presentation solar water heating

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PG&EPG&EPacific Energy Center, San FranciscoPacific Energy Center, San Francisco

Energy Training Center, StocktonEnergy Training Center, Stockton

Solar Hot Water Heating SystemsSolar Hot Water Heating Systems

Courtesy of DOE/NREL

Pete ShoemakerPete ShoemakerPG&E Pacific Energy CenterPG&E Pacific Energy Center

(415) 973(415) [email protected]@pge.com

InstructorInstructor

with assistance from

Paul Menyhearth of The American Solar InstituteJosh Plaisted of Kineo Design and PVT Solar

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Courtesy of NASA

PG&E Portfolio Solution

Reduce Energy

Use

Renewable Power Supply

ClimateSmart

Partnership

Education

Outreach

1) Reduce consumption as much as possible.

2) Get the “greenest”power you can.3) Offset any

remaining carbon emissions.

The Full Energy Picture

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Agenda

• Industry overview• Essential physics• Terms and concepts• Collector and System types• Site evaluation and design• Economics

Industry Overview

Courtesy ofNASA

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Two Types:1. Solar pool heating

Industry Overview

• Recreational use• Typically unglazed panels (no glass)• Temperature around 80 degrees• Works seasonally

2. Solar water heating (SWH)• Essential use• Glazed panels• Temperature around 120 degrees• Works year-round• Heats domestic hot water (DHW)

Solar Pool HeatingSwimming pool water heating

80 - 85 degrees from May to October

Source: Fafco


Mature industry with main markets in California and Florida.

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SHW Industry Overview: World

By Permission: REN21. 2008 ”Renewables 2007 Global Status Report”(Paris:REN21) © 2008 Deutsche Gessellschaft fur TechnischeZusammenarbeit GmbH

Industry Overview: U.S.

Federal Tax Credit:• Extended through 2016• 30% for both commercial and residential• MACRS depreciation for commercial

Favorable regulatory environment

Other state and local rebate programs exist or are in the planning stages.

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Upcoming state rebate program: AB1470

Industry Overview: California

• Applications accepted 4/1/10 (residential) and 5/1/10 (commercial).

• Systems installed after 7/15/09 eligible.

• Allocation is 20% residential, 80% commercial and multi-family.

• Handbook and online calculator to be developed within 90 days.

• Public meetings to determine EE measures within 60 days.

Essential Physics

It all starts with the sun.Courtesy ofNASA

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Electromagnetic Spectrum

Continuum of energy.

Courtesy of Wikipedia

10 -3 10 -7

heat light

Greenhouse Effect

Earth

Ozone layer

Short waves get through

Long waves are trapped

light

heat

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Greenhouse Effect

Short waves get through

Long waves are trapped

light

heat

SWH collector

Glass

Heat absorber

Color Absorption

Dark colors absorb a lot, reflect little

Light colors absorb little, reflect a lot

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Metal Conductivity

Some metals transfer more heat than others.

Copper IronPipe cross-section

Fluid Fluid

Water Behavior

Water expands both when heated and frozen.

Steam IceIce

Moving water will NOT freeze.

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Water Behavior

Warm water will rise, cold water will sink.

Water Behavior

Water contains dissolved minerals, which can cause unwanted buildup and clogging.

• “Hard” water contains more minerals, “soft” water less.

• Most common minerals are calcium and magnesium.

• The buildup of minerals is called “calcification” or “scaling”.

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Essential Physics: Summary

• Greenhouse effect• Light enters but heat trapped

• Color absorption• Dark colors absorb and light colors reflect

• Metal conductivity• Copper conducts more than others

• Water behavior• Expands when heated and frozen• 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 water …

With protection against freezing, overheating, and mineral buildup.

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And they must be tough …

Extreme temperatures, constant expansion & contraction, infrared rays, mineral pollutants …

… solar collectors lead hard lives.

Terms and Concepts

Courtesy ofNASA

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Terms and Concepts

Therm

Glazed

Vacuum tube

Flow gaugeSensor

Pump

Valve

Heat exchanger

Controller

Thermosiphon

BTU

Stagnation

T (Delta T)

Solar Fraction

Kilowatt

Hard freeze

Stratification

Terms and Concepts

BTU: 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 BTUTherm: 100,000 BTU (29.3 kWh)

Glazed: Covered with glass.Valve: Device for controlling flow of liquid or gas.Flow gauge: Device for measuring flow of liquid or gas. Pump: Device for causing liquid or gas to flow.Sensor: Device for detecting temperature.Controller: Device for managing system components.

