Post on 12-Sep-2021
Solar Hot Water Heating SystemsSolar Hot Water Heating Systems
Courtesy of DOE/NREL
PG&EPG&EPacific Energy Center, San FranciscoPacific Energy Center, San Francisco
Energy Training Center StocktonEnergy Training Center StocktonEnergy Training Center, StocktonEnergy Training Center, Stockton
InstructorInstructor
Pete ShoemakerPete ShoemakerPG&E Pacific Energy CenterPG&E Pacific Energy Center
(415) 973(415) 973--88508850pjsy@pge.compjsy@pge.compjsy@pge.compjsy@pge.com
with assistance fromG Paul Menyharth of theG Paul Menyharth of the American Solar InstituteG. Paul Menyharth of the G. Paul Menyharth of the American Solar Institute
andJosh Plaisted of Kineo Design and PVT Solar
Agenda
• Industry overview• Essential physics• Terms and conceptsp• Collector and System types• Site evaluation and designSite evaluation and design
The Full Energy Picture
PG&E Portfolio Solution
1) Reduce consumption asReduce Energy
Use
1) Reduce consumption as much as possible.
2) Get theUse
Partnership
2) Get the “greenest” power you can.3) Offset any
Renewable PowerClimateSmart
Education
Outreach
) yremaining carbon emissions. Power
SupplyClimateSmart
Li htLi ht
Different Types of “Solar”Light energyLight energyPhotovoltaic (PV)Electricity produced directly from lightElectricity produced directly from light
Heat energyHeat energyC t t d S l P (CSP)Concentrated Solar Power (CSP)Electricity produced by steam
Solar Pool HeatingHot water for poolsHot water for pools
Solar Water Heating (SWH - Solar Thermal)Hot water for domestic use (DHW)
All courtesy of DOE/NREL
Solar Pool HeatingSwimming pool water heatingSwimming pool water heating
80 - 85 degrees from May to October
Courtesy of DOE/NREL
M t i d t ith i k t i C lif i d Fl idMature industry with main markets in California and Florida.
Overview
Courtesy CCSE
Overview
Courtesy CCSE
Overview
Courtesy CCSE
Overview
Courtesy CCSE
SHW Industry Overview: World
By Permission: REN21. 2008 ”Renewables 2007 Global Status Report”By Permission: REN21. 2008 Renewables 2007 Global Status Report (Paris:REN21) © 2008 Deutsche Gessellschaft fur Technische Zusammenarbeit GmbH
SHW Industry Overview: U.S. History
1890 to 1930’s: Beginnings in California
1930 to 1973: Growth in Florida
1973 to 1986: Oil Embargo and Carter Tax Credits
1986 to 2003: Removal of Tax Credits and Decline
2003 – present: Revival of Incentives and Climate Action
Industry Overview: U.S.
Federal Tax Credit:
Favorable regulatory environment
Federal Tax Credit:• Extended through 2016
30% f b th i l d id ti l• 30% for both commercial and residential• MACRS depreciation for commercial
Other state and local rebate programs exist or are in the planning stages.
Industry Overview: California
State rebate program: AB1470
• Applications accepted 5/1/10 (residential) and TBD (commercial).
• Systems installed after 7/15/09 eligible.
• Allocation is 40% residential, 60% commercial and multi-family.
Essential Physics
Courtesy ofNASA
It all starts with the sun.
Electromagnetic Spectrum
10 -3 10 -7
heat light
Continuum of energy
Courtesy of Wikipedia
Continuum of energy.
Greenhouse Effect
Ozone layer
Short waves get throughlight
Long a es are trapped
Earth
Long waves are trapped
heatEarth
Greenhouse Effect
Glass
Short waves get throughlight
Long a es are trappedHeat absorber Long waves are trapped
heatabsorber
SWH collector
Color Absorption
Dark colors absorb a lot, reflect little
Li ht l b b littl fl t l tLight colors absorb little, reflect a lot
Metal Conductivity
Some metals transfer more heat than others.
FluidFluid Fluid
Pipe cross-section
Copper Ironp
Water Behavior
Water expands both when heated and frozen.
