Solar Hot Water Heating Systems

Home , Water heating

Courtesy of DOE/NREL

PG&E Pacific Energy Center, San Francisco Energy Training Center, Stockton

Instructor

Pete Shoemaker PG&E Pacific Energy Center (415) 973-8850 [email protected]

with assistance from Paul Menyhearth of The American Solar Institute Josh Plaisted of Kineo Design and PVT Solar

1 Courtesy of NASA

The Full Energy Picture

PG&E Portfolio Solution

1) Reduce consumption as much as possible. Reduce Energy Use 2) Get the “greenest” power you 3) Offset any Partnership can. remaining Education carbon Outreach emissions. Renewable ClimateSmart Power Supply

2 Agenda

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

Industry Overview

Courtesy ofNASA

3 Industry Overview Two Types: 1. Solar pool heating • 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 Heating Swimming pool water heating 80 - 85 degrees from May to October

Source: Fafco

Courtesy of DOE/NREL

Mature industry with main markets in California and Florida.

4 SHW Industry Overview: World

Industry Overview: U.S. Favorable regulatory environment

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

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

5 Industry Overview: California

Upcoming state rebate program: AB1470

• 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

Courtesy ofNASA It all starts with the sun.

6 Electromagnetic Spectrum

10 -3 10 -7 heat light

Courtesy of Wikipedia Continuum of energy.

Greenhouse Effect

Ozone layer

light Short waves get through

Long waves are trapped heat Earth

7 Greenhouse Effect

Glass

light Short waves get through

Heat absorber Long waves are trapped heat SWH collector

Color Absorption

Dark colors absorb a lot, reflect little

Light colors absorb little, reflect a lot

8 Metal Conductivity

Some metals transfer more heat than others.

Fluid Fluid

Pipe cross-section Copper Iron

Water Behavior

Water expands both when heated and frozen.

Steam Ice

Moving water will NOT freeze.

9 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”.

10 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.

11 And they must be tough …

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

… solar collectors lead hard lives.

Terms and Concepts

Courtesy ofNASA

12 Terms and Concepts T (Delta T) Controller Pump

Therm Vacuum tube Solar Fraction Glazed Valve Thermosiphon Sensor Flow gauge Stratification Kilowatt Heat exchanger BTU

Stagnation Hard freeze

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 BTU Therm: 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.

13 Terms and Concepts

Vacuum (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

System design: Storage is the key.

Solar Electric: Solar Thermal:

Tied to the grid. No grid--you’re on Every kWh is used, your own. no waste. Potential for waste.

Courtesy of DOE/NREL

14 Terms and Concepts

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

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.

15 Solar Fraction: U.S.

Simulated Solar Fraction Using a “Base” (Current Technology) Residential SWH System Source: NREL report 2007

Terms and Concepts

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

16 Terms and Concepts

Courtesy of DOE/NREL

Figure courtesy Edwards Hot Water Fuel: Solar energy Engine: SWH collector. Transfer medium: Fluid (water, glycol). Goal: Heat gain.

Collector and System Types

Courtesy ofNASA

17 Standard Water Heaters

Typical gas heater:

Direct flue. Much heat loss “up the chimney”. Low efficiency. (50 – 70%)

Courtesy PG&E

Standard Water Heaters

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+%

Source: Energy Star

18 Standard Water Heaters

Tankless

Gas or electric. Can require special hookup service. Effectiveness related to usage patterns.

Source: Energy Star

Standard Water Heaters

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)

19 Collector and System Types

Five main aspects of solar systems: 1. Heat collection 2. Heat transfer 3. Heat storage 4. Heat backup 5. Extreme temperature protection (freezing/stagnation)

Collector and System Types

Five main aspects of solar thermal systems:

1. Heat 2. Heat 3. Heat 4. Heat 5. Extreme Collection Transfer Storage Backup Temperature Protection

Special valves, pumps, processes, Gas or etc. Water or Solar electric glycol panel Storage heater tank

20 Collector and System Types

Two types of heat transfer systems:

1. Open Loop 2. Closed Loop (Direct) (Indirect)

water glycol

Uses just the water Uses heat-transfer fluid from the main. in “closed” system. “Open” to outside Needs heat exchanger. elements.

ICS: Integral Collector Storage: 50% SF The Simplest Form of Solar

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

Disadvantages • Sensitive to ambient temperatures • Weight

Figure courtesy SunEarth

Sample specifications

Figure courtesy NREL

21 ICS: Integral Collector Storage: 50% SF

Courtesy energybychoice.com

Simple system with ICS

22 Heated water moves to top

Hot water is drawn into tank

120 degree water goes into house

Additional heating element boosts temperature as necessary Water comes in from main

Can also mix if water too hot

Other valves can relieve pressure

Drains can remove water Valves can bypass and isolate collector

23 Can work with any backup heating system:

Gas tank system.

