I am working on a project involving a Peltier (TEC) module, and I need to calculate the total heat load for the hot side so I can spec out a heatsink. I'm sure it's pretty straight forward, but I'm having trouble finding an exact formula that shows that value.

For a given electrical input on the TEC (Vtec [volts], Itec [amps]), and a given temperature differential (deltaT [deg C]), there is a specified amount of heat transferred from one side to the other (Qtransfer [Watts]). I can find that information very easily from the device datasheet. And as far as I understand it, Qtransfer will be subtracted from the cold side and will be added to the hot side, in an ideal case. So my question is: what is the thermal load on the hot side?

Is it:

1) Qtransfer + (Vtec x Itec)

or

2) Qtransfer + ( (Vtec x Itec) x efficiency constant), where the efficiency constant is between 0 and 1, and it accounts for the work being done due to the peltier effect.

So another way to ask the question is, does all the electrical power that goes into the TEC get converted to heat, or does some of it get used up by the peltier effect? If not all the electrical power is converted to heat, what are some typical values for the "efficiency constant"?

Thank you,

Owen