Steam IceIce
Moving water will NOT freeze.g
Water Behavior
Warm water will rise, cold water will sink.
Water Behavior
Water contains dissolved minerals, which can cause unwanted buildup and clogging.gg g
• “Hard” water contains more minerals, “soft” water less.
• Most common minerals are calcium and magnesium.
• The buildup of minerals is called “calcification” or “scaling”.
Essential Physics: Summary
• Greenhouse effect• Light enters but heat trappedg pp
• Color absorption• Dark colors absorb and light colors reflect
• Metal conductivity• Copper conducts more than others
W t b h i• Water behavior• Expands when heated and frozen• Moving water will not freeze• Moving water will not freeze• Warm water rises, cold water sinks• Water contains dissolved minerals
Which leads to …
Glass-covered collectors, dark-colored, with copper or aluminum piping…
Systems designed to take advantage of the movement of heated waterof heated water …
With protection againstWith protection against freezing, overheating, and mineral buildup.mineral buildup.
Terms and Concepts
Courtesy ofNASA
Terms and ConceptsBTU: British Thermal Unit Amount of heat needed to raiseBTU: British Thermal Unit. Amount of heat needed to raise one lb. of water one degree F.
Watt-hour: 3.4 BTU Kilowatt-hour: 3,413 BTU,Therm: 100,000 BTU (29.3 kWh)
Th i h N t l f h t t i i (i t b )Thermosiphon: Natural process of hot water rising (in a tube).Stratification: Separation of hot and cold water (in a tank).H t h D i th t t f h t f di
Climate zones: Areas of distinct seasonal temperatures
Heat exchanger: Device that transfers heat from one medium to another.
Climate zones: Areas of distinct seasonal temperatures.Hard freeze: A freeze in which seasonal vegetation is destroyed, ground is frozen solid, and heavy ice is formed.y g y
Stagnation: Condition when collectors are not used and become overheated.
Terms and Concepts
System design: Storage is the key.
Solar Electric: Solar Thermal:
Tied to the grid. Every kWh is used,
No grid--you’re on your own.
no waste.yPotential for waste.
Courtesy of DOE/NREL
Terms and ConceptsSolar Fraction: Percentage of building’s hot water requirements that can be met by solar—at optimum economics (no waste).
Example:Design to cover 100% of usage year-round, including winter.Minimal sun in winter, so need many collectors (expensive).
But in summer sun these collectors produce far more hot waterBut in summer sun, these collectors produce far more hot water than you use, and you can’t store it or sell it.Wasted energy, wasted money.
Solar Fraction: Design
Cover 100% in summer.Will result in 30 – 50% in winter.
Average year-round coverage of 60 – 70% in PG&E territory.
Will ALWAYS need a backup heating source (gas or electric).
Change in perspective
Solar Electric: Solar Thermal:
Selling / maintaining Selling / maintainingSelling / maintaining“solar”
Selling / maintaining “total hot water system” (solar + backup)
Courtesy of DOE/NREL
Change in perspective
One overall system
solar + backupp
One overall costO ll ffi i
One overall maintenanceO ll lifOne overall efficiency One overall lifespan
Collector and System Types
Courtesy ofNASA
Standard Water Heaters
Typical gas heater:
Direct flue.
M h h t l “Much heat loss “up the chimney”.
Low efficiency.
(50 – 70%)( %)
Courtesy PG&E
Standard Water Heaters
Improved model:
Same basic technology, better insulationbetter insulation.
Efficiency around 70 –80%80%.
Source: Energy Star
Standard Water Heaters
More improved model:
Condensing heater.
Extended flue which releases much of its heat to the water before
tiventing.
Vent gases are cool enough to condense.
Efficiency around 80 –
Source: Energy Star
y90+%
Standard Water Heaters
New model:
Heat pump.
Like refrigerator in reverse.
Electric powered, no gasElectric powered, no gas burning.
Best to replace electricBest to replace electric water heater.
Source: Energy Star
Standard Water Heaters
Tankless
Gas or electric.
Can require specialCan require special hookup service.
