Vorstellung

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Montagsseminar
Verbesserte Auswertungen zur Strahlungserfassung
mit METEOSAT und deren Anwendung für die
Bewertung thermischer Solaranlagen
Improved evaluations of the radiation data
acquisition with METEOSAT and its usage for
DHWS (Domestic hot water system) performance
calculations
Aleksander Undynko , 14.07.2003
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Contents
1. Scheme of DHWS (regarding of the present
job).
2. Measured characteristics of DHWS storage
tank.
3. Energy balance for DHWS storage tank
3.1 Scheme 3.2 Energy balance dynamics 3.3
Approximation for constant internal energy of
DHWS storage tank.
4. Performance characteristics of DHWS
definitions, numerucal and graphical
representation.
5. TestSolar tool
5.1 Main idea 5.2 Block-scheme 5.3
Demonstration of work with TestSolar.
6. Testing of TestSolar for the 1999 year data
set from the DHWS in Hohkeppel (NRW)
6.1 Parameters of DHWS 6.2 Global radiation data
for the year 1999 in Hohkeppel 6.3 Performance
calculations results and accuracy.
7. Conclusions
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1. Basic scheme for one tank forced circulation
system
Pump
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2.1 Measured parameters of DHWS
November,27 November, 28
Days, Year 1999
A two days set of DHWS storage tank parameters
for the year 1999 in Hohkeppel versus time step
0.25 hour
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3.1 Energy balance dynamics
Qint

• Tank energy balance, showing energy gains and
• losses for the DHWS storage tank

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Tank loss coefficient

• t1, t2 start, end time moment
• C Heat capacity
• Tenv environment temperature 
• Ttank(t1), Ttank(t2) tank temperatures at the
  time moments t2 and t1 , t2 gt t1

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3.3.1. Energy balance approximation for Qint
const
It is interesting to evaluate system performance
for a time ?t when all the energy flows from
QSolar, QDraw, QAux are much greater then
internal energy change ?Qint
The following approximation is true
with
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3.3.2 Numeric energy balance equation for
Qintconst
with
Draw energy
Measured parameters with time step ??  (??
0.25 hour) Tin cold water supply
temperature   Tout hot water (outlet)
temperature   QAux  auxiliary energy added to
the DHWS storage tank (Wt)   Vout water
volume rate (L)   QSolar  sun radiation
energy transmitted from the collector to the
storage tank (Wt).  
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4.1 DHWS performance calculation definitions
Solar fraction
Solar effectiveness
System effectiveness
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4.2 DHWS performance calculation graphical
interpretation
If two values from D, NA, NS are known, one can
calculate the third parameter
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5.1 TestSolar Main Idea

• Substitution of sun radiation data by the
  values extracted from the METEOSAT global
  horizontal sun radiation maps

• According to the date a daily radiation map is
  selected

• According to the geographical position a value
  for the horizontal radiation
• is extracted

• Hourly horizontal radiation sums are generated
  from the daily radiation value
• on the basis of TAG (Time dependent,
  Autoregressive, Gaussian) model

• Qsolar values are calculated from the hourly
  radiation sums on the basis of Klucher
• model for insolation on the tilted surfaces,
  Perez anisotropic hourly diffuse
• radiation model for sloping surfaces.

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Horizontal sun radiation daily maps generated
by RadiCal (example)
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6.1 Performance test for the real DHWS

• Object
• DHWS in Hohkeppel (a two story residental
  building with heated area 163 m2).
• DHWS parameters
• -         Geographical longitude 7.39
• -         Geographical latitude
  51.29
• -         collector area (flat-plate)
  7.4 m2
• -         collector elevation angle
  52
• -         collector azimuth angle 12
  (west) 
• -         tank volume 400 litters.

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6.2 Performance test for the real DHWS
radiation data
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6.3.1 Performance test for the real DHWS results
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6.3.2 Performance test for the real DHWS solar
fraction
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6.3.3 Performance test for the real DHWS solar
effectiveness

• Monthly solar effectiveness for DHWS in Hohkeppel
  in the year 1999

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6.3.4 Performance test for the real DHWS system
effectiveness

• Monthly system effectiveness for DHWS in
  Hohkeppel in the year 1999

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6.4.1 TestSolar calculations accuracy

• For longer time interval and higher sun
  radiation during this interval the performance
  calculations are more precisely

Relative deviations for hourly radiation sums
generated from daily radiation values - one
day 30-80 (depends from the sun radiation
intensity) - one month 10 20 (less in
the summer and bigger in the winter) -
three monts 8 15 - one year about 6
.
The method limitation performance calculations
are realistic for the time intervals with
following relation for the energy flows
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6.4.2 TestSolar calculations accuracy
DHWS performance test will be strictly dependend
from the statistical nature of calculations Relat
ive spread of calculations according to generated
hourly sums - one day 20 50
- one month 5 10 - three months
3 6 - one year less than 1 .
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Conclusions

• - TestSolar tool allows to calculate DHWS
  performance on the basis of measured parameters
  and radiation data extracted from the METEOSAT
  global radiation data

• Calculations accuracy is restricted by accuracy
  of extracted
• radiation data and statistical nature of
  calculations

- Calculations method is also restrictded by
minimal incoming energy flow to the DHWS
storage tank for the given time interval
HELIOSAT system must be controlled at least one
time per week