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OG-300 Certification of Solar Water heating Systems

Table of Contents:

  1. About SRCC Rating and Certification

  2. About OG-300 System Certification

  3. How Systems are Certified under OG-300
    Figure 1 SRCC OG-300 Test and Certification Process

  4. Certification Criteria
    Table 1:  Features Evaluated During the SDHW System Design Review
    Table 2:  Features Evaluated for Durability and Reliability Criteria
    Table 3:  Features Evaluated for Safety Criteria
    Table 4:  Features Evaluated for Operation and Service Criteria
    Table 5:  Features Evaluated for Installation Criteria
    Table 6:  Features Evaluated for Operation & Maintenance Manuals

  5. On-Site Inspection

  6. Types of Solar Thermal Systems
    Forced Circulation
    Integral Collector Storage (ICS)
    Thermosiphon
    Self-Pumping

  7. Thermal Performance Rating
    Solar Energy Factor (SEF)

  8. Rating Parameters
    Table 7: Rating Parameters

  9. Fluid Class

  10. Freeze Tolerance

  11. Certification Labels

  12. Symbols Shown in the System Schematics

  13. Comparing System Costs (Electric Auxiliary)

  14. Comparing System Costs (Gas Auxiliary)

About SRCC, Rating and Certification

The Solar Rating & Certification Corporation (SRCC) is an independent third-party certification organization that administers national certification and rating programs for solar energy equipment.  The SRCC was incorporated in October 1980 as a non-profit corporation.  It is governed by a twelve-member board of Directors with representation from the public, private, and generalist Sectors.

The SRCC currently operates two major solar programs: collector certification (OG-100), and heating system certification (OG-300).  The OG-100 collector certification program applies to that part of a solar energy system that is exposed to the sun and collects the sun's heat.  The collectors can be used to heat water, air or other heat transfer media.  The OG-300 rating and certification program for solar hot water systems integrates results of collector tests with a performance model for the entire systems and determines whether systems meet minimum standards for system durability, reliability, safety and operation.  Factors affecting total system design, installation, maintenance and service are also evaluated.

A direct comparison of an SRCC rated collector to an SRCC rated solar water heating system is not possible.  The reason for this is two-fold.  First, the collector rating shows the performance of one component in the solar package while the system rating shows the performance of an entire solar package.  Second, each rating, whether a collector rating or a system rating, is developed using a separate set of assumed conditions. 

The OG-300 directory contains information about solar water heating systems that have been certified and rated by SRCC.

The information in the directory will provide you with reliable and comparable data for solar water heating systems you may be considering buying.  The rating information is a helpful tool for comparing the efficiency of the various solar systems on the market.  Remember, though, that not all solar energy systems are tested and rated as a "package" or a system.  Many systems you consider may have only the collectors rated by SRCC.  While you can, and should, compare collector ratings, you cannot compare collector ratings with system ratings.  All systems which have been certified by SRCC will bear the SRCC label, which is your assurance that an independent party has verified the performance and basic durability of the solar product you are considering.  Copies of SRCC labels available in the directory.

The directory contains descriptive information about the solar systems and also "performance" information about them.  "Performance" data relates to the energy output of the system.  The SRCC performance information contained in the directory provides a way to compare the relative performance of different solar water heating systems, not the actual performance you can expect from a given system.  This is because the collectors and systems are tested under standard laboratory conditions which are certain to be different from those in your home.  Think of the SRCC ratings as you do the MPG ratings for cars -- a benchmark, but not necessarily the same performance you will experience.  Remember, too, that performance (or energy output) is only one criteria in choosing a solar energy system.  Quality of installation, cost, availability of service and parts, and the expected life of the equipment are also important points to consider.  Equipment which is well-designed and well-built, but poorly installed, cannot perform according to the manufacturer's specifications.

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OG-300 Certification of Solar Water Heating Systems

Experience has proven that product certification by a “third party” is essential to both the industry and the consumers.  Third party certification gives four major advantages to its participants.

First and foremost, product certification helps sell products by creating customer confidence in products that are certified; certification acceptance by code officials reduces installation costs; and financing is facilitated when the product is certified.

Second, certification extends a company's engineering capabilities by helping to build products with improved safety; field installation problems are identified and resolved during the certification process.

Third, certification minimizes the number of inferior products competing in the market place.

Fourth, certification gives consumers an unbiased appraisal of available products, which allows for comparison shopping.