Effectiveness related toEffectiveness related to usage patterns.
Source: Energy Star
System Overview
Five main aspects of solar systems:
1. Heat collection2 Heat transfer2. Heat transfer3. Heat storage4 Heat backup4. Heat backup5. Extreme temperature protection
(f i / t ti )(freezing/stagnation)
System Overview
Five main aspects of solar thermal systems:
1. Heat Collection
2. Heat Transfer
3. Heat Storage
5. Extreme Temperature Protection
4. Heat Backup
Special valves, pumps, processes,
Solar panel
Water or glycol Storage
etc.Gas or electric heaterp g
tank
System Overview
Two types of heat transfer systems:
1 O L 2 Closed Loop1. Open Loop (Direct)
2. Closed Loop (Indirect)
water glycolwater glycol
Uses just the water from the main.
“O ” t t id
Uses heat-transfer fluid in “closed” system.
“Open” to outside elements.
Needs heat exchanger.
Collector and System Types
Two types of heat transfer systems:
1 O L 2 Closed Loop1. Open Loop (Direct)
2. Closed Loop (Indirect)
water glycolone fluid Heat
loopPotable water
HX
water glycol
Uses just the water from the main.
“O ” t t id
Uses heat-transfer fluid in “closed” system.
“Open” to outside elements.
Needs heat exchanger.
System Overview
Further categorized by “pumping” source:
1 P i1. Passive (natural)
2. Active (electric pump)
Thermosiphon process.
T k t b hi h
Must have electric source.
Tank must be higher than collector. Tank can be anywhere.
Collector Types
ICS (Batch) Flat Plate Evacuated Tube
Fi NRELFigure courtesy NREL
ICS: Integral Collector Storage
Heat St
Heat C ll i StorageCollection
Storage tank
Solar panel
ICS: Integral Collector Storage
Courtesy energybychoice.com
ICS: Integral Collector Storage
Hot water out
Roof tiltout
Cold water in
Holds 20 to 40 gallons of waterg
ICS: Integral Collector Storage
Courtesy NREL
Flat Plate Collector
Headers Risers
Figure courtesy SunEarth
Flat Plate Collector
“Fin” for heat absorption
Souce: PG&E
Flat Plate Collector
H t t
Header
Hot water out
R fRoof tilt
Ris
ers
C ld
Header
Cold water in Holds about one gallon of fluid
Evacuated Tubes
Photo courtesy Industrial Solar Technology Photo courtesy William Lord
Figure courtesy Edwards Hot Water
Courtesy of DOE/NREL
Evacuated Tubes
Copper rod: may be solid or hollow.
Heat moves eat o esup to bulb.
Double glass wall with vacuum between.
Souce: PG&E
Evacuated TubesFigures courtesy Thermomax
1. Vacuum tube2 Heat pipe
67
2. Heat pipe3. Cold liquid4. Hot vapor 2
1
3
89
4. Hot vapor5. Absorber 4
3
6. Collector return (hot)
5
(hot)7. Collector supply
(cold)8. Heat exchanger9. Shock absorber
H d
Evacuated Tubes
Cold water in Hot water out
Header
Roof tilt
Holds little or no fluid
H d
Evacuated Tubes
Cold water in Hot water out
Header
Roof tilt
Holds little or no fluid
Plumbing Different Collectors
Photo courtesy Industrial Solar Technology
Flat Plate Evacuated tube
ReturnReturnSupply
S lSupply
ICS: Integral Collector StorageThe Simplest Form of Solar
Benefits
p
• Low first cost• No moving parts• Inherent overheat protection• Moderate freeze protectionModerate freeze protection
Disadvantages• Sensitive to ambient temperatures• Sensitive to ambient temperatures• Weight
Figure courtesy SunEarth
Sample specifications
Figure courtesy NREL
Simple system with ICS Courtesy of EERE
Simple system with ICS
Heated water moves to top
Hot water is drawn into tank
120 degree water goes into house
Additional heating element boosts temperature as
into house
Water comes in from main
boosts temperature as necessary
System Characteristics
F t i l ICS t
Passive
For typical ICS system:
Passive• No pumps, nothing requiring outside power
Open Loop• New fluid (water) is constantly entering—system is “open”
to outside elementsto outside elements
Figure courtesy NREL
Flat Plate CollectorsThe Industry Workhorse
