10.07.2015   Particle Image Velocimetry (PIV)

Implementation of the procedure

The procedure described above is applied for a CPC collector. The collector parameters gained during the collector test are summarised in Table 2.

Л0

Ked

a1

a2

ceff

[-]

[-]

[W/(m[5]K)]

[W(m2K2)]

[J/(m2K)]

0.651

1.012

0.688

0.004

13060

Table 2: Collector parameter

The incident angle modifier K0b(0) of the investigated collector is calculated according to equation (6) /3/, the corresponding values of 0| and 0t are documented in Table 3.

angle of incidence 9

0

10

20

30

40

45

55

60

70

90

Keb(9l,0)

1.00

1.00

1.00

0.99

0.97

0.95

0.89

0.84

0.70

0

Keb(0,9t)

1.00

0.97

0.99

1.01

1.01

1.02

0.99

1.05

1.12

0

Table 3: Incident angle modifier

The characteristics of the test sequence used for validation are summarised in Table 4, a graphical overview is given in Figures 2 and 3.

Criteria

actual value

Total solar irradiation in collector plane

15.3 MJ/m2

Standard deviation of the change in total irradiance with time dG/dt (variability of irradiance)

1.1 W/(m2s)

Increase of the inlet temperature

5 K/h

Difference of mean fluid temperature and ambient temperature

27 K

Angle of incidence of beam irradiance 9

0° to 59°

Time step dt during storage of mean values

< 36 s

Table 4: Actual values of the test sequence used for validation

hour of the day [h]

Figure 4: Measured and calculated collector output during the test sequence used for validation together with the difference between measured and calculated collector output

4. Conclusions

The validation of collector parameters obtained from collector testing is desirable if the parameters are used for performance prediction using dynamic simulation. For this purpose an additional test sequence and a set of acceptance criteria have been defined taking typical every day operation into consideration. This method is able to detect parameter sets that are not fully able to mirror the thermal behaviour of a collector under dynamic conditions. The implementation of the method shows for the presented example very promising results. It is strongly recommended to introduce the presented method into the EN 12975 standard.

References

/1/ EN 12975-2:2001. Thermal solar systems and components — Solar collectors — Part 2: Test methods

/2/ EN 12977-2:2001. Thermal solar systems and components — Custom built systems — Part 2: Test methods

/3/ Mclntire W. R., Factored approximations for biaxial incident angle modifiers. Solar Energy 29, 315-322, 1982