Beat the Sun - Keep Your Equipment Cool
Solar Shade Roof
Solar
Shade
Wall
Roof’s Thermal
Chimneys In Cavities
Between Roof Sheets
Vertical
Thermal
Chimney
In Cavity
Between
Wall Sheets
Solution: Solar Shade Wall/Roof Concept
Author:
Peter Brackett
Engineer, S&C Development and Quality Assurance
Chairman AREMA Committee 38
Phone: 403-319-7781
Email: Peter_Brackett@cpr.ca
Canadian Pacific Railway
Operations, Engineering Services, Signals & Communications
5th Floor, Gulf Canada Square,
401, 9th Ave., S.W.
Calgary, Alberta
T2P 4Z4
Date: August 2003
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Beat the Sun - Keep Your Equipment Cool
A “Solar Shade Wall/Roof” can reduce the temperature rise of buildings or equipment without using
energy (fans or air-conditioning). Canadian Pacific Railway hopes, by sharing this information, that
energy consumption can be reduced and the railways can get credit for improving the environment.
Most equipment is designed to operate within certain temperature ranges. When this same equipment
must operate in conditions outside these temperature ranges the results are often unpredictable. For
example: there is a considerable difference in the cost of designing equipment for a maximum ambient
temperature of 40C versus designing for a maximum temperature of 70C caused by solar radiation. A
small black metal housing can easily reach 70C in the summer sunshine of the southern latitudes.
Between 1999 and 2000, Canadian Pacific Railway constructed and deployed over a 100 new
8’by8’by16’ buildings to house trackside fiber and radio equipment. As per the railway norm, these
buildings were made of welded aluminum and air- conditioning was installed to provide a controlled
environment for this communication equipment. See Figure 1: Heat Transfer due to Ambient Temp.
Differences.
Since these buildings (bungalows in Canadian railway terminology) house our mission critical fiber
network (Alcatel SONET and Newbridge telephone/data multiplexing equipment), heating, ventilating
and air conditioning (HVAC) units and temperature alarm monitoring were installed to provide the best
environment for fibre functionality.
After initial installation, a series of high temperature alarms triggered an investigation into improved
ways to maintain the temperature within the desired limits.
On a day that I will never forget, since it was the day after September 11, 2001, I visited Somers,
Wisconsin. We recorded 125º F on the sun-exposed walls, versus 85º F on the non-sun exposed wall.
Now, the expression “Hot Enough to Fry Eggs” took on new meaning with a measurement to back how
hot “HOT” was. (Trivia note: Eggs fry at 158F). An extensive temperature modification and
measurement program was initiated to determine the best way to keep the equipment within the desired
temperature limits.
It was quickly determined that solar radiation heat gain was a key factor in causing the high temperature
alarms. A measurement project was initiated to record multiple building temperatures and to determine
the amount of solar radiation being absorbed by the buildings, and how this affected the inside
temperature of the buildings.
One result of this investigation was to install a “Solar Shade Wall/Roof” on the roof and sun exposed
sides of a test building in Calgary, Alberta, Canada. This “Solar Shade Wall/Roof” was able to prevent
the solar radiation temperature rise and keep the sun exposed building surface at the same “ambient”
temperature as the north- facing wall.
The Solar Shade Wall/Roof concept can reduce or eliminate the solar radiation heat gain of any building
or enclosure. This reduces the energy consumption of air conditioning that is currently used to control
the temperature rise caused by solar radiation.