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Terms and ConceptsVacuum (evacuated) tube: Tube with no air.Thermosiphon: Natural process of hot water rising (in a tube).Stratification: Separation of hot and cold water (in a tank).Heat exchanger: Device that transfers heat from one medium to another.

T (Delta T): Change in temperature.

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.

Stagnation: Condition when collectors are not used and become overheated.

Terms and Concepts

Solar Electric:

Tied to the grid. Every kWh is used, no waste.

System design: Storage is the key.

Solar Thermal:

No grid--you’re on your own.Potential for waste.


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Terms and Concepts

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 water than you use, and you can’t store it or sell it.Wasted energy, wasted money.

Solar Fraction: Percentage of building’s hot water requirements that can be met by solar—at optimum economics (no waste).

Terms and Concepts

• Design to cover all the usage on the hottest days.

• Do not “over-design”, since that will lead to wasted energy.

• Then let the rest of the year take care of itself, and make sure you have a backup heater.

• The total percentage of year-round usage that you cover with solar is the solar fraction.

• This is the most efficient design—the one with the least waste.

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Solar Fraction: U.S.

Simulated Solar Fraction Using a “Base” (Current Technology) Residential SWH System

Source: NREL report 2007

Terms and Concepts

Fuel: GasolineEngine: Internal combustion device.Transfer medium: Rods, gears, shafts. Goal: Move the car.

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Terms and Concepts

Fuel: Solar energyEngine: SWH collector.Transfer medium: Fluid (water, glycol). Goal: Heat gain.

Figure courtesy Edwards Hot Water


Collector and System Types

Courtesy ofNASA

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Standard Water Heaters

Typical gas heater:

Courtesy PG&E

Direct flue.

Much heat loss “up the chimney”.

Low efficiency.

(50 – 70%)

Source: Energy Star


More improved model:

Condensing heater.

Extended flue which releases much of its heat to the water before venting.

Vent gases are cool enough to condense.

Efficiency around 80 –90+%

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Source: Energy Star


Tankless

Gas or electric.

Can require special hookup service.

Effectiveness related to usage patterns.

Efficiency• AFUE rating

• Annual Fuel Utilization Efficiency• Percent of total heat generated that enters

ducts, or water• Higher AFUE = more efficiency

• Old systems typically around 60 - 65, newer ones up to 95

• Current minimum 78 (most sold are 80)


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1. Heat collection2. Heat transfer3. Heat storage4. Heat backup5. Extreme temperature protection

(freezing/stagnation)


Five main aspects of solar systems:

1. Heat Collection

Solar panel


Five main aspects of solar thermal systems:

2. Heat Transfer

Water or glycol

3. Heat Storage

Storage tank

5. Extreme Temperature Protection

Special valves, pumps, processes, etc.

4. Heat Backup

Gas or electric heater

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Two types of heat transfer systems:

1. Open Loop (Direct)

Uses just the water from the main.

“Open” to outside elements.

2. Closed Loop (Indirect)

Uses heat-transfer fluid in “closed” system.

Needs heat exchanger.

water glycol

Benefits• Low first cost• No moving parts• Inherent overheat protection• Moderate freeze protection

Disadvantages• Sensitive to ambient temperatures• Weight

ICS: Integral Collector Storage: 50% SF

Figure courtesy SunEarth

Figure courtesy NREL

The Simplest Form of Solar

Sample specifications

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ICS: Integral Collector Storage: 50% SF

Courtesy energybychoice.com

Simple system with ICS

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Water comes in from main

Heated water moves to top

Hot water is drawn into tank

Additional heating element boosts temperature as necessary

120 degree water goes into house

Valves can bypass and isolate collector

Drains can remove water

Other valves can relieve pressure

Can also mix if water too hot

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Can work with any backup heating system:

Gas tank system.