In response to its industry participants, SRCC has developed a solar water heating system rating and certification program, short-titled OG 300.  The purpose of this solar water heating system certification and rating program is to improve performance and reliability of solar products. It integrates results of collector tests and system tests with evaluations against minimum standards of system durability, reliability, safety and operation; as well as factors affecting total system design, installation, maintenance and service.  Giving suppliers the opportunity to submit their solar domestic hot water (SDHW) system designs to an open-ended review encourages them to produce the best products possible.

Under the OG 300 system rating and certification program:

Unique features of this certification program include:

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How Systems Are Certified Under the OG 300 Protocol

The process for rating and certifying solar water heating systems under the OG 300 protocol includes five steps for each system being rated.  The process is described below and illustrated in Figure 1.

1.   The collectors which are part of the system must be tested and rated under the OG 100 protocol.

2.   Passive systems in which the collector can not be tested separately must be rated and certified under a system test protocol.

3.   The complete specified system of collectors, tanks, pumps, motors, valves, piping, etc., is evaluated for essential elements related to:

During this evaluative process, SRCC reviews the components, assemblies and materials in the system for compatibility, drawing on nationally recognized resources such as the Recommended Requirements to Code Officials for Solar Heating, Cooling and Hot Water Systems, jointly prepared by the Council of American Building Officials, Building Officials and Code Administrators International, Inc., International Conference of Building Officials, National Conference of States on Building Codes and Standards, Inc., and Southern Building Code Congress International, Inc.

4.   Data from the OG 100 collector test, the system test, and review of design and installation guidelines are input to a computer program called TRNSYS.  That program projects system performance.

5.   Numerical results of the design and installation review (step 3) and the TRNSYS evaluation are integrated and entered on a certification to the supplier.  Data pertinent to solar distributors, retailers, installers and homeowners is specified for printing on the rating pages.  The rating pages which follow are a good means by which to compare systems and select the best one for your needs.

Testing Process

Figure 1 SRCC OG-300 Test and Certification Process

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Certification Criteria

Major system components, the contents of the manual delivered with the system, and the supplier's instructions for system installation must be approved by SRCC.  Certification is based upon the determination by SRCC that the system successfully meets its minimum criteria for design, reliability and durability, safety, operation and servicing, installation, and operation and maintenance manuals.

Tables 1-6  summarize the features evaluated for each of the six major criteria during system certification under the OG 300 protocol.  Most of those features are self-explanatory.  Obviously, some of the features will not be applicable to certain systems.  Systems conforming with the applicable criteria will be in compliance with HUD Use of Material Bulletin 100.

Table 1:  Features Evaluated During the SDHW System Design Review

  • Operating Limits
  • Solar Loop Isolation
  • Thermal Expansion
  • Auxiliary Water Heating Equipment
  • Back Thermosyphon Prevention
  • Fluid System Sizing
  • Collector
  • UV Radiation Protection
  • Collector Flow Distribution
  • Collector Circulation Control
  • Vacuum Induced Pressure Protection
  • Thermal Shock Protection
  • Different Metallic Materials
  • Airborne Pollutants
  • Effects of Decomposition Products
  • Storage Tank
  • Tank Insulation
  • Expansion Tanks
  • Heat Exchanger
  • Manual Control Override
  • Wiring Identification
  • Temperature Control
  • Code Compliance
  • Insulation
  • Piping
  • Filters
  • Joints
  • Materials

Table 2:  Features Evaluated for Durability and Reliability Criteria

  • Stagnation
  • Solar Degradation
  • Operation Conditions
  • Incompatible Materials
  • Freeze Protection
  • Protection From Leaks
  • Fluid Compatibility
  • Deterioration of Fluids
  • Thermal Storage System
  • Buried Components
  • Deterioration Protection
  • Water Hammer
  • Sound and Vibration Control

Table 3:  Features Evaluated for Safety Criteria

  • Protection of Electrical Components
  • System Failure Prevention
  • High Temperature Control
  • Protection Against Auto-Ignition of Combustibles
  • Fluid Safety Labeling
  • Contamination of Potable Water
  • Entrapped Air
  • Backflow
  • Toxicity
  • Combustible Liquids
  • Liquid Flash Point
  • Pressure Relief
  • Heated Components

Table 4:  Features Evaluated for Operation and Service Criteria

  • Operating Indicators
  • Tanks
  • Waste Disposal
  • Dirt Retention and Staining
  • Maintenance and Servicing
  • Permanent Maintenance Accessories

