Solar Collector Testing Capabilities
The test equipment and configuration used at the Florida Solar Energy Center were chosen to meet the American Society of Heating Refrigerating and Air-conditioning Engineers (ASHRAE) requirements described in ASHRAE Standards 93-86 and 96-80. These documents detail the procedures that should be followed to measure instantaneous collector efficiency accurately and with repeatability. They also set standards of accuracy on the measuring equipment used.
After 20 years of operation at the site in Cape Canaveral, FSEC moved its facilities to 1679 Clearlake Road in Cocoa. The new facilities include offices and laboratories and share the campus with Brevard Community College - Cocoa and the University of Central Florida - Brevard. Geodetic position is 28.4° N. Latitude and 80.8° W. Longitude. The collector testing site is located on the south side of the office building in a grassy field. Any of four pads may be used, each having a power supply, data and voice hook ups. The site is located far enough from any structures, objects, trees, or parked vehicle so no shadows or reflections are cast onto the collectors during a test. A wind screen is being evaluated for use in tests requiring very low wind. A high bay area provides indoor space for setup and set-down of collector tests, and a conditioned low bay lab area with roof access will allow testing of complete solar systems under conditions approximating actual usage. A solar simulator is also located in the high bay area for indoor collector testing.
Collector testing may be accomplished on one of four moveable carts known as Mobile Tracking Platforms (MTPs). Each MTP provides independent, two-axis tracking of the sun, with an azimuth range of ±135 degrees from south and an elevation range from 0 to 90 degrees from horizontal, with an accuracy of ±0.1
degrees in wind up to 25 mph. Each MTP may carry a collector up to 4 ft by 10 ft and weighing up to 300 lbs. Each MTP is independent of the others in instrumentation, tracking, flow control, and temperature control. Temperature and flow control is provided by a separate utility cart with an onboard chiller, heater, and variable speed pump. A meteorological cart collects data for wind speed and direction, relative humidity, ambient temperature, global normal radiation and direct normal radiation.
Currently, one MTP and cart are configured to accept pool heating-type solar collectors and one MTP and cart are configured to accept flat plate-type solar collectors. The third MTP is configured to calibrate pyranometers and the fourth MTP is used as a platform for exposure testing of collectors.
The complete testing facility is still under construction. When complete, the facility will be able to test solar collectors and complete solar systems to ASHRAE standards. Four mobile test platforms will be available to test up to four solar collectors simultaneously.
Gear pumps circulate solution between the utility cart and MTP, and through the collector. The pump on the flat plate MTP produces 2.10 gpm at 0 psi and 1.20 gpm at 150 psi. The pump on the pool MTP produces 10.6 gpm at 0 psi and 9.00 gpm at 150 psi. Both pumps are outfitted with relief valves. Digital motor speed controls provide closed loop control of the pump motors by sensing and controlling the motor speed to a value set by the operator with an accuracy of ±1 rpm. The systems are calibrated in the lab to correlate flow rate to motor speed.
The utility cart heats the circulating solution with a 3 PH, 240 V, 9.6 kW heater. Heat is provided by energizing up to three elements. Sensors indicate if there is flow, if any element is on, which element is on, and over-temperature condition.
The utility cart cools the circulating solution with a 22,000 Btu/hr chiller. The chiller cools up to 10 gpm of water to temperatures between +5° C and +90° C, within ±0.05 degrees C. A microprocessor controls the chiller output by reading temperatures from RTDs placed around the circuit and controlling pulse-width-modulated refrigerant valves to vary the flow of refrigerant sent to the evaporator. Safety features include coolant over-temperature shutdown, low water tank level shutdown, refrigerant high pressure protection and thermal protection of motors. The chiller on the utility cart supplying the flat plate MTP is closed loop and has a heat exchanger installed between the chilled water loop and the collector loop. This allows collectors to be tested with fluids other than water.
