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[Phys-L] Re: Natural Gas vs Electricity



Actually Robert's questions bring up another which (I think) is related to
the answer to (1). What really is the optimal 'set-back' for night-time
(unoccupied) temperatures as a function of desired daytime (occupied)
temperatures. I play around with my home setback but am always concerned
that the lower I make the setback, the longer it takes the furnace, running
continuously, to bring the temperature back. I know we should be able to
calculate this based on the 'heat-flow' (sorry JG) equation, but this has
probably been done.

To expand on home options--most people are heated by gas or fuel oil but
both of these tend to be all or nothing systems. That is, it takes a fairly
new, fancy, and expensive gas heating system to have zones. With a
reasonably large home, then one must heat the whole thing. I have a couple
strategies that I keep playing with. Getting ready for work in the morning
at a much reduced temperature 55-65 F, is not too comfortable. Most of that
time is spent in the bathroom(s) however. While heating those with electric
space heaters (on timers) is one solution, I don't like having high current
devices so near water. However, keeping the doors of these rooms closes,
and then getting the furnace to run a while before getting up, can increase
the temperature in the bathrooms MORE than in the house as a whole.
Therefore the 'morning' temperature can be set lower than what might be
optimal for the whole house. The second strategy is pretty obvious--keep
the whole house temp reasonably low, and use electric space heating in the
room(s) that one occupies during the evening in a more sedentary mode (TV,
computer, reading rooms).

Anybody else have any helpful hints here? Anybody know of a source for
maximizing the use of setback thermostats?

Rick
----- Original Message -----
From: "Robert Cohen" <Robert.Cohen@PO-BOX.ESU.EDU>
To: <PHYS-L@LISTS.NAU.EDU>
Sent: Wednesday, October 26, 2005 8:42 AM
Subject: Re: Natural Gas vs Electricity


Two questions:

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.

____________________________________________________
Robert Cohen, Chair, Department of Physics
East Stroudsburg University; E. Stroudsburg, PA 18301
570-422-3428; www.esu.edu/~bbq

-----Original Message-----
From: Forum for Physics Educators
[mailto:PHYS-L@list1.ucc.nau.edu] On Behalf Of Michael Edmiston
Sent: Wednesday, October 26, 2005 12:57 AM
To: PHYS-L@LISTS.NAU.EDU
Subject: Natural Gas vs Electricity


For my most recent gas bill, the cost per 1000 cuft hit
$15.27 not including transportation charges, taxes, and
monthly service fees. That comes out to $15.27E-6 per BTU
for heating my house (plus the other fees that are not
included; and, if I were achieving 100% efficiency in my furnace).

Let's convert this to kilowatt hours so we can compare it to
electricity costs....

Natural gas comes out to $0.052 per kilowatt-hour for heating
for gas cost alone. Taxes, delivery, and service in my area
bring this up to about $0.062/kWhr, and this still assumes I
don't waste any thermal energy out my flue.

Electricity in my area is 90% generated by coal and 10% by
nuclear, and is fairly inexpensive at $0.062 on my last bill
including tax, transmission, and monthly service charges.

This means that for the first time I can remember, the cost
of heating with natural gas has hit the cost of heating with
electric resistance heat, if you assume a 100% efficient
furnace. Some furnaces hit 95% efficiency, but most are more
like 80%. This means that today I can heat my house with
electric resistance heaters for less out-of-pocket cost than
heating with natural gas. Of course electricity costs are
also expected to rise, but not as much as further increases
in natural gas. In my area we don't use gas turbines for
electricity except for just a few small peaking plants, and
those only tend to run in the summer.

I did this calculation today because there has just been a
big push at the local school, and the push is about come at
my university, for us to turn our computers and monitors off
at night in order to save money. I have always told people
that turning off lights and computers and other things at
night during the heating season does not save as much money
as they think. It only saves the cost differential between
gas heat and electric heat.

Well, as of today, there is no cost savings to be gained by
turning electric things off at night. If you heat with
natural gas in my area, you can now actually save money by
leaving your computers on all night.

The truth of the matter is that it's not much money either
way. To receive Energy Star status a computer in sleep mode
must use less than 15 watts and a monitor must use less than
2 watts. But most computers are better than this. The most
recent round of computers purchased by the university use 1.6
watts in the computer and 0.7 watts in the monitor for a
total of 2.3 watts when in sleep mode. That's about half of
a 4-watt night light or one-third of a 7-watt night light.
*One-hundred* of these computers left on from 6 pm to 8 am for *one
month* would cost $5.80 if you don't consider the benefit of
the heat generated, and would save the university about $1.27
if you do consider that natural-gas heat now costs more than
electricity.

I presented these numbers to the administration today, and
they were flabbergasted. They thought they were going to
save several-hundred dollars per month in electricity costs
by making us go around our offices and labs each night and
turning off all computers and monitors. Where do they come up
with these ideas? We are small, and only have about 400
university-owned computers on our campus. All are Energy
Star compliant. The maximum savings would be less than $25
per month not considering the benefit of 2.3 watts of
electrical heat per computer. Currently we save four or five
dollars a month by leaving all computers on during the night.

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