Table 5:  Features Evaluated for Installation Criteria

  • Firestopping
  • Auxiliary System
  • Space Use
  • Accessibility
  • Building Penetrations
  • Water Damage
  • Structural Supports
  • Expansion and Contraction of Supports
  • Penetration of Structural Members
  • Emergency Egress and Access
  • Protection from Thermal Deterioration
  • Tilt and Azimuth
  • Shading of Collector
  • Pipe and Component Supports
  • Pitch or Angle of Piping Installation
  • Underground Piping
  • Control Sensor Installation
  • Penetrations Through Fire-Rated Assemblies

Table 6:  Features Evaluated for Operation & Maintenance Manuals

  • Provision for Manuals
  • Installation Instructions
  • Operation Instructions
  • Maintenance Plan
  • Fluid Quality
  • Service and Replacement Parts
  • Hazards
  • Warranty Coverage

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On-Site Inspection

Compliance with many of the installation requirements of OG 300 can be verified only by an on-site inspection made after installation.  SRCC may randomly inspect installed systems to verify that: (1) approved components have been installed; (2) an approved O&M manual has been provided; and (3) the installation conforms to the approved installation guidelines.

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Types of Solar Water Heating Systems:

As you shop for solar water heating systems, you will probably see several different types.  In general, all solar water heating systems fall into one of these four categories:

1.   Forced Circulation or "active systems" are those that use a pump to circulate the water or other fluid from the collector where it is heated by the sun to the storage tank where it is kept until you need it.

2.   Integral Collector Storage (ICS) systems, or "batch" water heaters, combine the collector and the storage tank into one.  That is, the sun shines into the collector and strikes the storage tank directly, heating the water.

3.   Thermosyphon systems have a separate storage tank, located above the collector.  Liquid (which could be water or an antifreeze solution) warmed in the collector rises naturally to the storage tank where it is kept until needed.

4.   Self-Pumping systems are those that use a phase change (liquid-vapor) or other passive means to cause the fluid in the collector to circulate and transport heat from the collector to the storage.

The ICS, thermosyphon and self-pumping systems are often called "passive" solar systems because they do not use mechanical energy to move the heated water.  All four types of solar systems work well, and you should compare the performance of one type with the others.

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Thermal Performance Rating

Most rating programs require the equipment to be tested in accordance to a standard test with specified test conditions.  This provides a repeatable performance within an accepted uncertainty band.  There are, however, some rating programs which combine a standard test and a calculation procedure to produce a performance rating.  Such is the case for the energy guide label for electric and gas residential hot water heaters.  SRCC has used a similar method to develop a consumer friendly, practical rating system.  The intent is to present to consumers an easily understood comparison between SDHW systems and conventional hot water systems.  Note that the performance any individual consumer will experience may differ due to location and hot water usage.  Additional location specific information on the performance of SRCC certified solar water heating systems is provided in the SRCC Directory of Annual Performance Ratings.

The thermal performance rating is based on the system design and performance projections derived from testing of the collector components used in the system, or from testing and evaluation of the system as a whole.  The type of auxiliary system (e.g. gas or electric) utilized will have a large impact on the overall performance of the system.  These differences arise because different types of auxiliary systems have varying standby losses and fuel conversion efficiencies.  Although the auxiliary system may affect the solar system's performance, in many cases, the solar output is mostly independent of the auxiliary system used.  Because gas backup systems have lower efficiencies and higher standby losses than do electric systems, it should be expected that the entire system's (including backup) performance will be lower, even if the solar output from both system types is equal.

SRCC uses the Solar Energy Factor (SEF) as its performance rating for solar domestic water heating systems.  The SEF is defined as the energy delivered by the system divided by the electrical or gas energy put into the system. The SEF is presented as a number similar to the Energy Factor (EF) given to conventional water heaters by the Gas Appliance Manufacturers Association (GAMA)1, but with the exceptions noted in the Rating Parameters Section.

SEF Formula 1
Where:

QDEL   =    Energy delivered to the hot water load:  Using the SRCC rating conditions, this value is 43,302 kJ/day (41,045 Btu/day).

QAUX  =   Daily amount of energy used by the auxiliary water heater or backup element with a solar system operating, kJ/day (Btu/day). To convert to kWh, divide this value by 3,600 (3,412).  To convert to therms, divide this value by 105,000 (100,000).