Measurements and data collection are automated in the FSEC test station to allow multiple tests without excessive manpower requirements. An instrument transducer converts the parameter of interest (flow rate, temperature, etc.) into an analog voltage, resistance, pulse rate, etc. The analog signal is converted into digital form by a high accuracy analog-to-digital data acquisition system. The raw digital data is accepted by a DEC VMS mainframe computer where it is stored on a magnetic disk. The raw data is printed out immediately to give a hard copy of the data. Processed data printouts are made at the end of each test day and examined for reasonableness and conformance to test requirements. A computer program compares the data against preset criteria such as inlet temperature stability and flow rate stability. The processed data includes each data point's parameters and its calculated efficiency. A plot of the data points is also made with first and second order curve fit information. The collected data is normally reviewed daily. Tests are examined and if any anomaly exists, corrective action is taken. Before removing solar collector from the test stands, complete and valid data collection is confirmed.
Measurements made for performance determination include:
Solar irradiance (total and direct)
Flow rate of collector fluid
Fluid temperature at the collector inlet
Fluid temperature at collector outlet
Ambient air temperature
System pressure at the collector inlet
Each of the above parameters and their instrumentation are discussed in the sections below.
Solar irradiance is measured by an Eppley Laboratory Precision Spectral Pyranometer (PSP) mounted on the test stand in the plane of the collector. A second Eppley PSP and an Eppley Normal Incidence Pyrheliometer (NIP) are located on a tracker on the meteorological cart. The Eppley PSP is classified as a first class instrument by the World Meteorological Organization. It meets all the requirements of ASHRAE 93-86 and 96-80. One pyranometer is stored as a reference for calibrations, comparisons, and as a backup test instrument if necessary.
Specifications for the pyranometer are as follows:
Sensitivity: 9 microvolts per Watt per square meter approximately
Receiver: Circular, 1 square cm, coated with Parsons' black optical lacquer
Temperature Dependence: ±1% over ambient range -20° to +40° C
Response Time: 1 second
Cosine Response: ±1%, 0 - 70°, +3%, 70-80° zenith angle
Orientation: No effect on instrument performance
The pyranometer measurement indicates total solar irradiance, which is the sum of direct irradiance plus diffuse irradiance. To determine the value of each of the two components, a separate measurement of direct irradiance is made with a Eppley Normal Incidence Pyrheliometer (NIP). Characteristics of the Eppley NIP are:
Sensitivity: 8 microvolts per Watt per square meter
Temperature: ±1% over ambient range -20° to 40° C
Time Response: 1 second
All pyranometers and pyrheliometers used at FSEC are calibrated to the absolute pyrheliometer scale. Calibrations are performed at intervals of no longer than one year. Calibrations are normally conducted with FSEC's absolute cavity pyrheliometer.
The fluid flow rate at each of the test stands is measured with a turbine flowmeter mounted in the fluid line. Fluid flow causes the a turbine to turn at a speed proportional to flow rate. As the blades of the turbine pass by, an inductive pick off generates an electrical pulse stream. The frequency of this signal is converted to a dc voltage and then digitized by the Data Acquisition System (DAS).
The flowmeters were initially calibrated at the factory and are checked periodically. The flowmeters are checked before each new collector test sequence by comparing the indicated rate against a measured volume over a measured time. Visual reading rotameters, accurate to ±1.0% also give an immediate gross check of flow measurement. The flow measurement system exceeds the requirements of ASHRAE 93-86, Section 6.
Flow specifications are as follows:
Range: 0.25 to 2.5 gallons per minute,
0.5 to 5.0 gpm, and 5 to 50 gpm
Accuracy: ±0.25% of reading
Repeatability: ±0.02% of reading
Response time: 2-3 seconds
Temperature tolerance: -430° to +750° F
Pressure tolerance: Limited by end connections only
Frequency to d/c converter specifications are:
Input sensitivity: 10 millivolts, 20 to 3000 Hz
Common mode rejection: 40db at 60 Hz
DC output (selectable): 0-5 volts
Response time: 1 second
Temperature coefficient: ±0.005% of range per °F
Short term stability (8 hrs): ±0.05%
Long term stability (years): ±0.02%
Platinum resistance thermometers are used to measure the inlet and outlet temperatures. The electronic bridges used with the temperature sensors exceed the requirements of ASHRAE 93-86. Specifications are as follows:
Accuracy: better than ±0.1° C
Output: 1 millivolt per degree C
Ambient temperature effect: ±0.005° per °F change in ambient
Leadwire effect: 0.05° for ±ohm change in 3 ohm of lead wire
Temperature tolerance (sensor): -100° C to +400° C
Pressure tolerance (sensor): 2500 psig at 200° C
Calibrations are performed at the Florida Solar Energy Center using a constant temperature bath and calibrated mercury in glass thermometers. The calibration bath has a temperature uniformity of ±0.006° C. The bridge outputs are digitized by the Data Acquisition System.
