Has anyone else noticed the increasing popularity of DC motors?
Years ago, it was only toys and shavers that employed DC motors. Except for the starter on my car (which does not spin very fast), all those DC motors were in relatively small low power gadgets.
It seems the popularity of DC motors surged first in power tools. Screwdrivers that began as $30 Christmas gifts now have transformed into expensive heavy duty power tools for the professional. Newer hybrid cars have powerful DC motors that not only crank out gobs of torque, but will turn some pretty high RPMs too.
I noticed that even the furnace in my house came with a DC motor. And it makes a difference – a big difference. The AC blower motor in my furnace of yesteryear ran at just one speed. Yes, I know more expensive units could be had with AC motors that were really two motors in one, and therefore could be run at one speed for heat and another for air conditioning. But the DC motor in my new furnace can run at five different preset speeds.
So what? Who cares? Well, it matters because a DC motor can be run at very slow speeds efficiently, while still having the ability to jump to higher speeds. If my house is chilly, the fan can run slowly to warm it up without generating drafts. If my house is humid, the fan can run slower to remove more water from the air. If my house is hot, the fan can create blizzard conditions to cool things down. And if I want to let the fan run slowly all day so the temperature is uniform throughout the house regardless of whether window shades and doors are open or closed, I can do so for about $2 per month.
It’s no wonder DC motors are showing up in more and more places.
2 comments:
My new furnace came with a variable speed blower. The HVAC company said letting it run at a slow speed all day, every day would create uniform temperatures throughout the house.
Guess what? It doesn't work that way. At least not in my house. Maybe it's better than it would have been with an old-fashioned on/off blower. It's hard to compare it to the 30 year old beast it replaced. But my office is a whole lot hotter in the winter than my dining room addition will ever be, at least without supplemental heat.
The good news is, continuous air circulation does help somewhat with whole-house filtration. It's also a lot quieter and more discrete since it doesn't go from "off" to "full blast" every time the furnace or A/C kicks in. Especially since I use a heat pump when it's not super cold outside.
I should have mentioned that the terminology used by the furnace company (and on the $150 energy rebate incentive) is ECM blower, which stands for Electronically Commutated Motor.
While an ECM may help, I don't think it can overcome inadequate duct work. Where it shines is on Thanksgiving Day, when people can't stand the heat in the kitchen. In that case, a continuously running fan distributes that heat around the house so it does not accumulate as much in one location. This is an extreme example, but the principle applies to any source of heat or cold drafts - provided the air in the building circulates properly when the fan runs.
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