Collector Efficiency - Viessmann Vitosol
100 Technical Manual

2.2 Collector efficiency

2.2 Collector efficiency
Some of the solar radiation striking the
collectors is lost through reflection and
absorption. The optical efficiency h
these losses into account.
When the collectors heat up, they transfer
heat to the environment as the result of
conduction, radiation and convection.
These losses are allowed for by the heat
loss factors k and k .
1 2
Collector type Opt. efficiency
level
h
*1 *1
in % i %
o
Vitosol 100
H Type s/w 2.5
84
H Type 5 DI
84
Vitosol 200 85
Vitosol 250 77.6
Vitosol 300 82.5
h
*1
based on
o
H aperture area for Vitosol 100 and 250
H absorber area for Vitosol 200 and 300.
0.9
0.8
0.7
1
0.6
0.5
0.4
0.3
0.2
0.1
0
0 10 20
Temperature difference in K
A Vitosol 100
B Vitosol 200
C Vitosol 250
D Vitosol 300
1 Solar heating system for DHW with low coverage
2 Solar heating system for DHW with higher coverage
3 Solar heating system for DHW and heating system backup
4 Solar heating system for process heat/solar air conditioning
14
The thermal loss coefficient and optical
efficiency combine to form the collector
takes efficiency curve which can be calculated
o
on the basis of the following formula:
h + h * k
o
Heat loss factors
2
k in W/(m · K) k in W/(m
1 2
3.36 0.013
4.16 0.0073
1.61 0.008
1.97 0.0047
1.19 0.009
2
3
30 40 50 60
@ DT @ DT
2
* k
1 2
E E
g g
Spec. thermal
capacity p y
2 2
kJ/(m kJ/( · K) K)
2 2
· K )
6.4
7.2
25.5
52.0
5.4
D
B
4
C
A
70 80 90 100
If the difference between the collector and
ambient temperature is zero, the collector
loses no heat to the environment, and the
efficiency h is at its maximum level; this is
known as the optical efficiency h
The table below lists comparative values
for the optical efficiency and the heat loss
factors:
VITOSOL
.
o