Various other temperature measurements such as cover plate, back side, etc., may be made using special limits of error Type T Thermocouples. The electronic referenced junction for these is within the Data Acquisition System which also linearizes the readings. The thermocouple measurement system is calibrated using the constant temperature bath mentioned previously.
The ambient air temperature is measured using a platinum resistance thermometer mounted in a power aspirated shield. The shield protects the sensor from direct solar heating and allows flow of ambient air across the sensor. The platinum resistance probe is the same kind as mentioned above.
Fluid line system pressure is measured on the inlet side of the collector. The information from the transducer is returned to the Data Acquisition System where it is recorded with other data during testing.
Specifications for the pressure instrument are:
Accuracy: ±0.3% of BFSL, including linearity, repeatability and hysteresis
Range: 0-100 psig
Compensated Temperature Range: -25° to 75° C
Pressure differential across the collector is measured under the flow conditions during the pre-performance test. The instrument is setup and measurements made under test conditions on a one time basis for each collector.
Specifications on the differential pressure instrument are:
Accuracy: ±0.25% of span
Range: 0-50 psi
Compensated Temperature Range: -1° to 54° C
Pressure tolerance: 100 psi
Wind velocity across the collectors is measured using a three cup anemometer on the utility cart and in the plane of the collector for pool-type collectors. The anemometer rotates a photo chopper which converts the rotation rate into electrical pulses. Frequency of the output signal is proportional to wind speed. The variable frequency signal is converted to a dc voltage by the signal conditioning equipment in the instrumentation room and digitized by the Data Acquisition System.
Specifications on the wind velocity instrument are listed below. The specifications exceed the requirements of ASHRAE 93-86.
Accuracy: ±1.0% or ±0.15 mph whichever is greater.
Threshold: 0.5 mph, Range: 0.5 to 100 mph
Wind velocity is measured in the collector test field (within 20 feet of the collector) at a height above ground approximately seven feet above ground.
The direction of wind is measured at about seven feet above ground level. The wind vane is mounted on the meteorological cart located in the collector test field.
Position of the wind vane is sensed by a potentiometer which provides a resistance output. A signal conditioner converts the signal to dc voltage and presents it to the Data Acquisition System.
The DAS sequentially samples the instrument channels and digitizes the input value. The DAS outputs information in two ways. It has a LED display which an operator can view. The display is typically used to set up operations and calibrations. The second output is an electronic interface with the VMS computer. The computer accepts the data and records it on magnetic disk. Regular backups of these disks are performed by computer support personnel.
Accuracy of the DAS analog to digital conversion is greater than the measuring sensors and thus adds very little error to the measurements. Calibration against a reference voltage source is performed once a month.
The Florida Solar Energy Center is situated on 15 acres of land on the campuses of Brevard Community College - Cocoa, and University of Central Florida - Brevard. Structures on the site consist of an office building, a lab building with conditioned low-bay space and unconditioned high-bay space, and a utilities building. The site provides ample space for outdoor solar test facilities and building expansions.
The solar device test facility occupies portion of the FSEC grounds. The present facility consists of four mobile tracking platforms, two utility carts, one meteorological cart and high bay space to receive, inspect, test and store collectors and solar systems, a conditioned facility for testing solar systems, an indoor solar simulator, a partial meteorological station located on top of the office building and a complete meteorological station located several miles away.
FSEC possesses state of the art computing tools to serve testing, research and administrative staff. The computer hardware at FSEC is composed of a DEC VMS Cluster serving over 200 personal computers, workstations, and terminals, interconnected with fiber optic and twisted pair cables to create a local area network called SolarNet.
