How to Choose

Calculate the heat load

To calculate “how much heat should be taken off” when the cooling target is going to be cooled down. The heat released from the cooling item is not generally included, and it is ok to only consider “the heat quantity from the ambient environment coming into the cooling target”.

A.To cool an enclosure like a refrigerator

Since it is a closed space, the thermal resistance can be calculated from the thermal conductivity and thickness of insulation.

B.An object without any insulation (cannot add)

Calculate convectional thermal conductivity from the surface area of cooling target.

C.To cool fluid (liquid or gas)

Necessary heat removal for cooling from the temperature at inlet to the temperature at outlet in the decided period (flow rate) can be calculated by the product of liquid’s specific heat density, flow rate, and temperature difference. Depending on the flow rate, it might need a much large cooling power that a thermoelectric cooler (module) cannot realistically reach. Moreover, ambient heat will come into cooling liquid in half way of tube, so please consider the last item(-B) as well.

Efficiency

The thermoelectric module is also owns energy efficient, 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 the 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, a large temperature difference will make heat absorption go up as well. Therefore, it is not necessary to care about 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 to the maximum heat absorption as an indicator, but in realistic conditions of larger temperature difference and smaller heat absorption, around 10%-30% of maximum heat absorption is the most used case. In actual situations, you have to consider the operating voltage or module size, etc., so please refer the performance graph to make your final decision.

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.