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Table of Content
Heat Transfer Principles: ........................................................................................................................ 4
Heat Transfer due to Ambient Temp. Differences.................................................................................. 5
Heat Transfer Due to Solar Radiation ..................................................................................................... 6
Solar Energy Daily Fluctuations ............................................................................................................. 7
Requirement: Method to block solar energy heat transfer ...................................................................... 8
Solution: Solar Shade Wall/Roof Concept ....................................................................... 8
Shade Wall combined with natural Convection Thermal Chimney ....................................................... 9
Shade Wall/Roof Implementation at Canadian Pacific Railway’s Test Site ........................................ 10
Thermal Chimney’s .............................................................................................................................. 11
Additional Solar Shade Wall Measurements ........................................................................................ 12
Building Data Comparing Temperatures without Solar Shade Wall/Roof to Temperatures with Solar
Shade Wall/Roof ................................................................................................................................... 13
Plot of Data Comparing Building Temperatures .................................................................................. 14
Conclusion: ........................................................................................................................................... 17
Potential Railroad Applications: ........................................................................................................... 17
Simple Implementations: ...................................................................................................................... 17
Further references: ................................................................................................................................ 18
The Field Guide for Energy Performance, Comfort, and Value in Hawaii Homes .............................. 18
Radiated Heat Transfer ......................................................................................................................... 19
Field Guide Chapter 7: Insulation and Radiant Barriers ....................................................................... 20
Field Guide Chapter 8: Heat Mitigation in Roofs ................................................................................. 21
Recommended Technique: Integrate roof strategies............................................................................. 21
Radiant Barriers as referenced in the Field Guide. ............................................................................... 22
Website URL additional References:.................................................................................................... 23
Permissions for quoted material: .......................................................................................................... 24
List of Figures
Figure 1: Heat Transfer due to Ambient Temp. Differences ...................................................................... 5
Figure 2: Heat Transfer Due to Solar Radiation ......................................................................................... 6
Figure 3: Solar Energy Daily Fluctuations ................................................................................................. 7
Figure 4: Solar Radiant Energy Blocking Solution .................................................................................... 8
Figure 5: Shade Wall = Solar Radiant Energy blocking ............................................................................. 8
Figure 6: Shade Wall/Roof combined with Natural Convection Thermal ................................................. 9
Figure 7: Shade Wall Framework being added to Test Site ..................................................................... 10
Figure 8: Bungalow view from East with Wall and Roof Solar Shade Wall Visible ............................... 10
Figure 9: Thermal Chimneys - Ducts made by Outer Skin ...................................................................... 11
Figure 10: Dramatic Proof of Temperature Differences ........................................................................... 11
Figure 11: Aug 29th Clad vs July 16 Non-Clad Temp. Comparisons ...................................................... 12
Figure 12: Temperature Comparison Table .............................................................................................. 13
Figure 13: Bare Roof Temperatures and Reduced Temperature under Shade Roof ................................ 14
Figure 14: Ambient North Wall Temperatures comparing July16th to Aug29th ..................................... 14
Figure 15: Chart of Temperature Comparison Table ................................................................................ 15
Figure 16: Wall/Roof Temperature measurements July 2003 .................................................................. 16
Figure 17: Simple Solar Shade for Equipment Enclosure ........................................................................ 17
Figure 18: Modes of Heat Transfer ........................................................................................................... 18
Figure 19: Radiated Heat Transfer ............................................................................................................ 19
Figure 20: Insulation: Barrier to Heat Transfer ........................................................................................ 20
Figure 21: Hawaii Field Guide's "Solar Shade Wall" ............................................................................... 21
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Heat Transfer Principles:
Heat Transfer is directly proportional to Temperature Difference (for Steady Heat Conduction). It is
easy to understand if you use the Thermal Resistance Concept. The Equation for heat conduction
through a plane wall is:
Qconduction_through_wall 
Toutside  Tinside
(W)
Rwall
Where
Rwall 
THickness wall
kave._thermal_conductivity * Area
( C/W)
Rwall is the thermal resistance of the wall against heat conduction or simply the conduction resistance
of the wall.
Note that the thermal resistance depends on the geometry and the thermal properties of the wall.
The equation above for heat flow is analogous to the relation for electric current flow I, expressed as
V1 - V2
R
Where
Icurrent 
R is a function of the per unit electrical resistance times the length of wire
V1 _ V2 is the voltage difference across the resistance
Analogy between thermal and electrical resistance concepts.