QPAR   =   Parasitic energy: Daily amounts of AC electrical energy used to power pumps, controllers, shutters, trackers, or any other item needed to operate the SDHW system, kJ/day (Btu/day). To convert to kWh, divide this value by 3,600 (3,412).

The Solar Energy Factor can be converted to an equivalent Solar Fraction (SF) as follows:

            SEF Formula 2

The EF for the SRCC standard electric auxiliary tank is 0.9 and for the gas tank is 0.6.

In this context, the Solar Fraction is the portion of the total conventional hot water heating load (delivered energy and tank standby losses) provided by solar energy. Note that an alternate definition for Solar Fraction is often used.  In this alternate definition, solar fraction is the portion of the total water heating load (losses are NOT included) provided by solar energy.  The alternate method of calculating solar fraction will yield higher solar fractions. Therefore, use caution when comparing the solar fraction for specific systems, inputs into energy codes (such as California's Title 24), or outputs from software (such as F-Chart) to ensure that the same calculation procedure for solar fraction has been used.

The Solar Energy Factor can be converted to an equivalent Solar Savings (QSOLAR) as follows:

      SEF Formula 3

Where:

QCONV   =   Daily amount of energy used by the auxiliary water heater or backup element without a solar system.  The SRCC standard electric auxiliary tank has an energy usage of 47,865  kJ/day (45,369 Btu/day).  The SRCC standard gas auxiliary tank has an energy usage of 72203 kJ/day (68,439 Btu/day).

EF  =  The Energy Factor is the ratio of delivered energy to input energy for the reference electric auxiliary tank without a solar contribution. The balance of the energy is lost to the surroundings due to standby losses and conversion efficiency.

QSOLAR   =   The Solar Savings is the amount of the total conventional water heating load (delivered energy and tank standby losses) provided by solar energy minus any parasitic energy use. To convert to kWh, divide this value by 3,600 (3,412).

In this context, the Solar Savings is the amount of the total conventional hot water heating load (delivered energy and tank standby losses) provided by solar energy minus any parasitic energy use.

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Rating Parameters

The following parameters are used for calculating the daily energy savings and the solar energy factor.  These conditions are the same as those used in the U.S. Department of Energy test for water heaters (Federal Register volume 55 number 201 pages 42161  -  42177, October 17, 1990) except for the following:

Table 7: Rating Parameters

RATING PARAMETER (SI Units) (I-P Units)
Environmental Temperature 19.7°C 67.5°F
Auxiliary Set Temperature 2 57.2°C 135°F
Water Mains Temperature 14.4°C 58°F
Total Energy Draw (QDEL) 43,302kJ 41,045Btu
Approximate Volume Draw 243l 64.3gal
Draw Rate 0.189l/s 3.0gpm
Draw Type: Energy
Number Of Draws: 6 - One at the beginning of each hour starting at 9:30 am

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Fluid Class

The American Water Works Association (AWWA)  has created a classification system for heat transfer fluids that are used in heat exchangers.  This classification system is intended to indicate the potential for contamination of the water supply during a heat exchanger failure and as a basis for the types of heat exchangers which should be used with these fluids. The rating system consists of the following three categories:

  1. Fluid Class I: Potable Heat Transfer Fluid (e.g. Water)
  2. Fluid Class II: Non-Toxic Heat Transfer Fluid (e.g. Propylene Glycol)
  3. Fluid Class III: Toxic Heat Transfer Fluid (e.g. Ethanol)

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Freeze Tolerance

Each system has a freeze tolerance temperature specified by the system Supplier. If the air temperature falls below this temperature, a fluid in the system is likely to freeze.  Unless a system is installed in a non-freezing climate, every system must have an automatic mechanism to at least partially protect it from freezing (eg. automatic draining, antifreeze fluids, or thermal mass).  For systems using water in portions of the system exposed to outdoor air conditions, the mass of the water itself, along with insulation can provide limited protection from freezing, after which manual intervention may be required.   For systems using water in the collector, the freeze tolerance temperature may actually exceed the freezing temperature of water because of radiative cooling by the sky.   All systems are required to have the capability to be manually drained to protect them from extreme freezing conditions.

As a consumer, you should be aware of the freeze tolerance temperature of the system you plan to purchase.  The system may protect itself under all conditions occurring at your site or you may be required to interact with the system to protect it from freezing.