Figure courtesy SunEarth
Sample specifications
Figure courtesy SunEarth
Figure courtesy NREL
Thermosiphon Passive Systems
Photo courtesy NREL
Thermosiphon Passive Systems
Courtesy CCSE
Thermosiphon Passive SystemsT k t bl tTank—potable water
Heat-exchange loop—”closed” to outside elements
Separation between water in tank and heat-exchange fluid
Figure courtesy SunEarth Inc
Thermosiphon Passive SystemsAdditional heating element boosts t t
W t i
temperature as necessary
120 degree water goes Water comes in to tank from main
g ginto house
Heated fluid rises
Heat is transferred to
Cooled fluid sinks
Heat is transferred to water in tank
Solar fluid circulates
Figure courtesy SunEarth Inc
Solar fluid circulates through collector
System Characteristics
F t i l t k f t
Passive
For typical tank-on-roof systems:
Passive• No pumps, nothing requiring outside power
Closed Loop• Heat-exchange loop is closed to new elements
Open LoopAlso can be:
Open Loop• New fluid (water) is constantly entering—system is open
to new elements
Figure courtesy NREL
Active Systems
P
Can be Open- or Closed-loop
Active Systemsp p
Benefits• Highest thermal performance• Freeze protection to –60 F• Lightweight low roof profile
DisadvantagesDisadvantages• Some active components• More expense and maintenance
Figure courtesy SunEarth Inc
Courtesy of DOE/NREL
Active Systems
Courtesy University of Central Florida
Active Systems
Courtesy University of Central Florida
System Characteristics
F t i l fl t l t t d t b t
Active
For typical flat plate or evacuated tube systems:
Active• Uses pumps and other active elements
Open Loop• Potable water itself is heated
oror
Closed Loop• Glycol is heated and heat-exchanger is usedGlycol is heated and heat exchanger is used
Figure courtesy NREL
Freeze Protection
1 Thermal mass (ICS)
Six different methods (can be combined):
1. Thermal mass (ICS)2. Antifreeze (closed loop glycol)3 Auxiliary heater (electric element)3. Auxiliary heater (electric element) 4. Drip valves (moving water won’t freeze)5. Forced circulation of hot water (DFC) 6. Draining (removing water from collector)
Figure courtesy NREL
Thermal Mass
20 to 40 gallons of water will only freeze under extreme conditions.
ICS systems are freeze-protected in mild (coastal) climate zones.
Antifreeze
• Closed-loop (indirect) systems
• Uses food-grade glycol, specific mixture depending on climate zone.
• Must be serviced every 5 – 15 years.
• The hotter the glycol is run, the more it breaks down and the sooner it needs to be replaced.
• Freeze protection up to 40 degrees below zero.
Auxiliary Heater
• Electric resistance (strip) heater on pipes, collectors.
• Like a heating padLike a heating pad.
• Triggered at specific temperature.
Vulnerable to power outages• Vulnerable to power outages.
Drip Valves
Membrane in valve retracts at around 40 degrees, permitting water to drip out onto the roof.
Courtesy University of Central FloridaCourtesy University of Central Florida
Drip valves are good backup protection against mild freezes, but are vulnerable to failure, particularly in hard-water areas.
Direct Forced Circulation (DFC)
Freeze drain valve Always combined with drip valve(s).
Courtesy University of Central Florida
Direct Forced Circulation (DFC)
Freeze drain valve
In freeze conditions, reverse flow gi es p heatgives up heat to protect the system.
Hot water
Courtesy University of Central Florida
Drain-back System (closed loop)
Collectors are always empty
hen s stemwhen system (pump) is not running.
Courtesy University of Central Florida
Drain-back System (closed loop)
Start up: Collectors areCollectors are filled and heating cycle begins.
Courtesy University of Central Florida
Drain-back System (closed loop)
Shut down: CollectorsCollectors automaticallydrain and heating cycle ends.
