European modelling group for SHSD and DHW

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Energy research

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• Publié par: EUROPEAN-COMMISSION
• Nombre de lectures: 7
• Langue: English
• Poids de l'ouvrage: 3 Mo

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Commission of the European Communities
energy
EUROPEAN MODELLING GROUP
FOR SHS AND DHW
Report
EUR 9148 EN
Blow-up from microfiche original Commission of the European Communities
energy
EUROPEAN MODELLING GROUP
FOR SHS AND DHW
JÜRGEN REICHERT, DIETER SCHLAG, HERMANN HERZ
FRAUNHOFER GESELLSCHAFT zur FOERDERUNG DER ANGEWANDTEN FORSCHUNG eV
Sebastian-Kneipp-Strasse 12-14
D-7500 KARLSRUHE 1
Contract No. ESA-M-025-80 D
FINAL REPORT
Directorate-General for Science, Research and Development
1984 EUR 9148 EN Published by the
COMMISSION OF THE EUROPEAN COMMUNITIES
Directorate-General
Information Market and Innovation
Bâtiment Jean Monnet
LUXEMBOURG
LEGAL NOTICE
Neither the Commission of the European Communities nor any person acting on behalf
of then is responsible for the use which might be made of the following
information
©ECSC — EEC — EAEC, Brussels · Luxembourg, 1984 Preface
The Commission of the European Communities is, as part of its Solar Energy
Programme, conducting a Research and Development programme on Solary
Applications for Dwellings. The cooperative work within the European Model­
ling Group for Solar Heating Systems and Domestic Hot Water is one of the
activities undertaken within this programme.
During the first one and a half year of operation of the current CEC 4-years
programme this group has undertaken work in the following areas:
- analysis of data from the Solar Pilot Test Facilities
- validation of simulation models
- parameter sensitivity analysis
- investigation of simplifications and assumptions in
simulation models
- simplified design methods.
These activities have not only been coordinated within the group but also
performed in close cooperation with two other concerted actions within the
CEC programme for Solar Energy Applications for Dwellings: The Solar Pilot
Test Facilities Group and The Performance Monitoring Group.
This report documents work performed as a participant of the CEC Modelling
Group for SHS and DHW. For a full picture of the work is referred to the
project summary report: "Common Solar Simulation and Validation in Europe"
/l/ released in the autumn of 1981 from the Thermal Insulation Laboratory,
Technical University of Denmark.
Ove Jørgensen
Co-ordinator 1. Brief review of the research programme of the group
The European Modelling Group for Solar Systems is mainly concerned with the
development of computer simulation models, detailed as well as simplified,
and with the knowledge of the accuracy and validity range of these models
simulating thermal solar energy use by flat collector systems. All part­
icipants carried out the validation work with their own models developed
before the beginnung of this project.
The group was organized in the following way:
- the coordinator (Ml)
- participants directly linked to their national Solar pilot Test
Facility (M2)
- other participants interested in validation work (M3)
FhG-ISI was linked to the German Solar Pilot Test Facility (SPTF) of the
Technische Universität Berlin (Prof. Hanitsch), Institut für elektrische
Maschinen, and is therefore an M2 participant.
Main tasks for M2 participants were:
1. Guidance to the national SPTF in subjects related to modelling (see
Chapter 3)
2. Sensitivity analysis (for results see report of the coordinator)
3. Validation of Models with data from the national SPTF (see Chapter 3)
4. Common validation with data from different SPTF's (see Chapter 4)
Some minor activities not carried out by all participants consisted of
- development and testing of new models (e.g. stratified storage)
- modelling of alternative systems
-t of simplified methods
- validation ofd methods.
Participants had to change their models for the validation work making
allowance for calculation of the special SPTF system, more detailed input
data, comparison of measured and calculated results, calculating components
(e. g. collector only, see Chapter 4) of the total system, reducing the time
step from one hour to five minutes, etc.
A short description of the model used for validation work is given in
