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Unformatted text preview: Name: K61 5142th ZOQﬂ ECE 398RES
Exam #2 Tuesday, April 21, 2009 Closed book, closed notes
One note sheet allowed 1. /21
2. /25
3. /28
4. /26 Total / 100 1. (21 points total) A building requires 300 tons of cooling for 12 hrs/day for 200 days/yr . From 6 A.M.
— 6 P.M., the energy charge is $0.10/kWh and the demand charge is $10/mo—kW.
From 6 RM. — 6 A.M., the energy charge is $0.05/kWh and there is no demand
charge. Find the annual cost of the following two options and determine which is
lowest. Assume a capital recovery factor of 0.10. Note one ton of cooling is
equivalent to 12000 Btu/hr, and one Btu is 1055 J. (a) Option A — 300 kW, 300ton chiller costing $500,000 which runs for 12 hours
each night and makes ice to melt during the day (b) Option B — 150 kW, ISO—ton chiller costing $250,000 which runs all day. Ice is
made at night, and the melting ice delivers 150 tons during the day, and the
chiller delivers the other 150 tons. @ AWW anng egg,— Afsfgﬁioxm airs/W mam/5,17” am he >< s «GS/wk; £3 WOO/yr“
13350000ij wk“: gaﬁgﬁr
® WV EngﬂE Cog?
Ajfgfgox m 63$” \Lhti/Aayﬁ zoogawyr “50wa $ 09/in : ‘3; 2% (CW/yr
: SEW/W ragga,“g \lmtaayx zoo sagsiyw lee mix 5 .lO/Wh :— $ awe/fr
Demon/A gosh” MwW  z
60”” Myrnaw mama/’7’” ’2 wgﬁmgﬂr swam; x“ W, 2. (25 points total)
The following ﬁgures give the probability density function for the wind at a site and the
power output of a wind turbine at that site. «cm 31%
\ windspeed v (In/s) ——> _5 15 20
wmdspeed v (m/s) ——> (a) Find the value of k in the probability density function.
\5xx< 4 a {:31 :\\333 2.“ l5 memw—mwy (b) What is the probability that the wind blows between 5 and 15 m/s? \ ‘3; i
F L t. \‘§ 512mm 125 ? ans; 125
 ‘ 2:1 \5 5 {0V ‘5
‘ 1/15 \ ~ 117.5 5
(c) What is the annual energy (kWh/yr) from the wind turbine? _ 50 Le q
" _9. “’ fw ’; 1"— ; law x87 b0 \wsl 7W _ at 4’ 3?
5‘ :1;
: 778loota'l MNvaY M, (d) What is the average power density (W/mz) in theawind? l ‘L 20 tip/kg Lugqu
.. 3 z . 15 I ..—— "‘ “W
§av51m / Z/g é'v ¥CV)Q§.’V 2 Q L 215$“! glts év‘] \\ ﬁnal?» 3V5 to» W 119
'LLSXB 5 Hilﬁga M éxltnsésé‘aiétsgr \“I'IO.63>
I: ZEQMEE‘E’E m $2”me 3 Short Answer, four points each (28 points total) a. Explain the thermodynamic operation of a heat pump and tell how it could be
GA used to reduce residential heating and cooling costs? \
Q my)“ 'CONQYQSSDY‘ Wat/«team‘s we presst a; yne‘ﬂgot which, at
V, .. “‘8 *3“?!qu .