the rate of heat transfer through a wall corresponds to the electric current
the thermal resistance corresponds to electrical resistance
the temperature difference across the wall corresponds to voltage difference across the resistor
For more details on the Thermal Resistance Concept, see Heat Transfer: A Practical Approach, 2/e,
Yunus A. Çengel, University of Nevada-Reno
http://highered.mcgraw-hill.com/sites/0072458933/information_center_view0/sample_chapter.html
To understand the Solar Shade Wall/Roof concept, heat transfer should be
separated into two separate transfers to best understand the Solar Shade Wall/Roof
Effect.
a) Heat Transfer due to Ambient Temp. Differences
b) Heat Transfer Due to Solar Radiation
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Heat Transfer due to Ambient Temp. Differences
Figure 1: Heat Transfer due to Ambient Temp. Differences
The temperature difference between the outside wall surface and inside wall surface drives heat energy
through the walls. Heat energy transfer is directly proportional to this temperature difference.
Heat Transfer due to Ambient Temperature Differences
We can identify one component of this heat transfer as energy driven through the wall by the difference
between the outside wall’s ambient temperature (temperature directly affected by outside air touching
the outside walls) and the inside wall of the bungalow. This is recorded as the temperature difference
between the outside wall’s temperature (that is not exposed to the sun) and the inside wall’s temp.
This heat transfer rate is a function of the surface area of all the walls of the building.
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Heat Transfer Due to Solar Radiation
Figure 2: Heat Transfer Due to Solar Radiation
The second component of heat transfer is driven by the outside wall’s temperature rise above the outside
ambient temperature. This temperature rise is directly related to the absorption of solar radiation energy
on the sun exposed wall and roof surface area. On sunny days, the solar radiation temperature rise over
ambient is very significant but the difference in surface area affects the balance between the two
components of energy transfer.
The strength of this solar radiation heat transfer varies constantly as a result of:
a) Atmospheric - cloud cover
b) Sun angle versus time of day and angle above horizon versus time of year
c) Air movement over the building’s outside surface (affects heat loss)
To understand how variable the solar radiation heating is see Solar Energy Daily Fluctuations below.
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Solar Energy Daily Fluctuations
F
64 °C or 148 °F on
Bare Roof
Fluctuating
Solar Energy
F
36.8
°C or
98 °F
on
Roof
under
cladding
27.9°C or 52°F
Roof Temp.
Diff
Figure 3: Solar Energy Daily Fluctuations
Conclusion:
Solar Radiation can drive a lot of heat through a surface
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Requirement: Method to block solar energy heat transfer
From practical experience, it is evident that shaded surfaces are cooler and sun exposed surfaces
Figure 4: Solar Radiant Energy Blocking Solution
Planting trees is not feasible for buildings along the railway for many reasons.
So we had to develop another alternative and hence Canadian Pacific Railway designed the following.
Solution: Solar Shade Wall/Roof Concept
Figure 5: Shade Wall = Solar Radiant Energy blocking
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Shade Wall combined with natural Convection Thermal Chimney
The outer skin blocks the solar radiation and heats up. If the air filled cavity between the new outer skin
and the original inner skin was sealed at the top and bottom, the closed wall cavity would just act as
another insulating layer. Heat can still be transferred across the cavity by conduction (contact) transfer
of heat from the inside of the outer skin to the trapped air, which creates a convection (air movement)
transfer to the inner surface; this, in turn conducts the heat energy to the original building skin.
To minimize this heat transfer, the natural convection or “Thermal Chimney” concept was used.
Shade Wall = Solar Radiant Energy blocking when
combined with natural Convection Thermal Chimney
Figure 6: Shade Wall/Roof combined with Natural Convection Thermal
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Shade Wall/Roof Implementation at Canadian Pacific Railway’s Test Site
Calgary Radio Tower
Figure 7: Shade Wall Framework being added to Test Site
This building is aligned east-west. This view is from the northeast looking southwest.