Passive• No pumps, nothing requiring outside power

System Characteristics


For typical ICS system:

Open Loop• New fluid (water) is constantly entering—system is “open”

to outside elements

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Sample specifications

Flat Plate CollectorsThe Industry Workhorse

Figure courtesy SunEarth

Benefits• High thermal performance• Not sensitive to ambient temp• No moving parts• Array is freeze protected

Disadvantages• Can’t you get that tank off my roof!• Supply & return lines not freeze protected

Thermosiphon Passive Systems: 65% SF

Figure courtesy SunEarth Inc

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Photo courtesy NREL



Water comes in to tank from main

Heated fluid rises

Solar fluid circulates through collector

Additional heating element boosts temperature as necessary

120 degree water goes into house

Cooled fluid sinks

Heat is transferred to water in tank

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Passive• No pumps, nothing requiring outside power



For typical tank-on-roof systems:

Closed Loop• Heat-exchange loop is closed to new elements

Open Loop• New fluid (water) is constantly entering—system is open

to new elements

Also can be:

Low-Profile Active System

Benefits• Highest thermal performance• Freeze protection to –60 F• Lightweight low roof profile

Disadvantages• Some active components• More expense and maintenance

Closed-Loop Active Systems: 75-85% SF



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Pump circulates fluid.

Heat is exchanged.

Backup heater.

Sensors detect collector temp higher than tank.

Photo courtesy Industrial Solar Technology Photo courtesy William Lord

Figure courtesy Edwards Hot Water


Evacuated Tubes

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Evacuated TubesLower Losses for Colder Climates

Figures courtesy Thermomax

1. Vacuum tube2. Heat pipe3. Cold liquid4. Hot vapor5. Absorber

6. Collector return (hot)

7. Collector supply (cold)

8. Heat exchanger9. Shock absorber

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5

67

89

Photo courtesy Industrial Solar Technology


Evacuated Tubes

Supply

Photo courtesy William Lord

Return

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Evacuated tube system is essentially the same as flatplate.

Supply and return both at top of collector.

Active• Uses pumps and other active elements



For typical flat plate or evacuated tube systems:

Closed Loop• Heat-exchange loop is closed to new elements

Low or High Pressure• Different pressures for different system requirements

Also can be:

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1. Thermal mass (ICS)2. Auxiliary heater (electric element)3. Antifreeze (closed loop)4. Water flow (moving water won’t freeze)5. Draining (removing water from collector)

Freeze Protection


Five different methods:

Drain-down and Drain-back Systems


Drain-down:• Drain “down & out”• Open loop• Removes water from collector and completely

out of system onto ground or roof

Drain-back:• Drain “back in later”• Closed loop• Removes HX fluid from collector into tank, to be

put back after freeze passes

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Drain-down System (open loop)

Courtesy University of Central Florida

Collector ratings from SRCC

Courtesy www.solar-rating.org

OG-100 (Collectors)

OG-100, Page 1

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Site Evaluation and Design

Courtesy ofNASA

Criteria:• Solar resource• Climate zone (temperature range, freezes)• Hot water usage amount and patterns• Available space and orientation• Economics

Site Evaluation and Design


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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

Solar Resource

Climate Zones

California climate zones

http://www.energy.ca.gov/maps/building_climate_zones.html

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Gas Electric

Usage

PG&E Baseline Territory Map

Baseline = guaranteed minimum amount of low cost electricity for everyone.

Baseline allocation determined by geographic needs.

Usage

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Usage

Usage

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Usage

Avg. statewide annual use (2004): 431 therms

44% of that = 189 therms.In the study, avg. house size = 1,500 sf., avg. # people = 3

My usage

My usage history from PG&E online account.

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Bill AnalysisBill Analysis

Use to determine baseload and seasonal variationsCan often infer specific appliance usage

Process:• Get at least full year data• Check for unusual situations (shut down, vacation)• Take 3 lowest months, toss out the smallest,

average other two• Same process for highest months

Bill Analysis: GasBill Analysis: Gas

24 3031

3 lowest: 24, 31, 30 – avg. 30.53 highest: 76, 76, 71 – avg. 73.5

7671 76

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Average Usage Assumptions

Around 180 - 200 therms per year for typical household.

Cost per therm is about 110% of baseline cost, if you include second tier and taxes.

