# Peltier AC Operating curve

I was looking at the product description of a 300W Peltier AC (Link) and encountered a curve like this

While I'm aware that there will be a dT between the Peltier hot and cold sides, I am not able to understand what's going on in the curve. Also, how can dT be an operational parameter considering it's dependent on the cooling setup on the hot side.

This curve tells you that this Peltier can move 20W from cold side to hot, against a 40C temperature gradient. Or 160W against a 20C gradient. Or 300W, but the cold side will reach the same temperature as the hot side.

So the cooling setup on the hot side determines the hot side temperature for any given power dissipation. Note the power dissipation is not just the pumped power, but the sum of pumped power and electrical power (apparently 48V * 13.6A or 650W).

Then use this table plus the specifics of what you are cooling to determine the cold side temperature.

So if you can keep the hot side to, say, 30C at 650+160W, you can cool something producing 160W down to 10C. Or at 650+20W, something producing 20W down to -10C.

Or given the mass and thermal capacity of the item being cooled, you can determine how the rate of cooling declines as the temperature falls.

• In the product description table in the shared link, it says 300W for both cooling and heating, how is this possible considering the heat rejected is much more than the cooling load? – Kv07 May 6 '19 at 8:12
• I think you would have to ask the manufacturer. It may be the amount of heat that can realistically be delivered by the small "cooling" side, the rest being sunk through the fan-cooled side. – Brian Drummond May 7 '19 at 22:02

Qc is the amount of heat that the device can pump from the hot side to the cold side.

Even with zero thermal load on the cold side it can only maintain ~42° deltaT.

With zero deltaT the device can pump 300W.

The graph dictates how much heat sinking you need to provide for the device to obtain a specific amount of cooling. For example if you want to maintain 20° cooling you can only support 160W of pumping.

Peltier devices have significant amounts of thermal conduction within the device itself from the hot to cold side that has to be supported in addition to the heat pumped from the cold side.

The heat sink not only needs to cool the heat pumped but also the losses of the Peltier device. There should be another graph giving information on the amount of electrical power input at that working point.