Energy use at Goshen College
- GC (natural gas) consumption, 1991-2012, graphed together with indoor area of the College (.pdf)
- GC electricity consumption, 1991-2012 (.pdf)
- What would you guess is the cheapest among the sources of utility energy (comparing $/kWh)?
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...
- Winter of 2012 new geothermal unit heats three buildings, the Record, November 8, 2012.