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[Phys-L] Re: Natural Gas vs Electricity



Robert Cohen asked:

1. It seems that you are either assuming that (a) during the night, with
the computers turned off, gas heating would be on or (b) the heat
generated during the night is available during the following day (i.e.,
the building is perfectly-insulated). Am I wrong or are these
assumption not pertinent?

2. What about printers? I've just always wondered about them.

Response:

1. Yes, gas heat is on all night, but in the newer buildings there is an
"unoccupied" set-back to lower temperature at night. The presence of
"left-on" computers and other appliances will slow the rate of cooling
to the set-back temperature, and that slightly reduces the set-back
savings during the cool-down phase. Once the set-back temperature is
reached, the left-on items again work in tandem with the heating system
to maintain that temperature, and right now the "heating help" that the
left-on items provide is saving a little bit of money. Then in the
morning when the system switches to the "occupied temperature" the
left-on items help the heating system get back up to temperature.

Turning the heating system completely off at night cannot be done in our
area because (a) in cold weather we could get frozen pipes and other
freezing around the perimeter rooms of the building, (b) the re-heat
time gets pretty long so you can't stay at the low temperature very long
before you have to begin the re-heat process.

2. I did not include printers because we don't have very many.
Depending on the location we have anywhere from 5 computers to 30
computers sharing a printer. (Our printers are on the network as
opposed to hooked to individual computers.) I have not done a count,
but whereas we have about 400 computers, we probably have less than 40
printers.

I did just do a check at www.energystar.gov and found that typical
printers in sleep mode use anywhere from 3 watts up to 15 watts. On
average that's actually a bit more than the typical computer, but we
have way fewer of them.

Michael D. Edmiston, Ph.D.
Professor of Chemistry and Physics
Bluffton University
Bluffton, OH 45817
(419)-358-3270
edmiston@bluffton.edu