Environmental Engineering Reference
In-Depth Information
Table 21. Comparison between performance values used in basic
design, measured values and simulation program
Item
Basic Design
Measured value
Simulation
Heat collection
efficiency
Catalog efficiency:
η = 0.913 - 2.46 x - 1.92 x
2
Value of η when x=0 is:
Winter = 0.83 ~ 0.84
Summer = 0.80 ~ 0.81
Average = 0.82
Slope of curve is:
Winter = large
Summer = small
Efficiency of block F includes heat loss
from internal piping and dust effect
* Efficiency used for simulation is:
η = 0.84 - 2.46 -1.92 x
2
x={ (T
i
+ T
o
)/2-T
a
}/ I
t
o
C hr m
2
/kcal
* For completely clean condition, the
value of η for x=0 has been increased
by 0.2 to 0.84 because of the fact that
dust isn't completely removed after
cleaning.
Heat loss from piping
Calculated value ignores valves and piping
supports. For a single block:
Q
loss
= 93.5 (T
w
- T
a
) kcal/hr
T
w
= water temp., T
a
=air temp.
Value measured for a single block is:
Q
loss
= 66.6 (T
w
- T
a
)
1.3
kcal/hr
Value used is:
Q
loss
= 66.6 (T
w
- T
a
)
1.3
kcal/hr
Dust influence
It is assumed that the solar radiation is reduced
by 10% due to dust effect throughout the year
Dust effect varies seasonally. In winter
about 4% and in summer reaches more than
20%.
Based on measured values, a model
was developed to estimate the monthly
dust influence.
Heat collecting system
Bypass operation is not considered. Water enters
the accumulator immediately after pump start up.
A heat collecting system using bypass
operation and control valves are used.
Heat collection amount takes into
consideration bypass operation.
Heart accumulator
* When calculated heat loss from accumulator is
converted to
ΔT = T
w
- T
a
= 69
o
C, the heat loss is Q
loss
=
312123 kcal/day.
* Based on measured values the heat loss at
ΔT = 69
o
C is
Q
loss
= 765000 kcal/day.
* After heat loss is calculated,
compensation is performed using
(Q
loss
)
measured
/(Q
loss
)
calc
.=2.45
* Thermal stratification ratio was measured
as 7.5% during daytime and 6.5% at night
* Heat accumulator is divided into
1000 equal parts, mixing takes place at
the top and bottom of tank. Mixing at
top = 7.5% and mixing at bottom =
5.0%.
* Heat loss is based on complete mixing in the
tank and no stratification considered
Search WWH ::
Custom Search