The shade wall’s support framework utilized 2’by4’s and had an open air space at the top and bottom.
Since this was an experimental test site, the framework was designed to be removable without leaving
any holes in the existing welded aluminum building skin.
The roof is a hip roof design, ie: 4 slopes. For ease of installation, only the north-south centre roof
sections where covered with the shade Wall/Roof.
Figure 8: Bungalow view from East with Wall and Roof Solar Shade Wall Visible
Natural convection draws air up the “Thermal Chimney” created by the vertical studs on walls and
roof and the extra new aluminium outer skin (Solar Shade Wall/Roof).
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Thermal Chimney’s
Roof Thermal Chimney
Wall Vertical Thermal Chimney
Figure 9: Thermal Chimneys - Ducts made by Outer Skin
Solar Shade Wall/Roof Temperature Measurements Changes Prove It Works
Figure 10: Dramatic Proof of Temperature Differences
Temperature of Outside Solar Shade Wall/Roof
versus
Temperature of Original Roof under Solar Shade Wall/Roof
Measurement Results:
Solar Shade Wall Reduces Original Roof Temp. from 136F/58C to 93F/34C
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Additional Solar Shade Wall Measurements
Since the exterior building surface is kept at the outside ambient temperature (versus outside ambient
plus solar radiation temperature rise), much less cooling energy is required.
Amount of energy reduction is dependent the amount of solar surface temperature rise on the sun
exposed building surfaces less the ambient temperature of the non-sun exposed reference wall.
Figure 11: Aug 29th Clad vs July 16 Non-Clad Temp. Comparisons
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Building Data Comparing Temperatures without Solar Shade Wall/Roof to
Temperatures with Solar Shade Wall/Roof
Without outer skin-Solar Shade Wall/Roof
Temperature Measurement Locations
Temp.
Degree-Hours
C
F
14 hr Integration Window
Outside Bare Roof Temp
54
129
567
Outside Roof Temp without Solar Shade (bare roof)
56
133
579
North Wall’s Ambient “Air” Temp (includes sun in PM)
28
83
423
Inside Ceiling Temp Between Ribs
28
83
388
Inside Ambient Air Temp
27
80
349
Temperatures as recorded 1 PM
HVAC’s daily running hours
12.5 hrs
(above temperature readings on from July 16/02 08:39 AM to 10:35 PM)
With outer skin-Solar Shade Wall & Thermal Chimney
Temperature Measurement Locations
C
F
Degree-Hours
Outside Bare Roof Temp
55
131
530
Outside Roof Temp Under Solar Shade
31
88
383
North Wall’s Ambient “Air” Temp
32
90
373
Inside Ceiling Temp Between Ribs
27
80
374
Inside Ambient Air Temp
27
81
366
HVAC’s daily running hours
5.8 hrs
(above temperature readings on Aug 29/02 from 08:39 AM to 10:35 PM)
Key Differences
% Differences
HVAC running time reduction
6.7 hrs
54%
Solar Shade Wall Outer Skin to Roof Temp. Reduction
147hrs
138%
50 hrs
12%
Comparison Adjustment
Outside Ambient Degree-Hour difference between days
(non-shade wall day appears hotter-but includes sun heating in PM)
See: Figure 11: Aug 29th Clad vs July 16 Non-Clad Temp. Comparisons.
July 16th’s non-shade ambient degree-hours were 50 hrs (423non-shade-373shade) greater that Aug 29th’s shade.
Since July 16th was warmer, the actual HVAC run time should be reduced by 5-20% to~ 50%.
But 50% reduction in HVAC energy usage is still significant.
Figure 12: Temperature Comparison Table
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Plot of Data Comparing Building Temperatures
Bare Roof Temperatures
July 16th = No Shade =plain Red
Aug 29th = Shade = green dot on red
C
Roof Temp. Under Solar Shade Roof
Figure 13: Bare Roof Temperatures and Reduced Temperature under Shade Roof
The total daily solar radiation amounts are similar for both days, with Aug 29th peaking higher but rising
slower in the morning (AM) and falling faster and afternoon (PM). It is very difficult to get highly
comparable data when dealing with the high fluctuations of temperature data.
Roof Temp. Under Solar Shade Roof
C
PM Sun on
North Wall
North Wall Ambient Temp. July 16th
North Wall Ambient Temp. Aug 29th –Shade Wall
Figure 14: Ambient North Wall Temperatures comparing July16th to Aug29th
This shows the daily north wall temperature profile versus the shaded Aug 29th roof temperature.
It also shows the effect of the sun heating the north wall on July 16th. For the Calgary latitude, the
summer sun sets to the north of an east-west line, so it shines on the North wall in the early AM and late
PM. It does not affect the results in a significant manner when the east wall temperatures were
substituted for the 3 pm to 10:35 pm readings. The reference wall degrees hours only dropped from 423
to 390.
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Upper Aug 29th Shade
C
HVAC only runs intermittently on day with Solar Shade Wall
C
Lower: July16th No Shade
North Wall Ambient
HVAC Thermostat
Plots of Output Air Temp. From HVAC
Low Temp. indicates HVAC is on and cooling
HVAC runs almost continuously
Figure 15: Chart of Temperature Comparison Table
This chart shows the difference in air conditioning demand between the day the building had the
Solar Shade Wall/Roof installed and the day without the Solar Shade Wall/Roof.
During the day without the solar shade protection the air conditioner had to run continuously. This is
determined by monitoring the HVAC’s output air temperature. When the unit is working the air
temperature drops approximately 16 C from the interior temperature. Per above, on the non-protected
day the HVAC started running almost continuously from 11:31 AM until after 9 pm. This indicates the
heat rise in the building is exceeding the HVAC’s cooling capacity.
For the solar shade protected building on Aug29th, the HVAC oscillated on and off indicating it was
able to control the internal building temperature and that it only had to run approximately 50% of the
time.
The conclusion is the solar shade can reduce air-conditioning by 50% or better on the hot days.
Effects will be less dramatic on days with less solar radiation.
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In summary, the Solar Shade Wall works
Temperature Measurement Locations
Bare Roof (No Shade wall on South East corner)
South Solar Shade Wall (The Outer
skin)
Top of Airspace between Walls
South Wall Original Bungalow Skin
South Roof Original Bungalow Skin
C
F
52 125
34 94
28
26
26
83
78
78
North Wall Ambient Reference (in
Shade)
26
78
Interior Wall
22
72
Recorded on July 25, 2003 at 2:47 PM
Figure 16: Wall/Roof Temperature measurements July 2003
Because
a) The outer solar shade Wall/Roof absorbs the Solar Radiation (short wave Infrared) and heats
up ( to 34C /94F in this example)
Note: Unprotected roof heated to 52C/125F.
From previous tests, the roof’s Solar Shade skin would be approximately the same temperature as the bare roof.
The roof’s shade skin was not measured on for this date but from previous recordings the temperatures do track.
The sidewall absorbs less energy than the roof because of the angle of the sun relative to the roof and wall respectively.
b) The heated outer solar shade wall transfers energy to the air in the cavity (Thermal Chimney) by a
solid to gas conduction. The hot outer surface heats air touching it.
c) The heated outer aluminum solar shade wall also re-transmits the energy from both its surfaces to the
air and from the inner surface to the original bungalow skin (to 26C/78F) by re-radiating the energy
at long wave Infrared wavelengths.
Aluminum does not absorb a lot of short wave radiation compared to other materials and hence does not have as much
energy to re-radiated as long wave infrared radiation (near infrared).
Possible explanation of why the original bungalow’s wall temperature remains at the ambient
temperature.
d) The heated air in the between wall cavity rises up the thermal chimney (28C/83F at top of chimney)
but this natural convection air movement flows out the top of the chimney faster than the time
needed for this warmed air to transfer its energy to the inner wall (by gas to solid conduction).
e) The long wave radiation emitted by the outer wall into the cavity is partially reflected by the
polished aluminum wall surface of the original bungalow wall which reduces the long wave
radiation heating effect. See Radiant Barrier technology described below.
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Conclusion:
The combination of natural air upward movement in the thermal chimney and the reflective
nature of aluminum to long wave infrared radiation keeps the original bungalow’s walls (that are
shielded by the solar shade Wall/Roof) at the same outside ambient temperature as the walls that
are not exposed to the sun.
Hence the solar shade wall concept works and keeps the protected surfaces at the “ambient”
temperature. Air conditioning energy usage reductions of 50% or greater are potentially
obtainable.
Potential Railroad Applications:
The “Solar Shade “ benefits can be gained in different applications such as:
a) Railway Trackside Communication and Signals buildings.
b) Electronic equipment housed in small outdoors cases.
c) Track work equipment and vehicles.
Reduce overheating of radiators, hydraulic tanks and operators.
d) Locomotive cabs, work trains, refrigeration containers, etc.
e) Any building or storage container where temperature must be regulated.
Simple Implementations:
Buildings:
The figures above indicate a simple method of retrofitting an existing building.
The same affect can be at manufacture by using different building designs that incorporate the solar
shading and the thermal chimney convection cavity. Controllable vents could be used to block the
chimney in the colder months when solar warming is desired. Preliminary tests indicate that the extra air
cavity reduces heat loss from the inner surface in the evening even when the thermal chimney is open.
Equipment Enclosures:
Implementation of the solar shade wall concept on an equipment housing can be achieved by simply
mounting the solar shade material on ½” - 1” standoffs around the outside of the box. This material
would shade the equipment housing and reduce the solar radiation temperature rise of the electronics
housed in the enclosure.
Solar Shade
Equipment
Enclosure
Standoffs
Figure 17: Simple Solar Shade for Equipment Enclosure
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Further references:
http://www.state.hi.us/dbet/ert/fieldguide/fieldguide.html
The Field Guide for Energy Performance, Comfort, and Value in Hawaii
Homes
"Information for the Field Guide publication was funded by the U.S. Department of Energy Grant #DE-FG51-97R020881.
Information does not reflect the views of, nor constitute an endorsement by the USDOE."
This is an excellent source of information on reducing solar heating. It provides a detailed explanation of
heat transfer including conduction, convection, and radiation modes of transfer.
(Note: Peter Brackett’s added notes are indicated in green for the referenced article. The article has also
been edited to reduce material to items relevant to this paper)
Fig.5-2:Modes of Heat Transfer.
Heat is transferred to and through your home in the same
way it is transferred to
and through your body:
 conduction,
 convection, and
 radiation.
Fig.5-3:Heat Transfer by Conduction.
In conduction, heat is transferred when warm and hot
surfaces are in contact.
Insulation works by acting as a buffer between materials
with significant temperature differences, such as hot
exterior siding, and cool(er)interior wall
surfaces.(Insulation may also reduce heat transfer through
walls by radiation and convection).
Fig.5-4:Heat Transfer by Convection.
In convection, heat is transferred through
a fluid (air or water).
Warm fluids rise, cooler fluids sink.
Venting hot air can prevent heat build up in attics and
occupied spaces.
Natural ventilation uses convective heat transfer to carry
heat away.
