Energy use at Goshen College

Slow your fans down!

Think of heating a classroom by heating a set volume of air, $V$, and then blowing it into the room through a duct with a cross-section $A$, and a fan that moves the air at a speed $v$.

Depending on the speed, it will take a time $t$ to move this air through a duct into the room: $$V=A\, l=A\,v\,t \Rightarrow t=\frac VA\,\frac 1v.$$

The energy needed to move this air is ~ the energy necessary to accelerate the volume of air, $V$, (with a mass density $\rho$) up to a speed of $v$, which is the final kinetic energy of the air: $$E=\frac 12 m_\text{air}v^2=\frac 12(V\,\rho) \cdot v^2.$$

The energy $\propto v^2$ and the time it takes move the air $\propto \frac 1v$.

To conserve energy: Slow your fans down! If you're willing to take 3 times as long to move the air into a classroom, you can cut fan speed to $v_0/3$, and only spend $E_0/9$ the energy. Equipment needed:

  • a variable speed fan motor controllers.
  • Programmable energy management system "wakes up" fans early enough to warm classrooms to daytime temperatures over the course of hours instead of minutes.
In the United States, an estimated 60-65% of electrical energy is used to supply motors, 75% of which are variable-torque fan, pump, and compressor loads.[31] Eighteen percent of the energy used in the 40 million motors in the U.S. could be saved by efficient energy improvement technologies such as VFDs.[32][33]

-Wikipedia, Variable frequency drives (VFDs)

Generalizations of this strategy:

  • Send oil by pipeline (walking speed) instead of in a truck or railcar.
  • (Arab Oil Crisis of 1970's) Drop speed limits nationwide from 75 mph to 55 mph.
  • Most efficient freight service is the slowest: Barge is cheapest!

More tweaks to the campus

The "heating plant" is positioned beside the railroad because once-upon-a-time we heated the campus with steam, by heating water with coal. But now, inside that building...