Courtesy University of Central Florida
Drainback System
• Closed loop• Can use water or glycol in heat-collection loopg y p• Fluid is drained from collectors whenever
system is not runningsystem is not running• Needs large pump to push water into collectors• Pipes must be sloped properly for drainagePipes must be sloped properly for drainage
Figure courtesy NREL
Site Evaluation and System Design
Courtesy ofNASA
Site Evaluation and Design
Criteria:• Solar resource
A il bl d i t ti• Available space and orientation• Climate zone (temperature range, freezes)• Hot water usage amount and patternsHot water usage amount and patterns• Economics
Courtesy of DOE/NREL
Solar Resource
Peak SunPeak Sun--hours Measured in kWh/mhours Measured in kWh/m22/day/day
Source: DOE National Renewable Energy Laboratory (NREL) Resource Assessment Programhttp://rredc.nrel.gov/solar/old_data/nsrdb/redbook/atlas/serve.cgi
Shading
• SWH panels not as sensitive to shading as solar electric (PV) panelssolar electric (PV) panels
• Shade measurements and tools similar to that of PVthat of PV
• Major difference: the SWH rebate program l id h di f 10 3only considers shading from 10 to 3.
Solar WindowSunriseSunset
Solar Window“Shade-free from 10 to 3”
Tilt and Orientation
Tilt l f th h iTilt = angle from the horizon.
Orientation = Azimuth = direction north-south in which the panels are facingwhich the panels are facing.
tilt angleºEx. 30º axis
From Horizon
Tilt Azimuth
Surface Orientation Factor (SOF)
90San Francisco, CA
600.40-0.500 50 0 60
SOF
30
Tilt0.50-0.600.60-0.700.70-0.800 80 0 90 300.80-0.900.90-1.00
Chart courtesy NREL
-90 -60 -30 0 30 60 900
AzimuthEast Westy
Rough Home Estimate
D h 60 80 f f f (• Do you have 60 to 80 square feet of roof (or ground) space that is unshaded from 10 to 3?
• Is it on a non-North facing slope (flat is OK)?
If you pass this first screening then the next step is to solicit bids from contractors. They can determine the yappropriate system and give a financial assessment.
Solar PathfinderSolar PathfinderUsed toUsed to gain a quick and approximate understanding gain a quick and approximate understanding
of of solar accesssolar access and objects on the horizon that shade a and objects on the horizon that shade a jjgiven location.given location.
• Latitude specific sun path diagram is placed in the pathfinder.
• The transparent convex plastic domeThe transparent, convex plastic dome reflects objects on the horizon, enabling the user to see the relationship between th bj t d th th f ththese objects and the path of the sun.
• Obstructions can be traced onto sunpath diagram.p g
Solmetric SunEyeSolmetric SunEyeTMTM
• Handheld measurement d i th tdevice that accurately measures solarmeasures solar access and shading (about g ($1400)
Courtesy: Solmetric, Corp.
Mounting
Mounting
Usage
How much energy are you using to heat water?
Usually it’s not easy to determine, since water heating bills can include space heating and cooking as well.p g g
Three ways:Three ways:
1. Direct measurement
2 Bill l i2. Bill analysis
3. Estimation from industry standards
Industry Standards / Surveys
Average hot water usage per home per day:
• 20 gallons for the first person0 ga o s o t e st pe so
• 15 gallons for the second
• 10 each for all others• 10 each for all others
4 person household =
20 + 15 + 10 + 10 = 60 gallons per day
These assumptions are used in the CSI Thermal li l l tonline calculator.
Industry Standards / Surveys
Natural Gas Water Heating
Averages for typical 4-person home in PG&E territory:
Natural Gas Water HeatingYearly usage: 200 thermsYearly cost: about $300 (current prices)Typical solar fraction: 65 70%Typical solar fraction: 65 - 70%Typical solar savings: about $200 per year.
Electric Water HeatingYearly usage: 3,500 kWhYearly cost: about $700 (current prices)y $ ( p )Typical solar fraction: 65 - 70%Typical solar savings: about $500 per year.