“4&2.th ‘e habits game; an Wan/m mmde my» m cal/idem or 4:04 “i>0\$$€.5 JAN/Du \n at army; \fOLWtJ qs a. iiibu‘é, ands Whitk
mmlces‘er 56% dogun x. Y‘ 4 6A? ’ﬂtsseg wroWMPomjDV where. ‘ﬁr ab53(’bg he a+ Romy/ta
COO\ eymfw ‘i" «law have cit/gum gouge, heat P‘J‘M' s W estéec/JWHC. WW?“ {Exchmﬁe
e Mm W items. 1 s rctwaElL; coméami.» b. As discussed in class, explain what is meant by the term “distributed
generation” and list three potential benefits. asthma gonemmmm smarter..de We #3 abs“ 30 MW
W pg Guam atng mm so $8M
 hemvaleve Wﬁesﬁom by atDpsOQWCLK, flooding g3? dismath
enmth
—§oim\omec§ hea+ét power W we. hem“ can be was @
Same Quake. power ‘ts ms Utth F V i
~Cusi0‘m6e3 can sen bar/K pews/Wm Wat/:3: at «Wig have
we (blamed Nazca money c. A power ﬂow tool was demonstrated in class. Brieﬂy explain how the power
ﬂow can be used to help with the siting of new generation (such as wind farms). iﬁls‘wh90fmm Watt, We Whemisgw‘w Susie?“ m heroism Woman of WIM. Powet‘ J? tow Quit“
W “a? W QSCEV—lett Mikel/tier” \‘i’WUULleL‘oQ. 4.430990%
M) mama. 0L Wm J9va somewhat/‘9 . d. Give a situation when Rayleigh assumptions may be used. Breiﬂy explain the
pros and cons of using a Rayleigh distribution to approximate the wind
distribution. Kwﬂﬂg‘h aéSerbWJ 00W be was WW me me; mg
mevx QWOUGYGK \A/Md She ES???» avevcﬁe waﬂalspaedtd 19h
Qag\e‘®\n\s 41.5910; may?) tummy 3
Pray extremely Saw #0 use) 40% Lt Mickie \ComfoK 1.5)
can Witt/£56: LVQV53> g‘mpiiﬁecl aim) \G hi’He is my)“ cask not» a; act/woke: as tealclceaj ﬁgiwt qutwmmg e. Calculate the average windspeed for the data given below. 0.35 A? : hot H Li kalﬁpxﬂ$5+ 91%;25
at. m x O. \
s (O. l Wags
5
2 4 6 8 10
velocity (m/s) f. Derive an expression for the maximum efﬁciency of a fuel cell in terms of Q and H. Assume H = We + Q, where H is the enthalpy supplied by the chemical reaction, We is the electricity produced, and Q is the amount of heat rejected. %;W :1 .WS, 1 H”®  E,‘ﬁ.
mew H H; ' H W
M g. Consider a 35 % efficient 70 kW microturbine used in a combined heat and
power (CHP) application illustrated in the figure below. Assume that 40% of
the input fuel ends up as useful heat. The heat offsets the need for fuel for an
85 % efﬁcient boiler. Find the displaced boiler input in Btu/hr. Note, one Btu
is 1055 J. l
l
l 4 (26 points total). True/False — Two points each. Circle T if statement is true, F if statement is False. T®
T69 1. Fuel cells are a relatively new technology, with the concept ﬁrst
described in the 1980’s and the first commercial applications
appearing in the 1990’s. Assuming a 10% interest rate, the net present value of $3000 in
year 5 would be $2000 (rounded to the nearest dollar). Maw/1L4 One of the goals of electric utility demand side management is to
do “peak clipping (peak shaving), ” shifting electric load away
from times of high use. An advantage of a horizontal axis wind turbine is no yaw control
is needed to keep them facing into the wind. The higher the internal rate of return, the slower the investment
recovery. hgﬁ Egg; is 3 00$ According to the 2007 National Academy of Sciences report
discussed in class the top three causes for bird fatalities are
vehicles, cats, and wind turbines. On a large interconnected power system (like the Eastern
Interconnect) a sudden loss of generation (say 5000 MW) would
result in a fairly rapid (seconds) decline in system frequency. In order to enCourage the development of wind energy, the State
of Illinois has decided wind turbines are excempt from local
property taxes. For winds less than the furling windspeed the output of a wind
turbine is zero. “Rayleigh assumptions” means that the probability density
function of the wind has a Weibull distribution with shape parameter k = 2. In 2006 the total wind energy production in the USA was about
equal to the total electric energy produced in the state of Georgia. While not practical, it is theoretically possible to use a wind
turbine to extract all the energy contained in the wind. Men M We stiles wtsuté‘ts’m
a? no Mtﬁ’e. OdMA (>613?)
so Ame. wwﬁr‘“ WQkk‘gAWQQ gem T ® 13. In a squirrel cage induction motor the three phase currents
applied to the rotor are used to “induce” a current in the stator. ...
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