ENGR103 GRP06603 POSTER (PDF)

RetrofiVng  Roofing  Systems  
by  Bridget  Frasca,  Hope  Lewis,  Anita  Ting  
Advisors:  Dr.  Masoud  Soroush,  Nathan  Taylor  
Drexel  U  niversity  

INTRODUCTION  

Figure  1.  First  house  is  with  conven/onal  roofing  with  ultraviolet  rays    
entering  the  home,  while  the  second  house  is  with  cool-­‐roofing  

OBJECTIVES  
•  The  primary  goal  of  this  project  was  mo/vated  by  the  
ul/mate  need  to  determine  an  alterna/ve  to  a  
tradi/onal  roofing  system,  constructed  of  more  
sustainable,  energy  efficient  materials  that  reflect  
more  heat.    
•  Exis3ng  solu3ons  to  this  problem  have  been  found  to  
be  the  employment  of:  
•  Green  roofs  
•  White/lighter  colored  roofs  
•  Heat-­‐resistant  material  
•  A\empted  to  quan/fy  the  differences  between  roofing  
types  in  terms  of  absorp/on  of  heat  
•  Generaliza/ons  were  made  about  the  performance  of  
different  materials  in  a  climate  in  which  absorp/on  of  
heat  would  be  a  significant  issue    
•  Roofing  materials  for  tes/ng  were  selected  according  
to  their  heat  transfer  capabili3es,  specifically  their  
thermal  conduc,vity  and  resis,vity,  cost  and  
maintenance  
•  The  conclusion  that  was  to  be  drawn  from  the  data  
collected  was  the  material  that  absorbed  the  least  
amount  of  heat,  thus  would  perform  the  best  in  such  a  
climate  

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•  To  control  the  experiment  with  the  type  of  roofing  being  
the  only  variable,  a  heat  lamp  was  used,  which  produced  
a  constant,  high  temperature  that  would  simulate  long  
hours  under  the  sun.    
•  The  prototype  design  was  a  constructed  box  with  
12”x12”x10”  dimensions,  featuring  interchangeable  
roofs  of  varied  materials  that  were  chosen  to  effec/vely  
test,  shown  in  Figure  2  and  3.  

•  The  final  deliverable  was  the  results  of  the  data  collec/on  
and  analysis,  showing  the  best  material  in  terms  of  
energy  absorp/on.    
•  From  using  the  equa/on  q=S·∙U·∙(Tout-­‐Ti)n+qrad,  final  
experimental  U-­‐values  were  calculated.  In  order  of  lowest  
U-­‐value  to  highest:    
 

Table  1.  Results  of  analysis  through  equa/on  

2.  Experimental  prototype    with  thermal    
Figure  3.  Experimental  roofing  types  
  Figure  
couple  and  green  roof  sample  
 
•  A  small  hole  was  drilled  into  a  side  of  the  box  for  
inser/on  of  one  probe  from  the  thermocouple,  and  the  
other  probe  was  placed  close  to  the  surface  of  the  roof  
to  compare  both  temperatures.  
•  A  thermocouple  was  used  to  measure  the  change  in  
temperatures  every  30  seconds  for  the  first  5  minutes  
and  then  every  10  minutes  for  2  hours.    
•  ARer  data  was  collected  each  material  was  evaluated  on  
effec/ve  insula/ng  performance,  seen  in  Figure  4.  

Inside  Temperatures  over  Time  
40  
38  
Temperature  Inside  (in  Celsius)  

•  Many  roofing  types  are  not  always  suited  to  the  
climate  in  which  they  are  used.  A  roof  that  would  
perform  well  in  a  temperate  climate  would  not  
necessarily  perform  with  similar  results  in  a  warner  
climate.  
•  Solar  radia3on  can  enter  buildings  directly  through  
the  roof,  therefore  proper  insula,on  in  a  warm  
climate  is  necessary  to  help  reduce  the  heat  transfer  
through  the  building  envelope,  as  seen  in  Figure  1.  
•  The  primary  focus  of  this  project  was  to  iden3fy  a  
more  energy  efficient  system  of  a  building’s  
insula3on  through  study  and  experimenta/on,  
specifically  through  the  roofing  system,  to  reduce  
energy  consump/on  due  to  hea/ng  and  cooling.  
•  The  desired  end  result  would  amount  to  a  more  cost-­‐
efficient  system  when  maintained  for  a  long  /me  
period.    