• Collectors needn’t be racked due South at latitude plus 15°• Typical penalty is less than 10-20%• Always possible to augment collector area

OrientationProper Orientation Does not Require Perfect Orientation

Chart courtesy NREL

-90 -60 -30 0 30 60 900

30

60

90

Azimuth

Tilt

San Francisco, CA

0.40-0.500.50-0.600.60-0.700.70-0.800.80-0.900.90-1.00

SOF

East West

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Mounting

Mounting

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Design Exercise: Residential

Considerations:• Usage• Geography—climate zone• Space and collector location• Type of system• Size of collector(s)• Size of storage tank• Mounting• Financials

Design Exercise: ResidentialStandard Assumptions (California):• 20 gallons of hot water per person per day• 1 sq. ft. of collector will produce 1.5 gallons of

hot water per day• Tank size should hold one full day’s usage

Typical residence (4 people):• 80 gallons of hot water daily usage• 80/1.5 = about 60 sq. ft. of collector area• 80 gallon storage tank

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Our system:• Active, closed-loop for freeze protection• Two 8’ x 4’ flat plate collectors• 80 gallon storage tank• Standard flush roof mount• 75% solar fraction


Savings:• Average yearly usage 210 therms• Solar saves 75% of that, or 150 therms• Average cost per therm $1.25• Yearly savings about $200 (first year)

Cost:• Total installed price $6500• State rebate $1500• Tax credit ((6500-1500) * .3) = $1500• Net cost = (6500 – 1500 – 1500) = $3500

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Payback:• Add $500 maintenance cost over lifetime• Total cost about $4,000• Straight payback (no inflation factor) =

4000 / 200 = 20 years• With inflation factor of 5%, payback shortens

to about 17 years.

Both PV and Solar Thermal systems tied to owner’s unit.

Case Study: Residential

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Residential Pilot Program Data


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Commercial System Issues

Courtesy ofNASA

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Additional concepts:• Balancing flow—FILO (first in, last out)• Thermal expansion of headers—limits rows• More sophisticated plumbing• Larger and more varied storage tanks• Often higher temperatures required

Commercial System Issues


SUPPLYRETURN

BV1 PRVBV2

AE

DP

TBV

Balancing Flow

Water takes the path of least resistance.

So make sure all water has the same resistance to flow—the same length path.

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SUPPLY RETURN

Parallel flow

Balancing FlowParallel flow—dividing system into two parts to allow for thermal expansion.

System 1All output here

SUPPLY RETURN

Parallel flow

Balancing FlowParallel flow—dividing system into two parts to allow for thermal expansion.

System 2All output here

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Design Exercise: Commercial

Payback:• With economies of scale and tax depreciation,

commercial system paybacks will likely be much better than residential

• This also applies to multi-family units, which are usually commercial investments.

• Recognizing this, the rebate program allocates the bulk of the money to commercial and multi-family.

Case Studies

EarthKind Energy, New York State's leading authority on solar thermal technologies, explains the process: Solar panels containing a mixture of water and a food-grade glycol (the same substance contained in ice cream and toothpaste), which absorbs 94 percent of the sun's energy, will be installed on the roofs of the Brooklynbuildings. The heated solution transfers the heat to water in a storage tank, which provides pre-heated water for the buildings' existing hot-water tanks and reduces the energy used by 50 percent or more. And provides plenty of hot water for your morning shower.

First Solar Hot Water Systems For Multifamily Buildings In NYC

www.solardaily.com

--Solar daily 3/25/09

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ResourcesRatings & Listings

• Solar Ratings & Certification Corporation: www.solar-rating.org

Other Useful Links• California Solar Energy Industries Association: www.calseia.org• Energy Efficiency & Renewable Energy Office: www.eere.energy.gov• National Renewable Energy Laboratory: www.nrel.gov• Database of State Incentives for Renewable Energy: www.dsireusa.org• Copper Development Association: www.copper.org

Books• Solar Installation – practical applications for the built environment

• Lars Andren, James x James 2003, ISBN 190291645X• Solar Thermal System – successful planning & construction

• Felix Peuser, James x James 2002, ISBN 1902916395• Solar Water Heating: A Comprehensive Guide to Solar Water And Space Heating Systems

• Bob Ramlow, New Society Publishers 2006•Active Solar Heating Systems Design Manual

• ASHRAE 1988, ISBN 0910110549

presentation solar water heating

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