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Calculation and Measurement Methods for the Performance of Solar Collectors. Models of Flat Plate Collectors, Transparent Insulation and Efficiency Factors.

Hellström, Bengt LU (2005) In Report EBD-T 05:2.
Abstract (Swedish)
Popular Abstract in Swedish

Denna avhandling handlar om modeller för plana solfångare, transparent isolering och verkningsgradsfaktorer. En ekvation för energiutbytet från en glasad plan solfångare härleds genom att modellera verkningsgradsfaktorn, F´, som en summa av en konstant och en temperaturberoende del. Ett alternativt sätt att testa en plan solfångare, baserat på denna modell, föreslås.



En komplett uppsättning algoritmer för att beräkna energiutbytet for en plan solfångare med plana filmer eller en bikakestruktur mellan täckskivan och absorbatorn presenteras. Algoritmer för att beräkna strålningsutbytet mellan de olika lagren eller skikten i en bikakestruktur ges. Formler för att beräkna den... (More)
Popular Abstract in Swedish

Denna avhandling handlar om modeller för plana solfångare, transparent isolering och verkningsgradsfaktorer. En ekvation för energiutbytet från en glasad plan solfångare härleds genom att modellera verkningsgradsfaktorn, F´, som en summa av en konstant och en temperaturberoende del. Ett alternativt sätt att testa en plan solfångare, baserat på denna modell, föreslås.



En komplett uppsättning algoritmer för att beräkna energiutbytet for en plan solfångare med plana filmer eller en bikakestruktur mellan täckskivan och absorbatorn presenteras. Algoritmer för att beräkna strålningsutbytet mellan de olika lagren eller skikten i en bikakestruktur ges. Formler för att beräkna den absorberade solinstrålningen i varje skikt ges också. Algoritmerna kan användas i ett beräkningsprogram för att bestämma energiutbytet, verkningsgraden och solfångarparametrar.



Mätingar av värmekonduktivitet och värmegenomgångstal för glasningar, utförda med olika transparenta isoleringsmaterial, presenteras och jämförs med beräkningar. Mätningar av infallsvinkelberoende hemisfärisk solljustransmittans presenteras också.



För en koncentrerande solfångare med en ojämn instrålning mot absorbatorn är verkningsgradsfaktorn för tillskottsdelen av energiutbytesekvationen, här benämnd den optiska verkningsgradsfaktorn, F´c, ej lika med F´ och är en funktion av instrålningsfördelningen på absorbatorn. Formler för att beräkna F´c(x) för läget x på en flänsabsorbator med konstant flänstjocklek härleds. Medelvärdet för den optiska verkningsgradsfaktorn, F´c,a, kan sedan beräknas från F´c(x) och fördelningen av den absorberade instrålningen. Formler för att beräkna temperaturfördelningen tvärs absorbatorn för fallet med ojämn belysning härleds också.



En metod för noggranna mätningar av F´ presenteras och testas. Metoden använder noggranna temperaturmätningar tvärs absorbatorn, i värmebärarvätskan och i den omgivande luften, för värmeförluster utan instrålning. Två absorbatorer av olika typ testades. För laminärt flöde var de mätta F´-värdena något högre än de beräknade värdena för båda absorbatorerna, medan de mätta värdena var något lägre än de beräknade i övergångsområdet till turbulens. (Less)
Abstract
This thesis deals with models of flat plate collectors, transparent insulation and efficiency factors. An equation for the energy output from a glazed flat plate collector is derived by modelling the collector efficiency factor, F´ as the sum of a constant and a temperature dependent part. An alternative way of testing a flat plate collector, based on this model, is suggested.



A complete set of algorithms for calculating the energy output for a flat plate collector with flat films or honeycombs between the cover and the absorber is presented. Algorithms for calculating the radiation heat exchange between the different sheets or layers in a honeycomb glazing are given. Formulas for calculating the absorbed solar energy in... (More)
This thesis deals with models of flat plate collectors, transparent insulation and efficiency factors. An equation for the energy output from a glazed flat plate collector is derived by modelling the collector efficiency factor, F´ as the sum of a constant and a temperature dependent part. An alternative way of testing a flat plate collector, based on this model, is suggested.



A complete set of algorithms for calculating the energy output for a flat plate collector with flat films or honeycombs between the cover and the absorber is presented. Algorithms for calculating the radiation heat exchange between the different sheets or layers in a honeycomb glazing are given. Formulas for calculating the absorbed solar energy in each layer are also given. The algorithms can be used in a computer program for determining the energy output, the efficiency and collector characteristic parameters.



Measurements of heat conductivity and total heat loss coefficients of glazings, performed for different transparent insulation materials, are presented and compared with calculations. Measurements of directional-hemispherical solar transmittance are also presented.



