TECs are a wonderful invention and when implemented correctly can provide lower temperaturess than water or air cooling can ever achieve.

There are some considerations that need to taken into account when planning your TEC-based system. One of these is the increased heat dumped into the loop from the TEC.

The TEC requires electricity in order for it to transfer heat from one side to the other.

Though the electricity is ‘used up’ in this process, the energy within the electricity is not used up. In fact none of it is ‘used’; it is instead converted into heat and lost though the hot side of the TEC. All this energy is lost as heat because there is no other realistic form of energy that it can leave the TEC as. The energy can't be lost as light cause the TEC doesn't produce any light. It can't be lost as sound because it doesn't make any sound. This list could go on but you get my point. The energy leaving the TEC must equal that of the energy entering it. In the case of a TEC, the energy entering and leaving it is equal to the input wattage plus the wattage of the heat load being cooled.

An analogy of this is to think of electricity like petrol in your car. The petrol gets used up but the stored energy within the petrol does not. It is converted into kinetic energy (movement) light sound heat... the sum of the energy leaving the car will be the same as the energy entering it though the petrol. What goes in must come out in some form.

What this all means is that there can be a significant amount of extra heat being added to your loop, by the electricity being used by the TEC. I will now give you an example of how much more heat can be created by a TEC.

A 172 watt TEC cooling a 172 watt heat load (CPU) will use 360 watts of electricity, so the total heat load needing to be cooled by your cooling system would be 532watts... 360 watts form the TEC and 172watts from the CPU.

If we were to assume our cooling system has a C/W of 0.15 this would mean the CPU temps would be 80 degrees C above ambient!!! ...so about 100C. If we were to compare this to cooling our 172 watt heat load with only our cooling system (no TEC) the temps would be just 26 degrees above ambient.

This of course begs the question of how can a TEC cool a load below ambient. (Cooling your load at ambient or below should always be your goal. Otherwise you could probably do it cheaper with just straight water cooling.) The answer to the question is TEC selection. You never want to use a TEC that can only just manage to move the heat load applied to it. If you do you will get results like the above or worse!

What you want to do is buy the most powerful TEC that is practical. This is desirable because the effective delta (difference) between the hot side and cold side is affected by the heat load applied. The ΔT_max of a TEC is an indication of the maximum temperature difference between the hot and cold side with NO heat load applied. When a heat load is increased, this delta will decrease until it reaches 0 at Q_max. So therefore you always want a TEC to have a significantly higher Q_max than that of the load you are cooling.

I will now compare a 131 watt Q_maxTEC and a 65watt Q_maxTEC cooling a 65 watt load. The TEC's hot sides are being cooled by a cooler that has a C/W of 0.15 and the ambient temperature is 20 degrees C.

A 131 watt Q_max TEC running at U_max will cool a 65 watt load to 14.2 C (a delta of 5.8)

A 65 watt Q_max TEC running at U_max will cool a 65 watt load to 35.2 C (a delta of -15.2!)

You can now tweak the input voltage to find the TEC's sweet spot. This sweet spot will always be lower than U_max. This sweat spot occurs because as you lower the input voltage the TEC becomes more efficient and therefore more heat is moved for less heat being produced. The trade-off is that as you lower the voltage, less heat can be moved and the maximum temperature difference between the hot and cold side of the TEC is decreased. So you'll probably need to experiment to find this sweet spot for your system.

I will now compare two 131 Q_max TECs: one at Q_max (24.6v) and the other at 19 volts. The TECs are cooling a 65 watt load. The TEC's hot sides are being cooled by a cooler that has a C/W of 0.15 and the ambient temperature is 20 degrees C

A 131 watt TEC running at U_max (24.6 volts ) will cool a 65 watt load to 14.2 C (a delta of 5.8)

A 131 watt TEC running at 19 volts will cool a 65 watt load to 11.4 C (a delta of 8.6)