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SRCC Certification Labels

All solar products certified by SRCC are required to be labeled with an approved SRCC certification label within sixty (60) days of receipt of certification. label shown below should be on each system certified under SRCC's OG 300 protocol.

SRCC LOGO This product certified by:
Solar Rating & Certification Corporation
400 High Point Drive, Suite 400
Cocoa, FL 32926
(321) 213-6037

www.solar-rating.org
Sample Solar Corporation
P.O. Box 12345
Anytown, CA 97402
System Serial No.___________
SRCC Document OG-300
System Model:
  1. Super Sample 2B
  2. Super Sample 2C
  3. Super Sample 2D
  4. Super Sample 2E
SRCC Certification Number:
300-2001-078A
300-2001-078B
300-2001-078C
300-2001-078D
300-2001-078E
Solar Energy Factor:
2.0
2.6
1.8
3.7
4.2
The installed system is checked above.

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Symbols Shown in the System Schematics

These symbols define elements in the system schematics found on the rating pages.

Schematics Symbols

NOTE:  The symbols shown above, except those denoted with an asterisk, reference the 1989 American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) Fundamentals Manual.  Those symbols indicated by an asterisk are either modifications of the ASHRAE standard or are diagrams of the actual part.

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COMPARING SYSTEM COSTS (Electric Auxiliary)

The Energy Factor (EF) and the Solar Energy Factor (SEF) can be used to compare different water heating systems with one another and to estimate typical yearly operating costs for the specified rating conditions.  The SEF includes all of the specified conditions for the DOE EF test, plus several solar specific conditions.  The EF and SEF can be used to compare solar and electric system's energy use on a one-to-one basis.  A higher SEF or EF indicates less conventional energy use, and consequently, lower operating cost.

'For electric systems, the following calculation can be used:
Yearly Cost ($) = 365 days *12.03 kWh/EF*$x/kWh

Examples: (Assume that electricity costs $0.12/kWh)

      1.  TYPICAL ELECTRIC WATER HEATER (EF = 0.86)

                   YEARLY COST = 365*12.03/0.86*0.12 = $612.69

      2.  TYPICAL SOLAR SYSTEM (SEF = 2.0)

                   YEARLY COST = 365*12.03/2.0*0.12 = $263.46

Note the solar system saves $349.23 ($612.69 - $263.46) per year. 
This figure can be used as the energy cost savings basis for an economic analysis of a solar hot water system based on the assumptions for the standard DOE (EF) and SRCC-OG 300 rating conditions (SEF).  Other factors such as initial cost, maintenance, inflation, interest rate, and replacement costs also need to be considered when making an economic analysis.

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COMPARING SYSTEM COSTS (Gas Auxiliary)

The Energy Factor (EF) and the Solar Energy Factor (SEF) can be used to compare different water heating systems with one another and to estimate typical yearly operating costs for the specified rating conditions. The SEF includes all of the specified conditions for the DOE EF test, plus several solar specific conditions. The EF and SEF can be used to compare solar and gas system's energy use on a one-to-one basis. A higher SEF or EF indicates less conventional energy use, and consequently, lower operating cost. 

For gas systems, the following calculation can be used:
Yearly Cost ($) = 365 days*0.4105/EF*$x/therm

Examples: (Assume that gas costs $1.60/therm)

  1. TYPICAL GAS WATER HEATER (EF = 0.6)

    YEARLY COST = 365*0.4105/0.6*1.60 = $399.55

  2. TYPICAL SOLAR SYSTEM (SEF = 1.1)

    YEARLY COST = 365*0.4105/1.1*1.60 = $217.94

Note that the solar system saves $181.61 ($399.55 - $217.94) per year.  This figure can be used as the energy cost savings basis for an economic analysis of a solar hot water system based on the assumptions for the standard DOE (EF) and SRCC-OG 300 rating conditions (SEF).  Other factors such as initial cost, maintenance, inflation, interest rate, and replacement costs also need to be considered when making an economic analysis.

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Footnotes:

1. Gas Appliance Manufacturers Association, "Consumer's Directory of Certified Efficiency Ratings for Residential Water Heating and Water Heating Equipment", 1994, pp. 138-218

2. This set temperature was chosen to be compatible with the U.S. Department of Energy test method for water heaters.  Most plumbing codes, however, are moving toward lower set temperatures.  SRCC will continue to monitor standard practice and requirements and adjust the parameter as needed to be consistent.

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