Environmental Engineering Reference
In-Depth Information
Table 3.10
Recommended Diameters of Copper Pipes for Thermosyphon
Systems with Mixtures of Water and Antifreeze Agents
Height difference between collector and storage tank
Collector area
0.5 m
1 m
2 m
4 m
6 m
below 4 m
2
22
1
22
1
18
1
18
1
15
1
below 10 m
2
28
1.5
28
1.5
22
1
22
1
18
1
below 20 m
2
42
2
35
1.5
28
1.5
28
1.5
22
1
Source:
Ladener, 1995
Piping heat-up losses
When the collector is not operational, for instance during the night, the
connecting pipes and the fluid inside cool down until they reach the ambient
temperature. When starting up the heating cycle again, pipes and heat transfer
fluid must be heated up again first before they can transfer heat from the
collector to the storage tank. Hence, energy is needed to heat both the pipes
and the heat transfer fluid.
To heat pipes with mass
m
P
and heat capacity
c
P
as well as the heat transfer
fluid with mass
m
HTF
and heat capacity
c
HFT
from temperature
ϑ
1
to
temperature
ϑ
2
, heat
Q
Pheatup
is needed for
n
heat-up cycles:
(3.27)
The heat-up losses for a 20-m-long copper pipe with a cross-section of 15
1 mm are calculated as an example. It is assumed that the pipe is filled with a
mixture of water and antifreeze agent and must be heated from a temperature
of
ϑ
1
= 20°C to
ϑ
2
= 50°C. The mass of the pipe with a heat capacity
c
P
=
0.109 Wh/(kg K) is
m
P
= 7.8 kg, the mass of the heat transfer fluid with heat
capacity
c
HTF
= 0.96 Wh/(kg K) and density
ρ
HTF
= 1.06 kg/litre is
m
HTF
=
2.82 kg. With (
m
·
c
)
eff
= 3.6 Wh/K, the heat-up losses for one heat-up cycle
(
n
= 1) come to:
Q
Pheatup
= 108 Wh
There are additional heat-up losses for heating the stop valves, pump and other
components of the piping cycle. These losses can be calculated similarly if the
mass and heat capacity of the components are known.
Piping circulation losses
Once the pipes and heat transfer medium are heated up, they still cause losses
of heat to the environment. A pipe with length
l
, heat transition coefficient
k'
and with an ambient temperature of
ϑ
A
with continuous circulation over the
circulation time
t
circ
produces
circulation losses
of:
