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ACTIVE SOLAR THERMAL SYSTEMS
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Reminder—Solar versus Terrestrial Radiation
Heating, Cooling, Lighting: Norbert Lechner
shorter ……………… longer
wavelengths
not
to s
cale
the energy action is here
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Reminder—Solar Radiation Components
lots of energy
some energy
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Reminder: Solar Paths
NORTHERN HEMISPHERE
orientation and tilt of a surface will affect magnitude of received solar energy
focus of sunpath diagrams is direct solar
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Possible Solar EnergyConversions
• Helio-chemical conversion– Solar radiation to chemical energy
• Photosynthesis: food, biomass
• Helio-electrical conversion– Solar radiation to electrical energy
• Photovoltaics (PV)
• Helio-thermal conversion– Solar radiation to heat energy
• Passive and active approaches
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Active Solar Thermal Systems
Configuration Options• Water or air as the heat exchange medium
• Flat-plate or concentrating collector configurations• Fixed or tracking collector installations
Potential Applications• Domestic hot water (potable water)
• Space heating• Space cooling (via an absorption chiller)
• Process heat (product production)
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Solar Thermal System Components
These systems involve an energy SOURCE (solar radiation—a renewable resource with zero carbon emissions)
harvested by acollector with aperture (the aperture defines system “size”)
and absorber (to convert radiation to heat) that isconnected to heat storage (generally required by the nature
of the cyclical solar source) and often involving abackup heat source (for extreme conditions). The collected heat is moved via a heat transfer medium (air or water) that is part of the DISTRIBUTION and DELIVERY subsystems.
CONTROLS make the whole thing work well.
the focus herein is on active systems, with “dedicated-purpose” components
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Example—Air-Based Collector
inlet duct
outlet duct
flat plate collector, fixed, used for space heating
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Air Collector System Schematic
solar radiation is captured and converted to heat in a collector—then conveyed via hot air (in ductwork) to storage in a masonry mass (rock bed)—and then delivered where the heat is needed
cooler air returns to the collector to be reheated, and the cycle continues
there is no solar heatingpotential at night; thus the need for heat storage
supply air
return air
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Example—Solar Rock Bed Storage
air has virtually no thermal capacity, but hot air can transfer its heat to rocks; this type of storage seeks a balance between density (to provide thermal capacity) and porosity (to permit air flow without excessive pressure loss)
peop
le.u
mas
s.ed
u/
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Air Collector System Diagram
source
storagedelivery
distribution
controls
backupsource
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Backup? Storage?The backup heat source shown in the previous schematic is
a necessary part of a solar thermal heating system—if space conditions need to be maintained under any and all
weather conditions. This adds to the first cost of the system (the system has both solar-source and
conventional-source components). The need for such a backup should be carefully considered.
The basic elements of a solar heating system (source, distribution, delivery, control) are common to all heating
systems. Storage, an additional element (and expense), is required to deal with the variable and cyclical nature of
the energy source (the sun). It is very difficult to eliminate thermal storage.
a first-cost analysis will seldom favor active solar thermal (more investment); a life-cycle cost analysis may often favor active solar thermal (reduced energy)
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Example—Water-Based Collector
housing
fluid outlet
fluid channels
(tubing)
insulation
glazing(aperture)
…it was that way
when I found it
collector surface(absorber)
flat plate collector, fixed, use not obvious (could be space heating or domestic hot water)
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Water Collector System Schematic
solar radiation is captured and converted to heat in a collector … then conveyed via hot water to storage in a tank; a heat exchanger (radiator, etc.) is needed to get heating effect into the room
as with an air system, the water flows in a cyclical (but always closed) loop
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Water Collector System Diagram
showing common elements of source,distribution, and delivery—plus storage and a backup source typical of a solar system (controls would also be provided)
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Example—Solar Hot Water Storage
one hopes (aesthetically) that this is a retrofit installation;
but in any case storage tanks can be large—especially in a residential occupancy where
times of greatest use (mornings and evenings) do not match time of greatest solar collection (daytime)
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Example—Evacuated Tube Collectors
this type of collector provides some concentration, has low losses, high efficiency
www.solardecathlon.org/
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Example—Custom Collector
aperture area = absorber area … this is the definition of a flat plate collector
the collector serves as roofing and structure (for a
mechanical room)
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Library, Los Alamos National Lab
a quite large flat plate solar collector array, integrated into a building usingcustom collectors (see previous slide)
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Los Alamos Solar System
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rsid
e of
col
lect
ors
is r
oof o
f mec
hani
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oom
;da
rker
yel
low
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ts a
re fl
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head
ers
clos
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of c
olle
ctor
edg
e sh
owin
g du
st/le
akag
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Active Solar Aestheticsspace heating systems
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Building-ScaleTracking, Concentrating Collectors
Fresnel lens concentrating and tracking collector (one-axis tracking; only the orientation changes), may be used for space cooling and space heating
image shows small part of a large roof-mounted array
absorber tube (contains water)
faceted (Fresnel) lensconcentratesdirect solar radiationonto absorber tube
axis of rotation
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District-Scale Tracking, Concentrating Collectors
test
inst
alla
tion,
San
dia
natio
nal L
abs
concentrating and tracking collector,with one axis tracking(the tilt changes)
axis
of r
otat
ion
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District-Scale Tracking, Concentrating Collectors
mun
icip
al p
ower
gen
erat
ion,
Aus
tral
ian
outb
ack
parabolic concentrating and tracking collectors (two axis tracking)
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Concentrating Solar Power (CSP)Collector Array
flat, concentrating and tracking (two axis) solar collectors with tower receiver; used for commercial electricity production
power tower with heliostats, Sandia (NM)
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Concentrating Solar Power (CSP)Collector Array
CSP installation, Morocco)
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Active SolarAesthetics
one of the first actively solar heated buildings in the US; collector panels were site fabricated and are actually refrigerator “coil” panels
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Active Solar Aesthetics
domestic hot water heating
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Active Solar Collector Efficiencies
note relative efficiency of various collector types and drop in efficiency with difference in fluid versus ambient temperature; compare these efficiencies to PV modules (≈18%)
sola
rpro
fess
iona
l.com
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End note
A cat sunning himself in the doorway of a barn knows all about solar
energy. Why can’t man learn?
E.B. White
As quoted in The Return of the Solar Cat Book
Michael Toland Grondzik
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the DOE Solar Decathlon as a Showcase of Solar Homes
the following slides are provided as a window
into current design thinking about what a solar-powered
single-family residence might look like;
The majority of the collectors shown are PV (necessary to
reach the net-zero-energy goals of the competition), but
most of the homes also include solar
thermal collectors (to provide domestic hot water)
these projects will not appear on the quiz
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2005 Solar Decathlon Entries
all 2005 images from USDOE WWW site:
http://www.solardecathlon.org/highlights_2005.html
all 2005 entries (buildings) had both solar thermal and PV
collectors; consider theaesthetics of the various building
designs and integrations
sited in Washington, DC
(National Mall)
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Cal Poly San Luis Obispo
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Concordia and Universite de Montreal
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University of Colorado
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Cornell University
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Crowder College
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Florida International
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New York Institute of Technology
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Pittsburgh Synergy
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Rhode Island School of Design
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Universidad de Madrid
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Universidad de Puerto Rico
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University of Maryland
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University of Michigan
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Rolla (Missouri) Consortium
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University of Texas at Austin
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Virginia Tech
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2009 Solar Decathlon: Illinois
sited in Washington, DC
(West Potomac Park)
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2009 Solar Decathlon: Illinois
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2009 Solar Decathlon: Germany
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2009 Solar Decathlon: Germany
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2009 Solar Decathlon: Cornell
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2009 Solar Decathlon: Cornell
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2013 Solar Decathlon: Louisville / Ball State
sited in Irvine, CA
(Orange County Great Park)
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2013 Solar Decathlon: Louisville / Ball State
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2013 Solar Decathlon: Louisville / Ball State
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2013 Solar Decathlon: Louisville / Ball State
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2015 Solar Decathlon: Buffalo
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2015 Solar Decathlon: Buffalo
PV
solar
thermal