RESULTS  

TECHNICAL  ACTIVITIES  

•  As  seen  in  the  Table  1,  the  green  roof  prototype  absorbed  
the  least  amount  of  heat  and  transferred  it  to  the  room  
below.    
•  The  green  roof  would  perform  the  best  in  terms  of  
reducing  the  amount  of  heat  absorp/on.    
•  Darker  materials,  the  black  asphalt  and  the  rubber,  
performed  the  worst  in  experimenta/on    
•  Lighter  materials,  white  thermoplas/c  and  aluminum,  
performed  be\er,  showing  the  role  that  the  color  of  the  
material  has  in  reflec/ng  radia/on  before  it  can  become  
heat    

Economic  Analysis  
 
•  Each  roofing  type  was  analyzed  according  to  the  average  
respec/ve  material  and  installa/on  costs  per  square  foot  
in  the  hot  climate  of  Miami,  Florida.  [3]  

36  

Rubber  

30  

Asphalt  
Grass  

28  

Thermoplas/c  

26  

Aluminum  

24  
22  
20  
0  

20  

40  

60  

80  

100  

120  

Table  2.  Es/mated  cost  per  square  foot  of  chosen  materials  

Time  (mins)  

Figure  4.  Graph  of  results  from  experimenta/on    

•  Using  the  value  of  the  slope  from  each  graph,  a  value  of  
q  was  found  using  the  equa/on  for  heat  energy  
q=mC(dTin/dt)  [4]  
•  From  the  result  of  q,  using  the  equa/on  for  heat  transfer  
or  heat  flow,  q=S·∙U·∙(Tout-­‐Tin)+qrad    [5]  
•  Solving  for  U  gives  the  conduc3vity  of  each  material,  
used  to  compare  the  materials  and  determine  the  best  

•  The  best  roofing  type,  in  terms  of  increased  energy  
efficiency,  was  the  green  roof,  which  tested  with  the  
lowest  conduc,vity  of  .03071  W/°C  and  therefore  the  
highest  resis,vity,  32.5627  °C/W.  It  was  the  most  
expensive  however,  with  a  cost  of  $10  per  square  foot.    
•  Has  a  natural  ability  to  cool  through  soil  
temperature  and  growth  of  greenery  [1]  
•  Aids  in  increased  thermal  resistance  and  
capacitance  of  a  building  roof  
•  A  green  roof  is  more  expensive  to  implement  and  more  
difficult  to  maintain,  which  is  not  reflected  in  energy  
costs.  However,  over  the  course  of  the  life  of  the  green  
roof,  the  energy  cost  savings  offset  the  ini/al  cost.    
•  It  was  found  that  the  white  thermoplas3c  was  a  
cheaper  alterna3ve,  which  performed  just  as  well  with  a  
significantly  minimal  cost.    
•  Maintains  a  high-­‐temperature  tolerance  and  
low-­‐temperature  flexibility,  which  is  most  
resistant  to  ultraviolet  and  ozone  exposure  [2]  

FUTURE  WORKS  
•  Steps  that  would  need  to  be  taken  to  improve  through  
future  work  include  extending  the  period  of  /me  for  data  
collec/on  and  it  would  be  preferable  to  test  mul/ple  
prototypes  outdoors.    
•  Will  u/lize  the  realis/c  condi/ons  of  climate  for  more  
accurate  readings  
•   Crea/ng  individual  prototypes  to  house  each  respec/ve  
roofing  type  would  also  evenly  distribute  the  tes/ng    
•  Would  provide  less  room  for  human  error,  but  produce  
more  uncontrolled  variables,  such  as  the  changing  
environmental  aspect  

REFERENCES  

34  
32  

CONCLUSIONS  

•  The  green  roof  is  the  most  expensive  of  the  materials  in  
both  installa/on  and  maintenance  costs,  with  the  asphalt  
shingles,  rubber,  and  thermoplas/c  being  cheaper.    
•  Metal  roofing  resulted  in  a  median  material  cost,  but  
proved  to  be  low  in  maintenance  costs  due  to  its  
durability.  

[1]  W.  T.  Grondzik  and  A.  G.  Kwok,  “Design  Strategies,”  in  The  Green  Studio  
Handbook,  2nd  ed.  
[2]  N.  Sturdevant,  Reflec,ve  Roofs  Return  Mul,ple  Dividends  
h\p://www.energystar.gov/ia/partners/manuf_res/bom2.pdf?54f0-­‐d129    
[3]  h\p://www.homewyse.com/costs/index.html#roofing  
[4]  Thermal  Energy  h\p://physics.weber.edu/schroeder/eee/chapter3.pdf  
[5]  Basics  of  Heat  Transfer  
h\p://www.pathways.cu.edu.eg/ec/Text-­‐PDF/Part%20A-­‐3.pdf    

ACKNOWLEDGEMENTS  
We  would  like  to  acknowledge  the  guidance  and  advice  of  
our  advisor  Dr.  Masoud  Soroush  and  our  teaching  
assistant,  Nathan  Taylor.  Also,  we  would  like  acknowledge  
Von  Schifferdecker  for  allowing  us  to  use  some  technical  
equipment  for  our  tes/ng.