Figure 18: Modes of Heat Transfer
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Radiated Heat Transfer
Heat from the sun radiates through space as electromagnetic energy in the near infrared range (near
IR).Heat re-radiated from hot surfaces is in the form of electromagnetic energy in the far infrared range
(far IR). Understanding the difference between near infrared solar heat and far infrared heat radiated by
materials that have been warmed by the sun is important in understanding radiated heat transfer.
Figure 19: Radiated Heat Transfer
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Field Guide Chapter 7: Insulation and Radiant Barriers
Insulation and radiant barriers can significantly reduce heat buildup in a building.
To use insulation and radiant barriers effectively, it is important to understand these materials and how
they work.
Insulation
Insulation works by resisting the transfer of heat through building walls, roofs, and ceilings. The higher
the R-value (Thermal Resistance),the greater the ability of the material to insulate.
Insulation is like a resistor, it does not stop the transfer of energy, it just slows it down. If you have two
boxes joined by one wall with ideal thermal isolation in all the other walls, ie: no heat transfer through
those walls, and you start with one room hotter than the other, the two rooms would end up at the same
temperature after a sufficient period of time. So insulation does not prevent the heat transfer, it just
slows it down.
It is easier to understand the heating condition. For example, you want to maintain a building at 20C
when the temperature is 0C outside. The inside heat energy is always trying to move through the walls
to reach thermal equilibrium with the outside colder air mass. By doubling the R-Thermal Resistance
(Insulation), you will reduce the amount of heat you have to add by 50%.
It works the same for cooling, the more insulation you add the less cooling energy you have to add to
use to maintain the same temperature (actually the temperature difference between the outside ambient
and the inside temperature).
Figure 20: Insulation: Barrier to Heat Transfer
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Field Guide Chapter 8: Heat Mitigation in Roofs
The roof is the greatest source of heat gain for homes in Hawaii, receiving about 1,700 Btu per sq. ft. per
day. Solar radiation coming through the roof can account for a third of the heat build-up in a house. A
roof can reach a temperature of 150  F, even when the ambient outdoor temperature is only 80 F. By
paying special attention to the roof, you can make significant strides in preventing uncomfortable heat
build-up in your home.
Several strategies address heat transfer through the roof. These include:
 •Shading from existing trees, nearby structures, and topography
 •Light colored roof surfaces
 •Insulation
 •Radiant barriers
 •Roof vents
Using a combination (or all) of these strategies is the most effective way to achieve a comfortable, cool
home, significantly reducing or even eliminating the need for air conditioning.
Recommended Technique: Integrate roof strategies.
Using a combination (or all)of the measures listed above is the best, most complete way to ensure a cool
home. Using these materials and techniques will reduce heat gain and can reduce or eliminate the need
for air conditioning.
Figure 21: Hawaii Field Guide's "Solar Shade Wall"
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Radiant Barriers as referenced in the Field Guide.
Radiant barriers are thin sheets of highly reflective material that prevent heat from building up in the
home by “reflecting ” rather than absorbing and then re-emitting heat. The lower the “emissivity ”
rating, the more effective the radiant barrier. The higher the emissivity, the more energy an object reradiates when it is heated by an external source.
Radiant barriers reduce the heat transfer since the radiant barrier reflects the short wave infrared
radiation back towards the source.
Compare the above section Field Guide Chapter 8: Heat Mitigation in Roofs”, with the Canadian
Pacific Railway’s Solar Shade Wall. There are many similarities in approach and net results.
The natural convection of airflow into the “under eaves” opening and out through the ridge vent acts like
CPR’s Thermal Chimney.
The radiant barrier is more important for conventional roofing because typical roofing materials absorb
and re-radiate (the emissivity factor) more than the railway’s aluminum buildings. The aluminum
original skin of the building also acts as an excellent radiant barrier.
Canadian Pacific Railway’s current conclusion is that the natural convection “thermal chimney” is the
key to the main heat transfer reduction achieved for the railway aluminum buildings.
Instrumentation:
Data was collected using a Fluke Hydra 21 channel Datalogger.