The VMS Cluster system serves high speed disk drives, tape drives, and communication devices to the network. In addition, workstations and personal computers have access to storage media such as magnetic disks, erasable and read-only optical drives, and tape drives, independent of the VMS Cluster system.
Over 300 Communication ports on the SolarNet provide ethernet and asynchronous connections to the network users and peripherals such high speed laser printers, color plotters and printers, slide cameras, modems, 8mm and 9 track tape drives, data acquisition and other scientific equipment.
FSEC uses a T1 for data communication with the main campus. This T1 line is also used to connect to the Internet. An additional T1 line as well as ISDN lines are used for video conferencing.
The computing functions on the SolarNet are large scale real-time data collection and analysis, experiment control, software development, simulation, and administration.
There are over 250 software licenses on the VMS Cluster and over 1000 licenses on the personal computers, solving varied needs of testing, research, administrative, and student assistant staff at FSEC.
Some of the more important scientific and office automation software include BLAST, DATAPLOT, EDBMS, DOE, F-CHART, FIDAP, FSEC, GKS, Ingres, HEATPUMP, NCAR, PV-FORM, PV-FCHART, PHIGS, SAS, SURFACE, TARP, and TRNSYS. FSEC has made valuable improvements to TARP, TRNSYS, PV-FORM and other state of the art scientific software.
All equipment used at FSEC is owned by FSEC.
Quality control is overseen by the Quality Control Manager as well as procedures and references described below.
Testing and Operations report certification are under the control of the Technical Manager.
A training program is implemented for all new employees engaged in solar thermal testing. This has been an effective program for training technical personnel to conduct the thermal performance/reliability durability test.
Copies of all applicable standards and test procedures are readily available to testing personnel.
An FSEC Test Procedures Manual is maintained as a quality document and copies made available to the testing personnel. It shall contain the following:
1. Applicable FSEC Standards
2. Applicable ASHRAE Standards
3. Other applicable standards
B. Calibration Control Documents
1. Equipment Lists
4. Authorized Personnel
C. Testing Control Documents
Current and previous versions of all documents pertaining to quality assurance, calibrations, and test procedures are retained by the Testing and Operations Division secretary. Changes to these documents are made only with the approval of the Technical Manager. The Test Engineer and technician shall be informed of the changes. The documentation shall be reviewed on at least a yearly basis by the Technical Manager and the Test Engineer to see if any changes are needed. The documents will be made available to all employees and will be open for review to any auditors.
At a minimum, each test item shall be labeled with a unique FSEC file number upon arrival. Randomly selected test items will be assigned a number and marked with tamper proof labels bearing that number before being shipped to FSEC. The item is inspected and physical characteristics measured and indicated on a check-in form bearing its FSEC number. The test items physical construction and condition are compared against data and drawings provided by the test requestor. If any shipping damage or other anomaly is noted the test client is notified and a review process is started to see if the test item is suitable for testing.
When not undergoing outdoor testing, test items are stored in a enclosed and secure building not open to the public. Items are treated with care and stored in specially constructed racks. During the outdoor testing phase the weather forecast is monitored by the test engineer and technician. This allows the test item to be moved into storage if damaging weather is imminent. In general, any conditions or activities which might affect test results are specifically avoided.
After testing is complete and the test client has reviewed the results the test item is disposed of. The method of disposal is indicated by the test client on a form submitted prior to testing.
Periodic checks are performed from time to time to validate the testing process. Items which have been retained may be retested and results compared to previous tests. One particular collector has been set aside for this purpose. During the test review process the results of the current test will be compared to results of previous tests on items of similar construction. A database has been established which contains several hundred tested collector's results and construction details. The statistics of all collectors of similar construction are recalled and presented to the Technical Manager. If results are not comparable then the cause shall be investigated. Performance data is collected over five minute test periods. Although only four complete test periods are required eight to twelve are normally taken. This extra test data provides an inherent replication of tests using same methods. Inter-laboratory comparisons have been performed in the past. Currently there are no other solar collector test labs in the United State. If the solar test industry expands again inter-laboratory comparison can be expected to continue.
