Actually a lot of the pump heat comes from electrical resistances in the motor itself as a result of the electro-magnetive effect that is turning the shaft impeller.
Pumps are anywhere from as little as 5%, to as high as 70% efficient in terms of input power being converted in motive force.
The balance of the input power is typically converted into heat within the pump's body, which can either be radiated out through the pump's surface, or absorbed into the water flowing through the pump, or some combination of both.
What Ben is referring to is also a valid effect, and its effect grows in proportion to the total back-pressure head of the system. However for pumps consuming <40W of power, the frictional effect is rarely large enough to have a major impact on temperatures, but for pumps consuming 100W+, the frictional effect can be quite substantial. Between 40-100W is a grey area where how effective it all is depends on how well your radiators are dissipating the extra pumping heat.
|