Environmental Engineering Reference
In-Depth Information
Table 3.14
Hot Water Demand of Hotels, Hostels and Pensions in Germany
Hot water demand in
Specific heat content in
litres/(day and person)
Wh/(day and person)
ϑ
HW
= 60°C
ϑ
HW
= 45°C
Room with bath
95-138
135-196
5500-8000
Room with shower
50-95
74-135
3000-5500
Other rooms
25-35
37-49
1500-2000
Hostels and pensions
25-50
37-74
1500-3000
Source:
VDI, 1982
Because the tables give only a rough estimate, it is recommended that a
more exact analysis be made when planning a solar thermal system. Table 3.15
gives some further information.
Besides the annual hot water requirements, the demand on shorter
timescales must also be considered. If there are significant differences between
various days or considerable seasonal differences between summer and winter,
the sizing of the solar energy system changes. In this case, computer
simulations are prerequisites for an exact system sizing and output prediction.
The heat demand
Q
D
, the heat losses (piping heat-up losses
Q
Pheatup
,
circulation losses
Q
circ
in the collector cycle and storage losses
Q
S
) and the
solar collector power output
Q
out
define the amount of auxiliary heat required:
Q
aux
=
Q
D
+
Q
Pheatup
+
Q
circ
+
Q
S
-
Q
out
(3.58)
Besides piping losses in the collector cycle, there are also piping losses from the
storage to the taps. These losses can be calculated similarly to the losses in the
collector cycle. Simulations usually calculate the heat flows and add them to
give annual heat values.
An important parameter for solar energy systems is the
solar fraction SF
.
This parameter describes the share of the heat demand provided by the solar
thermal system. It is defined as the ratio of the heat that the solar cycle feeds
into the storage to the total heat demand that consists of the heat demand
Q
D
and the storage losses
Q
S
:
(3.59)
Table 3.15
Hot Water Usage for Various Activities
Demand
Temperature
Heat content
Dishwashing per person
12-15 l/day
50°C
550-700 Wh/day
Hand wash (one time)
3-5 l
37°C
95-160 Wh
Bath (one time)
150 l
40°C
5200 Wh
Shower (one time)
30-45 l
37°C
940-1400 Wh
Hair wash (one time)
10-15 l
37°C
310-470 Wh
