How to Choose
Calculate the heat load
To calculate "how much of heat should be taken off" when the cooling target is going to be cooled down. Not included the cooling item releasing the heat, generally while the cooling target is getting cold, and it is ok to only consider "the heat quantity from ambient environment come into the cooling target".
A.To cool the enclosure like refrigerator
Since it is the closed enclosure, the thermal resistance can be calculated from the thermal conductivity and thickness of insulation.
B.Object without any insulation (cannot add)
To calculate convectional thermal conductivity from the surface area of cooling target.
C.To cool fluid (liquid or gas)Necessary heat removal for cooling inlet to outlet temperature in the decided period (flow rate) can be calculate by the product of liquid's specific heat density, flow rate, and temperature difference. Depending on the flow rate, it might need quite large cooling power that thermoelectric cooler (module) cannot reach in reality. Moreover, the heat from ambient will come into cooling liquid in half way of tube, so please consider the last item-B as well.
Efficiency
Thermoelectric module also owns energy efficiency, which is defined as COP (Coefficient Of Performance). Based on the rate of how much you input the electric power (P) on cooler and how much it actually worked (=Heat Absorption Q), which is (Q / P). However, this value of thermoelectric cooler in application is very small, for example, compact refrigerator (in general) is approximately 0.2.
The maximum value of coefficient of performance (COPmax) is decided by current value and temperature difference. However, it is not possible to obtain a maximum COP in the region of small current value and temperature difference. In real application, large temperature difference will make heat absorption go up as well. Therefore, it is not necessary to care the maximum of efficiency (COPmax), but in order to increase a little COP, it is very important to "raise the heat exchange capability" on both sides of thermoelectric module.
Choice
Choose a thermoelectric module based on your needed cooling capability. You can refer the maximum heat absorption as an indicator, but in reality used in the condition of larger temperature difference and smaller heat absorption, so around 10%-30% of maximum heat absorption is the most used case. In actual situation, you have to consider the operating voltage or module size, etc., so please refer the performance graph to decide finally.
In case of needing small heat absorption and large temperature difference on application, Cascade (multi-stage) model will be a choice. Please use the following maximum temperature difference as an indicator. If internal temperature difference of a general thermoelectric module is around 50 C, it is smart to use single-stage module.
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The maximum temperature difference (Th=27°C)
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Single stage Thermoelectric Module
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68~70°C
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FPH1/FPM1 series
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2-stage Thermoelectric Module
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85~95°C
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FPK2 series
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