Review of testing results may occur at any time. At a minimum, test reports shall be reviewed by the Technical Manager and one other Testing and Operations Division engineer. The purpose of the review is to check the reasonableness of the results and to look for any errors in the data. Any necessary corrections are made before test report is released to the client.
Audits of testing activities will be conducted at the request of the Center Director or the Technical Manager at least once per year. The audit will be conducted by a competent party chosen from outside the Testing and Operations division. The audit will include at least a review of relevant documentation, calibration procedures, testing procedures, personnel proficiency, and observation of test performance.
The results of an audit will be given in written form to the Center Director, Technical Manager, and Quality Manager. Any necessary corrective actions will be documented. The Quality Manager will insure that these actions are discharged within a reasonable time scale. Corrective action will be taken if discrepancies are found which cast doubt on the validity of published test results and the affected parties will be notified immediately in writing.
Whenever a discrepancy in testing is found the following process will occur. The Technical Manager is notified of the discrepancy. The Test Engineer determines if data was affected, how much data was effected, what tests were affected, and how to correct the data if possible. Any affected test clients are notified. All of this information is presented to the Technical Manager who makes a decision as to a course of action. The decision is passed on to the test client and the Test Engineer carries it out. Better test methods, training, and/or documentation are investigated to prevent reoccurrence of problem. If a test client disagrees with the actions taken they may file a complaint.
The Solar Collector Test Laboratory primarily tests flat plate solar collectors to standards of FSEC, ASHRAE and SRCC. The equipment, procedures and documentation are all in place to perform these standard tests.
On occasion, a nonstandard test will be requested or a test item will be constructed in such a way that the standard test and equipment cannot be used. Whenever a nonstandard test is requested or is necessary, a review will be conducted by a technical team with the test client. The technical team will include a test engineer, the Test Program Director and the Director of Testing and Operations. The test engineer will be responsible for presenting technical details of the equipment to be tested and any proposed test methods and configurations. The review committees will decide if the proposed test is possible and valid with the resources which can be applied. If the test is conducted, the test configuration, test methods if any, noncompliance with standards will be clearly identified in the test report.
Complaints are initially referred to the test engineer for consideration. Response is made to the complaint based on consultation with other engineers. If the answers or actions provided are not acceptable to the test client the complaint will be referred to the FSEC Certification Review Board. This board is comprised of FSEC technical employees not directly associated with the testing of the item in question. After due consideration the Board will make a decision. Their decision will be final. This process is formalized in collector certification program information.
All equipment used at the Florida Solar Energy Center to test solar equipment will be maintained in current calibration. The purpose of this plan is to define standard procedures for these calibrations.
Historical records are kept of all instruments used for testing and calibration of testing equipment from the time of purchase until the property is disposed of. This period, for some items, may exceed five years.
The calibration plan shall be the top level document for equipment calibration and will define calibration frequency requirements, traceability requirements, calibration sources, and documentation requirements. Detailed calibration procedure requirements and/or measurements accuracies are included in the equipment manuals and other documents.
All measurement equipment used for thermal performance/durability tests will be maintained in calibration as recommended by the equipment manufacturer to maintain accuracy or as required by ASHRAE 93-86 or 96-80. In case of conflict between the two recommendations on frequency of calibration, the shorter time period will be used. In no condition will the calibration period be greater than one year. All equipment which require calibration are listed. Equipment by type are listed below.
Solar Radiation Pyranometers and Pyrheliometers
Flow Rates Turbine Flow Meters, Scale
Temperatures Platinum Resistance Thermometers and Electronic Bridges
Analog to Digital Computer Data Logger
Calibration Voltage Source Fluke Voltage Standard
Temperature Calibration Glass Thermometers
Solar Radiation Equipment
All solar radiation measurement equipment will be calibrated. The period of time between calibrations will be no greater than one year. The instruments will be calibrated to the absolute scale.
Calibrations will be performed by outside calibration laboratories such as the manufacturer Eppley Laboratory Inc., DSET Laboratories, the National Oceanic and Atmospheric Administration Laboratory, or by FSEC using the Absolute Cavity Radiometer.