Chapter 2. 2. Description of the Solar Simulation Model SOLPTF of the FhG­ISI
The program SOLPTF is a special version of SOLH which has been developed
from FhG­ISI to design and optimize solar systems. Some changes had to be
made to meet the specific requirements for validation work as mentioned
above. These changes do not concern the physical basis of the program but
only data handling, summing up of different parameters, system control, etc,
The program is written in Fortran IV.
2.1 Time and Radiation Processor
2.1.1 Time:
Once a day the declination of the sun and the equation of time EOT are
computed for the midth of the day by
δ = 0.3958 + 23.2569 sin |g£ ( (TAG ­ 0.5) + 284.04)
+ 0.3909 sin |g| (2·(TAG ­ 0.5) + 281.29) (1)
+ 0.1754 sin |g£ (3­(TAG ­ 0.5) + 303.41)
EOT = 0.00017 + 0.12240 sin |¿ ( (TAG ­ 0.5) + 179.47)
+ 0.16561 sin |gï (2­(TAG ­ 0.5) + 203.91) (2)
+ 0.00564 sin |¿ (3'(TAG ­ 0.5) + 201.35)
where TAG is the day of the year, 6 comes out in degrees and EQT in hours.
True Solar Time (W0Z) for the midth of every time­step (DT) is given by:
WOZ = ST + EQT + (LONG ­ STMJ/15 ­ DT/2 (3)
where ST = standard time (houroftheday)
LONG ■ longitude in degrees(+East,­ West)
STM * standard meridian ofthetimezone
and the hour angle of the sun (STW) is
STK * 12 ­ WOZ (4) 2.1.2 Radiation:
Direct and diffuse radiation are treated separately. They are transformed to
the collector plane and then corrected to give the same value as the
measured CGR (collector global radiation). The measured horizontal diffuse
radiation DIF is first corrected for the shadow ring.
DIFK = 1.1 · DIF (5)
The differencebetweenthemeasured global horizontal radiationHTOTand
DIFK is thentakenashorizontal beam radiation from whichthenormalbeam
radiationDIRiscalculated by dividing by θζ, the zenith angleofthesun
(after Duffie/2/2.5.3).
DIR = (HTOT ­ DIFK)/8Z(6)
The collector beam radiation is then given by
HBEAM = DIR · CTH (7)
where CTH=cosOiiscalculated by the formula 2.5.2 fromDuffie.Diffuse
radiationistreatedafterthe following formula as proposedbythecoor­
dinator inthepreviousmodelling group.
F" =0.55+(0.437+0.313 · CTH) · CTH
(8)
F" =0.45ifCTH< ­ 0.2
F = (F" · (1 ­ cos (TILT)) + cos (TILT) ­ 0.5 . (1 + cos (TILT)))
■ 0.5 + 0.5 · (1 + cos (TILT)) (9)
HDIFF = DIFK · F + (1­cos(TILT))·GR'HT0T/2(10)
where TILT is the collector­tilt
and GR the ground reflection.
Then both values are corrected to give CGR:
FAK = CGR / (HBEAM + HDIFF)
HBEAM = HBEAM ­FAK (11)
HDIFF=HDIFF·FAK2.2 Collector
2.2.1 Reflection and absorption by the cover
Reflection and absorption are treated as in Duffie Chapters 6.1 and 6.2.
First the refraction angle is calculated by
sin 02 = sin Gi/n2 (12)
with therefractionindex n2 of the cover. The reflectedportionçbecomes
then
?2
1 sin(G2­©j)tan(02­0j) (13)
P=7 _-,_
.sin(ø2+0j) tan(G2+ ©j)
Taking into account multiple reflection but not absorption, the transmit­
tance through the single cover is
(14) 1 ­ Ρ
τ„ =
ΤΊ-ρ
The transmittance considering only absorption is
(15) Τςχ = exp (-K · D/cosØ)
where Κ is the extinction coefficient and D is the thickness of the glass.
For combined reflection and absorption the product is taken
(16) τ = τ · τ
1 lr α
To evaluate the transmittance absorptance product, the absorptance « of the
absorber plate is first corrected for angular dependant absorption by
0,25
α = α · (cos©) (π;
then, taking into account multiple reflection between absorber plate and
cover ( r« ) becomes
(τα) ­ τ · oc / (1 ­(!­<*<.) Pd) (18)
?¿ is the diffuse reflectance,i.e. the reflectance at anincidenceangle
of 60°.
For diffuse radiationtheincidenceangle is assumed to be always60°,
therefore (£w)d is constantandiscalculated only once whereas[T>)for
beam radiation is calculated at every time step. The energy received by the absorber plate H then comes out as
H = (τα) · HBEAM + (ra)d · HDIFF (19)
2.2.2 Collector losses
The formula of Klein (Duffie7.4.9)is used for the top loss coefficient
u « / Ν + Λ -l
1 \(344/Tp)[(Tp­Ta)/(N♦ f)]'0'31 + hj
σ(Τρ+T.)(T2p + Τ2. )
+ L a Η tl (20)
[ερ+0.0425Ν (1 ­ ep)]'1+Γ(2Ν+f ­ 1) /el ­Ν
with correction for other tilt anglesthan45degrees
Ut / Ut (45) = 1 ' (TILT ' 45) " (0­00259­0.00144 · ερ) (21)
The variables have the same meaning as in Duffie 7.4.9.
2.2.3 Collector energy gain and temperature
For the collector the Hottel, Whillier and Bliss model is used, presented by
Duffie in Chapter 7, with an additiona