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Ed Anderson wrote:
Hi Al, Rusty,
My take is not that the EWP is 57 times more efficient than a mechanical water pump. If I understood the charts on the Davies EWP site, it indicates to me that a mechanical pump at engine rpm of 6000 may be a case of a lot of wasted power. In other words, at the higher rpm a lot of the energy is simply wasted in churning water through restrictions, surface friction and against head pressure.
That would seem to imply that perhaps a mechanical pump could be turned at a lot lower rpm and still provide adequate coolant circulation flow rate for cooling. If however, this is the case - you would have thought the OEM of autos would have jumped on that like a dog on a bone to gain a 5% increase. Although the cost/benefit trade-off reasons for manufacturing mulit million units may have dictated otherwise.
You also forget that the pump has to have sufficient pressure at low RPM. Think of the mechanical as a one speed pump with no off switch. You have to have sufficient pressure at all RPM, so there will be way to much at high RPM. "Well," the early engineers said, " gas is cheap." Then they had to put in a restrictive thermostat to regulate the temp. Again, gas is cheap.
I went to a school that had a HVAC system that ran the airconditioning whenever the fans blew, even in the winter. To get any circulation, the cooling had to be on. Each vent had a propane heater for the winter months. This building was put up before the oil crisis of the '70s, when gas was cheap. The reasoning was that the design was cheaper to build than a seperate system for heating and AC.
The EWP is the same game. Pump a lot of water and restrict what you don't need. Simple old school thinking. Don't hink of the EWP as 57 times more efficient, think of it as only pumping the 1/57th of coolant that is actually needed at 6000RPM vs 800RPM.
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