Electric heating is 2 to 3 times as expensive as gas.
State Rebate Program: AB 1470Modeled after the very successful solar electric program (CSI)Modeled after the very successful solar electric program (CSI) to lower costs and raise product and contractor quality.
Uses online entry/calculation program:Uses online entry/calculation program:
• Only allows approved systems.
• Makes sure system is sized appropriately.
• Ensures proper freeze protection for climate zone.
• Gives conservative estimate of production.
• Determines rebate.Determines rebate.
State Rebate Program: AB 1470In additionIn addition…
All contractors or self-installers who want to participate in the rebate program must attend a one-day workshop given by therebate program must attend a one day workshop given by the Program Administrators.
After attending they will receive a unique ID number to use in g y qthe online entry program.
The URL for the CSI Thermal site is: www.csithermal.com
For a list of registered contractors go toFor a list of registered contractors go to
http://www.gosolarcalifornia.ca.gov/solarwater/contractors.php
Rebate Program: AB 1470Systems must be SRCC certified: www solar rating orgSystems must be SRCC certified: www.solar-rating.org
OG 300OG-300
System ratings
OG-100OG-100
Panel ratings
Sample Costing
Savings:• Average yearly usage 210 therms• Solar saves 70% of that, or 147 therms• Average cost per therm $1.37• Yearly savings about $200 (first year)
Cost:• Total installed price $7000• State rebate $1875 (147 * $12.82 up to max)• Tax credit ((7000-1875) * .3) = $1537• Net cost = (7000 – 1875 – 1537) = $3588
Glycol:Sample Costing
y• Will need to be recharged every 5 – 10 years• Best to be professionally done• Estimate of $250 per visit• Total about $750
Pump(s):• At least one replacement
E ti t f $500 $1000 $750• Estimate of $500 - $1000, use $750
Tank + heat exchanger• At least one replacement• Estimate $1000
Estimated total = $750 + $750 + $1000 = $2500
Natural Gas:
Sample CostingNatural Gas:• Typical heater costs $500• Labor costs can be another $300 - $500• Lifespan is 7 – 10 years• Electric heaters may be somewhat less
Conservative total approx. $2500Similar to solar maintenanceSimilar to solar maintenance
What’s a reasonable assessment?
Sample Costing
Solar needs to maintain both systems (solar + backup), but backup works 70%(solar backup), but backup works 70% less.
Can we assume 70% less maintenanceCan we assume 70% less maintenance costs for backup?
If so backup costs with solar would beIf so, backup costs with solar would be about $2500 * .3 = $750.
Maintenance with solar (25 yrs.)
M i i h lMaintenance costs with solar:
$2500 (solar) + $750 (backup) = $3250
Maintenance costs without solar: $2500
Difference: $3250 - $2500 = $750
Conclusion: solar maintenance costs areConclusion: solar maintenance costs are about $750 extra than before, and this should be added in to the overall cost of a solar system.
Works out to about $30/year, or aboutWorks out to about $30/year, or about 0.5% of the purchase price per year.
Sample Costing
Payback:First cost: $3 600• First cost: $3,600
• Maintenance adder: $750T t l lif l t $4350• Total lifecycle cost: $4350
• Savings first year: $200• Straight payback (no inflation factor) =
4350 / 209 = 21 years• With inflation factor of 5.5%, payback
shortens to about 15 years.
EconomicsIt’s recommended that you get at least three bids fromIt s recommended that you get at least three bids from reputable contractors. The bids should all contain the following, clearly specified:
• Full price, including tax, permit, and any additional charges.g
• Estimated maintenance costs and maintenance schedule.
• Estimated production, based on the CSI Thermal calculator output.
• Estimated first year and system lifetime savings, based on reasonable assumptions of utility costs and inflation.
• Warranties for all products and labor, clearly written.
Solar Water Heating Benefits
• Saves money• Lowers greenhouse gas emissions (local
and national goals)• Qualifies for state and federal incentives• Promotes energy independence• Keeps money in local economy
Thank you for participating!PG&E P ifi E C tPG&E Pacific Energy Center
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