For a concentrating collector with an uneven irradiation on the absorber, the efficiency factor for the gain term of the energy output equation, here called the optical efficiency factor, F´c, is different from F´ and is a function of the irradiation distribution on the absorber. Formulas for calculating F´c(x) for the location x on a fin absorber with constant fin thickness are derived. The average optical efficiency factor, F´c,a, can then be calculated from F´c(x) and the absorbed intensity distribution. Formulas for calculating the temperature distribution across the absorber for the case of uneven irradiation are also derived.



A method for accurate measurements of F´ is presented and tested. The method uses accurate temperature measurements across the absorber plate, in the heat carrier fluid and in the ambient air for heat losses without irradiation. Two absorbers of different types were tested. For laminar flow, the measured values of F´ for both absorbers were slightly higher than the calculated values, while in the transition region, the measured values were slightly lower. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Associate Research Professor Furbo, Simon, Technical University of Denmark
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Transparent insulation, Test method, Calculation method, Concentrating collector, Efficiency factor, Fin efficiency, Flat plate collector, Heat conductivity, Honeycomb, Measurement method, Performance, Solar transmittance, Solar collector, Collector model, Energy research, Energiforskning
in
Report EBD-T
volume
05:2
pages
126 pages
publisher
Lund University, Lund Institute of Technology, Div. of Energy and Building Design, P.O. Box 118, SE-221 00 LUND, Sweden
defense location
Room B, School of Architecture, Sölvegatan 24, Lund Institute of Technology
defense date
2005-03-11 10:00
ISSN
1651-8136
ISBN
91-85147-06-0
language
English
LU publication?
yes
id
76e5af45-a84a-4890-a3db-9604b003e27d (old id 24501)
date added to LUP
2007-05-31 15:49:27
date last changed
2016-09-19 08:44:55
@phdthesis{76e5af45-a84a-4890-a3db-9604b003e27d,
  abstract     = {This thesis deals with models of flat plate collectors, transparent insulation and efficiency factors. An equation for the energy output from a glazed flat plate collector is derived by modelling the collector efficiency factor, F´ as the sum of a constant and a temperature dependent part. An alternative way of testing a flat plate collector, based on this model, is suggested.<br/><br>
<br/><br>
A complete set of algorithms for calculating the energy output for a flat plate collector with flat films or honeycombs between the cover and the absorber is presented. Algorithms for calculating the radiation heat exchange between the different sheets or layers in a honeycomb glazing are given. Formulas for calculating the absorbed solar energy in each layer are also given. The algorithms can be used in a computer program for determining the energy output, the efficiency and collector characteristic parameters.<br/><br>
<br/><br>
Measurements of heat conductivity and total heat loss coefficients of glazings, performed for different transparent insulation materials, are presented and compared with calculations. Measurements of directional-hemispherical solar transmittance are also presented.<br/><br>
<br/><br>
For a concentrating collector with an uneven irradiation on the absorber, the efficiency factor for the gain term of the energy output equation, here called the optical efficiency factor, F´c, is different from F´ and is a function of the irradiation distribution on the absorber. Formulas for calculating F´c(x) for the location x on a fin absorber with constant fin thickness are derived. The average optical efficiency factor, F´c,a, can then be calculated from F´c(x) and the absorbed intensity distribution. Formulas for calculating the temperature distribution across the absorber for the case of uneven irradiation are also derived.<br/><br>
<br/><br>
A method for accurate measurements of F´ is presented and tested. The method uses accurate temperature measurements across the absorber plate, in the heat carrier fluid and in the ambient air for heat losses without irradiation. Two absorbers of different types were tested. For laminar flow, the measured values of F´ for both absorbers were slightly higher than the calculated values, while in the transition region, the measured values were slightly lower.},
  author       = {Hellström, Bengt},
  isbn         = {91-85147-06-0},
  issn         = {1651-8136},
  keyword      = {Transparent insulation,Test method,Calculation method,Concentrating collector,Efficiency factor,Fin efficiency,Flat plate collector,Heat conductivity,Honeycomb,Measurement method,Performance,Solar transmittance,Solar collector,Collector model,Energy research,Energiforskning},
  language     = {eng},
  pages        = {126},
  publisher    = {Lund University, Lund Institute of Technology, Div. of Energy and Building Design, P.O. Box 118, SE-221 00 LUND, Sweden},
  school       = {Lund University},
  series       = {Report EBD-T},
  title        = {Calculation and Measurement Methods for the Performance of Solar Collectors. Models of Flat Plate Collectors, Transparent Insulation and Efficiency Factors.},
  volume       = {05:2},
  year         = {2005},
}