Re: [Phys-l] modern light sources

["Richard Tarara" <rbtarara@sprynet.com>]

While half of the building was built in 1985 or so--the south half (think 
big rectangle with a new big rectangle attached to the north side--which did 
solve the problem of the initial, effectively non-existent wall to the north 
(aluminum and single pane glass) is concrete and brick--little or no 
insulation and while new window treatments are double paned they also get 
little direct sunlight in the winter (blocked by trees and other buildings). 
An identical looking (but newer brick and concrete north face is of course a 
heat sink.  The original building (where I reside) was 'early soviet 
architecture' in that it was built quick, cheap, and with no regards to 
energy savings.  The then president was forced to build a science building 
(after a fire in the make do facilities) when she actually wanted to build a 
performing arts building--that was back in the 50s.  It is also the case 
that being on the East side of Lake Michigan, the number of 'sun' days from 
November through March can usually be counted without taking off one's 
socks--at least not both.  The summers however can be pleasant--not overly 
hot--however with our building, about half of the floor space (classrooms 
and labs) have no outside wall which again solved the old north wall 
problem.  With these spaces, air-conditioning is essential as they would 
tend to warm to 10 degrees (Fahrenheit) above outside temperatures.  That's 
not good enough in the winter, but with classes starting in August, 
unbearable without the AC.  Windows don't open in the building--that would 
have doubled the cost of the heating/cooling system which has never worked 
all that well anyway but this was all done by a good architect but a 
marginal heating/cooling engineering firm.  One indication of that is that 
we had requested a low-pressure high volume air system for our air tracks. 
They started to install a $50,000 system to do this until we caught that 
fiasco and the two of us Physicists (with a little help from the campus 
plumbers) cut that cost by a factor of 10 with a system that still works 
today without having undergone any maintenance (amazing what a few 
commercial air track blowers mounted in the basement and some plastic pipe 
can accomplish).

Anyway--somebody has to live in the northern climes so that there is room 
(and water) for all you 'fair-weather' types in the south and west!

Cheers,

Rick



-----Original Message----- 
From: brian whatcott
Sent: Tuesday, January 18, 2011 8:33 PM
To: phys-l@carnot.physics.buffalo.edu
Subject: Re: [Phys-l] modern light sources

On 1/18/2011 1:21 PM, Dr. Richard Tarara wrote:
> ----- Original Message -----
> From: "John Denker"<jsd@av8n.com>
> > We should also keep in mind that in an office building of any
> > reasonable size, there is no need for heating of any kind --
> > not from heat balls, heat pumps, or anything else -- because
> > the people and the office equipment produce more heat than is
> > needed.  They have to run the cooling equipment year-round.
> Not sure about this--certainly not in my 'neck of the woods'.  I can look 
> at
> our Science building which is regularly occupied by many more people than
> would be in an office building, computers and the like in every office 
> with
> extra computers around the building, lab and office equipment running
> constantly.  The building gets damn cold in the winter even though the
> building is heated.  Now to be sure, all our lights are flourescent and 
> the
> building is not occupied (or barely so) in the evenings and weekends, but
> then neither are most office buildings.  Maybe I've missed something 
> earlier
> in this thread though?
>
> Rick
>
> Richard W. Tarara
> Professor of Physics
> Saint Mary's College
> Notre Dame, Indiana
I wondered about this myself. Your observations may be saying something
about the Science building's design standard, as well as the climate there.
I did a back of the envelope estimate to get a feel for the issue.

It is certainly the case that a bigger building ought to be easier to
keep comfortable for the usual reason:  volume increases with L cubed
while surface area grows with L squared,
and heat loss goes through the surface for some representative length L.
Still, its simpler to balance the least unit  case: one office cubicle:
10 ft X 10ft with a ten ft ceiling. There's a total surface of 600 sq ft.
Suppose the whole shebang is insulated at 0.04 W/m.K, and suppose that
the sole occupant whose dietary input is 2000 Cal, puts out 100 watts,
and has a 60 watt lamp and a 60 watt appliance.     What temperature
rise are we talking about here?
Say 600 sq ft =  56 sq m.   That thermal conductivity for a 15 cm
insulation thickness
ought to transfer energy at this rate: 0.04W/m.K  X 56 m^2 / 0.15 m = 15W/K

The 220 W input should lift the inside temperature by 220/15 K = say15degC

But a window that provides an insolation of 700 W for 4 hrs/day on
average and is shuttered at other times gives an extra 700/6 watt on
average  say 120 W
which lifts the temperature an extra 8degC.
 23 deg C inside  from an OAT 0degC?
Now we're cooking!   That is, if I worked the numbers appropriately for
my optimistic inputs  - - 6 inches of glass fiber insulation all round?
Shuttered window?  Probably not!

Brian W

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