Raw data is available on request.
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Website URL additional References:
Examples of broader forms of "thermal chimney" design, as used by the architect Virginia McDonald,
are listed on the State of Hawaii’s website at http://www.state.hi.us/dbedt/ert/macdonald.html and
http://www.state.hi.us/dbedt/ert/usethesun.html.
For more information on Radiant Barrier’s, see http://www.ornl.gov/roofs+walls/radiant/. This site deals
with Building Envelope Research per the Oak Ridge National Laboratory
For more information on building temperature measurements; see http://blt.colorado.edu/.
For more information on Cool Roof Designs, see http://eetd.lbl.gov/HeatIsland/ and/or
http://www.fsec.ucf.edu/.
For information on heat transfer through walls, see the National Research Council of Canada’s
“effect of temperature gradients through building envelopes” (CBD 36) http://irc.nrccnrc.gc.ca/cbd/cbd036e.html and/or CBD-52.“Heat Transfer at Building Surfaces” http://irc.nrccnrc.gc.ca/cbd/cbd052e.html.
For examples of double building envelope construction, wee http://www.enertia.com/science.htm.An
airflow and access channel, or Envelope, runs around the building, just inside the walls creating a miniature biosphere.
For partial implementation of the shade concept incorporated into a product, see
http://www.colbond-usa.com/. Enkamat or Enkatherm replaces furring strips in commercial
roofing when a ventilation layer is needed between the insulation and the sheathing.
http://www.benjaminobdyke.com/html/products/tech/tech_upward.html
Attic air heated by contact with a hot roof on a sunny day tends to rise. Thus, in a zero wind
condition, without the benefit of a positive airflow across the roof, it is important for an attic
ventilation system to function. Additionally, this system should work with a small difference in
attic air temperature and outside air temperature (called delta T and expressed as T).
See http://www.verdatech-inc.com/ which links to
http://www.toolbase.org/tertiaryT.asp?DocumentID=2140&CategoryID=1017 for multiple links.
See http://irc.nrc-cnrc.gc.ca/practice/wal3_E.html for Facts and Fictions of Rain-Screen Walls.
Rain Screen walls may act as thermal chimneys depending on the actual implementation of
the wall cavity.
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Permissions for quoted material:
Dear Mr. Brackett:
Thank you so very much for your interest in energy efficiency and in our publications. As project manager of the
"Field Guide for Energy Performance, Comfort, and Value in Hawaii Homes," please permit me to state that as
long as you give credit to the U.S. Department of Energy and the Hawaii Energy Division, you may quote from
that publication. There is no "copyright holder" because this publication was developed and printed from USDOE
grant funds.
Dean Masai
Energy Analyst
Energy, Resources & Technology Division
Department of Business, Economic Development & Tourism
State of Hawaii
Voice: 808-587-3804
Honolulu, HI 96804E-mail: dmasai@dbedt.hawaii.gov
From: Carilyn Shon [mailto:CShon@dbedt.hawaii.gov]
Sent: July 11, 2003 5:24 PM
To: Dean Masai
Cc: Howard Wiig; Maria Tome; Peter Brackett; eileen.yoshinaka@ee.doe.gov
Subject: Re: Request from railway engineer for permission to quote from Field Guide
Mr. Brackett:
At minimum, the citation should read: "Information for publication was funded by the U.S. Department of Energy Grant
#DE-FG51-97R020881. Information does not reflect the views of, nor constitute an endorsement by, the USDOE."
I'm glad that you find the information useful and encourage you to use whatever will be of value for your program.
Aloha,
Carilyn O. Shon
Energy Program Manager; Energy, Resources, and Technology Division
Department of Business, Economic Development, and Tourism
235 South Beretania Street
P.O. Box 2359
Honolulu, Hawaii 96804
Phone: (808) 587-3810; Fax: (808)587-3820
e-mail: cshon@dbedt.hawaii.gov
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