill be higher than its ambient
and the heat inside will transfer out through
the wall of cabinet to outside. The temperature
will balance by heat transfer Fig. 2.1 Show the
inverter working around 50°c and the smaller
working at 40°c . while the total temperature
inside is 37-39°c. Most of cases

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

The top side of cabinet will shown higher temperature.
How much heat transferring out is depend on how
different temperature 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. 2.3 : Illustration of heat distribution in cabinet after installation cooling unit.

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.
     
  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.

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

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
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) , m2
dt, different temperature between inside and ambient , °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

 
     
       
     


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