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re: what's the right number?
21 feb 2003
iain mcclatchie  wrote:

>nick> you might enjoy "heating and cooling of buildings" by kreider and rabl
>
>thanks, i'll go pick that up this weekend.

   the list price is $132.19. pine associates, ltd. is pleased to offer
   these 890 page books with floppy disks for $115.00 plus $5 shipping!

>after i've verified that the book actually does show the numbers you
>just wrote, i'll send them an errata note.

it still seems surprising they missed this...

   a number of reviewers took considerable time to examine the book closely,
   finding errors that the authors missed and suggesting improvements in
   the presentation. the review process began with helpful comments on the
   original outline by louis burmeister, university of kansas; thomas hellman,
   new mexico state university; doug hittle, colorado state university;
   ronald howell, university of south florida; dennis o'neal, texas a&m
   university; maurice wildin, university of new mexico; and byron winn,
   colorado state university, and continued with reviews of the draft by
   john lloyd, michigan state university; and trilochan singh, wayne state
   university. the exceptionally detailed and constructive comments by prof.
   wilding on the entire manuscript are especially appreciated. likewise,
   wendy hawthorne made a careful reading of the text and checked most of
   the examples, and bill shurcliff contributed a thorough review of several
   chapters. various colleagues offered comments on parts of the book: mike
   brandehuehl (who also contributed novel end-of-chapter problems in the
   first half of the book), manuel collares-pereira, jeff haberl, j. y. kao, 
   john littler, john mitchell [between watergate activities?], leslie k.
   nordford, mike riley, gideon shavit, and mike scofield. of course, any
   remaining errors are the sole responsibility of the authors. 

   peter curtiss wrote the software that accompanies this book. the thousands
   of lines of code that he wrote in producing the final product set a new
   standard for instructional software used in building systems. wendy
   hawthorne prepared the solutions manual for the end-of-chapter problems. 

the end-of-chapter problems are arranged in approximate order of difficulty
indicated by a number from 1 to 10 in parentheses at the end of the problem.
some examples:

   1.1 list the major pieces of energy-consuming equipment in your
   everyday life. for each, estimate the peak power, average power,
   and annual consumption. (2)

   1.6 consider a house with a 1-ton air conditioner, running 500 h/yr
   at full power.
   a) what is the annual thermal energy delivered to the house?
   b) what is the corresponding energy consumption, with a 2.0 cop?
   c) suppose one stores winter ice in a tank for summer cooling. 
   how large a tank is needed, if there are no heat losses from storage?
   d) how much is the cooling energy of 1 ton of ice worth? (5)

   7.9 two people own a house with a total conductive heat loss coefficient
   kcond = 120 w/k and a ventilation system that is controlled by an occupancy
   sensor to provide 7.5 l/s of outdoor air per person for the number of
   people actually present. they are giving a party for 30 guests. everyone
   is so pleased that they are staying until steady-state conditions are
   established. assume that the heat gains from other than occupants remain
   constant at 1 kw.
   a) estimate the latent and sensible heat gains as well as the outdoor
   air requirements, before and during the party. 
   b) if the outdoor and indoor temperatures are to = 0 c and ti = 20 c,
   how much does the heating load change relative to steady-state conditions
   before the party? 
   c) does the latent heat gain have any effect on the heating load if
   there is no humidity control in the house? (8)

   5.48 describe analytically the effect of pipe size on pump power
   consumption. if the cost of the pipe depends on the amount of material
   in the pipe (recall that larger pipe sizes have thicker walls--see
   table a5.5), how would you go about selecting pipe sizes based on the
   joint minimization of pipe material cost and pump initial and operating
   costs? the costs of pump and motor assemblies vary according to the
   0.6 power of the size (9)

   6.13 consider a sundial built as a vertical rod of 1-m length that casts
   a shadow on a flat horizontal surface. the location is princeton, new
   jersey, with approximate latitude 40 n and longitude 75 w. 
   a) what time of day (solar time) and time of year is it when the shadow
   is 0.50 m long, pointing due north? how many solutions are there?
   b) what time of day (solar time) and time of year is it when the shadow
   is 0.50 m long, pointing 45 degrees (in the horizontal plane) east of
   north? (by contrast to part a, this requires two equations in two
   unknowns; but they can be solved in closed form.)
   c) what are the corresponding standard times? (10)

   8.12 toward the end of the roman empire, the technology of glassmaking had
   advanced to the point where some villas could be built with a sunspace
   (called a solarium.) make reasonable assumptions about the construction
   and use a simple thermal network to estimate the temperature in a solarium
   during a sunny day in rome when to = [1+cos(pi(t-16h)/12h)]x4c and i(t)
   = max[0,-0.2+cos(pi(t-12h)/12h)x800 w/m^2 as a function of time of day t.
   plot ti and to. (10)

>nick> it says 70 f sea-level air... has density rho = 0.075 lb/ft^3
>nick> kreider and rabl give rhocp = 1.2kg/m^3
>
>uh, 0.075 lb/ft^3 == 2.07 kg/m^3, right?
>    1 lb == 0.454 kg
>    1 ft == 0.254 m
> - am i missing something really obvious here?

maybe.

>nick> specific heat cp = 0.024 btu/lb-f
>nick> ... 1kj/(kg-k)
>
>and 0.024 btu/lb-f == 0.09 kj/kg-k, right?
>    1 lb  == 0.454 kg
>    1 f   == 5/9 k
>    1 btu == 1/3412 kwh == 1.055 kj
>
>please, go ahead and show i'm an idiot.  i'm willing to be shown basic
>math.  did i multiply when i should have divided?

this looks like good exercise for the student.

nick




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