System Characteristics

For typical ICS system:

Passive • No pumps, nothing requiring outside power

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

Figure courtesy NREL

24 Flat Plate Collectors The Industry Workhorse

Figure courtesy SunEarth

Sample specifications

Figure courtesy NREL

Thermosiphon Passive Systems: 65% SF

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

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

25 Thermosiphon Passive Systems: 65% SF

Photo courtesy NREL

Thermosiphon Passive Systems: 65% SF Additional heating element boosts temperature as necessary

120 degree water goes Water comes in into house to tank from main

Heated fluid rises Heat is transferred to water in tank

Cooled fluid sinks

Solar fluid circulates through collector

Figure courtesy SunEarth Inc

26 System Characteristics

For typical tank-on-roof systems:

Passive • No pumps, nothing requiring outside power

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

Also can be: Open Loop • New fluid (water) is constantly entering—system is open to new elements

Figure courtesy NREL

Closed-Loop Active Systems: 75-85% SF Low-Profile Active System Benefits • Highest thermal performance • Freeze protection to –60 F • Lightweight low roof profile Disadvantages • Some active components Figure courtesy SunEarth Inc • More expense and maintenance

Courtesy of DOE/NREL

27 Sensors detect collector temp higher than tank.

Pump circulates fluid. Backup heater.

Heat is exchanged.

Evacuated Tubes

Photo courtesy Industrial Solar Technology Photo courtesy William Lord

Figure courtesy Edwards Hot Water

Courtesy of DOE/NREL

28 Evacuated Tubes Lower Losses for Colder Climates Figures courtesy Thermomax 6 1. Vacuum tube 7 2. Heat pipe 1 8 3. Cold liquid 2 9 4. Hot vapor 3 4 5. Absorber

5 6. Collector return (hot) 7. Collector supply (cold) 8. Heat exchanger 9. Shock absorber

Evacuated Tubes

Photo courtesy Industrial Solar Technology

Return Supply

Photo courtesy William Lord

Courtesy of DOE/NREL

29 Supply and return both at top of collector.

Evacuated tube system is essentially the same as flatplate.

System Characteristics

For typical flat plate or evacuated tube systems:

Active • Uses pumps and other active elements

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

Also can be: Low or High Pressure • Different pressures for different system requirements

Figure courtesy NREL

30 Freeze Protection

Five different methods:

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)

Figure courtesy NREL

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

Figure courtesy NREL

31 Drain-down System (open loop)

Courtesy University of Central Florida

Collector ratings from SRCC OG-100 (Collectors)

Courtesy www.solar-rating.org OG-100, Page 1

32 Site Evaluation and Design

Courtesy ofNASA

Site Evaluation and Design

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

Courtesy of DOE/NREL

33 Solar Resource

Peak Sun-hours Measured in kWh/m2/day

Source: DOE National Renewable Energy Laboratory (NREL) Resource Assessment Program http://rredc.nrel.gov/solar/old_data/nsrdb/redbook/atlas/serve.cgi

Climate Zones

California climate zones

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

34 Usage

ElectricGas

Usage

PG&E Baseline Territory Map

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

Baseline allocation determined by geographic needs.

35 Usage

Usage

36 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.

37 Bill Analysis

Use to determine baseload and seasonal variations Can 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: Gas

3 lowest: 24, 31, 30 – avg. 30.5 3 highest: 76, 76, 71 – avg. 73.5

7671 76

31 24 30

38 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.

Orientation Proper Orientation Does not Require Perfect Orientation

• Collectors needn’t be racked due South at latitude plus 15° • Typical penalty is less than 10-20%

• Always possible to augment collector area San Francisco, CA 90

SOF 0.40-0.50 60 0.50-0.60 0.60-0.70 Tilt 0.70-0.80 0.80-0.90 30 0.90-1.00

0 -90 -60 -30 0 30 60 90 East Azimuth West Chart courtesy NREL

39 Mounting

Mounting

40 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: Residential Standard 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

41 Design Exercise: Residential

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

Design Exercise: Residential

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

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)

42 Design Exercise: Residential

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.

Case Study: Residential

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

43 Case Study: Residential

Case Study: Residential

44 Case Study: Residential

Case Study: Residential

45 Residential Pilot Program Data

Residential Pilot Program Data

46 Residential Pilot Program Data

Commercial System Issues

Courtesy ofNASA

47 Commercial System Issues 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

Courtesy of DOE/NREL

Balancing Flow

Water takes the path of least resistance.

TBV

BV2 BV1 PRV SUPPLY RETURN

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

48 Balancing Flow

Parallel flow—dividing system into two parts to allow for thermal expansion. System 1 All output here

SUPPLY RETURN

Parallel flow

Balancing Flow System 2 Parallel flow—dividing system into two parts to allow for thermalAll output here expansion.

SUPPLY RETURN

Parallel flow

49 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

First Solar Hot Water Systems For Multifamily Buildings In NYC --Solar daily 3/25/09

www.solardaily.com 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 Brooklyn buildings. 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.

50 Resources Ratings & 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