Calibration at FSEC and the other laboratories is performed using reference instruments traceable to a primary radiometer maintained by the World Radiation Center at Davos, Switzerland.
Installation and maintenance of the pyranometers and pyrheliometers will be in accordance with the manufacturers recommendations. Detailed calibration records will be maintained for each instrument.
All turbine flowmeters used to measure flow rate shall be calibrated over the measurement range. The time interval between calibrations shall be no longer than one year. Calibrations are continually monitored during each test. Prior to each collector change a current calibration is performed.
Calibration of the flowmeters shall be performed using water or military standard fluid. Temperature of the calibrating fluid can be in the range of 80° F to 200° F. Viscosity shall be less than 1.5 centistokes.
The turbine flowmeters generate a stream of electrical pulses, the frequency of which is proportional to flow rate. The calibration determines the number of pulses generated (K-factor) per volume of fluid or the frequency versus flow rate relationship.
Since the K-factor curve is not linear for graphite sleeve flowmeters, the calibration K-factor shall be used to set up the electronic measurement system each time a new flow rate is used.
A gross indication are the visual rotameters installed in the fluid lines. These units have been calibrated to ±1.0% accuracy.
The primary method for in-place testing of the turbine flowmeters is by measuring volume of liquid and time and comparing to the indicated flow. This method shall be used prior to each series of collector tests.
Detailed calibration and maintenance records shall be maintained for each flowmeter.
The electronic frequency to DC converter shall be reset for each flow rate change. Each time a new collector to be tested is installed the flow rate measurement system shall be set up for the specific flow rate to be used. A pulse generator and calibrated pulse counter shall be used to simulate input from the flowmeter. The pulse generator shall be set to output a frequency equal to the K-factor at the test flow rate multiplied by the flow rate. The converter zero shall be set and the span control adjusted to give the correct DC voltage level or current output for the test flow rate. This will insure highest achievable accuracy under actual test conditions. The pulse generation shall be disconnected and the flowmeter reconnected.
Platinum Resistance Thermometer/Bridges
Temperature measuring equipment shall be recalibrated at intervals of no greater than three months. The calibration shall be done on-site using calorimeter thermometers as a reference.
The RTD sensors to be calibrated shall be removed from the test stand fluid stream but remain electronically connected as in the normal test configuration. Temperature readings shall be made as is normal at the digital output of the data logger.
Accuracy of the temperature measuring system shall be checked at the freeze point of water 0° C and at least three other temperatures up to 100° C (50° C for pool stands). Data shall be taken but no adjustments made until the entire calibration check is finalized. If necessary the span and zero of the bridge may be adjusted and the test then repeated. Temperature measurement accuracy must be better than +0.01° C. Accuracy potential of the measuring system is much higher than the requirements.
Temperature measuring equipment for all test stands shall be calibrated sequentially. Estimated time for complete calibration is two days.
The Omega pressure instrument and differential pressure units are piezoelectric transducers and are accurate to ±0.3% of the reading. These instruments shall be recalibrated at intervals no greater than one year.
Detailed maintenance and calibration records shall be maintained.
Analog to Digital Converter (A/D)
The A/D converter is part of the Kaye 8000 Data Logger. A calibration shall be made at periods no greater than one month. The Fluke 335D shall be used as the reference voltage source.
Fluke Voltage Source
The Fluke 335D voltage source shall be returned to the manufacturer for calibration at intervals no greater than one year. The test laboratory used is:
Fluke Southeastern Technical Center
940 N. Fern Creek Road
Orlando, Florida 32803
For testing collectors outdoors, the computer controlled collector testing Mobile Tracking Platform (MTP) keeps the collector properly aligned with the sun throughout the day allowing for optimum irradiance for the longest period. The MTP is used in conjunction with a support cart to maintain stable flow and temperature input to the collector. A weather cart monitors ambient conditions. Separate data acquisition systems collect data from the collector and ambient cart.
Additional information specific to the FSEC solar collector testing and certification program is available at the main Testing & Certification page.